expansion rom system for your amstrad · 2019-07-17 · frequency meter, noise operated clap...
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CONSTRUCTSATELLITE RConstruction D
TONS OF PRO
High QualityLead Acid BStepper M
FASCINATI G FVideo Mo ators180 Mac ine deProject ault Fin
Expansion ROM System for your
AMSTRADCOMPUTER 1C24 MM:17:017 f 1. .11.1
MO We MOOD. C OM."nierManittalar
MAPIIN5 REMOSHOPS
HELP SERVE YOU BETTER!Birmingham: Lynton Square, Perry Bar. Tel: 021 356 7292.
London: 159-161 King Street, Hammersmith W6. Tel: 01 748 0926
Manchester: 8 Oxford Road. Tel: 061 236 0281.
Southampton: 46-48 Bevois Valley Road. Tel: 0703 225831.
Southend-on-Sea: 282-284 London Road, Westcliff-on-Sea. Essex.
Tel: Southend-on-Sea (0702) 554000.
Before you send your next order tous by post, take a look and see ifthere's a Maplin shop near you. Inour shops you'll find that personalservice that even the best mail-order operations cannot match.And you can look at the productsbefore you buy. If you're comingfor a particular item, a quickphone call will enable you to becertain the shop has everythingyou want in stock.
Our shops are pleased to acceptAccess, Barclaycard, AmericanExpress and Mapcard, and alsocheques up to £50 with a chequeguarantee card. We'll even acceptordinary money as well!
All our shops are close to excell-ent parking facilities, meters inLondon and Manchester, and freeelsewhere.
The SouthIn the South our Southampton storeis conveniently placed for easyaccess from all parts of Hampshireand surrounding counties and isjust 15 minutes from Portsmouth.
LondonOur London store situated just tothe west of the pedestrian shopp-ing centre in Hammersmith, is just5 minutes from the end of the M4and only a short walk from the
District, Piccadilly and Metropol-itan lines' Hammersmith station.
The Midland,In the Midlands our Birminghamstore is just 5 minutes from the M6on the A34, and only a little fartherfrom the M5 (junction 1) on theA4040.
The NorthOur self-service store in Man-chester serves the North and isjust off the Mancunian Way,opposite the BBC, about 5 minutesfrom the end of the M602 orjunction 10 on the M63.
South -EastEssex and Kent are served by our
Southend shop which is right onthe A13, just 2 minutes before youreach the centre of Southend. Andwe're only 30 minutes from theM25 (junction 29) as well.
All our shops are open from 9 a.m.to 5.30 p.m. Tuesday to Saturday(closed all day Sunday and Mon-day) and do not close for lunch.
There's a friendly welcome instore for you at any Maplin shop.Our helpful staff may often be ableto help with a technical problem ora constructional difficulty.
Call in at a Maplin store and getwhat you want today. We lookforward to serving you.
Volume 5 Number 18 ackNTENTS Anil%CO
March to May 1986
THE MAPLIN MAGAZINE
PROJECTS
Weather SatelliteReceiver 2There are now a number of satellitesorbiting the Earth for the purpose ofobserving world-wide and regionalweather systems. Receiving the pictureinformation from such satellites is actuallynot as complicated as might be imagined.
The current level of electronics tech-nology now available to the hobbyistmakes it easy to save such images ontape and display them on a TV ormonitor. In Part 1 the Receiver isdescribed, with a preview of thecomplete system.
'Mixing It' 16Part 2 deals with the construction and useof the utility mixer and amplifiermodule projects as shown in the Projectsand Modules section of the catalogue.This time the mono and stereo highimpedance microphone input preamp-lifiers, mixer amp, line amp, VU meterand headphone monitor amplifier aredescribed.
Fantastic Five 26Another five quick and useful circuits thatcan be assembled on veroboard, com-prising a high frequency tremolo unit, acrystal checker which enables you tomonitor your oscillator crystals with afrequency meter, noise operated clapswitch, active low resistance ohmmeter,and a snooze timer for use with yourbedside radio.
Stepper Motor Driver 35Describes the construction and use of theStepper Motor Kit as shown on page 437of the 1986 Maplin catalogue.
Amstrad ExpansionSystem 36Introducing the Maplin Amstrad externalROM card system, providing for up to
128K bytes of pre-programmed ROM orEPROM, fully mechanically and electric-ally compatible with the CPC 464, CPC664 and 6128 Amstrad computers. Thesystem exploits the Amstrad's ResidentSystem Extension' feature and allowsimmediate access to machine code rout-ines, BASIC extension commands andother useful utility features without havingto load from tape or disk.
Sealed Lead AcidBattery Charger 48A fully regulated and temperaturecompensated battery charger intended tooperate with our range of sealed leadacid batteries recently introduced in the1986 catalogue. The charger offers a highstability voltage output tolerance req-uired by these batteries, and automatic-ally switches into trickle charge modewhen the fully charged condition hasbeen reached.
FEATURES
The Care and Feeding ofVideo Modulators 10This article looks at the UM1111, UM1233and UM1286 video modulators. Now thatwe have TV sets with chassis isolatedfrom the mains, it is safe to utilise thesefor other imaging purposes via the aerialsocket using a suitable modulator. How-ever, some careful planning is needed ifyou are going to use such a modulator toproduce TV pictures of your own.
The Story of Radio 22Part two, continuing Marconi's deve-lopment of wireless telegraphy.Improvements to the efficiency, rangeand reception quality of the spark -gaptransmission process accelerates, and itrapidly becomes obvious that this extra-
ordinary, hitherto inconceivable comm-unications medium is to prove invaluableto ships at sea.
First Base 40The final part in this series completes thestudy of digital design principles with acursory review of that 'soft -wired' digitalsystem, the microprocessor.
Machine Code Programmingwith the Z80 44Part two of how to write machine code forthe popular Z80 processor describes howan assembler, and the use of assemblymnemonics, can make life much easierthan trying to write programs in 8 -bitbinary numbers.
Project Fault Finding 52The final part in this series deals withwhat is probably the most expensive,misunderstood and mal-used (and notnecessarily in the hands of amateursexclusively) item of test -gear, theoscilloscope. In spite of its high cost, theoscilloscope is the one instrument which,for professionals and hobbyists alike, hasa habit of making itself thoroughlyindispensible.
A/D/A ConversionTechniques 56If you have wanted to use or experimentwith any of the devices from the range ofanalogue to digital or digital to analogueconverter ICs now available, this articleshould be of great value if you areunfamiliar with the techniques used, andthe various different types of converterthat exist.
REGULARSCatalogue Amendments 63Classified Advertisements 64Corrigenda 64Project Servicing Rules 55New Books 42
New Products 62
Order Coupon 33
Price Changes List 31Price List of Items Since Catalogue 32Subscriptions 34Top 20 Books 43
Top 20 Kits 64
Mail Order Editorial & Production Published by Maplin Electronic Supplies Ltd.P.O. Box 3, Rayleigh, Essex SS6 8LR. Editor Roy Smith Typesetting by Essex Process and Engraving Co.Telephone: Retail Sales: (0702) 552911.Trade Sales: (0702) 552961. General: (0702) 554155.Computer Ordering: (0702) 552941.
Production ManagerTechnical Editors
Art Director
Mike HolmesRobert Kirsch,Dave GoodmanPeter Blackmore
Printed by
Graphic House, Stock Road,Southend-on-Sea, Essex.Greenaway Harrison Ltd.,555 Sutton Rd, Southend, Essex.
Shops: See inside front cover.All shops closed Mondays.
Technical ArtistsSecretary
John Dudley, Lesley FosterAngela Clarke
Distributed by Spotlight Magazine DistributionLtd., 1-11 Benwell Rd, London N7.
Copyright. All material is subject to world wide copyright protection, and reproduction or imitation in whole or part is expressly forbidden. All reasonable care is taken toensure accuracy in preparation of the magazine, but Maplin Electronic Supplies Ltd. cannot be held legally responsible for its contents. Where errors occur corrections will bepublished as soon as possible afterwards. Permission to reproduce printed circuit board layouts commercially or marketing of kits must be sought from the publisher.Jc.--:; Copyright 1986 Maplin Electronic Supplies Limited.
March 1986 Maplin Magazine 1
1 1111111111111111
SEIT
* High -sensitivity receiver
* Signal and T
uning meters
* Portable operaticm
possible* P
re -aligned ancitested module
* Internal Monitor am
plifier* N
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* Aerial kit available
"::::::::::::.:
MICtIWA
The idea of looking down uponthe world from space appealsto many people. With the aid ofWeather Satellites and thereceiving system described in
this series, it is possible to receive anddisplay pictures of cloud formations,weather systems and land masses frommany of the orbiting weather satellitesthat transmit in the 137-138MHz band.
This article describes the receiver,aerial and storage system to be followedby the Decoder and Frame Store.Pictures from the decoder may bedisplayed either by using the FrameStore, which is connected to an ordinarytelevision or monitor, or by using asuitable home computer such as the BBCB or Amstrad.Opposite page: TIROS -N in orbit(Inset: The Straits of Gibraltar)
by Robert Kirsch Part 1The prototype system, when used
with a fixed aerial of the type describedlater in this article, has regularly receivedpictures from as far away as North Africato the South, and Iceland and Norway tothe North.
FREQUENCY SATELLITE APPROX TIMEI ENGLAND I
137MET 30 1015 - 1145
METEOR VARIOUS& COSMOS
137.5 NOAA 6 0530-07301800-2000
0000-0200NOAA 9 1230 -1430METEOR VARIOUS
138
Receiving Times
There are several satellites regularlyorbiting the Earth and sending pictureinformation both in the visible and infra-red spectrum, most of which can bedecoded by the MAPSAT system.Satellites that are easily received in thiscountry include the American TIROS -Nseries (NOAA 6 and 9) see Figure 1, andthe Russian Meteor and Cosmossatellites. These satellites orbit the Earthroughly every 100 minutes but, due to therotation of the Earth, a satellite travellingin a roughly north/south orbit will crossthe equator 25 degrees further west oneach orbit, thus enabling the whole of theEarth's surface to be covered. Due to thiseffect, a satellite of this type will onlypass within usable range two or threetimes every 12 hours, making it
Array DriveElectronics
Solar ArrayDrive Motor
SolarArray
NitrogenTank (2)
HydrazineTank (2)
Reaction SystemSupport Structure
BatteryModules (4)
Rocket EngineAssembly (4)
EquipmentSupport Module
S -Band OmniAntenna
High -EnergyProton and AlphaParticle Detector
Thermal ControlPinwheel Louvres (12)
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Antenna
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Sounding Unit
Medium -Energy Protonand Electron Detector
Sun SensorDetector
InertialMeasurement Unit
Instrument MountingPlatform Sunshade
InstrumentMounting Platform
Advanced Very HighResolution
Radiometer
High -ResolutionInfra -Red
Radiation Sounder
StratosphericSounding Unit
Figure 1. TIROS -N SatelliteMarch 1986 Maplin Magazine 3
necessary to refer to a prediction chart toenable a particular satellite to bereceived. Prediction charts for NOAA 6and 9 and any other satellites for whichdata is available will be published infuture editions of Electronics. Thereceiving system can also be used toreceive geostationary weather satellitessuch as METEOSAT, by using a downconverter with a suitable aerial system.
The Complete SystemFigure 2 shows a block diagram of
the complete receiving, storage, decod-ing and display system. Incoming signalsfrom the receiver are normally stored ontape before decoding, although it ispossible to decode and display picturesas they are received immediately. Oncestored on tape, a picture can be decodedat leisure and several runs can be madewith various settings of the decoder toobtain the best results. The receiver,block schematic shown in Figure 3,includes interfacing for a standard monoor stereo cassette recorder via a DINsocket. A monitor amplifier is alsoprovided that can be switched to the tapeplayback and decoder monitor points aswell as receiver's output. The decoderis connected to the receiver by a DINconnector lead, and the decoder alsoprovides 12 volts DC to supply thereceiver. Connection to a computer orthe Frame Store is made via a fifteen wayD -range plug. The decoder also containsthe mains power unit and a VU meter forsetting the levels out of the tape system.The receiver may be run from any 12-14volt supply such as a car battery or mainsunregulated power supply (e.g. XXO9K),in the absence of the decoder. Provisionis also made to run the receiver frominternal batteries for portable operation.This enables the receiver to be usedoutdoors in conjunction with a portabletape recorder and a directional aerial fortracking satellites, by using the SIGNALmeter to obtain maximum strength whilstaiming the aerial. Figure 2. Complete System
L1 L2 L3
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The Receiver -Circuit Description
Figure 4 shows the circuit of thereceiver, monitor amp and switching.The 75 ohm aerial input is coupled to thefirst bandpass tuned circuit L 1 by a 11/2turn coil, which, after being decoupled toground by Cl, is fed with 10 volts via RI.This supply, connected to the centreconductor of the aerial coax, is to powera masthead preamplifier (if used). Thedual gate FET TR1 provides the firststage of amplification, with L2 and L3 inits output (drain) circuit to provide tunedcoupling into TR2, the second RFamplifier. The output of TR2, via the thirdbandpass and coupling circuit, L4 and L5,is fed to gate 1 of the mixer FET TR3.Gate 2 of TR3 is fed from the VFO circuit,and the drain of this transistor isconnected to the 10.7 MHz transformerT1.
The first of three ceramic filters isconnected between the output of TR 1and the 10.7MHz amplifier, TR4. Theoutput of TR4 is fed via the two remainingceramic filters into ICI, the FM IF anddemodulator sybsystem. This IC pro-vides quadrature detection of the IFsignal as well as providing outputs for theSIGNAL and TUNING meters andsquelch (not used in this application). T2is the quadrature inductor tuned to
The output from pin 6 of IC 1 isfed to the AF amplifier and filter formedby the op -amp IC2 and its surroundingcircuitry. This filter limits the audiobandwidth to that required for satellitereception, attenuating all frequenciesoutside this band.
The audio signal is now fed to theDIN socket for connection to the taperecorder and to the switching for themonitor amplifier. The rotary MONITORswitch is connected via the VOLUMEcontrol RV2 to the input of the poweramplifier IC3, which drives the loud-speaker.
The receiver is tuned by a voltagecontrolled oscillator, operating the range126.3MHz to 127.3MHz, which is 10.7MHzbelow the input frequency of 137MHz to138MHz (this provides an IF of 10.7MHz).The FET TR9 forms part of a Vacar typeoscillator, whose tuned circuit L8 is tunedby the varicap diode D2. ZD2 stabilizesthe power supply at 7.5 volts. This supplyalso feeds the tuning potentiometer RV1,whose wiper is connected via R47 to thecathode of the varicap diode. The anodeof D2 is connected to 0 volts DC by R48.
The varicap diode is reverse biasedand, as virtually no current flows throughit, R47 and R48 can be of high resistance(i.e. 1M52), thus having little effect on theRF signal present across the diode. Theoutput from the drain of the oscillator FETTR9 is taken to a source follower bufferFET TR8. The output from the bufferfeeds two emitter follower transistorsTR7 and TR6. TR7 feeds the mixer viaC43, and TR6 connects to a monitor pointthat can also be used to feed a frequency
Figure 5. Receiver PCB Overlay
6 Maplin Magazine March 1986
All dimensions In mm Hole dataa 0 3.2b 0 8.0c 0 12.7d 0 17.0
Rear panel
4 Existingholes N,
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All dimensions in mm
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Figure 6. Box Drilling
synthesiser input (not used in thisapplication).
The power supplies for the receiverare derived from an unregulated 12 voltinput connected via the 2.5mm powersocket on the pcb. DI provides reversepolarity protection. Internal batteriesmay be connected via PL9 if required;this necessitates the provision of anexternal power switch, and the cutting ofthe track between pins 1 and 2 of PL9.The power transistor TR4 forms a simpleseries voltage regulator circuit, with ZD1providing its reference voltage. Theoutput from this regulator feeds variousparts of the receiver, many via 105/ and10011 decoupling resistors.March 1986 Maplin Magazine
Solder toconductor
Insert into housing
OMRimmult_insulation
Locking tab
Sectionthroughsockethousing
Figure 7. Minicon Connectors
ConstructionThe receiver circuit board (the
overlay is shown in Figure 5) comesready -built, pre -aligned and testedmaking construction very simple. The
receiver should be housed in an all -metalcase, such as the Instrument Case NM2H(YM51F. see also New Products), forwhich drilling details (see Figure 6) and astick -on front panel are provided.
Excluding the aerial, all connectionsare made to the pcb by Miniconconnectors, and care should be taken toensure the correct wiring of these.Details of how to make up theseconnectors are shown in Figure 7.Carefully crimp and solder the requirednumber of minicon terminals onto thewires, making sure they all line up witheach other, and then ensure that each isfirmly fastened to its conductor and thatnothing will foul the minicon socket on
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Aerial Junction Box
insertion. If all is well insert them into thesocket the correct way round, and pushthem home until they click.Refering to the wiring diagram, Figure 8,note that the short length of coax thatconnects from the board to the aerialsocket has its screen connected to theground pin on the pcb and the outerconnection of the coax socket.
The meters and the loudspeakermay be held in position by using AralditeRapid (FL44X), making sure that themetal surfaces are cleaned and rough-ened first to form a good bond. Note thatif the recommended case and mountingmethod are not used, the pcb must be8
Aerial in use
mounted 12mm above a metal plate toensure correct operation.
When mounting the vernier dial, donot, at this stage, tighten the screw thatlocks the dial to the potentiometer spindle.
Connecting Upand Testing
Carefully check and recheck allwiring; then connect a suitable 12 voltpower supply to the receiver. Connectthe positive lead of a voltmeterof 20,000c2/volt sensitivity and set to 10Vf.s.d or an equivalent range, to the pointmarked 'x' on the tune potentiometer
(RV1), and the negative lead to 0 volts(e.g. the aerial screen connection). Areading of 0.7±0.2 volts should beobtained.
Now transfer the positive lead topoint 'y' on RV I. The reading at this pointshould be 7.25=0.3 volts. The positivelead should now be connected to thewiper of RV1, and the shaft of thepotentiometer rotated to obtain a readingof 4.5 volts (the shaft may be rotatedusing a screwdriver in the slot at the rearof the potentiometer housing). Set theVernier dial to '5', making sure thecorrect voltage is still present on thewiper, and tighten the locking screw.Rotate the dial in both directions andcheck that about 4.5 volts is still obtainedwhen returned to 5 on the scale.
Turn the MONITOR switch to its fullyanti -clockwise position (RECEIVE -TAPEIN). Rotating the volume controlclockwise should produce a rushingnoise from the speaker. The reading onthe SIGNAL meter should rise a smallamount when power is applied, and theTUNE meter should remain near thecentre of its scale.
Connect the receiver to a taperecorder via the DIN connector (theMaplin DIN pack A - RW14Q is suitablefor connection to cassette recordershaving a suitable DIN connection wiredto the DIN standard). For tape recorderswith VU meters, it should be possible to
Maplin Magazine March 1986
obtain a reading of 0dB or 100% whenswitched to record and input levelcontrols adjusted. A short recordingshould now be made from the system.Turn the MONITOR switch to TAPE OUT,rewind the tape and press play. Therecorded signal should now be heardfrom the monitor speaker.
The system is now ready for usewhen connected to a suitable aerial. Thereceiver has an input of 7552, andordinary UHF television low loss coaxcable is suitable for connection betweenthe receiver and the aerial. A suitablefixed aerial is available in kit form fromMaplin (LMOOA). The aerial should besited as high as possible and away fromsources of electrical interference.
Receiving SignalsAlthough pictures cannot be de-
coded at this stage, it is worth makingrecordings for future demodulation.Figure 9 shows a rough guide to therelationship between the receivedfrequency and the dial reading. Signalsfrom weather satellites can be easilyidentified by the 2.4kHz whistle that canbe heard in the background of theirtransmissions, together with the char-acteristic synchronisation tones. TheAmerican NOAA satellites produce a'clip -clop' type sound, and the Russiansatellites a buzzing sound about once asecond.
10 -
Vernier 8 -reading
6-
4-
2-
0.12 .4 .6 8
137 1375 138Frequency in MHz
Figure 9. Vernier Dial and ReceivedFrequency Relationship
The satellite signals can usually beheard some time before they are strongenough to produce a usable picture. Thereceiver should be tuned to obtain amaximum reading on the SIGNAL meterwith the TUNE meter as near centre aspossible. The receiver will probablyneed slight re -tuning during a satellitepass to compensate for Doppler shift ofthe signal as the spacecraft approachesand recedes. A good aerial systemshould give a reading of at least 4 on theSIGNAL meter for a close pass (within 10degrees east or west).
Should it be found that the bestreception does not coincide with theTUNE meter being in the centre position,a very careful adjustment to the core ofT2 may be made.
Coming Soon The decoder and optional synch-
ronisation unit will be described in futureissues, together with interfacing detailsand software for the BBC B and Amstradcomputers. The Frame Store, which has adefinition of 418 x 312 pixels, with 16luminance levels per pixel, givingapproximately twice the resolution of thatobtainable using the BBC, will also bedescribed.
Several associated projects areplanned for the future including an aerialpreamp. frequency scanner unit, and acomputer interfaceable frequency syn-thesiser.
Licence RequirementsThere is no actual licence available
for the reception of weather satellites, butit is necessary to obtain a 'Letter ofAuthority' from the Department of Tradeand Industry for reception of NOAA andESA satellites. There is no charge for thisauthorisation, and it can be obtained bywriting to: -
Room 309, Radio Regularitory Division,Waterloo Bridge House,Waterloo Road,LONDON SE1 8UA.
SATELLITE RECEIVERPARTS LISTRESISTORS
A complete kit of all parts, excluding optional items,is available for this project:
Order As LK99H (Satellite Receiver Kit) Price £59.95The following items included in the above kit list are also
available separately, but are not shown in the 1986 catalogue:RVI Pot. Lin. 10k I (F7/02C) Receiver PCB Assembled Order As YM59P Price £44.95RV2 Pot. Log. 470k 1 (FW27E) Instrument Case NM2H Order As YM51F Price £14.95
MAPSAT Front Panel Order As FA91Y Price £3.95MISCELLANEOUS Ceramic Filter 10.7MHz 50kHz UF71N Price 95pSI Switch 2 -Pole 6-W Rotary 1 (FF74R) PCB 6 -Pin DIN Socket Order As FA9OX Price 58pSK4 Socket Flush Coax 1 (HHO9K) MAPSAT Bracket Order As FA92A Price 80p
Vernier Dial Small 1 (RX39N)Knobs K10B 3 (RK90X)Receiver PCB AssembledBracket MAPSAT
1 (YM59P)(FA92A) SATELLITE AERIAL
SK5,9 Minicon Latch Housing 3 -Way 2 (BX97F) PARTS LISTSK6 Minicon Latch Housing 8 -Way 1 (YW23A)SK7 Minicon Latch Housing 10 -Way 1 (FY94C) MISCELLANEOUSSK8 Minicon Latch Housing 2 -Way (HB59P) ABS Box MB3 1 (LH22Y)
Minicon Terminal 26 (YW25C) Aerial Rod 4 (YM58N)LS1 Loudspeaker &I 1 (WB04E) Hole Plug 3/ain. 8 (FW37S)M1 Signal Strength Panel Meter 1 (LB80B) Self Tap No.2 x 3/1.6in. I pkt (BF84U)M2 Tuning Panel Meter (LB79L) Tag 8BA 1 pkt (LRO2C)
Miniature Wire Coax 1/rntre (XR88V) Low -Loss Coax Brown 5 rats (XR29G)Ribbon Cable 10 -Way Inure (XR060) Low C Cable I mtre (XR I9V)Bolt 6BA x lin. 1 pkt (BFO7H) Potting Compound 250g 1 (rrl9V)Threaded Spacer 6BA x Vain. 1 plct (LR72P) Tie Wrap 186 S (BF93B)Nut 6BA 1 pkt (BF18U) PVC Tape Blabk 20mm 1 (FM84F)Isobolt M2.5 x 12mm I pkt (BF55K) PL4 Coax Plug Plastic (YINO8J)Isonut M2.5 I pkt (BF59P)
OPTIONALOPTIONAL Wooden Pole lin dia.
Instrument Case NM2H 1 (YMSIF) Wood ScrewFront Panel MAPSATSPST Ultramin. ToggleAC Adaptor UnregulatedBattery PPI (6V)Battery Clips PP9Araldite Rapid
22
1
(FA91Y)(FH97F)(XKO9K)
(FM02C)(HF27E)(FL44X)
A complete kit of all parts, excluding optional items,is available for this project:
Order As LMOOA (Satellite Aerial Kit) Price £10.95The following item in the above kit list is also
available separately, but is not shown in the 1986 catalogue:Aerial Rod Order As YM58N Price 80p
March 1986 Maplin Magazine 9
or many years, since the daysof the Viewmaster and otherDIY television receiver kits, theprivate experimenter or homeconstructor has generally not
been very interested in video gadgetsand circuitry. This must have been atleast partly due to the use of the 'live -chassis' technique in almost all TV sets,where either one side of the circuit isconnected directly to the mains, or, inlater designs, a bridge rectifier is used inthe power supply, so that whichever wayround the mains lead wires are con-nected, the circuits are at half mainsvoltage to earth.
Safety First!The only safe way to use such a set
for experiments is to connect it to themains through a double -wound isolatingtransformer, which is a rather expensive
Video EquipmentWe now have TV sets with isolated
chassis, and even with video outputsockets, together with computers, videorecorders, video games and monitors. Sothere is no real problem in getting signalsto experiment with and to feed into allthose useful gadgets that have just beenwaiting to be built!
Many of these devices will berequired to produce a signal that can befed into the antenna (aerial) socket of aTV set of the live -chassis type, and this iswhere the video modulator comes in (atlast!). Maplin offer a range of small andreasonably -priced modulator modules,made by one of the largest manu-facturers in the field. The modulatortakes the video signal (and, for theUM1286 and UM2301, audio as well), and
achieve improved performance withextremely small size.
The Video SignalA video signal has a waveform, as
seen on an oscilloscope, quite differentfrom simple sine -waves or even musicsignals. In fact, it consists of three distinctparts, the picture signal itself, the DCcomponent and the synchronisation or'synch' signal, see Figure 1. The exactspecifications of these signals vary withthe TV system concerned, but this articlewill only be concerned with what isofficially known as `CCIR System I/PAL',which is used in the United Kingdom,Eire, South Africa and some othercountries. 'PAL' (Phase Alternation Line)refers to the colour -encoding system, ofwhich you will find a description in the
1111 CARE AND FEEDING
Of VIDEO MODULATORSby J.M. Woodgate C.Eng., M.I.E.E., M.A.E.S., M.Inst. S.C.E.
component. It is possible, in some cases,to use opto-isolators instead, but one thenhas to take many more extra precautions,such as enclosing the opto-isolatorcircuits in a plastic box, and earthing theisolated circuits without fail to the mainsearth. This is because most opto-isolatorsdo not give enough protection in terms ofbreakdown voltage and separation be-tween live and isolated circuits to allowthe isolated circuits to be safely left notearthed. (For reference, the require-ments are 3000V RMS (4240V DC)minimum breakdown voltage and 6mmseparation, and the plastic box is stillrequired, whatever the specification ofthe opto-isolator.)
impresses it on a UHF carrier, which ispre -tuned to Channel 36 (591.25MHz).The block of channels 35 to 38 cannot beused for broadcasting so they areavailable for feeding low-level localsignals into TV sets without too much riskof 'patterning', or other indication of co -channel interference. Of course, twomodulators on the same channel caninterfere quite effectively with eachother, so some 'tweaking' of the carrierfrequency of one of the modulators maythen be required.
This article looks at the UM1111,UM1233 and UM1286, together with apreview of the advanced UM2301, whichuses surface -mounted components to
tailpiece to the article on DigitalTelevision Receivers in Volume 4Number 15 of the Maplin Magazine. The`I' means that the picture is composed of625 lines, that 25 pictures are displayedper second, and that, when the signalsare modulated on to carriers for broad-casting, the sound carrier has a freq-uency 6MHz higher than the visioncarrier.
For System I, then, 625 lines arescanned in 1/25 second, so each line lasts64/..cs, of which about 58pts is actualpicture signal, the rest being timeallowed for the electron beam of thecathode-ray tube to 'fly back' to the left-hand side of the screen. During this time,
VIDEO
BLACK LEVEL
SYNCH
Line Synch Edges
BLANKING PERIOD
4 4 4 4 4 4 4 4 4 4
Field SynchEdge
1;14 4 4 4 4 4 4 4 4
r
I
Figure 1. Video 'signal waveform. showing the field synch edge. The short pulses between the line synch. pulses are known as 'equalising Pulses'.10 Maplin Magazine March 1986
Hi -GainInput0
LF351
51M
Lo -GainInput
0IF-0 ,Link for
100nF Hi -Gain
2 LF353
8k21 I -
10k 10k 100k
3k9
1k
15nF
15k 15k
15.n F
1 2 LF353
0To AudioInput ofUM1286
500pF±5%
1470pF +33pF I ov-0
Figure 2. Audio pre -emphasis and band -limiting filter. The supplyvoltage should be at least ±6V.
the line -synch pulse and the 'back porch'appear in the signal waveform. Theleading edge of the synch pulse triggersthe horizontal (or 'line') time -base circuitin the TV set to fly -back. After 312.5 lines,or one field, the electron beam hasreached the bottom of the picture and the
synch pulses are modified in such a waythat a synch signal for the vertical (or'frame') time -base can be extracted in thereceiver. The leading edge of this signalcauses the electron -beam of the cathode-ray tube to fly back to the top of thescreen. During this time, the video part of
CHARACTERISTICS UM1111 UM1233 UM12861
UM2301 , Units
Supply voltage
EXTERNAL Supply current
Change of carrierfreq. with supplyvoltage
Change of soundsubcarrier freq.with supply V
INFLUENCES Change of carrierfreq. with
temperature
6.5
±0.2
5.0
±0.2
5.0
±0.2
12.0
1-1.2
V
1.0 6.0 9.0 25.0 mA typ.
1.5 1.5 0.001 MHzV typ.
- - 30 '`kHz V
- 125 200 5 kHz deg.0
Video 3dB bandwidth
(Rs = 470 ohm)3.5 6.8 8.0
*MHz
Video modulator linearity 5 6*
% typ.
RF Output and Vision Carrier, atcarrier leak synch. tips(7511 load)
Peak white, ref.
synch. tips
Sound carrier,
ref. synch. tips
4 1.5
(±4dB)1.7
(i5dB)1.7 mV
-20 -17(±3dB)
-20(_t4dB)
*dB
-20(r4dB)
*dB
Sound:chroma beat, 1.54MHzref. synch tips
-45 -50 * dB
Video input Resistance,characteristics at peak white
Resistance,
at synch tips
Parallel
capacitance
4.1 150 150* kil
0.7 1.5 1.5*
MI
50 47 20*
pF
Audio inputResistance
characteristics
Series
capacitance
- - 64*
kIt
10*
nF
Spurious outputs, ref. synch tips - -30 -30 -30 dB (max.)
Sound sub -carrier fine tuning range - - 100±20 - kHz
Sound modulatordeviation sensitivity- - 20±5 35.4 kHz .V
Vision carrier frequencytolerance 25 deg.0
5 5 5 0.3 MHz (max.)
* Information not yet available.
Figure 3. Modulator characteristics.March 1986 Maplin Magazine
the signal is cut off, or 'blanked'. Becausethe fly -back begins after half a line hasbeen scanned, and takes a wholenumber of line periods, the next seq-uence of 312.5 lines, or 'second field' fallsbetween the previous set of lines on thescreen. This technique is known as'interlace', and is good for displayingpictures, but causes problems (interlineflicker) nowadays when displaying textor graphics. The two fields, togethermade up of 625 lines, are known as oneframe.
Because of the presence of theregular line -synch pulses, the spectrumof the video signal (or of the mono-chrome or Y component of a colour videosignal), which extends from zero -freq-uency (DC) to 5.5MHz, consists largely ofharmonics of the line frequency of15625Hz, around each of which aresidebands at harmonics of the fieldfrequency of 50Hz. Between the har-monics of the line frequency, there isvery little signal energy, and into thesegaps the colour information can beinserted. The technique for this isdescribed in the tail -piece mentionedabove, and the colour signals are fittedinto the gaps in the monochrome signalspectrum by choosing the colour sub -carrier frequency to be an odd multipleof one quarter of the line frequency, plusan offset equal to the frame frequency:
fm, = (1135/4+ 1/625)fH
For the L'PAL system, this gives a sub -carrier frequency of 4.43361875MHz.
The inherent DC component of thevideo signal arises from the fact that,while the amplitude of the synch pulses isconstant, the amplitude of the actualpicture signal varies with the brightnessof the scene. If the video signal is passedthrough a coupling -capacitor, the averagelevel of the signal drifts up and downaccording to the average brightness ofthe scene, which prevents the correctdisplay of dark scenes. This can be over-come by using a 'clamp' circuit to clampthe black -level of the signal to a constantDC voltage, usually OV. On the otherhand, it may be necessary, for somereason, to add an additional DC comp-onent to the signal, and this is the case forall of the modulators except the UM2301.Luckily, most modern TV sets includetheir own black -level clamp, so that wecan use AC coupling if necessary in add-on circuits, provided we do not lose toomuch of the low -frequency content of thesignal.
It is usual to pass video signals fromone piece of equipment to another at'standard level', with a peak -white signale.m.f. of 2V from a 75 ohm unbalancedsource, the synch pulse amplitude thenbeing 0.6V, negative -going. The totalamplitude drops to IV, of course, whenthe output is terminated in 75 ohm. Blacklevel, and blanking level (which are thesame for System I) are at OV. However, aswe shall see, the modulators requirequite different video input signals.
11
The ModulationProcess
The video signal is impressed on tothe high -frequency carrier by a form ofamplitude modulation. However this doesnot operate in quite the same manner asAM radio transmission. In AM radio, thecarrier amplitude is high when there isno modulation, (in the silences betweenprogrammes, for instance). But the videomodulator produces only enough carrieramplitude to reproduce the video signalat whatever level it happens to be, so thatthe carrier amplitude is low when there isno modulation.
For System I, the video signal isapplied to the modulator in such a sensethat the carrier amplitude is at its highestat the tips of the synch pulses, and at itslowest when the picture signalcorresponds to a brilliant white object, or'peak -white'. Because the positive side ofthe envelope of the modulated carrier isan inverted copy of the video signal, thisis known as 'negative modulation'. Theold 405 -line TV system, which closeddown earlier this year, used positivemodulation. With negative modulation,there is not much point in trying to tunethe TV to the modulator unless there issome video modulation present andproperly applied, because if there is novideo, or too much, the modulation of theoutput from the modulator will be low orzero. The video amplitude is correctwhen a peak white signal reduces thecarrier amplitude to 20% of the amplitudeat the tips of the synch pulses - where thelatter correspond to 100%. This 20% isthe official value for System I, but othersystems use a value of 10%. Too low avalue of this characteristic, which iscalled 'carrier leak', can give rise to buzzon the sound channel and other moresubtle effects. As the value approacheszero, the effect on the picture is toremove all detail from bright areas,producing a very distinctive, but almostindescribable visual effect, known as'white crush'. If, on the other hand, thevideo signal amplitude is too small, thea.g.c. circuit of the TV set will not workcorrectly, and it will probably not bepossible to tune the set properly, nor toproduce a synchronised picture. We alsohave to remember that the video inputs ofthe modulators are DC coupled, and(except for the UM2301) have a standingDC voltage on the 'hot' terminal. So, if wefeed the video in wrongly and disturb thisDC voltage too much, the modulator mayeither produce no output, or it mayproduce a strong carrier with almost nomodulation. For this reason it is quiteimportant to follow fairly precisely thevideo feed arrangements which will bediscussed later.
