nuts & volts 25-02 - feb 2004
TRANSCRIPT
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Digital Laser Tachometer*5 digit, 6” LCD Display*2.5-99,999 RPM test range
*Auto-Ranging*2” to 80” test range*memory function
*Ceramic heating element for more accuratetemp control
*Temp control knob in F(392° to 896°) &C(200° to 489°)
*3-prong grounded power cord/static safe tip*Seperate heavy duty iron stand*Replaceable iron/easy disconnect*Extra tips etc. shown at web site
*10 digit LCD Display*High speed 300MHz direct counter w/0.1Hz resolution*50 Ohm input for full range 1MHz to 3.0GHz coverage*Ultra sensitive synchronous detector w/16 segment
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CSI 830
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CSI3003: 0-30v/0-3amp/1-4..$89.00/5+..$85.00
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High stability digital read-out bench power supplies fea-turing constant voltage and current outputs. Short-circuitand current limiting protection is provided. Highl LEDaccuracy and stable line regulation make the 3000 seriesthe perfect choice for lab and educational use.
*Line Regulation: 2x10-4+1ma*LED Accuracy: Voltage±1%+2 digits
Current: ±1.5% +2 digits*Wave Line Noise:<1mvrms*Dimensions: 291mm x 158mm x 136mm
CSI5003: 0-50v/0-3amp/1-4..$99.00/5+..$95.00
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We've found more expensive units with more LEDs butthe performance of this unit is superior. Ideal for outdooror indoor nighttime monitoring. Heavy Duty metal casingis weatherproof for protection from rain or snow. $149.00
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*Resistance:200/2K/20K/200K/2M
*Size: 138 x 69 x 31mm
Regulated Power Supply WDADP-12..$14.95
Details at Web Site
ESD Safe Thru-Hole
Soldering/Desoldering
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High precision thermostatically
controlled station w/ 35W Iron
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Well equipped DMM with True RMS, 3-
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Circle #145 on the Reader Service Card.
Circle #60 on the Reader Service Card.
CoverInside.qxd 1/6/2004 12:38 PM Page 2
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♦See pg. 60, Feb. QST mag.
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Circle #72 on the Reader Service Card. 3FEBRUARY 2004
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Vol. 25 No. 2
PROJECTS
Nuts & Volts (ISSN 1528-9885/CDN Pub Agree#40702530) is published monthly for$24.95 per year by T & L Publications, Inc., 430 Princeland Court, Corona, CA 92879.PERIODICALS POSTAGE PAID AT CORONA, CA AND AT ADDITIONAL MAILINGOFFICES. POSTMASTER: Send address changes to Nuts & Volts, 430 PrincelandCourt, Corona, CA 92879-1300 or Station A, P.O. Box 54,Windsor ON N9A 6J5.
February 2004
HARVESTING ELECTRICITY FROM THE ENVIRONMENTLight a 100 volt bulb with the waves thatsurround you.by Dan Shanefield
A SIMPLE CAPACITANCE METER:USING THE ADuC812Clever programming yields a useful bench tool.by Schlomo Engelberg
MAKING YOUR OWN CUSTOMMEMBRANE SWITCHESA simple — yet effective — way to dress upyour projects.by Gerard Fonte
THE AMAZING FRISBEE BLACKBOX or BASIC STAMP FRISBEEInstrument your favorite sporting goods!by Ralph Lorenz
DEPARTMENTS97 Advertiser’s Index75 Classified Display Ads20 Electro-Net61 Electronics Showcase32 New Product News
62 News Bytes36 NV Bookstore7 Publisher’s Info6 Reader Feedback92 Tech Forum
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FEATURED AARTICLESHUMAN ERROR AND THE ENGINEERING DESIGN PROCESSSome thoughts about user-centered design.by R.B.Whittingham
WHAT IS VIRTUAL MEMORY?Learn about the secret way your operatingsystem manages limited physical RAM.by Mark Balch
NEAR SPACEPart 1 of 2: Start exploring the final frontierfrom your own backyard.by L. Paul Verhage
BIPOLAR TRANSISTOR COOKBOOKPart 8 of 8. In this month’s final installment,useful transistor circuits and gadgets arecovered.by Ray Marston
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COLUMNSELECTRONICS Q&AGood-bye 12 V, Hello 42 V; Low-BatteryIndicator; Iron Keeps its Cool; and Calibrate!Calibrate! Dance to the Music.
IN THE TRENCHESFor design engineers facing real world problems.This month: being successful.
JUST FOR STARTERSChoosing a 7400-series logic family.
OPEN COMMUNICATIONEthernet — Part 2:Wireless LANs.
PERSONAL ROBOTICSDiscover what an Isopod can do for you!
STAMP APPLICATIONSMakin’ It Motorized.
TECHKNOWLEDGEY 2004New Cooling Technique for Electronic Devices,HP Continues to Gain Workstation Market Share,... and more!
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SPECIAL FFEATUREHOBBY ELECTRONICS IS DOWN— NOT OUTA few more thoughts on the subject from oneof the pioneering teachers of our hobby.by Forrest M. Mims III
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ContentsFeb.qxd 1/6/2004 10:20 AM Page 5
Dear Nuts & Volts:I read your magazine from cover to
cover and find it very stimulating andinformative. It helps me keep up myskills in the electronics field.
However, I noticed an error in RayMarston's "Bipolar TransistorCookbook" feature (November 2003).In the last paragraph of the sectiontitled "L-C Oscillators," on page 70, theformula for determining resonantfrequency is given as "f=1/2LC". This isincorrect and should be "1/2 Pisqr(LC)".
Tim Leon, CETVacaville, CA
Good catch, Tim. That was ourmistake, not Ray's. — Editor Dan
Dear Nuts & Volts:I really enjoyed the article, “The
New Electronics Experimenter,” byLouis Frenzel, in the January 2004issue. He really hit the nail on the headin describing today’s electronicsexperimenter. I'm 63 years old and havebeen down most of the paths hediscussed, including building Heathkits, computer kits, projects in PopularElectronics, QST, and RadioElectronics. I also went through thevarious Heath Kit Education homestudy courses, from DC electronics todigital electronics and microprocessorsto the BASIC Stamp. I have dabbled inaudio, short wave radio, scanners, RCmodels, personal computers, digitalvideo and cameras, auto electronics,and even built radio telemetryequipment for tracking wildlife.
I work in natural resources, but mytrue love has always been electronics. Iam looking forward to learning morefrom Nuts & Volts and SERVO
Magazine and to having more time tospend with my hobby when I retire intwo years. Keep up the good work.Thanks.
James (Jeb) StuartAnchorage, AK
Dear Nuts & Volts:I enjoy the magazine as one of the
few remaining periodicals designed forthe electronics hobbyist in the US. In an age of disposable consumerelectronics, it's good to see qualitymaterials and projects. Thank you.
If I may, I have some quickcomments on several points of D.Prabakaran's, “'All About GPS”' article:
Location: The proper term forGPS location determination istrilateration, not triangulation.Triangulation involves angles indetermining a solution, wheretrilateration (GPS) does not.
Frequencies: Currently only L1and L2 are broadcast .
GPSPower: GPS broadcasts L1 @380 watts and L2 @ 80 watts.
Receiver Sensitivity: Receiversensitivity is around -130 to -140 dBm,depending on manufacturer andconfiguration.
Selective Availability: SA wasturned off, via presidential order, onMay 1, 2000. The proliferation of GPSdevices and location-based servicesthat have since spawned preclude thegovernment from ever turning it backon.
DOPS: There are many moreDOPS than just HDOP (HorizontalDilution of Precession). The othercommon ones are VDOP (Vertical),PDOP (Point), TDOP (Time), andGDOP (General.) These are all unitlessnumbers that reflect the relative
precision of the particular DOP.Different GPS manufacturers displaythis information differently.
Thanks again for a greatpublication!
Thomas Homan via Internet
Dear Nuts & Volts:I received my January 2004 issue
of Nuts & Volts last Saturday. I guessthe PO had a bunch of stuff to get outof there and just delivered it early. Noproblem for me! I do enjoy themagazine, and really appreciate thesmaller size, compared to the issues afew years ago, since they store morereadily. I keep good magazines like thatand still have the very first issues ofQST that I purchased just before WWII.
I am a multi-hobbyist. I received myham license in 1948, and rose to ChiefElectronic Technician in the USN. Itaught electronic servicing to themaintenance crew for the tollequipment on the Kansas TurnpikeAuthority when they changed over fromcard hole punch type machines withstepper motor accounting to moderncomputers (which used Motorola 6800type computer chips at the time!). Iretired nine years ago, yesterday, after37 years with the KS Turnpike, where Ihad been head of the CommunicationsDepartment.
I appreciate Nuts & Volts as amagazine for experimenters like few orno others. It seems like so manypeople want to have everythingengineered and they just buy it withoutgetting their hands dirty, so the field ofnew information has shrunk badly.
A year ago, I designed and built aprototype for a home siren device,interfacing with a paging receiver toalert people in an area not well servedby community sirens. The folks whohad me do that have been short oncash to promote it, so I don’t believe itwill go very far. They do have a patenton the design idea.
Keep up the good work. I do enjoythe magazine very much.
Carl FisherAugusta, KS
Dear Nuts & Volts:I easily identified myself as a
member of a dying breed in LouisFrenzel's article, "The New ElectronicsExperimenter," January 2004 Nuts &Volts. For some time, I have been
FEBRUARY 2004
Reader Feedback
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Published Monthly By T & L Publications, Inc.
430 Princeland CourtCorona, CA 92879-1300
(909) 371-8497FAX (909) 371-3052www.nutsvolts.com
Subscription Order ONLY Line1-800-783-4624
FOUNDER/ASSOCIATE PUBLISHERJack Lemieux
PUBLISHERLarry Lemieux
ASSOCIATE PUBLISHER/VP OF SALES/MARKETING
Robin [email protected]
MANAGING/TECHNICAL EDITORDan Danknick
EDITORIAL ASSISTANTAlexandra Lindstrom
CONTRIBUTING EDITORSForrest Mims Mike KeeslingJon Williams Louis FrenzelJeff Eckert Ray MarstonTJ Byers R.B.WhittinghamDan Shanefield L. Paul VerhageSchlomo Engelberg Gerard FonteRalph Lorenz Mark Balch
CIRCULATION DIRECTORMary Gamar
SHOW COORDINATORAudrey Lemieux
WEB CONTENT/NV STOREMichael Kaudze
PRODUCTION/GRAPHICSRosa Gutierrez
Shannon Lemieux
DATA ENTRYKarla Thompson
Dixie Moshy
Copyright 2004 by T & L Publications, Inc.
All Rights Reserved
All advertising is subject to publisher's approval.We are not responsible for mistakes, misprints,or typographical errors. Nuts & Volts Magazineassumes no responsibility for the availability orcondition of advertised items or for the honestyof the advertiser.The publisher makes no claimsfor the legality of any item advertised in Nuts &Volts. This is the sole responsibility of theadvertiser. Advertisers and their agencies agreeto indemnify and protect the publisher from anyand all claims, action, or expense arising fromadvertising placed in Nuts & Volts. Please send allsubscription orders, correspondence, UPS,overnight mail, and artwork to: 430 PrincelandCourt, Corona, CA 92879.
FEBRUARY 2004 7
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Electronics Q&AGood-bye 12 V, Hello42 V
QQ.. How about some details (or anappropriate website) about the
upcoming change in automotive elec-trical systems? I read somewherethat the new bus voltage will be 42volts. Is that 20 cells times 2.15 voltsper cell? What other interesting andunique features will be implemented?Will something like PCM be used forswitching appliances (lights, blower,rear-window heater, etc.)? Any infor-mation or clues that you could passalong would be very interesting andmost appreciated.
Joseph F. Richmondvia Internet
AA.. The new 42-volt automotiveelectrical system comes as a
result of ever-increasing powerdemands. Back in the days of old,way before many of you were born,six volts was the standard power busfor autos. That's because the cars inthose days had almost no electricaldemands —- typically head/tail light-
ing and maybe a heater motor.Somewhere in the mid 1950s, theante was upped to 12 volts. Thiscame as a result of a demand for airconditioning, brighter headlights, andhigher-compression engines (whichneeded bigger starter motors).
Today's cars really put a demandon the electrical system with powerwindows/seats, climate control, mon-ster stereos, and window defrosters —not to mention of what's up and com-ing: GPS, communications, PCs, on-board video, etc. It's no wonder the12-volt bus is feeling the strain. It'sestimated that, by the year 2010,some cars will require 10 KW ofpower! That's enough to power ahome. To meet these demands, thevoltage has to increase. Why?
Because Ohm's Law says so.Let's say you have a six-volt systemwith a 10-amp load (60 VA) connect-ed by a 0.1-ohm wire. Ohm's Lawsays the voltage loss across thewiring is one volt, making just fivevolts (50 VA) available to the load —a loss of 17%. If we up the voltage to12 volts and reduce the current to
Figure 1
In this column, I answer questions about all aspects of electronics, including computer hardware,software, circuits, electronictheory, troubleshooting, andanything else of interest tothe hobbyist.
Feel free to participatewith your questions, as well as comments and suggestions.
You can reach me at:[email protected].
What's Up:The usual assortment of requested circuits.My favorites are the soldering iron warmdown and low-batteryindicator. Discovered anew reader hobby, andspent a lot of ink on anemerging technology.Another reader comesthrough with a tip, andthere are many CoolWebsites! to check out.
FEBRUARY 20048
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Q&A with TJ Byers
Q&A.qxd 1/2/2004 1:12 PM Page 8
five amps (60 VA) runningthrough the same 0.1ohms, the loss is now 0.5volts — 11.5 volts to theload (57.5 VA). Quite animprovement. Applyingthe same analysis to 36volts (a.k.a., 42 volts) givesus 35.98 volts (59.9 VA) tothe load.
The first 42-volt sys-tems will be hybrids: a mix-ture of 12 volts and 42volts (Figure 1). The 42-volt system is actuallybased on a 36-volt battery,but it's called 42 voltsbecause it takes 42 volts to charge a36-volt battery. This is much liketoday's systems, which operate at 14volts but use a 12-volt battery. Thealternator will output 42 volts forcharging the 36-volt battery. A 14-voltbattery charger, based on DC/DCtechnology, will keep the 12-volt battery fresh.
For the moment, these controlswill be separate (42-volt headlampsare a ways off), but eventually, they'llmerge into a single 42-volt bus. Thereason for choosing 42 volts over ahigher voltage is the 50-volt barrier,which is considered the highest volt-age that is safe to work around with-out special precautions.
As for the immediate advantages:
•Wiring harnesses will be thinner and lighter in weight.
•Connectors will have less loss.•Window motors will be smaller and
more efficient.•Electric fans will replace pulley-
driven radiator fans.
For more details and features,check out the following websites:
Assembly Magazinewww.assemblymag.com/CDA/ArticleInformation/coverstory/BNPCoverStoryItem/0,6490,98697,00.html
Auto Speedwww.autospeed.co.nz/cms/A_0319/article.html
CMC Power Systemswww.cmcpower.com/html/electricity/why42volt.asp
Canadian Driverwww.canadiandriver.com/articles/jk/at_010515.htm
SAEwww.sae.org/42volt
Low-BatteryIndicator
QQ.. I have an electric guitar thatuses active pickups powered by a
nine-volt battery. I'm looking for asimple circuit that would live insidethe guitar and tell me at a glance ifthe battery is still good. I imagine anLED that turns yellow when the volt-age drops to five or six volts, other-wise the LED does not light. Do youhave any suggestions?
David Walkervia Internet
AA.. How about a blink-ing LED? The circuit
in Figure 2 monitors thevoltage of the nine-voltbattery, and flashes theLED every two secondswhen the voltage fallsbelow 7.2 volts (the volt-age most manufacturersconsider the end of bat-tery life). The circuitdraws a mere 120
microamps, which is justslightly more than the self-discharge current of thesame battery sitting on ashelf. To calibrate the mon-itor, connect it to a 7.2-voltsource (see insert) andslowly adjust R1 until theLED starts to blink.
Iron Keeps itsCool
QQ.. Most of us in the shopwork with an 80 W sol-
der iron and would like tocontrol its temperature in
order to prolong the tip and iron lifeby preventing overheating. Can youplease provide a simple yet effectivediagram for a solder iron heat controldevice with a 120 VAC socket? Thiswould also make a great project forbeginners in electronics!
D. Zillbermannvia Internet
AA.. If you're talking about turningdown the heat when the soldering
iron is in the holder, then turning itback up when it's removed, the circuitin Figure 3 is what you want. Thisdesign simply inserts a diode into theAC line to reduce the average voltageto the iron. The thermal switch (avail-able from All Electronics, 800-826-5432, www.allelectronics.com --catalog THSW-70) is positioned sothat it opens when in proximity to thesoldering iron with the iron in its hold-er. The heat from the soldering ironcauses the switch to open and reducethe AC Out voltage. When the iron is
Calibrator
Adjust to 7.2 volts
LEDLow-Battery Indicator
10k
+9V
+9V
10M
10kR1
25k
LM385-2.5
150k
68k
150k 1uF
2N3906
2N39044.7k
1k10k
470
4.7MLP339
Figure 2
FEBRUARY 2004 9
Figure 3
ers Q&A
Q&A.qxd 1/2/2004 1:13 PM Page 9
removed, the switch closes, shortingout the diode, and applies full powerto the soldering iron.
If you're looking for a variabletemperature controller for the solder-ing iron and want to keep it simple,check out the circuit in Figure 4. Thisis your run-of-the-mill triac dimmerthat's been reduced to the minimumnumber of parts. The temperature iscontrolled by varying the phase angleof the sine wave, creating a "dim-ming" effect just like in a light bulb.The limitation is that you can onlyguess at the temperature (or measureit and calibrate the dial) becausethere is no temperature sensor to control a feedback loop, as would bethe case with a true thermostatic controller.
Calibrate!Calibrate!Dance to theMusic
QQ.. The capacitancemeter circuit in your
July 2003 article is some-thing I'm very much inter-ested in. However, I don'tunderstand how to deter-mine the value of thecapacitor being checked.
John Cohoes, NY
AA.. All test equipment, whetherhomemade or commercial, has
to be calibrated. In the capacitancemeter described in the July column("Simple Capacitance Meter"), this isdone by inserting a 1.0 uF capacitoracross Cx, and adjusting the 5 k potuntil the 0-1 mA meter reads full scalewith the selector switch in the S2 posi-tion. The scale is linear, which meansthat a 0.5 uF cap will read mid-way onthe scale, or 0.5 mA. A 0.1 uF cap willread 0.1 mA, and so forth.
The accuracy of the meterchanges as you switch from onerange to another and depends on theaccuracy of the timing resistor, R. If
you use 5% resistors, then expect tohave as much as a 5% error when youswitch ranges. Using 1% resistorsimproves the accuracy.
Tolerance MakesCents
QQ.. I have a question about themeaning of parts specifications.
Let's say you buy 36-volt zener diodesat 5% tolerance. Does it mean thatthree-sigma from 36 volts is 5% andthat all the parts bought will fall with-in that tolerance? I'm looking to seewhat the sigma is so as to properlytune the design.
Fred Spraguevia Internet
AA.. Electronic components arerated on a fixed deviation of plus
and minus a fixed value, not three-sigma (which is a mathematical devi-ation curve). For example, a 36-voltzener diode with a 5% tolerancemeans that the voltage of the zener isguaranteed to be ±1.8 volts of thestandard value; in your example, thezener voltage is in the range of 34.2 to37.8 volts. The actual values tend tocluster by the batch run, with onebatch having a peak around onevalue and another batch centeringaround a different value. Temperaturealso affects the voltage of a zener,which is why the tolerance is alwaysrated at a specific temperature.Typical temperature ranges are 0° Cto +70° C (commercial) and -55° C to+125° C (military).
Tolerance is not an indication ofpoor manufacturing. Closer toler-ances can be achieved, but at greaterexpense. A zener (or resistor) with a10% percent tolerance costs less toproduce than one with a 5% tolerance.
Power Supply Design101
QQ.. Is there a formula to determinethe size of the output filter capac-
itor in a DC power supply? I findmany different sizes in different DCpower sources, and would like to
FEBRUARY 2004
Q&A
Soldering IronTemp. Controller
SolderingIron
100uH
400VTriac
6ADiacHT-32
200V0.1uF
200V0.1uF
TempAdj
50k
4.7k
AC In
Figure 4
10
NU
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Q&A.qxd 1/2/2004 1:13 PM Page 10
know what determines their size.Ted Asousavia Internet
AA.. The simple answer is: capaci-tance is used to reduce the
amount of ripple voltage that is everpresent on a DC power supply output.Unfortunately, the formula isn't assimple, but I think I've at least made itless math intensive. Here is the simpli-fied equation:
C = [(ILOAD x t)/P-PRIPPLE] x 106
where ILOAD = the DC output current; it is cal-culated using ILOAD = EOUT/RLOAD
P-PRIPPLE = the acceptable peak-to-peak DC output ripple voltage
So far, so good. Now comes t,which is the hard part because itdepends on the rectification methodused and the line frequency. Thecapacitor requirements are less strictif you use full-wave rectification(Figure 5).
t = 1/(2 x line frequency); t = 0.0083for 60 Hz and 0.01 for 50 Hz
How about an example? Let'sdesign for five volts out at one amp,with 100-mV peak-to-peak ripple, run-ning from a 60-Hz wall-wart. Pluggingthese values into the equationnets a capacitance value of 8300uF. An off-the-shelf 10,000uF capwill work perfectly.
C = [(1A x .0083)/0.1V] x 106
C = [.0083/0.1] x 106
C = [.083] x 106 = 8300uF
Sink the Bismark!
QQ.. I spend many of my week-ends sinking ships — really!
The hobby is called R/C WarshipCombat, and it is heavly into elec-tronics for just about every aspectof the sport. One of the tools ofthe trade is a bilge pump thatpumps water out of the hull to
keep the ship afloat afterbattle damage by pumpingwater out of the hull. I'vebeen playing with a circuitbuilt around a TIP120 tran-sistor and a relay to startthe pump when water isdetected. The problem Ihave with it right now is that it worksin most lakes, but not all. I'm guess-ing this is due to lower mineral con-tent or salinity. I would be most inter-ested in a simple circuit that would bemore reliable, but still compactenough to fit in very confined spaces.
Charley Stephens Battlers Connection
AA.. I looked over the circuit you sentand can tell you that your con-
nection of the level sensor to the col-lector of the TIP120 (Figure 6)reduces the detector's sensitivity.Think about it: you're using the tran-sistor as an on/off switch. The sen-sors are used to provide base currentto the transistor to turn the switch on,but when the transistor switch turnson, the top sensor no longer has anyvoltage to apply to the base, whichcauses the transistor to turn off.
The answer is to connect the sen-sor to the +6 volt source through a 10k resistor. This way, the base currentisn't dependent on the transistor's col-lector voltage, only the conductivityof the lake water, which makes the
sensor more sensitive. (If the sensorappears too sensitive, increase thesize of the resistor.) I also swapped theTIP120 for a smaller MPSA14 unit andrecommend you use a compact reedrelay, like the RadioShack 275-232(don't worry that it's rated five volts;relays are current, not voltage operat-ed, so no will be damage done).
Inverter Waveform
QQ.. I am curious about yourthoughts on using modified sine
wave inverters with switching powersupplies, like those used in PC com-puters. I've looked at the waveform ona scope, and noticed a big rush ofcurrent at the step from 0 to 170 voltsthat decays exponentially. With a truesine wave, the current influx is lesssharp at the beginning, and the wholething looks like a rectified half-wave.I'm using a Tripp-Lite modified sine-wave inverter on my old computerswith no apparent harm, but wouldappreciate an expert opinion.
John M. BuzbyBoston, MA
Figure 6
FEBRUARY 2004 11
Full-Wave Rectifier
+
C
+
C
Figure 5
Q&A
Q&A.qxd 1/2/2004 1:13 PM Page 11
12
AA.. I'm no expert, but I can tell youthe reason for the different cur-
rent profiles between the two wave-forms. Off-line switching power sup-plies have a capacitor input (see"Power Supply Design 101" above).Capacitors charge exponentially,with a heavy beginning current thattapers off as time increases. If theapplied voltage is gradually applied,as is the case of a sine wave, theinrush current is tempered. The mod-ified sine wave (Figure 7), on theother hand, causes sudden currentsurges with each step.
Is it damaging? Not likely. Mostof the stress is with the input rectifyingdiodes, which have to take the brunt ofthe current surge. Fortunately, diodeshave a greater surge rating than theydo an average current value and thesurges are relatively small and shortwith a stepped waveform. So unlessyou are using a power supply that'smarginally functional, I say go aheadand use a modified sine wave invert-er. Now, want me to comment onthose cheap, square-wave inverters?
Portable Cat 5Cable Tester
QQ.. I saw your circuits for testingCat 5 cables, but I was looking
for a circuit that will do a wire mapfor cables that are already installedin the walls. The first use is to checkfor proper pinouts and the second isto locate breaks or no contacts at thejack. I want something small,portable, and inexpensive; the testerI have is the size of a suitcase.
Doug Mooneyvia Internet
QQ.. I need to check the continuityof a custom-made cable with a
DB25 connector that uses pins 2through 8 and pin 20. Basically, it's aCat 5 cable, with twisted pairs and acustom connector. The cable ismoved around a lot, and after sever-al moves, the stiff wires shear at thecrimp-pins.
Although I'm in the process ofreplacing these stiff wires with some-thing more flexible, I need to find afast way to check out the pinouts forthe cables that are in service and ver-ify those to be placed in service. Iwould like it to be compact (pocketsize), battery operated, and have
LEDs to boot.lfostano
via Internet
AA.. The schematic in Figure 8 is anadaptation of a commercial Cat
5 cable tester. A 4017 sequences thetesting of the pins using LED indica-tors. Each Transmitter LED lights inorder and should correspond to itsrelated LED at the Receiver. If theReceiver LED doesn't light, the pin isopen. If more than one Receiver LEDlights, the wire is shorted. If the LEDlights, but doesn't correspond to itspartner, the pins are exchanged. TheLEDs are sequenced by pressing thePress To Select pushbutton.
If you wish, you can automatical-ly sequence the LEDs using a 555timer (see Auto Select insert). Thisallows you to connect the Transmitterin one room and monitor the sequencewith the receiver in another room.
Reader Tip
Here's a lamp delay circuit(Figure 9) I developed awhile backthat is simpler than the one you print-ed in the Nov. 2003 issue. I have botha bipolar and MOSFET design. Hereare some notes about the circuit:
1. R1 is optional and limitsthe charging current to pro-tect the car door switch fromarcing damage. It is probablyalso beneficial to limit thecharging current through thecapacitor.
2. The energy for running thelight an extra 15 seconds isstored in the capacitor, C1.
3. The capacitor dischargetime-constant should beapproximately C1 * (R1+R2).
4. A diode should not beneeded across the relay con-tacts since the turn off of the2N3906 will be slow andgradual, instead of a suddenswitch off.
FEBRUARY 2004
Q&AN
UT
S &
VOLT
SEv
eryt
hing
For
Ele
ctro
nics
Modified Sine Wave
Figure 7
Auto Select
Portable Cable Tester
555
8 4
1 5
37
6
2
ToCP0
Transmitter Receiver
10k
100k
.05.01
9V
SelectPress To
+9V
D16D8
Cable4
Cable3
Cable2
Cable1
D15
D14
D13
D12
D11
D10
D9
D7
D6
D5
D4
D3
D2
D1
4017
CP1CP0
MRQ0Q1Q2Q3Q4Q5Q6Q7Q8Q9
Q5-9
10k
1k1k
Figure 8
Q&A.qxd 1/2/2004 1:14 PM Page 12
5. Almost all of the bulb current will becarried by the relay, so the additionalIN4001 diode should not reduce bulbbrightness and can be eliminated ifyou trust the relay contacts.
Wayne via Internet
MAILBAG
Dear TJ,I have just read the question
about ferroresonant transformers inthe Dec. 2003 issue and wish to addthat Sola also supplies ferroresonanttransformers that are "HarmonicallyNeutralized" to minimize the impactof the third harmonics on the wave-form. This technology requires thatpart of the capacitor winding be sep-arated from the rest of the capacitorwinding by a set of silicon steelshunts. This additional winding com-prises approximately one-third of thetotal capacitor winding. A visualinspection will reveal three coils, sep-arated by two sets of shunts.
The output waveform looks pret-ty close to a sine wave, with none ofthe flattening out that you mentioned.I have measured harmonic distortionvalues in the range of 1.5%-3.0%,which is not bad for ancient technolo-gy. However, I have noticed some"clipping or apparent commutating"distortion when using dynamic loads,such as switch-mode power supplies.Even this distortion does not seem tobe catastrophic.
Another potential problem for fer-
roresonants is that theycan be audibly noisy, sositting in the same roomas one can become irri-tating.
Dick ClarkeTotal Recoil Magnetics
Dear TJ,In the December
issue's schematic for a+5 to -5 converter (Figure10), is the 10 uF capbetween -5 volts out andground reversed — or amI missing something?
Jim Balderramavia Internet
No, I missed it whenI drew the schematic.Good catch!
TJ Byers Q & A Editor
Dear TJ,Your articles are usually accurate
and informative. However, in theDecember 2003 issue, page 24, youstate that the circuit illustrated inFigure 5 features a bandpass filter, ofwhich you show the frequencyresponse in Figure 6. In fact, the net-
work composed of the series 100-ohm resistor and 1-uF capacitor toground, at pin 3 of the second 555, isa low-pass filter which, as you correct-ly state, attenuates the off harmonics.
André Kestelootvia Internet
Q&A
FEBRUARY 2004 13
Reader Circuit Dome Light
RadioShack
275-233 Relay(12V, 1050 ohm coil,
1A contact rating)
275-233 Relay(12V, 1050 ohm coil,
1A contact rating)
10W12V
R115 R2
15Meg
SPST12V
+ C11uF+
12V Q1IRFD9110
switch
S1door
+12V
+
C1100uF
Q12N3906
switch
S1door
D11N4001
SPST12V
R2100K
R115 12V
10W
Figure 9
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FEBRUARY 2004
Personal Robotics by Mike Keesling
Personal Robotics
Isopod: Any of numerous crus-taceans of the order Isopoda,characterized by a flattened
body bearing seven pairs of legsand including the sow bug(www.dictionary.com).
Well, that's the dictionary defini-tion, but what it means to me, is asmall, flat microcontroller system ona board, with many groups of func-tions, a board suitable for controllingmany actuators, and reading manysensors.
In the last two years, the IsoPodhas grown in popularity, and evengraced the top 100 products of theyear in EDN magazine in 2002. It hasgrown into a family of related prod-ucts with more functions or smallerdimensions to accommodate thetask at hand whatever it is.