There is one other difference be-tween the output of these modulators andthe broadcast signal. To save power atthe transmitters, one sideband of thevision signal is largely suppressed('vestigial sideband transmission'),whereas the modulator produces both12
E 100_
E 90-_ni 80-E 70-O 60..cn 50-a 40-
30-"Ea. 20 -O 10_LL
ce 0
2.2Synchtips
2.4 2.6 2.8 3.0
2.67Peak white
32
Instantaneous video modulation voltage IVI
Figure 4. Typical modulator linearitycharacteristic.
sidebands. This does not normally causeany problem, because the TV set doesnot need both sidebands, and theunwanted one is filtered out in the visioni.f. amplifier.
Adding ColourWe saw before that the video signal
bandwidth extends up to 5.5MHz.Actually, while the top 2MHz is nice tohave, household video recorders getalong quite nicely without it , and withoutsome of the low -frequency end as well!
take some liberties with thebandwidth, particularly if we are onlyhandling monochrome signals (whichmay come out as green or amber on amonitor, of course). For these signals, abandwidth of 3MHz or so is adequate.However, for colour we have toreproduce at least up to 4MHz, andpreferably higher, without too much lossof amplitude nor too much phase -shift.These defects would distort the edges ofobjects in the picture and upset thealignment of the colour and brightnessedges, which is most noticeable on redobjects. If the circuits do not cope withthe colour sub -carrier frequency toowell, the colours will appear 'washed-out', or desaturated, so there must be aresponse at this frequency. If theresponse is too weak, the 'colour burst'(see the tail -piece again, or take it asread) will not be properly reproducedand the TV set will promptly shut downits colour circuits.
It is for this reason that the colour -capable modulators UM1233, UM1286and UM2301 require a PAL -encodedcolour video signal as input, and do notcontain the colour sub -carrier andencoding circuits. They would alsoaccept NTSC, or even SECAM, encodedsignals, but other equipment is notreadily available in this country foroperation on these standards.
Adding SoundThe sound is transmitted by freq-
uency -modulation of the sound carrier,with a maximum deviation of 50kHz. Thesound carrier frequency is 6MHz above
the vision carrier frequency, and this isusually ensured by first frequency -mod-ulating the sound signal on to a sub -carrier of 6MHz, and then to modulate thesound sub -carrier and vision signalsseparately on to the vision carrier. Toimprove the signal-to-noise ratio of thesound channel, the higher audio freq-uencies are boosted before transmission(pre -emphasised) with a time -constant of50gs. This gives a response which is 3dBup at 3.18kHz, but a simple treble -boostcircuit will probably cause difficulty if itsresponse carries on rising well past thehighest audio frequencies. It is advisableto add a band -limiting filter with a cut-offfrequency of 15kHz to 20kHz to ensurethat spurious signals do not upset thesound channel. A typical circuit is shownin Figure 2.
The modulators require a ratherlarge sound signal input, so this filter hasbeen designed to give a gain of 3.5 times.The output from the filter will thus beabout 5V p -p when the filter is fed fromthe 0.5V r.m.s. signal available from theoutput of a cassette recorder or hi-fipreamp. To work from the DIN -standard(current -source) recording output of anaudio system, more gain is required, andthis can be obtained by changing to thehigh -gain input.
There is no direct way of measuringthe deviation of the sound signal at theoutput of the modulator, unless you haveaccess to a UHF deviation meter. Thebest way to check it is to compare theamplitude of the audio signal from a TVbroadcast (measured with an oscillo-scope or, even better, a proper peak -programme meter, if possible, at someconvenient place in the TV set), with thatproduced by your own sound signal fromthe modulator. It is essential to have acorrectly -applied video signal presentfor this test to ensure that the TV set'sa.g.c. and sound -extraction circuits arecorrectly operating. You can assume thatthe peaks of music signals from the TVbroadcast, especially of commercials,correspond to the full 50kHz deviation.
Characteristicsof Modulators
In order to get good results from themodulator, its characteristics should beunderstood. There are quite a fewproblems and strange effects which canoccur if the modulator is misused. A tableof the most important characteristics isgiven in Figure 3 and we can now look atthese in detail.
1. External InfluencesIt may seem strange to start with
these, but they are very important and afrequent source of unexpected effects.The three main influences are the supplyvoltage, temperature and magneticfields.
It is important that the supply voltageis within the recommended range ofvalues, and that it is stabilised. If
Maplin Magazine March 1986
Video
Sync
Ground
UM1111
1.80V
0.52
_ 0.08 Sync
UM1233 UM1286
3. 4V Video 2.67V
2.84 _ \,..._ 234
2.6 Sync
OV Ground OV Ground OV
UM2301
Figure 5. Video input signal requirements.
possible, the modulator should have itsown 78L -type stabiliser whose output hasa 10µF electrolytic and a lOnF ceramiccapacitor in parallel. This will not onlystabilise the DC voltage, but also removehum (ripple) from the supply, providedthat there is not too much of it on the inputto the stabiliser. Low ripple is importantin avoiding 'hum -bars', broad dark or
light bands which drift slowly up or downthe picture, which are caused by mains -frequency voltages getting into the video.For the UM1111, with its low current -drain of lmA, a Zener diode stabilisercould be used, but it must be very welldecoupled because Zener diodes cangenerate strong r.f. noise voltages.
There should not be any difficulty in
VideoIn
OV
Audiof 'netune
V+12V
AudioIn 177V
AudioIn 1V
a. The UM1111 requires 1.8V,, input,which can be pbtained by notterminating the video input with 75ohm. This would not be a good idea if along video cable is necessary. Thisvery simple circuit is consistent with therather basic. but effective, design ofthis module.
b. The UM1233 requires rather a smallvideo input obtained from the inputattenuator. For some samples of thisunit, the 27 ohm resistor may need tobe varied to get a good. contrastypicture without black -or white -crush.The DC bias voltage of 3.2V isobtained from a separate voltagedivider. The AC coupling should notcause any problem.
c. The UM1286 obtains its 0.5Vp_pvideo signal from the input attenuator,which also terminates the video cable.The DC bias voltage is set by the 2.7kand 1.5k resistors. The 39k resistormay be replaced by a 100k pre-set forfine tuning the sound sub -carrier toexactly 6MHz.
d. The UM2301 has an AC -coupledvideo input and its own DC restorer.The audio input requires 1V rms for-50kHz deviation.
Figure 6. Obtaining the required video signal from video at standard (1V,) level.March 1986 Maplin Magazine
providing the small supply currentsrequired by these modulators, but it isworth noting that the UM2301 requiresmore than twice as much current as theUM1286, and becomes noticeably warm.
Temperature variations can causethe vision carrier frequency to drift, andthe modulator sensitivity to change.There is not much self -heating in thelarger modulators, and the UM2301 useslow -drift circuit techniques, so the mainprecaution is to keep the modulator awayfrom outside sources of heat.
Magnetic fields can affect the mod-ulators through the ferrite cores of somecoils, and induction into the UHF circuitloops. The effects of permanent magnetsshow up as shifts in tuning or picturequality when the equipment isassembled. Alternating fields, from trans-formers etc., can cause hum -bars on thepicture and/or hum on the sound channel.Again, the best way to avoid these effectsis to know that they can occur and tokeep the modulator away from sources offield.
2. Vision CarrierFrequency Stability
Lack of carrier frequency stability isa most annoying problem because itmeans that you have to keep retuning theTV set as the modulator drifts, to avoidloss of picture quality, buzz on sound orother defects. But, provided that thesupply voltage is stable and the temp-erature rise is kept down, these mod-ulators do not drift much. However,particularly for the UM1111, the initialfrequency may be rather different fromthe official Channel 36 frequency whichcan be a problem with modern TV setswith 'frequency -synthesis tuning'. It maybe necessary to find the modulator signalon Channel 35 or Channel 37, in extremecases.
3. Video BandwidthThe UM1111 has sufficient band-
width only for monochrome TV andvideo games. All of the other modulatorshave sufficient bandwidth for coloursignals. Bandwidth is affected by thevideo source impedance (see Videoinput characteristics, below).
4. Video ModulatorLinearity
The effect of non -linearity on videosignals is nowhere near so easy to see ona picture as the effect of non -linearity onan audio signal is to hear (as distortion).
13
Severe non -linearity at the limits ofmodulation shows up as 'white -crush' or`black -crush', with loss of detail and theappearance of 'flat' areas in the picture.Intermediate non -linearity can be seenon a grey -scale test -card, but is notusually a problem. An example of amodulator linearity characteristic isshown in Figure 4.
5. R.F. Outputand Carrier Leak
The r.f. output signal must be strongenough to give a noise -free picture onthe TV screen, but not so strong that itoverloads the receiver or radiatessufficiently to cause interference withother transmissions. An output voltage of1.5mV across 75 ohm is suitable, on theunderstanding that individual samples ofmodulator may vary by 5dB or so, eitherway. The UM1111 has a rather higheroutput of 4mV or so.
Carrier leak is controlled by theamplitude of the video signal input andthe alignment of the balanced tunedtransformers in the modulator. Theeffects of an incorrect value have alreadybeen described.
6. Sound CarrierFrequency Stability
This characteristic is importantbecause the TV set expects the soundcarrier frequency to be exactly 6MHzabove the vision carrier frequency. It isdifficult to use a quartz crystal in thesound modulator, because the require-ment is for frequency -modulation, andeven the best 'rubber -crystal' circuits willnot allow linear ±50kHz deviation of a6MHz crystal. The UM1286 is therefore,provided with an LC -oscillator which canbe fine-tuned by means of a voltageapplied to a vari-cap diode (actually theemitter -base junction of a transistor). TheUM2301 uses a ceramic resonator, whichis more stable than an LC -oscillator butcan be frequency -modulated more easilythan a quartz crystal can. It does notrequire fine-tuning.
7. Sound DeviationLinearity
This directly affects the distortioncontent of the reproduced sound, andconsequently must be carefullycontrolled. There should be no problemif the input signal is not greater than1.78V r.m.s. (5V p -p) for the UM1286, orIV rms for the UM2301.
8. Cross -modulationThis is interference between the
sound and vision signals caused by bothsignals encountering a non-linear circuitin the modulator. It can produce severeproblems of streaking and patterning onthe picture. With colour pictures, thesound and colour sub -carriers can beattogether to produce a signal ('sound-chroma beat') at 1.57MHz, which covers14
Figure 7. Bass eqttaliser for the UM1286.This replaces the second stage of the circuitin Figure 2. The supply voltage should beincreased, preferably to 18V.
the TV screen with vertical bars! Cross -modulation is minimised in these mod-ulators by careful circuit design whichprevents non-linear circuits affecting thecombined vision and sound signal.
9. Video InputCharacteristics
This is the most intriguing part of thesubject. Each modulator requires adifferent video input signal and, exceptfor the UM2301, this signal requires anadditional positive DC component. Thereason for these differences is that themodulators are mainly intended to be fedwith digitally -generated signals fromcomputers or video games, and themodulators were designed to acceptthese signals directly. Consequently,they do not so easily accept picturesignals at standard level, but can bearranged to do so. The input impedanceat the video input looks like a non-linearresistor in parallel with a capacitor, sothat to maintain both linearity andbandwidth, a low source impedance isnecessary. The input signal requirementsof the modulators are shown in Figure 5,and simple circuits for obtaining thesesignals from video at standard level areshown in Figure 6.
10. Audio InputCharacteristics
There is not much difficulty inproviding the required audio signal,
especially if the pre -emphasis and band -limiting filter (Figure 2) is used. Theaudio input of the UM1286 looks like aresistance of 64161 in series with lOnF.This gives a low -frequency 3dB point of250Hz which is rather high, but in mostTV sets, the loudspeaker will notreproduce lower frequencies anyway. Ifa response down to 20Hz (-3dB) isrequired, the equaliser shown in Figure 7could be used.
11. Supply Voltagesand Currents
Most of this subject has alreadybeen covered under 'ExternalInfluences', but it must be emphasisedthat these units are very sensitive tosupply voltage. Under no circumstancesshould they be operated from supplyvoltages different from the specifiedvalues.
12. Spurious OutputSignals
It is very important that the mod-ulator should not produce significantoutput at frequencies other than thewanted ones, as this can result in seriousinterference with other signals. TheUM1111 is rather out of date in thisrespect, and might give a problem incertain, rather unusual, circumstances.The later products have been designedto meet much tougher specifications, inline with current interferenceregulations. However, care is required toensure that a modulator is neverconnected to an antenna, as the radiatedsignal could interfere with neighbouringVCR's and TV sets!
How theModulators Work
The typical video modulator (Figure8) consists of two stages. The first is thecarrier -frequency oscillator, from theemitter circuit of which, a signal at591.25MHz is transformer -coupled to thesecond stage, which is the modulator
J.I
Video 0In
0-1-vcC
0 ModulatedB.F. Out
Oscillator591.25MHz
BalancedModulator
0 OV
Figure 8. Basic video modulator circuit.Maplin Magazine March 1986
DCfinetune 22k
68k
AudioIn lOnF 39ko--11
39k
0
Varicaps 6MHzOscillator
1FM Soundcarrier
UHF- Carrier
In
T T T ov
BalancedModulator
Figure 9. Basic sound modulator circuit. The circuit values given are useful for designingperipheral circuits for the UM1286.
proper. This consists of two matchedtransistors in a push-pull circuit, and thevideo signal is applied to the emitters ofthe transistors. The bases are biased to+4V, so that an emitter voltage of +3.4V,derived from the video signal, will justbring the transistors into conduction andallow a small amount of r.f. to appear atthe output. This is the 'carrier leak'condition, corresponding to a peak -whitesignal. When the video signal brings theemitters down to 2.6V, the transistors arepassing 0.7mA each, thus giving sign-ificant gain, and the r.f. output is high.This condition applies at the tips of thesynch pulses. Note that, because of theemitter and collector resistors, the trans-istors will not be damaged if the videoinput is taken down to OV, but themodulator will not work because theoverall gain is almost independent ofcollector current at high currents.
The typical sound modulator (Figure9) consists of a 6MHz oscillator, whichhas the reverse -biased base -emitterjunction of a suitable transistorconnected in parallel with the tunedcircuit. As the reverse bias is varied bythe sound signal, the capacitance of thereverse -biased junction, and thus theoscillation frequency, varies accordingly.Although the frequency shift is typicallyinversely proportional to the fourth -rootof the voltage change, and is thereforevery non-linear, we only need a deviationof 50kHz above and below 6MHz, so thatthe distortion is acceptably low. Asecond reverse -biased transistor isconnected across the oscillator tunedcircuit to allow fine-tuning of the sub -carrier frequency by means of a DCvoltage, as mentioned before. The outputof the 6MHz oscillator is passed to abalanced -modulator stage rather like thevideo modulator, but with the video inputreplaced by the vision carrier. The outputof this stage consists of two frequency -modulated sound signals, at 6MHz aboveand below the vision carrier frequency.There is no vision carrier signal,provided that the modulator is accuratelyMarch 1986 Maplin Magazine
alliJ ir=rezzirsi
*A. 4114..00
" Se114'
Figure 10. Current Maplin modulator range.
Figure 11. Typical picture using the UM1286.
Figure 12. Video waveform as seen on the oscilloscope, of a white picture with a black bar.
Figure 13. A camera control unit and modulator using the UM1286.
balanced. The unwanted lower -freq-uency sound signal is rejected by thereceiver.
In order to add the sound and visionsignals from the two modulators linearly,thus avoiding cross -modulation, resistivemixing is used. This also allows thecorrect sound -to -vision carrier voltageratio of 1:10 to be set. The r.f. output of themodulator appears on a phono-socket,which is a rather surprising use of anaudio connector, at 75 ohms impedance.Don't try to insert a phono-plug with along centre pin, as this might damage themodulator components.
Summary andConclusions
Video modulators, together with thespread of video recorders and changesin TV receiver technology, open up anew field for private experiments and thecreative design of new equipment. Theyare quite easy to use, provided that theircharacteristics and requirements areunderstood.
AcknowledgementI would like to thank Mr J. Groves of
Astec Europe, for valuable information.15
'XING by Dave Goodman
Part 2 Using Maplin High Quality Mixer Modules
The Maplin range of HQ Mixerpre -amplifier modules serve asuseful building blocks in audiocircuits requiring high qualitysignal processing. General in-
formation and technical specificationsare detailed here for a further fourcircuits, available in ready -built or kitform.
PU or Mic Input ModuleThis module is available in either
mono (single channel) or stereo (dualchannel) versions; Figure 17 shows theleft channel circuit only of the stereoversion, but the circuit is common to bothmono and stereo. It is suitable for use
MODULE SPECIFICATIONSMic Mag' PU Ceramic
PU
InputImpedance 561d) 56kf2 2001d1
InputSignal Level 25mV 5.5mV 100mV
Max 0, P beforeClipping 7.75V rms (22V Pk)
Total HarmonicDistortion
FrequencyResponse
Signal toNoise Ratio
Better than 0.2%
Flat (-3dB (it 40kHz)to RIAA -ldB
Better than 90dBPSU Max 30V DC @ 12mA (stereo)
@ 6mA (mono)
Circuit shown for Left channel only. Right channel identical exceptcomponent designations have prefix 10.
C210uF
C1 R1
1uF 1k
L.I -
10111E
R282k
R747k
R5 R612k 100k
OVOV
C4 4p7F
+--11
TR22SC2547
2SC2547
-11C3 2n2F
R45108
R3270k
R108208
R91k8
MN CS10uF
R822k
T R3BC547
C6
.7.00uF
R11
3k3
81207R
0.30v
WL 0813 220k
10737-1--12k2 C7 10pF
2
R15 220k
3 C9 22nF
RIB 680k
814 56k C10 4n7F
i11
C8.171 R16 6k8
L.0 P
0 E IOVI
Link forRC. Ormag. P Uonly.
ScreenLeft I P
Right I,P -
Link forrnle. orMag-Pfli only
with the following:
a) High impedance microphone: Oftencalled dynamic or electret, with 47ki2to 100kil impedance. This moduleshould not be used with 80 to 2000 lowimpedance microphones.
b) Magnetic pick-up cartridge: Mostcommonly used on record playerpick-ups with 47k0 impedance and5mV sensitivity.
c) Ceramic pick-up cartridge: Oftenused, but not so common as magneticpick-ups. Usually high output, highimpedance in nature.
Any one input device can be usedper channel (or board) and appropriateequalisation can be selected by fitting
Left channel
0fOIL
Stereo PCB
LI P
RI P
018
0
Right channel
E0 Left channel
WL 0equalisation link
10Niko
I Mag P U
Ceramic P U20
30-
Lett 0 PO
- - -30V 0-
i:tight° P 0
30-
20Ceramic P/U
1 0 t Meg P,UMin
WR 0Right channel
(:)__ equalisationlink
110 MXR 2
+V Bus
OV Bus
Figure 17. Mic Input Circuit16
Figure 18. Equalisation link SelectionMaplin Magazine March 1986
Mono PCB
Use contacts1-3, 10-12 and A,D.(Above dotted line/
Magnetic orCeramic Pick-up
Mono or StereoHigh Impedance Mic
Stereo PCB
Figure 19. Using a switch for Selection
links as shown in Figure 18. Alternatively,it may be found desirable to fit a switchselector instead of links and Figure 19shows an example of this using screenedwire for all signal connections and a 4 -pole 3 -way rotary switch on the stereoPCB version. Also, use screened wire forboth input and output connections on themodule, as hum pick-up and noiseproblems are greatly reduced this way.
The graph in Figure 20 shows theexpected frequency response character-istic of the module when equalised formagnetic pick-up, and this closely fol-
Screened wire
+V OV
PSU
L I P0-1C1
100uF
Figure 22. Mixer Circuit
lows the RIAA standard for replay.Records are manufactured with a boost-ed high frequency and attenuated lowfrequency signal content, effectivelyexhibiting a replay curve with an averagerise of <6dB/octave with a small step inthe mid -range, hence the replay charac-teristic for the pre -amp has to be theopposite to this. Ceramic pick-ups bynature exhibit increasing output levels atincreasing frequencies; therefore withthe ceramic pick-up equalisation sel-ected, it can be seen (Figure 21) that lowfrequency signals are given a consider -
+20
+15
---
+10
+5
ti 0
5
-io
-15
20
l'x'"' FREQUENCY 1kHz 10kHz 20kHz
Figure 20. Magnetic PU Response Curve
+20
+15
+10
+5
5,20
5
10
-15
2010*Hz FREQUENCY
1kHz 10kHz 20kHz
Link
Leftchannelr Link
channel
able amount of boost. In both instances,the object of equalising circuitry is for thefinal production of a flat frequencyresponse from 20Hz to 20kHz. No plot isgiven for the module when used with amicrophone, as the frequency responseis flat throughout the useful audio range,dropping by 3dB at 40kHz.
The specifications given assume thata 30V DC power supply is used with themodule. Lower voltage supplies will notunduly affect circuit performance, butwill require lower input signal levels toavoid clipping the waveform.
22k
SignalInputs
s/ LI P-00
Left Channel
r--0 0Link Left 0Channel
LOPto -/-1Mixers 22k
IOVIE
1-seiD Signal
22k HO MXR 7 r -o +30V
OutputsfromMixers
10 VI E -022k Link Right
s
_..-FM -)s. -R1 P-022k
Channel 0L...0 0 R OP
Right Channel
Figure 23. PCB wiring
Mixing two identical
In -Phase signals.
F1
4
F2
V2
F1= F2VI = V2F3= IFI or F2IV3 = 31 VI + V21
22k
Output waveformis inverted by 150°
.F3
V3
Figure 21. Ceramic PU Response CurveMarch 1986 Maplin Magazine
Figure 24. Mixing Identical in -phase Signals17
Mixing two identical
Out of Phase 1180°1 signals.
,4:-04%a
V5:
F4
F4 = F5V4 = V5F6=V6= 0 (Null I
22k
F6 V6
Figure 25. Mixing Identical out -of -phase (1800) Signals
Mixing two signals
1 Octave apart.
F7. lkHz V7
V7=V8= 1V peak
V9. 4i6V peak09
F7
F8
I
I
I
I
3V
Figure 26. Mixing 2 signals 1 Octave apart
Mixer Amp ModuleMODULE SPECIFICATIONSFrequency
Response 15Hz td 60kHz (-3dB)Maximum
Input Signal 5V Pk into 22kMaximumOutput Signal 15V Pk (Pre -Clipping)
Distortion((i 1kHz) 0.02%
Noise Level 100/.4.V
PSU 30V DC (ci 14mA
The mixer amplifier is only availableas a stereo (dual channel) module. Bothcircuits are identical, except for prefixnumbers on the right hand channel, asusual. From the circuit diagram, Figure22, it can be seen that the supply reg-ulation comes from R10 and zenerdiode Dl. This part of the circuit is notrepeated on both halves of the PCB andregulated 18V DC is extended to eachmixer via links, see Figure 23. TR1 andTR2 form a DC coupled amplifier with anoverall gain of approximately x3.
Virtual earth mixing is effected bycoupling input signals via a 22k resistor(Figures 23 to 26), therefore, as anexample, if a 1kHz sinewave signal with apeak -to -peak amplitude of IV is conn-ected to a 22k resistor and then to themodule input at Cl, the output signal fromR8 will be a 1kHz, 3V peak sinewave18
I 'P
06122k
IOVIE
Cl1uF
TR1RI 2N3707
22k
R233k
11533k
TR2BC107
C422uF
R6 R72k2 15k
+30V
OP
E
61001
Figure 27. Line Amp Circuit
leveladjust
Inputs frommixers ortone stages
leveladjust
Output toPower Amp
/OR
\Outputto tape
Right
LeftSpeaker
P.A.
RA.
RightSpeaker
Figure 28. Driving Speakers or Tape Recorder
(overall gain = x 3). If several differentsignal sources are to be connected to themodule input, each source must becoupled by a separate 22k resistor. Onepoint to note is that the pre -amp invertsall input signals, so the final outputwaveform does not follow the inputwaveform exactly in time! The math-ematics of mixing signals can be quitecomplex to both explain easily andunderstand, and a very general idea isgiven in Figure 24, 25 and 26. Basically,mixing two identical waveforms togetherproduces a similar waveform (in the caseof a sinewave) but with an increasedpeak -to -peak (amplitude) level. Themaximum peak signal output from themodule, before clipping occurs, is 15Vwhich corresponds to a 5V peak inputsignal. Obviously, attempting to connecttwo 5V in -phase signals at the same freq-uency would effectively produce a 30Vsignal which cannot occur due to supplylimitations, and therefore, heavy clippingof the output waveform will be evident. Intheory, an infinite number of input signalscan be applied via an infinite number ofresistors as long as the sum total voltagesdo not exceed 5V, including all in -phaseand out -of -phase products. In practice, itis probably advisable to connect no morethan six inputs per channel, especially ifhigh (IV peak or more) signal levels areenvisaged.
Line Amp ModuleMODULE SPECIFICATIONS
FrequencyResponse 10Hz to 100kHz Flat
MaximumOutput Level 26V peak (Pre -Clipping)
Minimum InputSignal for full
Output 2.6V PeakMaximum
Input Signal Continuously VariablePre -amp Gain x10THD 0.02% 1kHzPSU Max 30V DC if 14mA
The line amp module circuit shownin Figure 27, is used as a high level bufferstage output drive to amplifiers or taperecorders, see Figure 28. Maximum gainof the circuit is ten times which makes itunsuitable for direct connection withmicrophones, and other low level inputsignal devices.
Wiring of the PCB is shown in Figure29. In the typical application shown inFigure 30, line amp modules are shownin two output configurations, main outputand unequalised output. The module isavailable in dual (stereo) version onlyand each input has its own level controlwhich is infinitely variable from zero tomaximum (see Specification).
Maplin Magazine March 1986
Figure 29. Line Amp wiring
InputDevices
Guitar
Recorder
HeadphonesMonitor
VU Meter
Recorder
Figure 30. Typical Application
L I/P
VRL100k
10V1E
IOVIE VAR100k
R I/P
C222nF 'Cis
C10222nF
CartridgeOr
Pickup
inputModule
General
Purpose
Input
Module
Line
Amp
Output
Module
Un EqualisedOutput
220uF
C1034u7F OV
1M R102
Peak
Over oad
Module
V.U.Meters
k
Mixer
4s Module
Pre -Equalised
E1131/)
E
LOT0
+30V0
0E
R
0E
+30V DC
Tone
ControlModule
104=2k7
V.U. Meter
Line
AmpModule
MainOutput
Amp
Speaker
Recorder
L O P.
MeterLettChannel
L pl.
E OVA
R 0 P
RightChannel
Meter
R 0 P
J
Figure 31. Basic Amplifier Circuit Figure 32. VU Meter Circuit
March 1986 Maplin Magazine 19
OV
C4 Link R4
E IOW
*R4/104 =470Rfor 8/16R Headphone OR
Fit Links for 200 600RC104 I and Hi Z Headphones
Link
*D104
Link
Headphone Monitor
L 0 Pi -
R 0 P
StereoHeadphones
Figure 33. Headphone Monitor Circuit
Left ChannelBCfee
Signal UP
E t tLI P Max Min
Right ChannelScreen
Signal A,,,) RI P (4..9\I P Max Min
4-Ve ° 5
LI+11
1021 _L
Link 2D104
11 -lo
Left Channel
ER01L
E
V
POP
Fit:- Link 1 in D2: position andLink 2 in D104 position onlyR4 104 = 470R for 8 16RLow Z Headphones
R
Right Channel
Note Mount R5 Verticallyon the PCB
Figure 35. Headphone Monitor wiring
Left ChannelScreen
Signal Cl :LI Max
'P
Right ChannelScreen
SignalIP
Min
Left I P
level
Right I P
level +
oRI PMax Min
E
+Ve +30V
Fit: -R4 /104 12k71C5/105 14u71
D1-134/101-104 10A471
C4
C104
D2
-1=1-D1
D3
D4
D102
D101
-=11-D103
-1=1-D104
C105
-L-
cc
_L-
0
-r
1+ 10 --LOP
0
E 0
E 0
E
I I^R 0/P(+10
-20-+3 IY04781dB Dual
V U MeterL
Note :- Mount R5 Verticallyon the PCB
-20-+3 150uA at 0 dBdB 1KR Resistance
OVPSU
+30V,
Max 30 VDCat 40mA
Figure 34. VU Meter wiring
VU/Monitor AmpModuleMODULE SPECIFICATIONSPre -AmpFrequencyResponse 50Hz-20kHz flatInput
Sensitivity 75mV r.m.s. maximum,Continuously variable
Max OutputLevel 10V pk
(0/P open circuit)150mV pk (into812 'phones)
VU ModeInput Level 18mV r.m.s.
for OdB scalePSU Max +30V DC qi 40mA
The VU/monitor module can be usedin one of two ways: driving headphonesor twin meter movements. Figure 3120
shows the basic amplifier circuit, whichis based around an LM377 power amp IC.Each channel input can be adjusted forthe required output level via on board'presets, VRR and VRL.
VU MonitorFor VU meter mode, fit the add-
itional components DI to D4, D101 toD104, C5/105 and R4/104 (see Figures 32and 34). With the specified components,a reading of OdB on the meter scale isindicated with an 18mV r.m.s. inputsignal, and with the sensitivity presets(VR1, VR101) at maximum (both channelsdriven).
Headphone MonitorTo use the module in this mode, use
wire links in place of D2 and D104, andinsert 470f1 resistors in R4 and R104positions only (see Figures 33 and 35). Donot insert any of the components req-
uired for the VU version!When driving 811 low impedance
headphones, the maximum (pre -clipp-ing) signal developed will be approx-imately 150mV, which should be loudenough for most applications. It may benecessary to insert links in place ofR4/104 if medium impedance (200 -60011) headphones are being used, or toreduce the 47011 rating accordingly. Thepower amp IC can only drive loadsabove 20011 in this circuit configuration,before overheating of the packagebegins to cause problems. Power supplyrequirements are in the range of 15V to30V DC at 40mA.
This module would normally beused for monitoring all signal lines in amixer or disco, each line being selectedby suitable switching. Alternatively, itcould be used as a low power/low coststereo headphone driver for most audioapplications.
Maplin Magazine March 1986
HI -Z MIC I/P (MONO) PARTS LISTRESISTORS: All 0.6W I% Metal FilmR1 1kR2 82kR3 270kR4 5100R5 12kR6 100kR7 47kR8 22kR9 1k8RIO 82012R11 3k3R12 47f1R13,15 220kR14 56kR16 6k8R17 2k2R18 680k
CAPACITORSC1C2,5,6C3C4C7C8C9010
1AF 35V Tantalum10AF 63V Axial Electrolytic2n2F Poly Layer4p7F Ceramic10pF Ceramic1n5F 1% Polystyrene22nF Poly Layer4n7F 1% Polystyrene
SEMICONDUCTORSTR1,2 2SC2547TR3 BC547
1 (MIK)1 (M82k)1 (M270K)1 (M510R)1 (MI2K)1 (M100K)
(M47K)1 (M22K)1 (M I K8)1 (M820R)1 (M3K3)1 (M47R)2 (M220K)1 (M56K)1 (M6K8)1 (M2K2)1 (M680K)
1 (WW6GQ)3 (FB23A)1 (WW24B)1 (WX40T)1 (WX44X)1 (BX58N)
(WW33L)1 (BX64U)
2 (QY I IM)(00140)
MISCELLANEOUSHi -Z Mic I/P (Mono) PCB 1 (GD11M)Veropin 2145 I Pkt (FL24B)
OPTIONALSW1 4 Pole 3 -Way Rotary Switch 1 (FH45Y)
A complete kit of all parts and a ready built module,excluding optional item, are available for this project:
Order As LK92A (Hi -Z Mic Input Mono Kit) Price £4.95Order As YM26D (Hi -Z Mic Input Mono Assembled) Price £5.95
MISCELLANEOUSHQ Mixer No.2 PCB 1 (LR13P)Veropin 2145 1 Pkt (FL24B)
OPTIONALSW1 4 Pole 3 -Way Rotary Switch 1 (FH45Y)
A complete kit of all parts and a ready built module,excluding optional item, are available for this project:
Order As LK91Y Mic Input Stereo Kit) Price £8.50Order As YM25C (Hi -Z Mic Input Stereo Assembled) Price £9.95
LINE AMPLIFIERPARTS LISTRESISTORS: All 0.6W 1% Metal FilmR1,101R2,5,102,105R3,103R4,104R6,106R7,10788,106VRI,101
CAPACITORSC1,101C2,102C3,103C4,104
22k33k220k68k2k215k12kVert S -min Preset 22k
IAF 100V Axial Electrolytic47,AF I6V Axial Electrolytic10,AF 63V Axial Electrolytic22AF 25V Axial Electrolytic
SEMICONDUCTORSTR1,101 2N370?TR2,102 BC107B
MISCELLANEOUSHQ Mixer No.8 PCBVeropin 2145
2 (M22K)4 (M33K)2 (M220K)2 (M68K)2 (M2K2)2 (M15K)2 (M12K)2 (WR72P)
2 (FBI2N)2 (FB38R)2 (FB23A)2 (FB3OH)
2 (QR31j)2 (0831])
1 (LR23A)I Pict (FL24B)
A complete kit of all parts and a ready built moduleare available for this project:
Order As LK87U (Line Amp Kit) Price £3.95Order As YM21X (Line Amp Assembled) Price £5.50
HI -Z MIC I/P (STEREO) PARTS LISTRESISTORS: All 0.6W 1% Metal Film
MIXER AMPLIFIERPARTS LISTRESISTORS: All 0.6W I% Metal Film
R1,101 lk 2 (MIK) R1,101 22k 2 (M22K)
R2,102 82k 2 (M82k) R2.3,102,103 33k 4 (M33K)
R3,103 270k 2 (M270K) R4,5,104,106 68k 4 (M68K)
R4,104 5101) 2 (M510R) R6.106 5k6 2 (M5K6)
R5,105 12k 2 (M12K) R7,107 15k 2 (M15K)
R6,106 100k 2 (M100K) R8,108 331I 2 (M33R)
R7,107 47k 2 (M47K) R9,109 6811 2 (M68R)
R8,108 22k 2 (M22K) RIO 82011 1 (M820R)
R9,109 1k8 2 (M1K8)R10,1010 8200 2 (M820R) CAPACITORS
R11,1011 3k3 2 (M3K3) CI,101 100AF 10V P.C. Electrolytic 2 (FF 10L)
R12,1012 4711 2 (M47R) C2,102 22AF 25V Axial Electrolytic 2 (F)330H)
R13,15,1013,1015R14,1014R16,1016R17,1017
220k56k6k82k2
42
22
(M220K)(MS6K)(M6K8)(M2K2)
C3,103 39pF Ceramic 2 (WXSIF)C4,104 2A2F 100V Axial Electrolytic 2 (FB15R)C5,106 10AF 25V Axial Electrolytic 2 (FB22Y)C6,106 150gF 25V Axial Electrolytic 2 (F1156L)
R18,1018 680k 2 (M680K)SEMICONDUCTORS
CAPACITORSC1,101 1AF 35V Tantalum 2 (WW60Q)
TR1,2,101,102 BC109C 4 (QB33L)DI BZY88C18V 1 (QH2OW)
02,5,6,102,105,106 IGAF 63V Axial Electrolytic 6 (FB23A)
MISCELLANEOUSVeropin 2145 1 Pkt (FL24B)
C3,103C4,104
2n2F Poly Layer4p7F Ceramic
2
2
(WW24B)(WX40T)
Mixer No.7 PCB 1 (LR22Y)
C7,107 10pF Ceramic 2 (WX44X) OPTIONALC8,108 1n5F 1% Polystyrene 2 (BX58N) 22k Input Resistor (M22K)C9,109 22nF Poly Layer 2 (WW33L)C10,1010 4n7F 1% Polystyrene 2 (BX64U) A complete kit of all parts and a ready built module,
excluding optional item, are available for this project:SEMICONDUCTORS Order As LK86T (Mixer Amp Kit) Price £4.75TR1,2, 101,102 2SC2547 4 (0Y11M) Order As YM2OW (Mixer Amp Assembled) Price £6.50TR3,103 BC547 2 (Q0140)
March 1986 Maplin Magazine Continued on page 25. 21
The Storyof Radio
aving now proved to a doubtingworld that the Atlantic couldbe bridged by wireless waves,
Marconi's next act was to establish apermanent station at Glace Bay, CapeBreton Island on the east coast of Canada.This station was augmented on December21st 1902 and tests began straight awaywith transmissions between this newstation, the one at Cape Cod and Poldhu inCornwall. It was now vital to show thattransatlantic contact was no freak occur-rence but could be depended upon at alltimes. If this could be done, it would open upa whole new world of possibilities, of whichthe most obvious, at the time, seemed to bein the realm of marine communications.
Ever since man first set the bows of hisvessel toward the open sea, he had had to
by Graham DixeyC.Eng., M.I.E.R.E.
Part Two-The First Decade
accept the fact that once out of sight of land,he was totally isolated from humanity,unless he came across another seafarer ofcourse. Now all that could be changed. Rightacross the breadth of the Atlantic he wouldbe able to send messages to ports at bothends of his route, informing his employers asto his likely time of arrival, giving warning
TEABv°gue Dolan 0tin° Jll
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SUNDAY r,Pt ci AL EDITION.
st,. 4,01
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CRIPPEN'S LIFE AT SEA DESCRIBED BY 'WIRELESS.',2
of bad weather or icebergs or some otheremergency.
The first widespread use of marinewireless was the setting up of a long rangenews service for transatlantic liners, usingthe Glace Bay and Poldhu stations. This wasan interim measure because it had beendecided to build new, larger aerials at thesestations in order to benefit more from thebetter service that longer wavelengthsseemed to give. Until these new aerials werecomplete, some sort of practical use wouldpresumably increase public confidence inthe new technology. The commercial use ofwireless at sea pre -dated this event by acouple of years because in 1900, the Marconi
1-75 CRIPPE-011..5) MILL (2.11E__L__
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Company had installed untuned equipmentin the German liner, Kaiser Wilhelm derGrosse. Such was the growth of this newservice that, by the end of 1902, there weresome seventy ships operating with wirelessand twenty-five land stations available fortheir use, including several on the easternseaboard of the North American continent.
Magnetic DetectorA significant technical development
was made by the Marconi Company at thistime. This was the superseding of the ratherinsensitive coherer with the new 'magneticdetector'; this also allowed higher signallingspeeds and better discrimination againstinterference. The experimental prototypehad been made by Rutherford in 1895 butMarconi developed it into a practical device.Its action was to use a high frequency bias toovercome the 'hysteresis' in magneticmaterials, in much the same way that, inmodern tape recorders, a high frequencycurrent is superimposed on the signalcurrent in the recording head. However, inthe case of Marconi's magnetic detector, theend result was achieved in rather a differentway.
An endless band of iron wires wasdriven past a system of permanent magnetsby a clockwork motor, the speed being about8cm/s. At the point of maximum magneticfield strength due to the permanentmagnets, the iron wire band was surroundedby a pair of coils, one carrying the radiofrequency energy from the aerial, the otherbeing connected to the headphones. Thesignal itself consisted of bursts of energyrecurring at an audio frequency. In theperiods when no radio frequency energy waspresent, the permanent magnets had littleeffect, but when their action coincided withthe bursts of radio frequency energy, anoutput, at audio rate, was produced in theheadphones by way of the previouslymentioned coil. This device remained in usefor about twenty years and was known asthe 'Maggie'.
Radio for HireIt is interesting to note that the
Marconi Company did not actually sell theirwireless equipment to the shipping lines,but hired it out instead - presumably thefirst example of 'radio rentals'! The installa-tion came complete with a Marconi -trainedoperator, and the rental included the use ofall of the shore stations in the Marconinetwork. There were naturally competitorsat the time, and these were not allowed theuse of the Marconi shore stations, since theyhad not paid the rental charge for their use.Obviously this restriction did not apply todistress calls. Furthermore, the shipsequipped with Marconi wireless equipmentwere not allowed to communicate with shipsequipped by their competitors. This mayseem a strange state of affairs but shouldonly be judged in the context of the times.The chief competitor of the Marconicompany was the German firm ofTelefunken, which was a governmentMarch 1986 Maplin Magazine
Magnets -
Iron Wire Band
TerminalsCoils Pulley
Wooden Base Housing Clockwork Mechanism
Simplified diagram of Marconi's magnetic detector (the Maggie).
backed consortium of German radioexpertise. It was this latter company who, in1903, called an International WirelessTelegraphy Conference with the object ofallowing all to have free intercommunica-tion regardless of the source of theequipment carried. However, Marconi werenot prepared to hand over their dominantposition so readily and did not finally agreeto this until 1912.
Musical Spark Disc used at Poldhu in 1907.
LicencingAn amusing and extremely significant
event took place in 1903. The ability to tunethe transmissions so that adjacent stationscould operate without mutual interferencehad been developed to a practicable level.However, the case had been rather over-stated because it had also been claimed thatthe medium of wireless allowed 'secret'communication between parties, free from
23
Ships wireless cabin, 1910. A 1.5kW installation that was standard for large ships.
the possibility of interference by a thirdparty. This clearly wasn't true, and oneparticular person was determined todemonstrate this in as public a manner aspossible. The person concerned was NevilleMaskelyne, son of the famous illusionist,whose father owned the Egyptian Theatre inPiccadilly, London. Neville Maskelyne hadcommercial interests in certain of Marconi'scompetitors, and it was in his interest todisprove unsound claims made by Marconi.This he did by setting up a transmitter onthe roof of the Egyptian Theatre at the timethat a demonstration was taking place atthe nearby Royal Institution. A lecture wasbeing given by professor Ambrose Flemingin the said Institution, which was to have, asits 'piece de resistance', the reception of aceremonial message from the MarconiCompany at Chelmsford. During the lectureFleming's assistant was supposed to bereceiving some test transmissions. To hissurprise, indeed no doubt to his horror,rather odd messages began to come through,along the lines of, 'Rats', or 'There was ayoung fellow of Italy, who diddled the publicquite prettily'. This had exactly the effectintended, since Maskelyne ensured that theepisode attracted the maximum publicity.
The real significance of this episodewas, of course, the fact that some form ofcontrol was needed for operators of wirelessequipment. This led, in Britain, to the Wire-less Telegraphy Act of 1904, which becameeffective the following year. This was toensure that wireless was developed underdirect government control, for the good of24
the country and the people, and to enforceinternational legislation. All stations had tohave licences, which included Marconi'sshore stations. The latter were supposed tohave licences with an eight -year span but,by 1909, the British Post Office obligedMarconi to sell the stations to them.However, it now became possible to extendthe Inland Telegrams service to ships at sea,where they became known asMarconigrams.
New DirectionsIn 1905 Guglielmo Marconi married. He
was considered an eligible bachelor, becauseof his fame and, to be fair, also because of hispersonality, which exuded self-confidenceand a quiet determination. He had had anumber of romances, including twoengagements to American girls as a result ofthe many transatlantic crossings that hemade. However, his bride was notAmerican, but Irish, a 19 -year old by thename of Beatrice O'Brien. Shortly aftertheir marriage, Marconi took his new wife tothe inhospitable site chosen in Nova Scotiaas a replacement for the original Glace Baystation. Here a new aerial system had beenbuilt, which consisted of an inverted conesupported by four 64 -metre towers, sur-mounted by an umbrella roof with adiameter of 615 metres! This gives a fairindication of the dimensions of the aerialrequired for the long waves in vogue at thetime. Having seen to the tuning of the newstation, Marconi set off by sea (leaving his
wife behind!), to test the range. In daylight arange of 2,900 kilometres was achieved. Thisoffered a significant but still insufficientimprovement. However, Marconi then madethe interesting discovery that, at thereceiver, the signal received was muchstronger when the aerial wire, as it lay onthe ground, 'pointed away from the trans-mitter'. This led to the 'inverted -L' config-uration, with the horizontal arm beingmuch longer than the vertical one. As aresult, the aerial at Glace Bay was modifiedby having three-quarters of the umbrellaremoved, the remaining quarter being thatwhich faced away from the Poldhutransmitter. The received signal fromEngland was substantially stronger.
Thus, the innovation that had improvedthe strength of the received signal showedalso that an aerial could have the propertyof directionality. Put another way, a givenaerial in which the directional property wasenhanced, achieved a gain in signalstrength. This invention was patented in1905 and became the Company's standardlong range aerial. Because the Poldhu sitewas too small for a directional aerial of anyreal size to be built, a new site was chosen.This was in the west of Ireland at Clifden,later to be famous as marking the end ofAlcock and Brown's first flight across theAtlantic. A propitious choice indeed! Thenew station put out a power of threehundred kilowatts and generated its ownelectricity, the boilers often being fuelledwith peat cut from the bog nearby; theCompany built their own light railway to
Maplin Magazine March 1986
give access to the station, so remote was it.A rather incredible feature of the site
was the capacitor building, which was overone hundred metres in length, and housed agiant air -spaced capacitor in which theradio -frequency energy was temporarilystored, before being discharged through theaerial transformer!
New SparksAfter the directional aerial came
another important development. The sparksuffered from the disadvantage of having toobroad a bandwidth, which made nonsense ofthe selectivity that could be achieved withreceivers. Also, the erratic nature of thespark meant that it was not always easy todistinguish it from the atmospherics thatwere a normal accompaniment of long rangewireless communication. To overcome this,Marconi made the spark strike and exting-uish in a more regular fashion, by means ofa studded steel disc in which the length ofthe spark gap narrowed as each studapproached a stationary electrode producingthe spark, and then widened as the studpassed on, thus extinguishing the spark.This gave the received signal a character-istic musical sound, much more easilydistinguished against a background ofstatic. Furthermore, the way in which thespark energy was transferred to the aerialreduced the bandwidth of the transmittedenergy, so reducing the interference.
Viable ServiceWith these two significant develop-
ments, Marconi was at last in a position toopen a viable transatlantic service, whichwas done in October 1907. Within threemonths of opening the service, over 100,000words had been transmitted. However, therewere obviously some technical problems tobe overcome, because some messages had tobe repeated a number of times before theywere understood. Notwithstanding, it wasan excellent achievement.
Within three months of opening theservice, over 100,000 words had
been transmitted.
As a culminating achievement, in 1909,Guglielmo Marconi was jointly awarded theNobel Prize in Physics. The other recipientof this honour was K. F. Braun ofTelefunken, later to invent the cathode raytube.
By the year 1910, there were a goodmany vessels on the high seas equipped withwireless. Marconi themselves had their owninstallations in about 250 of them. It was in1910 also that the very fact of ship -bornewireless put paid to the plans of one par-ticularly notorious character, whose name isstill well enough known today. This was themurderer Dr. Crippen, who, with hismistress Ethel le Neve, was fleeing
Dr. Crippen
westwards in the liner S.S. Montrose. Theship's captain was able to broadcast this factback to England where Scotland Yard werealerted and were able, presumably alsothrough the transatlantic wireless link, toarrange for the Canadian police to arresthim when the ship docked.
Also in 1910, Marconi's position in thefurther developments of wireless took a newturn. So much was happening that it wasbeyond one man to explore all thepossibilities. From then on, he was to leadothers to shape the future. In that future,very close at hand, lay the 'wireless valve'.
MIXING IT Continued from page 21.
YU METER PARTS LISTRESISTORS: All 0.6W 1% Metal Film unless specifiedR1,101 IMR2,102 2k2R3,103 100kR4,104 2k7R5 3905/ 1W Carbon FilmVRL,VRR 100k Hor Sub -min Preset
CAPACITORSC1,4,104C2,102C3,5,103,105
2204F 35V Axial Electrolytic22nF Ceramic4,u7F 100V Axial Electrolytic
SEMICONDUCTORSIC1 LM377NZDI BZX61C15VD1,2,3,4,101,102,103,104 0A47
MISCELLANEOUSHQ Mixer PCB No.1014 Pin DIL SktVeropin 2145
OPTIONALDual VII Meter
HEADPHONE MONITORPARTS LIST
2
2
(M1M)(M2K2) RESISTORS: All 0.6W 1% Metal Film unless specified
2 (M100K) R1,101 1M 2 (M1M)2 (M21(7) R2,102 2k2 a (M2K2)1 (C390R) R3,103 100k 2 (M100K)2 (WR6IR) R4,104 47011 2 (M470R)
R5 3900 1W Carbon Film 1 (C390R)VRL.VRR 100k Hor Sub -min Preset 2 (WR61R)
3 (F/362S)2 (WX78K) CAPACITORS4 (FB18U) C1,4.104 220/./F 35V Axial Electrolytic 3 (FB625)
C2.102 22nF Ceramic 2 (WX78K)C3,103 4,47F 100V Axial Electrolytic 2 (FB18U)
1 (QH38R)1 (QF57M) SEMICONDUCTORS
8 (QH70M)ICIZID I
LM377NBZX61C15V 1
(QH38R)(QFS7M)
1
1
I Pkt
(LR2SC)(BL18U)(FL24B)
MISCELLANEOUSHQ Mixer PCB No.1014 Pin OIL SktVeropin 2145
1
1
1 Pkt
(LR2SC)(BL18U)(FL24B)
1 (YQ47B)
A complete kit of parts and a ready built module, excludingOptional item, are available for this project.
Order As LK88V (VU Meter Kit) Price £8.95Order As YM22Y (VU Meter Assembled) Price £10.95
A complete kit of parts and a ready built moduleare available lb:: this project:
Order As LK89W (Headphone Monitor Kit) Price £6.95Order As YM23A (Headphone Monitor Assembled) Price £8.95
March 1986 Maplin Magazine 25
Lowpass FilterEffects Unit
There are a great many forms ofmusical effects unit, and most rely onsome form of frequency selective filter-ing for their operation. The unit featuredhere is in this category, and it is basicallyjust a 12dB per octabe lowpass filterwhich is swept by a low frequencyoscillator. This gives a sort of tremoloeffect on the high frequency content ofthe processed signal, producing arelatively mild but useful effect. It is aneffect that is available on many synth-esisers, but which seems to be somethingof a rarity as far as stand-alone effectsunits are concerned.
The circuit breaks down into twosections; the filter which is built aroundIC1, and the oscillator which is based onIC2 and IC3. Starting with the filter, thisuses two transconductance operationalamplifiers which are contained in asingle LM13700N device. A darlingtonpair emitter follower output stage is alsoincluded for each amplifier, and thesehave discrete load resistors R8 and R12.
-°.1.11.11111.1111.1111.by Robert Penfold
The two amplifiers are connected inseries, and in this application functionmore as voltage controlled resistors thanamplifiers. They act as simple 6dB peroctave lowpass filters in conjunction withC3 and C4, giving a combined atten-uation rate of 12dB per octave. Feedbackthrough R6 and R7 gives what is actuallya bandpass response at pin 8 of IC1, andby taking the output signal from here aform of waa-waa effect can be obtained.IC1 is current rather than voltage
operated, but the inclusion of R14 inseries with the control inputs gives acurrent flow that is roughly proportionalto the applied voltage, and effectivelyconverts the filter to voltage controlledoperation. R13 reduces the input voltagerange from the oscillator slightly, bring-ing it into a more suitable range to drivethe filter.
The oscillator uses IC3 in a wellknown configuration which is based on aMiller Integrator (IC3a) and a Schmitt
SiON OFF
R1
3 k9
R31k
IC1aLM13700N
3
R41k R5
27k
C2luF
R77
C1JK1
22k
R2 mt 100uF3k9 In
6R6
22k
11
5
8
R91k
R101k
IC1b16
914
O._R1110k
12
C3270pF
ENR8 C4 E. R124k7 270pF 4k7
R1427k
RV22M2
R1647k
RV1 R15100k 100k
---1
C2CA3140E
R1312k
C510uF
+ve
7
4
2
34
R1756k
IC3a
C61uF
-1111-4
1-*
R18100k
T
+ve
IC3bLF353
JK2Out
R1910k
R2010k
B 1
9V
Low Pass Filter
26 Maplin Magazine March 1986
Trigger (IC3b). This type of circuit givesboth squarewave and triangular outputs.In this application a triangular waveformgives good results with a smooth sweep-ing of the filter frequency, and it is thisoutput that is utilized. The operatingfrequency can be varied by means ofRV2, and the nominal frequency range isfrom 10Hz at minimum resistance to0.2Hz (one cycle every five seconds) atmaximum resistance.
It is more than a little useful to havesome control over the sweep range, andthis is provided by RV1. This controls thefeedback applied to IC2, and hence thevoltage gain of this device. When set at alow value IC2 has only a low voltage gain,resulting in the cut-off frequency of thefilter being varied over a narrow range offrequencies in the lower treble range.Higher resistance gives greater sweepwidth, with the cut-off frequency being
swept over most of the audio frequencyrange with RV1 set at maximum value.
As with any effects unit, it isadvisable to build the unit into a strongmetal case such as a diecast aluminiumtype. If a bypass switch is needed astandard DPDT bypass configuration canbe used, and the switch should be aheavy duty push button type mounted onthe top of the case so that it can beoperated by foot.
Low Resistance MeterNormal multimeters, including some
quite expensive digital types, do not givevery good results at low resistances. Thisis something that obviously varies fromone instrument to another, but a resolu-tion of one ohm or more is notuncommon, and this is obviouslyinadequate when testing very low valueresistors. Open circuit or seriously over-value components can be detected wellenough, but it could prove to beimpossible to distinguish between aclosed circuit component and a service-able one. This is often important as lowvalue resistors are commonly used inapplications such as current limiters inpower supplies, where a faulty comp-onent could result in expensive damage.
This resistance meter has tworanges with full scale values of one ohmand ten ohms. It can therefore give anaccurate assessment of resistances aslow as a fraction of an ohm. It is ananalogue instrument, but unlike conven-tional analogue resistance meters it has aforward reading linear scale. With an in -range resistance across the test prods, ituses a test voltage of no more than about10 millivolts, and it will consequently notrespond to semiconductor junctions. Thiscan be useful when making continuitychecks on circuit boards, where forwardbiased semiconductor junctions canoften give misleading results by suggest-ing the presence of a short circuit wherenone exists.
The system used in this meter is tofeed a constant current to the testresistance, and to measure the voltagedeveloped across it. As this voltage isproportional to the resistance present,the meter can be calibrated dirctly inohms using a forward reading linearscale, rather than the awkward reversereading logarithmic type which isnormally associated with analogue resist-ance meters. Here the constant current isprovided by IC1 which is an integratedcircuit designed specifically for currentregulator applications. The current iscontrolled by a discrete resistor, and inthis circuit two switched resistors (R1 andR2) give current options of 1 and 10milliamps. MI, RV2, and R5 form thevoltmeter circuit, and the nominal fullscale value is 1 volt. However, IC2 booststhe sensitivity by a factor of about onehundred, giving a full scale value of 10millivolts to the voltmeter circuit as awhole. Using Ohm's Law this gives fullMarch 1986 Maplin Magazine
S2
2
IC1L M334
3
R1
1 6R8
R2s°1--""tH
68R
1+VI IRI 1-VI2 1 3
LM334Bottom View
0SK1
TestResistance
R3
-.10k
R41M
7
IC2CA3140E
5
RV122k
M1100uA
R55k6
- D21N4148
RV2RV210k
TR1BC547
R64k7
D31N4148
R84k7
D1
TIL209
R74k7
R94 k7
On Off
R101k
IMO
B1
9VJ.
TR2BC 547
Low Resistance Meter
scale values of 1 ohm with a 10 milliamptest current, and 10 ohms with a 1
milliamp test current. RV2 is adjusted togive good accuracy, and RV1 comp-ensates for offset voltages in IC2.
One problem with the basic circuit isthat the meter would be driven hardagainst its end stop with no in -rangeresistance across the test prods. This isovercome by using TR I as an electronicswitch, which bypasses the meter circuitif the output of IC2 goes to more thanabout +1.2 volts. This prevents seriousoverloads of the meter, but makes itimpossible to determine whether a validreading or an overload is present. This isovercome by using TR2 to switch on LEDindicator DI if an overload is present. DI
switching off therefore indicates that avalid meter reading is present.
The unit is calibrated on the 10 ohmrange using 1 and 10 ohm 1% resistors.First RV2 is adjusted for fsd with the 10ohm resistor in circuit, after which the 1ohm resistor is connected across the testprods and RV1 is adjusted for the correctreading of one tenth fsd. This procedureis repeated until no further adjustment isnecessary.
In the interest of good accuracy it isimportant to keep resistances at the inputof the circuit as low as possible. Inparticular, use short test leads of heavygauge wire, and test prods that provide alow resistance (some spring types seemto be unsuitable).
27
R15
470uF R2 R5100k
R4
C23k3
3n3F TAl 1-* -1I I 1M C3 C4
3 n 3F 3n3F
R35k6
T
ICI741C
R6100k
1N4148 + 9 -12V
220RR8 R11 - C8 so C74k7 10k T=470uF 100nF
R10 4C6 10k100nF D2 -
IIIIIC5 6-II >1100nF IN4148
HR71M
TR2BC549
R1210k
6 10
11 16
IC2CA3140E IC3
4020BE
R13100k
8
9
D3
RLA
R143k9
TR3©BC547
- ye
Clap SwitchThis circuit was designed mainly as
a novelty project, but although intendedto be in the 'impress your friends'category, it could in fact be used as apractical alternative to simple ultrasonicand infra -red remote control systems. Itis merely necessary to clap once in orderto switch on the piece of controlledequipment, and to clap once more inorder to switch it off again. Being a soundactivated switch it is not totally immune tosounds other than handclaps, but acombination of moderate sensitivity andbuilt-in filtering minimise the risk ofspurious triggering.
TR1 operates as a high gain commonemitter preamplifier, and its input is feddirect from a crystal microphone. Thiscan be an inexpensive microphoneinsert, although many of these seem togive poor sensitivity, and a ceramicresonator was found to provide betterresults. A crystal microphone needs tofeed into a very high load impedance inorder to give a flat frequency response,and a fairly low input impedance (such asthat of TR1) gives poor bass and middlefrequency response. In this case though,we are only interested in the pre-dominantly high frequency content of ahandclap, and the lack of bass andmiddle frequency response is anadvantage as it reduces the risk ofspurious triggering. In fact, the inputstage is followed by an active highpassfilter based on IC1 which gives an 18dBper octave roll -off below about 7kHz. Theoutput of the filter feeds the input of asecond high gain common emitter amp-lifier, this time based on TR2.
The output from TR2 is rectified andsmoothed by DI, D2, and C6, but understand-by conditions there will be nosignificant output signal. However, ahandclap will produce a strong positiveDC bias across C6 that will decay over aperiod of a few hundred milliseconds.IC2 operates as a comparator whichconverts this signal into a pulse that willreliably drive the next stage, which is aCMOS divide by two circuit. In fact the28
4020BE used for IC3 is a 14 stage type,but only one stage is used here. Thisdrives the relay via switching transistorTR3, and the purpose of the dividercircuit is to give the required successivetype of operation, with alternate inputpulses switching the relay on and off. C7and R13 provide a reset pulse to IC3 atswitch on, starting the relay in the offstate. D3 is the usual protection diode.
The specified relay has a change-over contact with a rating of 5A at 240volts AC. However, the unit should workproperly using any relay havingadequate contact ratings for yourintended application, and a 6 volt coilwith a resistance of about 200 ohms ormore. Of course, a relay having a nominal12 volt operating voltage is suitable if theunit is used with a 12 volt supply. If amains load is controlled by the unit it isessential to observe all the normal safetyprecautions, and beginners would bewell advised not to attempt control ofmains powered equipment. The micro-phone must be reasonably well acoustic-ally isolated from the relay if oscillationdue to acoustic feedback is to beavoided. The current consumption isabout 5 milliamps with the relay switchedoff, and around 40 milliamps when it isactivated. In most cases batteryoperation will only be viable if some formof rechargeable type is used.
Snooze TimerVirtually all clock radios include a
'snooze' or 'sleep' facility which simplyswitches off the set after a preset timehas elapsed. The general idea is toactivate the timer when going to bed, andthe radio then switches itself off when theuser has become drowsy and is justdropping off to sleep. A somewhatsimpler version of this feature (with non-adjustable delay) is sometimes found inother types of radio, ranging from cheapportable radios to expensive communi-cations receivers, and it is quite easy toadd a simple 'sleep' function to smallbattery operated radios. A suitablecircuit is shown here, and this gives aswitch -off delay of about 10 minutes.However, by changing the value of onecomponent it is possible to obtainvirtually any required delay time.
Simple C - R timing circuits workquite well when only short pulse lengthsare required, but for periods of about aminute or more, the required valuesbecome impractically high. The standardsolution to the problem, and the oneadopted here, is to use an oscillator anddivider chain arrangement. In this circuittwo CMOS NOR gates (ICla and IC1b)are used as inverters and connected in astandard CMOS astable configuration.IC2 is the divider, and is a CMOS 7 stagebinary type, giving a total division rate
Maplin Magazine March 1986
of 128 with all seven stages used (as theyare here). TR1 operates as a commonemitter switch which is driven from theoutput of stage seven of IC2. TR2 is cut offwhen this output is high, and turned onwhen it is low. C3 and R2 provide a resetpulse to IC2 at switch -on, and this takesall seven outputs low, causing TR1 to turnon and supply power to the radio set.
After 64 clock pulses from IC1, theoutput of the final binary divider goeshigh, switching off both TR1 and theradio set. After a further 64 clock pulsesthe circuit would revert back to itsoriginal state, and it would continue tocycle indefinitely in this way. Thisproblem is overcome by using a gatedastable clock oscillator, with the gateinput being fed from pin 3 of IC2. Theclock is therefore muted when pin 3 ofIC2 goes high at the end of the switch -offdelay.
In order to reactivate the circuit it ismerely necessary to switch off using SI,and then switch the unit on again. Si andR4 ensure that the capacitors in thecircuit discharge rapidly, leaving thecircuit ready to operate from the begin-ing once again. S2 can be used to bypassthe unit when normal operation of theradio is required. An important point isthat the use of CMOS devices gives thecircuit a very low quiescent currentconsumption so that the battery does not
Crystal CheckerAlthough at one time crystals
seemed to be vanishing from the amateurelectronics scene, with the revival in thepopularity of radio and the increasinguse of crystal oscillators in digital andmicro circuits, these components areprobably more widely used now than atany time in the past. Crystals are notcomponents that can be checkedproperly using an ordinary multimeter,and a more elaborate system of testing isrequired. In its most simple form a crystalchecker can consist of an oscillatorcircuit into which the suspect componentis connected, and some form of detectorcircuit to indicate whether or notoscillation is present. An oscillator outputsocket is useful as it enables a check onthe output frequency to be made with theaid of a suitable frequency meter or radioreceiver.
This checker is of the basic typeoutlined above, and it has a LED indicatorMarch 1986 Maplin Magazine
IC1 pins8.9.12.13 & 14
C2470pF
R1--110M
3
2 ICU4001BE IC1b
C3i0OnF
2 14
40018E
IC24024BE
R32 k2
3
T100nF 1C1 pin 7
Snooze Timer
I T
R2100k
On Off
TR1BC 559
S2
Bypass
Out
R410R
B1
9V
run down significantly when the radio isswitched off. In fact, the quiescentcurrent consumption is typically only afraction of a microamp.
The unit should be quite easy toconstruct, and the only real complicationis in taking the output of the unit to thebattery connector of the radio. Theoutput can be carried via an ordinarybattery clip lead, but it will probably benecessary to make a small notch in thelid of the radio's battery compartment toenable the lead to pass through into theset. Be careful to connect the lead the
right way round. The circuit can handlecurrents of up to 100 milliamps, and it willalso work with a 6 volt battery. It willtherefore function properly with themajority of transistor radios.
The switch -off delay is proportionalto the value of C2, and also to that of RI.
Different times can therefore be obtainedby altering the value of one or both ofthese. For instance, a value of 220nF forC2 would give a delay of just under 5minute, or using two 10M components inseries for RI would increase the delay toaround 20 minutes.
Crystal Checker
C1100nF
Crystal
-1-c >1-SK1
R21k5
-f "c"--11C4R1 1M Si
M°-11-1001FL°T-11-
C5470pF
TR1
wis C2BC547
T330pF
C310pF
TR2BC547
C6
11
32,O
On OffD3 v7
LED --
R41k
10nF
HIC7
15nF
R32k2
TR3D2 BC5470A91
71:)1 C80A91 7 22nF
SK2
QCOut
B19V
which switches on if the test componentis producing oscillation. The circuit willwork with crystals having fundamentalfrequencies from around 100kHz to about20MHz or so. Most crystals are in thiscategory since those having marked
frequencies of more than 20MHz areusually overtone types which have fund-amental frequencies at typically only athird or a fifth of the marked frequency.This checker will not work with very lowfrequency crystals having operating
29
HIGH FREQUENCY TREMOLOPARTS USTRESISTORS: All 0.6W I% Metal FilmR1,2 3k9R3,4,9,10 lkR5,14 27kR6,7 22kR8,12 4k7R11,19,20 10kR13 12kR15,18 100kR16 47kR17 56kRV I 100k Lin. PotRV2 2M2 Lin. Pot
CAPACITORSClC2C3,4C506
100/AF Axial Electrolytic 10V1,(AF Axial Electrolytic 100V270pF Ceramic104F Axial Electrolytic 25VI/AF Poly Layer
SEMICONDUCTORSIC1 LM13700NIC2 CA3140EIC3 LF353
MISCELLANEOUSSK1,2 jack SocketSi SPST Ultra -Min ToggleB1 PP7 9V Battery
Battery ClipsDIL Socket 16 -pmDIL Socket 8 -pin
LOW RESISTANCE METERPARTS USTRESISTORS: All 0.6W 1% Metal FilmRIR2R3R4R5R6,7,8,9R10RV1RV2
6R868R10k1M5k64k7lk22k Sub -min Hor Preset10k Sub -min Hor Preset
SEMICONDUCTORSIC1 LM3341C2TR1,2D1D2,3
CA3140EBC547Red LED1N4148
MISCELLANEOUSSK1,2 linrn SocketSI SPDT Ultra -Min ToggleS2 SPST Ultra -Min ToggleM1 100/AA Panel MeterBI PP7 9V Battery
Battery ClipDIL Socket 8 -pin
CLAP SWITCHPARTS UST'RESISTORS: All 0.6W 1% Metal FilmR1,7,9 1M
R2,8 4k7R3R4R5,6,13R10,11,12R14
5k63k3100k10k3k9
2 (M3K9)4 (M1K)2 (M27K)2 (M22K)2 (M4K7)3 (M1OK)1 (M12K)2 (MIOOK)1 (M47K)1 (M56K)1 (FWO5F)1 (FWO9K)
1 (FB48C)(FBI2N)
2 (WX61R)(FB22Y)
1 (WW53H)
(YH64U)(QH29G)
1 (WQ31j)
2 (HF90X)(FH97F)
1 (F14104E)1 (HF27E)I (BL19V)2 (BLI7T)
1 (MGRS)1 (M68R)1 (M10K)
(MIM)1 (MSK6)4 (M4K7)1 (MIK)1 (WRS9P)1 (WR58N)
1 (WQ32K)1 (QH29G)2 (QQ140)
1 (WL27E)2 (QLBOB)
2 (WL59P)1 (FH98G)1 (FH97F)I (RW92A)
(FM04E)1 (HF27E)1 (BL17T)
3 (MIM)2 (M4K7)1 (M5K6)1 (M3K3)3 (MIOOK)3 (MIOK)1 (M3K9)
R15
CAPACITORSC1,8C2,3,4C5,63C9
220R
4704F Axial Electrolytic3n3F Poly Layer100nF Polyester470nF Poly Layer
SEMICONDUCTORSD1,2,3 1N4148TR1,2 13C549
TR3IC1IC2IC3
BC547,u.A741CCA3140E4020BE
MISCELLANEOUSMic 1 Min-Piezo SounderRLA Open Relay 6V
DIL Socket 8 -pinDIL Socket 14 -pin
SNOOZE TIMERPARTS LISTRESISTORS: All 0.6W 1% Metal FilmRI IOM
R2 100kR3 2k2R4 IOR
CAPACITORSC1,3 100nF Disc CeramicC2 470pF Ceramic
SEMICONDUCTORSIC1 4001BEIC2 4024BETR1 BC559
MISCELLANEOUSSI SPDT Ultra -Min ToggleS2 SPST Ultra -Min ToggleB I PP9 9V Battery
Battery ClipsD1L Socket 14 -pin
CRYSTAL CHECKERPARTS LISTRESISTORS: All 0.6W I% Metal FilmR1 1MR2 1k5R3 2k2R4 lk
CAPACITORSCIC2C3C4C5C6C7C8
100nF Disc Ceramic330pF Ceramic10pF Ceramic100pF Ceramic470pF CeramiclOnF Polyester15nF Polyester22sF Polyester
SEMICONDUCTORSTR1,2,3 BCS47D1,2 0A91D3 Red LED
MISCELLANEOUSSKI Crystal SocketSK2 Coaxial Socket FlushSI 3 -way 4 pole RotaryS2 SPST Ultra -min ToggleB1 PP3 Battery
Battery Clips
1 (M220R)
10V 2 (FB71N)3 (WW25C)3 (BX76H)1 (WW49D)
3 (QL80B)2 (WisR)
(QQ14Q)1 (QL22Y)1 (QH29G)1 (QX11M)
1 (FM59P)1 (FX23A)2 (BL17T)1 (BL 18U)
1 (M10M)1 (M100K)1 (M2K2)1 (MIOR)
2 (BX03D)1 (WX64U)
1 (QX01B)1 (QX13P)1 (QQ18U)
1 (FH98G)1 (FH97F)1 (FM05F)1 (HF27E)2 (BL18U)
1 (MIM)1 (M1K5)1 (M2K2)1 (MIK)
1 (BX03D)(WX62S)
1 (WX44X)1 (WX56L)1 (WX64U)
(BX70M)1 (BX71N)1 (BX72P)
3 (0014Q)2 (01172P)1 (WL27E)
1 (HX61R)1 (H1109K)1 (FF76H)1 (FH97F)1 (FK58N)1 (HF28F)
30 Continued on page 39. Maplin Magazine March 1986
1986 CATALOGUE PRICE CHANGESThe price changes shown in this list are valid from 17th February 1986 to 10th May 1986. Prices charged will be those ruling on the day of despatch.
For further details please see Prices' on catalogue page 15.
Price ChangesAll items whose prices have changed since the publication of the 1986catalogue are shown in the list below.A complete Price List is also available free of charge - order as XFO8J.
VATIf the rate of VAT changes during the life of this price changes list then thenew rates will take effect immediately.