When you buy an IsoPod, youare not just buying a microcontrollerboard; you are actually buying a dig-ital signal processor, voltage regula-tors, communications transceivers,and a full-featured programming lan-guage called IsoMax™. All this comeson a 1.27" by 3.05" board that looksmore like a studded breakfast barthan a microcontroller. Based on the56800 series of digital signal proces-sors and running at 80 MHz, you willfind that fully tasking it will be quitea challenge.
The feature set of the IsoPod isimpressive, to say the least. To fullyunderstand its power, you have toconsider that all of its features arehardware based. What this means, isthat you have access to a lot of "setit and forget it" functionality. Theadvantage to this is that there is littleor no processor overhead required toget a lot of stuff done. This frees you
to write the software that imbuesyour project with the behavior youare interested in, without having tocode the functionality.
As an example, you can pro-gram just about any microcontrollerto drive a multitude of R/C servos,but how much overhead does thisrequire? With the IsoPod, 26 R/C ser-vos can be driven without interven-tion on the part of the software, Yes,that is correct, 0% overhead on theprocessor.
Unfortunately, there is a price forall this functionality. The IsoPod is lit-erally bristling with connections.When you connect to it, you reallyhave to be careful to avoid connect-ing the wrong signals or permanentdamage can result, especially to theanalog inputs which will in no waytolerate over-voltage. In addition,there is a weird sort of right angleconnector on one end, but this hasbeen phased out in the other mem-bers of the IsoPod family.
The PWM module is very com-plete. With two banks of six PWMpins, PWMA, and PWMB, you caninstantly control 12 R/C servos, anda variety of different configurations
of H-bridges for driving a variety ofdifferent motors. Each bank has itsown frequency setting, so you couldhave six R/C servos connected toPWMA, and six DC motors off ofPWMB.
The PWM pins in each bank canbe configured as pairs, completewith dead-time insertion and polaritycontrol, or as individual pins. You arelimited to all pairs or all individuals ineach bank, but because of the rea-sons for using one or the other, thiswould rarely be an issue. One limita-tion is the minimum frequency theycan generate. Without slowing downthe processor to half speed, you arelimited to 76 Hz. This can causeproblems with some R/C servos, butso far, my experience has been okay.In any case, if it is a problem, thereare the timer registers that can alsogenerate PWM, and can easily go asslow as necessary to drive R/C ser-vos.
The timer module is hands downthe most versatile part of the IsoPod.Consisting of four banks of timers(TA-TD), it can generate PWM, readquadrature encoders, decodestep/direction signals, count pulses,or measure pulse lengths. Forinstance, I have an application thathas the timer unit configured to readsix quadrature encoders into 32 bitcounters, and perform high-resolu-tion pulse measuring on eachencoder, to provide ultra-high resolu-tion velocity information. I have yetto scrape the surface of its function-ality. Covering an address space of128 bytes, it is quite a bit to getacquainted with.
The GPIO module is fairlystraightforward, with two full banks
All About the Isopod™
Understanding, Designing, and Constructing Robots and Robotic Systems
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of eight pins each availableon one header, and a smattering of port pins ondedicated connectors. It is fairly generic in its implementation. One real-ly nice feature is havingthree LEDs onboard fordebugging purposes.
The analog is a bitmore complicated than the GPIO, butnot by much. It is comprised of twobanks of four 12-bit A/D converters.They are a bit persnickety in that it isrecommended they only be used inthe 0-3.0 volt range, which makesinterfacing voltage output sensors abit of a hassle. But that's nothing avoltage divider and a bit of Ohm'sLaw can't handle.
The communications sectionsare also really quite powerful. Tostart, there are two asynchronousserial ports of which the second onecan be ordered as standard RS-232,
RS-422, or RS-485. The one draw-back here is that the highest standardbaud rate is only 38400. Nonetheless,having two hardware based serialchannels is really useful.
There is also a single SPI portwhich can run at up to 20 MHz, andcan be configured as either a masteror a slave. On its connector, there arethe necessary SPI signals, and a cou-ple of port lines, the reset line, Gnd,+5, and +3.3 V. This makes interfac-ing to other devices really easy.
In addition, there is a basic imple-mentation of CANbus on board.
While not a "full implemen-tation", it is still goodenough for most CANbustasks where it isn't respon-sible for being the masterof the bus where a highlevel protocol is beingused. This really isn't anissue, since most of uswon't be spending the
licensing fees to implement the popu-lar CAN protocols. We will simply bewriting our own, or at worst, buildingslaves that do follow a higher proto-col. In any case, with error checking,checksumming, automatic re-trans-mission, and bus conflict arbitration,CANbus holds a lot of promise. NewMicros was even good enough to puta CAN transceiver chip on board.
Now, before I delve into the nativelanguage of the IsoPod, I want you tosit back and ponder what you can dowith the IsoPod. Even if you are adyed-in-the-wool Intel, Atmel, PIC, or
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even BASIC Stamp user, the differentcommunications methods, combinedwith its full set of hardware featuresoffered on the IsoPod make it theideal universal peripheral. You couldeasily use it as an R/C servo engine,quadrature reader, sensor reader, andspoon-feed the data to and from yourmicrocontroller or microcomputer ofchoice. There are many users whohave gone this route, then find them-selves handing more and more pro-cessing power to the IsoPod.
The IsoMax programming lan-guage supplied with the IsoPod isreally quite unique as well. IsoMax isactually a superset of FORTH, anarcane and venerable language oftenassociated with users who havealmost a religious reverence for it.While covering FORTH is beyond thescope of this article, IsoMax incorpo-rates enough sufficiently novel con-cepts that it is worth mentioning.
The lack of FORTH's popularity,
in my opinion, is that it is really a lan-guage construction set. When youdefine a function, you actually end upfactoring it into common elements,and re-using them over and overagain. In doing this, you are writingwhat I call MYFORTH, and every-body's MYFORTH is different. Backwhen everyone was trying to classifyand sort the different languages outthere, FORTH was left looking a bitchaotic. This has lead to finding doc-umentation difficult. You will not driveto your local mall, grab a coffee, anddecide which FORTH text you aregoing to buy. Fortunately, there isenough documentation on NewMicros' website to get you going.
To begin, the most novel thingabout IsoMax is the fact that it actual-ly lives in the IsoPod itself. All youneed is a serial port, terminal soft-ware, and a power supply. I often starta project by simulating the hardwareon my desktop, and getting the bulk
of my program code going before iteven sees the real hardware it will beworking with.
The other truly unique thingabout IsoMax is that it is multitasking,and even the multitasker is imple-mented in a unique way. The multi-tasker is actually time-synchronous.What this means is that you establisha frequency at which all of yourprocesses — called virtual machines— get run, and the multitasker runsthem one by one, in the order youwant them to be run. In essence, youbreak the flow of time into granules.In every granule of time, everythinggets done.
Another neat thing about themultitasker is that while your pro-grams are running, you can actuallystill communicate with the processorduring the foreground task slice. Youcan set or read registers, change thecontents of variables, even write newwords that get compiled.
FEBRUARY 2004
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This does take a bit of gettingused to, but it does work well onceyou get the hang of it. One potentialdrawback of this method is synchro-nization to other hardware that oper-ates at a different (or even variable)period than the IsoPod. This has beenovercome by adding data buffers tothe serial lines, for instance. Thebuffer stores the data transparently inthe background, and presents it toyou when you ask for it. The oneexception here is that the CANbusdoes not have a buffer like this in theclassical sense, but it does receiveeight bytes of data at a time. Sincethe implementation of the buffers, Ihave not been troubled by the syn-chronous nature of IsoMax.
This brings me to another point.IsoMax, currently at V0.6, is a lan-guage in flux. While I believe it is fin-ished, it is not fully accessorized tothe level that New Micros wants it tobe. This means that improvementswill happen and, in fact, have hap-pened through the versions, but thenet effect is always a better platformto work from.
Because the sheer volume of reg-isters for hardware access is mindnumbing at times, IsoMax incorpo-rates very high-level object-orientedwords. I like to call them templatewords. They are great for the begin-ner, and can help you get somethingup and running quickly, but some ofthem are notoriously slow. The rea-son for their slowness is that everytime you use them, they have to"pave the way" for themselves. Theymake no assumptions; they configureeach and every register that isrequired, each and every time theyare called. I usually start out withthem, and then if things show signs ofslowing up, I go through and replacethem with lower level code. They arealso handy for seeing how registersget configured when you use them.This makes them ideal as a teachingtool.
Interestingly enough, IsoMax alsoprovides words called trinaries forworking with numbers at the bit levelthat are lightning fast. Trinaries allow
you to read, test, and set registers orother memory locations at the bitlevel. They are great for reading but-tons or registers, or changing a regis-ter's contents rapidly.
Another unique thing aboutIsoMax is the way it handles flow con-trol. While its FORTH underpinningsare available for stodgy FORTHusers, IsoMax prohibits the use ofloops in procedural sections entirely.IsoMax allows you to have runningindexes to track how many timesthings have been run, which is reallythe essence of using a loop. InIsoMax™, if you put an endless loopinside the procedural portion of aVirtual Machine, I guarantee you thesystem will crash.
Another interesting addition toIsoMax is finite state machine flowcontrol, or FSM. This is a novelapproach to programming embeddedsystems, and has real applications inthe fields of control and robotics.State machines perform a functionsimilar to if-then-else statements, butthe end result is a direct line to theoutput you are interested in, not arat's nest of multiple nested condition-als. This results in easier program-ming and faster program execution,because you only test inputs relatedto a particular state, instead of allpossible inputs and computationsevery time.
In IsoMax, a Mealy model of statemachine is used, as they tend to bemore efficient in the number of statesrequired. But Moore model machinescan also be simulated in the lan-guage. State machines are close inconcept to inference engines used inexpert systems and ArtificialIntelligence, and some are imple-mented that way. Today, statemachines are seeing wide usage inthe video game industry, and are par-ticularly useful for communicationsprotocols, and compiler design.
Overall, the IsoPod is an extreme-ly flexible system on a board. To illus-trate this point, I have shelved myPICs, 68332s, and 68HC11s in favorof the IsoPod. It's the micro I like toreach for first! NV
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Open Communication
In the last Open Communicationscolumn, I covered wiredEthernet. This is the universe's
most popular local area network(LAN) whose physical layer (PHY) ortransmission medium is usually cate-gory 5 or 6 (CAT5/6) twisted pair orfiber optic cable. Now, a wireless ver-sion of Ethernet is quickly expandingEthernet LANs and creating a wholenew way to access the Internet fromalmost anywhere.
Known by its IEEE (Institute ofElectrical and Electronic Engineers)standard number 802.11, wirelessEthernet is extending the LAN outsideof the enterprise and small businessesinto homes, airports, restaurants,hotels, and many other public areas.Like the cell phone, wireless Ethernetlets you stay in touch with your Emailwhile you are on-the-go via your laptopor PDA. Wireless Ethernet is certainlyrevolutionary rather than evolutionaryin the development of Ethernet.
Background
Radio-based LANs first showed
up in the mid-1980s but they werelarge, expensive, and had low datarates. While a few companies adopt-ed them, it has not been until the late1990s that wireless local area net-works (WLANs) really took off in themarketplace. What made the differ-ence was all of the work put in bycompanies to form a universal stan-dard that could be used world wide.
After years of work, the IEEEWLAN standard 802.11 was ratifiedin 1997. This gave us 1 and 2 Mbps(millions of bits per second) connec-tivity. Then in 1999, a revised stan-dard 802.11b was formalized. Thatstandard — which offers an 11 Mbpsdata rate — made wireless Ethernetinstantly acceptable. Today, WLANsare the fastest growing segment ofthe electronics industry.Furthermore, even newer, faster ver-sions have been developed,approved, and converted into rapidlyselling products.
Another reason for the growthand success of 802.11 WLANs wasthe establishment of the Wi-FiAlliance. Wi-Fi, meaning wireless
fidelity, is the trade name forthe organization of equip-ment, chip, and softwarecompanies making WLANproducts. While the exis-tence of a standard helpsensure that equipment madeby one company works withthat of another, it is no guar-antee. As it turned out earlyon, there were enough inter-operability glitches andissues to make companiesget together and solve these
problems. The Alliance was set up to pro-
vide testing and certification ofWLAN products to ensure interoper-ability. Companies submit their prod-ucts to Wi-Fi for testing and, if theymeet the rigid specifications, they areblessed with the Wi-Fi label. The Wi-Fi effort removed the last doubtabout the interoperability of WLANproducts from one vendor to another.The market blossomed as a result.
The acceptance of 802.11 prod-ucts has increased sales exponential-ly over the past several years therebydecreasing prices and encouragingeven greater adoption. This is trulyone of the most successful wirelessproducts ever, other than the cellphone. If you don't know about oruse this technology, it’s time to geton board, as surely it will affect youor provide you with a communica-tions option that can benefit your life.
Benefits
What makes WLANs so popular?It's simple. People love their freedomand mobility. Just as most of us havebecome addicted to our cell phones,so have many become addicted toEmail and Internet access. It is agreat benefit to be able to accessyour Email and the Internet from any-where with your laptop. It lets thosein companies move from office tooffice with their PC and it allows youto take your laptop to meetings inconference rooms and other officeswithout losing touch.
In addition, you can now useyour laptop from an airport, restau-
The Latest in Networking and Wireless Technologies
FEBRUARY 200422
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ETHERNET — PART 2:Wireless LANs
FIGURE 1. Typical WLAN plug-in adapter for laptops. Courtesy SMC Networks.
Open Communication by Louis E. Frenzel
OpenCommunication.qxd 1/5/2004 2:18 PM Page 22
rant, or other local place with a wire-less connection. At home, it is purepleasure to do any computer workfrom your deck, patio, or easy chairwithout dragging a long, twisted paircable. Flexibility, mobility, and free-dom made WLANs the reigning LANconfiguration.
So, as companies expand theirEthernet LANs, they are going wire-less. There is no messy and expensivewiring to add and no reconfigurationhassles if people move offices, and itadds the mobility that people love.But the real revolution has been thedevelopment and deployment of pub-lic access points called hot spots.They first showed up in airports andnow most major airports have one ormore such access points. Hotelsbegan adding hot spots about thesame time and now most majorchains offer this as a guest benefit.
Coffee shops, like Starbucks, alsohave wireless access. SomeMcDonald’s also offer this service.And it is becoming more popular thanever in convention centers. Today, wehave over 12,000 hot spots to choosefrom, but some projections say thatwe can expect over 100,000 by 2007.Thanks to technology, you can take itwith you.
How it Works
Wireless Ethernet is implementedwith sophisticated microwave radiotransceivers. Every PC or server con-tains a digital two-way radio thatsends and receives Ethernet format-ted data. Also known as radiomodems or wireless adapters, theseinterfaces appear in several forms.They can be plug-in cards for regulardesktop PCs or PCMCIA cards for lap-tops. See Figure 1.
External transceivers that con-nect via a USB port are also available.Many of the newer laptops come withWi-Fi radios built in. Intel's widely pro-moted Centrino chip set is an exam-ple of an embedded Wi-Fi interface.Each of these transceivers forms onenode in the LAN. Finally, there is thetransceiver that is part of what is
called the access point (AP). Alsoknown as a wireless gateway orrouter, this is the unit that services allthe remote transceiver nodes. Figure2 shows a typical home networkingaccess point.
In a large enterprise or smallcompany LAN, the AP is connected tothe existing wired Ethernet LAN bythe usual twisted pair line. The AP ismounted high on a wall or ceiling sothat its antenna has a good "view" ofthe area it is to cover. Then, manyradio modem equipped PCs or lap-tops in that area can communicatewith the LAN via the gateway. Theradius of the coverage is from 100 to300 feet, depending upon the environ-ment, especially if walls, ceilings, andfloors are involved.
The connection at a hot spot hasthe gateway or router connected backto an Internet service provider (ISP),usually by way of a leased T1 or T3line. At home, the gateway or router isusually connected to a high speedbroadband Internet source, such as acable TV or DSL modem. The gate-way usually provides coverage for thewhole house.
The Standard
The 802.11 standard is not justone standard, but many. By far, themost popular is the 802.11b standardthat almost everyone uses today.802.11b defines what we call the PHYand MAC layers of a multilayer proto-col scheme that Ethernet uses. PHY
means physical layer, which, in thiscase, is radio. The standard defineswhat we call the air interface. TheMAC, or media access control layer,takes care of all the addressing, formatting, and transmission betweenthe air interface and the network.
The PHY in 802.11b uses the unlicensed 2.4 GHz industrial-scientif-ic-medical (ISM) band defined in theFCC's Part 15 rules and regulations.This band is 83.5 MHz wide and isdivided into 11 overlapping 22 MHzwide channels. Since only three of thechannels are non-overlapping, theseare the only useful ones that do notinterfere with one another. Their cen-ter frequencies are 2.412, 2.437, and2.462 GHz. With 22 MHz of band-width, it is possible to achieve a datarate up to 11 Mbps. But, of course,that data rate also depends upon therange of transmission, the environ-ment, as well as sources of interfer-ence and noise.
The 802.11b standard specifiesthe use of direct sequence spreadspectrum (DSSS). This is a techniquethat takes the raw serial binary dataand exclusive ORs it with a uniquehigh speed chipping code. The resultis a high speed serial signal that isthen modulated onto the carrier. The802.11b standard specifies multiplemodulation methods depending uponthe speed of transmission. If the envi-ronment is favorable and the trans-ceivers are within range and noise andinterference are at a minimum, themaximum data rate can be achieved.
FEBRUARY 2004
FIGURE 2. A common home network access point or wireless broadband router.Check out the dual antennas for diversity reception. Courtesy SMC Networks.
23
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OpenCommunication.qxd 1/5/2004 2:18 PM Page 23
802.11b uses complementary codekeying (CCK) to get 11 Mbps. Thismethod transmits eight bits per mod-ulation symbol (carrier phase).
If the range and environmentconditions are not ideal, the speed ofthe radio automatically backs off apredetermined lower speed to ensurereliable data transmission. This lowerspeed is 5.5 Mbps, also using CCK. Ifconditions worsen, the speed dropsfurther to 2 Mbps, using DQPSK (dif-ferential quadrature phase shift key-ing) or a low of 1 Mbps, using plainold ultra reliable DBPSK (differentialbinary phase shift keying).
As for range, it really variesdepending upon local conditions.Normally, microwave transmissionsare strictly line-of-sight (LOS), mean-ing that the receive antenna must"see" the transmitting antenna.However, if sufficient power is avail-able, the signal will punch throughwalls, floors, ceilings, office dividers,and even trees and other buildings.Obviously, the signal is greatly weak-ened as it passes through theseobstacles.
Range is also a function of trans-
mitter power and the antenna. Withmost equipment, you can rely upon arange of about 100 feet radius fromthe gateway antenna. This assumesan omnidirectional antenna and thestandard 100 mW of transmitterpower. A directional gain antenna willboost the range significantly. Byusing more power and a gain anten-na high up and in the clear, you canachieve a range up to several miles.In some rural communities, 802.11bWi-Fi networks, with higher powerand high-mounted outdoor antennas,have been set up to give high speedbroadband Internet access to thosewithout cable or DSL lines.
A newer standard 802.11a wasratified in 2001. It uses the FCC des-ignated U-NII or Unlicensed NationalInformation Infrastructure band inthe 5 GHz range. This band is far lesscrowded than the already over sub-scribed 2.4 GHz band. Besidesmicrowave ovens, cordless phones,Bluetooth wireless devices, HomeRFwireless networks, and now jillions ofWi-Fi transceivers, it is a miracle thatany reliable communications can beobtained in the 2.4 GHz band.
If interference is a problem as itis for some, the 802.11a equipmentgives you all the benefits of a WLANand with even higher speed and virtu-ally no interference. Using orthogo-nal frequency division multiplexing(OFDM) — a form of wide band mod-ulation — speeds up to 54 Mbps arepossible. The range is a bit less at 5GHz but is satisfactory for most appli-cations. The speed backs off to 48,36, 22, or 11 Mbps, as conditionsdeteriorate.
The most recent version of thestandard is 802.11g, which was rati-fied last year. This version specifiesoperation in the 2.4 GHz band, but, byusing OFDM, it can achieve an upperspeed of 54 Mbps. And it is fully back-wards compatible with 802.11b. Thisoption, which is now becoming avail-able in most products, gives you802.11a speed over 802.11b range.While most networks and hot spotsstill support only the 802.11b stan-dard, many will soon upgrade to theg version. And the a version will alsogrow, especially in companies whereinterference is a problem.
Chip companies are recognizing
FEBRUARY 200424
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Open Communication
FIGURE 3. Agere SystemsWaveLAN chipset for
multimode 802.11a/b/g accesspoints and interface cards.The
WL54040 is the dual band (2.4 and 5 GHz) transceiver
with direct conversion (zero IF)for CCK operation and a lowIF for OFDM.The WL54240 isa dual band power amplifier
with 24 dBm for 802.11g and20 dBm for 802.11a.The
WL64040 is the multimodeprocessor that handles the Ato D and D to A conversionsbetween the transceiver chipand the baseband processor.This chip also does the CCKand OFDM modulation anddemodulation.The WL60040 is the MAC baseband with itsown embedded processor and
provides the encryption, as well as the interfaces to the
PCMCIA or CardBus, USB portor other PC connection.Courtesy Agere Systems.
OpenCommunication.qxd 1/5/2004 2:19 PM Page 24
the need for transceivers that complywith all three standards (a/b/g). If youtruly want mobility and the ability toconnect to anything available, youneed an adapter that handles all ofthem and switches automatically. Anexample of a chipset that does allthree is Agere', as shown in Figure 3.
But that's not all. The IEEE justrecently approved a study group todevelop the next version of the stan-dard. Tentatively designated 802.11n,this new standard which won't beavailable for a few years promisesdata rates from 108 to 320 Mbps.
Critical Issue
If WLANs are so great, why isn'teveryone using them? The answer tothat question is usually one word:security. Almost anyone can pick up awireless signal. With a sensitivereceiver and a directional antenna,you can easily eavesdrop on almostany WLAN. If you are transmittingsensitive information, this is notsomething you want to take a chanceon. There have been numerous exam-ples of hackers sitting in a parking lotof a major retailer stealing credit cardnumbers from the 802.11b-basedcash registers and credit card scanners.
The creators of the 802.11 stan-dard anticipated the security problemand provided for encryption. Knownas Wireless Equivalent Protocol(WEP), this capability is built intoevery Wi-Fi chipset. It does provide aminimum data encryption processthat can protect most information.WEP is not turned on automatically,meaning the user has to enable it. For that reason, most users don't useit. It is rarely used in home networksor at hot spots. Many companies donot enable it despite their need forsecurity.
WEP has also proven to be vul-nerable to hacking. Some Wi-Fi vendors, like Cisco, have come upwith their own security/encryptionmeasures like the Temporal KeyIntegrity Protocol (TKIP). The Wi-FiAlliance developed an improved inter-
im solution called the Wi-Fi ProtectedAccess (WPA). Both of these areincluded in most transceivers.
The IEEE has also developed newsecurity techniques under its 802.11istandard for encryption and 802.11xfor authentication. If that is notenough, many companies have imple-mented virtual private networks(VPNs), a popular technique forsecuring the transmission of data overthe Internet, to handle their wirelessnetworks. So, while security is anissue, there are many solutions forthose who want and need to send sen-sitive data over their WLAN.
Antennas: The Keyto a SuccessfulWLAN
While the reliability of a wirelessconnection depends on a variety offactors, many of them are beyondyour control. Transmitter power isone. With most units you get the max-imum allowable power, usually 100mW. Next is AP location. You can con-trol this to some extent. You shouldplace your AP high and in the clear soit sees as many of the remote nodesas possible. If possible, experimentwith the location of the access pointfor best overall results. In some cases,you may find that you need more thanone access point. This is especiallytrue in large companies with lots ofemployees and space to cover.
A real help for those installingmultiple APs is the IEEE’s newlyapproved 802.3af standard, alsocalled Power over Ethernet (PoE).This standard provides a way to senda DC voltage over the standard CAT5or CAT6 twisted pair Ethernet cable.In this way, the AP does not need aseparate AC or DC power sourcewhich can be a problem in placing anAP in an optimum location. Most ofthe newer access points now comewith PoE capability.
One thing you do have controlover in your AP is your antennas.While all access points and wirelessadapters come with an antenna,sometimes you have a choice. Select
25FEBRUARY 2004
Open Communication
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an antenna that fits your plan. Anomnidirectional unit is best if youhave lots of space to cover in all direc-tions. But, if all of your wireless clientsare off in one direction, you may wantto consider a directional antenna thatfocuses power where you need it.Such directional antennas exhibitgain and give the same effect asincreasing transmitter power. Sometypical directional antennas are theever popular Yagi, as well as verticalcollinears and the flat patch antennas.
Most home access points havedual antennas for receive diversitythat helps improve performance. Theantennas are spaced from one anoth-er by at least one wavelength and thereceiver switches between them tosee which gives the best signal. Referto Figure 2 again. After market anten-nas are also widely available so if youneed to fix a problem or improve reli-ability, experiment with the antennas.
WLANs: What's in itfor You?
Actually, there is something foreveryone. If you are thinking ofextending your company's EthernetLAN, give some serious thought to802.11. It offers many benefits. Itimproves work productivity because
of the mobility it provides. You can docompany work from anywhere. It alsosimplifies installation. No need to pullcables. This reduces labor and mate-rials cost. Free space is ... duh ... free.Users can move offices or do workwherever. And the network alsoscales better as the number of usersgrows.
As an individual, you may wantor need the ability to work while trav-eling. Road warriors — those peoplewho travel frequently for their compa-nies — are real big fans of WLANsbecause they can stay in touch bylaptop and hot spots with Email andhave Internet access virtually any-where. Even some new PDAs are get-ting Wi-Fi capability thanks to thelower power chipsets. If you don'thave Wi-Fi service now, you will findthat your productivity will increasetremendously on the road if you do.
For consumers, a WLAN is also aviable option. The cost of setting up ahome network with Wi-Fi is less than$200.00 today and getting lower. Youcan get a wireless access gateway orrouter for under $100.00 if you shoparound. Add a few bucks more for theadapter card and you are on yourway. No need to do any wiring. If youhave a laptop, be prepared to rapidlyget addicted to the freedom that wire-less provides.
P.S. I've been writing this columnfor over a year now. I have lots of greatideas for future installments, but Iwould like to hear what you want toread about. Do you want more tutori-al articles, like how spread spectrumor OFDM work, or would you like tosee more hands-on construction/applications articles on wireless?What about ham radio or SWL? Dropme a line via Email ([email protected]) and give me your wish list. NV
Institute of Electrical andElectronic Engineers
grouper.ieee.org/groups/802/dots.html
This is the Ethernet standardswebsite with more than you ever
wanted to know about it.
Wi-Fi Alliancewww.wi-fi.com
The trade association that certi-fies 802.11 WLAN equipment.
Palo Wirelesswww.palowireless.com
A general website with tons ofdata on WLANs and lots of other
wireless technologies.
Cool Websites
FEBRUARY 2004
Open Communication
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Stamp Applications
Idon't know about you, but I'mstill exhausted by last month'scolumn — wow, that was a real
workout, wasn't it? I do hope youfound it useful though. This month,we're going to go a lot easier, butstill have a bunch of fun! And afterits terrific comeback the last coupleof months, we're going to have that fun with the venerableBASIC Stamp 1.
There's no denying that personal robotics is one ofthe fastest growing aspects of hobby electronics. Thereare clubs all across the globe devoted to it, and each weekseems to bring another television show with robotics as itscenterpiece. An easy way of getting started in homegrownrobotics is to convert an existing motorized toy. They're allover the place, in fact, your family may have a few leftover from the holidays that no longer seem interesting.Why not spice up an old toy with a brain you can programyourself? Okay, then, let's do it.
Micro Motor Control
Since virtually all motorized toys use small DCmotors, and controlling them requires full-time PWM thatwe can't do natively with the Stamp, we'll use an externalmotor controller. Pololu Corporation makes and sellscomponents devoted to small robotics and their MicroDual Serial Motor Controller is perfect for our task of con-verting a motorized toy. The SMC02 accepts instructionsthrough a serial connection and will control two motors(speed and direction). Motor voltage can be from 1.8 to 9volts, with currents up to one amp per motor! This littledude rocks. And little is accurate; you can see what it lookslike in Figure 1 next to a penny and a BS1-IC module.
Let's get right into it. A typical first robotic project isa "bumper bot" — the kind of robot that when it bumpsinto an obstacle will turn away and then keep moving.
There are BS2 examples of thiskind of robot everywhere; I wantedto see if there was enough space inthe BS1 to pull it off. As it turnsout, there is with room to spare,which means we can add more"intelligence" to our robot once weget in going.
Figure 2 shows the schematicfor our simple robot controller. Twopins are used to communicate withthe Pololu controller (SMC02), twoothers for our bumper inputs
(using our standard "safe" circuit). The first control line tothe SMC02 is the serial connection. The SMC02 willautomatically detect baud rates from 1200 to 19.2 kBaud.As our top-end limit on the BS1 is 2400, that's what we'lluse. The second line controls the Reset input to the SMC02.Using the hard reset line will let us stop both motors at oncewhen required without having to send serial commands.
While interfacing to the SMC02 is simple and straight-forward, it is very specific. Let's have a look at the set-upportion of the program:
Setup:HIGH SOut GOSUB Reset_SMC
...
Reset_SMC: LOW ResetPAUSE 1 HIGH ResetRETURN
The first line sets the idle state of the serial connec-tion. Since we're using a "true" mode, this is important sothat the start bit (high-to-low transition) of the first trans-mission is properly detected. Next, the controller is resetby taking the Reset input low and holding there for a mil-lisecond before retuning it high. The Pololu docs suggestthat one millisecond is overkill, but I found that at leastone millisecond was required for proper operation.
Okay, the robot is now ready to run. Since our only
Makin’ It Motorized
From discarded toy— to mobile robot!
Putting the Spotlight on BASIC Stamp Projects, Hints, and Tips
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Stamp by Jon Williams
Figure 1. The Pololu Motor Controller (right) with a BS1 module.
Stamp.qxd 1/2/2004 1:19 PM Page 28
FEBRUARY 2004
inputs are the bumpers, we'll use them as an indicator tostart running the program.
Wait_For_Start:GOSUB Get_Bumpers IF bumpers = %11 THEN Wait_For_Start PAUSE 1000
...