Key
NYADISTEMPFEB
NV
Not yet available.Discontinued.Temporarily unobtainable.Out of stock; new stock expected in month shown.To be discontinued when stocks are exhausted.Indicates that item is zero rated for VAT purposes.See 'Amendments To Catalogue'. Note that not allitems that require amendments are shown in this list.
1986CataloguePage No.
AERIALS
Page 30XQ23A Mushkiller FM1083 ............)0125C Mushkiller FM1085.. .....X0275 Mushkiller FM1087 ............X0296 Trucolour TC10 Grp AXO3OH Trucolour TC10 Grp B
VATInclusive
Price
E14.50122.30129.50E11.25111.25
X031J TrucolourTC10 GrpC/0 £11.25XG23A Trucolour TCIO Grp E........ £11.250032K Trucolour TC13 Grp A £13.35X033L Trucolour TC13 Grp B.......... £13.35X034M TrucolourTC13 GrpC/D. ...... £13 35
Page 31X13.3511 Trucolour Teta Grp A ...............£15.85X038P Trucolour TC113 Grp B.......... £15.85X0375 TrucolourTC18 GrpC/D 115.85X6248 Trucolour TCI8 Grp E... £15.85X0386 Estrogen, X05.. 120 95
X039N Extragain XG8 GroupA......... E27.50X1140T Extragain XG8 GroupB......... £27.50XQ4IU Extragain XG8 GrpC/0 67.50)(1142V Extragain XG8 Wdlind £27.50XY30H £4.95
Page 33BW46A Masthead UP1300NV 114.959W4913 Masthead UP1300N £14.95BW50E Power Unit PU1240......... £19.95
Page 34YX73Q Amp %Et I U . .
Yr122Y Xtra Set Amp... ..... ...........BK76H TV Amp XB12
BOOKS
1986CataloguePage No.
PA3IJPA49DPA32KPANEPA33LPA51FPA34MPA52GPA35NPA53H
PA36PPA54JPA370PA55KPA3E1R
PA64UPA65VPA613WPA67XPA68YPA69APA7OMPA71NPA72PFA35Q
VAT 1986Inclusive Catalogue
Price Page No.
1000m 7/0.2 Wire Grn ... ....... .. C21.951000, 7/0.2 Wire Gry E2.40DOCirn 7/0.2 Wire Gry E21.95007 7/0.2 Wire Orn E2.40000m 7/0.2 Wire Orn E21.95
Page 158HMO5F EE -1003 Anlg Don Crs
Page 159HM27E EE -110 Laser Course E99.95
1000 Wire Red. E2.40 Page 160100Orn 7/0.2 Wire Red E21 95 1411/132K 57542E0 Laser Tmr £279 95100m 7/0.2 Wire Vio E2.40
1000m 7/0.2 Wire Vio £21.95 Page 163100m7/0.2 Wire Wht HK911 EWA-3400 Assembled 671951000m 7/0.2 Wire Wht.. HM15R EC -2001 Cmptr Fndmnt .. .E99.95100m 7/0.2 Wire Yel. £2.40 MD26D Heethkit EC -2002 619510007 7/0.2 Wire .................£21.95
100m 16/0.2 Wire Blk £4.00007 16/0.2 Wire Blu 14.00
100,0 18/0.2 Wire Bm £4.00ElOrn 16/0.2 Wire Gm £40000m 16/0.2 Wire Gry E4.00
00rn 16/0.2 Wire Orn .......... £4.00
Page 164MD31J Heethkit EC -2003
Page 186HM26 D ET -18-9 Hem 1 Basic £49.95
007 16/0.2 Wire Red 14.00 Page 169007 18/0.2 Wire Vio 1400 KAOOA Hero Jr Kit RTR-1-16/0.2 Wire 10M Wht ..... . ..... ....... 45p
PA73Q 100m 16/0.2 Wire Wht rcoo Page 170PA74R 100m 16/0.2 Wire Vel .............___£4.00
Page 76XR66W 4 -Wire Phone Cable... 12p
Page 79XR23A Cable Quad
£23.50 PA18U 507 Cable Quad £11.191
£17.95
Page 44WGI1M Book JW748 0310 NV
Page 46RH53H Book BP160......... ........ . ........ NVWAIOL TI Linear Circuits ..E9.130 NVWA140 TI TTL Data 110.00 NVWG58N Book FT1199 114.20 NV
Page 47RR27E Book 082026 13.95 NV
Page 48WM60(1 Mastering Electronic... _13.95 NV
Page 49R(1290 Book BP49..........
NV
Page 50WGBOQ Book 8P95 £1.95 NVWG18U Book 110748........
Page 51XWO7H Book 8P57 DIS
Page 52WG43W Book BP87 11.35 NVWPOOA Fib Op Laser Hendbk £16.20 NVWAOBJ TI Opto Data 15.00 NVLY05F Book 8P45......... ......... . ....... E1.95 NV61138R Book BP205 ......................................DIS
Page 53WG82D Book FT1364 E9.45 NVXW4OT Book BP74 . 12.50 NV
Page 54WA90% Book NB112 DIS
Page 55R033L Book 0P52 DISWA61R Book FT1409 ............ DISWM86T Elect Servicing. £7.95 NV
Page 56WG24B Book HD165 f15.25 NV
Page 57XW98G Book FT1070 £14.20 NV
Page 58XW7OM Book M3 E19.95 NV
Page 60WG48C Book HD162 E15.25 NV
Page 65XW731:1 Book FT1241 £10.55 NVWG82A Book FT1341 E14.20 NVWG8IR Book 110192 E14.35 NV
CABLES
Page 74PA56L 100m Bell Wire Blk E2.00PA57M 100m Bell Wire Blu...-.P4580 100m Bell Wire Brn .....PA59P 100m Bell Wire Orn .....PA600 100m Bell Wire Orn .....
PA61R 100m Bell Wire Red £2.00PA62S 10Orn Bell Wire Wht 6.00PA63T 100m Bell Wire Val 12.00PA45V 1007 7/0.2 Wire Blk 12.40PA28F 1000m 7/0.2 Wire Blk £21.95
COMPUTERSPage 102YX87U S/S D/D Disk 525 .........................£1.55YJODA 10 S/S D/D Disk 5.25 £13.50FT8OB D/S D/D Disk 5.25 E1.70YJ70M 10 EMS 13/12 Disk 5.25 £15.95FT81C S/S 13/D Disk 525 ........YJ71N 10 S/S 0/1) Disk 5.25 E17.95FT820 D/S WD Disk 5.25 E2.10TJ720 10 WS 0/D Disk 5.25 £18.95
PA46A 100,0 7/0.2 Wire Blu £2.40PA296 1000rn 7/0.2 Wire Btu 121.95PA4713 100m 7/0.2 Wire Bre 12.40PA3OH 1000m 7/0.2 Wire Brn £21.95PA48C 100m7/0.2 Wire Grn E2.40
March 1986 Maplin Magazine
Page 104KF02C Hellfire Wrrior Cam 1310KF03D Hellfire Wrrior Disk DISK8755 Baja Buggies Disk DISBG36P Bug Attack Cassette DIS
Page 105KF57M Fortune Hunter Can ............ DISB0637 K -Racy Sht Out Cart DISBG49D Lunar Lander Disk DISKFO1B Monster Maze Cart DISKF45Y Mountain King Cart . ............. DIS
KB140. Nautilus Disk .DISKF12N Planermanie Cart. DIS81136P Shoot Gallery Cass D1SKF27E Sky Blazer Disk DISBG63T Battle Shiloh Cass DIS
50.97F Battle Shiloh Disk DID
Page 106BG91Y Stocks and Bonds Cas...................DISBOHM Bob's Business Cass ......... ..... _....DISBOOS/ Mini Word Price Gess DISKF77J Memory Map Tutrl Dis............ DISKH66W Basic Prop Tools Dalt.
Page 108KL62S Word Pros Cas1321.............. D1SKS03D M5 Tank Battalion DISKSO4E M5 Step Up DIS
Page 109KKIOL Crsh & Cmp -,18K Cass DISBC22V MM Data 1 _WS
CONNECTORS
Page 128RW61R Cas Lead Pare._.62pRW66W Ca s Lead Telefunken 58P
Page 130HL30H Mains Plug SA2019A DISHL31J Mains Socket SA2020 010
HEATHKIT
Page 146HK61R HW5400 Syn HF Xcyr .. £549.95
Page 147HT27E Heethkit SW -7800HT28F Heethkit HOP -/B00........
£299 95£64.95
Page 148HT3OH Heethkit HD -I986 ................._...£44.95
Page 149HK25C HD -1234 Antenna Sw..... .... £22.95HC53H Heethkit SA -20604 £269.95HC51F Heathkit HL -2200 ..E699.95
Page 150110234 HD -1250 Dip Meter. £8195
Page 152HC91Y Heathkit CO -1015 127915HC95D Heathkit CMA-1550-1 115.95HK31J CI -1080 Exhst Anlysr £12195
Page 154HK02C G0-49 Ultra Intruder.......HCO5F Heethkit GD-1183..............
VATInclusive
Price
1986 VAT 1986Catalogue Inclusive CataloguePage No. Price Page No.
Page 176 GABET Data Decoder PCB...........£69.95 115120 Heethkit 10-5292_____ £59.95 GA875 IR Tx PCB.
IIK2813 1G.5290 RF Oscilltr ....................£59.95HK34M 18-5281 RCL Bridge 6995
Page 177HOOP Heethkit IT -5283............_._.......159.9596140 Heethkit IPA -5280-1 ___..........E39.95HK28F IT 2250 Capactnc Mtr 1159.95HE95D HeathkitIT-3120...... ......... . £99.95H56013 GD-1703 Bat Test Kit....._ £16.95
Page 178HE986 Heethkit IT -5230. ............. . £149.95M0090 Heethkit ITA sno-1 ...... ....._......£29.95HE960 Heathicit IM -4190 £179.95
£69.95 HK520 IN -3117 Resistnc Box 019.9511119313 IMA-100-10 DC Probe 66.95HT5IF Heethkit IM -5215 1334.95
Page 179HK54J IM -2410 Free Counter .....-....1139.95
ErAgg HK67X PS2405 Hand -Free PSU-.- 62.95HK94C SMA-2400-1 Antenna 6.95
MD36P Heathkit RTC -1-9 129.95HM2OW RTC -1-10 Jr Programr 139.95HM21X RTC -1-11 Jr Mad Chr........ 134.95
Page 172HM11M EB-6140 C of E Text . 124.95 NVHM12N EB-6140-40 C E Wkbk......... £10.95 NVHM13P 586140-50 C E NVHM140 EB-6140-30 CE Parts.. ..... ..... ..tnasHMISS EB-6101 DC Elea £19.95 NVHM177 EB-610140 DC Wkbk .........E10.95 NV1166180 086101-5013C !man .6.95 NVH1355K Heethkit EEA-3101A .E1995HM19V EB-6101-30 DC Parts £2415HM22Y EB-6102 AC Elea Text . . 119.95 NVHM23A EB-610240 AC Wkbk ......... 110.95 NVHM248 E86102-50 AC NVH0500 Heathkit EEA-3102A £1995HM25C EB-6102-30 AC Pans 119.95 NVHM28F 59-6103 Sernicnd Text__ £1195 NVHM29G EB-6103-40 Semi Wkbk 110.95 NVHM30/1 096103-50 Semi Mon L9.95 NVH061R Heethkit EEA-3I03A .£19.95HM31J 03-6103-30 Semi Part £19.95HM34M EB-6I04 Elc Cir Text £19.95 NV
HM350 EB-6104-40 Elec VVkbk . 110.95 NVHM36P 096104-50 Cleo Instr .19.95 NVHM375 ER -6104-30 Elec Pert 134.95HM4OT 03-6105 Test Eci Text . s19.95 NVHM41U EB-6105-40 Test Wkbk....... £10.95 NVHM42V 5913105-50 Test Instr £9 .95 NV9087% Heathkit CEA-3105A..................£19.95HM43W 6B-61135-30 Test Pert £29.95HM46A EB-6I06 Carman Text__ 119.95 NVHM479 EB-6106-40 Comm Wlibk 110.95 NV
HM413C EB6106-50 Comm NVH068Y Heethkit EEA-3106A 119.95HM491) EB-61136-30 Comm Part £34.9511M520 E8-6201 Digital Tex........... £24.95 NVHM53H EB-6201-40 Digi Wkbk... ..... £11.95 NVUMW 686201-50 Digi Instr 1195 NVHD70M Heethkit EEA-3201 £1195HM55K EB-6201-30 Dig Part 134/5HS23A Heethkit 6E1-6001 £17.95 NVII524E3 Heethkit 5643001-40 ....... E10.95 NV
HS25C Heathkn 013-6031-50 £9.95 NVHS260 Heathkit EB-6001-30 £10.9511527E Heathkit 0E3-6002 ........ ......119.95 NVHS28F Heethkit 08-6002-40 110.95 NV115295 Heathkit 03-6002-50 ....... 1195 NV
HS3OH Heethkit 09-6002-30 E19.95HM56L 03-6401 Micro Text ..... 124.95 NVHM57M EB-6401-40 Micro Wbk £1115 NVHM58N EB6401-50 Micro Inst 19.95 NVHM59PHM61R 613-6402 Intlece Text 12415 NV11M625 EB-6402-40 IntfINkbk £10.95 NVHM637 E86402-50 Inn Instr 19.95 NVHM64UHM67% EB-8088 16 -Bit Text E24.95 NV
HM77J EB8088-40 16 -Bit Wbk. ..... 111.95 NVHM78K EB8088-50 18 -Bit Ins £9.95 NVHM79L EB-8088-30 113 -Bit Pt 69.95/15730 Heathkit EB-6405 124.95 NVHS74R Heethkit EB-13405-40 £10.95 NV
HS75S Heethkit EB-6405-50 03.95 NV45764 Heethkit 03-6405-30 £54.95HM81C 613-1801 Robotic Text._ 12195 NVHM82D 091801-40 Robot Wkbk .....114.95 NVHM83E 091801-50 Robot Inst. _£9.95 NV
HM84F EB-1801-30 Robot Prt £44.95HS69A Heathkit EB-1812 £19.95 NVHS7OM Heethkit EB 1812-40 110.95 NVHSS7211P% Heathki EB-1812-50..... ........ £9.£9459 .NVH7 Heethkit EB 1812-30 95
HM72P 566100-40 BASIC Wkbk £10.95 NVHM730 596100-50 BASIC Inst 139.95NVMD32K Heathkit EB-6003 £19,958/VMD33L Heethkit 03-6003-40 £10.95 NVMD34M Heethkit EB-6003-50 E9.95 NV
M1)350 Heethkit 08-6003-30 £1195HE11M Heethkit EB-601 119.95 NVMD41U Heethkit 03-610-40. ....... 110.95 NVHE12N Heathkit EB-40t.50 19.95 NVHE13P Heathkit EB-001-30 124.95
M01131.1 Heathkit CB -2001 £19.95 NVM019V Heethkit EB-200I-40 E10.95 NVMD2OW Heathkit EB-2001-50 19.95 NVMD22Y Heethkit E8-2032 ...............119.95 NVMD23A Heathltit EB-2002-40 110.950VMD2413 Heathkit 58-2002-50 £9.95 NVMD27E Heathkit EB-2003 £1195 NVMD28F Heathkit EB-2003-40.... 110.95 NVM0290 Heethkit EB-2003-50..... E9.95 NVMD3OH Heethkit 03-21303-30 ........ ..... ...69.95
Page 175179.95 HT63T Heathkrt HS -317-10 695.00£19.95 MD44% Heathkit HS -317-20 £119500
Page 1801111950 16-4244 Osc Calibru ......... £149.95HT526 Heathkit IP-2760................ 1179.95HK53H IP-2718 Tri-Otpt PSU £119.95HK.303 IP-2728 Low -Volt PSU ....... £49.95
Page 181H6464 Heethkit IP-2717A £189.951111561 10-4001 Weather Crap,- 1399.95
MICROPHONES
Page 188YW78K Mic Hldr Adhesive ....................TEMP
Page 192X945Y 5 -Foot Mic Stand TEMP
OPTO-ELECTRICAL
Page 201BV85V Red Bargraph Dslpy. 12.25YG33L Green Bargraph Oslpy 12.25
Page 207HY19V 5KV Laser PCB £498
ORGAN COMPONENTS
Page 21001170 Reverb PSU Module. E4.95
PROJECTS & MODULES
Page 224X6066 Burglar Alarm Box El I /5GA48A Brock Contact PCB 12.20LW57M Burglar Alarm Kit 159.95LW58N Ex Horn Kit £44.95
Page 225GA81C ChanneVPSU PCB E1.80GA820 Erne Channel PCB £1.20LVV83E Usonic Xceivar Kit £11.95LVV84F Usonic Interlines Kit
Page 226:163;71F IF,1.7111 a
Button KitKit
Page 227LK600. Expleve Gas Alnn Kit £24.9510140 Codelock Kit £22.95G975S Musical D.Bell PCB 12.9511.57M Musical Announce Kit £14.95
129.95£4.45
Page 228GA04E Stopwatch PCB 132.80LW65V Stopwatch Kit ...£44.9568248 Enlarger Timer PCB E6.95LKO7H Enlarger Timer Kit.... ....... ... ...E45.95GE1640 Enlarger Exp Mtr PCB E1.20
Page 229G878K Flash Meter PCB £1.95GA625 Timer Switch Booed._ 14.95GA637 Timer Relay PCB.... ....... - ...... £1.10GA64U Timer Front Panel £4.50
Page 230
LK34M 2.8kW Pwr Cntrlr Kit. ..... £113.12GA25C Power Control PCB
LK/5Q Fluor Tube Deer Kit £8.50
Page 231£025CCIY6OrlGBO5FG13066 T/E MotherboardG807H T/E PSU PCB
LW81C Digi-Tel Connect Kit 111.95LW820 Di Tel Main Kit.. . 629.95LK375 Digi-Tal Expdr Kit £139.95
Page 232XX476 Train Cnr1 Front Pnl 13.30GA72P Trein Common PCB £3.30GA7SS Train Receiver 2 PCB........ £1.20LVV61R Train Common/PSU Kit..... ..... .131.95LW63T Train Rawl ML9261(a................E11.95LWEAU Train Rcyr2 ML9213Kit.... 111.95LW68Y Train Rawl ML927Kit. . E9.95LW69A Train Bora ML927Kit. .19.95GA84F Remote Data Itch PCB. .12.20GA85G Data Encoder PCB..__.........._ _12.80
VATInclusive
Price
..E2.80
..E1.80
.. £1.80
..11.10
Page 233FT40T Cntd-A-Train Fr Pan . ...... E1.95LK64U Control -A -Train Kit . .. . 113.95
Page 235GA19V Ban Mon PCB_LK42V Car Ben Monitor.LK79L Car Digtl Tacho Kit
)0(41U Ign Mtg Plate .....
Page 236GA980 Car Burglar Alrrn PCB.LW78K Car Butyl, Alarm Kit....GA40T Car Aerial ester PCB...08938 U/Sonic Car Atm PCB
E1.3017.50
.£17.95
£1.40
Page 237GA76H MPG Meter Main PCB ...............12.20GA77J MPG Meter Disply PCB.... ......... E1.6060894 LM1871 %miner PCB. E1.40LK55K 27MH: Transmitu Kit _....._.........17.95613836 4 Ch Servo Crurt PCB 18.95
LKBIR 4 CS Servo Cntrlr Kt .£27.95
Page 238LK45Y Servo & Driver Kit...................._£14.95FJ54J TU 1000 Rear Panel.. . 12.5068670 RTTY Terminal PCB £9.95LK53H TU1000 RTTY Kit £54.95
Page 239GIME TDA 7000 Radio PCB E2.60
Page 2400615R Stereo Amp Chassis..................£8.9504710 Stereo Amp PCB ..............GA78K Stereo Amp Sw PCB ......................80pLW IN 25W Stereo Amp Kit......... .69.95LW77J Amp Remote Cntrl Kit....... .134.95
Page 241XX03D 10 -Channel G.E. PCB ti2.50LR13P HQ Mixer PCB No.2 E2.50
Page 24218158 HQ Mixer PCB No.4 £2.20LR34M HO Mixer PCB No.2I £2.90LR16S HO Mixer PCB No.5 E1.13016350 HO Mixer PCB No.25 £2.40LR22Y HO Mixer PCB No.7 C2.40
Page 2431824E1 HO Mixer PC8 No.9 £2.40LR25C HO Mixer PCB No.10 6.40L/12131) HO Mixer PCB No.14 £2.80
Page 244
FJ36P Mapmix Front Penel.....10490 Mapmix Kit £39.950443W Noise Gate PCB 6.5011143W Noise Gate Kit....... ... £10.95
Page 245GA3OH Compander PCB.LK38R Mk 110/ Unit Kit.........0644% Stereo DNL PCB.._.......
Page 246LK69A Active Crssvr Kit .... .LK70M 3 Channel Amp Kit.
E3.50.E44.95
.::Page 2478Y730 8W Amp PCBLW36P 8W Amp Kit £5.95Y039R 30/2 PSU PCB £2.20V043W 15W Amp Kit 03.50
Page 250LW32K 150W Power Amp Kit £2235
Page 251GA28F 100W MOSFET Arno PCB..LW51F MOSFET Amp Kit E17.9554410 Combo Amp PCB 17.9500030 Combo Amp Fret Panel 14.95GA17T MOS-Amp Bridge PCB £2.95
111031) MOSFET Bridging kit 111.95
Page 252BEISIC Disco Pre -Amp Tn PCB £5.508819V Disco PSU PCB £2.95130260 Motor Switch PCB E1.50
Page 2536442V Partylite PCB. £2.208841U Synth Mixer PCB 03.50BB44X Synth VCA PCB .. . £2.50BY9OX Synth Smpl & Nse PCB 15.509E143W Synth Trns Gen 1 PCB........ 6.95BB45Y Synth Trns Gen 2 PCB____ /4.95BY82D Synth &int& Phs PCB £194:505
C24.95 BY835 Synth VC Pn & AncPCB£6.95 BB48C Synth Est I/P's PCB E2.20
BB65V 3800VCF PCB 13.30
9134713 Synth Otpt Stge PCB £8.95
Page 254GA03D Spectrum PSU PCB 12.80GA36P Spectrum VCO PCB £8.95GA55K Spectrum CthrlIr PCB £3.30100856 Hexadrum Kit £22.95
Page 255GB72P Conthinadrum PCB ......... £3.30LIC520 Computadrum Kit.. .. 111.95GAO5F Syntorn PCB E1.10100867 Syntom .E13.95LVV87U Synwave Kit 113.95
31
1986CataloguePage No.
VATInclusive
Price
1986CataloguePage No.
VATInclusive
Price
1986CataloguePage No.
VATInclusive
Price
1986CataloguePage No.
Page 256 *8111459 BSR ST15,,,,, *YX066 ADC RS(130 £5.95 QX561 747098p 9F213F 741554 25p YF I8U 741527 ... ...
55p 1021X 761532.......02335 *FV25C ADC 85033 £12.50 QX57M 7472 48p
_02195 *FV248 Fuji Onk o 0X58N 7473 46p*FV229
C195YF3OH
*89900 Philips GP4DO11
E3.95 YF31J*FM76*FV33L YF32K
0X600 7475 55p
*FV2OW CIX616 7476 46p*FV34M Shure 697 -HE YF33L 741176 . . .. 32p*FC151F Tenorel 200ID 02.95 0X850 7483 97p*F0520 Tenorel 2001ED £8.95 QX64U 7486 40p*BK19V Stanton D5107AL £5.95 1138R
£4.95 *HR89W Philips GP205 78p CD(86T
*FM7OM Garrard GKS25 98p 11%67X 7492 63pge 259 *HR97F Sanyo 2611K £495 YF39N 741592.. 57p
*HR48C Goldring D110SR £345 YF4OT
it. .E23.95 .11117611
£2.95 QX87U 7496 82p10701 CMOS Xtal Clbrtr KGB2IX CMOS Xtal Clhrtr PCB E3.30 *HR77J Goldring 011011
£5.95 QX71N 74107 46pGoldring D120SR .............. ... C145 QX889 74109 69P*HR49D
Page 260 *FV29G Panasonic EPS36.. .. . £3.50 YF459Sonotone V100 . .. . ......*88616 ..... . .. .. £4.95 5X72P 74118 £1
*HR99H C1054J 7415122....
C1LKO6G Sweep Osc Kit .................01.10 4116951) WHOOA 74122GB3OH Probe Upper PCB.............
01331J Probe Lower PCB ............WHO1B 74123 82p
p
11(13P Logic Probe Kit. ..E6.50...E14.95 *FV32K Shure 670-B .
GB36P Pulsar PCB £160 *1-111791 Hitachi ST103 £5.95 YF48C 69p*FV28F Sharp STY104 £3.95 9F490
Page 261 *FV23A Panasonic EPS270......... E1.95 YF50E 7415126... 42p0.7, WH11.30 74132 09p
*FV2IX*BK12N Audio Tech ATS1OL
Audio Tech ATN340I 05.75 YF5IFE2.80 *130078 Audio Tech ATN3400.......... £6.95 YF52GElm *FG94C Sharp STYI23 £6.95 YF53H
YF54J 74LS139 ...55pWHOSE 74141 . .......... .............................. 90pWHO6G 74145 97p
10156 Synchinte Kit1W55K Synclock KitLW889 Volume Pedal Kit.......
Page 257LW89W Auto Swell Kit ...... .......GB54J Auto -Wee PCB.........LK36P Auto-Waa Kit .........LK746 Guitar Equaliser
Page 2588872P Sine/Square Gen PCB
RK39N Freq Cnt Front Panel.... ..... ..... C2.95BO2C Frecjancy Counter PCI3 £8.95
6E1030 Freq Ctr Display PCBGB40T Frqncy Mtr Adptr PCB
Page 262GB09K Modem Maur PCBGB10L Modem PSU PCB.LW99H Modem Kit............
Page 283...............£5.95 68078 Rota -Rack ....TEMP
Page 263LK689 Mains Tx/Rx Drvr Kit........... .E34.9511(17T RS232/TTL Cnvdr kit............ ...C8 50
Page 264LK67% Z80 CPU Module Kit E29.95GB3911 BBC Motherboard PCBLK47B BBC Motherboard Kit.£27.95
Page 265
RESISTORSPage 288YY13P Rennet 2206.....YY14Q Rennet 47ORYY156 Rennet 7k ..........
Page 290FW44X Ow Pot Lin 47k..
SEMICONDUCTORSPage 294
LK28F Oric Talkhack Kit .C2165 QFIOL 8F167.0855K Oric Ma-Mo I/F PCB.................... £4.50 9975S ICL7660CPA
LK4OT Oric Maplin Mo !Face. .....0972P 2716/M9 EPROM Shp IF.............. £9.95LK7IN Sharp Serial IF ....................£29.95LK39N Spctrm Easyload Kit £12.95
YF52G 74LS136.91990 7415266.VF27E 741551...YF28F 741554
Page 309WI4030 74132 69pYF5IF 7415132C1X459 7413 40pYFI IM 741513 34p5X460 7444 57p
Page 310OX40T 7404 28pYFO4E 74LSO4 25p Page 326QX41U 7405 28p WHOOA 74122 57p
YFOSF 0054) 7415122QX75S 7406 44p WHO1B 74123 82pYH12N 48p YF48C 7415123911140. 7410388. 48p YF86T 7415221......._.._ax21X 4049UBE 40p5x76H 7407 44p Page 327YHIIMYH13P 7410367. 48p9F490 Page 3359950E 7415126. 42p
BRO2C SW Amp PCB....
Page 3119F90% 7415243...9F889 7415241. 92p
.51:1561. 7415244. 80p
01 .00 YF919 7415245 C100 Page 34501.48 QXO4E 4007UBE ................ . 281, RABIC SAA1099 NYA
62p74p Page 353
Page 312 YY7311 LM335Z £1.85
WHO2C 7415629 = 7415124..... ......... .........£1.35
..£2.20
YF61R 7410157.... .....YF62S 7415158 55pWHO9K 74160 E1.00YF63T 74LSI60 69p
£1.35 YF66W 74LSI63 69p
Page 295YY73111 LM335Z ........... E1.65
01.25RABIC SAA1099 NYA
Page 266 CIL22Y u.A74 I C 8 -pin 18p
E9.95 Q1199 TIS43 64p11f21% Spcom/RS232 Inff Irt £24.95 11375 W005 25pLK65V Spctrrn I/O Cntrlr Kt £17.95LK72P Sped Pallel/Srl Kit .................._£17.95
Page 267LK260 Spectrum ADC Kit..... .........E32 95GB34M DAC PCB..................................03.30LK25C Spectrum DAC Kit .....................£18.95613478 Spectrum Kbd Pcb . ...£11 95GB48C Spectrum Kbd Con Pcb 02.20
LK291 Spectrum Kybd Kit E39.95LK30H Sptrrn Kybd Adplr Kit E8.95
Page 268LK229 VIC20 Extendiboard.GB17T VIC 20 Talkback PCB06281 VIC20/115232 Intice
Page 269GA83E 0%81 Eor Kyboard PCB1W729 Z%81 Keyboard Kit......GA90% I/O Port PCBLW76H 7X81 IJO Port Kit.
£34.95£31503.50
03.95......027.95
£2.80... £10 95
Page 270GBIIM ZX8I Sound Gen Pcb E2.205E1140 TV Snd/Inv Vid PCB £2.95LKO2C ZX81 TV snd/inv vid........... £24.95GB23A ZX81 Mod/Intface PCB 05.5009520 2716/M6 6695LK08J ZX8I Modem Irides Kt £34.95
Page 271
0843W ZX81 Hi Res Grph PCB E14.95LK23A ZX81 11. -Res Graphics...034.950890X Trundle Sensor PCB. £2.60 9F08J
YFO9KYFIOL
RECORD, TAPE & VIDEO 5X459YFIIM5%46AYFI3P
*HR39N BSR TC8 65p YF14Q*HR5IF Ronerte BF40 98P QX48C*FV27E 135R ST4 9F158*HR25C Acos GP91-10C 94 YF16S*1811870 Philips AG3306....... ............... .. 98p QX80B4- FIR600 Sonotone 9TAHC .. ................. 98p 0X81C*66429 BSR ST10 98p YFI7T*YX270 Sony NCI15P £5.95 0)(490*FV2613*68536 Garrard KS40A 98p IF18U
QX50E*HR3IJ Acos GP104 98P YF2OW*66470 BSR STI7 98p YF21X*68746 BSR ST21 98p wYF2211*F0459 Garrard 001131.. 98p YF23A*11681C Vacco Luxor .................... ....... 980 YF25C*FV19V Shure N75-6 08.95 00520*F930H Shure N75-ED.............................£14.95 50536*FV31J Shure 675-EJ El I 45 YF27E
01.386 W01 28p01395 W02 32p(1140T W04 35p
Page 296
YH88V 27128... .............................
5X04E 4007UBE.. ........................12X2100W616 4o 1038E59746 41256 110ns.QW83E
C1X31JC1W84F 451213E 53P 981200W85G0044X 68p 94140UF33L 6116 (446) 15Eins ............. E1.70
UF34M 16264-150ns) £4.5094I5094160
OX37SYFOOA ...25P YH19VQX386 7401 25P 9822Y
741.501 25
DIS£450£2.30E3 45£5 50
Page 279
£12.9502.40
£13.95£29 95
Page 297YF55K 741S145.-.-.-..QX89W 74150
68p68p YF59P 7415155. ..... .......68p68p
28P40p
02.25E550
9F67% 80pYF689 74LS165 £1.08YF69A 7415166 Et 00YF71N 7410169_ Et 00YF72P
YF730WHI1MYF74RYF75S 7410175 ...69pYF78K 7415190 86pYF79LYF8OBYF81C 74LSI93 86pWH13P 74194 90pYF82D
YF83EYF84F 7415196 86pYF85GYF86T 7415221 74pYF881/ 7411241 92p`090% 7415243 92p
*00561YF91YYF92A11950YF96E 7411258 62pYF97F 7415259YF99H 7415288YHOOA 74102739/1018YH02C 7415283
*C1X3919 7402 25PYH23AWHO2C
*YFO291030 C 255 50639
CIXOOT 7404 UF13P
YFO4E 741504 "' 25P Page 3055X411.1 7405 28p QX37S 7400
QX75S 7406YFOOA 741100
YFO5F
44411 C1X386 7401(1X7611 7407 YFOIB 741101YFO7H
YFEOD 741103'25P QX81C 7426
YF17T 741526
.......................-.................
7415245 E1.00
YF31J 741574....._32pYF75S 7415175 69pWHIIM 74174 £1.10YF746 7410174. ...........................690
YHOOA 7415273. 90p911165 7415374. 90p94180 7415377 ..........................................£1 .10
Page 3149F730 7415173. 90p5X6011 7475 55p Page 372YF32K 741075...........96156 7415373.........YF97F
YF72P 7410170
Page 337BR04E LM381 PCB E2.80
Page 361rass 1C1.7660CPA E2.85
Page 362XX04E 15V Supply PCB 98p
Page 364Page 313 90396 0 IA Reg PSU PCB £1.605)(561. 7470 55p riagn- 0.5.10 Reg 99 PS PCB E1.10QX57M 7472 egp YQ4IU 0.5/1A Reg -V PS PCB ..EI.10QX58N 7473 egp 01:154J 0.5/1A Vareg Pas PCB £1.10
9055K 0.5/1A Vareg Neg PCB. E1.105X61R 7476 46pYF33L Page 37055710 74107 46p UF33L 6116 14461 15Ons....... ................ ...£1.705588V 74109 69p UF34M 16264-150ns1................................£4.509F409 7415112. 46pYHO1B
0X72P 74118 ELIO Page 3715974R 41256 - 15000
zev Page 315WH13P 74194 90p....62P YF82D 7415194 80p
80p YF83E 7416195 .69pE7.15
5)(870 7496 82p
QX867 7491 74p80p
£1 089F69A 7411168 ....... -...... .......... ...... C1.00
£1.10
7413 40p741511._ .
7414
7415378 DID55p
74LS395 £1.15741.5829 w74LS124 ............ El 35
Page 317YF38R 74LS90... .4690X670 7492 63p
57pWHOSK 74160 El 00
69p9F78K 7415190
25p 91841 741S196.CIWE13E 45108E ..... .-
25p YF4OT 741513250
91140 74LS20 25pYF165741741520.
7421Dir YF25C 741
741522. 25p Page 3067425 . ... . ...................... ... .. 37p CIX50E 7430 25p7426741126_ .... DIS YFO7H 741109 25p7427 34p YFO9K 741111 25p
YF13P 741515 ...25p7435277430 . .. . DIS741530 ggp YF15R 74L521 25p741532. 25p741533. 26P Page 307
.......N:54
YH881/ 27128 E3.450Y755 27256 - 25Ons £5.50
Page 383YB261) Heatsrnk 600N DIS
SPEAKERS & SOUNDERSPage 387YM43W SC Old Freq Sterophn ............._TEMPYM44X SC Wcntrl Ste rophon................TEMP
Page 391X9791 Ceiling Speaker TEMP
SWITCHES & RELAYS
Page 40118919 Flasher Un1 2 -Way....- .....
86p86p TEST GEAR86p Page 40763p.51, XE3820 Crotech 3031 E239.95
X8830 Crotech 3132........
090041p YF79L 7410191. .63p
YF131C 7410193 .86p 9J791 Multi -purpose EIMM E64.95VFBSG 7415197 ...86p9H2211 7415313. ........................55pC1C144% 45266E .68p
25p741140 DIS *YFO2C 741502 25p741547 86p *YF22Y 741533 26p741548. 86p 0)(8013 7425 37p
34p
YF66W 7410163
Page 318540616 4010385
Page 3085)(64U 7486 40p
4028p
VAT 1986Inclusive Catalogue
Price Page No.
Page 321YF61R 7415157 54p
55pYF950 7415257. 62pYF96E 7415258. .62p
YF561 7415151. .. 62pYF92A
25p QW84F 451213E_ . .63p(1%89W 74150 EI 48
Page 323UF13P 74HC4316........
Page 32400631 7415684.. £3.400%856 7483 97p
Page 412
TOOLS
VATInclusive
Priee
Page 420* FY459 Adjust Spanner 150 £4.95
Page 425196139 CS Kit SKS_ ....
Page 319 FY69A XS Kit SK6.. ....YF54J 7415139. 55p9F59P 7415155. 62p Page 4279F53H 7415138... ... 55pWHOSE 74141 90pWHO6G 74145 97p91550 7415145.. E1.00 WOUND COMPONENTS
Page 435Page 3205W850 451413E55520 741547 861750536 701_546 86p Page 437
*10766 Stppr Mtr -t- Drvr Kit ..... .... E13.95
£2.25
HYI3P Desldr Nozzle Type 2 DIE
DIS
The following is a list of allitems introduced since our1986 catalogue, excluding newitems in this issue.
PROJECTS AND MODULESFA85G Temperature ControllerFront Panel. Price £1.80GB96E ASCII Keyboard PCB.
Price £8.50GB97F IBM Golfball Printer I/F PCB.
Price £19.95GDOOA Hobbyist's Temp.
NEW ITEMS PRICE LISTController PCB. Price £2.95GDO1B High Volts PCB.
Price £2.95GDO2C Digitiser PCB.
Price £11.95GDO3D Digitiser Controller PCB.
Price £11.95GD1OL Play Along Mixer PCB.
Price £1.95LK78K ASCII Keyboard Kit.
Price £19.95LK81C General Purpose Input Kit(Mono). Price £2.95LK82D General Purpose Input Kit(Stereo). Price £4.50
LK83E Tone Control Kit (Mono).Price £3.30
LK84F Tone Control Kit (Stereo).Price £5.75
LK85G Peak Overload Detector Kit.Price £2.20
LK93B Play Along Mixer Kit.Price £13.95
LK94C Hobbyist's TemperatureController Kit. Price £24.95LK95D Video Digitiser Kit.
Price £41.95LK96E Digitiser Controller Kit.
Price £29.95RA98G Programmed Golfball
EPROM 2716/M10. Price £9.95YM15R Gen. Purpose InputModule (Mono). Price £3.95YM16S Gen. Purpose InputModule (Stereo). Price £6.40YM17T Tone Control Module(Mono). Price £4.40YM18U Tone Control Module(Stereo). Price £7.75YM19V Peak Overload DetectorModule. Price £3.20SEMICONDUCTORSQY8OB 8155 I/O Ports, 256 byte RAMand 14 -bit programmable Timer IC.
Price £1.95
32 Maplin Magazine March 1986
In any correspondence please quote your customer number. Date
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* ONLY S3FOR A WHOLE YEAR'S SUBSCRIPTIONTO 'ELECTRONICS - THE MAPLIN MAGAZINE'* Every issue sent to you as soon as it's printed,
post free.* Packed with interesting and novel projects that
you can build with all components easilyobtainable.
* Many features on electronics subjects to keepyou up-to-date with latest developments.
* More pages to read than the monthly magazines* And much, much cheaper too. Many of the
monthlies are now £1 or more per issue!
BUYING A SUBSCRIPTION IS THEBEST WAY TO BUY 'ELECTRONICS''Electronics' is different from any other electronics magazine for tworeasons:
1. It's quarterly, so it's hard to remember when a new issue is dueout both for you and your newsagent.2. We don't carry any advertising, which means that having lots ofcopies sitting on the newstands waiting for casual sales is of noadvantage to us. The newsagent will normally have plenty in stock ofthose magazines which advertise because in almost all cases, he canreturn them if they are not sold - so he doesn't pay for them.'Electronics' has no advertisers to pay for unsold copies, nor does itneed to have an impressively large circulation, so the newsagentmust buy all of his delivery of 'Electronics' and cannot return those hedoesn't sell. Therefore, he may not want to take stock of too many.Before you know where you are, 'Electronics' has sold out!That's why you'll need to place a firm order with your newsagent tobe sure of obtaining each new issue. Better still, place the orderdirectly with us by sending £3.00 now and we will send you everyissue for a year, post free.Despite having very few casual sales, 'Electronics' sells as manycopies as the top selling monthly magazines. So we can justly claim ifnot quite the largest, definitely the largest committed readership inthe U.K. of any electronics magazine.
Please send me the next issues of 'Electronics -The Maplin Magazine' at 75p per copy (minimum£3)*. Please start with issue number Overseassurface mail add 24p per copy, air mail add 87p percopy. I enclose cheque/P.O. for £Customer No. (if known)
NameAddress
Post Code* Order as many copies as you wish, you will not be affected by future price XA19V Issue 19 9th May 1986 Price 75p NVincreases until your subscription ends. XA2OW Issue 20 8th August 1986 Price 75p NV
XA21X Issue 21 14th November 1986 Price TBAMaplin Magazine March 1986
Publication dates are as follows:
I
Stepper ifDriverby Mark Brighton
The Stepper Motor is an increas-ingly popular means by which
positional and or speed control may beachieved in motor driven systems,especially those controlled by digitallogic or microprocessor circuits. It is,however, rather awkward to controlusing simple digital electronics as itrequires several sequential combina-tions of logic states on its control lines tocause it to rotate.
* Simple to Use* Based on the
SAA1027 IC* Easy to Construct
In Figure 1, the SAA1027 is aMullard IC designed to simplify thedriving of 4 -phase unipolar SteppingMotors, such as that shown on page 437of the 1986 Maplin Catalogue. It requiresonly a 12V pulse for each step of themotor, and a 12V/OV logic state to controlthe direction of rotation. A reset pin isalso available to internally re -initialise thestepping sequence within the chip. Thischip, together with the necessaryexternal parts and a pcb, is offered as akit and is small enough to be mounted onor nearby the motor, where availablespace is limited.
ConstructionReferring to Figure 2, insert fully and
solder all veropins, R1, RB, C1, and the ICsocket onto the pcb, noting alignment mark onthe legend. Fit the IC into its socket with thesame orientation. Check for short circuits andwash off excess flux with thinners.
TestingWire the pcb to the motor as shown in
Figure 3. Connect the 'M' pin to OV. and apply12V pulses to the 'C' pin. 'R' should beconnected to +12V if reset is not required.The motor should rotate clockwise. Onconnecting `M' to +12V. it should runanticlockwise.
LL
g 19-
r.) Tr,
14
cc
0
+12V
IC1 cc cvcn 3
SAA1027 T
13 M1
J,,,NNN\
6 IYELL I
8
9'V_LH11-y-y-1_ I
11
Stepper Motor
Figure 1. Circuit
e(IAAAAAAA
GRN
BW
+12V OV M Lo =ClockwiseHi = Anti -Clockwise
Step Input
MOTOR
Figure 3. Wiring
r,,.,.._i_{,3_...,,,,,i1x4 c
3".n R,al 71
-cr-. -o.ta nion E
+12V C1
0 0L00000jP BL Yel'OV:Rd Wht
Figure 2. PCB Layout
MAPLIN
ficjain
IS>1
STEPPER MOTOR
STEPPER MOTOR DRIVERPARTS LISTRESISTORS: All 0.6W 1% Metal Film unless specifiedRI 100RRB 220R 1W Carbon Film 1
CAPACITORSCl 100nF Disc Ceramic
SEMICONDUCTORSICI SAA1027
MISCELLANEOUSMI Stepper Motor
SAA1027 Data SheetVeropin 2145Stepper Motor PCB
(M100R)(C220R)
1 (BX03D)
1 (OY76H)
1 (FT73Q)1 (DSO0A)1 Pkt (FL24B)1 (GD14Q)
A complete kit of all parts is available:Order As LK76H (Stepper Motor Driver Kit)
Price £15.95The following item in the above list is also availableseparately but is not shown in our 1986 catalogue:Stepper Motor PCB Order As GD14Q Price £1.45
March 1986 Maplin Magazine 35
AMSTRADEXPANSIONSYSTEMExternal ROMCard and I/O
The Amstrad computershave proved to be very popularover the past few years, possiblydue to the excellent value andfacilities provided as standard.One very important feature is theAmstrad's RSX (Resident Sys-tem Extension) and External or'sideways' ROM supportingfirmware, which allows BASICcommand extensions, machinecode routines and utilities to beadded quite simply. The potentialprovided by this facility is wellrecognised by many manufac-turers, and has led to a steadilyincreasing number of preprog-rammed ROMs becoming com-mercially available, usually of the8K and 16K variety.
However, before theseROMs can be used, it isnecessary to fit a decodingsystem, designed for this pur-pose and the Maplin ExternalROM Card has been produced tothis end.
SpecificationSockets are provided for a
maximum of eight ROMs whichcan be 2K, 4K, 8K or 16K in sizegiving a total of 128K memory
by Dave Goodman and
John AttfieldPart 1
909.9944XL
* ROM Card with facilities for up to 8 ROMs* Accepts 2K(2716), 4K(2732), 8K(2764), and18K(27128) EPROM types* Extension board and socket for DD1 Disk Drive (CPC484)* Buffering and mapped decoding for up to 128, 8 -bit I/O addresses* Motherboard extension for plug in (Eurocard) modules* Mechanically and electrically compatible with CPC464,
664 and 6128 computers
36 Maplin Magazine March 1986
Input Expansion
DataPorts
+50
SoundlOV
ICIkI OV
ROMENS
A15
!VIZWR
ROUEN
HALT
NMI
RAMDIS
RAND'S
U71(
DO
D1
D2
D3
D4
D5
D6
D7
AO
Al
A2
A3
A4
AS
AR
A7
A8
A9
A10
Al2
Al5
All
Al3
A14
SOUND
IVATe5
RFSH
117r7
IFU-STIT)
READY
BUS RESET
RESET
CURSOR
L/PENL K
D=0"7. +5VCONTROLLER BUFFER R4
4k7
I+1.ii I. LT T T T T T
C9 CB
+5V 100nF 100nF
i Bo"' 0+111 +1) le .c43 r_CcC2 C3 C4 C6100uF - OV +5 v
C10 al''' T TT TluF Tont.
6I
51C1 = 74 LS 32 Pins 7 14
IC3 = 74 HC 30 Pons 7 14 1jKC7LIGHT 00 100uF 4-C4 PEN ! I BLOW) ..__c
I
-oHa - (1,, +57 OV
1 I
0A47ICJ 2 ICS 57 8 = 74 HC 24 4 Pins 20 1.10.19--C
1 I
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9 D7 9 11(H
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1 1
2>15 /9 Al 171).,3
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4) HI
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3 AT11>" 1?-) H
25 AB 2>10124 Al 17[>3
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w4 C>16 1
2 412 6>14
3 22 BRD _ 6>121EN.14
ICU1*--
26 3- 26 3 26 23 25 23 28 23 26 23 23OV
0y R24 k7 15C>5
Link..') *o o Q o
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3 7 ,
) i8>12> 3
I
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_
Figure 1. Circuit Diagram
expansion. Amstrad recommendfast access types of 200nsalthough the 250ns EPROMsavailable from the Maplin rangehave been found adequate onthe prototype system. ROMs aredecoded and given a positional(0 to 7) address during cold startor system reset, and any ROMfound will be 'logged in' automat-ically. An eight position switchbank allows any ROM to beswitched in or out of service asrequired. ROM position 7 shouldnot be used if Amstrad's DD1disk interface module is fitted tothe 464, and this also applies tothe CPC664 and 6128 versions!Therefore, only 464 machines.
March 1986 Maplin Magazine
with no disk fitted, can use ROM 7.A socket is provided for the
connection of a Light Pen, whichis wired to the Amstrad L'PENinput and OV, +5V supply. AnyLight Pen used here must have apositive pulse output at TTLlevels to be compatible. Aseparate buffer and decodingsection extends address, dataand control lines out via an IDCcable to a Motherboard. IN OUTaddress blocks are decodedHEX, F8, F9, FA and FB for theupper byte (A8 to A15). Lowerbyte decoding (AO to A7) will beperformed on individual Eurocardprojects which plug into theMotherboard.
ExtensoonV Rai
+50 11 'PI
+50 II, PI00
OV
OV
OV
RONDOS
BA15
BIORO
BWR
ROUEN
BIOSEL
DO
DI
D2
D3
D4
D 5
D6
07
B AC)
BA1
BA2
SA3
8A4
BA 5
BA 6
BA]BAB
BA9
BA 10
B A12
BBD
Ball
BA13
BA14
SOUND
B MR EO
BMI
BRFSH
INT
BUSRD
BUSAK
READY
BUS RESET
RESET
CURSOR
L PEN
El CLOCK
CONTROLLERPCe G"sr
37
IDC
OV
C9
9
C8
1c6 I
+5V fromP. S.U.
IC51
1 R4 R3
IC 8IC7
_Ilt_
L
10
R2
C3
r-L2_
IDC1
2
EXT. SKT. A
+13C 1
3
CONTROLLER PCB GDO5FMARLIN
0C7
IC4C6
01 IC 11 IC2
0
234567
SWITCH
4
All A17231111111
S23 S
+5V 5V
S261 S26
49 A Al35013
1 2 3 4 5 6 7+a4
5
L' PEN 0
DIov 0 All
+5v0 S23+5V
1=1" S2611
SIL
R11 IC3 Al
C5
Figure 2. PCB Layout
The Amstrad expansion busis extended out from the back ofthe ROM Card using a 2 x 25 -way edge socket and a smallplug-in extension board, thusproviding facilities for disk drives,etc.
Motherboardand Modules
This card will accept up to 6plug-in Eurocard modules. Eachposition uses a DIN 41612 2 x32 -way receptacle, and the boardcan be extended with a 50 -wayIDC transition cable, if required.A separate PSU is required topower modules on the Mother-board and also to supply thebuffering components used onthe ROM Card. Eurocard sizemodules to be available infuture issues are:
a) 6 x 810 Port. Decodes loweraddress byte for Port 1 in fourblocks: E0, E8, FO and F8 andPort 2 in four blocks: E4. EC,F4 and FC. Each lower blockaddress is selectable as arethe upper decoded addressblocks, thus allowing maximumflexibility and compatibility withany other devices used on theAmstrad. Port 1 and Port 2each have three 8 -bit busses
for a total of 6 x 8 -bit (48 -bit)input output lines.
b) EPROM Programmer. Anextension to the 6 x 8 I 0 Portmodule will be an EPROMProgrammer. This project is amust for constructors who wishto design their own externalROMs for use on the ROMcard. A background ROM willbe available for driving thisproject (via the I 0 Port) whichallows copying of differentsized ROMs. standard and fastburn algorithms. modifyingprogram bytes and copyingfrom assembler buffers.
c) Power Supply Card. Producesa regulated +5V and unregu-lated supply for powering mod-ules and buffer section.
d) Serial I 0 Port. Will have fullprotocol availability and select-able Baud speeds, compatiblewith most networks includingRTTY and printers. The mod-ule will be both TTL and RS232compatible and the systemcontrolled by a backgroundROM.
External ROMCard Details
Full construction, opera-tional details, descriptions and
A
0
6
0 +0 C2
7
38 Maplin Magazine March 1986
PLUG INEURO CARDS
MOTHERBOARD
CONNECTINGIDC CABLE
Figure 3. Overall System
ROM programming techniquesare available in a separatepamphlet which is supplied withthe kit version of this project.Pamphlets may also be pur-chased individually.
Figure 1 shows the completeROM Card circuitry and buffersection. Figure 2 shows the ROM
BUS EXTENSIONBOARD
2 A 25 WAYSOCKET
EXT. ROMCARD
IDC FLEXICABLE
EXPANSION PORT
AMSTRAD
CPC 464, 664. 6128
Card layout and Figure 3 givesan overall impression of the com-plete system.
The kit for the ROM Cardcontains the main PCB, socketsfor mounting the ROMs, a cableharness for connection to theAmstrad computer, an extensionconnector with expansion card
EXTERNAL ROM CARD PARTS
A kit of parts for the ROM Card is available:Order As LK97F (External ROM Card Kit)
Price £39.95
The following parts are also available separatelybut are not shown m our 1986 catalogue:
Controller PCB Order As GDO5F Price £11.95Amstrad Pamphlet Order As XH65V Price £1.50 NV50 -way Amstrad Cable Order As FA86T Price £7.99
2 x 25 -way Edge Connector Order As FA87U Price £4.95Front Panel Order As FA88V Price 55pRear Panel Order As FA89W Price 45p
Expansion PCB Order As GB99H Price £1.95Test ROM 2716/M11 Order As UF73Q Price £5.95
PCB, the case with front and rearpanels, the pamphlet and ancil-lary components. The Mother-board Kit contains the mother-board PCB, a cableform forconnection to the ROM Card.buffer components to be fitted toROM Card and ancillary comp-onents. Note that the ROM Card
kit does not contain any ROMs sothat the types the constructorwishes to use can be selected byhim. Also, the Motherboard Kitdoes not include the 64 -wayexpansion sockets; these arerather expensive and can bepurchased as required for eachadd-on card fitted to the unit.
MOTHERBOARD PARTSA kit of parts for the motherboard extension is available:
Order As LK98G (Motherboard Kit) Price £29.95The following item is also available separately,
but is not shown in our 1936 catalogue:Motherboard PCB Order As GDO4E Price £9.95
READY -BUILT CONTROLLERThe ROM card is also available ready -built
into its case. together with front and rear panels,.Expansion pcb and cable for connectionto the Amstrad. The buffer componentsare also mounted onto the pcb together
with the cable to connect to the motherboard.No ROMs are included however.
Order As YM57M (Amstrad Controller Assembled) Price £59.95
FANTASTIC FIVE Continued from page 30.
frequencies of around 10 to 40kHz asthese require special oscillator circuits.
TR1 acts as the basis of theoscillator, and this is a standard config-uration which uses two capacitors toform a tapping on the crystal whichoperates as a parallel resonant tunedcircuit. The crystal and capacitive tapp-ing effectively form a single -woundresonant transformer, connected so thatit provides a signal inversion. Thus,although the base and collector ofcommon emitter transistor TR1 are out -of -phase, the inversion through the tunedcircuit gives positive feedback over thecircuit, and oscillation results providedthe losses through the tuned circuit arenot too high. Any reasonably activecrystal will produce oscillation, but theMarch 1986 Maplin Magazine
values of the capacitors in the tappingcircuit must have suitable values for thefrequency of the test component. In thiscase one capacitor (C2) has a fixed value,while the other capacitor is one of threeswitched components (C3 to C5). Use C5for low frequency (about 100kHz to500kHz) types, C4 for medium frequency(500kHz to 6MHz) components, and C3for high frequency (above 6MHz) types.
TR2 is an emitter follower outputstage which can be used to drive areceiver or a frequency meter connectedto SK2. TR2 is also used to drive a simplerectifier and smoothing circuit compris-ing DI, D2, and C8. If oscillation isproduced, the strong positive bias gen-erated across C8 is sufficient to turn onTR3 which in turn switches on LED
indicator D3.
The circuit is quite easy to construct,and the only slight complication is inmaking the connections to the testcrystals. One approach is to use severalfront panel mounted crystal holderswired in parallel in the SKI position.These should be of different types so thatany normal type of crystal will connect tothe unit via one or other of the holders(even wire ended types can normally beconnected to one of the holders wellenough to facilitate testing). Of course, ifyou only use crystals with one type ofbase, a single holder will suffice. Anotherapproach is to use two short leadsterminated with small crocodile clipswhich fit onto the pins or leadout wires oftest components.
39
by Mike Wharton
The last article in this series men-tioned the Z-80 based CPUmodule design published in theMaplin Magazine issue 15 as thebasis for some practical exp-
erimentation. We shall begin thereforewith a brief explanation of this circuit(See Figure 1), since it represents auseful means of microprocessor exp-erimentation.
MicroprocessorBased Systems
First, it is useful to look at thesimilarities between this design and thecrude model of a system shown in Figure2. At first sight, the two may seemcompletely un-related, but there aresome important similarities which can bepointed out. Both have such features as aData bus, Address bus and Control bus.For the Z-80 the data bus is 8 bits wideand the address bus 16 bits wide. The Z-80 control bus consists essentially of fourlines, MEMREQ, LOREQ, READ andWRITE, rather than just a single READ/WRITE line used in the model. There areother signals used by the processor forcontrol purposes, such as BUSAK andMl, but we shall leave these alone for thetime being. The main purpose of each ofthese is as follows: -
1. MEMREQ - This is an active lowsignal, as indeed are the others in thisgroup, which is asserted to indicate thatthe address bus contains a valid address.
2. FOREQ -A feature of the Z-80 isthat it has a separate 110 space, apartfrom the main 64K of memory. It is theintention for this to be used to contain allthe peripheral devices with which theprocessor needs to communicate. Thisline is asserted low to indicate that thebottom eight address lines contain a validaddress for an I/0 port.
3. READ - This is asserted low toindicate that the processor is able toaccept data from a memory location or40
A Beginner's Guide To Logic Design.
input device.4. WRITE - Similar to read, this is
used to indicate that the data buscontains valid data for sending to aselected device.
In some so-called minimum systems,the L 0 line may be left unused, but sinceit is a feature of the Z-80 it seems worthyof further explanation.
Memory MapsWe have seen memory maps in
previous articles. These are notionalmaps and simply represent the totalamount of memory and LO space whichthe processor is capable of addressing.In any real system physical memory, or110 ports, may only occupy a portion ofthe total available. The particular featureof the Z-80, not shared by other 8 bitdevices such as the 6502, is the existenceof this separate I/O space. This could beshown as a smaller map alongside themain memory map. The usual function ofthis space is to act as 256 individual'ports'. That is, addressable locations towhich peripheral devices may beconnected to the buses via suitablehardware, like latches or buffers. Ofcourse, such devices could be containedwithin the main memory map when theyare referred to as being memorymapped 110 devices. This is unavoidablewith some processors, but with the Z-80,they can all be put neatly in their own I/0space, leaving the 64K of main memoryuncluttered. This produces the minorproblem of how to distinguish betweenthe first 256 bytes of memory and the I/0ports, since they both share a commonaddress bus. This, of course, is achievedby the inclusion of the I/OREQ line in theaddress decoding. Thus: -
To READ from memory location100D, then the address bus would contain0064H (= 100D), the READ line low andMEMREQ low, but with I/OREQ high.
To READ from Port 100D, then again
Part Ten
the address bus will contain 0064H,READ line low, but this time with I/OREQlow and MEMREQ remaining high.
Stored ProgramWe can now look at the operation of
the micro -based module, and explain thesignificance of some of the other signallines present. Perhaps at this stage, it isworth reminding the novices there reallyis nothing magical about a micro-processor! A Z-80, a fairly simple deviceby present day standards, could be madeup from discrete logic gates, along thelines that we have been looking at overthe past articles in the series. It would bea rather pointless exercise, since it is thegreat advantage of VLSI technology thathas allowed such circuitry to be'compressed' onto a single chip.
The main function of the micro is towork through a set of instructions, the'program', rather like someone followinga recipe in a cook -book. The programconsists of specific instructions which theprocessor understands, and it resides inmemory. Without such a program, thehardware can do precisely nothing, nomatter how sophisticated it may be. Thisleads us to something of a paradox, forwith any home computer one wouldexpect to enter the program from thekeyboard or perhaps a cassette or diskunit. However, the machine must alreadycontain an operational program in orderto make any sense of such attempts atdata entry.
Such a program, often referred to asthe Operating System, would need toreside in a ROM as part of the wholemachine, ready to spring into action assoon as the power is turned on. Themodule under discussion has space forboth ROM and RAM, but as yet, noprogram to act as an Operating System.
The idea here then, would be towrite some suitable controlling softwareon another machine, transfer this when
Maplin Magazine March 1986
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debugged into an EPROM, and plug thisinto the target system. Likewise, in orderfor the module to do anything useful,there is still a need for some means ofcommunicating with it, and also, someway in which it can deliver the results ofits working.
The Maplin module can be fittedwith a special type of peripheral device,namely the Intel 8279. This has the abilityto be interfaced with a simple keyboardfor data entry and a 7 -segment LEDdisplay for data output. This wouldrequire a controlling routine as part ofthe operating system to allow suitabledata to be entered into RAM, or to modifythe contents of RAM in order for furtherprograms to be written and executed.This would then make it possible for themodule to act as, say, a micro -basedcontroller for such applications asregulating the central heating, stageMarch 1986 Maplin Magazine
"Address decoding
Clock
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Figure 2. Simplified Microprocessor Continued on page 47.41
Computer MusicProjectsby R.A. PenfoldComputers have been the majorcontributory factor to the informationrevolution and increasingly fantasticarcade games, but outside of therealms of business and games theyhave had limited impact as yet.However, one exception is in the areaof electronic music instruments andeffects machines, which have trans-formed out of all recognition in recentyears with the introduction of evermore specialised digital circuitry. Apartfrom gaining digital accuracy, suchinstruments now lend themselves todirect computer control, especially nowthat the MIDI (Musical InstrumentDigital Interlace) system is now fastbecoming an established standard,with increasing availability.
Computer MusicProjects
This book will show some of the waysin which a home computer can be usedto good effect in electronic musicgeneration and control, and includessequencing and control via analoguechannels, use of computers as digitaldelay lines and sound generators forcomputer control. Everything has beenkept as simple and jargon free aspossible, but it is assumed that thereader has some knowledge andexperience of computer software andable to construct some simpleelectronic projects.1985. 178 x 110mm.96 pages. illustrated.Order As WP38R (Computer MusicProjects) Price £2.95NV
How to Get YourComputer ProgramsRunningby J.W. PenfoldFor those inexperienced in programm-ing in BASIC, finding the exact causeof an error or a bug in the program canbe a problem even when help is givenby the computer with error messages,the exact meaning of which areexplained to a point by the manual.This is especially true where BASICprograms are copied from listingspublished in books and magazines,and have to be adapted because they
New looksHow to Get YourComputer ProgramsRunning
W WIOOLD
were written for a different machine. Ifthe BASIC is a fundamental version(not an advanced version with featurespeculiar to one machine), this is not toodifficult, but some translation isnecessary, and along with theinevitable typing error there are nearlyalways a few errors which needlocating and correcting before theprogram will RUN without stopping.The purpose of this book is to teachyou firstly how to identify errors inprograms and to understand errormessages, and secondly how tocorrect those errors. Some advice isalso given on how to write programs ina way which will make error tracingsimpler and correction easier.The book only deals with programswritten in BASIC, but most of the majordialects of the language. as used bypopular home computers, are covered.1985. 179 x 112mm.84 pages. illustrated.Order As WP37S (How to Get ProgsRunning) Price £2.50NV
The LinCMOSDesign Manualby David P.E. DaleLinCMOS is the latest in deviceintegration technology following onfrom CMOS logic. In a similar manner,LinCMOS offers much reduced powerdissipation and supply current con-sumption, and is therefore ideal forremote, battery and solar poweredapplications. The TLC series devices
The LinCMODesign
anu.al
described in this manual haveselectable bias adjustment so as toobtain the best compromise betweensupply consumption and throughputfrequency.The manual lists the TLC single, dualand quad op -amps, comparators andtimers. Also included are copious notesand application examples with dia-grams, which include oscillators. activefilter designs, sampling and signalrectifier circuits, amplifiers and voltageregulators. Fully documented datasheets are also included.1985. 210 x 148mm.212 pages. illustrated.Order As WP35Q (LinCMOS DesignManual) Price £5.60NV
Digital ICEquivalentsand PinConnections
Digital IC Equivalentsand Pin Connectionsby Adrian MichaelsShows the equivalents and pinconnections for the most popular digitaland logic integrated circuits. The bookis divided into two parts: the first partconsisting of the equivalents tableswith the European. American andJapanese type numbers listed for anylogic device, including details ofpackaging, the families. functions,manufacturer and country of origin.The listings incorporate a crossreference for the second section, whichshows all the pin -outs diagrams for thedifferent case styles and includesinternal schematic diagrams.1985. 265 x 194mm.312 pages. illustrated.Order As WP39N (Digital IC Equiv-alents) Price £4.95NV
Linear IC Equivalentsand Pin Connectionsby Adrian MichaelsShows the equivalents and pinconnections for a popular user -oriented selection of linear integratedcircuits. The first section of the bookcontains the equivalents tables show-ing the European, American andJapanese type numbers for any onedevice, along with the country of originand a manufacturers guide. The
Linear ICEquivalentsand PinConnections
listings incorporate a cross referencefor the second section, showing all thepin -outs diagrams for the different casestyles and includes internal schematicdiagrams. This latter provision makesfor a very useful source of data shouldyou wish to choose an IC for aparticular application.1985. 265 x 194mm.246 pages, illustrated.Order As WP4OT (Linear IC Equiv-alents) Price £4.95NV
Cost -EffectiveElectronicConstructionby John WatsonOriginally printed under the title 'Cost -Effective Projects around the Home,'this revised edition contains 26detailed projects with full circuitdescription including infra -red burglaralarm, automatic porch -light switch,feedback drill speed controller,freezer boiler alarm, computer I/O port,light dimmer, automatic TV switch -off,xenon strobe. and many more inaddition to many simple but usefulbuilding block type circuits. One majorproject is for a complete multi -channelradio control system, using linear andCMOS ICs wherever possible forcompactness.1985. 215 x 137mm.142 pages. illustrated.Order As XW3OH (Cost EffectiveElec) Price £5.95NV
42 Maplin Magazine March 1986
Projects inMicroelectronicsby D.L. ThompsonTwenty-six projects originally intendedto provide practical hands-on exper-ience of electronics hardware, for bothGCE electronics and physics coursesand technology courses in colleges,but they could also be invaluable asexercises for anyone about toundertake electronics as a hobby.Various 'diciplines' of the subject areexplained, together with a guide forgood soldering, and descriptions ofmost of the components regularly usedin the projects. The projects are dividedinto two main levels of aptitude: thereader can proceed onto the 'harder'projects once he she has becomepracticed at construction and trouble-shooting.
Many of the projects will form usefulmodules for the furtherance of thehobby, such as test oscillators, a digitalcounter, a voltmeter input buffer,supply voltage dividers for OV tap forop -amp circuits and other powersupplies. Other projects include lightmeters, single transistor and single ICradios, audio power amplifier, temp-erature controller. LCD thermometer,electronic combination lock.1985. 247 x 188mm.72 pages. illustrated.
Order As WP41U (Prof in MicroElectronics) Price £4.95NV
Projects forthe Car and Garageby Graham BishopThis is the 1985 revised edition of thispopular book, containing more than 30projects for the car owner, fullydocumented with constructionaldetails, circuit diagrams, circuit boardlayout and installation recommenda-tions. The projects are divided into thefive main areas of ignition. anti -theftand security, lighting, accessories andtest gear for the garage workshop.For those who do not have it fitted asstandard already. the first sectiondescribes a complete Capacitive -Discharge Ignition (CDI) system whichrequires no irreversible 'conversions'of your standard contact breakersystem, yet it offers higher energysparking for less supply current fromthe battery and is invaluable for winterstarting. Various useful extras are
included such as an ignition timing lightand a dwell meter.Other useful add-on projects includedare lights -on reminders. lamp failureindicators, rev -counter, wiper delay.digital car clock, emergency beacon.car radio add-ons and many more,1985. 215 x 137mm.115 pages. illustrated.Order As XW31J (Projects for theCar and Garage) Price £4.95NV
International RadioStations GuideA fully revised and updated edition ofan earlier publication. "Radio StationsGuide", which includes as much up-to-date information as possible. eliminat-ing that which is no longer current oraccurate. It is presented in a most
il±(1).,/ il.Ariti,tf1. (1) Loudspeaker Enclosure Design and
Construction. (WM82D) Cat. P52.2. (2) Remote Control Projects, by Owen
Bishop. (XW39N) Cat. P50.3. (5) Power Supply Projects, by R.A.
Penfold. (XW52G) Cat. P49.4. (4) International Transistor Equivalents
Guide, by Adrian Michaels. (WG30H)Cat. P45.
5. (3) Mastering Electronics, by JohnWatson. (WM600) Cat. P48.
6. (11) IC555 Projects, by E.A. Parr. (LY04E)Cat. P51.
7. (9) How to Design and Make Your OwnPCB's, by A.A. Penfold. (WK63T)Cat. P48.
8. (17) Electronic Synthesiser Projects, byM. K. Berry. (XW68Y) Cat. P53.
9. (15) A Z80 Workshop Manual, by E.A.Parr. (WA54J) Cat. P59.
10. (13) Audio Amplifier Construction, by R.A. Penfold. (WM31J) Cat. P52.
11. (8) Radio Control for Beginners, by F.G.Rayer. (XW66W) Cat. P50.
12. (-) Electronic Music Projects, by A.A.Penfold. (XW40T) Cat. P53.
13. (19) Counter Driver & Numeral DisplayProjects, by F.G. Rayer.(XW34M) Cat. P52.
14. (20) Micro Interfacing Circuits Book 1,by A.A. Penfold. (WM79L) Cat. P57.
15. (-) How to Get Your Electronic ProjectsWorking, by A.A. Penfold.(WA53H) Cat. P48.
readable way, and includes in many ofthe tables the town and country inwhich the radio station's transmitter issited. The transmission frequency inkHz MHz and or wavelength in metres,plus the ERP in kW is listed.The book is divided into nine sections:European Long Wave stations: Euro-pean. Near East and North AfricaMedium Wave: World Wide ShortWave: Broadcast Band USA: Broad-cast Band Canada: Broadcast Bandstations in Latin America and theCaribbean: programmes in Englishwith transmission times: and UK localradio. Also includes wavelength freq-uency conversion formula?.1985. 178 x 112mm. 126 pages.Order As WP36P (Int Radio StationsGuide) Price £2.95NV
internationalRadio StationsGuide
16. (-) An Introduction to Programming theAtari 600/800XL, by R.A. and J.W.Penfold. (WM80B) Cat. P63.
17. (-) 30 Solderless Breadboard ProjectsBook 1, by R. A. Penfold. (WA51F)Cat. P48.
18. (-) Audio Projects, by F.G. Rayer.(WG46A) Cat. P52.
19. (6) How to Use Op -amps, by E.A.Parr.(WA29G) Cat. P47.
20. (-) Electronic Household Projects,by A.A. Penfold.(XW44X) Cat. P49.
These are our top twenty best sellingbooks based on mail order and shop salesduring October, November and December1985. Our own magazines and publications arenot included. The Maplin order code of eachbook is shown together with page numbers forour 1986 catalogue. We stock over 500different titles, covering a wide range of elec-tronics and computing topics.
March 1986 Maplin Magazine 43
MACHINE CODEPROGRAMMING WITH THE Z80
by Graham Dixey C.Eng., M.I.E.R.E. Part Two
Assembler Format andMachine Code
These two formats are known as 'lowlevel' languages, as compared with a'high level' language such as BASIC. Thisis because they work right down atmachine level, or very nearly. The Z80works solely in binary numbers, as doesany other processor, but for a humanbeing to be constantly handling longstrings of is and Os is asking rather toomuch. Consequently, what is needed issome form of 'interface' (using the term inits broadest sense), which is essentiallywhat a computer language is. BASIC, toquote the best known example, makeslife very easy because of its relation toeveryday English; furthermore, it allowsa user to communicate with the computerwithout actually knowing anything aboutthe way in which the machine works. But,because of its interpretive nature, it isslow. A knowledge of machine basicsplus the ability to program at low levelgives one a much greater degree of con-trol, leading to increased speed andefficiency. It is also very rewardingintellectually. Now consider the followingline.