Get_Bumpers:bumpers = PINS & %00000011RETURN
We start by scanning the bumpers — a very simpletask. You may wonder why I would devote a subroutine callto what is, essentially, a single line of code. The answer isoptimism. Huh? Well, I'm pretty sure I'm going to do otherthings with this core code, so I can simply update this sec-tion using different sensors without upsetting the rest of theprogram. Okay, to collect the state of the bumpers we willread the Stamp input pins and mask those that aren't used(Bit2-Bit7).
Since our inputs are active-low, we'll get a value of %11in bumpers when there is no contact. If this is detected at thestart, we will loop back to Wait_For_Start until one or bothinputs change. Once a bumper input is detected, the programdelays for one second to let us get our hand out of the way.
And now we get to the heart of the program. Before wedo, let's look at the serial communication between theStamp and the Pololu Motor Controller. Communicationtakes place in four-byte packets like this:
SEROUT SOut, Baud, ($80, $00, control, speed)
The first byte of the packet is a sync byte and willalways be $80. The second byte identifies the device typeand will be $00 for motor controllers. The third byte — con-trol — identifies the motor number and direction (more in asecond), and finally, the fourth byte holds the speed (0- 127).
The control byte holds the motor direction in bit 0 (1 =forward, 0 = reverse) and the motor number affected by thecommand in bits 1-6 (see Figure 3). It may seem odd thatthere are six bits (0-63) for the motor number when there
are only connections for two. If you need tocontrol more than two motors, you can getadditional modules that will respond to dif-ferent motor number sets. The standard unithas a "-1" at the end of the part number.
Additional units are labeled "-2", "-3", and so on.To simplify our program, we can create a set of con-
stants for each motor (left and right) and for each direction.
SYMBOL MLFwd = %11 SYMBOL MLRev = %10 SYMBOL MRFwd = %00 SYMBOL MRRev = %01
The reason for the apparent contradiction of the direc-tion bit for the right motor is that the motors installed in arobot are flipped 180 degrees of each other. In order to makethe robot go in one direction, the motors must spin oppositeeach other. If both motors were going forward or reverse, therobot would just spin in place (we use this fact for turning).
Okay, then, the rest of the code should be easy tounderstand and it's fairly modular, so we'll go through it asection at a time.
Main:GOSUB Get_Bumpers IF bumpers = %11 THEN AccelerateGOSUB Reset_SMC speed = SpdMin PAUSE 10BRANCH bumpers, (Back_Out, Right, Left)GOTO Main
The purpose of the main loop is to scan the sensorsand BRANCH to the code section that handles robot direc-tion control. The first check is for a bumper,s value of %11which means no sensor contact. When there is no sensorcontact, we will continue forward and accelerate if notalready at top speed. When a bumper input is detected, theSMC02 will be reset to stop both motors, the robot speedwill be reset to its minimum, and BRANCH is used toselect the object avoidance code.
Accelerate:speed = speed + SpdRamp MAX SpdMaxSEROUT SOut, Baud, ($80, 0, MLFwd, speed)SEROUT SOut, Baud, ($80, 0, MRFwd, speed)PAUSE 50GOTO Main
29
ms Stamp
Figure 2. Bumper-Bot schematic. Figure 3. Control byte mapping.
Stamp.qxd 1/2/2004 1:21 PM Page 29
FEBRUARY 2004
When the robot isn't bumping into things, it will beallowed to accelerate. The speed is increased up to theSpdMax constant by the value set in SpdRamp. We cancontrol the acceleration by modifying SpdRamp, thedelay time, or both.
Our biggest chunk of work will come when we runhead on into an object; this is indicated by activity on bothbumpers. What we'll want to do is back up, turn out, andthen start again.
Back_Out:SEROUT SOut, Baud, ($80, 0, MLRev, speed) SEROUT SOut, Baud, ($80, 0, MRRev, speed)PAUSE 250GOSUB Reset_SMC SEROUT SOut, Baud, ($80, 0, MLFwd, speed)SEROUT SOut, Baud, ($80, 0, MRRev, speed)PAUSE 500SEROUT SOut, Baud, ($80, 0, MRFwd, speed) GOTO Main
This simple program uses a fixed turn time which will, ofcourse, require adjustment for each robot's specific mechan-ics (wheel size). A bit of interest can be added by randomiz-ing this delay beyond a specified minimum; this will make therobot look slightly more organic in its behavior.
Turning left or right based on a single bump input isvery easy. The motors already been stopped, we simplyhave to reverse the motor opposite the active sensor, andthen proceed forward again.
Right:SEROUT SOut, Baud, ($80, 0, MRRev, speed)PAUSE 200GOTO Main
Left:SEROUT SOut, Baud, ($80, 0, MLRev, speed)PAUSE 200GOTO Main
Once again, the size of the wheels on our robot willaffect how quickly it spins so we may need to adjust thedelay timing. Remember that we can "tune" the robot'sbehavior by adjusting movement delays and speed values.One note is that — depending on the size and weight of yourrobot — you may need to adjust the SpdMin constant. Somerobots will need just a little more oomph to get started.
And there you have it; a simple "bumper bot" usingthe BS1 — and only about half the code space at that.What this means is that we haveample room to add different"behaviors" to the robot. Let's takea look at one such behavior.
Go to the Light ...
In nature, there are animalsthat seek light (like moths to aflame). We can mimic this behav-
ior in a robot, and, when we do, we call the robot a pho-tovore. As our eyes detect light, we can use a photocell todetect light levels for the robot. By using two sensors, wecan compare the light levels of each and determine thedirection the robot should move to seek the light.
Figure 4 shows the connection of a single photocell tothe BS1 that will be read with the POT function (we'll needtwo of these circuits for our robot "eyes"). Note that theconfiguration of the RC components is different that thoseused with the BS2's RCTIME function. The reason for thisis that POT actually does more than RCTIME. The POTfunction charges the capacitor by taking the specified pinhigh for 10 milliseconds. It then starts a timer and active-ly discharges the capacitor by taking the pin low momen-tarily, then changing it to an input and checking to see ifthe capacitor voltage has dropped below the pin's switch-ing threshold. Scott Edwards wrote a very detailed descrip-tion of POT versus RCTIME back in Column #15 (May1996 — If you don't have the issue, you can download thecolumn as a PDF from the Nuts & Volts website).
In order to experiment with photovore code, I createda test program. I will leave it to you to fold it into yourrobot. The reason I created an experiment program toshare here is that I want to encourage you to do the samething with your projects. Yes, I am a very big proponent ofknowing the outcome of a project (having a specifica-tion), but we don't have to get there in one step. I frequent-ly get requests for assistance from youngsters who arejust starting out and trying to solve everything at once.I'm like a broken record and will continue to suggest thatwe work with intermediate or experimental programsbefore "going for the gold."
Okay, so what do we want to do? Knowing that themore light on the photocell will cause its reading to fall, wewill read both sensors and move in the direction of thesmallest reading. That's the broad stroke. What we'll find,however, is if our logic remains that simple, the robot willbe too sensitive and will appear "twitchy." We solve thetwitch by adding a threshold to the readings; that is, thedifference between the two readings must exceed a certainthreshold before we actually move. This helps accommo-date differences in components and smoothes things out.
Finally — and I only learned this after running the pro-gram a while — we need to accommodate the sensors beingsubjected to conditions where the readings will fall to zero.Due to the component values used, this can happen in total
darkness or when the sensor is bom-barded by bright light (swamped).
Before we get into the code,we need to run a calibration pro-gram to determine the scaling factorrequired by the POT command. LikeRCTIME, POT reads a 16-bit valuebut it will scale it to 8-bits for the pro-gram. The idea is to set the scalingfactor such that the maximum value
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Figure 4. Photocell circuit for the BS1 POT function.
Stamp.qxd 1/2/2004 1:23 PM Page 30
of the POT function is 255.After connecting our POT cir-
cuit, we'll select Pot Scaling fromthe editor's Run menu (Note: Thisfeature became available in Version2.1, Beta 1). Figure 5 shows the dia-log for POT Scaling. We must firstselect the POT pin from a drop-down. Then when we click Start, ashort program will be downloadedto the Stamp (yes, this overwritesthe current program). Normally, we would turn the potuntil we get the lowest reading in scaling factor. Since we'reusing a photocell, we adjust its value by shading it fromlight. I decided to use a translucent foam cup over my com-ponents to determine the scale level (max resistance).
I applied the same scale factor to both circuits andfound that I got significantly different values given thesame light level (both covered with the foam cup). Toadjust for component differences, I tweaked the scalingfactor of the second "eye" circuit until both sensorsreturned the same value under the same lighting.
Okay, let's look at the code:
Read_Eyes:POT EyeL, 145, lfEye POT EyeR, 175, rtEyeDEBUG CLS, lfEye, CR, rtEye, CR
Check_Eyes:IF lfEye = 0 AND rtEye = 0 THEN Is_Dark IF rtEye < lfEye THEN Is_Right
Is_Left:move = %10 IF lfEye = 0 THEN Eyes_Done lfEye = rtEye - lfEye IF lfEye >= Threshold THEN Eyes_Done move = %00 GOTO Eyes_Done
Is_Right:move = %01IF rtEye = 0 THEN Eyes_DonertEye = lfEye - rtEyeIF rtEye >= Threshold THEN Eyes_Donemove = %00GOTO Eyes_Done
Is_Dark:move = %11
Eyes_Done:RETURN
The code starts by reading each "eye" into its own vari-able and displaying the readings in the DEBUG window.Then we check to see if both values are zero; this will happenin total darkness (due to the POT function timeout) or whenboth photocells are swamped with light. In either, case wewant the robot to hold still. Setting the move variable to %11tells our main code that this is the case.
Under most conditions, we'llhave at least one photocell read-ing, so we do a comparison to seewhich side is getting the most light(it will have the lowest value). Let'sassume that the left photocell had alower reading and go through thatsection of code. The code for theright side works identically.
We'll assume that the thresh-old is going to be exceeded and
preset the move variable to left (%10). Next, we check thevalue of the left photocell. If it's zero (swamped), there isno need to check the threshold and we can exit. If it is notswamped, we will subtract the right photocell reading fromthe left and compare the result against the threshold. If thethreshold is exceeded, we exit, otherwise the move variableis set to forward (%00). Since this is a demo program, weshould have some code to show us what's happening withthe sensors. Here's a short bit of code to do that:
Main:GOSUB Read_EyesBRANCH move, (Go_Straight, Go_Right, Go_Left,
Stay_Still)
Go_Straight:DEBUG "Straight"GOTO Main
Go_Right:DEBUG "Right"GOTO Main
Go_Left:DEBUG "Left"GOTO Main
Stay_Still:DEBUG "Holding..."GOTO Main
There's no magic here, we're simply using BRANCHto jump to code that will display the direction of robot trav-el. This lets us test our "robot eyes" on a breadboard. Bendthe photocell leads so that they're oriented on the horizon-tal plane, and then turn them out from each other toexpand the field of view. By shining a flashlight spot infront of the photocells, the DEBUG window will show therobot's movement behavior.
All that's left to do is replace the DEBUG statementswith appropriate motor controls (and you know how to dothat) to create a robotic photovore — kind of like an elec-tronic kitten (cats love to chase flashlight spots), only thisone won't scratch furniture or need a litter box!
Well, I told you we'd take it easy this time, and hopeful-ly you agree with me that this was no less fun that we usu-ally have. Modifying an existing motorized toy is a great wayto get kids into robotics — no matter what their age.
Until next time, Happy Stamping. NV
FEBRUARY 2004
Stamp
31
Figure 5. POT Scaling dialog in the Windows editor.
Stamp.qxd 1/2/2004 1:23 PM Page 31
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FEBRUARY 200432
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programming in mind. It features a convenient 10-pinheader that can be connected to a target board. Thisallows you to update a PIC's memory without removing thedevice from the board. This speeds the developmentprocess and allows you to program a surface mountdevice that is soldered in place.
The programmer isn't limited to in-circuit operation. Alarge selection of adapters is available for programmingindividual PICs. The programmer is available withaccessories, including an adapter for 8-pin through 40-pinDIP packages. Optional ZIF adapters support surface-mount and PLCC devices with up to 80 pins.
Windows software is included with the programmer. Itaccepts standard Microchip format .HEX files that aregenerated by MPLAB, C compilers, and BASIC compilers.Command line options allow the programmer to becontrolled from a batch file or shortcut for production use.
The software is loaded with selectable options,allowing you to customize your interaction with theprogrammer. A detailed memory view shows you eachsection of the memory in the PIC. The PIC's configurationbits can be set with convenient dropdown selections. Thelist of configuration settings is updated automatically whenyou select a device, so the list you see is tailored to the PICyou are programming.
The meLabs Serial Programmer with accessoriesretails for $119.95. This includes the programmer board,software, ZIF adapter for 8-pin through 40-pin PICs, ACpower adapter, and 9-pin serial cable.
MICROENGINEERING LABS, INC.PO Box 60039
Colorado Springs, CO 80960719-520-5323 Fax: 719-520-1867
Web: www.melabs.comCircle #140 on the Reader Service Card.
LOW-COST MC9S12C32 MCUMODULE DOUBLES ASEVALUATION/TRAINING
PLATFORM
TTechnologicalArts has
launched twonew MCU prod-
ucts, broadening itshighly popular line of
New Product News
FEBRUARY 2004 33Circle #143 on the Reader Service Card.
New Products.qxd 1/2/2004 2:15 PM Page 33
modular microcontroller boards.Offering engineers and educators a versatile and
economical platform for evaluating and applyingMotorola's latest HCS12 microcontroller offering,M68MOD912C32 and M68DKIT912C32 smooth themigration path from development to productimplementation/production. Because the same coremodule used in the evaluation phase is economicalenough to be incorporated into the end product, time tomarket for commercial applications is shortenedconsiderably. Motorola has built the MC9S12C MCU familywith a high-speed, low-voltage 16-bit core, up to 4K RAM,up to 128K sector-erasable flash, along with an array ofhardware subsystems — all in a low-cost surface-mountpackage.
The 9S12C32 contains an asynchronous serialcommunications interface (SCI), a serial peripheralinterface (SPI), an 8-channel 16-bit timer module (TIM), a6-channel 8-bit Pulse Width Modulator (PWM), an 8-channel, 10-bit analog-to-digital converter (ADC) and aCAN 2.0 A, B software-compatible module (MSCAN12).The subsystems, together with the on-chip single-wireBackground Debug Module (BDM), make this chip idealfor use in the evaluation and development of all "C"-seriesderivatives of the 9S12 family.
The M68MOD912C32 MCU Module implements the48-pin version of the MCU. Combining all the essentialMCU support circuitry with a small-footprintmonitor/loader program in Flash, this module comesready-to-use "out of the box" with little added hardwarerequired in many applications. The MCU Module,designed in a standard 32-pin DIP footprint, includes thefollowing features: 5-volt regulator, 8 MHz crystal, PLLcircuit, RS232 transceiver circuit, and standard 6-pin BDMconnector.
To facilitate evaluation of the 9S12C32 MCU, severalproduct bundles are being offered. An MCU Modulepackage — including MC9S12C32 MCU Module, usermanual, Metrowerks CodeWarrior™ HC(S)12 version 4.0CD, and resource CD — is available for $24.95(USD)(M68MOD912C32). A Demo Kit — including MC9S12C32
MCU Module, Demo DockingBoard, CDs, Serial Cable,
and DC power supply — isavailable for $49.95 (USD)(M68DKIT912C32). Thereis also a European
version, which includesa universal power
supply, for $64.95 (USD)(M68DKIT912C32-E).
For more information, contact:
TECHNOLOGICAL ARTS877-963-8996 Fax: 416-963-9179
Web: www.technologicalarts.comCircle #135 on the Reader Service Card.
WIRELESS MODULES DELIVERLONGEST-RANGE AND LOWESTCOST
TThe new LR Seriesof RF modules
from Linx Technologiesprovides a 5-0 timesrange improvementover previous discrete
FEBRUARY 2004
Development Tools for PICmicro MCUs
microEngineering Labs, Inc.
EPIC Programmer - $59.95
EPIC Assembled $59.95EPIC Bare PCB $34.9540/28 pin ZIF Adapter $34.95AC Adapter $9.95EPIC Bundle $99.95(bundle includes EPIC, AC Adapter,25-pin Cable, and 40/28 pin ZIF)
Low cost programmer for PIC12Cxxx, 12CExxx, 12Fxxx, 14Cxxx, 16C505, 55x, 6xx, 7xx, 84, 9xx, 16CE62x, 16Fxxx, 17C7xx, 18Cxxx, and 18Fxxx microcontrollers. Can be used for In-Circuit programming. Connects to parallel port. Software included for DOS and Windows 9x/ME/2K/XP.
PicBasic converts your BASIC programs into files that can be programmed directly into a PICmicro MCU. Make use of the latest microcontroller technology without learning C or Assembler. Compatible with DOS and Windows 9x/ME/2K/XP.
PicBasic Compiler
PicBasic Compiler $99.95PicBasic Pro Compiler $249.95
LAB-X1 for 40-pin MCU (shown)LAB-X2 for 28 or 40-pin MCULAB-X3 for 18-pin MCULAB-X4 for 8 or 14-pin MCU
Assembled hardware platforms for development. Each has RS-232 serial port, clock oscillator, power supply, plus other hardware. ICSP connection allows you to make program changes without removing the MCU. Bare PCBs available.
LAB-X Experimenter Boards
Assm: $199.95, Bare: $49.95Assm: $69.95, Bare: $24.95Assm: $119.95, Bare: $24.95Assm: $124.95, Bare: $24.95
PICProto3 for 28-pin PICmicro MCUs (3" x 3") $14.95PICProto4 for 8-pin or 14-pin (1.5" x 3") $9.95PICProto8 for 8-pin (1.2" x 2") $8.95PICProto18 for 18-pin (1.5" x 3") $9.95PICProto18L for 18-pin (3.6" x 4.1") $19.95PICProto64 for 40-pin (3.6" x 4.1") $16.95PICProtoUSB for 28-pin or 40-pin (3.6" x 4.1") $19.95PICProto80 for 64 or 80-pin TQFP (3.6" x 4.1") $19.95PICProto80 with pre-soldered PIC18F8720 $60.00
PICProto prototyping boards are designed to help you get your PICmicro projects finished faster, with less effort. There is a high-quality blank PICProto board for almost every PICmicro microcontroller. Each double-sided board has a solder mask on both sides and hundreds of plated-through holes for your parts.
PICProto Prototype Boards
Programming PIC Microcontrollers with PicBasic $49.95Experimenting with the PicBasic Pro Compiler $39.95PIC Basic - An Introduction $34.95PIC Microcontroller Project Book $29.95Easy Microcontrol'n $29.95Time'n and Count'n $34.95Microcontrol'n Apps - PIC MCU Application Guide $44.95Serial Communications Using PIC Microcontrollers $49.95
Books on PicBasic and PICmicro MCUs
Phone: (719) 520-5323Fax: (719) 520-1867
Box 60039Colorado Springs, CO 80960
Order online at:www.melabs.com
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and modular solutions, thereby estab-lishing a new range benchmarkamong comparable products.
These tiny SMD modules providea complete and cost-effective solu-tion for the wireless transfer of serialdata, control, or command informa-tion over distances in excess of 3,000feet.
No external components arerequired (except an antenna), allow-ing for easy design integration, evenby engineers without previous RFexperience. The modules interfaceto virtually any data source, includ-ing microcontrollers and decoderchips, making them ideal for appli-cations, such as remote control, keyless entry, and periodic datatransfer.
LR Series modules operate in thefavorable 260-470 MHz band, and aredesigned for full regulatorycompliance and interferenceimmunity, ideally suiting them todomestic, as well as export wirelessapplications.
The modules operate over a 2.7-5.2 VDC range and feature low powerconsumption, (5.2 mA operational, 28µA sleep), a wide operationaltemperature range (-40° to +70° C),adjustable transmitter power, and areceiver sensitivity in excess of -5 dBm.
A precision-crystal locked PLLarchitecture allows for transparentdata transfer at rates of up to 10kbps.
The LR Series is in full productionand priced at approximately $3.58(TX) and $6.78 (RX), in volumeproduction quantities. Visit LinxTechnologies’ website for more onthis product.
For more information, contact:
LINX TECHNOLOGIES,INC.
575 SE Ashley Pl.Grants Pass, OR 97526
800-736-6677Fax: 541-471-6251
Web:www.linxtechnologies.com
Circle #125 on the Reader Service Card.
Visit www.sgcworld.com
for more information on the entire line
of ADSP2 solutions.
SG-2020TransceiverCat. # 05-04
Your HF Solution
Got Noise? Get ADSP 2!
SG- 2020 ADSP2The SG-2020 HF Transceiver covers 1.8 to 29.7 Mhz in USB, LSBor CW. It adjusts from 1 to 20 watts of output power, uses a 9-18 VDC supply, and draws as little as 400 mA in receive. Thetransceiver has built in ADSP2 for 12 to 26 dB of superior qualitynoise reduction, and 3 proprietary digital bandpass filters. Only2-3/4 inches high, 6 inches wide, and 7-1/4 inches deep, with a metal case that weighs in at under 5 pounds complete. It’srugged, dependable and goes where you want to go.
Basic HF
Deluxe performance in a back-to-basics design: The SG-2020 ADSP2
Anyone from a first-timer to an old-timer can be on the airNOW. No menus, no confusion, two-step operation. Justselect your frequency and transmit! The SG-2020 with ADSP2
is perfect for base, backpacks, or business trips.
phone us at
800.259.7331SGC, Inc. 13737 SE 26th St, Bellevue, WA 98005
35FEBRUARY 2004 Circle #120 on the Reader Service Card.
New Products.qxd 1/2/2004 2:15 PM Page 35
The Robot Builder’s Bonanzaby Gordon McComb
A major revision of thebestselling "bible" of ama-teur robotics building —packed with the latest inservo motor technology,microcontrolled robots,remote control, LegoMindstorms Kits, and othercommercial kits. $24.95
Encyclopedia of ElectronicCircuits,Volume Sevenby Rudy Graf
Designed for quick reference and on-the-jobuse, the Encyclopedia ofElectronic Circuits, VolumeSeven, puts over 1,000 state-of-the-art electronic andintegrated circuit designs atyour fingertips.This collec-tion includes the latest designs from indus-try giants such as Advanced Micro Devices,Motorola,Teledyne, GE, and others, as wellas your favorite publications, including Nuts& Volts! $39.95
Electronic Troubleshootingby Daniel Tomal / Neal Widmer
If you work with elec-tronics — either throughyour profession or yourpastime — here’s oneresource you need handyat all times: the updated,Third Edition ofMcGraw-Hill’s ElectronicTroubleshooting. Revampedto include the latest elec-trical and electronic devices and problem-solving methods, this information-packedvolume provides a fundamental under-standing of electronic troubleshooting the-ory. $49.95
Robots,Androids, andAnimatrons, Second Editionby John Iovine
In Robots, Androids, andAnimatrons, Second Edition,you get everything youneed to create 12 excit-ing robotic projects usingoff-the-shelf productsand workshop-builtdevices, including a com-plete parts list.Also idealfor anyone interested in electronic andmotion control, this cult classic gives youthe building blocks you need to go practi-cally anywhere in robotics. $19.95
Building Robot Drive Trainsby Dennis Clark / Michael Owings
This essential title is justwhat robotics hobbyistsneed to build an effectivedrive train using inexpen-sive, off-the-shelf parts.Leaving heavy-duty “techspeak” behind, the authorsfocus on the actual con-cepts and applications nec-essary to build — andunderstand — these criticalforce-conveying systems.
Everything you need to build yourown robot drive train:
* The Basics of Robot Locomotion* Motor Types: An Overview* Using DC Motors* Using RC Servo Motors* Using Stepper Motors* Motor Mounting* Motor Control* Electronics Interfacing* Wheels and Treads* Locomotion for Multipods* Glossary of Terms/Tables, Formulas
Troubleshooting & RepairingConsumer Electronics Without a
Schematicby Homer Davidson
In this book, HomerDavidson gives youhands-on illustrated guid-ance on how to trou-bleshoot and repair awide range of electronicproducts — when youcan’t get your hands onthe schematic diagrams.He shows you how todiagnose and solve circuit and mechanicalproblems in car stereos, cassette players,CD players,VCRs,TVs and TV/VCR com-bos, DVD players, power supplies, remotecontrols, and more. $34.95
JunkBots, Bugbots, and Bots onWheels: Building Simple Robots With
BEAM Technologyby David Hrynkiw / Mark Tilden
Ever wonder what to dowith those discardeditems in your junk draw-er? Now, you can useelectronic parts from oldWalkmans, spare remotecontrols, and even paperclips to build your veryown autonomous robotsand gizmos. Get step-by-step instructions from the Junkbot mastersfor creating simple and fun self-guidingrobots safely and easily using common andnot-so-common objects from around thehouse. Using BEAM technology, ordinarytools, salvaged electronic bits, and theoccasional dead toy, construct a solar-pow-ered obstacle-avoiding device, a mini-sumo-wrestling robot, a motorized walking robotbug, and more. Grab your screwdriver andjoin the robot-building revolution! $24.99
Applied Robotics IIby Edwin Wise
Instructive illustrations,schematics, part num-bers, and sources arealso provided, making thisbook a “must” foradvanced builders with akeen interest in movingfrom simple reflexes toautonomous,AI-basedrobots. Create larger andmore useful mobilerobots! Ideal for serious hobbyists, AppliedRobotics II begins by discussing PMDCmotor operation and criteria for selectingdrive, arm, hand, and neck motors.$41.95
WE ACCEPT VISA, MC, AMEX, andDISCOVER
Prices do not include shipping andmay be subject to change.
Ask about our 10% subscriber discount on selected titles.
Robotics
Electronics
The Nuts & Volts Hobbyist BookstoreS e l e c t e d T i t l e s f o r t h e E l e c t r o n i c s H o b b y i s t a n d T e c h n i c i a n —
CNC Roboticsby Geoff Williams
CNC Robotics gives youstep-by-step illustrateddirections for designing,constructing, and testinga fully functional CNCrobot that saves you80% of the price of anoff-the-shelf bot — andcan be customized tosuit your purposesexactly, because you designed it.Written byan accomplished workshop botdesigner/builder. $34.95
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10 Cool LEGO Mindstorms: DarkSide Robots,Transports, and Creatures
by Kevin Clague / Søren Rolighed /Miguel Agullo / Hideaki Yabuki
Okay, you bought thekit for yourself or oneof your kids.You usedthe instructions in thebox to build a robotor two. Now what?You may not be readyto design and buildyour own robots, butyou don't want tobuild the same robotover again.This book is the perfect way tobuild additional projects from the same kit,then improvise and design your own.Tencool projects — one hour each — perfect!$24.95
FEBRUARY 2004
$24.95
NNEEW!W!
BookstoreFeb04.qxd 1/2/2004 1:59 PM Page 36
37
Call 1-800-783-4624 today! or order online at www.nutsvolts.com
Homemade Lightning: CreativeExperiments in Electricity
by R.A. FordEnter the wide-openfrontier of high-voltageelectrostatics with thisfascinating, experiment-filled guide.You'll discoverhow to make your ownequipment, how electrici-ty is used in healing, andhow many experimentsin high potential physicswork! $24.95
The Audiophile's ProjectSourcebook: 120
High-Performance Audio ElectronicsProjects
by G. Randy SloneThe Audiophiles ProjectSourcebook is devoid of thehype, superstition, myths,and expensive fanaticismoften associated with high-end audio systems. It pro-vides straightforward help inbuilding and understandingtop quality audio electronicprojects that are based on solid science andproduce fantastic sound! $29.95
The Nuts & Volts of BASICStamps,Volumes 1-4
In 1995, Scott Edwards began authoring acolumn on BASIC Stamp projects in Nuts& Volts Magazine.The column quicklybecame a favorite of Nuts & Volts readersand continues today with Jon Williams atthe helm. The Nuts & Volts of BASIC Stampsis a four-volume collection of over 100 ofthese columns.
PIC Microcontroller Project Bookby John Iovine
This project-orientedguide gives you 12 com-plete projects, including:using transistors to con-trol DC and AC motors,DTMF phone number log-gers, distinct ring detectorand routers, homeautomation using X-10communications, digital oscilloscopes, simula-tions of fuzzy logic and neural networks ...and many other applications. $29.95
Programming & CustomizingPICmicro Microcontrollers,
Second Edition by Myke Predko
This book is a fullyupdated and revisedcompendium of PIC programming information.Comprehensive coverageof the PICMicro’s hardware architecture and software schemescomplement the host ofexperiments and projects making this atrue "learn as you go" tutorial. $49.95
Guide to PICMICROMicrocontrollers
by Carl BergquistAimed at both studentsand seasoned users, thisbook will take the readerthrough the peripheralinterface controller (PIC)like no other text.Hardware and softwareare also discussed indetail.Topics include: physical appearance,electrical structure, software requirements,hardware requirements, prototype layoutboards, simple PIC programmers, PICinstruction set, use of the Microchip toolsincluding MPLAB and Technical Library,software applications, software codes, and8-10 PIC projects. $45.95
Programming and Customizingthe OOPic Microcontroller
by Dennis ClarkIf you’re a robotics pro-fessional or hobbyist,here’s the one bookyou’ll need to keep yourwork on the leading edge— Programming andCustomizing the OOPicMicrocontroller.This is theofficial OOPic Handbook,fully endorsed by Savage Innovations, theworld’s only manufacturer of OOPicmicrocontrollers.As the first book of itskind, this volume is destined to becomethe standard against which all other OOPicbooks will be judged. $39.95
CD Rom &PCB
Included
STAMP 2: Communications andControl Projects
by Thomas PetruzzellisWith the help of detailedschematics, informativephotos, and an insightfulCD-ROM, STAMP 2Communications andControl Projects leads youstep by step through 24communications-specificprojects.As a result,you’ll gain a firm understanding of Stamp 2and its programming methodologies — aswell as the ability to customize it for yourown needs and operating system. $29.95
Guide to Electronic Surveillance Devices
by Carl BergquistEnjoy the peace of mindthat comes from know-ing how to set up andmaintain an effectivesurveillance system!Perfect for do-it-your-selfers, ElectronicSurveillance Devices con-tains all of the informa-tion needed to enhancethe safety and security of a home or office,from safeguarding against theft to monitor-ing employee performance and preventingillegal activities from occurring on site.$35.95
Microcontrollers
High Voltage
Build Your Own PC HomeEntertainment System
by Brian UnderdahlLearn to use PC DVDdrives, DVD recorders,and massive hard drivesto create a home enter-tainment system that'scomparable to whatyou'd enjoy from expen-sive, individual compo-nents.Who needs themovies? Now, you canachieve stunning audio and top qualityvideo results through your PC.This bookshows you how to build your own homeentertainment center using an ordinaryPC.Watch and record TV shows andmovies, put your entire CD collection onyour hard drive, and listen to radio stationsfrom around the world. $24.99
Home Entertainment
$14.95Volume 4
$49.95All 4 Volumes
PICmicro MCU C by Nigel Gardner
This second edition bookis a complete introductionto programming MicrochipPICmicros in C with theuse of the CCS C compil-er. The book overviewsthe ease of using C andthe CCS compiler foroptimization of your pro-gramming. There are many examples toget you started on while using the compil-er. $29.95
CD RomIncluded
CD RomIncluded
$9.95Volume 3
FEBRUARY 2004
NNEEW!W!