BEGIN LD A, (HL) Get value &003A 7E
For new programmers this intro-duces some very important ideas. In thisline an instruction has first been writtenin assembler, and then in the cor-responding machine code. What are theconstituent parts of this line?BEGIN...
From left to right, we first have theword BEGIN: this is known as a 'label',because it labels the program line with aspecific function, a rather obvious one inthis case - the start of the program. Notall lines need labels as will be seen, butfor those that do it performs a valuablefunction. A label is also often called a'symbolic address'....LD A, (HL)...
Next is found LD A, (HL). This isknown as a 'mnemonic' instruction, whichin this case means 'load the A registerwith the data found in a memory location44
pointed to by the contents of the HLregister pair'. If this conveys nothingmuch else, then it should illustrate howsuccinct mnemonics are at getting themessage across, once you know whatthey mean! In an instruction of this type,A is said to be the 'destination' and (HL)the 'source', an order that must beadhered to....Get Value...
The words 'Get value' form a'comment', which states what the line isintended to achieve; they should be usedliberally as they help everyone to under-stand later how the program worked, andif it didn't, they are then useful when itcomes to debugging.
This completes the assembler ver-sion of the line. What follows is itsmachine code equivalent....&003A 7E
The two -byte HEX number &003A isa memory address and defines the loca-tion where the associated load instruc-tion is stored. The ampersand (&) is aconvention that reminds us that 003A is inHEX. It could hardly be anything else, butI think you'll agree that the number 5100could be denary (or even octal!), where-as if we put &5100, there's no doubt thatit's HEX. Leave the ampersand out if youwish, but beware of the chance of amb-iguities. Where it will invariably have tobe included is when using assemblersoftware, since it is a means of instruct-ing the assembler that a HEX number isbeing used. In a machine code programlisting it's not really necessary to includeit since machine code is always in HEXanyway, whether generated by anassembler or produced the hard way, byhand encoding from tables.
The single -byte HEX number 7Efollowing the address is called an 'op -code', and is the machine code version ofLD A, (HL). It is the means by which theZ80 knows exactly what is expected of it.Obviously, the right op -code must betaken from the tables; there is no roomfor error, none whatever. Why not checknow from the table of 8 -bit loads in PartOne that 7E is the correct op -code? If youcan't see why at the moment, don't worry
as all the tables will be explained andused as the series develops.
Algorithms andFlowcharts
An algorithm is a step-by-stepprocedure, defining the solution of aproblem. Algorithms may be quite trivialor very elaborate. To take an example,suppose we have ten keys, only one ofwhich will open a certain door, but wedon't know which one. The procedure isso obvious that we don't consciouslythink of the individual steps. But, to solvecomputer problems, we have to be ableto develop the ability to see the solutionas a series of steps. And, because acomputer is a complete idiot, each stepmust be explicit and none can be left out.
So the algorithm for finding the rightkey is:
Try first key; does it fit?No! Try second key; does it fit?No! Try third key; does it fit?And so on for ten keys.This is not a very elegant form for
the algorithm. Writing it in the form of anIF THEN procedure would be muchbetter, as follows.
Try a keyIF: this key doesn't fit,THEN: try the next one.
This is actually a looping procedurethough the algorithm hasn't expresslyhighlighted the fact. What will make thisobvious is a 'flowchart'; see Figure 1.
Figure 1. Flowchart for simple loopingprogram
Maplin Magazine March 1986
A picture conveys a thousandwords, or so they say. That may be anexaggeration, but the flowchart doesquite clearly show the repeated opera-tion of trying a key until one that fits isfound. The loop is formed automaticallyby the NO output of the 'decisiondiamond'; the rectangle contains a state-ment of an operation to be executed.
Figure 2 shows another flowchart,which has more to do with computingthan the previous example. The keys Zand X on the computer keyboard areused to control the lateral position ofsome on -screen object, such that Z = leftand X = right. Though this flowchartdoesn't show all the program details, it isas complete as it needs to be to illustratethe way in which a series of questionsdetermines the ultimate action. The firstdiamond describes a common pro-cedure for scanning a keyboard. Theprogram loops endlessly until it finds thata key has been pressed. It then askswhether the key is Z. If it is, the object isdriven left; if not it asks if it is X, in whichcase a positive answer drives the objectright. If it is neither Z nor X (we all makemistakes!) it doesn't need to ask what itis; it just goes back to the beginning andwaits for you to get it right.
Layout of ProgramIt is important that the program is
written down in a logical manner. Mostprograms of any size need some debugg-ing or modification, and it is much easierto do it if the program isn't just acollection of scribbled, random jottings.Whether you design a custom programsheet or just use plain paper doesn'tmatter at all. What is important is that thedevelopment of the program is clearlyseen. Some programmers lay out theirprograms with the machine code on theleft side of the sheet and the assemblerversion on the right. Not being aninscrutable oriental, I prefer to work fromleft to right, putting down the sourceprogram first (i.e, the assembler code)and then the object program (themachine code). In fact, the logicalprocedure must involve writing down theprogram in mnemonic form and thenencoding it into machine code whenfairly confident that it ought to work. Youcan rule up actual columns or just visual-ise them mentally. You will need to allowfor the following:
Assembler:LABEL MNEMONIC OPERAND COMMENTS
Machine Code:
PC OP -CODE BYTES 2; 3: 4
In the machine code part, PCrepresents the program counter, that is,the addresses in turn at which theprogram is stored. The op -code plusbytes 2, 3 and 4 will be filled dependingupon the addressing mode used. Some-times only the op -code column is used,sometimes all four. Two examples illus-trate this.March 1986 Maplin Magazine
Figure 2. Flowchart for key -press routine
FRED EX * Exchange AF -AP contents
001F 08
(* no operand required since this is'implied addressing mode'; hence onlythe op -code byte in the machine codeversion if filled)
FRED is a label to identify the line(for example if we need to jump to it fromsomewhere else in the program). Youcan use what names you like for labelsbut it is generally better to choose aname that has some relevance to whatthe program is doing at that point, e.g.LOOP1, START, etc.
GET LD B, (IY + d) Load B register with data&031E FD 46 OA
This program line looks more com-plex but is, in fact, just an 8 -bit load, i.e.the B register is being loaded with asingle byte; that is the LD B part of themnemonic. Where the byte is comingfrom is indicated by (IY + d) whichmeans that the byte is found at a memorylocation whose address is equal to thecontents of index register IY, plus anumber 'd' (known as a signed displace-ment since it can be positive or negative).For example, if IY held &0140 and 'd'was &OA, then the address for the datawould be &0140 + &OA = &014A.Because the addressing mode is that bitmore complex it needs more bytes inmachine code to express it, hence FD 46OA. These will be found in the table of 8 -bit loads at the intersection of SOURCE =(IY + d) and DESTINATION = B register.
Comments in the assembler prog-ram are invaluable. They play the samepart as REM statements in BASIC, withthe exception that they are not actuallyentered into memory. They just remindyou why you wrote a certain line. Theyshould, therefore, be explicit but not toowordy.
The points just discussed are con-cerned with an approach to programm-ing, preparation being half the battle. Thefull instruction set has been given in PanOne, together with a brief description ofthe Z80 addressing modes. In eachsubsequent part of this series, some timewill be spent on discussing some of the
Z80 instructions, and the rest of the timeon programming and applications.When, eventually, all instructions havebeen discussed all the space will bedevoted to using the Z80 by discussingboth software and hardware design for avariety of uses. It will be useful to spendsome time now on looking at the Z80'load' instructions before going on tosome real programming.
The 8 -bit and16 -bit Loads
The Z80 can handle data 8 bits or 16bits at a time with the use of theappropriate instructions. This doesn'tmake it a 16 -bit processor of course,because the data bus is only 8 bits wide.So the data is still sent a single byte at atime. It just makes programming that bitmore efficient. The load instructions arefound in Tables 1 and 2 of Part One.
For 8 -bit loads the form used is:
LD destination, sourcewhere LD is an obvious mnemonic forLOAD.
Taking an example from Table 1, aprogram line in assembler might read:LD A. H
which means 'load the A registerwith the contents of the H register'. It isobvious that this could also be called a'transfer' instruction, since a transfer ofdata is taking place from one register toanother. This compares with LD A, #nwhich means 'load the A register with thenumber n'. Obviously, this is a straight-forward load and not a transfer of data.
In the first case register addressingis being used, and the op -code is 7C,while in the second case, immediateaddressing is being used and the op -code is 3E followed by a byte specifyingthe value of n. Check these by referringto Table 1.
The 16 -bit loads cause data transfersto take place between register pairs andadjacent pairs of memory locations. Forexample, the contents of the AF registerpair could be loaded from the memorylocations 001A and 001B, or vice -versa.There are no 'store' instructions with theZ80; these are merely loads going theopposite way, from the processor tomemory. The register pairs can also beloaded with data directly e.g. LD AF, #nnloads the AF register pair with the twobyte number nn in what is called the'immediate extended addressing mode'.
As an example of a 16 -bit datatransfer, take the mnemonic LD BC, (nn).In this case, known as 'extended add-ressing', (nn) is an address where a byteof data will be found; this byte getsloaded into register C. The next address,(nn + 1) contains a byte of data that getsloaded into register B. Compare this withthe 16 -bit load in the previous paragraph,where the data to be loaded into theregister pair (AF in the example) is
45
specified immediately. As an example ofLD BC, (nn), consider the machine codeED 4B 50 OD. The ED 4B part is takenfrom Table 2 and means 'load the BCregister pair in extended addressingmode', and the part 50 OD is the (nn) partand means 'the data will be found inmemory locations 005D and 005E (since005D + 1 = 005E)'.
Push and pop are just special typesof load associated with 'stack' operations,which were explained briefly in PartOne. There is no significant differencebetween these loads and any other 16 -bitload, only in the application and in themnemonics, of course. Examples are:
PUSH BC (Push contents of registerpair BC onto stack)(Pop contents of register pairHL from stack).
That will be enough discussion ofZ80 instructions for now. Let's do a bit ofprogramming and learn some moreinstructions that way.
POP HL
Bubble Sort ProgramIt is often necessary to be able to re-
arrange the elements of a table into anumerical sequence that gives increas-ing values from the top to the bottom ofthe table, or vice -versa. In a 'bubble -sort'program, the smallest elements 'bubbleup' (or down!) from one end of the tableto the other. To do this, each value of thetable is examined relative to the one justabove (or below) it, and an exchangemade, or not made, depending upontheir relative values. Successive pairs ofvalues are compared in this way and,when all adjacent values have beencompared with their neighbours, a single`pass' is said to have been made. In alarge table a fair number of passes willhave to be made in order to complete thesort.
Design of the ProgramThink it out as fully as possible at this
stage. Don't be tempted into trying towrite a program from a mental outline.Sketch a flowchart to illustrate the steps,then use it with a 'dry run' to prove itsvalidity. This establishes the basic ideasand highlights some of the specificproblems that will have to be solved. Theflowchart is shown in Figure 3.
For example, it is obvious that thenumbers in the table are stored inmemory, in consecutive locations. Whenthe contents of two locations have to beexchanged, how can this be done? Arethere special instructions to do it? Thereare some exchange instructions in theZ80 set but, unfortunately, they cannot beused on memory locations, only oncertain registers and the stack. Figure 4shows what can and cannot be done.
Specifically, 4(a) shows that a directexchange is impossible for two reasons.These are, first, that no relevantexchange instruction exists as statedalready, and secondly, that moving the46
Figure 3. flowchart for bubble sort program
number B into A's location will cause A tobe over -written and so lost. Therefore,4(b) shows the use of a third party, in amanner of speaking, a memory locationcalled TEMP, whose function is topreserve one of the values while theother is being moved. Thus, the seq-uence for an exchange of the twonumbers A and B would be: move A intoTEMP; move B into A; move TEMP into B.Because of the rotation used in this tech-nique, it is known as a 'circular permuta-tion'.
The bubble sort idea is very easilydemonstrated by taking a short list (sincethe length of the list has no bearing on theprinciple) and seeing how each passsuccessively sorts out the numericalorder.
Figure 4. The right and wrong way ofexchanging data
Initial Second Third Fourth
state state state state
16 16 16 16?
8 8 8? 2?
20 20? 2? 8
3? 2? 20 20
2? 3 3 3
3>2; 20>2; 8>2; 16>2;
Exchange Exchange Exchange Exchange
This completes the first pass; noticehow the 2 has bubbled up; at thebeginning of the second pass it will be atthe top, since we have just exchanged itwith the 16. Now for the second pass.
Fifth
state
Sixth
state
Seventh
state
Eighth
state
2 2 2 2?
16 16 16? 3?
8 8? 3? 16
20? 3? 8 8
3? 20 20 20
20>3; 8>3; 16>3; 2<3;Exchange Exchange Exchange No Change
This completes the second pass andthis should be enough to convince youthat, on the third pass, the sort will becomplete when the 16 and the 8 changeplaces. However, although we can seefrom a diagram that the sort is complete,the program must be able, in some way,to deduce this fact also, otherwise it won'tknow when to stop. This can be done byusing a 'flag' which is set whenever anexchange is carried out during a pass.Then if this flag is reset at the start ofevery pass, the completion of the sort canbe determined by testing the flag to seeif, after a complete pass through thetable, no exchanges have taken place.
So what operations are going to becarried out in the bubble sort program?From the above discussions there arethree basic types of operation.
a) transfers between registers andmemory (the exchanges)
b) comparisons between numbers (tofind if an exchange is required)
c) testing of a flag (to establish whethersort is complete)
It will also be necessary to set up acounter and decrement it regularly inorder to find when a pass is complete.Thus, the initial value of the counter willbe equal to the number of elements in thetable less one and it will reach zero whenall values have been compared.
The Program inAssembler Format
The following registers will be used:A; B (TEMP); C (COUNTER); IX (access-ing the elements in the table). The tablewill be located in RAM in successivelocations, the lowest element at thelowest address. Bit 0 in the D register isthe 'exchange flag.'
Maplin Magazine March 1986
LABELAGAIN:
MNEMONIC OPERANDLD C,n
DEC
LD IX, BASE
RES O,D
GET: LD A,(IX + 00)
CP (IX -f- 01)
JP M,SWAP
INC IX
DECC: DEC
JR
JP
SWAP: LD
COMMENTS
Get number ofelements n
Set counterto n-1Loads bottomaddress oflist into IXExchangeflag = 0Get currentelement
Compare withnext elementIf larger thenexchangeSet up addr-ess of nextelement
Decrementcounter
Z,FTEST
GET
B, (IX + 01) Load TEMPwith NEXTelement
LD (IX + 01),A Load NEXTwithCURRENT
element
LD (IX + 00),B LoadCURRENTwith NEXTelement
SET O,D Record ex-change hasoccurred
INC
JP
FTEST: BIT
END:
IX
DECC
O,D
JR NZ,AGAIN
Is exchangeflag = 1?If yes, goround again
This short program will need a bit ofstudy before it is fully understood. Thebest way to do this is to compare it withthe flow chart to see how the blocks onthe latter have been implemented by theassembler program. Then, when youhave a rough idea of it, do a dry run. On asheet of paper sketch blocks thatrepresent the registers used, includingthe flag. Let them all contain zero to startwith; also draw a few memory locations,say five, and fill in the numbers to besorted in them. Then go through theprogram line by line entering the datainto the registers, swapping the data andsetting and resetting the flag until youexit from the program. It doesn't takethat long to do if only a small amount ofdata is used, but a lot can be learnt bythis procedure. Anyway, it is what shouldbe done when designing programsbecause it quickly shows up the bugs.You shouldn't find any in this particularprogram, though you may well make afew mistakes before you get a clean runthrough.
There are two conditional jumps, JPM,SWAP, which means jump to labelSWAP if the result of the previousoperation is Minus', and JR Z,FTEST,which means jump to label FTEST if theresult of the previous operation is Zero'.Incidentally, JP uses the 'immediateextended' addressing mode and JR the'relative' addressing mode. It will be aswell to refer back to Part One now unlessyou are fully acquainted with thesemodes, since the op -codes are depend-ent upon the mode used. The machinecode, line for line, equivalent will now be
given. If you feel like trying your skills,why not assemble the above programinto machine code by yourself first; thencheck it against my program. Again, it isthe sort of exercise that will teach you alot.
In the following program, the num-ber of elements, n, is assumed to be 5and the base address (lowest address oftable) is &0500. The program has beenlocated starting at &0000 but this choiceis an arbitrary one. Remember that whenaddresses are used as operands inmachine code, they are specified 'lowbyte first'. Thus, &0500 appears as 00 05and not as 05 00!
ProgramCounter Op -code Byte 2 Byte 3 Byte 4
0000 OE 050002 OD
0003 DD 21 00 050007 CB 82
0009 DD 7E 00
000C DD BE 01
000F FA 1A 00
0012 DD 23
0014 OD
0015 2B 13
0017 C3 09 00001A DD 46 01
001D DD 77 01
0020 DD 70 00
0023 CB C20025 DD 230027 C3 14 00002A CB 42
002C 20 D2
Machine code program for bubble sort
FIRST BASE Continued from page 41.
lighting, simple machinery or such -like.This 'chicken -and -egg' problem canreally only be resolved by access toother programming equipment; one suchpiece of equipment is the so-calledMicroprocessor Development System, orsimply MDS. These are not really withinthe scope of the home computerenthusiast, since they cost severalthousand pounds! However, this wouldenable the requisite software to bewritten and debugged very quickly forthe intended task of the module. The waythis is achieved is to replace theprocessor in the module, or the 'target'system, with a special plug connecting tothe 'host'. By this means the operation ofall aspects of the target system can becontrolled, or emulated, by the hostmachine. This would also containsufficient memory for software to bewritten and debugged using sophisti-cated programming aids, and then allowthe program to be run in the targetsystem, but with the host keeping fullcontrol of its execution. With such a toolat ones disposal, complex programs canbe produced relatively quickly, and theperformance of the target monitored atall times. As a final stage, the finishedMarch 1986 Maplin Magazine
program can be 'burned' into an EPROM,and then transferred to the target so itcan operate as a stand-alone system.
Another slightly more simplemethod is to do a similar thing with theROM resident in the target system. thisthen allows the program to be writtenand stored in RAM in a machine oftencalled a Romulator. The target systemhas access to this RAM, which 'looks' likethe operating system which wouldnormally be in ROM. The romulator hasthe ability to modify the RAM contents,and hence its effect on the operation ofthe target can be observed. The controlof the target is by no means as total aswith the MDS, but this is reflected in thelower cost of such a system.
First Base - Last BaseThis short discussion on the
principles of microprocessor operationbrings to an end this series of First Base.During its course, we have looked at
some of the aspects of digital electronics,and have of necessity left out a lot more.Hopefully, it may have stimulated someinto enquiring further into this fascinatingsubject. and may have encouraged you tohave a go at some construction orexperimentation. If you have followed theseries this far, then the whole world ofthe microprocessor lies stretched outbefore you, with all manner of delights instore! From now on, the rest is up to youwith, perhaps, a little help from Maplin.
47
by Mark Brighton
properly charging sealed lead -acid batteries is very importantfor long trouble free batteryservice. The circuit shown inFigure 1 is capable of quickly
and safely charging lead -acid batteries,and features temperature compensationin addition to two charging levels (withautomatic switchover).
Circuit DescriptionTemperature compensation in a
charger is important to prevent over-charging, especially if the battery issubjected to wide temperature varia-tions. A temperature coefficient of--5mVPC/cell at the output of the chargeris provided by ICI, a current modetemperature sensor which is eitherlocated near the battery, or if highcharging currents are involved, it couldbe attached directly to the battery.
The two-step charging featureprovides a higher initial charging voltage
* 4V, 6V 8112V Settings* Two Step Charging* Simple Construction
Fuse1Amp
TOr Red
240VAC
MainsYel
Blu
Grey
BR1PW06
+ yin Regi
011N4001
+ +C2o 100uF
63V ti 2.3mA2200uF
Regulator
Vin Vout
Adj
RI0.22R
LM338 R23R3
R16470R
R17560R
R5
1k5
4V
Temp,sensor
TITemp.compensationj
R41k
6V
18mV
3WR18
0.22R3W
R3R6 22OR2 k2
/R72k7 /
LED 1CHARGE
12V / -/- R13S1 / 4k7R11 /1k5
/ R14
+ Re9.2
LM334
R1027R
( R81k5
R910OR
Two step charging feature
ICI
- I
J
Vout
FS13 AmpA/S
2,3 or 6- cells--Zr 14,6 or--are- 12V I
Lead AcidBattery
Figure 1. Circuit Diagram48 Maplin Magazine March 1986
er: tt_as
00
1154
GD13PLEAD BATT.
e CHARGER
F4-.d £1.00
ElaDBYHO11VB CIV31
0
UT- o)
a4,
cu2i. f- Q'R12
0
0 0NI1dYIN
0coL°_11;),, R9
_,.- 00000
Figure 2. PCB Layout and Legend
Twinscreened
cableHeat shrink sleeving
Red r315A
FS1iView I rom inside box
Red I
Red
Fuse 1 AIMainsi CO'
EnsureSLEEVE good Earth
These two Contact to box,
I
Brn. joints heatsink,LEDthen shrink, bezel & metal
fit manta
/ IMains inl
I
.....
G Y
Blue
J
Cover
Haatsink- Shake washer InsulzZt1411--F Reg .1 IShalosi
Illi24rAtaff / r., 41t ( /wiW IMPAIS .., Sleeve
' BdshInsulating
p. 1 i
® ®Red
SIf I+TapScrew(S) ®
Blue Y
R Grey BlackOr Or
0
T1
(9
PCB
Q
.............,........
fig3bS
+
1..--.
Knob
Chargerend
Knot or tape Cables &Wiresinside box adjacent grommets,to stop solder joints being torn
Red apart if wires are pulled from outside.
FITclips on
of wires
0 See fig 3bfor fitting Reg.2.to end of cable.
/I
\
1 V
3
I
6V
/ I
I
4V
I
/
SI
\\ \o LED1 LED2V\
Figure 3b. Fitting REG 2March 1986 Maplin Magazine
Figure 3a. Wiring Diagram49
Rear panel
3
113
38
25
23
\ Base
75 13
All six holes Inhestsink 6 box.
ileatsinkoutline
30
7111
5.51-
13 41
5
ToBox,
.Chassla
II
20
t
115
b 25
12.5
45 365 42.....__
yb
62
All Dimensions In mm
Holesa 025b 0 3.2
040 b
0520
0 8 0f 0100o 0127 .. 33 10
......231
..
L
Front panel
20 30
35
20
25
Top
ease
45
33
Figure 4. Box Drilling Details50
(2.5 Volts/cell (4 25°C) to rapidly bring adischarged battery up to near full charge.The amount of charging current isdetermined by the amount of chargeremaining in the battery and the currentlimit of the regulator, REG 1. As thebattery approaches a fully chargedcondition, the current begins todecrease. When it drops below apredetermined level (----- 180mA) thecharger's output voltage drops to a floatcondition voltage of 2.35 Volts/cell (#25°C, which maintains the battery in afully charged condition. This float voltageprevents the battery from becomingovercharged, which can seriouslyshorten its life.
R1/R18 and R2 determine the currentlevel when the charger switches from acharge mode to a float mode, while R8and R9 set the amount of voltage change.The LEDs indicate which mode thecharger is in (charge or float). Theamount of temperature compensation iscontrolled by the value of resistor RIO.
A unique feature of this charger isthat it provides the correct temperaturecoefficient and the correct amount ofcharge -mode voltage boost for each cell,regardless of the number of cells beingcharged.
ConstructionInsert all veropins from the track
side of the board (shown in Figure 2), andpush them home firmly with a solderingiron. Solder the pins into place. Nowinsert all resistors and capacitors, notingthe polarity of Cl, and solder thecomponent leads in place. Insert andsolder the IC socket, ensuring that theend notch is at the same end as the whitebar on the legend; then TR1, referring tothe legend for correct orientation. PlugIC2 into the DIL socket with the notch onthe IC aligned with the cutout on thesocket, and/or pin 1 (marked with a dot)adjacent to the '1' on the legend. Bolt REG
Maplin Magazine March 1986
I onto the heatsink, using the mountingkit provided. Referring to Figure 3, wire -up the pcb to Si, LED 1 and 2, IC1, andREG 1 respectively, and also thetransformer/ rectifier etc. Figure 4 showsdrilling details of a suggested case.
Testing and UseThe accuracy of a digital voltmeter is
really required here in order to carry outthe following procedure. Apply power tothe circuit and connect the digital volt -
LEAD ACID BATTERY CHARGERPARTS LISTRESISTORS: All 0.6W 1% Metal Film unless stated
FS1FS2
R1,18 0.22f1 3W 5% Wirewound 2 (W0.22)R2 3113 1 (M3R3)R3 220f) 1 (M220R)R4 lk Hor. S. Min. Preset 1 (WR55K) SiR6 2k2 Hor. S. Min. Preset 1 WR56L)R7 2k7 1 (M2K7)R8,5,11 1k5 3 (MIK5)R9 10011 1 (M100R)R10 2711 I (M27R)R13,14 4k7 2 (M4K7)R12,15 lk 2 (M 1K)R16 470fI Hor. S. Min. Preset 1 (WR54J)RI7 560fi 1 (M560R)
CAPACITORSCI 2200/1F 63V Can Electrolytic (FF22Y)C2 100/ff 63V Axial Electrolytic (FB51F)C3 100pF Ceramic (WX56L)
SEMICONDUCTORSTR I 2N3906 (QR42V)IC1 LM301A (QH36P)REG1 LM338K 1 (RA88V)REG2 LM334 (WQ32K)LED1 Chrome LED Large Red I (YY60())LED2 Chrome LED Large Green (QY47B)BR I PW06 Bridge Rectifier (WQ58N)DI 1N4001 (QL73Q)
MISCELLANEOUST1 Transformer Toroidal 80VA 18V 1 (YK17T)
March 1986 Maplin Magazine
meter across the output leads. Set Si to4V, and adjust R16 for a 4.5V output. SetSi to 6V, and adjust R4 for a 7.05Voutput. Set S1 to 12V, and adjust R6 for a14.1V output. Now connect the outputleads to a partially discharged lead -acidbattery, first selecting the appropriatevoltage setting at Si, and via a multimeterset to read current up to a minimum f.s.d.of 5A. Check the direction of currentflow, (if the battery is discharging, youhave a problem: re -check your wiring,etc). Under NO circumstances should thecurrent exceed 5A.
The red 'charge' LED should be onand should remain on until the chargecurrent falls below =180mA, at whichpoint the green 'float' LED should light,indicating that the charge cycle hasfinished and the charger is in tricklecharge mode.
Lastly, if the temperature sensor isheld between finger and thumb, thecharge current should start to drop,indicating that the temperature comp-ensation is functioning correctly.
NOTE: When using the charger, youshould ensure that correct polarity of thebattery connections is always observedand that prolonged short circuit of theoutput leads is avoided. It is also worthbearing in mind that if the mains supply isremoved from the charger whilst it isconnected to a battery, the battery willcommence to slowly discharge throughthe charger, so always disconnect thebattery before switching off at the mains.
Safuseholder 20Fuse 3.15A 20mm Anti-SUrgeFuse IA 20mmHeatsink 4YInsulator Kit T03Transistor CoverGrommet SmallTerminal Block 5ASwitch Rotary SW3BBlue Case 231Knob K7CP.C. BoardSpacer 6BA x Vain.Bolt 6BA x V2in.Nut 6BAWasher 6BATag 6BAWasher Shake 6BASelf Tap No. 6 x vein.Extra Flex BlackExtra Flex RedHeat Shrink Sleeving CP48Ribbon Cable 10 -WayLapped Twin Screened Cable3 Core Mains BlackCharger Clip
2 (RX96E)1 (RA 11M)1 (WR03D)1 (FL41U)1 (WR24B)1 (FL56L)2 (RW59P)1 (HFOIB)1 (FF76H)
(XY44X)1 (YX03D)1 (GD13P)1 pkt (FW33L)2 pkt (BFO6G)2 pkt (BF18U)1 pkt (BF22Y)1 plct (BF29G)1 pkt (BF26D)I pkt (BF67X)2 mtrs (XR40T)2 mtrs (XR44X)1 mtre (BF89W)I mtre (XR06G)2 mtrs (XR2OW)2 mtrs (XR01B)2 (HF2SD)
A complete kit of all parts is available for this project:Order As LMO1B (Lead Acid Battery Charger) Price £39.95
The following item in the above kit list is alsoavailable separately, but is not shown in the 1986 catalogue:
Lead Acid Battery Charger PCB Order As GD13P Price £1.75A ready built version of this project will be
available soon - check future issues for details.
51
PROJECTFAULT FINDING
by Robert Penfold Part 5
HOW TO USE YOUR OSCILLOSCOPE TO THE FULL
Oscilloscope TestingOscilloscopes tend to be regarded
by many (particularly those electronicsenthusiasts who do not have access toone) as a sort of panacea for the ills ofany faulty piece of electronics. This isperhaps rather a naive view, but anoscilloscope can certainly be aninvaluable aid which, when usedproperly, will help to rapidly locate mosttypes of fault. Apart from enablingwaveforms to be displayed, it can also beused for AC voltage measurements, andwith a suitably sensitive type it will alsofunction as an AC millivoltmeter.
Measurements must be in the formof peak, or peak -to -peak, readings,rather than the usual r.m.s. value - but fora sinewave test signal simply dividing by1.414 or 2.82 respectively gives thenecessary conversion. Measurementsmade with a properly calibrated osc-illoscope can be much more accuratethan many people seem to imagine.
A DC coupled oscilloscope can alsofunction as a high impedance DCvoltmeter. Most oscilloscopes have aninput impedance of 1 megohm, which isfar higher than that of the ordinarymultimeter switched to a low DC voltagerange. The input impedance can beboosted using a so called X10 probe, andthe input impedance is then about 10megohms. The 'XIO' name is not due tothe boost in input impedance, but due tothe sensitivity (in terms of volts perscreen division), being boosted by afactor of ten. This expression is a littlemisleading, since an increase by a factorof ten (from say, one volt per division toten volts per division) is obviously areduction in sensitivity and not anincrease. These probes are purelypassive devices, and apart from givingincreased input resistance they alsoprovide reduced input capacitance.
Low input capacitance is importantas this factor causes the input impedanceof the instrument to fall substantially athigh frequencies, giving increased load-ing on the circuit under investigation. Thegreater the input capacitance the more52
pronounced the fall in high frequencyinput impedance. Of course, the pricethat is paid for the boosted inputimpedance is a reduction in the max-imum sensitivity.
It is probably true to say that mostoscilloscopes receive more use formaking measurements than they do fordisplaying waveforms, but as we shallsee later, it is not only voltage that can bemeasured.
Scope OperationWe will not consider voltage testing
using an oscilloscope here, since it isessentially the same as testing using amultimeter, as covered in a previousarticle in this series. We will mainly beconcerned with waveform testing in this,the final Project Fault Finding article.Although an oscilloscope provides aneasy way of testing most pieces ofelectronic equipment, the importantpoint which has to be made is that it doesnot represent a short cut to fault findingfor the novice. Without a certain amountof technical expertise an oscilloscope isof little or no value as the user would beunable to glean worthwhile informationfrom the displayed waveforms. A certain
amount of background information isneeded in order to be able to operate anoscilloscope at all, and we will thereforestart with some general backgroundinformation on oscilloscope operation.
In principle an oscilloscope is afairly simple piece of equipment, anddespite the fact that most practicalinstruments are so packed with extrafeatures that they become highlycomplex, they all have the same basicfeatures. Figure 1 illustrates the basicmake-up of an oscilloscope.
A ramp generator feeds into the X(horizontal) amplifier and sweeps thespot across the face of the CRT (cathoderay tube) at a linear rate. The input signalis coupled to the Y (vertical) input, andprovided the sweep speed is suitable,one or more cycles of the inputwaveforms will be reproduced on thescreen. At slow sweep speeds the spotwill be clearly visible as such unless theoscilloscope is one of the few typeswhich has a long persistence CRT, butmostly the sweep speed will be quitehigh. The human eye is then unable tofollow the action properly, and the spotappears to be a line across the face of theCRT.
Maplin Magazine March 1986
Normally the spot is repeatedlyswept across the screen so that acontinous display of the input waveformis produced, but for this to work properlythe sweep generator must be sync-hronised to the input signal. Otherwisethe trace would not be stable and in mostcases would in fact just be a completeblur of lines. The most common way ofsynchronising the sweep generator is tohave each sweep commence at a certaininput voltage level. This ensures that thetrace always starts at the same point inthe waveform, and providing the wave-form is of a repetitive and unchangingtype, the rest of the trace will also beidentical on each sweep.
Most scopes offer a variety oftrigger options, with triggering onpositive or negative edges of the inputsignal, and a 'level' control so that theprecise trigger point can be adjusted.There are usually other options, such asautomatic synchronisation, externalsynchronisation, and the choice of AC orDC coupling in the synchronisationcircuit, but this is something that variesfrom one instrument to another. For mostpurposes a basic form of synchronisationis perfectly adequate. A free -runningmode is usually provided, which as itsname suggests, gives repetitive sweep-ing regardless of what input signal (ifany) is present. Synchronisation is stillpossible and is needed so that trace'crawl' can be avoided. Triggered sweepis the more popular type though, as largevariations in the input frequency simplyresult in more or fewer cycles beingdisplayed on the screen. With the freerunning mode it is unusual for a stabletrace to be maintained over more than avery limited frequency range.
Sometimes the waveform to bedisplayed will be a non -repetitive type,and then the triggered sweep mode mustbe used. However, with just one sweepacross the screen, especially if a veryshort sweep time is used, an ordinaryoscilloscope will only give a fleetingglimpse of the waveform, and possibly arather dim one at that. Special storagescopes that will hold and display wave-forms are available, but are tooexpensive for most non-professionalusers to seriously contemplate.
The sweep rate should be adjustableover a very wide range of around 0.2seconds to 1p.s or less per division -oscilloscope screens are fitted with a`graticule', a grid of squares engraved orprinted onto a perspex 'window' in frontof the CRT screen, to assist with accuratemeasurements, and the main divisionsare normally in centimetres, with lmm or2mm markings on the X and Y axis.
Two important parameters of anoscilloscope are the sensitivity and the Ybandwidth. For most purposes a sens-itivity of 10 or 20mV per division is quiteadequate, but most modern oscillo-scopes offer sensitivities somewhatbetter than this, making them that muchmore versatile. Most instruments ofmoderate cost offer a bandwidth of about10 to 20MHz, which may seem very wide,March 1986 Maplin Magazine
Y In 0 Y Gain
Control
Trigger
Sync.
Y Amp.
X In 0- X Gain
Control
Sweep
Generator
PhosphourScreen
/171
X Amp.
IY Deflection
Plate
Y DeflectionPlate
Figure 1. Basic Oscilloscope
but it has to be borne in mind that inorder to guarantee a reasonably accuraterepresentation of a waveform the Ybandwidth needs to be higher than thefundamental by a factor of around tentimes or more. This is because the inputsignal (assuming it is a repetitive wave-form) consists of the fundamental freq-uency plus harmonics (multiples) of thisfrequency. It is the particular harmonicspresent and their relative strengths thatdetermines the waveshape, and if theharmonics are outside the bandwidth ofthe oscilloscope the reproduced wave-form will be a sinewave type, regardlessof its true waveshape.