NNEEW!W!
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If you don’t see what you need here,check out our on-line store at
www.nutsvolts.com for a complete listing of the titles available.
BookstoreFeb04.qxd 1/2/2004 1:59 PM Page 37
Hobby electronics is often described as indecline. Sales of books and electronic parts aimedat the hobby electronics market have fallen. Highschool science fairs once included a fair number ofelectronics projects. Now such projects are scarce.RadioShack once sold hundreds of thousands ofhobby electronics books a year. Now they sellnone.
In view of these developments, is there a futurefor hobby electronics? The evidence shows thatthere clearly is. Before I explain why, let's turn theclock back a generation or so and review the evo-lution of hobby electronics.
From the 1950s to the 1970s, electronics hob-byists built light-controlled relays, solar batteries,tiny radios, and many kinds of electronic gameslong before such gadgets were sold in stores. Thisprovided a terrific incentive for both teens andadults to become interested in do-it-yourself elec-tronics.
The arrival of inexpensive TTL and CMOS inte-grated circuits in the early 1970s greatly expandedthe horizons for electronic hobbyists. Now we couldbuild counters, clocks, timers, and controllers thatwere far more sophisticated than basic transistorprojects. Hobby electronics was at its peak, and theelectrical engineering departments of colleges anduniversities could count on having many studentswho had learned the basics before they arrived on
campus.The arrival of Intel's 8080 microprocessor had
far more impact on hobby electronics than thetransistor and the integrated circuit. Now hobbyistscould build their own computers, the ultimate do-it-yourself project. They didn't even have to designthe machine, for they could buy a complete kit for$395.00 from MITS, Inc., a small company inAlbuquerque, New Mexico.
The MITS Altair 8800 was featured on thecover of the January 1975 issue of PopularElectronics. The article attracted the attention oftwo young computer enthusiasts, Paul Allen andBill Gates. Allen and Gates soon moved into theMITS building in Albuquerque, where they estab-lished a software company to develop BASIC forthe Altair. They named their company Microsoft.
From 1975 to the mid-1980s, eager hobbyistsbuilt many kinds of gadgets and circuits for theircomputers to control. Hundreds of booksdescribed do-it-yourself computer projects.
Yet the hobby computer era was a bubble, nota trend. As more and more companies entered thecomputer market, there soon came a time when itwas no longer practical to offer kit computers. Thehobby electronics magazines eventually fell victimto the computer era to which they gave birth.
So where does this leave hobby electronicstoday? Our numbers have declined, but the quality
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of hobby electronics today is as high as ever. Theold hobby electronics magazines have beenreplaced by a magazine with consistently highquality projects and articles. I feel the same senseof excitement opening up the latest issue of Nuts& Volts as I did back in the 1970s when I was writ-ing articles and columns for Popular Electronics.
The sharp decline in electronics projects at sci-ence fairs and the declining enrollment in engineer-ing courses at colleges and universities are trou-bling. But hope has arrived in the form of hobbyrobotics. Just a few weeks ago, my daughter Sarahparticipated in a high school robotics competition.The students learned a great deal about basic elec-tronics and mechanics from the experience.
The overall number of electronics hobbyistswas sharply reduced by the personal computer rev-olution they helped bring about. Yet there remainplenty of electronics enthusiasts who still enjoydesigning and building circuits even more powerfuland versatile than those we built a decade ago.Many hobbyists use computers to program theirprojects, which these days include many highlycreative robotic devices. Others have found spe-cialized niches for their electronics pursuits. In mycase, for example, I design and use various instru-ments that measure the ozone layer, haze, andultraviolet. Some of my inexpensive instrumentshave found errors in data from four remote sensing
satellites.So while the overall number of electronics hob-
byists has declined since the 1980s, there are stillplenty of fun, creative, and even scientific thingsthat we hobbyists can do. Thanks to mail ordersuppliers like Digi-Key and Jameco, we can ordervirtually any electronic parts we need. And thanksto eBay and other web resources, we can buy highquality test equipment at only a fraction of theprice we might have paid a decade ago. We canbuild lasers, radio-controlled electric aircraft, seis-mometers, and optical fiber communication links.
As for the future, I still remember the hundredsof excited spectators and participants who filled alarge gymnasium during the recent robotic compe-tition in which my daughter participated. Thesecompetitions are occurring all around the US, andthe number of students who have built radio-con-trolled "robots" is probably far greater than thosewho built their own computers back in the 1970s.
So while hobby electronics lost many of itsenthusiasts to the computer revolution it helpedbegin, there's still plenty to do for those of us whoenjoy designing, soldering, tinkering, and program-ming. Just imagine the possibilities. Maybe someclever hobbyists can show the high school roboticsmovement how to build remotely piloted, indoorhelicopters that score points by flying figure-8s anddropping plastic rings onto poles. NV
About the Author Forrest M. Mims III, an active member of the Society for Amateur Scientists(www.sas.org), develops lab kits for RadioShack when he is not doing professional science. His electronics books
have sold some 7.5 million copies.Visit him on the web at www.forrestmims.org
39FEBRUARY 2004
Mims.qxd 1/2/2004 11:36 AM Page 39
With "smart" cell phones, Wi-Fi, RFIDtag systems, and so many othernew applications for radio waves
these days, it is obvious that we are immersedin an electromagnetic field ("EMF") just abouteverywhere we go. Whether or not this isharmful to human beings is a controversialsubject, although many scientists will tell youit is not hurting us at the present intensitylevel. However, you can easily demonstratethat such fields can be pretty strong. At thevery least, this indicates an ever increasingneed for shielding in hobby electronics proj-ects, to avoid picking up troublesome noise.
Because there is so much EMF in the gen-eral environment, several research projects(mostly military) are purposely "harvesting"the energy and trying to use this to operatesensors, tiny transmitters, and other devicesthat will never require batteries or even solarcells. Another branch of the research aims touse strictly mechanical noise to harvest ener-gy from the environment, similar to the way aself-winding mechanical wristwatch operates.However, many useful things such as sensorsneed electric power in some way, and it is usu-
ally inefficient to collect low-level mechanicalenergy and convert it to electricity.
Although a radio aerial converts electro-magnetic waves into electricity, the voltagesthat are fed to cell phones from ferrite anten-nas are typically only a few microvolts. Itmight be a surprise to the reader, but a milliontimes more voltage — possibly four volts or so— can actually be harvested by simple meansfrom many common environments, by usinga fairly long antenna and a good ground. Thecurrents are small, but they can easily beaccumulated, enough to briefly light aTungsten incandescent bulb. With a trans-former, these voltages can be stepped upenough to flash a neon bulb. It's amazing, butquite true, and all this can be verified withexperiments that are easy to do.
The Experimental Set-up
The circuit is shown in Figure 1, but it isnot necessary to use any actual switches.Alligator clips could be used instead. Forexample, looking at S1 in the diagram, a cliplead could be temporarily connected from the
FEBRUARY 2004
HarvestingElectricity From The Environment
Light a 100 Volt Bulb with the Wavesthat Surround You
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TThhiiss MMoonntthh’’ssPPrroojjeeccttss
Harvesting Electricity . .40Capacitance Meter . . 43Membrane Switches . 48Blackbox Frisbee . . . . 52
TThhee FFuuzzzzbbaallll RRaattiinngg SSyysstteemm
To find out the levelof difficulty foreach of these
projects, turn toFuzzball for the answers.
The scale is from 1-4, with four
Fuzzballs being the more difficult
or advanced projects. Just lookfor the Fuzzballs inthe opening header.
You’ll also find information includedin each article onany special tools or skills you’ll
need to completethe project.
Let the soldering begin!
Project by Dan Shanefield
FIGURE 1
Shanefield.qxd 1/2/2004 11:48 AM Page 40
antenna to the AC voltmeter.For the antenna, a 15-foot-long extension cord can be
used, or any other insulated wire of roughly that length.For the first experiments, it can be stretched out on thefloor of your home, maybe extending into another room.
A "quiet" ground is needed, to avoid picking up strayvoltages that are not electromagnetic in origin. It should benoted that the "return" or "neutral" wire of 120 volt ACpower lines (color coded white in the US) is not suitable,because it often has considerable voltage on it, due toresistive ground connections. Usingthat would be cheating, if we are inves-tigating the power that comes strictlyfrom EMFs in the air. Similarly, thegreen coded safety connection mighthave about 10 volts on it — relative totrue ground — if a clothes dryer or airconditioner is running nearby. For theseexperiments, a better ground connec-tion can be obtained by hammering abare metal curtain rod into the earthand attaching a clip lead to it.
The meter to measure the ACvoltage can be any instrument withan input impedance of around 10megohms, such as a portable digitalmultimeter. This could also be usedto serve as the ammeter and DC volt-meter shown in Figure 1, if it is dis-connected from position S1 and thenreconnected at S2, and later at S3.Alternatively, of course, separatemeters could be used.
A full wave diode bridge can rec-tify the input, as shown. However,good results can be obtained with justdiode D1, with a plain wire in place ofD3, and no connections at all in posi-tions D2 and D4.
The LED should be a low currenttype, such as RadioShack catalognumber 276-044, which will producevisible light with only two milliamps.The Tungsten incandescent bulb alsohas to be a low current type, such asRadioShack catalog number 272-1139 or similar, which will light upwith only 20 mA. The transformercan be a step-down 120-volt to six-volt power supply type, which we willoperate "backwards," in a 20:1 step-up mode. Switch S6 (or just an ordi-nary clip lead) is going to be used todump the capacitor's charge into thelow voltage winding, and almost anyneon or argon lamp attached across
the high voltage winding will then flash.
The Waves that Surround Us
Unless you are down in an iron mine, you are probablyin a measurably strong electromagnetic field. Even insidea metal building, there is usually some oscillating fieldcoming from the 120-volt AC power lines in the walls, justbecause of the power that always goes to computers,"instant-on" TV sets, and even the multiplicity of electric
FEBRUARY 2004 41
eld Harvesting Electricity
Circle #122 on the Reader Service Card.
Shanefield.qxd 1/2/2004 11:49 AM Page 41
clocks that are in most people's houses. This is especial-ly true in an urban or suburban area, if there are powerlines up on telephone poles near the house — the amountof EMF radiation that they generate might surprise you.At any rate, you can sense such fields with the apparatusof Figure 1 and judge for yourself.
Inside a typical house or office building, quite a lot ofour environmental EMF is 60 Hz AC or harmonics of it.Weaker radiation is at the extra-low frequencies generatedby thunderstorms all throughout the world, as readers ofNuts & Volts already know from the article "DXThunderstorms in Africa" in the October, 2003 issue(page 44). A wide variety of radiation is being suggestedas sources of energy to be harvested, as described in thepublications that any Internet web search engine will turnup, if you enter "harvest electricity" in the dialog box.However, more and more RF will be at microwave frequen-cies, as we make increased use of things like the RFIDtags that Wal-Mart and other big businesses are putting inplace by the millions, and as Wi-Fi gets into more publicplaces and even into home networks.
A Few Measurements
With a 15 foot or longer antenna snaking along thefloor from room to room in a typical suburban house, andusing a grounding rod outside, you are likely to see fromtwo to four volts of AC (RMS). Surprisingly, this might notvary much as a high current appliance such when aclothes dryer is switched on and off. Taking the antennaoutdoors, draped horizontally over some beach chairsover a backyard lawn, you can expect a lower voltage,possibly only a few hundred millivolts. Arranging theantenna vertically up a tree, the measured voltage is notusually much different, in spite of the fact that many radiotransmissions are vertically polarized. Moving the wholeapparatus to a front yard, near power lines on telephonepoles, the measurements are likely to be more like what isseen inside a house, possibly a few volts. On the otherhand, in a rural setting, away from houses and power lines,the voltages are likely to be lower.
Looking at the input with an oscilloscope attached inplace of the AC voltmeter of Figure 1, there might be a lot
of 60 Hz content visible in the received signal. In somecases, there is much distortion of the basic sine wave, andthere is more harmonic content than fundamental, partic-ularly at 120 Hz, due to various phase delays. There isalmost always a great deal of continuously varying, highfrequency hash riding on top of the steadily repeating sig-nals. Some of this is at extremely high frequencies and con-sists of digital pulses, even though the simplified antennabiases the apparatus towards picking up low frequencies.
From observations such as these, it can be seen thatour electronic devices need good shielding against EMFsthese days. Maybe the shields will have to be improved inthe future, as more and more of these invisible fieldsbecome commonplace. In many cases, it is already nec-essary to use "guards" as well as "shields," for devicessuch as op-amps with very high amplification factors.(The difference between a shield and a guard is explainedin a textbook I wrote, Industrial Electronics forEngineers, Chemists, and Technicians, William AndrewPublishing, 2001.) It also seems sensible to re-evaluate thepossible effects on human beings from time to time, asthese fields get more intense, and their frequencies go up.
Accumulating the Energy
With the attachment of a rectifier, DC can be storedin the 1,000 µF capacitor. The full wave diode bridge inthe figure is efficient, but slower accumulation can beobtained with just D1, as mentioned above. By switchingS2 (or just using a clip lead), the interrupted DC flow canbe estimated, and typical readings inside a house mightbe (surprisingly!) as high as a few milliamperes, althougha tenth of that is more common.
After approximately an hour of charging, the 1,000µF capacitor voltage can be measured via S3. This will bethe RMS AC voltage times the square root of 2, and fourvolts is typical when measured inside a suburban house.In an electrolytic capacitor, it is enough energy to light alow current LED, through S4. In fact, a brief flash can bevisible in a low current Tungsten bulb, via S5.
Using S6 or the equivalent, the capacitor's chargecan be suddenly dumped into the primary of a step-uptransformer. (As mentioned above, a power transformerthat is normally step-down can be used "backwards" forthis experiment.) A ratio of 10:1 or 20:1 will usually lighta small neon or other gas discharge bulb for an instant.On the oscilloscope, this pulse can register as high as 100volts. Thus, a fairly high voltage can be harvested fromour environment, by very simple means. NV
FEBRUARY 2004
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Insulated wire 15 or 20 feet long (for antenna)Metal rod (for ground connection)Diode Or full wave rectifier bridgeCapacitor 1,000 µF or similarMultimeter 10 megohm input impedanceClip leads Or 3 SPST and 3 SPDT switches2 mA LED Like RadioShack 276-04425 mA bulb Like RadioShack 272-1139 Transformer 20:1 or similarMisc. A small neon or argon bulb
PARTS LIST
Dan Shanefield was a retired Bell Labs scientist, then becamea Distinguished Professor at Rutgers University, and is nowretired from that job, as well.You can visit his website at
http://homepage.mac.com/shanefield
AUTHOR BIO
Shanefield.qxd 1/2/2004 11:52 AM Page 42
There are many ways of measuring capacitance. Inthis article, I describe a simple method that makesuse of the features of the ADuC812 one of Analog
Devices MicroConverters®. The capacitance meter meas-ures capacitances between 100 nF and 100 µF with ease.The capacitance meter sends the measured capacitanceto a PC's COM port.
The MicroConverter
Before describing how I measure the capacitance, Iwould like to describe MicroConverters in general and theADuC812 in particular. Analog Devices has a line of prod-ucts that are essentially microcontrollers with data conver-sion peripherals on-board. They refer to this product line asMicroConverters. The ADuC812 (where ADuC stands forAnalog Devices MicroConverter) is essentially an 8052microcontroller with eight channels of A/D, two channelsof D/A, and 8 Kbytes of FLASH program memory that canbe programmed across a serial port. Other peripheralsthat I did not need for this project include user programma-ble FLASH memory, a watchdogtimer, and a ninth channel of A/Dthat is connected internally to a tem-perature sensor.
In my experience, the ADuC812is an excellent processor to workwith, and you can have a lot of funprogramming it. For this project, Iused the EVAL-ADUC812QS devel-opment kit. This kit provides youwith a nice interface to theADuC812. It has a user controllableLED, pushbuttons, buffers for someof the inputs to the ADuC812, andmany other helpful items. For thosewho would like to learn more aboutthe ADuC812 and MicroConverters,Analog Devices MicroConverter pagecan be reached by going to
www.analog.com, clicking on the "Data Converters" taband then selecting the "MicroConverter" tab.
How I Measure the Capacitance
Measuring the capacitance is fundamentally simple.Connect the output of the first D/A converter to one sideof a 10 KΩ resistor. Connect the other side of the resistorto the capacitor under test. The point between the resistorand the capacitor is also connected to the first channel ofthe ADuC812's A/D converter. Finally, the second side ofthe capacitor is connected to the ADuC812's ground. (SeeFigure 1.) When the user indicates that s/he is ready tohave a measurement taken, the ADuC812 raises the volt-age at the output of the D/A to 2.5 V. At the same time,the ADuC812 starts one of its timers (a standard featureon all 8052s) going.
One of the modes in which the ADuC812's A/D con-verter can work is to sample every second time the timeroverflows. I used this setting. From the point at which theD/A voltage goes to 2.5 V, the ADuC812 examines the
voltage between the resistor and thecapacitor every second time thetimer overflows. Each time the A/Dchecks the value on the capacitorand the voltage is less than 1.25 V, aset of counters are updated. Whenthe voltage on the capacitor reaches1.25 V, the ADuC812 records theelapsed time from the time the volt-age on the resistor went to 2.5V untilthe voltage on the capacitor reached1.25 V.
As the voltage on a capacitorwhose voltage was zero until, at t = 0,a voltage was applied follows the formula:
Vcap(t) = Vapplied(1—e-t(RC))
FEBRUARY 2004
A Simple CapacitanceMeter Using TheADuC812
Clever Programming Yields a Useful Bench Tool
FIGURE 1. The RC circuit and its connections to the ADuC812.
by Shlomo Engelberg Project
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FEBRUARY 2004
Project A S
The time that the capacitor takes to reach half of theapplied value, t1/2 is:
t1/2 = RCln(2)
As the MicroConverter has measured t1/2 and R isknown, it is easy to determine C. In fact:
C = t1/2
Rln(2)
Practical Matters
Fundamentally, this capacitance meter is easy tobuild. The devil is in the details. Calculating is no problemat all if you have a microprocessor that knows how todivide. Unfortunately, the 8052 barely knows how to mul-tiply. To avoid the necessity of multiplying or dividing, Iplayed a simple game. I set the timer to overflow every0.0347 milliseconds. Thus, to overflow twice took thetimer 0.0694 milliseconds. I had the microprocessor keeptrack of how many such periods went by from the timethat 2.5 V was first applied to the resistor until the voltageon the capacitor rose to 1.25 V. (That is how theMicroConverter stores the elapsed time.) Let the numberof periods that elapsed be N. Then, t1/2 = 0.0694N. Let ussee what that says about C as a function of N. Pluggingin the values we find that:
C = 0.0000694N = 0.0000694N ≈ 10NnF100001n(2) 6931.5
With the timer set like this, no calculations need to bedone. The number of cycles determines the capacitancein a very simple way. In order for a measurement to be rea-sonably accurate, should be at least 10. In order that themeasurements not take too long, should not be too large. Iallowed up to 10,000. Thus, the capacitances for which thissimple meter can be used range from 100 nF to 100 µF. Therange can be adjusted by changing the value of the resistor.
The Physical Connections
In order to connect the resistor and capacitor to thecorrect pins on the development kit, you must knowwhere each of the lines that is called for is physicallylocated. The analog ground of the circuit is available inthe prototyping area of the development kit on a striplabeled 'AGND.' For the A/D and the D/A connections,look for the ANALOG I/O connector on the developmentkit. This connector is clearly labeled and is locatedbetween LK1 and LK2. The first channel of the A/D(ADC0) is led off to the leftmost pin on the row of pinsthat is nearest to the edge of the development kit. Thefirst channel of the D/A (DAC0) is led off to the third-to-last pin on that row of the ANALOG I/O connector.
Many microcontrollers either do not support division or sup-port division to a limited extent.And even when they do, it is oftena time-consuming operation. In the case of 8051 type microcon-trollers, division of two eight bit words takes four instruction clockcycles to execute. (Multiplication and division are the only opera-tions that take so long.) To do 16 (or more) bit division takes moretime and is more complicated.
When time needs to be measured, it is best to set up yourtime-base in a fashion that minimizes the need to use expensive orcomplicated operations. One operation that can often be simplifiedis the calculation of a quantity that depends directly on a measure-ment of time. In order to measure capacitance, we measure a time — t1/2 .We have seen that:
C = t1/2
R1n(2)
We want to make sure that the calculation of the capacitanceis as simple as possible. Suppose that you check the voltage at theoutput of the RC filter every τ seconds. Then the first time forwhich the voltage is greater than half the input voltage is t1/2 = Nτ.Thus, the capacitance is:
C = τ
NR1n(2)
In order to avoid the need to perform any calculations, and tocalculate the capacitance from N, you must choose the values of the
resistor and the sampling time in such a way that:
τR1n(2)
is particularly "nice." Suppose, for example, that you would like to measure capaci-
tances that are between 1 µF and 1 nF. Ideally, you would like tohave N be reasonably large, even for 1 nF. Let us suppose that wewould like N = 10 when C = 1 nF.Then we find that:
1x10-9 = τ 100.69315R
That is:t = 6.9315x10-11R
On practical grounds, we do not want to choose odd resistorvalues, nor do we want to have to sample too often. Suppose thatwe take R = 1MΩ.Then, we find that τ = 6.9315x10-5. Setting oursample rate to 1/τ = 11,427 samples per second will do the trick.With this sampling rate and resistor value, the capacitance meas-ured will be C = 10 NnF. Displaying such a value (as we do in theaccompanying program for the ADuC812) is a triviality. We con-verts the number N into a string and then add a "0" to the end ofthe string.The string now holds the capacitance in nanofarads, andno calculation was performed.
Thinking Smarter — Not Working Harder
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(Counting from the pin that connects to the first channelof the A/D, it is the ninth pin over.) See Figure 2.
The Serial Interface
When using the development kit, the serial interface isused for two purposes — downloading the program andcommunicating with the ADuC812 while the program isrunning. Downloading programs to the ADuC812 develop-ment kit is easy. First, connect the serial cable that comeswith the kit to the kit itself (being careful to match up thepins on the board with the markings on the cable). Thenconnect the cable to COM1. (For some reason, the down-loader that comes with the development kit does not seemto work from COM2.) Make sure that the jumper at loca-tion LK3 (PSEN) on the evaluation board is in. Run WSD,the Windows serial downloader. Go to the configurationmenu of the downloader and make sure that it is set toCOM1. Next click on DOWNLOAD. Find the program thatyou want to download and download it. Finally, click on theRUN button. At this point, the program is running on theADuC812.
The program that is running on the ADuC812 expectsto communicate with the outside world through the COMport, too. The program sets the ADuC812's internal UARTto transmit and receive at 19200 baud with one stop bitand no parity bit. Additionally, no flow control is used.Thus, the host computer must be set up similarly. I gener-ally use Hyperterminal (a Windows utility) to communicatewith the ADuC812. When using Hyperterminal, you musttell Hyperterminal which COM port you are using (COM1),and then you must set the properties of the COM port to19200 baud, one stop bit, no parity, and no flow control.
Once the set-up is taken care of, to initiate a measure-ment all that you need to do is to type a lower case 'm' inthe Hyperterminal window. The ADuC812 will measure thecapacitance and will send the capacitance value to theCOM port. Hyperterminal will pick up the value and dis-play it on your screen.
For those who do not want to type, the ADuC812 hasbeen set to start a measurement when the INT0 button onthe development kit is pressed. In order to see the value ofthe capacitance, you must still use Hyperterminal.
A Simple Capacitance Meter
FEBRUARY 2004 45
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Circle #109 on the Reader Service Card.
FIGURE 2. The location of the first channel of A/D and the first channel of D/A on the evaluation kit.
Engelberg.qxd 1/2/2004 1:38 PM Page 45
Programming the ADuC812
There is only one jumper on the evaluation board thatI regularly use — the jumper at position LK3. When thisjumper is in, resetting the ADuC812 causes the ADuC812to wait for instructions to come to its UART. This jumpermust be in when you want to send a new program to theADuC812. After you load a program, it is possible to tellthe ADuC812 to start running by sending the appropriatecommands to the UART. This is what clicking on the RUNbutton does.
Recall that the program memory of ADuC812 is (non-volatile) FLASH memory. Even after turning off the proces-sor, the program is still in the FLASH memory. If thejumper at LK3 is out, then when the ADuC812 is powered-up or reset, it does not wait for instructions to come fromthe UART. Rather, it jumps to the start of the programmemory and starts executing the current resident program.
If you have already downloaded the capacitance meterprogram and reset the ADuC812 after setting upHyperterminal, you will see that upon power-up the program clears the Hyperterminal screen and sends thecomputer the string "Hit 'm' to perform a measurement." (Infact, the messages that cause this to happen were sent whenthe RUN tab was hit the first time the program was run. Atthat point, however, there was no program running on thehost computer to "listen" to what the ADuC812 "said.")Pressing “m” now will cause a measurement to be made.
A Cautionary Note
A word of caution is in order. After the MicroConverterfinishes making a measurement, it resets the voltage onthe D/A to 0 V. This allows the capacitor to discharge. Ifyou have a fairly large capacitor, you must wait a secondor two for it to drain completely. If you don't, the capacitorwill not have completely discharged and the next measure-ment will be incorrect (too low). This is because the capacitor will not take as long to charge as it should — itstarted out partially charged.
Adding Bells and Whistles
I have presented a simple capacitance meter. It is rel-atively easy to extend this meter into a multimeter. Ofcourse, doing so would increase the complexity of themeter and would take a fair amount of time. Enjoy! NV
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Circle #128 on the Reader Service Card.
Shlomo Engelberg received his B.E.E. in 1988,his M.E.E. in 1990, his M.S. (in mathematics) in 1991,and his Ph.D. (in mathematics) in 1994. He teacheselectronics at the Jerusalem College of Technology-
Machon Lev. In his spare time, Shlomo enjoys walking,reading, and playing with his children.
Author Bio
FEBRUARY 2004
Circle #111 on the Reader Service Card.
Engelberg.qxd 1/2/2004 1:40 PM Page 46
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Full Page.qxd 1/2/2004 4:37 PM Page 47
Membrane switches are useful for a number ofreasons. They're thin, water resistant, and canbe customized. Unfortunately, custom set-up
costs are high and take a lot of lead time. This article will
show you how to make your own custom "pre-produc-tion" membrane switch quickly and at very low cost.There are many variations that you can do, so use thisas a starting point and follow your imagination. Figure 1shows the basic idea of how this works.
What You Need
Photo 1 shows the basic parts needed. The PrintedCircuit Board (PCB) in the lower left has just four switch-es on it. These switches must be the very common"membrane" push-button type, but the housing can vary(more details on this later). Typical switches are shownto the right of the PCB. You will also need the overlaygraphics (upper left). This is just a piece of paper withwhatever you want on it.
Obviously, the push buttons on the overlay must lineup with the PCB switches. I also make a second "workoverlay." This has the mounting holes for the PCB andfront panel (lower right). This makes alignment mucheasier.
Generally, this paper overlay is created with whatev-er computer software graphics package you have.Although, you could do it by hand.
The "special" items you need are two-inch widetransparent package sealing tape and double-sided cel-lophane tape. Both of these are available at any officesupply store. You don't really need the package sealingtape dispenser (about $20.00) but it makes things mucheasier. You'll also need basic hand tools and a drill (adrill press is much easier).
Drill the Front Panel
The first step is to drill the front panel with holes forthe switches and mounting holes for the PCB. You needto provide good alignment between the overlay, frontpanel, and PCB. Photo 2 shows the paper work overlayattached to the front panel with a couple pieces of dou-ble-sided tape. The center points of the switches andmounting holes are center punched through the paper.
Note that the tape extends beyond the front panel.
FEBRUARY 2004
Make Your Own CustomMembrane Switches
A Simple — Yet Effective —Way to Dress up Your Projects
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Photo 1. The basic parts needed.
Figure 1. Here is the basic approach for the membraneswitch.The paper overlay is protected with package sealing
tape on the top, and attached to the front panel with double-sided tape on the bottom.The PCB is mounted with spacers so that the top of the switch actuator is
even with the top of the front panel.
Fonte.qxd 1/2/2004 11:25 AM Page 48
This makes removing iteasy. Also, this particularfront panel is aluminum.If you use a plastic frontpanel, don't center punchtoo hard or else you'llbreak the plastic.
Big Holes forthe Switches
Photo 3 shows theresults. The PCB is tem-porarily mounted to thefront panel and the workoverlay has beenremoved. Note that theswitch holes are about0.5-inch in diameter. Thisallows the switch body to extend part way through thefront panel. (Be careful with shorts to a metal frontpanel.) If you use long actuator switches, still use about0.5-inch diameter holes. This is because the overlay hasto flex a little. Holes that are too small won't flex very well.You may want to experiment.
You will also have to adjust the spacing of the PCB sothat the top of the switch actuator is just about level withthe top of the front panel. In this case, a single nut pro-vides the proper spacing.
Attaching the Overlay
Remove the PCB and put double-sided tape on thefront panel. Use strips side by side, without any overlap.Be sure that this tape is wider and taller than the overlay— the excess will be trimmed off.
Again, extending the tape beyond the front panelmakes trim removal easier. Remove tape from all open-ings in the front panel. An Xacto knife works well for this.See Photo 4.
Use the package sealing tape to cover the overlay —and be careful — this step showsany and all mistakes. (It's oftenworthwhile to have several sparepaper overlays.) If the overlay iswider than the tape, you caneither put the next strip side- by-side or overlap slightly (about1/8-inch). If you overlap, try toplace the seam away from switchopenings.
Note, I find that putting tapeon the overlay and then trim-ming/cutting the overlay to sizefrom the paper easier than tryingto put tape on an already
trimmed-to-size overlay. If you have air bubbles, carefully pierce the paper to let the air out. Don't pierce the tape or else it willeventually tear there.
Carefully place the overlay on the frontcover. This is the hardest part. You have to make sure thatthe alignment is perfect before you press down. If you tryto move the overlay after it's stuck to the tape, it willalmost certainly tear. I shine a bright light behind the frontpanel so that the holes shine through the overlay. Thismakes alignment easier. Once you are sure the alignmentis correct, press the overlay down from the middle to theedges. There is no easy way to remove air bubbles.
Trim away the excess double-sided tape. This shouldlook like Photo 5.
Final Assembly
Carefully cut through the overlay for the PCB mount-ing holes. Attach the PCB with the proper spacers. Themembrane switch should now work (see Photo 6). Youmay want to experiment with the spacing to provide theswitch feel you like.
Variations and Notes
This particular version had only the switches on thePCB. If you want to mount parts onthe PCB, there are two basic waysto do that.
First, use tall actuator switches.This allows parts to be placed onthe same side as the switches. Thisrequires longer spacers and obvi-ously limits the height of the parts.The second way is to put the partson the "back" side of the PCB.However, in practice, it would be theswitches that are mounted on theback of the PCB while the parts areon the front.
But what about LEDs or dis-
FEBRUARY 2004 49
te Custom Membrane Switches
Photo 2. The paper work overlay isattached to the front panel with a couple
of pieces of double-sided tape.
Photo 4. Remove tape from all openings in the front panel using an Xacto knife.
Photo 3. This shows the results — the PCB is temporarily mounted to the front panel and
the work overlay has been removed.
Fonte.qxd 1/2/2004 11:25 AM Page 49
plays? Yes, windows are easy tomake. Just remove the proper areaon the paper overlay before applyingthe package sealing tape. Thisleaves a window with sticky tape onthe inside face. Now, cut a piece ofpackage sealing tape a little largerthan the display opening. Carefullyattach that to the inside of the win-dow — sticky side to sticky side. Nomore stick! And the window will be very clear. (Watch out for air
bubbles.)Finally, PCB
flex can be a prob-lem. That is, thePCB flexes insteadof the switch clos-ing. This happensif there is too muchdistance from theswitch to the PCBmounting holes.Usually this has tobe more than aninch or two. Thesolution is to add amounting holecloser to theswitch. However,sometimes it ispossible to get aswitch that needs
less pressure to close.
Conclusion
Attractive custom pre-produc-tion membrane switches can be fab-ricated quickly and cheaply usingsimple tools and materials. They arewater resistant and can be quite thin.Custom switch set-up costs and leadtimes are eliminated — while givingyour project that "pro" feel. NV
FEBRUARY 2004
Project
Photo 5. Trim away the excess double-sided tape.
Photo 6. Carefully cutthrough the overlay for
the PCB mountingholes.Attach the PCB
with the proper spacers.The membrane switch
should now work.
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Circle #50 on the Reader Service Card.FEBRUARY 2004 51
Full Page.qxd 1/5/2004 4:12 PM Page 51
Is it a bird? Is it a plane? No,it's a computerized Frisbeewith a BASIC Stamp! In this
simple project, I will show youhow to make an ultralight, buteasy-to-assemble, accelerationrecorder that you can use tomeasure the dynamics of smallvehicles, much like the "blackbox" aircraft flight recorders.
FrisbeeBackground
I wanted to understand the aerodynamics of a Frisbeeby taking in-flight measurements of lift and drag.Although Frisbees (the name — a corruption of that ofWilliam Frisbie, a Connecticut baker whose pie tinsformed the inspiration for flying disks — is a trademark ofWham-O, Inc.) are very familiar objects, their impressiveflight performance is only documented with a handful ofpublished studies and wind-tunnel measurements. Some
background can be found atwww.discwing.com and athttp://mae.engr.ucdavis.edu/~biosport/frisbee/frisbee.html. By taking in-flight meas-urements, I would understandthe changing aerodynamicforces throughout a free flight.
The challenge was to makea super-lightweight and com-pact instrument package. Theaccelerometer and the micro-
controller were tiny enough, but the power supply pre-sented a problem. Two lithium button cells (CR2032) inseries can provide 6 V, but only about 10 mA of current.This is, however, just enough to run a BASIC Stamp II(although not enough to run other, faster microcontrollerslike the BS2-SX or a BasicX-24.) The accelerometer drawsjust a few milliamps at most.
The circuit itself is very simple, as the accelerometerinterfaces very easily with the microcontroller. Given 5 V,it spits out two square wave signals, which are pulse-width
FEBRUARY 2004
The Amazing FrisbeeBlack Box or BASICStamp Frisbee
Instrument Your Favorite Sporting Goods!
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Charted Data
Figure 1. Circuit diagram for the ADXL202 (A) and MEMSIC 2125 (B) accelerometer options.
(A) (B)
Lorenz.qxd 1/2/2004 11:57 AM Page 52
modulated (PWM) by the acceleration in two axes. If itsenses zero-g, if that axis of the accelerometer (there aretwo) is horizontal, or if the device is in free-fall, the dutycycle of the output is 50%. The duty cycle increases by12.5% for each "g" of acceleration, up to two in each direc-tion. So, all the circuit does is measure the pulse lengthson the two accelerometer axes, record those numbers, andread them out afterwards. Simple!
Choice of Accelerometer
The best device to use is the Analog ADXL202. Theaccelerometer itself is a tiny surface-mount device, but it isconveniently sold on an evaluation board. This unit used tobe sold by Parallax (the makers of the BASIC Stamp), butthey have replaced it in their catalog with a MEMSIC unit,which is a little smaller.
There are three big differences between these devices.The Analog device uses a bending beam to sense acceler-ation and can be tuned to optimize bandwidth against signal-to-noise (two 0.1 mF capacitors and a 120K resistoron the board set the pulse width and sensing bandwidth correctly for this application, the PWM period being about1 ms), and draws only about 0.5 mA. The MEMSIC unituses a different sensing principle, measuring the "gravity-driven" convection of heated air. It, therefore, has an intrin-sically slower response, and draws more current — about 4mA. The evaluation board sold by Parallax has the PWMperiod fixed at 10 ms — giving great accuracy, but a slowresponse. For convenience, I give construction details(Figure 1 A, B) for both kinds of accelerometer, but theADXL202 is better.
Construction
Most of the lift on the Frisbee comes from its top, so itwas safe to mount the circuit on the underside of the disc
where it doesn't greatly affect the airflow. I put clear plas-tic tape over much of the circuit after assembly to smooththe airflow and minimize any drag effects.
I assembled my first circuit on a piece of stripboard forsturdiness, but, since there are actually very few connec-tions, it is easier (and lighter) to make individual wire con-nections to an IC socket. Complete with batteries andswitch, the circuit board version weighed around 28 g; thebare-bones version was under 20 g (Figure 2). Theseweights are minimal when compared with the 175 g weightof the Frisbee — less than 20%.
I added an LED, just to be able to see what the pro-gram was doing. The program strobes it rapidly when it istaking data, and goes on constantly afterwards when thecode is reading out the data. A dark LED is a sure sign thatsomething isn't working.
The other items in the circuit are the two cells connect-ed in series (I gave them a few inches of wire, so that thecells could be placed around the center of the Frisbee, bal-ancing it) and a slide switch. Placing this near the rim ofthe disc meant the circuit could be turned on just as I threwthe Frisbee. I mounted all the items on the underside of thedisc with silicone adhesive (Figure 3). It is important tomount the accelerometer as close to the center as possi-ble. One accelerometer axis should be along the spin axisof the Frisbee.
One approach, if you have a BASIC Stamp bread-board, is to download the program to it, and transfer thechip to the Frisbee set-up. However, if you want to tweakthe program, this can be tedious and tends to bend pins onthe Stamp. What I did was to make a separate cable to linka nine-pin serial connector to pins 1-4 on the Stamp via asmall header (Figure 4.) Because the serial handling fordownloading the data from the unit after flight is easier, thedata output is on pin 5 (P0) — a two-wire header (or two pinsof a five-pin) connects pin 4 (ground) and pin 5 to a serialconector. This connector is easily attached after the flight.
FEBRUARY 2004 53
nz The Amazing Frisbee
Figure 2. Arrangement of parts on the underside of the Frisbee (A) with a close-up of the ADXL202 version, built on a small circuit board (B).The two circles are the lithium button cells.
Green chip is the BASIC Stamp, small green board is the ADXL202EB.
(A) (B)
Lorenz.qxd 1/2/2004 12:21 PM Page 53
The Program Operation
The BS2 has a 2 K EEPROM, which must contain theprogram, as well as any data. The program itself is quiteshort and leaves about 1,600 bytes of EEPROM memoryspacefor data storage. The BS2 reads the accelerometer withthe PulseIn command, which returns the length of a positivePulseIn the PWM output stream, measured in units ("ticks")of two microseconds. (I found that using two PulseIn com-mands reduces noise for the ADXL202, although for theMEMSIC, this slows the execution speed too much.)
Now, numbers like the PulseIn output are 16-bit (twobyte) words. To store each reading for each of the twoaccelerometer axes would not only require two EEPROMwrite operations (which are slower than most of the BS2
operations, like arithmetic) and would require two of theprecious bytes of EEPROM. But, adequate precision(about 2%) for this application can be had with only eightbits of data. The ADXL202 output is easily scaled to aneight-bit range (0-255) by subtracting about 80 from theoutput. The much slower MEMSIC device has a longerpulse length, and so the output, in ticks, needs to be divid-ed by a factor of 10, as well as subtracted — you mightneed to fine-tune these numbers yourself. The programreads the sensors, performs this conversion, and storesone byte per reading in EEPROM.
Once the program has finished sampling (about 12seconds for the ADXL202 version — long enough for any-thing except a record-breaking Frisbee flight!), it readsout the data to the serial port as two columns of numbersseparated by a comma. The two accelerations are report-ed as eight-bit integers. To convert to real accelerations, Iread the data into a spreadsheet program and convertaccording to a formula such as:
Acceleration(g) = Reading - Reading(0g) Reading(1g)-Reading(0g)
where the 1 g reading is for that axis of the accelerome-ter pointed downwards, and the 0 g reading for theorthogonal axes.
For testing/debugging and getting these calibrationreadings, I found it easier to have the BS2 read data out inreal time to the serial port, rather than storing and readingit out later. Rather than reprogramming the BS2 each time,I switched between the two modes with a jumper cable thatacts as a switch on pin 12 — you could easily install aswitch, although this might be heavier than a jumper. Tosimplify the wiring, I took the lazy approach of supplyingthe 5 V for this test from pin 11; pin 12 is pulled low by a100 K resistor to ground, unless pins 11 and 12 are linked.
The data can be captured by setting up a terminalprogram (Hyperterminal is installed on most WindowsPCs) — the settings have to be 9600 baud, 8 data bits, 1stop bit, no parity, and no flow control. The data can becaptured to a text file, converted as above in a spread-sheet program, and then graphed for analysis.
Making Sense of it All
The 800 readings in 12 seconds correspond to about65 two-axis samples per second. (Using the MEMSICdevice gets only about 30 samples per second, althoughthe record lasts longer). You can get the sample rate bywatching the LED to determine the exact time of therecord and dividing by 800.
The record shows a violent disturbance as the disc isthrown. The axial accelerometer channel shows analmost constant time-average value of about -0.8 g, indi-cating almost level flight up to the end, although there area lot of oscillations added from the wobbling of the slight-
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Project
Figure 3. Close-up of "skeleton" boardless constructionaround the 24-pin IC socket, with the MEMSIC
accelerometer on the left. Note the header pins for the realtime/sample-and-readout switch and serial connector.
24-pin IC socketBASIC Stamp 2 (Parallax BS2-IC or Jameco #130892CF)330 Ohm 1/4W resistorRed LED100K 1/4W resistorslide switch2x 2 pin header and connector
2x CR2032 lithium button cell (Jameco #14162CF)2x button cell holder (Jameco #38535)
9-pin female D-type socket
MEMSIC 2125 (Parallax #28017) orAnalog ADXL202EB accelerometer (Jameco #177287)
(optional, for programming Stamp in-situ)Replace one of 2-pin headers above with 5-pin headerand add one 4-pin connector and one 9-pin female D-type
www.jameco.comwww.parallax.com
See also
www.analog.comwww.memsic.com
PARTS LIST & VENDOR INFORMATION
Lorenz.qxd 1/2/2004 12:21 PM Page 54
ly imbalanced Frisbee just after thethrow. The radial accelerometer alsoshows a -0.5 g offset, due to the factthat the accelerometer isn't quitedead-center, and so it records a con-stant offset due to the centripetalacceleration, proportional to thesquare of the spin rate. The radial sig-nal has a spin-modulated componentabout this mean, due to theaccelerometer axis alternately beingalong and against the drag force(actually, the disc flies with a slightnose-up "angle of attack", so what issensed here is drag force and a bit oflift that is inclined backwards). Theperiod of this oscillation directly indi-cates the spin rate of the Frisbee,which a careful study shows to bedecreasing from about 6.5 to about5.5 revolutions per second.
Interpreting these results in quan-titative aerodynamic terms is, ofcourse, an involved business, but justlooking at the graphs gives you agood idea of what is going on.Analyzing data like this might make agood science fair or other project.
Other Ideas
You could use this sort of circuiton a radio-controlled airplane, car, orboat. A similar circuit could be usedfor a model rocket, although the g-loads will be much larger than the ±2g range of the ADXL202, so a differ-ent accelerometer would need to beused — the ADXL210 is similar to the202, but with a 10 g range. For high-er accelerations, you may need to use
more sophisti-cated circuitrywith an analog-to-digital con-verter, as PWMoutputs are nottypical for suchhigh-g devices.
You couldalso try all kinds of variants on acircuit like this — photodiodes tomeasure the position of the sun andhence the "wobble" on the Frisbeeor pressure sensors to measure thesuction that causes the Frisbee's lift.Maybe infrared or ultrasonic rangerscould tell you the altitude as a func-tion of time. Happy flying! NV
The Amazing Frisbee
Figure 5. Flight results (see text). Diamonds show the wobble-modulated axial (lift) accelerometer, with a solid line
showing smoothed data. Crosses are the spin-modulated radial (drag) accelerometer.Accelerations go out-of-range for the throw at the beginning and the impact at the end.
Figure 4. Serial connection details.
Dr. Ralph Lorenz is a planetary scientist atthe University of Arizona, where his studiesfocus on Saturn's moon, Titan. He enjoys building small sensor systems and learningabout the physical world with them. Visit hiswebsite at www.lpl.arizona.edu/~rlorenz
ABOUT THE AUTHOR
FEBRUARY 2004 55Circle #126 on the Reader Service Card.
Lorenz.qxd 1/2/2004 11:58 AM Page 55
The Health and Safety Executivehas estimated that 80% of acci-
dents are caused by human error insome form. Loss of production andprofitability due to human error isprobably incalculable, but is likely torun to many hundreds of millions ofpounds per year. There is a commonmisconception that human error isunavoidable and usually arises fromcarelessness or neglect. From this,there follows a general belief thathuman error can only be preventedby identifying, blaming, and correct-ing the individual who made theerror. In reality, nearly all instancesof human error are the consequenceof badly designed systems. The sys-tems may be technological, such asthe design of the human machineinterface (e.g., an aircraft cockpit dis-play) or the work environment (e.g.,how an item of industrial machineryis operated). Alternatively, the systemsmay be organizational, varying froman operating or maintenance proce-dure to a managementsystem, or indeed, the cul-ture of a whole company.
In all cases, the sys-tems which influence theway work is carried outare the main cause ofhuman error. If a systemis badly designed from ahuman operability per-spective, then the proba-bility of errors occurring
will be increased. Errors caused bysystem deficiencies are known assystemic errors and it follows fromthis that, by careful attention todesign, their incidence can be limit-ed. Once it is accepted that mosterrors are caused by defective sys-tems rather than neglect, then humanerror is no longer seen as inevitable.Indeed, if the system faults can beidentified and corrected, then there isa possibility for error reduction andblame can be virtually eliminated fromthe equation. However, it also meansthat the remedy for human error oftenlies in the hands of the mechanicaland electrical engineers who designedthe system in the first place.
There are two basic approachesto the design of equipment from anoperability point of view. The sys-tem-centered approach has tendedto be the traditional method adoptedin the design process. Here, theattention of the design engineer isalmost totally directed towards the
system to the exclusion of thehuman beings who will have to oper-ate or maintain it. Today, manydesigners are still tempted to adoptthis old-fashioned approach. Theirnatural inclination is to focus uponthe system rather than the humanbeing because of the perception thatit is the system that delivers the spec-ified requirements. However, it needsto be seen that the system comprisesboth human and machine. The endresult of such an approach is that theoperator or maintainer must adapt toa system that is not designed to takeaccount of their needs. Quite oftenthe discovery that the human beingcannot easily adapt to the system isnot realized until the product isbrought into operation. By this time,it is often too late or very expensiveto make the required changes.
It is sometimes argued thatdesigners do not have the requiredknowledge of ergonomics (seeresources) to be able to take into
account human factors intheir designs. However, inmany cases, all that isrequired is an ability tounderstand how the systemwill eventually be operatedor maintained. This mayinvolve no more than theapplication of simple com-mon sense. The result ofdesigning equipment with-out the application of such
1. Ergonomics is "an approach which puts human needs and capa-bilities at the focus of designing technological systems.The aim isto ensure that humans and technology work in complete harmo-ny, with the equipment and tasks aligned to human characteristics."The Ergonomics Society, 2003, www.ergonomics.org.uk/ergonomics/definition.htm
2. The Blame Machine — Why Human Error Causes Accidents,Elsevier Science and Technology Books, Oxford, R.B.Whittingham,2003, ISBN 0750655100
RESOURCES
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FEBRUARY 2004
thinking is that when it is brought intooperation, even the most highly trainedand well-motivated personnel will makesystemic errors leading to accidents orloss of production.
By contrast, the user-centeredapproach ensures that the design ofthe system is matched as closely aspossible to human capabilities andlimitations. The Blame Machine —Why Human Error CausesAccidents (see Resources) providesnumerous case studies of accidentscaused by designs that ignoredhuman capabilities. The most seri-ous aircraft accident to occur in theUK for many decades occurred atKegworth near Nottingham in 1987.The accident resulted from an engineinstrument layout that presentedimportant information in a mislead-ing way. The system may haveappeared adequate until the pilotswere faced with an emergency whererapid decisions were called for basedon engine data from the instrumentpanel. Under conditions of highworkload and stress, the mentalresources of the pilots were over-stretched. This restricted their capac-ity to properly assimilate informationfrom a vibration monitor resulting inthe shutting down of the wrongengine. Because the presentation ofthat information was poor, the prob-ability of an error was increased andwas the main cause of the accidentat Kegworth.
Unfortunately, the need to adopta user-centered approach is still —even today — not fully understood bymany designers. As a result, thereare numerous examples of complextechnological systems designedmainly with system functionality inmind, ignoring the capabilities andlimitations of the user. Such systemsinvariably result in degraded levels ofhuman performance with grave con-sequences for productivity, equip-ment availability, and safety.However, the need of the engineeringdesigner — who is not necessarily anexpert in human factors — shouldalso be recognized. A basic apprecia-tion of techniques such as TaskAnalysis, Human Error Analysis, andan understanding of the various Error
Types, Forms, andTaxonomies willhelp designers torecognize how com-mon human errorsoccur. This under-standing will lead tosafer and more costeffective designs ofequipment whichtake full account ofpotential human
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ABOUT THE AUTHOR
57
Whittingham.qxd 1/5/2004 2:33 PM Page 57
Virtual memory is a technology embedded in mostpersonal computers that enables many of the
advanced operations that we are so accustomed to.However, the term is only vaguely familiar to many peo-ple. When you paste text from your web browser into yourword processor, multiple applications are running simulta-neously with the operating system (OS) to make it all hap-pen. Virtual memory plays a key role in allowing thoseapplications to coexist with each other and with the OS.
Multitasking
Multitasking operating systems execute multiple pro-grams at the same time by assigning each program acertain percentage of the microprocessor's time and thenperiodically changing which instruction sequence is beingexecuted. This is accomplished by a periodic timer interruptthat causes the OS kernel to save the state of the micro-processor's registers and then reload the registers with apreserved state from a different program. Each programruns for a while, is paused, and then execution resumeswithout the program having any knowledge of beingpaused. In this respect, the individual programs in a multi-tasking environment appear to have complete control overthe computer, despite sharing the resources with others.
Aside from fair access to microprocessor time, con-flicts can arise between applications accidentally modify-ing portions of each other's memory — either program ordata. How does an application know where to locate itsdata so that it will not disturb that of other applications
and so that it will not be overwritten? There is also theconcern about system-wide fault tolerance. Even if notmalicious, programs may have bugs that cause them tocrash and write data to random memory locations. Insuch an instance, one errant application could bringdown others or even crash the OS if it overwrites programand data regions that belong to the OS kernel.
Virtual Memory
Virtual memory is a hardware enforced and softwareconfigured mechanism that provides each applicationwith its own private memory space that it can use arbi-trarily. This virtual memory space can be as large as themicroprocessor's addressing capability — a full 4 GB inthe case of a 32-bit microprocessor. Because each appli-cation has its own exclusive virtual memory space, it canuse any portion of that space that is not otherwise restrict-ed by the kernel. Virtual memory frees the programmerfrom having to worry about where other applications maylocate their instructions or data because applications can-not access the virtual memory spaces of others.
The MMU
Clearly, multiple programs cannot place differentdata at the same address or each simultaneously occupythe microprocessor's entire address space. The OS kernelconfigures a hardware memory management unit (MMU)to map each program's virtual addresses into unique phys-ical addresses that correspond to actual main memory.Each unique virtual memory space is broken into manysmall pages that are often in the range of 2 KB to 16 KBin size (4 KB is a common page size). The OS and MMUrefer to each virtual memory space with a process ID(PID) field. Virtual memory is handled on a process basisrather than an application basis because it is possible foran application to consist of multiple semi-independent
This material was originally published in Complete Digital Design:A Comprehensive Guide to Digital Electronics by Mark Balch, ©2003by The McGraw-Hill Companies. Reproduced with permission.
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FIGURE 1. 32-bit Virtual Memory Mapping
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processes. The high-order address bits referenced by eachinstruction form the virtual page number (VPN). The PIDand VPN are combined to uniquely map to a physicaladdress set aside by the kernel as shown in Figure 1.
Low-order address bits represent offsets that directlyindex into mapped pages in physical memory. The mappingof virtual memory pages into physical memory is assignedarbitrarily by the OS kernel. The kernel runs in real memoryrather than in virtual memory so that it can have direct accessto the computer's physical resources to allocate memory asindividual processes are executed and then terminated.
Despite each process having a 4 GB address space,virtual memory can work on computers with justmegabytes of memory because the huge virtual addressspaces are sparsely populated. Most processes use only afew hundred kilobytes to a few megabytes of memory and,therefore, multiple processes that collectively have thepotential to reference tens of gigabytes can be mappedinto a much smaller quantity of real memory.
If too many processes are running simultaneously, or ifthese processes start to consume too much memory, a com-puter can exhaust its physical memory resources, therebyrequiring some intervention from the kernel to either sus-pend a process or handle the problem in some other way.
Memory Allocation
When a process is initiated, or spawned, it is assigneda PID and given its own virtual memory space. Some ini-tial pages are allocated to hold its instructions and what-ever data memory the process needs available when itbegins. During execution, processes may request morememory from the kernel by calling predefined kernelmemory management routines. The kernel will respondby allocating a page in physical memory and then return-ing a pointer to that page's virtual mapping. Likewise, aprocess can free a memory region when it no longerneeds it. Under this circumstance, the kernel will removethe mapping for the particular pages, enabling them to bereallocated to another process — or the same process — at alater time. Therefore, the state of memory in a typical multi-tasking OS is quite dynamic and the routines to managememory must be implemented in software due to their com-plexity and variability according to the platform and thenature of processes running at any given time.
Swapped!
All mapped virtual memory pages do not have to beheld in physical RAM at the same time. Instead, the totalvirtual memory allocation on a computer can spill overinto a secondary storage medium such as a hard drive.The hard drive will be much slower than DRAM, but notevery memory page in every process is used at the sametime. When a process is first loaded, its entire instructionimage is typically loaded into virtual memory. However, itwill take some time for all of those instructions to reachtheir turn in the execution sequence. During this wait time,
the majority of a process's program memory can bestored on the hard drive without incurring a performancepenalty. When those instructions are ready to be execut-ed, the OS kernel will have to transfer the data into physi-cal memory. This slows the system down, but makes itmore flexible without requiring huge quantities of DRAM.
Part of the kernel's memory management function isto decide which virtual pages should be held in DRAM andwhich should be swapped out to the disk. Pages that havenot been used for a while can be swapped out to makeroom for new pages that are currently needed. If a processsubsequently accesses a page that has been moved to thedisk, that page can be swapped back into DRAM to replaceanother page that is not needed at the time. A computerwith 256 MB of DRAM could, for example, have a 512 MBswap file on its hard drive, enabling processes to share acombined 768 MB of used virtual memory.
This scheme of expanding virtual memory onto a diskeffectively turns the computer's DRAM into a large cachefor an even larger disk-based memory. A virtual memorypage that is not present in DRAM is effectively a cachemiss with a large penalty because hard disks are muchslower than DRAM. Such misses are called page faults.The MMU detects that the requested virtual memoryaddress from a particular PID is not present in DRAM andcauses an exception that must be handled by the OS ker-nel. It is the kernel's responsibility to swap pages to andfrom the disk. For a virtual memory system to functionwith reasonable performance, the working set of memoryacross all the processes running should be able to fit intothe computer's physical memory. The working setincludes any instructions and data that are accessed with-in a local time interval. Processes with good locality char-acteristics will do well in a virtual memory system.Processes with poor locality may result in thrashing asmany sequential page faults are caused by randomaccesses throughout a large virtual memory space.
Page Tables
The virtual to physical address mapping process isguided by the kernel using a page table, which can take var-ious forms, but must somehow map each PID/VPN combi-nation to either a physical memory page or one located onthe disk drive's swap area. Virtual page mapping is illustrat-ed in Figure 2, assuming 4 KB pages, a 32-bit addressspace, and an 8-bit PID. In addition to basic mapping infor-
FIGURE 2. Virtual Page Mapping
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mation, the page table also contains status informationincluding a dirty bit that indicates when a page held inmemory has been modified. If modified, the page must besaved to the disk before being flushed to make room for anew virtual page. Otherwise, the page can be flushed with-out further action. Given a 4 KB page size and a 32-bitaddress space, each process has access to 220 = 1,048,576pages. With 256 PIDs, a brute-force page table would con-tain more than 268 million entries! There are a variety ofschemes to reduce page table size, but there is no escap-ing the fact that a page table will be large. Page table man-agement schemes are largely an issue of OS architectureand are outside the scope of this discussion. The fact thatthe page table is large and is parsed by software meansthat the mapping process will be extremely slow withouthardware assistance. Every access to virtual memory, in other words almost every access performed on thecomputer, requires mapping, which makes hardwareacceleration critical to the viability of virtual memory.
Translation Lookaside BufferWithin the MMU is a translation lookaside buffer
(TLB), a small, fully associative cache that allows theMMU to rapidly locate recently accessed virtual pagemappings. Typical sizes for a TLB are just 16 to 64entries because of the complexity of implementing afast fully associative cache. When a process is first
spawned, it has not yet performed virtual memory access-es, so its first access will result in a TLB miss. When a TLBmiss occurs, an exception is generated that invokes thekernel's memory management routine to parse the pagetable in search of the correct physical address mapping.The kernel routine loads a TLB entry with the mappinginformation and exits. On subsequent memory accesses,the TLB will hit some and miss some. It is hoped that theratio of hits to misses will decline rapidly as the processexecutes.
As more processes actively vie for resources in amulti-tasking system, they may begin to fight each otherfor scarce TLB entries. The resources and architecture ofa computer must be properly matched to its intendedapplication. A typical desktop or embedded computermay get along fine with a small TLB because it may nothave many demanding processes running concurrently. Amore powerful computer designed to simultaneously runmany memory intensive processes may require a largerTLB to take full advantage of its microprocessor andmemory resources. The ever-present trade-off betweenperformance and cost does not go away!
The TLB is usually located between the microproces-sor and its cache subsystem, as shown in Figure 3, suchthat physical addresses are cached rather than virtualaddresses. Such an arrangement adds latency to micro-processor transactions because the virtual-to-physicalmapping must take place before the L1 cache canrespond. However, a TLB can be made very fast because of its small size, thereby limiting its time penaltyon transactions.
Virtual Memory for the Masses
Years ago, virtual memory was found only on large,expensive computers. As more gates were squeezed intointegrated circuits, the MMU became an economical com-plement to the microprocessor. Modern operating systems,and the applications that run on them, gain substantial func-tional and performance enhancements, from this technolo-gy that was once reserved for mainframe computing. NV
FIGURE 3. Location of TLB
FEBRUARY 2004
Mark Balch is the author of Complete Digital Design. He is an electricalengineer in Silicon Valley, CA, who designs high-performance computer-networking hardware. His responsibilities have included PCB, FPGA, andASIC design. Mark has designed products in the fields of HDTV, consumerelectronics, and industrial computers. Mark holds a bachelor's degree inelectrical engineering from The Cooper Union in New York City. He can bereached via email at [email protected].
About tthe AAuthor
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Many of us dream of exploring space. Two outlets forthis dream are amateur astronomy and rocketry.
Neither of these hobbies, though, can match the sheerawe of building and launching a private spacecraft.Unfortunately, there are major roadblocks to this dreamof amateur space exploration.
No doubt, you can list the many obstacles that stopus from constructing a spacecraft; my list goes like this.We cannot build our own spacecraft because of the highcost of space-rated materials, the difficulty of machiningspacecraft parts, and the amount of time involved in con-struction. In addition, our lack of access to a clean roomand our inability to properly test a spacecraft at variousstages of its construction will stop us, even if we do havethe necessary parts, skills, and free time.
If we manage to build a spacecraft, I can think of twoadditional obstacles stopping us from launching it. Theseafter-construction obstacles are the length of time wemust wait for the launch and the cost of the launch itself.How can we justify the time and money needed to assem-ble a spacecraft when we know that we will wait a year forlaunch and that we can hardly afford the launch in thefirst place?
Even if we construct and launch our spacecraft,there's one final obstacle: telemetry. As amateurs, wehave no access to professional telemetry stations, norcan we afford to build a series of public telemetry stationsaround the world. If we can't collect data from our space-craft, then we simply will not build it. Until the hobbyistcan create, launch, and record data from his or her ownspacecraft, there will be no such thing as amateur space
exploration. Recently though, hobbyists have found a creative
solution to the dream. They substitute weather balloonsand helium for costly rocket boosters. They use off-the-shelf components to assemble a functioning model of aspacecraft, and they use amateur radio for spacecrafttelemetry. These few hobbyists are constructing whatare called near spacecraft and launching them deep intothe stratosphere, or near space. A near space programis often called the poor man's space program and itmakes an amateur science hobby that is nearly out ofthis world.