,011
Figure 2. Inadequate Bandwidth
The oscilloscope of Figure 2
demonstrates the importance ofadequate bandwidth. The two traces areproduced from the same squarewavesignal, but with one of them thebandwidth has been purposly restrictedto a slightly inadequate level and itclearly shows the waveform distortionthat results. Of course, for voltagemeasurement the bandwidth of the scopeneeds to be no wider than the maximumfrequency you will wish to measure. Abandwidth of around 10 to 20Mhz willsuffice for most applications, and the costof wider bandwidth instruments is suchthat few amateur users could seriouslyconsider using one.
Oscilloscopes almost invariablyenable the user to switch out the sweepgenerator and couple an external signalto the input of the X amplifier. This is a
X Deflection Plates
useful feature, as we shall see shortly.Some instruments have a 'Z' input, whichis one that enables the brightness of thespot to be modulated externally. This isundoubtedly a useful feature, but far froman essential one.
'Dual Trace' and 'Dual Beam'oscilloscopes are available, and bothpermit two waveforms to be displayedsimultaneously for comparison purposes.A Dual Trace oscilloscope is one that hasa CRT with only a single electron beam,but has gating circuits controlled by thetimebase which alternately select eitherof two inputs for the Y amplifier. Thiseither operates by very rapidly choppingthe beam from one trace to the other, ordrawing first one trace then the other onalternate sweeps of the screen. Someoscilloscopes give the option of eithertype of trace splitting.
In a Dual Beam oscilloscope the CRTcontains a 'splitter plate' which dividesthe electron beam in two - the X axis anddeflection amplifier are common to both,but there are separate Y amplifiers anddeflection electrodes for each. With adual beam oscilloscope no inputgating is required which keeps theamplifiers simple. The dual beam varietyis the superior but more expensive type.However. modern dual trace typesfunction very well and are just as good inmost applications.
The best type of oscilloscope toobtain obviously depends on the type ofequipment you will be dealing with.While bandwidth may be of onlysecondary importance to someone whowill only be dealing with audio gear, it isobviously of greater importance if logiccircuits or radio equipment are the mainarea of interest. Oscilloscopes are quiteexpensive and available funds are likelyto take a bigger hand in deciding whichone you buy than are such things as theideal sensitivity and bandwidth. For mostpurposes an instrument with a bandwidthof 15MHz or more and a sensitivity of afew millivolts per centimetre or betterwill suffice. Dual beam or dual tracefacilities are probably more useful forcircuit designers than they are forgeneral purpose service work, and areunlikely to justify the extra cost unless
53
you intend to design and develop yourown circuits. Old secondhand oscillo-scopes may not prove to be the bargainsthat they at first appear to be. Complexvalved instruments lack good reliability,and service information and spare partscould well be impossible to obtain. It ismuch easier to find someone who hasbought an old oscilloscope and regrettedit than it is to find a satisfied user. It isalmost certainly better to pay the add-itional cost of a new or recent second-hand instrument if at all possible.
Signal TracingAn oscilloscope is ideal for use as a
signal tracer, and although it is used inmuch the same way as an ordinary signaltracer, it has definate advantages.Probably the most important one is that itenables signals levels to be accuratelymeasured rather than just roughlygauged. Whereas a lack of gain some-where in the test circuit might be missedwhen using an ordinary signal tracer, itshould be quite apparent when using anoscilloscope. Another important advan-tage is that it enables waveform distortionto be readily detected. Something likeclipping can be detected using a signaltracer, but it is not usually possible to tellwhich set of half cycles are beingclipped, or if both are affected. Whatsounds like clipping could in fact besome other form of distortion such ashigh frequency instability. Using anoscilloscope obviously shows quiteclearly the nature of the clipping or otherdistortion, as in Figure 3 where clippingof the positive half cycles is evident. Bearin mind than an excessive input signallevel will cause clipping on stages thatare functioning perfectly well, and thatthe input signal needs to be set at arealistic level.
An oscilloscope can also bring tolight any imperfections on the waveformthat are less obvious when simplylistening to the audio output signal. Forinstance, instability in an amplifier canproduce (inaudible) radio frequencies onthe output signal, as in Figure 4. Thisshows the result of a very severe case ofinstability, and things are sometimes lessapparent than this. Squarewave testing isoften used with audio equipment, andthis just consists of applying a square -wave input signal at a middle audiofrequency (around 800Hz to 11Cliz) whilemonitoring the output signal using anoscilloscope. Mild high frequencyinstability gives the ringing effect presenton the waveform of Figure 5.
Irregularities in the frequencyresponse distort the waveform, and apartfrom being a useful general check on apiece of audio gear, this effect can beused to permit a quick check of tonecontrol operation. The waveforms inFigures 6 to 9 respectively show theeffect of extreme bass boost, bass cut,treble boost, and treble cut.
PhaseWhat sets oscilloscopes apart from
other types of test gear is their extreme54
Figure 3. Clipping
Figure 4. Instability in an amplifier
versatility. They can be used to measurea wide variety of parameters, includingsome that could not easily be checked inany other way. Phase measurement is agood example of this. While this is notsomthing that needs to be checked veryoften, it does crop up occasionally (whentesting a phase shifter circuit in a phasingeffects pedal for instance). With a dualbeam or dual trace oscilloscope there isno difficulty in checking the comparitivephasing of two signals, and it is just amatter of displaying them simultaneouslyand checking the displacement of onerelative to the other. If one lags the otherby (say) a quarter of a cycle, thisrepresents a 90 degree phase lag (a fullcycle passes through 360 degrees - 360/4= 90 degrees). With a dual tracingoscilloscope it is better to use the'chopping' mode rather than the'alternate' one for this type of testing, asthe 'chopping' mode can not introduceany slight phase shifts, whereas the'alternate' mode might do so. Incident-ally, the 'alternate' mode is better whereoptimum trace resolution is required.
Phase can also be measured using asingle beam instrument, and quite
Figure 7. Extreme Bass Cut
I
\p-,Itle-,I
I I I
Figure 5. Ringing Effect
r r rFigure 6. Extreme Bass Boost
accurately, but the oscilloscope musthave full X input. The two signals areapplied to the X and Y inputs, and thegain controls are set up so that the X andY deflections are approximately equal.Figure 10 shows the trace obtained withzero phase shift. Any deflectionhorizontally is matched by an equalamount of vertical deflection, giving atrace that is just a line at an angle of about45 degrees. If one of the inputs signals isinverted to give antiphase inputs theeffect is much the same, but while thevertical deflection is positive (abovecentre) the horizontal deflection isnegative (to the left of centre). The line istherefore tilted through 180 degrees (i.e.it extends from the bottom -right cornerof the screen to top -left corner). Onemight expect a 90 degree phase shift togive a vertical line, but with intermediatephase shifts the trace opens out, and at 90degrees the trace is actually a circle, asshown in Figure 11. This makes it slightlymore difficult to judge the degree ofphase shift, but it can still be judged quiteaccurately from the figure's angle of tilt.Incidentally, waveforms produced in thisway are termed 'Lissajous Figures'.
Figure 8. Extreme Treble BoostMaplin Magazine March 1986
(71 (I\\ 1 /
\,41
Figure 9. Extreme Treble Cut
FrequencyMeasurement
Lissajous Figures can be used mconjuction with a calibrated signalgenerator to permit audio frequencymeasurement, but most oscilloscopeshave accurately calibrated sweepspeeds, and frequencies over a widerange can be gauged reasonablyaccurately by measuring the period ofone cycle. Use the ordinary triggeredsweep mode to avoid any slight shiftaway from the set sweep speed, andchoose a sweep speed which gives onlyabout one or two complete cycles on thescreen. The frequency is simply equal tothe reciprocal of the sweep time. Forexample, a cycle time of 2.5ms
Figure 10. Zero Phase Shift
Figure 11. 90 Degree Phase Shift
represents a frequency of 400Hz (1/2.5 =0.4kHz or 400Hz). Note that measure-ments in seconds, milliseconds andmicroseconds give answers in Hertz,kilohertz and megahertz respectively.
This method will not give accuracyto rival a digital frequency meter, but it ismore than adequate to check that clockoscillators are functioning properly, thatdivider chains are operating correctlyand so on.
Delay lines can be checked using adual beam or dual trace instrumentsimply by feeding an input signal into thedelay line and then comparing thedelayed and non -delayed signals. Startwith a fairly low input frequency and along sweep time, and then graduallyswitch to shorter sweep times to permitmore accurate measurement of the delay.This avoids errors due to an apparentdelay of (say) half a cycle actually beinga one and a half cycle delay. With longdelay lines it is usually necessary to use asingle pulse or tone burst in order toavoid ambiguous results.
It has only been possible to coversome of the more important aspects ofoscilloscopes in this acrticle, and theycan be used in many other ways. Anincreasingly common feature these daysis a built-in component tester, and this isobviously ideal for use when projectsfault finding. Do not overlook thevarious oscilloscope add-ons that canextend the versatility of an instrument stillfurther, such as the 16 Channel Logic ICTester unit described in a previousissue of Electronics.
MAPLIN SERVICEWith most electronic projects, per-formance will depend on the cond-itions of use. Recommendations andsuggestions made in the articles inthis magazine are for guidance only,since conditions of use are beyondour control.
Repairs andGet -You -Working ServiceOur 'Get -You -Working Service' is
available for any of the projectspublished in this magazine, providedthey are constructed on our ready -etched printed circuit boards, andthat they use a majority of comp-onents supplied by us. We regret wecannot extend this service to the'interest' circuits, for which we do notprovide ready-made boards, orsupply as projects or kits; nor forprojects or kits that have beencustomised or modified by the con-structor.
We cannot enter into correspond-ence with regards to fault-finding,and recommend you return the unitto us for servicing if you are unable torectify the fault yourself.
Project ServicingIf the problem has been caused by afaulty component supplied by us,then there will be no charge for thework performed or the componentsused. If the fault has been caused byerror(s) in construction, then therewill be a charge for the workperformed at a rate of £10 per hour,or part of an hour plus the cost of anydamaged components which need tobe replaced. If no fault is found onthe unit. then there will still be a
charge of £10 per hour or part of anhour for the time involved in estab-lishing this fact.
Projects returned for repair shouldbe addressed to:-
Service DepartmentMaplin Electronic Supplies LtdP.O. Box 3RayleighEssexSS6 8LR
March 1986 Maplin Magazine 55
ADAConversionTechniques
by Ray Lowe
Why Are ConvertersRequired?
Digital electronics, computers, etc.,represent numerical values in terms ofbinary coded words. However, very fewparameters of interest in the real worldallow direct measurement of their mag-nitude, etc., in terms of such binarywords.
The underlying physical principalsby which the majority of electricaltransducers, e.g. microphones, thermo-couples, strain gauges, etc., operate donot lend themselves to directly outputtingbinary coded values. Usually, a para-meter in the real world will be measuredin terms of the magnitude of the e.m.f. ofcurrent that it produces at the output ter-minals of the transducer.
Analogue to digital converters aretherefore necessary to complete the in-terface between the physical world anddigital electronics in an input sense, anddigital to analogue converters are req-uired in an output sense.
The most obvious example of the'state of the art' in everyday terms is theCompact Disc system which was origin-ally developed by Phillips. Sony nowmarket a range of domestic digital audiorecorder adaptors for domestic videomachines. Digital multimeters, digitalfrequency synthesisers etc., all requireaccurate conversion devices. Manyvideo effects, video 'frame grabbers',etc., have high speed converters as anessential element so that the complexvisual effects can be performed by highspeed manipulation of digitised picturedata.
Methods ofDigital Coding
Different coding methods have beendeveloped, each of which have particularadvantages or disadvantages, dependantupon the nature of the signal being codedand the performance/system character-istics imposed by the designer.
The most well-known codingmethod is Pulse Code Modulation, PCMfor short. Others are differential PCM orDelta Modulation. These methods will beconsidered in turn, however only PCMwill be considered in any detail.
Pulse Code ModulationIn PCM the binary code produced is
proportional to the signal amplitude,measured with respect to an arbitrary,but stable, reference voltage which iscommonly but not necessarily chosen tobe zero volts. Thus, the code directlyrepresents the 'height' of a sample pointon the signal waveform, imagining it
were displayed on an oscilloscope, seeFigure 1. There are many varieties ofPCM data converter available. Thechoice of which to use depends upondesign trade-offs and the overall per-formance that is required in terms ofsampling rate or conversion accuracy.
PCM D/A ConvertersSince the majority of A/D converters
actually contain an internal D/A converteras an internal circuit element, it will beuseful to consider briefly the (simpler)D/A process first.
At the heart of all conventional D/Aconverters is a network of precision
Sampled signal
PCM Representation
Figure 1. PCM Representation56 Maplin Magazine March 1986
current sources and a set of switcheswhich allow current to be tapped off fromthe network at points dependent uponthe binary input code to the converter. Inaddition there may be signal condition-ing output circuitry such as an amplifierto scale the output signal and to adjustoffset etc., in accordance with the usersrequirements. Precision resistors mustbe fabricated on chip in order to realisethe set of current sources; whosecurrents increase along the chain bypowers of two. The switches, whenturned on by a binary 'one' at their res-pective point in the input code, connecttheir respective current source to acommon summing node which may be anoutput pin. Thus the most basic converterwill have a current output which isproportional to the input binary code. Byresistively loading the current output andbuffering the resultant voltage, a voltageoutput DAC (D/A converter) is produced,see Figure 2. There are a large variety ofDACs available with widely varying per-formance in terms of accuracy, thermalstability or `tempco', and settling time forthe output etc.
PCM A/D ConvertersRamp Type Converters
There are several sub -species of thistype. The simplest uses a linear rampgenerator i.e. a stable current sourcecharging a low leakage capacitor, astable oscillator driving a binary counter,and a comparator. Upon receipt of a`Convert' command, capacitor chargingand counting operations commence fromzero. The comparator decides whencapacitor voltage and the input signalvoltage being sampled are equal. Thisdecision latches the current binary countinto the converters' output register.
Sub -species two is a Multiple SlopeRamp Converter. In this type the finalapproach to equality is slowed down,thus ensuring a more accurate con-version for the least significant bits, seeFigure 3. Slight variations occur as to howthe ramp is generated. Some convertersuse a pulsed charge in synchronisationwith the counter rather than a currentsource to charge the capacitor. Someincorporate built-in correction for zeroinput integration error, i.e. the offsetbetween what the comparator 'sees' aszero, and a true external zero voltagepoint; this is done by actually setting theinput to external zero, and then perform-ing a conversion. This error 'count' issubtracted from the result of any con-version digitally before the data is madeavailable.
Successive ApproximationType Converters
The successive approximationmethod sets the output code bits insequence, starting with the MSB andfinishing with the LSB. Upon receipt of a'Start Conversion' signal, all bits are setinitially to zero. These bits, as well asbeing buffered internally and beingmade available at IC pins to representMarch 1986 Maplin Magazine
+ Full scalereference
Set of precisioncurrent sources.Increasing inpowers of 2
Si
Current switches -under control of input data
,/
-Full scalereference
LSB
LBinary data In
Current summingnode
Isum
1/7
Rf
Vout = Rf .Isum
Offsetad ust
Figure 2. Basic D/A Converter
CURRENTSOURCE
1
Used forReset
CURRENTSOURCE
2
Select CurrentSource, Count Rateand Reset.
BINARYCOUNTER
VoltageRamp
I
CONTROL
InputSignal
Buffer
End of ConversionComparator
Start End ofBinary Conversion ConversionData
Output
VoltageRamp
InputSignal Amplitude
Lower Threshold -
0
LowerStart ThresholdConversion Reached
MSB's
Set duringtthis Set during this period
End ofConversion
LSB's
- t
LowerThresholdComparator
Figure 3. Basic Dual Slope Converter57
the output code, also drive an internalD/A converter. This converter, in turn,drives one input of an internal voltagecomparator; the other input being drivenby the sampled signal. Obviously, thisconverter must have sufficient resolutionto match the required A/D resolution, ornumber of 'bits'. Initially, all bits are reseti.e. at receipt of a 'Start Conversioncommand. During the first external (orinternal for some chips or hybridconverters) clock period, which we shallcall the 'IVISB period', the MSB is set toone (e.g. 128 in binary for an 8 -bitresolution converter); the comparatoroutput now shows whether the sampledsignal is above or below this half full-scale reference, where fullscale is thevoltage corresponding to all bits set toone (e.g. 255 for 8 -bits).
If the comparator output is zero, thenwe know that the input signal lies belowhalf full scale. It is the comparator outputwhich is saved as the bit concerned (MSBin this case).
During the second, MSB -1, period,the MSB- 1 bit is set (with the MSB nowremaining in the state dictated by thecomparator output during the `MSBperiod'). The D/A output is once againcompared with the input signal, and thenthe MSB- 1 bit is saved to correspondwith the comparator output during this,MSB-1, clock period. This comparisonand bit setting procedure is repeated forall the following bits, until the LSBchecking 'period' is done and then theconversion is complete, and an 'End ofConversion' pin goes active to make thisknown.
Some converter chips make thecomparator output accessible, which isuseful if the data is to be saved in serialfashion. The serial 'frame' will commencewith the MSB, and finish with the LSB.Figure 4 illustrates the successivetechnique.Tracking Type Converters
The tracking converter is, in somerespects, similar to the ramp converter.However, instead of the count represent-ing an integration time for a currentsource to generate a voltage ramp; here,the counter drives a D/A directly. Insteadof the ramp count starting from zero foreach conversion cycle, the counterinvolved in this 'type' is an up/downcounter whose count is controlleddirectly by a comparator according towhether the signal being sampled has agreater or smaller instantaneous ampli-tude than the output of the A/D's owninternal D/A. The internal D/A is drivenby the counter. This type of convertercan operate in a free running or 'tracking'mode, whereby the count is continuouslybeing adjusted to keep track with thechanging input signal. Obviously, therewill be a maximum rate of change of theinput signal above which the counter willnot be able to keep track fast enough tomaintain resolution down to the LSB.Therefore, a trade-off exists betweenresolution and input signal 'slew rate'once a critical rate has been exceeded.58
VREF
VREF/
Input signal__Amplitude
Quantisat Ionlevels
Internal DAC2
- - - - Output
Conversion0Input
1 clocksignal 0
Comparator
INTERNAL ComparatorDAC 0 Output
DATAREGISTER 0
MSB LSB
OutputData 1 1 Data word
produced asresult ofconversion
ResetBit if0/P=0
SET BITS ONE ATA TIME
STARTING WITH
ConversionMSB
Clock CONTROLConversion
cycle
StartConversion
End ofConversion
Figure 4. Successive Approximation ADC
Flash ConvertersAs befits its name, the conversion
time for a flash converter merely de-pends upon propagation times throughthe internal circuitry, and hence con-version times are very short, of the orderof a hundred nanoseconds beingpossible. The essentially simple conceptemployed is that each quantisation level(2*"N for an N bit converter) has adedicated comparator e.g. an 8 bit
converter requires 256 comparators(matches in terms of drift, etc.) seeFigure 5. The output from the compar-ators is in the form of a 'thermometer' or'pulse height' representation if looked atin parallel. These comparator outputlines then drive a priority encoder toproduce a conventional binary outputword.
Half Flash ConvertersThese are a compromise between
+ Full ScaleReference Voltage
PRECISION
REFERENCE
NETWORK
Buffer
- Full Scale Input SignalReference Voltage
PRIORITY
ENCODER
High SpeedComparator
>DigitalBinaryOutputWord
Figure 5. Basic 'Flash' ConverterMaplin Magazine March 1986
the speed of full flash conversion, and therelative ease of fabrication of successiveapproximation converters in that themost significant bits are flash encodedfirst, then the residue error is found bysubtracting the present result (i.e. feed-ing a D/A with the MSB's only) from theinput signal. The residue error is accur-ately amplified to scale it correctly, andthen it is flash converted with the sameflash conversion circuit as used before.The result of this conversion is the LSB'swhich are combined with the previouslycoded MSB's to produce the completebinary output word.
Serial Type ConvertersThese are a compromise between
the simplicity of a successive approx-imation type converter and the con-version speed of a flash converter. In thistype, the successive technique is appliedin a 'ripple through' fashion. A com-parator; the `MSB comparator', decideswhether the input signal is above orbelow zero (full scale/21). The result setsthe MSB output accordingly. If above,then (full scale/21) is subtracted from theinput signal before it feeds the `MSB-1comparator'. The MSB-1 stage decideswhether this remainder is above orbelow (full scale/22), and the MSB-1 bitis set accordingly. The process continuesi.e. feeding the next stage with theremainder from the present stage, untilthe function has rippled through and setall bits.
CodingUpon commencing a design for a
converter it must be established at anearly stage what resolution is required interms of the number of quantisationlevels to be used in representing thesampled signal. This choice is based onmany factors, and can greatly influencethe complexity and cost of the overalldesign. The number of quantisationlevels available with an N -bit converterwill be 2**N. See Figure 6.
Another decision must be made; onthe coding format desired of the digitaldata words. Where the converter is usedfor positive going signals, it is normal touse straightforward binary words, whereall bits=0 corresponds to minus fullscale, i.e. OV, and all bits= 1 correspondsto full scale. Where the converter is usedin bipolar mode, i.e. for signals that varyabout OV, there are several possibilitiesfor the data format. Bipolar codes arecodes which give polarity information.
Several possibilities exist: OffsetBinary is normal binary except that allbits=0 corresponds to minus full scale,which in this case is a negative voltage,and all bits=1 corresponds to plus fullscale. In Sign Magnitude the MSBconveys the polarity of the sample, theremaining bits giving the magnitude of`height' of the sample. One's complementand two's complement are other codesparticularly useful if arithmetic oper-ations are to be performed on the data. Inchoosing a bipolar code format, it is
March 1986 Maplin Magazine
Converter Converter Input voltage RangeResolution (bits) 20V 10V 5V
8 39.06mV 19.53mV 9.77mV10 9.77mV 4.88mV 2.44mV12 2.44mV 1.22mV 610/2V14 610µV 3050/ 1530/16 153/2V 76p.V 38µV
Voltage resolution for 1/2 LSB,equivalent to 1/2 a quantisation step.
Figure 6. Converter Resolution
useful to consider the conversionprocess itself. For example, if usingOffset Binary to represent a smallamplitude signal swinging about OV, thedata will contain many sequences whereall the bits change polarity, for example0111 1111 (127) to 1000 0000 (128) as thesignal goes - to + through OV. Basically,every -time a bit changes, a 'dynamic'error voltage or current will be producedby a D/A converter using this code. Thisis due to internal component tolerances,supply loading etc. Hence, it is advisableto limit the number of 'simultaneous' bittransitions that can occur to the minimumpossible, preferably to that in the regionof the resolution required, especially atthe zero crossing point. This is par-ticularly important for the handling of lowlevel signals as considered above, other-wise noise problems will be the result ofhaving 7 bits changing state at once. Byusing Sign Magnitude representation, thenumber of bit transitions is minimised forlow level signals and hence the con-verters' transfer characteristic' will showlittle error (non -linearity) over this criticalregion (say, in the case of audio signals).
To take advantage of this, a SignMagnitude compatible D/A convertermust obviously be used where the `signbit' decides whether the basic DiA isto be followed by an inverting or non -inverting output stage.
Some UnusualImplementationsCompanding Converters
Up to now only linear quantisingconverters have been considered. TheSignal/Noise ratio for a linear converter is
approximately 6*N dB where N is thenumber of data bits per data word. Thus,a straightforward 8 bit system has atheoretical 48dB and a sixteen bit systema (very large) 96dB theoretical S/N ratio.However, due to the fact that convertercosts escalate rapidly with an increase inthe number of bits, it is preferable tominimise the number of bits per dataword where possible. Note also that datawords have to be stored or transmittedusually, which also points to reducing thenumber of bits where possible. The`noise' referred to is called quantisationnoise. See Figure 7. Since for a number ofapplications, noise is only objectionalwhere dealing with low level signals, itwould be satisfactory if the amplitude ofthe noise component were to be in someway proportional to the signal amplitude.That is, providing that the S/N ratio wasalways kept below the objectionablevalue, and if there were overall benefitsin doing this. By making the quantisationor 'transfer characteristic' of a converternon-linear, i.e. dependant upon signalamplitude, it is possible to increase aconverters' dynamic range. Note thatalthough the dynamic range is increasedthe max S/N ratio is not, because (quanti-sation) noise is now also dependant uponsignal amplitude, see Figure 8. This typeof converter is known as a CODEC or A -
Law converter, and is widely used in tele-communications to significantly reducedata handling requirements; because agiven noise performance over a range ofsignal levels can be obtained with fewerdata bits. Due to the subjective nature ofaural noise, this system is suitable for usein musical applications e.g. delay linesetc., except in some cases: When a very
Descrete
Quantisationlevels
Typical Signal'continuousBefore A, DConverter Stage
V
Corresponding[Unfiltered)D/A ConverterOutput Voltage
(Lint i ltered IQuantisationNoise
Sample Times I t I
Figure 7. Production of Quantisation Noise as a result of A/D Conversion
59
low frequency signal (below 20Hz) iscompanded the changes in quantisationnoise may become distinctly audiblewhereas the signal itself is not!
Ratiometric OperationA/D (and D/A) converters must have
references provided to determine thosevoltages corresponding to all output(input) data bits=0 i.e. minus full scale;and all bits=1 i.e. plus full scale.Normally the lower reference point isfixed, say at analogue ground. Thehigher reference point however may bevariable and provided externally oversome acceptable range. By using avariable reference the converter cangenerate 'ratiometric' data i.e. of onevoltage - the input signal sample voltage- as a ratio of the reference voltage.
Differential PCMIn PCM absolute signal 'height' data
is produced. However, there is a certainamount of redundancy in this data,depending upon the nature of the signalbeing sampled. Differential PCM datarecords only the changes in pulse heightas binary words.
Delta ModulationIs based upon differential PCM,
however, in this case the data is simply aseries of O's and l's which give only thedirection of change of the signal i.e.increase or decrease of voltage. Toobtain reasonable reproduction with thissystem, the sampling rate must be veryhigh. There are modulation methods inthe 'middle ground' between DifferentialPCM and Delta Modulation where anindication is given of the rate of changeas well as the direction.
Comparing PCM A/DConverter Types
In summary, a wide range of PCMencoding techniques exist; amongstthese are Ramp, Successive Approx-imation, Tracking, Flash, Half -Flash, andSerial type converters. Which to choose?
The choice of which type ortechnique to utilise is usually based onobtaining a satisfactory level of per-formance in terms of sampling rate,conversion accuracy, and maybe in somecases, factors such as power consump-tion etc., for the minimum cost. Due to thelarge number of variables involved, it canbe very time consuming to make the'perfect' choice, bearing in mind that newproducts are appearing regularly and, ingeneral, prices are falling. However,distinct advantages and weaknesses areapparent with certain techniques thatpoint the designer in the right direction.That is, it is a case of swings androundabouts, and to obtain the best ofboth worlds will always cost more. Ifconversion speed is a foremost require-ment, say for a video 'frame grabber,then it is almost certain that a flashtechnique will be required. For samplinglower frequency signals, successiveapproximation and tracking converters
DigitalBinaryCodeProduced
loft setbinaryshown I
1111
1110110111001011
10101001
1000011101100101010000110010-
00010000
-Fullscale
OVInput Signal
Figure 8. Transfer Characteristic of Log Converter
become the ideal choice. Whereabsolute accuracy is important, it ismultiple slope converters with built-inerror correction that have the edge; atthe expense of conversion speed. Thecost/performance ratio can escalate quiterapidly as state of the art demands aremade. A sixteen bit successive approx-imation AiD converter of good accuracy,intended for audio applications can costseveral hundred pounds. A similarquality twelve bit converter can beobtained for tens of pounds. An eight bitdevice costs well under ten pounds.
When choosing a converter caremust be taken to assess the accuracy andstability of the device. All converterssuffer from some non -linearity. What thismeans is that a voltage that a converterequates with the digital code 0100, say,will not be exactly eight times the voltage(as would be expected) that the sameconverter equates with the code 0001.This is due to component mismatchinginside the chip. The situation is furthercomplicated by the fact that internalcomponent values change with temp-erature and time at slightly differingrates. This may, for example, be due totemperature gradients in the chip as aresult of the microcircuit layout. Thus thetransfer characteristic at 25°C may bequite different to that at 50°C, or at 25°Ctwo years later. The change of character-istics with temperature and time isreferred to as the 'tempco' of the device.
+Fullscale
PracticalConsiderationsSample/Hold Amplifiers
An important subject in relation toAD conversion, not yet considered is theuse of sample/hold (amplifiers). It isobvious that whilst an A/D conversion isin progress it would be silly to changethe amplitude of the input signal - unlessit changes only by an amount which ismuch less than the resolution of theconverter. This would give a corrupteddata word. When digitally sampling anynormal signal therefore, it is important to'freeze' the current signal amplitude sothat a stable signal level is maintainedthroughout the conversion cycle. SeeFigure 1. This technique is known assample/hold and requires careful con-sideration, especially when converting togreater than, say, twelve bits resolutionsince any noise fluctuations or drift of thesignal level during a conversion willrender the (expensively obtained) A/Dconverters' resolution useless. It isrelatively easy to implement a S/H forconverters of up to 12 bits accuracy, seeFigure 9. There are many S/H chips andmodules available.
Beyond twelve bits, it becomesincreasingly difficult and expensive andcan be an exceptionally tiresomeexercise to maintain sixteen bitsresolution. The main performancecriteria for S/Hs are 'acquisition time' and'droop rate', which are parameters
Signal Input
Sample Hold Control['HOLD' When Switch Open I Has High Input Impedance
and Low Output Impedance
_I
717 Storage Capacitor
Sampled Output
PCB'GUARD RING' Driven fromLow Impedance VoltageFollower Output HelpsPrevent Charge Leakageand Hence 'DROOP!
Figure 9. Sample/Hold Scheme60 Maplin Magazine March 1986
expressing behaviour before and afterhold mode is initiated respectively, andare fairly self-explanatory bearing inmind that voltage is stored on a capacitorwhich must have a finite, however small,load attached. In audio applicationshowever, it has been found that it makesa subjective improvement to a digitalrecording for example if a very slightamount of white noise is added (or noteliminated! - as the case may be). Thereason for this is that for extremely lowsignal levels, the correlation betweenquantisation noise and signal becomesmore subjectively annoying without theaddition of this so called 'dither'; whitenoise is more aurally pleasing!
AliasingA well-known but very important
area for consideration is aliasing andhow to avoid it. There is a well knownmathematical proof (Nyquists' theorem,otherwise known as the 'SamplingTheorem') which proves that: To fullyreconstruct a signal from a set of samplepoints, the samples must be taken at afrequency which is greater than twice thefrequency of any component of theoriginal signal. Failure to comply with thiscriteria will result in a nasty phenomenoncalled aliasing - which is nothing to dowith little green men from Outer Space!
See Figure 10. In audio terms, thisform of distortion sounds like gurgling.The bottom line is that, assuming anupper limit on sampling frequency ofS Hz; the sampled signal must be band-width limited to have no significantcomponents above S/2 Hz. In practicalterms, this means low pass filtering thesignal before it can be sampled. Thename given to a filter used for thispurpose is an anti -alias filter. The roll -offof the filter to be used depends uponperformance requirements and howmuch of the potentially available band-width one wishes to use. Using theexample above, to maintain a usefulbandwidth of S/2 Hz would require theuse of a 'brick wall' or infinite cut-offfilter. Of course, such filters cannot berealised in practice. If one were happy tolose some bandwidth, then a muchsimpler filter could be used, see Figure11.
If the sampling frequency must bevariable, then tracking filters may beconsidered. A particularly useful form oftracking filter for some digital applica-tions is the Switched Capacitor Filter,since cut-off frequency is proportional toan externally applied clock signal. Inmany cases care must be exercised tominimise phase distortion of the signal bycareful choice of filter type i.e. Butter-worth or Chebychev etc. Absolute phaseis not critical in subjective terms foraudio signals, however, if various combfiltering effects are to be realised bymixing delayed and undelayed signalpaths, then phase control becomesimportant.
EqualisationIn making the most of what you've
I
Sampling points
Input Signal
Reconstructed Signal
Figure 10. Too Low a Sampling Rate leads to reconstruction of a different `Alias' Frequency
got terms; a useful technique sometimesemployed is the use of pre -emphasisbefore a signal is encoded, accompaniedby de -emphasis after decoding (tomaintain the original signal content). Pre -emphasis is simply filtering in reverse i.e.selective boosting of some frequencyranges over others. The idea is toenhance the amplitude of minor freq-uency components of a complex signalsuch that they suffer less from the de-grading effects of quantisation distortionwhen the signal is coded. Typicalmusical signals are a case in point. De -emphasis is used after the D/A end of thedigital chain to restore the originalspectral balance.
GlitchesImagine feeding the input of a DAC
with a binary counter in order togenerate a staircase type waveform. Thenumber of data bits involved in eachcode change establishes 'major' and'minor' transitions. The most major trans-ition being at half full scale, where theinput code changes from 0111 to 1000(assuming four bit offset binary coding).If digital inputs are faster to switch offthan on, as they can be, then for a shorttime the DAC will seek zero outputfollowed by settling back at one LSBabove the previous reading. Thus a largetransient spike voltage can be generatedwhich is known as a glitch. Becauseglitch size is not linearly related to theinput code, linear filtering may in factworsen rather than improve the faithfull-ness of the output signal. A solution to thisproblem is the use of a `deglitchercircuit, surprisingly enough! A deglitcher'sample/holds' the DAC output until it hassettled properly to its new value.
FilterResponse
dB o
D/A FiltersThe ramp -like signal from a D/A
output has many frequency componentsoutside the band of interest (defined bythe anti-aliasing filtering). As they stand,the sharp corners of the samples in theoutput stream can be considered quiteharmless in many cases, including audio- since the frequency components defin-ing them are outside the band of interest.However, problems can arise if anyfollowing circuitry shows non -linearityover their range since in -band inter -modulation products could be formed.Hence it is normal to include efficient lowpass filters straight after the D/A stage toremove any higher order components;thereby rounding the edges. This willreconstruct the original waveform. Onceagain, attention may have to be paid tophase.Grounding
When implementing a design ona PCB, special attention must be paid togrounding and layout. Some A/D con-verter chips provide two ground pins;one labelled analogue, the other digital.The reason for separation is to helpprevent relatively heavy digital groundcurrent spikes from upsetting the opera-tion of the analogue circuitry on the chip.Providing that a stable and substantialEarth connection is available near thechip, possibly a ground plane, these twopins can be connected to the same PCB`track'. Otherwise they should be sep-arately tracked to a distant reliable Earthpoint. Care should be taken with shield-ing and Earthing arrangements for S/Hdevices, as these are particularly sens-itive to interference. It is when dealingwith resolutions in excess of 12 bits thatthings become a bit of a headache!