This article explores the amateur's version of a nearspace program and how it solves the many obstaclesmentioned above. Read this article and you'll learn howsimilar near space is to outer space. Then, you'll see howeasy it is for the hobbyist to build his or her own nearspacecraft and launch vehicle. Finally, you'll becomefamiliar with some of the benefits of starting your ownamateur near space program.
My article is too short to teach you everything youneed to know; however, I hope it will convince you thatan amateur near space program is a hobby that youcan, and should, take up. From there, you can get thehelp you need from the resources listed at the end ofthis article.
The Earth's Atmosphere
Before learning about near space, you must firstbecome familiar with the structure of our atmosphere.
by L. Paul Verhage
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There are five layers in our atmosphere, each with its ownname and set of characteristics. We live and play in the tro-posphere, the lowest layer of our atmosphere. Ourweather occurs in this layer and most aircraft fly in it.The troposphere extends to an altitude of around 50,000feet at a boundary called the tropopause. The exact alti-tude of the tropopause depends on the time of the yearand latitude.
The next highest layer is called the stratosphere.Residing in the stratosphere is the ozone layer that protectsus from the sun's harmful ultraviolet radiation. Very few air-craft can fly in this layer. For the most part, we are veryunaware of the stratosphere. The stratosphere extends toan altitude of around 160,000 feet at a boundary called thestratopause.
Above the stratopause is a layer of the atmospherecalled the mesosphere. Only rockets and meteors travelthrough this layer. Above the mesosphere is the thermos-phere and then the exosphere. There is a boundarybetween the thermosphere and exosphere (called, youguessed it, the thermopause), but no top boundary to theexosphere. Outer space exists in the two topmost layers ofour atmosphere.
Environmental Conditions inNear Space
Now that you're familiar with the structure of ouratmosphere, we can put near space into perspective bydiscussing its location and environmental conditions. First,where is near space located? I define near space as thosealtitudes in the stratosphere and mesosphere between75,000 feet and 330,000 feet. I selected the lower bound-ary because of the environmental conditions found at thisaltitude and the higher boundary because it is the interna-tionally defined boundary for outer space. For an altitudecomparison, many of you have flown in commercial aircraft, which fly at an altitude between 30,000 and40,000 feet.
Now, what's it like in near space? There are a numberof unique conditions found in near space. The first is itstemperature. Let's launch a near spacecraft and see whatit tells us about temperature (please see the charts accom-panying this article). As our near spacecraft ascends in thetroposphere, we find that the air temperature continuouslydecreases. The troposphere cools with altitude because it'swarmed by its contact with the ground. You might thinkthat the troposphere should be warmed by sunlight, but,the troposphere is very transparent to sunlight, so sunlightshines right through it without warming it. Once our nearspacecraft passes through the tropopause, sensors findthat the air temperature stops cooling. During the summer,the tropopause occurs at an altitude of 50,000 feet for mid-latitudes and the air temperature is a chilly -60° Fahrenheit.In the winter, the tropopause lowers to an altitude of 40,000feet and its temperature can drop to an even colder -90°Fahrenheit.
Once our near spacecraft enters the stratosphere, we
find that the air temperature increases with altitude. At analtitude of 100,000 feet — which is easily reached by ournear spacecraft — the air temperature can warm to 20°Fahrenheit or warmer. The stratosphere warms withincreasing altitude because of its ozone content. The sun'sultraviolet radiation is blocked by our ozone layer. Recallthat energy cannot be created or destroyed; it may be inanother place and possibly in a new form. In the strato-sphere, energy from the sun's ultraviolet radiation is eventu-ally converted into higher air temperatures. As our nearspacecraft gets closer to the sun, there is more ultravioletradiation for the ozone to block, and, therefore, warmer airtemperatures.
The second condition found in near space is reducedair pressure. As opposed to the up and down changes inair temperature that our near spacecraft detected, air pres-sure can only decrease with increasing altitude. Our nearspacecraft sees air pressure dropping by a factor of two for
Near Space
Layers of the Earth’s atmosphere.
Air temperature cycles as altitude increases.
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Near Space
FEBRUARY 2004
every 18,000 foot change in altitude. At 75,000 feet, ournear spacecraft measures an air pressure less than 6% ofthe air pressure found at sea level, or about 95% vacuum.At 100,000 feet, our near spacecraft measures an airpressure only 1% of the air pressure at sea level. It is 99%
vacuum at 100,000 feet! As a result of these low air pres-sures, the sky becomes inky black in color. The reductionin air pressure (or more specifically, air density) has onemore effect and that deals with cosmic rays. In nearspace, with fewer air molecules to create a shield, the cos-mic ray flux is over 100 times greater than at sea level.
The third condition found in near space is what hap-pens to the earth's horizon. There are three amazingeffects.
First, the distance to the horizon increases.Remember that a six foot tall adult sees a horizon that istypically three miles away. At an altitude of 75,000 feet,our near spacecraft sees a horizon that is 335 miles away.At 100,000 feet, the horizon is closer to 400 miles away.So at 100,000 feet, our near spacecraft can see our entirestate in a single glance.
Another effect of altitude on the earth's horizon isthat it makes the earth's curvature noticeable.Photographs taken of the earth's horizon from near spaceshow the edge of the earth to be curved and this shouldbe enough to satisfy the members of the Flat EarthSociety (not!).
The final effect that altitude has on the earth's hori-zon is that the horizon gets lower. This effect is sometimescalled depression of the horizon. The effect is very notice-able to astronauts on the Space Shuttle where they orbitearth at an altitude of 300 nautical miles. You don't haveto orbit the earth, though, to see this effect. Even our nearspacecraft can detect this effect. At an altitude of 100,000feet, our near spacecraft sees a horizon that is more thanfive degrees lower than it is at sea level. So the angulardistance from horizon, to zenith, to opposite horizonspans more than 190°.
The final condition found in near space that I will dis-cuss is gravity. The higher our near spacecraft climbs, theless gravitational force earth exerts.
Now, this is not the same effect noticed by astro-nauts. When in orbit about the earth, an astronaut is in astate of constant freefall. As a result, s/he feels weight-less. This weightlessness overwhelms the reduction ofgravity due to the distance that the Space Shuttle orbitsfrom the earth's center.
However, in near space, we can detect a change inthe earth's gravity. At an altitude of 100,000 feet, theacceleration due to gravity is 1% less. Consequently, ournear spacecraft weighs only 99% of its weight at sealevel.
You can see that the conditions in near space lookand feel much like space. There is no means for the hob-byist to create these conditions on a large scale. If wewant to experience space vicariously, then the amateurnear space program is the only game in town.
Getting Into Near Space
Now that you're familiar with the location and condi-tions found in near space, let's talk about how we getthere. There are two elements to getting into near space:
Not surprisingly, atmospheric pressure decreases with altitude.
The “Stack” — Component parts of the integratedlaunch vehicle and near spacecraft.
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the launch vehicle that does the heavy lifting and the nearspacecraft that does the thinking.
The Launch Vehicle
To get into near space, you need a launch vehicle.Amateurs most frequently use a launch vehicle consistingof a latex weather balloon, helium, and a length of nyloncord. Amateurs purchase their weather balloons fromeither Kaymont or Kaysam (see Resources). You shouldexpect to pay about $50.00, plus shipping, for a 1,200-gram balloon. A balloon this large has enough volume toget a 12-pound near spacecraft to an altitude of 85,000feet. If you use a larger balloon or lower the weight of yournear spacecraft, you can reach even higher altitudes.
Purchase your helium from a welding shop and neverfrom a department store. Department store helium is finefor filling party balloons, but your 1200-gram weather bal-loon requires over 300 cubic feet of helium. If you pur-chase helium from your local welding shop, they'll sell youa purer grade of helium and a lower cost per volume.
The load line of the launch vehicle is just a length ofnylon cord. This is the same kind of nylon cord or twinesold in places like hardware stores. The cord is strongenough to lift the near spacecraft and able to separate fromthe balloon nozzle with a minimum of force. The load line iscut to a length of between 20 to 30 feet and all its knots arewrapped in small pieces of duct tape for extra security.
The Near Spacecraft
Your near spacecraft consists of a recovery parachuteand one or more modules. If more than one module isused, you will connect them together with link lines. Youmay also use an umbilical to share power and databetween the modules. On some occasions, you mightplace a cutdown on the load line between the near space-craft and its launch vehicle. A cutdown is not required, butwhen it is used, it separates the near spacecraft from itslaunch vehicle. A cutdown is used to terminate missionsearly or to separate the balloon remains from the parachuteduring the descent phase of a mission.
The Recovery Parachute
The recovery parachute protects private property andyour near spacecraft. You can either purchase your para-chute from a rocketry company or sew it yourself (I preferto sew my own). Depending on the porosity of the canopy'sfabric, your 13-pound near spacecraft (12 pounds for themodules and one pound for the recovery parachute) willrequire a parachute about six feet in diameter.
Never launch the recovery parachute folded; instead,the launch vehicle lifts the parachute by its apex in a pre-deployed position. This way, the parachute opens immedi-ately upon balloon burst. Remember how long the load linewas? It's this long to make sure that the burst balloon(which remains tied to the other end of the load line) can fall
over the side of the parachute canopy, rather on top of theparachute canopy, possibly collapsing it.
Modules
A module consists of an airframe, avionics, and possi-bly experiments. Some airframes are purchased ready tofly while others are specially constructed. The avionics areeither a radio tracker or a flight computer. Some avionicsare mounted to a pallet that fits inside the airframe, whileothers are packed in foam rubber. A pallet is a lightweightmeans to keep elements of the avionics from bouncing
Preparing for lift-off!
Near Space
More spacecraft than the Baikonur Cosmodrome.
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FEBRUARY 2004
around during a mission, just like foam rubber does. Whenpossible, use a standardized airframe design and avionicspallet. This way, you can have several airframes and avion-ics pallets that can be mixed and matched as needed.
Experiments are the element that changes the most.Typically, each new mission switches out the old experi-
ments for new ones. These experiments are what exciteme the most about the amateur near space program.
Airframes
The fastest way to get an airframe is to purchase aninsulated and reusable lunch bag. In this style of airframe,the avionics are either mounted to a sheet of correplast (apallet) with zip ties or fitted into a block of foam rubberthat has been cut to fit the interior space of the lunch bag.Never rely on the rubber ducky antenna that comes withmost handheld radios, as they tend to have poor gain.Instead, use a flexible J-Pole or dipole antenna connectedto the handheld radio's antenna jack. The rest of the anten-na is left dangling outside of the closed bag. Parachuteshroud lines are attached securely to the hand strap. Neveruse a snap swivel to attach the parachute to the airframe,as it can pop open. A popped snap swivel terminates anear space mission much sooner than planned. A reusablelunch bag and simple tracker, as described below, make anideal first near spacecraft or backup tracker for a moreadvanced near spacecraft design.
More elaborate airframes are constructed from a 3/4"thick Styrofoam sheet. The best source of this material isthe blue or pink Styrofoam sheeting used to insulatehomes. This material is very popular and can be found atvirtually every home improvement store. Styrofoam is theideal material because it is strong, warm, lightweight, andinexpensive. Styrofoam is also very easy to machine; youonly need a sharp Xacto knife and metal straight edge tocut the foam. A good adhesive to glue the sides of your cutStyrofoam panels together is hot glue. As it sets veryquickly, hot glue is as easy to work with as Styrofoam. Justbe sure to keep the glue below its maximum temperature,because it can begin to melt the Styrofoam.
After constructing your airframe,you may wish to add more insulationto its exterior. To keep spacecraftwarm, aerospace companies wraptheir spacecraft in multilayer insula-tion (MLI). Their MLI is constructedfrom alternating layers of space-ratedaluminized Mylar or Kapton and ascrim (plastic mesh) inner layer. Ahomemade version of MLI is madefrom space blanket and wedding veilmaterial. At this time, however, I'mnot certain the vacuum of near spaceis "hard" enough to make the MLIeffective.
During its mission, the interior ofyour near spacecraft module will chillin the freezing air. The cold of nearspace is severe to some items, likebatteries. From personal experience,I can tell you that cold batteries canmake for a bad day. In some casesthe batteries get so cold that they fail
Components of the near spacecraft.
Near Space
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and shut down telemetry from your near spacecraft (eversee the movie, Lost In Near Space?).
There are two things you can do to prevent this. Thefirst is to use lithium cells. The chemistry of lithium cellsholds up to cold much better than most other batterychemistries. The second is to cover the exterior of the air-frame in dark fabrics. A jacket of dark fabric absorbs solarradiation and will passively heat the interior of the mod-ule. Besides warming the module, a fabric jacket will alsoprotect the MLI and airframe exterior from abrasion dur-ing landing. It's also a great place to attach link linesbetween modules. I use ripstop nylon for my fabric jack-ets, which I call abrasion jackets. You've most likely seenripstop nylon used in fabric kite sails.
Avionics for Near Space
The electronics used to operate a near spacecraft arecalled avionics (aviation electronics). For your first nearspace mission, I recommend using a simple amateurradio tracker. A simple and inexpensive amateur radio trackerconsists of a terminal node con-troller connected to a GPS receiverand a handheld, two-meter, amateur radio (see Resources).
The terminal node controller(TNC) is a modem built for radiouse. When used in avionics, itaccepts sentences from a GPSreceiver and formats them fortransmission over the radio.
Afterwards, it keys the radioand sends the proper tones. A sim-ilar set-up on the ground decodesthe tones and displays the data ona laptop or PC. This method isreferred to as the AutomaticPacket Reporting System (APRS)and is very popular with the ama-teur radio community.
Because of APRS, the posi-tion of the near spacecraft in threedimensions, its speed, and itsheading are known to chase andrecovery crews.
The simple tracker costsaround $250.00, but don't let thecost scare you. Assembling yourtracker is a one-time expense,because it is used on every mis-sion. Besides, the cost of a trackeris less than the cost of a good set ofgolf clubs. Not only does a trackercost less, but the aggravation asso-ciated with it is less than the aggra-vation associated with the same setof golf clubs.
The next step up from a radio tracker is a flight com-puter. Most of the flight computers used by amateurstoday are based on programmable microcontrollers likethe PIC, Rabbit, or BASIC Stamp.
Upgrading from a radio tracker to a flight computerdoesn't add much to the cost of avionics, but it does per-mit complex experiments and mission profiles that aren'tavailable with a simple tracker. More information on flightcomputers is available from groups like ANSR, ProjectTraveler, or myself.
Your experiments will change on each mission, butyour modules shouldn't. Give some thought to designingand building a generic style of airframe and flight com-puter. This way experiments are designed to meet thestandards for the modules, rather than having modulesdesigned to match the experiment. Be sure to documentthese standards. This is a much faster approach to flyingmissions, making failures less likely. Now your nearspacecraft is more like a Space Shuttle than a Mercuryspace capsule. NV
ANSRwww.ansr.org
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HABITAThabitat.netlab.org/index.shtml
Kansas
HamBONEfrodo.bruderhof.com/hambone/
index.htmlNew York
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NSTARmembers.cox.net/mconner1/nstar.html
Nebraska
Project Travelerwww.rckara.org/project_traveler
Kansas
Ralph Wallio (2)users.crosspaths.net/~wallio
Iowa
TVNSPwww.voiceofidaho.org/tvnsp
Idaho
Aware Electronicswww.aw-electronics.com
RM-60
Byonicswww.byonics.comTiny Trak III (TNC)
Garminwww.garmin.com
GPS Receivers
HROwww.hamradio.com
Amateur Radios
Kantronicswww.kantronics.com
KPC 3+ (TNC)
Kaymontwww.kaymont.comWeather Balloons
Kaysamwww.kaysam.comWeather Balloons
Parallaxwww.parallax.com
BASIC Stamps
Rocketmanwww.the-rocketman.com
Parachutes
APRS/Packet Radio www.tapr.org
Packet Radio/APRS
ARRLwww.arrl.org
Amateur Radio Clubs
Some Helpful Websites — Amateur Near Space Programs
FEBRUARY 2004 69
Near Space
NearSpace.qxd 1/2/2004 2:59 PM Page 69
The opening piece of this eight-part seriesdescribed basic transistor principles and configu-rations; subsequent articles went on to describe a
wide variety of practical transistor circuits ranging fromcommon-collector amplifiers (Part 2), common-emitterand common-base amplifiers (Part 3), and small-signalaudio amplifiers (Part 4), to various practical oscillator(Part 5), multivibrator waveform generator (Part 6), andaudio power amplifier (Part 7) circuits. This month's finalepisode rounds off the "Transistor Cookbook" subject bypresenting a miscellaneous collection of practical anduseful transistor circuits and gadgets.
A NOISE LIMITER CIRCUIT
Unwanted electronic "noise" can be a great nuisance;when listening to very weak broadcast signals, for exam-ple, peaks of background noise often com-pletely swamp the broadcast signal, making
it unintelligible. This problem can often be overcome byusing the noise limiter circuit in Figure 1. Here, the signal-plus-noise waveform is fed to amplifier Q1 via RV1. Q1amplifies both waveforms equally, but D1 and D2 auto-matically limit the peak-to-peak output swing of Q1 toabout 1.2 V. Thus, if RV1 is adjusted so that the signal out-put is amplified to this peak level, the noise peaks will notbe able to greatly exceed the signal output, and intelligi-bility is greatly improved.
ASTABLE MULTIVIBRATOR CIRCUITS
The astable multivibrator circuit has many practicaluses. It can be used to generate a non-symmetrical 800Hz waveform that produces a monotone audio signal inthe loudspeaker when S1 is closed (Figure 2). The circuit
can be used as a Morse codepractice oscillator by using aMorse key as S1; the tone fre-quency can be changed by alter-ing the C1 and/or C2 values.
Figure 3 shows an astablemultivibrator used as the basisof a "signal injector-tracer" itemof test gear. When SW1 is inINJECT position 1, Q1 and Q2are configured as a 1 kHzastable, and feed a good squarewave into the probe terminal viaR1-C1. This waveform is rich in
harmonics, so if it isinjected into any AFor RF stage of anAM radio, it pro-duces an audibleoutput via theradio's loudspeaker,unless one of theradio's stages isfaulty. By choosinga suitable injectionpoint, the injectorcan be used to trou-
FEBRUARY 2004
Figure 1. Noise limiter. Figure 2. Morse code practice oscillator.
Figure 3. Signal injector-tracer.
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BIPOLAR TRANSISTOR COOKBOOK — PART 8
Ray Marston describes a miscellaneous collection of usefultransistor circuits and gadgets in this month's final episodeof an eight-part series.
bbyy RRaayy MMaarrssttoonn
Figure 4. Simple lie detector.
RayMarston8.qxd 1/5/2004 4:59 PM Page 70
ble-shoot a defective radio.When SW1 is switched to TRACE position 2, the
Figure 3 circuit is configured as a cascaded pair of com-mon-emitter amplifiers, with the probe input feeding toQ1 base, and Q2 output feeding into an earpiece orhead-set. Any weak audio signals fed to the probe aredirectly amplified and heard in the earpiece, and anyamplitude-modulated RF signals fed to the probe aredemodulated by the non-linear action of Q1. The result-ing audio signals are then amplified and heard in the ear-piece. By connecting the probe to suitable points in aradio, the tracer can thus be used to trouble-shoot afaulty radio, etc.
LIE DETECTOR
The lie detector of Figure 4 is anexperimenter's circuit, in which the vic-tim is connected (via a pair of metalprobes) into a Wheatstone bridge,formed by R1-RV1-Q1 and R3-R4; the1 mA center-zero meter is used as abridge-balance detector. In use, the vic-tim makes firm contact with theprobes and, once he/she has attaineda relaxed state (in which the skin resistance reaches a sta-ble value), RV1 is adjusted to set a null on the meter. Thevictim is then cross-questioned and, according to theory,the victim's skin resistance will then change, causing thebridge to go out of balance if he/she lies or shows any signof emotional upset (embarrassment, etc.) when beingquestioned.
CURRENT MIRRORS
A current mirror is a constant-current generator inwhich the output current magnitude is virtually identical tothat of an independent input control current. This type ofcircuit is widely used in modern linear IC design. Figure 5shows a simple current mirror using ordinary npn transis-tors; Q1 and Q2 are a matched pair and share a commonthermal environment.
When input current Iin is fed into diode-connected Q1,it generates a proportionate forward base-emitter volt-age, which is applied directly to the base-emitter junctionof matched transistor Q2, causing it to sink an almostidentical (mirror) value of collector current, Isink. Q2 thusacts as a constant current sink that is controlled by Iin,even at collector voltages as low as a few hundred milli-volts.
Figure 6 shows a pnp version of the simple currentmirror circuit. This works in the same basic way as alreadydescribed, except that Q2's collector acts as a constantcurrent source that has its amplitude controlled by Iin. Notethat both of these circuits still work quite well as current-controlled, constant-current sinks or sources, even if Q1and Q2 have badly matched characteristics, but in thiscase may not act as true current mirrors, since their Isinkand Iin values may be very different.
ANADJUSTABLEZENER
Figure 7 shows the circuit of an adjustable zener thatcan have its output voltage pre-set over the range 6.8 Vto 21 V via RV1. The circuit action is such that a fixed ref-erence voltage (equal to the sum of the zener and Vbe val-ues) is generated between Q1's base and ground(because of the value of zener voltage used) and has anear-zero temperature coefficient. The circuit's outputvoltage is equal to Vref multiplied by (RV1 + R1)/R1, andis thus pre-settable via RV1. This circuit is used like anordinary zener diode, with the RS value chosen to set itsoperating current at a nominal value in the range 5 to 20mA.
L-C OSCILLATORS
L-C oscillators have many applications in test gear andgadgets, etc. Figure 8 shows an L-C medium-wave (MW)signal generator or beat-frequency oscillator (BFO), withQ1 wired as a Hartley oscillator that uses a modified 465kHz IF transformer as its collector load. The IF trans-former's internal tuning capacitor is removed, and variableoscillator tuning is available via VC1, which enables theoutput frequency (on either fundamentals or harmonics)to be varied from well below 465 kHz to well above 1.7MHz. Any MW radio will detect the oscillation frequency ifplaced near the circuit; if the unit is tuned to the radio's IFvalue, a beat note will be heard, enabling CW and SSBtransmissions to be clearly heard.
Figure 9 shows the above oscillator modified so that,
Figure 5. An npn currentmirror.
FEBRUARY 2004
Figure 6. A pnp current mirror.
Figure 7. Adjustable zener.
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Figure 8. MW signal generator/BFO.
RayMarston8.qxd 1/5/2004 5:02 PM Page 71
when used in conjunction with a MW radio, it functionsas a simple metal/pipe locator. Oscillator coil L1 ishand-wound and comprises 30 center-tapped turns ofwire, firmly wound over about a 25 mm (one-inch)length of a 75 to 100 mm (three- to four-inch) diameternon-metallic former or search head and connected tothe main circuit via a three-core cable. The search headcan be fixed to the end of a long non-metallic handle ifthe circuit is to be used in the classic metal detectormode, or can be hand-held if used to locate metal pipesor wiring hidden behind plasterwork, etc. Circuit opera-tion relies on the fact that L1's electromagnetic field isdisturbed by the presence of metal, causing the induc-tance of L1 and the frequency of the oscillator to alter.This frequency shift can be detected on a portable MWradio placed near L1 by tuning the radio to a local sta-tion and then adjusting VC1 so that a
low frequency beat or whistle note isheard from the radio. This beat notechanges if L1 (the search head) isplaced near metal.
Figure 10 shows another applicationof the Hartley oscillator. In this case, thecircuit functions as a DC-to-DC convert-er, which converts a 9 V battery supplyinto a 300-V DC output. T1 is a 9V-0-9Vto 250 V transformer, with its primaryforming the L part of the oscillator. Thesupply voltage is stepped up to about
350 V peak at T1secondary, and ishalf-wave rectifiedby D1 and used tocharge C3. With nopermanent load onC3, the capacitorcan deliver a pow-erful but non-lethalbelt. With a perma-nent load on theoutput, the outputfalls to about 300 Vat a load current ofa few mA.
FM TRANSMITTERSFigures 11 and 12 show a pair of low-power FM trans-
mitters that generate signals that can be picked up at arespectable range on any 88 to 108 MHz FM-band receiver.The Figure 11 circuit uses IC1 as a 1 kHz squarewave gen-erator that modulates the Q1 VHF oscillator, and pro-duces a harsh 1 kHz tone signal in the receiver; this cir-cuit thus acts as a simple alarm-signal transmitter.
The Figure 12 circuit uses a two-wire electret micro-phone insert to pick up voice sounds, etc., which areamplified by Q1 and used to modulate the Q2 VHF oscil-lator; this circuit thus acts as an FM microphone or bug.In both circuits, the VHF oscillator is a Colpitts type, butwith the transistor used in the common-base mode andC7 giving feedback from the tank output back to the
emitter input.These two circuits have been
designed to conform toAmerican FCC regulations, andthey thus produce a radiated fieldstrength of less than 50 µV/m ata range of 15 meters (15 yards),and can be freely used in theUSA. It should be noted, however,that their use is quite illegal inmany countries, including theUK.
To set up these circuits, setthe coil slug at its middle posi-tion, connect the battery, and
FEBRUARY 2004
Figure 11. FM radio transmitter alarm.
Figure 13. The frequency response of this1 V AC meter is flat to above 150 kHz.
Figure 12. FM microphone/bug transmitter.
Figure 10. 9 V to 300 V DC-to-DC converter.
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Figure 9. Metal/pipe locator.
Figure 14. Pseudo full-wave version of the 1 V AC meter.
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tune the FM receiver to locate the transmitter frequency. Ifnecessary, trim the slug to tune the transmitter to a clearspot in the FM band. RV1 should then be trimmed to setthe modulation at a clean level.
TRANSISTOR AC VOLTMETERS
An ordinary moving-coil meter can be made to readAC voltages by feeding them to it via a rectifier and suit-able multiplier resistor, but produces grossly non-linearscale readings if used to give FSD values below a few volts.This non-linearity problem can be overcome by connectingthe meter circuitry into the feedback loop of a transistorcommon-emitter amplifier, as shown in the circuits ofFigures 13 to 15, which (with the Rm values shown) eachread 1 V FSD.
The Figure 13 circuit uses a bridge rectifier type ofmeter network, and draws a quiescent current of 0.3 mA,has an FSD frequency response that is flat from below 15Hz to above 150 kHz, and has superb linearity up to 100kHz when using IN4148 silicon diodes or to above 150 kHzwhen using BAT85 Schottky types. R1 sets Q1's quiescentcurrent at about treble the meter's FSD value, and thusgives the meter automatic overload protection.
Figures 14 and 15 show pseudo full-wave and ghostedhalf-wave versions of the above circuit. These have a per-formance similar to that of Figure 13, but with better linear-ity and lower sensitivity. D3 issometimes used in these cir-cuits to apply slight forward biasto D1 and D2 and thus enhancelinearity, but this makes themeter pass a standing currentwhen no AC input is applied.The diodes used in these andall other electronic AC metercircuits shown in this articleshould be either silicon(IN4148, etc.) or (for excep-tionally good performance)Schottky types; germaniumtypes should not be used.
In the circuits in Figures 13to 15, the FSD sen-sitivity is set at 1 Vvia Rm, which cannot be reducedbelow the valuesshown withoutincurring a loss ofmeter linearity.
The Rm valuecan, however, safe-ly be increased, togive higher FSDvalues, e.g., by afactor of 10 for 10V FSD, etc.
If greater FSD
sensitivity is wanted from the above circuits, it can beobtained by applying the input signal via a suitable pre-amplifier, i.e., via a +60 dB amplifier for 1 mV sensitivity,etc. Figure 16 shows this technique applied to the Figure13 circuit, to give an FSD sensitivity variable between 20mV and 200 mV via RV1. With the sensitivity set at 100mV FSD, this circuit has an input impedance of 25 K anda bandwidth that is flat within 0.5 dB to 150 kHz.
AC MILLIVOLTMETER CIRCUITS
A one-transistor AC meter cannot be given an FSDsensitivity greater than 1 V without loss of linearity. Ifgreater sensitivity is needed, two or more stages of transis-tor amplification must be used. The highest useful FSDsensitivity that can be obtained (with good linearity andgain stability) from a two-transistor circuit is 10 mV, andFigure 17 shows an excellent example that gives FSD sen-sitivities in the range 10 mV to 100 mV (set via Rx). It usesD1 and D2 in the "ghosted half-wave" configuration, and itsresponse is flat within 0.5 dB to above 150 kHz; the cir-cuit's input impedance is about 120 K when set to give 100
FEBRUARY 2004
Figure 15. Ghosted half-wave version of the 1 V AC meter.
Figure 16. This AC voltmeter can be set to give FSDsensitivities in the range 20 mV to 200 mV.
73
Figure 17. Wideband AC millivoltmeter with FSD sensitivity variable from 10 mV to 100 mV via Rx.
Figure 18. This x10 wideband pre-amplifier is used to boost an AC
millivoltmeter's sensitivity.
RayMarston8.qxd 1/6/2004 1:03 PM Page 73
mV FSD sensitivity (Rx = 470 Ohms); when set to give 10mV sensitivity (Rx = 47 Ohms), the input impedancevaries from 90 K at 15 kHz to 56 K at 150 kHz.
Figure 18 shows a simple x10 pre-
amplifier that can be used to boost the above circuit's FSDsensitivity to 1 mV; this circuit has an input impedance of45 K and has a good wideband response. Note, whenbuilding highly sensitive AC millivoltmeters, great caremust be taken to keep all connecting leads short, to pre-vent unwanted RF pickup.
A wide-range AC volt/millivolt meter can be made byfeeding the input signals to a sensitive AC meter via suit-able attenuator circuitry. To avoid excessive attenuatorcomplexity, the technique of Figure 19 is often adopted;the input is fed to a high-impedance unity-gain buffer,
either directly (on "mV" ranges)or via a compensated 60 dBattenuator (on V ranges), and thebuffer's output is fed to a basic 1mV FSD meter via a simple low-impedance attenuator, which inthis example has 1-3-10, etc.,ranging.
Note, when using this circuitthat its input-to-unity-gain-buffer-output frequency response is vir-tually flat over the (typical) fre-quency range 20 Hz-150 kHzwhen used on the "mV" ranges,and that the primary attenuator's15 pF trimmer must — when ini-
tially setting up the circuit — beadjusted on test to obtain the samefrequency response on the basic "V"range.
Figure 20 shows a useful varia-tion of the above technique. In thiscase, the input buffer also serves as ax10 amplifier, and the secondaryattenuator's output is fed to a meterwith 10 mV FSD sensitivity, the neteffect being that a maximum overallsensitivity of 1 mV is obtained with aminimum of complexity.
Figures 21 and 22 show inputbuffers suitable for use with the abovetypes of multi-range circuits. TheFigure 21 design is that of a unity-gain buffer; it gives an input imped-ance of about 4.0 M. The Figure 22buffer gives a x10 voltage gain (set bythe R1/Rx ratio) and has an inputimpedance of 1.0 M. NV
Figure 20. A useful AC volt/millivolt meter circuit variation.
Figure 21. Unity-gain input buffer. Figure 22. Buffer with x10 gain.
Figure 19. Basic multi-range AC volt/millivolt meter circuit.
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FEBRUARY 2004Circle #147 on the Reader Service Card.
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FEBRUARY 2004
TechKnowledgey2004AdvancedTechnologiesNew Cooling Technique forElectronic Devices
YYou have probably noticed thattoday's microprocessors and
other devices have presented design-ers with thermal management prob-lems in recent years.
The traditional approach hasbeen to simply employ largerheatsinks and more powerful fans.However, heatsinks can take up a lotof space, and cooling fans havemechanical limitations.
For example, much of the circu-lated air bypasses the heatsinks anddoes not mix well with the thermalboundary layer that forms on thefins. Fans placed directly aboveheatsinks have "dead areas" wheretheir motor assemblies block airflow.
And, as designers boost air flowto increase cooling, fans use moreenergy, create more noise, and takeup more space. Researchers at theGeorgia Institute of Technology(www.gatech.edu) have concluded
that conventional fan-driven coolingis incompatible with future high-density, low-power systems andtherefore have been working on alter-native solutions. A concept thatseems to have great potential is theirpatented synthetic jet (SynJet)device. The operating principle issimple. Perhaps you have demon-strated the amazing power of yourstereo system by letting the "woofer"blow out a lighted match.
In much the same manner, theSynJet uses an electromagnetic orpiezoelectric driver, vibrating at arate of 100 to 200 Hz, to suck in andthen expel air from a cavity.
This creates pulsating jets thatare directed to precise locationswhere cooling is needed. Accordingto the inventors, the device is betterthan a fan in that it has no frictionparts to wear out, uses less energy,and creates less noise. They pointout that, although the jets move 70percent less air than fans of compa-rable size, "the air flow they producecontains tiny vortices which makethe flow turbulent, encouraging effi-cient mixing with ambient air andbreaking up thermal boundary lay-ers. You get a much higher heattransfer coefficient with syntheticjets, so you do away with the majorcooling bottleneck seen in conven-tional systems." Furthermore, "Theability to scale the jet modules to suitspecific applications and to integratethem into electronic equipmentcould provide cooling solutions overa broad range of electronic hardwareranging from desktop computers tomobile phones, and other portabledevices that are now too small or have too little power for activecooling."
Plastic Memories May OfferHigh-Density Storage
EEngineers at Princeton University(www.princeton.edu) and
Hewlett-Packard (www.hp.com)have discovered a combination ofmaterials that could lead to cheapand super-compact electronic mem-ory devices for archiving digitalimages or other data. The inventioncould result in a single-use memorycard that permanently stores dataand is faster and easier to use than acompact disk. The device could bevery small, because it would notinvolve moving parts such as thelaser and motor drive required byCDs. The concept is based on poly-ethylenedioxythiophene (PEDOT), apolymer material that is clear andelectrically conductive. It has beenused for years as an antistatic coat-ing on photographic film, and morerecently as an electrical contact onvideo displays that require light topass through the circuitry. PEDOTconducts electricity at low voltagesbut permanently loses its conductivi-ty when exposed to higher voltages(and thus higher currents), making itact like a fuse or circuit breaker. Thisled the researchers to think aboutusing PEDOT as a way of storing dig-ital information. As we all know, digi-tal images and computer data arestored as long strings of ones andzeroes. A PEDOT-based memorydevice would have a grid of circuitsin which all the connections containa PEDOT fuse. A high voltage couldbe applied to any of the contactpoints, blowing that particular fuseand leaving a mix of working andnonworking circuits. These open orclosed connections would represent
Events, Advances, and NewsFrom the Electronics World
Close-up of a prototype synthetic jet(SynJet).Vibrating diaphragms (on right) produce trains of turbulent air puffs thatflow out of the white tubes and into the
cooling fins of the electronic device. Photoby Gary Meek, courtesy of Georgia Tech.
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zeros and ones and would becomepermanently encoded in the device.A blown fuse would block current andbe read as a zero, while an unblownfuse would let current pass and act asa one. This grid of memory circuitscould be made so small that, basedon the test junctions the researchersmade, one million bits of informationcould fit in a square millimeter ofpaper-thin material. If formed as ablock, the device could store morethan 1 GB of information, or about1,000 high-quality images, in a vol-ume of 1 cc. The concept is said to beabout five years from commercialdevelopment.
Computers andNetworkingArtificial IntelligenceResearch Continues
WWe haven't heard much aboutartificial intelligence (AI) lately,
but it appears that some seriousresearch continues in an effort toachieve this holy grail of computerscience. Artificial Development, Inc.(www.ad.com), recently announcedthat it has completed assembly of thefirst functional portion of a prototypeof its CCortex, a 20-billion-neuronemulation of the human cortex, which
it will use to build a next-generationartificial intelligence system. Thecluster is a high-performance, parallelsupercomputer, composed of 500nodes and 1,000 processors, 1.5 ter-abytes of RAM, and 80 terabytes ofstorage. The software/hardware sys-tem runs on Linux, using Intel andAMD processors. When all sectionsare assembled, CCortex is expectedto reach a theoretical peak perform-ance of 4,800 Gflops, making it oneof the top 20 fastest computers in theworld. The cluster will be used as atest bed for beta versions of CCortex.CCortex is a massive spiking neuronnetwork emulation that will mimic thehuman cortex — the outer layer ofgray matter at the cerebral hemi-spheres, largely responsible for high-er brain functions. The emulation cov-ers up to 20 billion layered neuronsand 2 trillion 8-bit connections. Mostneural network models to date havebeen based on the Hebbian network,
The first CCortex cluster. Courtesy ofArtificial Development, Inc.
ert TechKnowledgey 2004
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a simplified version of the real neuralnetworks, based exclusively on connec-tivity properties between neurons.CCortex adds to classical Hebbian con-nections a time-sensitive, analog repre-sentation of the shape of "spikes," thepulsing patterns that enable neuron pop-ulations to communicate with eachother. This allows CCortex to tune vastpopulations of neurons and the informa-tion they hold to complex spiking pat-terns, adding a higher level of complexi-ty to a highly realistic simulation.
The CCortex software emulationapplies its Spiking Neuron SoftwareEngine to a database that has a repre-sentation of the layered distribution ofneural nets and detailed interconnec-tions in the brain. The data closely emu-lates specialized regions of the humancortex, corpus callosum, anterior com-missure, amygdale, and hippocampus.The emulation aims to actualize theestate of each neuron and its connec-tions several times per second, main-taining a myriad of competing spikingpatterns, while providing feedback andlimited interaction with simplified ver-sions of other nervous and sensory sys-tems.
Another Spam Defense
AAccording to a Reuters news report, Yahoo (www.
yahoo.com) is intending to introduce asoftware product called "Domain Keys"that will assist developers of the Web'smajor open-source Email software andsystems (including Yahoo itself) inreducing the current plague of unsolicit-ed commercial messages ("spam").According to the report, this technologywould make a slight change in the wayEmail works by embedding a secure, pri-vate key in all message headers. Areceiving system would compare thisprivate key with the presumed sender'sInternet's Domain Name System's publickey. If the public key can decrypt the pri-vate key, this will prove that the returnheader is not forged, and it will be deliv-ered. If not, the message will bedumped. As with all proposed spamcures, whether technological or legisla-tive, the plan cannot totally eliminate the
problem unless it is universally adopted,which is highly unlikely.
However, according to a Yahoo rep-resentative, "If we can get only a smallpercentage of the industry to buy in, wethink it can make a dent." In addition,Domain Keys is free and comes with nouse restrictions, so there is no over-whelming reason why an Email providershould not adopt it.
Circuits and DevicesVGA Image Sensor Introduced
MMicron Technology, Inc. (www.micron.com), has announced
the MT9V403 high-speed VGA imagesensor, which is capable of operating atup to 200 frames per second (fps) at fullresolution. Using Micron's proprietaryTrueSNAP™ technology, it features afreeze-frame electronic shutter that stopsfast motion with high accuracy.TrueSNAP technology was created foruse in high-speed applications that allowall pixels to be simultaneously exposed,similar to the "global shutter" of a CCDsensor. The device's digital interface pro-vides flexible control of performanceparameters such as exposure time,frame rate, and windowing functionality.The sensor includes on-chip 10-bit ana-log-to-digital converters outputtingmonochrome or color digital video in659H-by-494V-pixel format at 0-200 fpsand a responsivity of 2,000 bits per luxsecond. Currently, the MT9V403 isdesigned for high-speed machine-visionand special effects applications, includ-ing such things as airbag deployment
and golf swing analysis. It is intendedthat the TrueSNAP technology will even-tually migrate to other Micron imagingdevices.
Low-Cost Temperature Switch
MMaxim Integrated Products(www.maxim-ic.com), has intro-
duced the MAX6516-MAX6519 line oflow-cost, analog temperature switchesthat assert a logic signal when a presettemperature is reached. The devices fea-ture ±0.5°C typical accuracy while con-suming only 20 µA of supply current.Temperature trip thresholds are factoryset and available from +35°C to +115°C,in 10°C increments. Hysteresis is pinselectable at 2°C or 10°C. No externalcomponents are required to set the tripthreshold. These temperature switchesare designed for over/undertemperatureregulation, desktop and notebook computers, RAID, and servers. The MAX6516/MAX6518 provides anactive-high, push-pull output. TheMAX6517/MAX6519 provides an active-low, open-drain output. Each device alsofeatures an analog output with an accu-racy of ±3°C (max) over the entire tem-perature range. The devices operateover a temperature range of -40°C to+125°C, with a power-supply voltagerange of 2.7 to 5.5 V. They are availablein a five-pin SOT23 package. Prices startat $0.75 in quantities of 2500+.
Industry and theProfessionMuseum of Hard Disc DrivesPlanned
FForget about the Louvre, theHermitage, or the Prado. Don't both-
er with the Smithsonian, the AmericanMuseum of Science and Energy, orEngland's National Museum of Scienceand Industry. Put all your travel plans onhold, because the Museum of Hard DiscDrives will be opening during the 2004Komputer Expo Fair in (no jokes,please) Warsaw, Poland. After the fair,the exhibits will be transferred to theSilesian Museum in Katowice for viewingby the general public and, eventually,transferred to the headquarters of MBM
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Image sensor provides full-resolution operation at 200 frames per second. Photo
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Ontrack (www.mbm.com.pl), the datarecovery company that came up with the idea. According to a press release, the Museum of Hard Disc Drives "will popularize the history ofdynamic development of informatics among PC users."
Three of the items on display were magnanimously donated bySeagate Technology (www.seagate.
com): ST4038, ST225, and ST125drives. Developed in 1985, the ST4038was used in the IBM PC AT and had acapacity of 38 MB.
According to Marcin Musil, manag-ing director of MBM Ontrack, "We areglad that our initiative has gained the sup-port of the biggest manufacturer of harddisc drives. The drives donated to theMuseum by Seagate are the most pre-cious exhibits of our collection.""Precious," of course, is a relative term.
As I write this, a vintage ST225 driveand controller card is for sale on Ebaywith an initial price of $10.00, so farattracting no bids. Perhaps our readerscan provide additional assistance.
If anyone from the museum readsthis, please note that I am willing todonate a magnificent 44 MB Syquest car-tridge from my private collection (as longas I don't have to pay the postage). It'sgreat for propping up a wobbly table, andI would rate its current value at nearly$1.37.
HP Continues to GainWorkstation Market Share
HHewlett-Packard (www.hp.com)captured 27 percent of the world-
wide workstation market for unitsshipped for the third quarter of calendaryear 2003, according to a reportreleased recently by research groupIDC. In the US personal workstationsegment, HP grew at twice the rate ofthe overall market with a 17.5 percentincrease.
HP recognized year-to-year growthin the same market with an increase of24 percent, leading all other worksta-tion vendors ranked by IDC. In WesternEurope, HP continues to be the no. 1workstation provider with sequentialgrowth of 24 percent.
HP recognized the most growthwithin the Intel® Pentium® 4 and Xeonbased personal workstation segment,but it increased units shipped across itsentire workstation line. NV
Among the vintage drives to be displayed inthe Museum of Hard Disc Drives is the classic Seagate ST225. Photo courtesy of
Randolph Byrnes.
TechKnowledgey 2004
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EEngineers and hobbyists alikehave taken advantage of theubiquitous 7400-series logic
families for years. A 7400 devicecomes to mind when you need asingle AND gate, a flip-flop, orother basic logic function. Thesedevices are easy to use because oftheir standardized features. Acrossdifferent families, equivalentdevices generally have identical pinassignments and basic functionali-ty. 7400 logic is a de-facto standardthat everyone designing with elec-tronics should be familiar with.
There have been many familiesunder the 7400 canopy that havecome and gone. Some existingfamilies are just a few years old andothers are counting decades. Inthis column, we'll discuss a few ofthe more commonly used 7400families. Once you understand theareas of distinction, you'll be ableto do your own research to find thefamily most suited to your project.
IC Specifications
Integrated circuit (IC) manufac-turers provide many specificationsfor their products. The specifica-tions that define different 7400variants are essentially nominalsupply voltage, input/output volt-ages and currents, and propaga-tion delays. Supply voltage is his-torically denoted VCC, referring tothe collector voltage of transistorsin the original devices.Manufacturers sometimes rate VCCat ± 10%, but often specify electri-cal characteristics under a tighter ± 5% range.
Voltage specifications are treat-ed differently for each logic level.When a logic-0 is applied to an ICinput, the specification that reallymatters is the maximum allowablevoltage level that can be recog-nized as a 0 by the IC. This specifi-cation can be denoted as VIL(MAX).Conversely, a logic-1 specificationis the minimum voltage level thatcan be recognized as a 1, orVIH(MIN). Between VIL(MAX) andVIH(MIN) lies a "no-man's land" thatshould be avoided due to indeter-minate results.
Similar voltage specificationsapply to IC outputs. You are inter-ested in the maximum, or worst-case, output voltage that repre-sents a logic-0, VOL(MAX). If VOL(MAX)is higher than VIL(MAX), you won'tbe able to reliably drive a similarchip. Of equal interest is the worst-case logic-1 output voltage,VOH(MIN). VOH(MIN) cannot be lessthan VIH(MIN) for reliable inter-chipconnections.
Currents are signed specifica-tions because currents flow intoand out of the IC depending on thelogic level being applied or driven.The convention is that positive cur-rents enter the chip and negativecurrents leave the chip. On theinput side, the logic-0 input currentis actually negative because cur-rent flows out of the chip to a lowerapplied voltage. Logic-1 output cur-rent is also negative because cur-rent flows out of the chip. An IC"sinks" incoming currents and"sources" outgoing currents.Written specifications may simplifynotation by referring to currents in
absolute values, thereby foregoingmention of negative currents.
It should be noted that, as aload requires more current, the out-put voltage is pulled towards thecenter "no-man's land." A lightlyloaded output will exhibit a moredesirable voltage level closer toeither of the IC's power rails. Theoutput voltage specifications canno longer be guaranteed if youexceed a device's specified outputcurrent rating.
Propagation Delay
The parameters just men-tioned are called DC specificationsbecause they refer to steady-stateoperation of the IC. An output volt-age will not change if all circuitcharacteristics are held constant.Propagation delays are AC specifi-cations because they refer to tran-sitional behavior. An IC's outputvoltage changes some finite timeafter a corresponding input voltagechanges. This is a propagationdelay, generally measured innanoseconds, or in billionths of asecond.
Manufacturers should specifyminimum and maximum propaga-tion delays, but they do not alwaysdo so. Often, only the maximumpropagation delay is specified,which is adequate for many cir-cuits. Some circuits — especiallyhigh-speed circuits — also requireminimum delays. When these spec-ifications are unavailable, it takesexperience and care to avoid tim-ing problems. Timing analysis is adetailed topic beyond the scope of
Just For StartersBasics For Beginners
Choosing A 7400 Logic Family
Just For Starters by Mark Balch
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this article. My book,Complete DigitalDesign, contains an in-depth presen-tation of timinganalysis.
Watch out forthe trap of "typical"timing specificationsthat many IC datasheets provide.Typical numbers arenot worst-case speci-fications over theIC's specified operat-ing range. Propagation delays change dramatically withchanges in supply voltage and temperature. Minimumand maximum specifications are guaranteed across anoperating range. However, typical numbers can helpprovide a clearer picture of a device's operation. Justdon't get fooled into relying on them alone.
Bipolar (TTL)
Now that you know how to evaluate an IC's charac-teristics, let's get back to 7400 devices. The original7400 families are bipolar devices, also known as transis-tor-transistor logic (TTL). Bipolar logic is constructedfrom bipolar junction transistors, in contrast to CMOSlogic, which is constructed using a metal-oxide semi-conductor (MOS) process. Two of the common bipolarfamilies still in use today are 74LS and 74F. 74LS useslow-power Schottky circuitry while 74F uses faster cir-cuitry at the expense of higher power consumption.
Both families run on a single 5 V (nominal) powersupply. The 74LS and 74F families are available fromalmost every electronics component retailer and distrib-utor. Table 1 lists DC and AC characteristics for the fam-ilies mentioned in this article. The '00 device in eachfamily is a quad two-input NAND-gate. You can see thatthe 74LS00 is much slower than the 74F00 and that itprovides less output current. A characteristic of TTLlogic is the asymmetric drive strength between logic-1and logic-0. The logic-0 state can sink much more cur-rent than the logic-1 state can source.
On the input side, the logic-0 state sources morecurrent than the logic-1 state sinks. 74LS and 74Fdevices can be mixed because they have compatibleinput and output voltage thresholds. There are 0.7 V ofworst-case margin between VOH(MIN) and VIH(MIN) and 0.3V between VOL(MAX) and VIL(MAX).
Fan-out
Fan-out is an important characteristic to pay atten-tion to: it determines the number of inputs that a single
output can drive. From a purely DC perspective, fan-outis calculated by dividing the output drive strength by theinput current for each logic state. Then you take thelesser of the two numbers. Doing this for the 74LS00and 74F00 yields 22 and 33, respectively. However, fan-out should also be considered from an AC, or transitional, perspective.
Each additional load on an output driver adds asmall amount of capacitance. An IC pin typically addsabout 10 pico-Farads (pF) of capacitance (some more
74LS00 5.0 0.02 0.36 2 0.8 0.4 8 2.7 0.5 1574F00 5.0 0.005 0.6 2 0.8 1 20 2.7 0.5 574HCT00 5.0 0.001 0.001 2 0.8 4 4 3.98 0.26 2374ACT00 5.0 0.001 0.001 2 0.8 24 24 3.86 0.44 9
74LC3.3 0.005 0.005 2 0.8 24 24 2.2 0.55 5.22.5 0.005 0.005 1.7 0.7 8 8 1.8 0.6 6.2
Device VC
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TABLE 1: Basic 7400 family DC and AC characteristics (source: Fairchild Semiconductor)
ch Just For Starters
FEBRUARY 2004 83
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and some less). Capacitors take a finite time to chargeand slow down the rise and fall times of an IC's outputdriver. AC specifications, such as propagation delays,are often accompanied with a maximum load capaci-tance. Values from 20 to 50 pF are typical. A rough fan-out estimate is obtained by dividing the maximumcapacitance by 10 pF. This drops the fan-out to just sev-eral inputs rather than 20 or 30.
If an IC has much faster AC specifications than yourapplication requires, you may experiment with higherfan-out than what is actually allowed by the capacitancenumbers. It is important to understand the compromisebeing made.
CMOS Logic
Complementary MOS (CMOS) logic is a lowerpower alternative to bipolar. Several CMOS 7400 fami-lies were developed to complement the TTL variants.Some families such as C and HC are function-compati-ble with TTL, but have different voltage thresholds.Different thresholds make it difficult to mix differenttechnologies on the same circuit board. 74HCT wasdeveloped for the low-power benefits of CMOS whileretaining TTL-compatible voltage thresholds.
As seen in Table 1, HCT has lower input currentthan 74LS and 74F, which enables it to consume lesspower at steady-state. (Capacitance dominates powerconsumption during signal transitions due to thecharge/discharge process.) 74HCT also has symmetri-cal output drive strength.
Table 1 shows that 74HCT is slower than 74LS and74F. 74ACT increases the speed and drive strength ofCMOS logic, though it is not as fast as 74F. Both CMOSvariants do a better job than TTL of driving outputs clos-er to the power rails.
Low-Voltage Devices
Discrete logic has taken a diminished role in main-stream system design due to high-density ICs. More andmore systems have abandoned 5-volt logic in favor of3.3, 2.5, 1.8, and 1.5-volt technologies. The 7400 fami-ly has been energized in recent years by new variantsfrom several manufacturers. Fairchild Semiconductoroffers the 74LCX family that operates at lower supplyvoltages with relatively fast propagation delays.
Which Family to Pick?
Choosing a logic family is highly application specif-ic. If you are prototyping with mature technologies, 5-volt logic may be appropriate. The next aspect to con-sider is how fast your ICs need to operate. Generallyspeaking, it is best to use slower devices with lowerpower consumption whenever possible.
Slower devices have fewer tricky problems and it iseasier to work with lower currents. Then there are han-dling concerns of CMOS versus TTL. CMOS devices aresensitive to static electricity.
If you're not careful, you can zap a chip and destroyit. Finally, the choice may be made for you by the otherdevices that you are working with. If you need to work with a 3.3-volt IC, you'll have to pick a low-voltagefamily. NV
Mark Balch is the author of Complete Digital Design (see www.completedigitaldesign.com) andworks in the Silicon Valley high-tech industry. His responsibilitieshave included PCB, FPGA, and ASIC design. Mark has designedproducts in the fields of telecommunications, HDTV, consumerelectronics, and industrial computers. In addition to his work inproduct design.
Mark has actively participated in industry standards commit-tees and has presented work at technical conferences. Mark holdsa bachelor's degree in electrical engineering from The CooperUnion in New York City. He can be reached via Email [email protected].
AAAAbbbboooouuuutttt tttthhhheeee AAAAuuuutttthhhhoooorrrr
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saddened by the apparent lack of interest in circuit basics bythe current pocket-protector generation. Mr. Frenzel did asplendid job of explaining just what has happened over thepast 30+ years, and, to some extent, has allayed my fearsthat the electronics enthusiast will become an absolute slaveto off-the-shelf technology.
Nuts & Volts continues to present a broad spectrum ofinteresting articles, which I hope will continue. Ray Marston'sseries on bipolar transistors, Chris Hannold's introduction toFPGAs, and even Don Stulken's letter in “Reader Feedback”(including Nuts & Volts kind offer to distribute Don's circuitsand notes) help not only to maintain an interest inelectronics basics, but to prove that interest does, indeed,continue to exist at this level. I will always maintain that agrounding in basics is essential, for, as the quote implies,"Those who cannot remember the past are condemned torepeat it."
Jim Woodvia Internet
Dear Nuts & Volts:I greatly appreciate and enjoy your publication. As an
electronics student and hobbyist, I thank you and all yourcontributing editors. I've learned more from your publicationthan in the 18 months of tech-school that I attended (for agreat deal of money!). We live and learn.
Thank you, God bless, and keep up the good work!Freddy R. Lazzu Greensburg, PA
.
FEBRUARY 2004
Reader FeedbackContinued from Page 6 Tetsujin
2004
How muchcan you lift?
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How high?
TheJoiningOf Man AndMachine
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In The Trenches by Gerard Fonte
Everyone wants to succeed.But, some people are betterat it than others. Is it really
the person? Or is it how theyaddress their objectives? We'll lookat the skills needed to be successful.And, we'll see that anyone canimprove their success rate oncethey understand the steps for success.
What is Success?
A while back, I was one of anumber of people asked to partici-pate in a "Career Day" at a localhigh school. Before each of us start-ed to discuss our particular area ofinterest, the principal addressed thestudents and defined success interms of four clear and simple steps:1. Define a goal; 2. Decide what youwant to spend to get that goal; 3.Make a plan; and 4. Execute theplan. I was surprised to realize thatI'd been saying those same things(but with much less eloquence).
However, before we start onthese steps, there is an importantpoint that has to be made. Successis a subjective measure. Success iswhat you think it is ... not whatsomeone else thinks. You don't haveto get straight A's to be a successfulstudent. You don't have to make bil-lions of dollars to be successful inbusiness. You are a success if youthink and feel you are. (Of course,this doesn't preclude others fromtrying to change your mind.)Remember, success is achievingyour goal, not someone else's goal.
Defining a Goal
The first step is probably the
most direct and simple.Nevertheless, it seems to be over-looked with regularity. It's just defin-ing what you want. Naturally, thereare many things you want. Someare general like fame and fortune.Others are more specific like gettinga raise or a promotion. It's impor-tant to know precisely what youwant.
Unfortunately there are a fairnumber of people who want to besuccessful but don't really have anygoals. These people are really walk-ing through life without any direc-tion. They think that if they go towork each day and do their job that,in the end, they'll be a vice presidentof the company. Unfortunately, thisis not a very likely outcome.
These people are depending onothers to bestow success on them.Success is not something given byothers, it is something you craft foryourself. Let's be realistic, if you hadto choose between giving a promo-tion to yourself or some other work-er, you'd most likely choose your-self. Being selfish is human nature,and there's nothing wrong with that(within reasonable limits). Everyonewants to win.
It's important to choose a rea-sonable goal. I'm 5'5" tall. So, it'snot reasonable for me to have a goalas a center for the New York Knicksbasketball team. But, gymnasts aregenerally about my size. So, beingan Olympic gymnast might be areasonable goal for me (when I wasyounger — much younger — that is).Most academic or business goalsare usually less restrictive. There area lot more doctors, lawyers, andengineers than there are profession-al athletes. For most people, it's usu-
ally easier to learn how to be a bet-ter doctor or engineer than it is tolearn how to rebound better.
This leads to one of my favoritesayings which is, "Anyone can beanything they want, but no one canbe everything they want." What Imean is that is that anyone canexceed well beyond what they thinkthey are capable of. (If they work atit.) So, lofty goals are not unreason-able. You can be a senator or thevice president of a large company.
It's also important that yourmain goals in life be flexible andopen-ended. Athletes often haveproblems because they don't seepast the Super Bowl or World Series.How do you deal with a career thatends at age 27?
These are very competitive peo-ple who can no longer compete.They have no more goals in life. Ifthey don't make new ones, they canhave serious problems.
After you make a million dol-lars, will you stop? If you do, whatdo you plan to do after that? If youdon't stop, how many millions doyou want? (Making a million dollarsis fairly straightforward — more onthat later.)
I was talking to a businessfriend. She seemed serious whenshe said she wanted to retire andlive the rest of her life in the sun ona beach. I asked her how long shereally thought she could do thatbefore she went nuts from boredom.She paused and said, "You're right.Probably a month." Do your goals fityou? That's important, too.
Engineers are very fortunate inthat they often choose learning as alife goal. This is a great choice. It'sopen-ended. You can never learn
Being Successful
The Business of Electronics Through Practical Design and Lessons Learned
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too much. And, it's flexible.Engineering is always changing. So,there are always opportunities tolearn different things. And sinceengineers are pretty good at learn-ing, there's no reason to limit yourstudies to engineering. A surprisingnumber of older engineers like totake up completely different pursuitslike music, art, or photography.
This discussion may seem offthe point. How does this help you getthat promotion? What I'm trying toshow is that goal setting is part ofhuman nature. We do it all the time,but often don't realize that's whatwe're doing. When we say we wantsomething, we are setting a goal. It'simportant to have specific goals sothat you can direct your energy inthe most efficient manner. Successis about competing and winning. Noteveryone will win.
Note, some people don't want tocompete. They are happy to just dotheir job and get their paycheck.There's nothing wrong with this.Their lifestyle is just vanilla. This laid-back approach is a form of success, too. They have what theywant. They've reached their goal.Remember, your success is what youthink it is. Successful people are sat-isfied with themselves and satisfiedwith their life.
Paying for it
Would you rather be rich orhappy? An interesting recent pollshowed that Americans tend tochoose "happy" while Asians tend tochoose "rich". You have to decide theworth of your goal. How important isthat raise or promotion? Are you will-ing to work an extra 10 hours aweek?
You can see that determiningwhat it costs to achieve a goal isclosely linked to your plan. We'll lookat them separately, but realize thatthere are trade-offs between them. Infact, it's very common and reason-able to change a goal once you real-ize what it will cost. (You can be a "B"student with a social life or an "A"
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student without one.) Your cost isusually measured in work, risk,money, and sacrifice. Being an "A"student costs mostly work. Youspend time on a lot of all-nighters toace those exams. Being a poet,musician, or writer is risky. Your suc-cess depends on others appreciatingyour work. Money is often a compo-nent in success. It costs more to getinto a major university than a com-munity college.
Obviously, you'll have a betterchance at success with a businessdegree from Yale than fromWhatsamatta U. Sacrifice is a gener-ic term. This refers to the intangiblethings you have to give up to pursuea goal, for example, less time withfamily and friends, a small TVinstead of a big plasma screen onyour wall, or, often, ridicule. This isbecause successful people tend tobe independent, driven, and self-con-fident. This can be seen by others as
unconventional, narrow-minded, andarrogant.
Psychology ofSuccess and Failure
From my experience, there aretwo types of successful people. Thefirst I call "gifted". These are peoplewho have been marked as being suc-cessful from an early point in theirlife. They've always been supportedby their parents, teachers, profes-sors, coaches, etc. They are expect-ed to always do well by themselvesand with others. They go to specialschools, have special classes, andare treated in a preferential way.They never fail.
I say "never" because, if they dofail at something significant, theytend to have a very hard time with it.Failure is not something they under-stand. They are hurt, angered, andbewildered by failure. Sometimes
they never recover from a single bigfailure. I'm sure you've heard anannouncer say, "If they pull thatyoung quarterback now, he'll neverget his confidence back." These peo-ple tend to have a strong but brittleego. Like Humpty Dumpty, once it'sbroken, it's hard to put it backtogether.
The other successful type I call"relentless". These are self-drivenpeople who have had no supportgroup. These people tend to beextremely self-reliant and self-confi-dent. They view failure as a chal-lenge. They use failure as a learningtool. These people just never stop.The old saying "Nine times down andten times up," is their motto. Or per-haps, "Never make the same mis-take twice."
Most of us probably don't fit intothe "gifted" group. But you don'thave to be gifted to be "relentless".You can learn this. Realize that fail-
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ure is an opportunity to learn some-thing new. For "relentless" people,the only real failure is giving up.