Simple Low Order Filter -Wasteful of Bandwidth
More Complex Higher OrderFilter - Saves UsefulBandwidth
'IDEAL - Brick WallResponse - Not Practical
Frequency
SamplingFreq ÷ 2
Figure 11. Anti -Alias Filter Response Versus Useful Bandwidth
March 1986 Maplin Magazine 61
0000000000000000000000000000000000000000000000001
Multi -ElementHi -Tech TV AerialA smart, lightweight UHF TV aerial forindoor use. The aerial features twoparallel, staggered 7 -element arraysof matt finished aluminium, connectedto either side of a 75f1 coaxial feederand mounted on a square sectionplastic support. The unusual logperiodic' design offers up to 7dB ofgain at ±760MHz, and a minimum6dB at 470MHz. Covers all UHFbroadcast TV channels from 21 to 68.The aerial comes in three parts, atriangular base for a plug-in support,and the aerial itself which is normallymounted horizontally but can beinserted vertically to help excludeunwanted strong transmitters. Safetyisolated to BS5373. Fitted with 1metre of coaxial cable terminated witha UHF plug.
Order AsYM56L (Hi -Tech TV Aerial)
Price £10.95
Gold Plated PhonoLine Socket
A very high quality screened phonoline socket having a gold plated bodyin addition to gold plated contactsurfaces for ultimate contact relia-bility. Matches our gold platedscreened phono plug FK18U. Fittedwith coil spring strain relief sleeve.
Order AsFA93B (Gold Phono Line Skt)
Price 65p
Jack Socket Adaptor
An adaptor which enables a stereo3.5mm jack plug to be used with astereo 2.5mm jack socket.
Order AsFA94C (Adaptor W) Price 95p
Narrow Band 10.7MHzCeramic Filter
A ceramic filter witha centre operatingfrequency of 10.7MHz,and an especiallynarrow bandwidth of50kHz. Input and output impedance is3301/. Breakdown voltage 50V DC.Dimensions; width 8mm x height 7mmx 3mm thick. Pin spacing 2.5mm.
Order AsUF71N (Cer. Fltr 10.7MHz/50kHz)
Price 95p
62
NEWPRODUCTS
Precision Gold Multi -Function FrequencyCounter MF100A 10Hz to 100MHz multiple -functionfrequency counter with an eight digit,high brightness seven segment LEDdisplay. There are four ranges offeringresolutions of 0.1Hz or 100Hz from10Hz to 9.9999999MHz, or if thedivide by ten prescaler is selected,1Hz to 1 kHz switchable resolutionfrom 10MHz to 99.999999MHz. Thisis achieved by altering the gatesampling time. The accuracy is ±1count ±time base error x thefrequency, where the timebaseoscillator is maintained at constanttemperature in an 'oven' to produce10MHz ±1 x 10-5 from O`C to 40'C.Pulse period time measurements arealso possible in the period mode. Theinput range is 10Hz to 2.5MHz, andthe counter will read out the positivegoing pulse width time in seconds to aresolution of 1 0Ons
In the totaliser mode the instrumentbecomes an event counter andincrements the display by one unit foreach positive going input pulse, in therange 10Hz to 10MHz.Input impedance is 1MG via frontpanel BNC socket. Input sensitivity is25mV r.m.s. (sine) or 70mV pk-pk: adivide by 20 attenuator is included.Trigger level is continuously variableby ±350mV (x attenuator). Thedisplay includes decimal point, over-flow, kHz and As indication. Otherfacilities include HOLD to freeze thedisplay, RESET, sampling gate openindicator, and checkdisplay internaltime base clock.Supply input: 115/230V ±15% AC.45 - 70Hz.Dimensions: Width 205mm, Height76mm, Depth 267mm.Bench tilt stand included.
Order AsYJ82D (MF100 Freq Counter)
Price £89.95
Miniature Ultra -Bright LED
An ultra -bright red LED having a 3mmdiameter translucent package. Allspecifications as 5mm ultra -brightLED QY84F except: Light output istypically 45mcd at 20mA, with aviewing angle of 90°. Cathode isdenoted by a flat on the package andthe shorter of the two leads.
Order AsUF72P (Ultr-Bright Red LEDMiniature) Price 54p
NM2 Instrument Casewith HandlesA multi -part instrument case to beadded our NM range of cases in theboxes section of the 1986 catalogue.It is identical to type NM2 currently inthat range, but has handles formedinto the side plates, as have typesNM6H and NM7H.Width 300mm, Depth 150mm, Height90mm.
Order AsYM51F (Instrument Case NM2H)
Price £14.95
Miniature Clip Probes SetA pack of six test leads terminated ateach end with small clip probes whichcan be hooked onto IC or transistorpin -outs where the use of a smallcrocodile clip is impossible. The testleads are 41cm long and colourcoded Black, Red, Yellow, Green,Blue and White.
Order AsFA96E (Min Clip Probe Set)
Price £2.95
Plastic Lens
A cost effective, simple plastic lens foropto-electronic applications. The lensproper is 30mm diameter but also hasa flat rim for mounting purposesmaking the overall diameter 37mm.Overall thickness 3.5mm. The lenshas a focal length of =80mm in theinfra -red band.
Order AsFA95D (Plastic Lens) Price 48p
Right -Angled PCB Mounting6 -Pin DIN SocketA 240' 6 -pin PCB mounting DINsocket, having a front face 21mmsquare, and an overall depth of17mm.
Order AsFA9OX (PC DIN Skt 6 -pin) Price 58p
Portable Anti -Theft AlarmsThese new electronic security devicesprovide a second line of defenceagainst theft either in the home orbusiness premises. There is nosubstitute for good locks on windowsand doors and professionally installedalarm systems, but what if a thiefsuccessfully gains entry?
Alarm Box andJewellery BoxA portable electronic safe thatprotects your most valuable personalpossessions in three ways - if movedan extremely loud alarm is sounded,detering any would-be thief. Inconjunction with a high security 8tumbler lock, forcible entry is madevery difficult. Portability means thatthe box can also be hidden from view,or used away from home. The AlarmBox is big enough to hold yourprecious jewellery, documents and cash.
All these devices incorporate a batteryoperated system which uses adedicated logic IC for 'intelligent'operation - if moved the alarm issounded for a short period and then isswitched off, the unit resets itself inanticipation of a further trigger signal.Only if movement continues is thealarm retriggered, this preventspremature battery failure and annoy-
Maplin Magazine March 1986
ance from the continuous noise. Eachof the above units can only be armedor switched off with a key. The AlarmBox has a switch -on delay of 1 minuteduring which time you can put it awayout of sight.
The SpiderThe Spider can protect up to fiveitems at once using four sensor unitsconnected via umbilicals to themaster. unit. Ideal for a group of
valuable items. such as a stereosystem. home computer set-up(computer. monitor and disk driveetc.). or articles in a shop windowdisplay. Simply attach the Spider toone item and the Spiders 'legs' to upto four other items - sets off a loudalarm if any are moved.
Order AsYM53H (The Spider) Price £34.95
Order AsYM54J (Alarm Cash Box)
Price £44.95Order AsYM55K (Alarm Jewellery Box)
Price £54.95
The FlyIs a battery operated. highly sensitivemotion detector. which can beattached to valuable articles such as avideo recorder. TV set, stereo.documents safe etc. If moved the Flyresponds with a loud audible alarm.drawing attention to itself and deteringwould-be thieves. It may readily findapplications in shop or showroomdisplays to help prevent handlingor theft of goods.
Order AsYM52G (The Fly) Price £24.95
AMENDMENTS TO 1986 CATALOGUEPLEASE NOTE that the telephonenumber of MPS (Maplin Profes-sional Supplies) is 0702-552961.KINGDOM GAME CASSETTE(Page 104). This cassette game forthe Atari has been listed as havingthe stock code KB97F, whereas itshould be YG55K.PRINTER CABLES FG3OH & FG31J(Page 133). These 26 -way and 20 -way ribbon cables have had theirlengths quoted as 30cm, they shouldbe lm as before.SPINDLE COUPLER RX29G (Page184). The length of this brass coupleris 15mm and not 22.5mm.ULTRA -BRIGHT RED LEDsQY84F, QY85G (Page 199). It is theanode and not the cathode that isdenoted by the flat of the packageand the shorter of the two leads.5x7 LED ARRAY FT61R (Page 201).The dimensions of the 5x7 LED arrayhave been erroneously omitted fromthe catalogue. The dimensions of thearray are 53 x 38 x 8.5mm deepexcluding pins.REPLACEMENT STYLI (Page 279).The prices for the styli shown onpages 279 and 280 of the 1986catalogue have been omitted. Forprices refer to a copy of the currentprice list.ALL ROTARYPOTENTIOMETERS (Page 290,291). The shaft length of all types(single, single with switch and dualgang) is 50 -L 0.5mm minimum. Alsothe thread length of the single anddual gang is 9mm and not 7mm. Notethat the body length of the switchedtypes is 22mm not 20.8mm, and thatthe switch rating is 4A at 250V ACand not 2A.
March 1986 Maplin Magazine
4702B PROGRAMMABLE BITRATE GENERATOR (Page 296).The order code for this device isUF36P, not UF35Q.74HC4316 UF13P (Page 297). In thesemiconductors index on page 297,the 74HC4316 IC has been listed asbeing described on page 328, it is infact to be found on page 323.7402, 74LS02, 74HCO2 AND4001BE, 4001UBE QX39N - QL03D(Page 307). The captions for the pin -out diagram of the TTL devices havebeen accidentally transposed withthose for the CMOS diagram.74LS244, 74HC244, 74HCT244OCTAL BUFFERS QQ56L, UB65V,UB66W (Page 311). In the pin -outsdiagram for these octal buffers notethat the control input via pin 19should have an inverting inputsymbol at the control input buffer.4040BE, 74HC4040, 4060BE,74HC4060 RIPPLE COUNTERS(Page 318). The pin -outs diagramsfor these ICs have the wrongcaptions. The 4060BE and 74HC4060devices are actually the 14 -stageripple counter with oscillator, andthe 4040BE and 74HC4040 devicesare the 12 -stage ripple counter.AUDIO POWER AMP IC's QH39N,WQ33L, WQ66W, WQ67X, YY7OM,(Pages 335 - 337). Please note thatalthough these devices are des-cribed as having heatsink mountingtabs that do not need to beelectrically insulated from a chassis,this is on the condition that thechassis is the same potential as themost negative supply pin of the IC.The mounting tab is connected to theIC substrate, and it is required thatthis be equal to or up to 0.6V more
negative than the negative supplypin voltage. If chassis = IC 'ground'potential, then the omission of aninsulating kit will satisfy thiscondition, but do not overlook thepossibility of earth related instabilityproblems. If you intend to use a split -rail power supply, you must not boltthe tab direct to chassis without aninsulating kit!TEMPERATURE COMPENSATEDTWO STEP LEAD ACID BATTERYCHARGER (Page 364). In the circuitdiagram a value is missing for R14, itshould be 4k7.MID -RANGE SPEAKER WY15R(Page 389). This mid -range unit is foruse in systems up to 25W and not40W.RIGHT-ANGLED PCB ROTARYSWITCHES FT56L, FT57M, FT58N& FT59P (Page 395). The specifica-tions of these switches should beamended as follows - FT56L is 1 -pole 12 -ways, FT57M is 4 -pole 2 -ways (4 -pole changeover), FT58N is2 -pole 5 -ways, and FT59P is 3 -pole 3 -ways.PUSH BUTTON DIGITAL MULTI -METER M6000 YJ78K (Page 411).Note that the table of resistanceranges has been erroneouslyomitted from the catalogue. Theresistance ranges for the M6000 areas follows. written as 'Range.Resolution, Accuracy':20012, 10Orni!, (0.5% of rdg -ldigit): 2kil, Ill, -.z(0.3% of rdg -
Id): 20161. 1012, ±(0.3% of rdg - 1d);200ki1. 1000, n(0.3% of rdg - 1d);20M11. lOkf!, n(1.5% of rdgMax open circuit voltage dropacross probes, <3V. Overloadprotected to 250V DC or rms AC.
ADJUSTABLE SPANNERS FY45Y,FY46A (Page 420). The dimensionsof these spanners have changedslightly. The small adjustable is now150mm in length with a maximum jawopening of 19mm, and the largeadjustable has an overall length of200rnm with a maximum opening of24mm.SATURN MAINS DRILL YW65V(Page 423). Please note that thespecifications in the catalogue arenot quite correct. The mains supplyvoltage range is actually 220 - 250V.the off-load speed is 12,000 r.p.m.and the 3 -jaw pin chuck has amaximum capacity of 2.9mm and notVein.
SOLDERING IRON HOOK FT09K(Page 425). This clip -on hook fingerguard will fit the XS and MLXSsoldering irons only, and not the CStype.TOROIDAL TRANSFORMERYK33L (Page 436). In the case of thetoroidal transformer with 0-24, 0-24.0-100V secondaries, the wire colourcodes for the 100V secondary havebeen omitted. They are: start ofwinding, Black. Finish of winding.White.TRANSFORMER KITS (Page 436).The turns ratio quoted for the 20. 50.and 100 watt transformer kits are inthe wrong order. Correct turns/voltsratios are as follows:-20VA -- 6.04 turns per volt, + 1% foreach multiple of 1OVA loading.50VA - 4.8 turns per volt, +1% foreach multiple of !OVA loading.100VA - 4.16 turns per volt, - 1% foreach multiple of !OVA loading.STEPPER MOTOR KIT LK76H(Page 437). This kit now includes a pcb.
63
CLASSIFIEDVARIOUS FOR SALE
SIX CPU's for sale: Z80A, calculator,video -game, 'Mastermind game', syn-thesiser IC, Space Invaders. £2 each or£10 for the lot. Telephone Joel on (01)699 5354.ANTIQUE RADIO equipment for sale:200 valves, valve tester, oscillator, etc.Telephone Joel on (01) 699 5354.
TEKTRONIX 595A OSCILLOSCOPEwith 1A1 plug-in, not working £25.Taylor model 67A signal generator100kHz to 240MHz, working £10. Buyercollects. 01-470 4977.FERRANTI LR25 He Ne LASERcomplete with power supply, outputmeter and a variety of stands, mirrors,lenses, splitters, gratings, etc. £50 ono.Horrocks, 49 Wheelwright Rd, Erding-ton, Birmingham. G21-373 6188.
WIRELESS WORLD FM TUNER andhi-fi preamplifier, working. Black andwhite television camera, should work.Wireless World magazines 1968 --- 1982.Offers? Phone 05873 246 after 6 p.m.PRINTER, IBM GOLFBALL withinterface, or suit Maplin project £60.Chelmsford (0245) 355505.
BROTHER EP22 PRINTER/TYPE-WRITER. Integral RS232 interface.Only one year old. Offers in the regionof £55. Steele, Keighley (0535) 600034.ORGAN KEYBOARD 73 NOTE F -F£15. Organ switch banks 10p. Teletypemechanism, PSU and keyboard E.Electrostatic CRT's £1. Chart recordermechanism, £2. Model motors 25p.Farnborough (Kent) 55965.
IBM GOLFBALL PRINTER as inphotograph on page 26 of Decemberissue Maplin magazine. Offers to 028461870 (Bury St Edmunds).TYPING SERVICES for electronic andcomputer enthusiasts provided pri-vately and inexpensively by fully -experienced secretary: Sally Keyrealm,245, Colyers Lane, Slade Green, Kent.DA8 3QD.
If you would like to place anadvertisement in this section, here'syour chance to tell Maplin's 200,000customers what you want to buy orsell, or tell them about your club'sactivities - absolutely free ofcharge. We will publish as manyadvertisements as we have spacefor. To give a fair share of thelimited space, we will print 30words free of charge. Thereafterthe charge is 10p per word. Pleasenote that only private individualswill be permitted to advertise.Commercial or trade advertising is
strictly prohibited in the MaplinMagazine.Please print all advertisements inbold capital letters. Box numbersare available at £1.50 each. Pleasesend replies to Box Numbers to theaddress below. Please send youradvertisement with any paymentnecessary to: Classifieds, MaplinMag., P.O. Box 3, Rayleigh, EssexSS6 8LR.
For the next issue youradvertisement must be in our handsby 1st April 1986.
ELECTRONICS THE MAPLINMAGAZINE Nos. 1 to 16, in mintcondition. 50p each or £7 for the lot.Moore. 56 Archers Court Road,Whitfield, Dover, Kent, CT16 3HS.MULTIMETER ETU -100012/V. In mintcondition, still in original carton andwith original battery. £3.50 plus p & p,Mr. K. Lord, 82 Rossfold Road, SundonPark. Luton, Beds. LU3 3HH.MOBELEC CAR COMPUTER new,£25. Wanted. circuit diagrams for VoxContinental II and 300 organs. TMS 3802dividers, original metal Maplin draw-bars. Gibson, 14 Leigh Gardens.Wimbourne, Dorset. BH21 2EW.UHF TV AMPLIFIERS. Several X:1311JUHF and several Xtraset VHF UHF andone Extragain XG8 wideband UHFaerial. All at £10 each. Telephone 093426064.
COMPUTERSORIC TALKBACK speech synthesiserkit built and functioning, in goodcondition for £15. Telephone Joel on(01) 699 5354.10 ARCADE AND ADVENTUREGAMES on one cassette for theAmstrad CPC 464 664 6128. Sendcheque P.O. for £3 to Alan Cooper, 4,Carol Avenue, Martlesham, Wood-bridge, Suffolk.
VIC-20 CARTRIDGE -AREAMEMORY -EXPANSION KIT formachine code use, etc. Includes boardand instructions. Just add 2K RAM or2-4K PROM. Only £4.95 from Seddon,63 Portland Road, Birmingham.48K SPECTRUM AND SOFTWARE£70. Mutilated DKtronics keyboard £5.Kempston Pro interface and software£15. Phone 051-648 1694 after 6 p.m.COLOUR GENIE 32K, printer pluspaper. dual joysticks and keypad, LC24tape recorder, £200 worth of software,11 Genie mags, cassette case, leadsetc. All in original boxes, £250 the loto.n.o. Phone A.Fowler, Kibworth 2100.
CLUBSATARI MONITOR magazine issue 10is now available, filled from cover tocover with interesting Atari snippets,software reviews, tutorials and prog-ram listings. Send for a copy now forjust £1.30 (inc. postage) to: The UK AtariComputer Owners Club, P.O. Box 3,Rayleigh. Essex. SS6 8LR.
MUSICAL FOR SALECASIO PT -80 plus ROM cartridge withmanuals, in good condition. Approx-imately six months old and rarely used,you can have it for £60. TelephoneDaniel on (01) 699 5354.
MARBLE EFFECT ORGAN TABS (8organ voices plus 14 others e.g. reverb,sustain etc). As per Maplin type. Offersto 31, Channels Farm Rd, Southampton,SO2 2PF. Telephone (0703) 584603.WERSI HELIOS W2S ORGAN, superbcondition, complete specification withextras, price negotiable around £2,250.Telephone Abingdon (0235) 831391.
HOHNER SYMPHONIC 320ELECTRIC ORGAN with footswell andbass pedals and Laney 40W reverbcombo. Amplifier vgc, offers around£125. Buyer must collect. PhoneMatthew, (021) 552 5715.MES 53 ORGAN with 2 5 -octavekeyboards, auto -organ rhythm gen-erator (MES 55), pedal electronics(MES 54), but no pedalboard. Built andworking with minor faults in incompletecabinet. Offers. Phone (0270) 764993.
MAPLIN MATINEE ORGAN com-plete with handbook, one year old,£250. Akai 4000DS tape deck, 3 heads,sound on sound, 15 reels of tape £99.Telephone Cardiff (0222) 628473.MAPLIN SERIES 53/4/5 ORGAN. 2 x65 note keyboards. 30 note pedals.Cheap to good home. Details from StAlbans 59450.
WANTED16K ZX81 OR ORIC ATMOS 48K for£20 and £30 respectively. Also ZXprinter wanted for £20, black and whiteor colour TV for £25. Telephone Joel on(01) 699 5354.HAS ANYONE seen details of a plug-inteletext decoder project in anelectronics magazine? Any answersplease to Luke Walker, Department of
U G. ImperialCollege, London SW7.WANTED CIRCUIT DIAGRAM, kit orassembled unit of an FM stereotransmitter. Write to: HallvardTangeraas, Kvitsund Gymnas, 3850Kviteseid, Norway.
CORRIGENDAProject Book 2Burglar Alarm; External HornKit LWS8N. In the External HornKit, R2 is now 10k (M1OK), R5 isnow 4701) (M470R), and TRI is a2N4393 (RA99H).Project Book 6MOSFET Amp Bridging ModuleLKO3D. There are two errors inthe construction details for the'MOSFET Amp Bridging Module'under the section 'Test and Use'.(1) The reference to 'pin 12V'should read 'pin 12'. (2) Thesentence 'Remove the meter leadfrom pin 11 and reconnect to pin8.' should read 'Remove the meterlead from pin 11 and reconnect topin 7.' General notes - the 0 voltconnection from the powersupply should be made withheavy duty cable, and not thincable which can cause 0 voltsetting problems. If problems insetting 0 volts are encountered,R8 can be reduced in value, or
replaced with a wire link. The 0volt setting can be in the range OVto 20mV.Project Book 11Xenon Flash Tube DriverGB61R. C6 should be AxialElectrolytic FB72P, and not PCElect.Vol. 3 No. 13Explosive Gas Alarm LK60Q. Ifon inspection you find that bothsensors are marked with spots,then that which has a blue spot isthe one referred to in the text.Vol. 3 No. 9Infra -Red Movement DetectorLK33L. Please note that the Infra -Red Movement Detector, LK33L,has been superceded by a sup-erior model. We regret that wecan no longer supply the Infra -RedMovement Detector in kit form,since due to the construction of theimproved design it is too complexto assemble and test withoutspecial equipment.
MAPLIN'S TOPTWENTY KITS
THIS LASTMONTH DESCRIPTION OF KIT
ORDERCODE
KITPRICE
DETAILS INPROJECT BOOK
1. (2) s Live Wire Detector LK63T £3.50 14 (XA14Q)2. (4) s Partylite LW93B £9.95 Best of E&MM3. (1) a 100W Mosfet Amplifier LW51F £17.95 Best of E&MM4. (3) s Car Burglar Alarm LW78K £7.95 4 (XAO4E)5. (9) U Sonic Car Alarm LK75S £17.95 15 IXA15R)6. (51 a Ultrasonic Intruder Detector LW83E £11.95 4 (XAO4E)7. (6) a 8W Amplifier LW36P £5.95 Catalogue8. (19) a Computadrum LK52G £11.95 12 (XA12N)9. (7) a PWM Motor Driver LK54J £9.95 12 (XA12N)
10. (11) a 15W Amplifier YQ43W £6.50 Catalogue11. (8) a Logic Probe LK13P £14.95 8 (XAO8J)12. (12) p Light Pen LK51F £8.95 12 IXA12N)13. (-) s Scope Logic Tester LK77J £11.95 16 (XA16S)14. (10) s Syntom Drum Synthesiser LW86T £13.95 Best of E&MM15. (14) a Burglar Alarm LW57M £59.95 2 IXAO2C)16. (15) a Harmony Generator LW91Y £17.95 Best of E&MM17. I-) s Musical Announcer LK57M £14.95 13 (XA13P)18. (16) s ZX81 I 0 Port LW76H £10.95 4 (XAO4E)19. (-) s DXer's Audio Processor LKO5F £9.95 7 (XAO7H)20. (-) s Mains Tx Rx Driver LK68Y £34.95 16 (XA16S)
Over 150 other kits also available. All kits supplied with instructions.The descriptions above are necessarily short. Please ensure you knowexactly what the kit is and what it comprises before ordering, by checking theappropriate Project Book mentioned in the list above - see inside back coverfor details.
64 Maplin Magazine March 1986
DID YOU MISS THESE ISSUES? 1
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11.111111*MONSIMOINV
4.4011111$10112 YKOMPINOI VMS
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Project Book 1 Universal Timer. Programmablemains controller. Combo -Amplifier. 120WMOSFET power amp. Temperature Gauge.10`C - 100°C, LED readout. Pass The Bomb!Pass -The -Parcel with a difference. Six easy -to -build Projects on Vero -board. Car batt. monitor;Colour snap game; CMOS Logic Probe; PeakLevel meter; Games timer; Multi -colour pendant.Order As XAO1B (Maplin Project Book No. 1)Price 75p NV.
Project Book 2 Digital Multi -Train Controller.Controls up to 14 model trains. Home SecuritySystem. Six in -dependant channels. Digital MPGMeter. With large LED display, a must for moreeconomical motoring.Order As XAO2C (Maplin Project Book No. 2)Price 75p NV.
Project Book 3 ZX81 Keyboard. 43 keys, plugsdirectly into ZX81 with no soldering. Stereo 25WMOSFET Amp. 25W r.m.s per channel; Disc,Tape, Tuner & Aux. Radar Intruder detector.20 metres range, may be used with our securitysystem. Remote Control for Train Controller.Remote control by infra -red, radio or wire.Order As XAO3D (Maplin Project Book No. 3)Price 75p NV.
Project Book 4 Telephone Exchange. Up to 32extensions on 2 -wire lines. Remote Control forAmplifier. Volume, balance and tone controlledvia infra -red link. Frequency Counter. 8 digitDFM, 10Hz - 600MHz range. Ultrasonic IntruderDetector. Areas up to 400 square feet can becovered.Order As XAO4E (Maplin Project Book No. 4)Price 75p NV.
Project Book 5 Modem. 300 baud transmissionspeed over normal telephone lines. Inverter.240V AC 60W from 12V car battery. ZX81 SoundGenerator. 3 tone generators fully controlledfrom BASIC. Central Heating Controller.Optimised performance with this advancedsystem. External Horn Timer. Exterior intruderalarm. Panic Button. Add on to our HomeSecurity System. Model Train Projects. Add on toour Multi -Train Controller. Interfacing Microprocessors. How to use parallel I 0 ports, withcircuits.Order As XAO5F (Maplin Project Book No. 5)Price 75p NV.
Project Book 6 VIC20 & ZX81 Talkbacks.Speech synthesis projects. Scratch Filter.Tunable active circuit 'reclaims' scratchedrecords. Bridging Module. Converts two 75WMOSFET amps to one 400W full bridge amplifier.Moisture Meter. Finds damp in walls and floors.ZX81 TV Sound and Normal/Inverse Video. TVsound and inverse video direct. Four SimpleVeroboard Projects. Portable Stereo Amp; SineGenerator; Headphone Enhancer and StylusOrgan.Order As XAO6G (Maplin Project Book No. 6)Price 75p NV.
Project Book 7 CMOS Crystal Calibrator.For amateur radio receiver calibration. DX'er'sAudio Processor. Improved sound from Comm-unications Receivers. Enlarger Timer.An accurate timer for the darkroom. SweepOscillator. Displays AF frequency response on anoscilloscope screen. VIC20 and ZX81 Interfaces.RS232 compatable.Order As XAO7H (Maplin Project Book No. 7)Price 75p NV.
Project Book 8 Spectrum Modem/RS232Interface. 2400 baud self contained operatingsystem. Synchime. Simulates bells, gongs andother chiming sounds. Dragon 32 RS232/ModemInterface. Plugs into ROM expansion port.Codelock. Programmable electronic lock. CMOSLogic Probe. Digital display shows logic states.Minilab Power Supply. Versatile unit for the testbench. Dragon 32 I/O Ports. Two 8 -bit ports.Doorbell for The Deaf. Flashing lamp attractsattention.Order As XAO8J (Maplin Project Book No. 8)Price 75p NV.
Electronics Issue 9 Spectrum Keyboard. 47 fulltravel keys. VIC Extendiboard. Three expansionports, one switchable. Oric Talkback. Speechsynthesiser for the Oric 1. Infra -Red MovementDetector. 30 metres range outdoors. TDA7000FM Radio. Complete FM receiver on a chip. ZX81High Resolution Graphics. 256 x 192 fine pixeldisplay. Ten Projects! Personal Stereo DynamicNoise Limiter; Logic Pulser; ZX81 1K Extendi-RAM ; TTL RS232 Converter; Pseudo Stereo AMRadio; and more.Order As XAO9K (Maplin Magazine Volume 3Issue 9) Price 70p NV.
Project Book 10 Spectrum Easyload. Helpscassette loading with the Spectrum. 80mReceiver. Simple SSB direct conversion receiver.Fluorescent Tube Driver. 8W 12V for campingand caravanning. Auto-Waa. Automatic waa-waaeffects unit. Digi-Tel Expansion. Expands MaplinTelephone Exchange to 32 extensions. Oric 1Modem Interface. Adapts the Oric 1 to the MaplinModem. Dragon 32 Extendiport. Makes theDragon's cartridge socket more accessible.Order As XA1OL (Maplin Project Book No. 101Price 75p NV.
Project Book 11 Mapmix. Six channelaudio mixer. Xenon Tube Driver. Xenon flashtube module with strobe. Enlarger ExposureMeter. Simple inexpensive tool for the darkroom.8 Channel Fluid Detector. Check control fluidlevel in up to 8 containers. Servo & DriverModule. Servo mechanism with driver modulekit. Mk II Noise Reduction Unit. Improves signalnoise ratio of tape recordings. Cautious Ni-CadCharger. Controlled charging of ni-cad cells.Motherboard for The BBC Micro. Gives easyaccess to ports.Order As XA11M (Project Book No. 11)Price 75p NV.
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Project Book 12 RTTY Unit. The TU1000receives transmits Radio Teletype; connects tocomputer via RS232. Computadrum. Use yourcomputer as a drum synthesiser. Light Pen.Draw onto the TV screen or select menu options.PWM Motor Drive. Reversible model motordriver for 6V and 12V.Order As XA12N (Maplin Project Book No. 12)Price 70p NV.
Project Book 13 Explosive Gas Alarm.Flammable gas detector. Flash Meter. Get yourexposure right when using your flash gun.Musical Announcer. A doorbell with a difference.Mains Controller. An add-on for the 8 -ChannelFluid detector.Order As XA13P (Maplin Project Book No. 13)Price 75p NV.
Project Book 14 Live Wire Detector.Invaluable aid for the handyman. Trundle. Theline follower robot as featured on Channel 4. Zero2. High quality 'turtle' robot. 4 -Channel PWMController. Digital control of motors and servos.Display Driver Module. How to use our LEDbargraph display ICs. Control -A -Train. Full inertiacontrol of model trains.Order As XA14Q (Maplin Project Book No. 14)Price 75p NV.
Project Book 15 Z80 CPU Module.Expandable CPU based controller. Zero 2 Ins &Outs. Connecting up to the Commodore 64, BBC -B and Spectrum. Sharp MZ-80K Serial Interface.Get into communications with this project.Ultrasonic Car Alarm. Stop car thieves. ActiveCrossover. Includes matched output poweramplifiers. Guitar Equaliser. Specifically for sixstring electric guitatrs. Fabulous Five. A selectionof interesting circuits.Order As XA15R (Maplin Project Book No. 151Price 75p NV.
Electronics Issue 16 Floodlight Controller.Both power supply and mains switching unit forthe Infra -red Intruder Detector Kit. SpectrumParallel/Serial Interface. Provides 8 -bit I P andO P parallel or serial transfer with programmableUART. Mains Tx/Rx Data CommunicationsSystem. Sends or receives data via the mainswiring. 16 -Channel Logic IC Tester. Simult-aneously displays logic states for any logic IC ofup to 16 pin -outs on your oscilloscope.Order As XA16S (Maplin Magazine Volume 4Issue 16) Price 75p NV.
Electronics Issue 17 Video Digitiser. Interface aTV camera to your computer. Mixing It. Acomprehensive range of audio amplifier mod-ules. Hobbyist's Temperature Controller. Generalpurpose electronic mains power thermostat.ASCII Keyboard. Professional computer keyboardwith standard ASCII output. Play Along Mixer.Play along to your favourite records and tapes onyour own instrument.Order As XA17T (Maplin Magazine Volume 5Issue 17) Price 75p NV.
MODEL5010EC
MULTI-PURPOSE
A versatiledigital multimeter
with a
0.5in. 3' 2digitLCD displayand a
host of useful additionalfacilities.
Continuitybuzzer.
Conductancemeasurement.
Diode testingcapability.
hFE transistortester.
Digital thermometerprobe.
Capacitancetester.
Capacitancerange 1pF to 20/2F.
DC volts up to 1.000V.
ACvolts up to 750V.
DC AC currentto 10A.
Resistance100mi2 to20Mf2 and
2.8V or500mVdrop across
probes.
Fullyoverloadprotected.
As YJ79LPrice£64.95
Maplin
lATZ
20,:, 200. 260:1
FIFIRP9mapunalb , (3000
AUTO-RANGING
MODELM775
A fullyauto-rangingdigital multimeter
with 0.5in.high 31/2 digit LCD display.
Includeslow battery.
overange.
polarity,auto
mode and range
selectedindicators.
10M0-100Mi1input impedance.
Range hold mode available.
Memorisereading
capability.
DC volts upto 1.000V.
AC volts up to 750V.
DC AC currentto 10A.
Resistance100mi1 to 2MU.
Continuitybuzzer.
Suppliedwith battery.
safety test
leads and operatinginstructions.
OrderAs YJ80B Price£39.95
PRECISIONcir
4 MODELM6000 PUSH
BUTTONDIGITAL
Push button operateddigital
multi -
meterwith 0.5in
high 3' 2 digit LCD
display which includeslow battery
and overloadindicators.
Battery life
can be as much as 2.000 hours using
analkalinePP3.
Fullyoverloadprotected.
10M1/ inputimpedance.
Onehandedoperation.
DC volts up to 1.000V.
ACvolts up to 200V.
DC and ACcurrent to 20A.
Resistance100m11 to 20Mi1.
Switchable3V or 0.6Vmaximum
drop acrossprobes
all resistance
ranges.Diode test capability.
Bench tilt stand.
Suppliedwith battery.
safety test
leads and operatinginstructions.
Order AsYJ78K Price £39.95
MOM
HOBBYMULTIMETER
A rugged.easy to use general
purposeinstrument
offering
10,00011V DC and 400011
VAC.
DC AC voltsup to 1.000V.
DCcurrent up to 500mA.
Resistance211 to 10M1/.
Decibels-20dB to 62dB.
Overloadprotection.
I Suppliedwith battery. test leads
and operatinginstructions.
Order As YJ76H Price £8.95
MODELM105
LOW COSTDIGITAL
Compacteasy to use digital
multimeterat an affordable
price.
Full overloadprotection.
3' 2 digit LCD display.
Basic accuracy0.5%.
Screenedagainst
RFI.
10Mil input impedance.
DC volts upto 1.000V,AC to 750V.
DC currentto 2A FSD.
Resistance10 to2M12.
2.8V maximumdrop across
probes
all resistanceranges.
Onehandedoperation.
Suppliedwith battery,
safetytest
leads and operatinginstructions.
Order As YJ77J Price £26.95
MAPLINELECTRONIC
SUPPLIESLTD.
P.O. Box 3, Rayleigh,Essex
SS6 8LR.
Telephone:(0702) 552911.
Access.Barclaycard.
Amex.Mapcard -
phonebefore 2.00
p.m. forsame -day despatch.
Or call inat oneof our shops:
Birmingham.London.
Manchester.
Southampton.and Southend-on-Sea.
All pricesare valid until
10th May86 and
inc. VAT
Also availablein the Maplin
Precision Goldrange :-
YJO6G Generalpurpose
analoguemultimeter
£6.95
YJO7H Widerange analogue
multimeterM-102BZ with
continuitybuzzer and battery
tester £14.95
YJO8J Professionalanalogue
multimeter M-2020S with
transistor.diode and LED
tester £19.95
YJO9K Professional
quality FETinput elec-
tronicanalogue multi -
meter M-5050E £34.95
YJ1OLM-5010 high
performancedigital
LCD multimeter.ranges
start at20!2.20µA or
100µV ACDC FSD.
1 OM!iinput imped-
ance £41.95