Make a Plan
How you reach a goal can beeasy or complicated, creative or con-ventional, fast or slow. It's up to you.Here are two plans to make$1,000,000.00.
The first way is to take a secondjob that brings in $200.00 per weekafter taxes (or set aside $200.00 perweek from your regular job, if youmake a lot of money.) Deposit this$200.00 in an account that providesseven percent interest. In 30 years,you'll have your million. Then youcan retire and collect $70,000.00 peryear, forever, from interest. Thisapproach is mathematically guaran-teed to succeed.
Another method (which I don’tendorse or recommend), is to go to
the art museum and steal the mostexpensive item and sell it for$1,000,000.00. Obviously, this car-ries a great risk of being locked upfor 10 to 20 years — maybe with timeoff for good behavior. It's also social-ly unacceptable, difficult to accom-plish, and simply rude. And, whilethe movies may glamorize artthieves and cat burglars, real crimi-nals are not like the movies. Besides,what would your parents think?
These two plans are not accept-able to most people. Working 80hours a week for 30 years is simplytoo long to endure. Being a criminalis also not something most peoplewant. Obviously, a plan needs to fityou and your lifestyle.
Plans should be flexible, too.This is for two reasons. The first isthat any plan may have problems.For example, you have an importantjob interview in the morning at 9:00AM. The commute takes 30 minutes
so you plan to leave at 8:00. Byadding a half-hour, you will have theoption to take an alternate route ifyour planned route is too congested.(Note that even this small successhas goal, plan, cost, and executionphases.)
The second reason for flexibleplans is that goals change. Forexample, say that you are workinghard for a promotion. Then you findout that the company is on shakyfinancial ground. Your goal changesfrom getting a promotion to notbeing let go. Hopefully, your plan canbe modified for the new goal.
Execute the Plan
This is usually the hardest step.Most people fail here for the simplereason that it takes effort. Here iswhere you pay for your goal.TANSTAAFL! There Ain't No SuchThing As A Free Lunch (Robert
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Heinlein). No one is going to give yousuccess except yourself. Dieters are theclassic example of failing to execute aplan. The goal is to lose 10 pounds in amonth. The plan is to go to the gymtwice a week and to eat less. The cost istime and no more chocolate. But, I'mtoo busy this week to go to the gym.And I went out for lunch and they had abirthday party and I couldn't refuse thecake. And then there's your mother."You're not going to get that A if youdon't study!" She knows all about exe-cuting a plan.
Competition
In some things, you can be suc-cessful all by yourself. You can learn anew computer language by yourself, orride a bicycle, or design a circuit. Thereare other times when you have to com-pete with others to be successful.Obviously, you can't win a tennis matchwithout beating your opponent. Andlots of others want that trophy, job, orpromotion just as badly as you do. Thefirst thing to realize is that competingagainst others is always uncertain. Thesimple and obvious reason is "success"now depends on what others think anddo. Your boss chooses who is "success-
ful". Your co-workers may have advan-tages you are not aware of. This type ofsuccess cannot be controlled by you.However, you can certainly influenceand enhance your chance of winning byfollowing the four steps of success.
Getting that New Jobor Promotion
What is your real goal here? Doyou want more money? Do you wantthe prestige of a nice title? Do you wantto have a more interesting job? If youdon't know exactly what you want, youcan't plan for it. When competing, theplanning stage is usually second fol-lowed by the cost of implementing theplan. And in order to make any plan,you have to have information. What arethe others' qualifications and abilities?What are your strong points? Moreimportantly, what are your weakpoints? What are the standards you willbe measured on? If you don't knowthese things, you will have little chanceof success. If you are competing for anew job in a new company, learn every-thing you can about the company.Learn how it was founded, who runs itnow, their work ethic, what they do, whythey do it, how big it is, etc. With all the
websites nowadays, this is easier thanever. The most critical piece of informa-tion you need is to learn exactly whatthey want. Or, more to our point, whatis their goal? They want to succeed,too. They have a goal, plan, and costalready in place. Now they are execut-ing that plan. You need to match yourplan to their goal better than anyoneelse. Then you have to make themaware of that.
For example, a long time ago, Iwanted to work at a particular compa-ny. I researched them and determinedwhat mainframe computer system theywere using. I then called the local repre-sentative of that computer system toget some details about the system ingeneral. I had a nice conversation withthe representative and he mentionedthat the company had just ordered anew system. At the interview, I wasasked if I was familiar with the comput-er type they were using. I said yes butthat it would be interesting to learnabout their new system. You know, theone you ordered a few weeks ago. Theinterviewers looked at each other withtheir mouths open. The goal of mostinterviewers is to find aggressive, hard-working, and competent people. Thosetwo sentences clearly demonstratedthat to them. I should point out thatthese people wanted to hire me on thespot. However, another interviewer felt I"looked too young." I was later told thatthere was quite a battle between theinterviewers. I did not get that job. Thispoints out the fact that no one can planfor everything. Plans fail for reasonsyou might never consider. But, the fail-ure of the plan does not mean that theperson is a failure. It's important toknow this. Of course, it's disappointingand discouraging. It's not personal,though.
Cheating
Success through unethical behav-ior is a topic that clearly has to be dis-cussed. Some students cheat to get abetter grade. Athletes sometimes usedrugs to enhance their performance.Executives may take money from
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stockholders by manipulating thebooks. Some politicians lie to get votes.Sometimes it seems that there are nohonest people. Cheating is part of the"cost" of success. Are you willing to riskyour reputation? Your health? Your free-dom? How important is success to you?Fundamentally, it makes little sense torisk something big to get somethingsmall. Cheaters view success as beingthe most important thing. Or perhaps,failure as the most unacceptable thing.It is really just a matter of values.Cheaters usually have low self-esteem.
No one can judge another person'svalues. And society places ethics andsuccess in conflict. It's human nature towant to win. It's also human nature tobe fair. This is just because we aresocial beings and have empathy withothers. What is right and wrongchanges as society changes. But, it'snever been right to take advantage ofothers (but it's done on a regular basis,anyway). Whatever decisions you makeconcerning ethics, you will be bound bythem. The saying that "nice guys finishlast" does have some truth. On theother hand, there is usually a great sat-isfaction in seeing the bad guy get whathe deserves. And, if you do cheat, andsomeone finds out, you've just giventhat person power over you. Did youfactor that into your cost?
Success as a Habit
Success breeds success. Why?Actually, there are two basic reasons forthis. The first is that success builds self-confidence. That's because there isalways risk associated with success.This is the "cost" part. If you risk some-thing and succeed, you are more willingto try again. The second point is thatyou learn what works. Failures showwhat doesn't work. Obviously, it's easierto learn from what does work than whatdoesn't. (Although, sometimes it'sextremely important to know whatdoesn't work.) One other point: if youlike doing something, you will be muchmore likely to succeed. It's synergistic.You like it, so you do well. You do well,so you like it more. If you can find acareer doing something you like, your
chances of success are greatlyenhanced. There's the old story aboutBabe Ruth's first professional baseballcontract. Ruth was told, "It's $100.00per game." The Babe sadly replied: "Ican't pay you that much."
ConclusionThe road to success is basically a
four-step process. If you are aware ofthe steps, you will have a better chanceto succeed. Once you learn to succeedyou will find that it is very possible toachieve much more than you everthought possible.
And regardless of what anyone elsethinks or says, if you think you havereached your goals, then you are successful. NV
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FEBRUARY 2004
Tech Forum
QQUUEESSTTIIOONNSS
Does anyone have a schematicfor a well-regulated and efficient (littlewasted energy) 120 VACtransformerless power supply (nostep-down transformer of any kind —just diodes, resistors, caps, andvoltage regulators) with an output of9 or 12 VDC at 40 mA?#2041 Joe
via Internet
We are searching for a solution tothe problem of the ultrabass soundfrom stereos in cars that drive downthe busy street we live on. The loudbass noises and vibrations penetrateour house, setting off resonances thatrattle our walls and windows. The
rumbling from other vehicles —buses, trucks, and trains — is also anaggravation.
Is there a technology available, orone that could be easily developed,that could cancel out these noises?Or, perhaps, is there a metal screenthat could be plastered into the wallsand have applied to it a charge thatwould cancel out the low frequencysound waves, similar to the screenembedded in the glass of themicrowave oven door?
We would appreciate help withthis problem, which is becomingmore persistent.#2042 Melvin Pedersen
via Internet
I noticed that your magazine isfor the beginner, as well as the
professional. Where does someonestart who is interested in electronics?I checked with a local school, but theywanted thousands of dollars in tuitioncosts. I would appreciate anyinformation you can provide.#2043 Lodrick Price
via Internet
I have several USB flash memorysticks that I like to use simultaneously.Most USB "hubs" have the (typically,four) receptacles so close that, atbest, I can get three USB sticks in, andsometimes only two. What I need aresome short (preferably about eightinches or less) USB extension cables,but the shortest I've seen are threefeet and the "retractable" USB cablesare typically very pricey ($12.00+).Does anyone know either of a sourcefor short USB cables or a source forUSB cable connectors to allow me toroll my own?#2044 Larry Supremo
via Internet
I'm looking for a composite videolevel generator that sweeps fromblack to white, to simulate the outputof an iris control circuit in a videocamera. Any assistance would begreatly appreciated.#2045 Roy Bock
via Internet
I have a standard personalcomputer that has serial inputs. Isthere an adaptor I can build, orpurchase, to add USB ports to mymachine? #2046 Ken Johnson W9BIH
Dixon, MO
I need to generate a 0- to 5-volttriangle wave. I tried to obtain thisfrom a 555 timer chip, but it onlyproduced a waveform that variedfrom 1/3 to 2/3 Vcc. Can anyone helpme out with a circuit?#2047 Huseyin Akgul
Ankara/Turkey
The last two batteries on myCompaq Armada M300 notebookhave died and replacements arewickedly expensive. A simplealternative would be to supply anexternal 18.5 V at 2.5 A, with some
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sort of voltage converter using a 12 Vgel cell. Does anyone know of asimple circuit for accomplishing this?#2048 Mark Warner
via Internet
I am an electronics teacherhunting for electronics jokes to use inclass. The cornier the better! I amalready using the "mobile ohm" and"ohm ohm on the range," to give youan idea of what is working. #2049 Dave Brett
via Internet(Bring 'em on! — Editor Dan)
I have a surplus VFD displaymodule that I'd like to use in a clubproject, but it has no specs. It lookslike one of those large cash registerdisplays that's mounted on a pole.Inside is a pair of FutabaM202LD01DA vacuum fluorescentdisplays. The interface cable haseight pins where 20 VDC power isapplied and an RS-485 serial interfaceis used to talk to the modules. Futabawas unable to help, can anyone else?#20410 Kelly Small
Phoenix,AZ
I am about to purchase a DVDrecorder/player; however, there are somany supported formats that I needhelp understanding the differences. Asales person at a consumerelectronics outlet told me there werethree formats — plus, minus, andprogressive — but could not describeany of them. I know what progressivescan is, but what about the other two?I do not understand how a discrecorded in progressive scan can beplayed back on an interlaced monitor.Can anyone direct me to a sourcethat can give me the facts withouttrying to sell me something?#20411 E.A. Hill
via Internet
I would like to build an enginegovernor for my R/C helicopter, usinga set of points and the existingthrottle servo. I have beenexperimenting with 555 ICs as thetiming device. Does anyone know of acircuit I could use?#20412 Dean Nicholas
via Internet
Does anyone have a simplecircuit to test for continuity up to afew hundred ohms? I know these arebuilt into most digital voltmeters, but Iwant a small, knock-around unit.
Michael Herman(Read TJ Byer's column in the Januaryissue — Editor Dan)
AANNSSWWEERRSS
[11038 - November 2003]I have some Gateway 2000
4DX-66V computers that have aBIOS password that prevents themfrom booting. Is there a masterpassword that I can use to get in?
#1 Generally, there is not a masterpassword. There is, however, analternate solution. You need to forcethe system to forget that it ispassword protected. This is done bygenerating an invalid checksum toforce erase the CMOS RAM. Eitherremove the backup battery or find thejumper on the motherboard thatenables power to the CMOS memoryand remove it. It will be physicallyclose to the battery and the CMOS.
Some motherboards have athree pin header. The center pin iscommon. The outer pins are normaloperation and erase. Move the headerfrom one side to the other. It may take
several minutes if you are justdisconnecting the battery. Thecomputer should return to the factorydefault, with no password protection.When done, replace the battery orjumper, so that the computer canremember other settings, such ashard disk type and time.
Barry ColeCamas,WA
#2 There are zillions of sites whereyou can download software for BIOSpassword recovery, such aswww.cgsecurity.org
Olli Finland
#3 The easiest way to access apassword-protected BIOS setup is toremove the backup battery for a fewminutes. This will reset all of theCMOS settings, including thepassword. You will then be able toaccess the BIOS, but you will alsoneed to reset all of the hardwaresettings, such as the hard drive typeand floppy drive configuration.
Backup batteries vary bymotherboard vintage. Oldermotherboards have an externalbattery pack, which is connected tothe motherboard by a header. Justremove the header for a bit and thenreplace it. Newer motherboards use a
Tech Forum
FEBRUARY 2004 93
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coin cell that can easily be poppedout of its holder. Some, quite possiblyyours, will have a three-cell batterywhich is soldered in place near theedge of the motherboard. If this is thecase, then look for a small headerwith three pins and a shorting plugnear the battery. Moving the shortingplug to the opposite set of pins willdisconnect the battery from theCMOS backup memory. In all cases,be sure that the power to thecomputer is off, otherwise the backupmemory will be powered from themain supply and disconnecting it willhave no effect.
David SarrafElizabethtown, PA
[110310 - November 2003]I need a circuit that will track a
changing voltage (+0.1 to +0.9 V)and allow me to use apotentiometer to create an offset of± 0 to 3 millivolts and adjust to anaverage of 0.45 V. This circuit is totrack the output of an automotiveO2 sensor.
In this circuit (Figure 1), theLM78L05 provides isolation from thenoise on the 12 V supply. The U1Aamplifier circuit has unity gain for theinput signal and the ±5 volts that isavailable at the pot. You should use1% resistors for accurate results. TheMAX1681 is a +5 to -5 inverter; usefilm or ceramic 1 mF caps. Since the
LMC6082 is a dual, I used the secondop-amp in a low-pass filter so theaverage voltage can be measured.The capacitors should be film type foraccurate results. The internal offset ofthe op-amp is less than 1 mV, so Iassumed that was neglectable.
Russell Kincaid Milford, NH
[11037 - November 2003]Does anyone know of a simple
data logger I can use to record thetime and date of each instance aswitch is turned on and off andkeep it in memory?
The H06-001-02 Hobo™ DataLoggers from Onset will record up to2,000 different changes (on/off) andthe time each happens. They requirethe BoxCar 3.7 (BC3.7-DL) softwareto download the information. Thissystem was very user-friendly for me.Both should be at www.digikey.com
Brian Germanvia Internet
[12031 - December 2003]What is the difference between
an S-video input and the plain oldvideo input on a television set?
An S-video cable is a highergrade of the plain old compositevideo input. The difference betweenthe two is that S-video provides morebandwidth to the TV set. There arebasicially two feeds coming in atonce, chrominance and luminance(or color and brightness) and that'swhy there are four pins.
When using S-video, there isbetter picture quality. To put it ineasiest terms, a data path for colorand a path for brightness — wherecomposite video has to accomodatefor both and the picture sometimeslooks "washed out".
Video quality for home users is,from best to worst: fiber, component(RGB), S-video, composite video, andRF (audio and video AKA cable feed).
Shon KellyOntario, Canada
[110311 - November 2003]I want to build a current
Circle #34 on the Reader Service Card.
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Figure 1
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sensing switch to turn on an audioamp when my television isswitched on by remote. I want apass-though type sensor so as notto break the power circuit of thedevice being monitored.
#1 In the circuit in Figure 2, youwill have to break the line in order torun one of the AC wires through thecurrent transformer, but there will beno voltage drop due to the currentmeasurement. The transformer israted for 5 A. You will need a 50 Atransformer for the hot water heater.The diode at the op-amp inputprevents negative voltage fromdamaging it. The diode at the op-ampoutput rectifies the signal andproduces the voltage to operate therelay. The 1 M resistor ensures thatthe relay switch opens when thetelevision is turned off. The NPNtransistor is its own protection againstthe inductive kick of the relay coil, sono diode is needed.
Russell Kincaid Milford, NH
#2 I'm doing exactly this with theCraftsman Auto Switch, Sears item#00924031000 (www.sears.com). Ithas one master (sense) outlet andtwo slave outlets.
It's marketed as a shop tool, to dothings like turn on a work light and ashop vac on the slave outlets when atable saw is powered up on themaster outlet.
Best of all, it's only $19.99! Itwould be hard to purchase the projectparts for less than that.
Wil Higdonvia Internet
[12036 - December 2003]I'm building a three axis robot
arm using stepper motors,controlled through the parallel portof a PC. I'm having difficultybuilding the controller board, andwriting the software to run it.
Can anyone point me to anygood information?
There are many excellent sourceson the Internet that can show youvarious ways to control a stepper. Ifyou are looking for a place to start
which emphasizesthe basics, I cansuggest my site:www.taomc.com(The Art Of MotionControl).
I have tried todistill the process ofusing the PC printerport and inexpensivecomponents tocreate fun andinstructive stepper-based projects.
Over the pastfour years in the educationdepartment at the Science Museumof Minnesota, I have taught a classwhich has included kids as young as12. The course, "From Bits to Bytes toBots," showed how to build, wire up,and then control a two-axis sphericalplotter ("Eggbot").
The site contains severalexamples of do-it-yourself, PC-basedmotion control. The specific areawhich contains detailed explanations(including breadboard diagrams andQBASIC examples) is:www.taomc.com/bits2bots/
Bruce ShapiroEdina, MN
[12037 - December 2003]Does anyone know of a
reference book on electroniccomponent footprints?
If you mean footprints for a PCBpackage, the IPC Land calculator isgreat (see http://landpatterns.ipc.org). It includes a bunch offootprints for various packages and ifyou input the parameters of thepackage you are using, it will tell youwhat the PCB footprint should be.
Colin O'FlynnOntario, Canada
[1042 - January 2004]I would like to light a crystal
from underneath with lights thatslowly illuminate and fade toproduce different colors. I havemade a couple different circuits
FEBRUARY 2004 95
Tech Forum
Figure 2
Tech Forum.qxd 1/6/2004 3:47 PM Page 95
using blue, red, and green LEDsand triangle wave circuits, but theyare not as bright as I'd like.
Any suggestions out there?
#1 Go to www.BGMicro.com orwww.Goldmine-elec.com as bothoffer an integrated three-color LED ina T 1 3/4 package with an internalcontroller chip that does exactly whatyou want, for less than $3.00. Theyare bright enough to light a tennisball-sized crystal in a dark room. Justapply 4 VDC at 20 mA and you are alldone. Use several for a morecomplicated display.
David D. Speck MDAuburn, NY
#2 I really like that idea — so I hadto build one! Instead of using a slowtriangle wave, I used a square wavenear, but not exactly at, the linefrequency to turn an AC lamp on andoff (see Figure 3). When the 120 Hzsquare wave from the op-amp is high,it turns on the high voltage powerMOSFET (just about any will work)and the lamp sees the voltage fromthe bridge. If the line voltage happensto be high, the lamp is bright, but if itis more near zero volts, the lamp isdim. As the square wave drifts relativeto the line voltage, the brightnessgoes up and down.
Originally, I used 60 Hz and ahalf-wave rectifier, but the lamp wasoff too much of the time. Moving to120 Hz and a full-wave rectifier keepsthe lamp partially lit at all times.Simply adjust the potentiometer untilthe lamp is changing at the desiredrate. Use a non-polar 1 µF capacitorop-amp and a good multi-turn pot toset the frequency. The optoisolator isnot critical, as long as it can turn theMOSFET completely on and off. Thefull-wave bridge can be a molded typeor just four diodes rated for AC linevoltage. Make sure to use a fuse, too.
A quad op-amp could run fourlamps and the nine-volt battery couldbe a molded power supply or the linevoltage can be dropped down with apower resistor and zener, butremember that the op-amp circuitthen becomes a shock hazard, too.
Charles WenzelAustin,TX
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Tech Forum
FEBRUARY 2004
Figure 3
Circle #35 on the Reader Service Card.
Tech Forum.qxd 1/6/2004 3:48 PM Page 96
Ramsey Electronics, Inc. .......................................14-15SGC ............................................................................35Surplus Sales of Nebraska ..........................................32
Cunard Associates ......................................................61
Earth Computer Technologies......................................61Rogers Systems Specialist .........................................94
Autotime Corp. ............................................................61Circuit Specialists, Inc. ...........................................98-99Matco, Inc. ...................................................................63Ramsey Electronics, Inc. .......................................14-15
Autotrax EDA ..............................................................21Cunard Associates ......................................................61ExpressPCB ................................................................91IVEX ............................................................................87Maxstream ..................................................................25PCBexpress ................................................................18PCB Fab Express ........................................................46PCBPro .......................................................................88Pulsar, Inc. ..................................................................63SchmartBOARD ..........................................................61V&V Machinery & Equipment, Inc. ..............................62
Bellin Dynamic Systems, Inc........................................63Front Panel Express LLC .............................................74Lemos International Co., Inc. ......................................33Linx Technologies .......................................................41Maxstream ..................................................................25PCBexpress .................................................................18PCB Fab Express ........................................................46Pulsar, Inc. ..................................................................63Solutions Cubed ..........................................................17
HardwareActiveWire, Inc. ...........................................................63Autotime Corp. ............................................................61Connecticut microComputer, Inc. ................................83Earth Computer Technologies ....................................61Halted Specialties Co. ...................................................3Rogers Systems Specialist .........................................94Surplus Sales of Nebraska...........................................32
SoftwareEptsoft Limited ............................................................50IVEX ............................................................................87Pioneer Hill Software ...................................................81Trilogy Design .............................................................88
Microcontrollers / I/O BoardsAbacom Technologies..................................................60Akida LLC.....................................................................61Amazon Electronics .....................................................63AM Research, Inc. .......................................................62Conitec DataSystems...................................................96EMAC, Inc. ..................................................................79microEngineering Labs ...............................................34MVS .............................................................................79Net Media.................................................................2, 89
New Micros, Inc. ..........................................................68Parallax, Inc. ............................................... Back CoverRedpoint Controls, Inc. ..................................................7Scott Edwards Electronics, Inc. ...................................81Square 1 Electronics ...................................................26Technological Arts .......................................................93Trace Systems, Inc. ....................................................57
ExpressPCB ................................................................91Front Panel Express LLC ............................................74ONE PAS, Inc. ............................................................62Pulsar, Inc. ..................................................................63Solutions Cubed ..........................................................17Trace Systems, Inc. ....................................................57V&V Machinery & Equipment, Inc. ..............................62
Atlantic International Institute, Inc. ..............................18Cleveland Institute of Electronics ................................27Command Productions ................................................45EMAC, Inc. ..................................................................79Eptsoft Limited ............................................................50Global Specialties .......................................................55Hobby Engineering ......................................................13PCB Fab Express ........................................................46Syspec, Inc. .................................................................10
Global Specialties .......................................................55Tetsujin 2004 ...............................................................85
Amazon Electronics .....................................................63Autotime Corp. .............................................................61C & S Sales, Inc. .........................................................47Carl’s Electronics, Inc. .................................................61Earth Computer Technologies ....................................61EMAC, Inc. ..................................................................79Hobby Engineering ......................................................13HVW Technologies, Inc. ..............................................63Information Unlimited ..................................................50PAiA Electronics...........................................................61QKITS .........................................................................61Ramsey Electronics, Inc. .......................................14-15SchmartBOARD ..........................................................61Scott Edwards Electronics, Inc. ...................................81
Information Unlimited ..................................................50
All Electronics Corp. ....................................................51Anchor Optical Surplus ...............................................33Electro Mavin ..............................................................96Front Panel Express LLC .............................................74Halted Specialties Co. ...................................................3Surplus Sales of Nebraska ..........................................32
Anchor Optical Surplus ...............................................33
Amazon Electronics .....................................................63Conitec DataSystems...................................................96
HVW Technologies, Inc. ...............................................63Intronics, Inc. .................................................................62M2L Electronics ............................................................61microEngineering Labs .................................................34
Lakeview Research .....................................................62Mouser Electronics ......................................................46Square 1 Electronics ...................................................26
Abacom Technologies .................................................60Linx Technologies .......................................................41Matco, Inc. ...................................................................63
Akida LLC.....................................................................61Budget Robotics...........................................................85Hobby Engineering ......................................................13HVW Technologies, Inc. ..............................................63Kronos Robotics & Electronics ....................................19LabJack .........................................................................84Lemos International Co., Inc. ........................................33Lynxmotion, Inc. ......................................................61, 95Net Media ..................................................................2, 89New Micros, Inc. ............................................................68O-Navi LLC ...................................................................63Robodyssey Systems ....................................................61Solutions Cubed.............................................................17Zagros Robotics.............................................................62
Lemos International Co., Inc. .........................................33
Information Unlimited ..................................................50Linx Technologies .......................................................41Matco, Inc. ...................................................................63
Bellin Dynamic Systems, Inc..........................................63C & S Sales, Inc. ...........................................................47Circuit Specialists, Inc. .............................................98-99Conitec DataSystems ....................................................96Connecticut microComputer, Inc. ................................83Electronic Design Specialists.........................................57Global Specialties .......................................................55Intronics, Inc. .................................................................62LabJack .........................................................................84Pioneer Hill Software ....................................................81Syspec, Inc. .................................................................10Trace Systems, Inc. ....................................................57
C & S Sales, Inc. .........................................................47
Rogers Systems Specialist .........................................94
WIRE/CABLE& CONNECTORS
TOOLS
TEST EQUIPMENT
SECURITY
SATELLITE
ROBOTICS
RF TRANSMITTERS/RECEIVERS
PUBLICATIONS
PROGRAMMERS
OPTICS
MISC./SURPLUS
LASERS
KITS
EVENTS/SHOWS
EDUCATION
DESIGN/ENGINEERING/REPAIR SERVICES
COMPUTER
COMPONENTS
CIRCUIT BOARDS
CCD CAMERAS/VIDEO
BUYING ELECTRONICSURPLUS
BATTERIES/CHARGERS
AMATEUR RADIO & TV
Advertiser’s Index
Abacom Technologies ............60ActiveWire, Inc. .......................63Akida LLC ...............................61All Electronics Corp. ...............51Amazon Electronics ................63AM Research, Inc. ..................62Anchor Optical Surplus ...........33Atlantic International Institute, Inc. .18Autotime Corp. ........................61Autotrax EDA ..........................21Bellin Dynamic Systems, Inc. ....63Budget Robotics .....................85C & S Sales, Inc. ....................47Carl’s Electronics, Inc. ............61Circuit Specialists, Inc. ......98-99
Cleveland Institute of Electronics ...27Command Productions ...........45Conitec DataSystems .............96Connecticut microComputer, Inc. ..83Cunard Associates .................61Earth Computer Technologies ...61Electro Mavin ..........................96Electronic Design Specialists....57EMAC, Inc. .............................79Eptsoft Limited ........................50ExpressPCB ...........................91Front Panel Express LLC ........74Global Specialties....................55Halted Specialties Co. ..............3Hobby Engineering .................13
HVW Technologies, Inc. .........63Information Unlimited ..............50Intronics, Inc. ..........................62IVEX .......................................87Kronos Robotics & Electronics ...19LabJack ...................................84Lakeview Research .................62Lemos International Co., Inc. ....33Linx Technologies ...................41Lynxmotion, Inc. ...............61, 95M2L Electronics ......................61Matco, Inc. ..............................63Maxstream ..............................25microEngineering Labs............34Mouser Electronics .................46
MVS ........................................79Net Media ............................2, 89New Micros, Inc. ......................68O-Navi LLC..............................63ONE PAS, Inc..........................62PAiA Electronics ......................61Parallax, Inc. ........... Back CoverPCBexpress ............................18PCB Fab Express ...................46PCBPro ...................................88Pioneer Hill Software ...............81Poptronix, Inc. .........................90Pulsar, Inc. ..............................63QKITS......................................61Ramsey Electronics, Inc. ...14-15
Redpoint Controls, Inc. ..............7Robodyssey Systems .............61Rogers Systems Specialist......94SchmartBOARD .....................61Scott Edwards Electronics, Inc. ...81SGC ........................................35Solutions Cubed .....................17Square 1 Electronics ..............26Surplus Sales of Nebraska .....32Syspec, Inc. ............................10Technological Arts ..................93Tetsujin 2004 ..........................85Trace Systems, Inc. ................57Trilogy Design .........................88V&V Machinery & Equipment, Inc. ..62Zagros Robotics ......................62
FEBRUARY 2004 97
IndexFeb04.qxd 1/6/2004 10:36 AM Page 97
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Digital Storage Oscilloscope Module
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2 AMP 0-18VBench Power Supply LCD Display
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RF Field Strength Analyzer
The 3201 is a high quality hand-heldRF Field Strength Analyzer with wideband reception ranging from 100kHz to2060MHz.The 3201 is a compact &lightweight portable analyzer & is amust for RF Technicians. Ideal for test-ing, installing & maintenance ofMobile Telephone Comm systems,Cellular Phones,Cordless phones, pag-ing systems, cable &Satellite TV aswell as antenna installations.May alsobe used to locate hidden cameras usingRF transmissions
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Visit our website for a complete listing of our offers. We have over 8,000 electronic items on line @ www.CircuitSpecialists.com. PC based dataacquisition, industrial computers, loads of test equipment, optics, I.C’s, transistors, diodes, resistors, potentiometers, motion control products, capaci-tors,miniature observation cameras, panel meters, chemicals for electronics, do it yourself printed circuit supplies for PCb fabrication, educationalD.I.Y.kits, cooling fans, heat shrink, cable ties & other wire handleing items, hand tools for electronics, breadboards, trainers, programmers & muchmuch more ! Some Deals you won’t believe !
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Circle #145 on the Reader Service Card.
Full Page.qxd 1/6/2004 12:41 PM Page 98
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Digital Laser Tachometer*5 digit, 6” LCD Display*2.5-99,999 RPM test range
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*10 digit LCD Display*High speed 300MHz direct counter w/0.1Hz resolution*50 Ohm input for full range 1MHz to 3.0GHz coverage*Ultra sensitive synchronous detector w/16 segment
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Triple Output Bench Power Supply
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Circle #145 on the Reader Service Card.
Circle #60 on the Reader Service Card.
CoverInside.qxd 1/6/2004 12:38 PM Page 2
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Circle #154 on the Reader Service Card.
Cover.qxd 1/6/2004 4:23 PM Page 108