THE ELECTRONICS MAGAZINE WITH THE PRApril 1990

a 6

UK 0.70

rvn IV MI/ 61=11 II MI II IWO

Mandag 15. Januar

18.45 DENT TV TRIM11'419.00 "HJEMMETS LIFESTYLE"

19.30 MUSIKK MUSIKK MUSIKK20.00 CASINO21.15 POLITIET PA HILL STREET22.10 ENGELSK FOTBALL22.55 BEYOND 2000 (r)

I Ti cs kl 23.551

MUSIKK: OCEANS APART

Video line selector

Q meter

Automatic mains switch

RS232 splitter

Bridge rectifiers revisited

Coded locking circuit

f f.:-31-1

!")111110)f; H 1r()'

1-triciri1;z7iel It' H

H 11SIitSY.I

i;bikliiijltrk-2 H

tioLriniscit F

-10

3 GIL!

NORDIC CHANNEL

F ft I tIyour order on 01-2059558using VISA,Access Card

Orders welcome fromgovernment depts &educational establishments

TECHNOMATICTechno House 468 Church Lane, London NW9 8UF.

Tel: 01-205 9558 Fax: 01-205 0190

rchimedes COMPUTERS

A3000 (no monitor)A3000 (for TV use)A3000 Acorn ColourA410/1 (no monitor)A410/1 Acorn ColourA410:1 Taxan 770-

£649£698£829

£1199£1340£1559

Techno 410 1 systems upgraded to 420 1 spec.

Acorn Colour systemTaxan 770- systemAcorn 420/1 systems420/1 (no monitor)420/1 Acorn Colour

Acorn 440/1 systems440/1 Acorn Colour440/1 Taxan 770 -

Carriage £81compurer £12/system

£1559£1799

£1699£1888

£25792809

I TECHNO 410/40 UPGRADESA410/1 upgraded to 4 fvlB RANI and 40 MBHard Drive complete with Mouse Mat. 1

box of 3.5" discs, printer lead and FirstWord Plus Release 2.

Our 40 MB Hard Drive is a high spec. AutoPark.25ms. quality drive with a reliable Toshibamechanism.

techno 410/40 with Acorn Colour Monitor£1699

techno 410/40 with Taxan 770- £1899Finance available on chargeable basis.

All prices ex VAT.Prices are subject tochange without notice.Please add carriage(a) £8.00 (Courier)(b) £3.50(c) £2.00(d) £1.50

What we offer in addition to efficientsales service and professional backup!We not only offer professional advice when you are purchasing your systembut we will also provide friendly assistance afterwards. All our products carrya 12 month full Narranty for parts and labour.

SPECIAL FINANCIAL DEALComputers alone or complete systems can hepurchased at NO EXTRA CHARGE over 10 easilymanageable monthly payments. The deposit willbe payable with the order followed by 9 monthlypayments. Please phone or write for full detailsand a personal quotation. Subject to status. weshould be able to despatch your order within 7days of receiving your order.

TECHNO 410/1 SPECIALOffer extended due to popular demand.Archimedes 410 1 upgraded to full440 1 specification with 4 MB RAM

and 50 MB Hard Disc (Acorn)plus

Taxan 770- Multisync Monitorand including

a packet of discs. a printer leadand a mouse mat.

for only £1999 carr £12Finance available on chargeable boa's

MULTIPOD PROFESSIONALProfessional design and use of latest hardware/software technology have enabled this five functionpodule to provide the highest quality performance at economical and realistic price. The fivefunctions are:

FAST -SCAN VIDEO DIGITISER: Offers the highest resolution and number of picture levels of anyvideo digitiser for the Archimedes computers. Capable of digitising in any mode to 640 x 512 pixelswith 256 grey levels. Colour can be digitised with a camera and filters providing 24 bit colourresolution. Software operates within Desktop and offers contrasubrightness control. zooming. greyscaling and sprite saving.

SOUND DIGITISER: Samples for sound frequencies from4KHz to 80KHz can be manipulated. composed and saved.Editing functions include filtering. mixing. overlaying.swapping. cut/paste. Saved sound modules including stereosound samples can be used in various applications includinggames or can be exported to other sound packages. Operateswithin desktop environment.

SERIAL PORT: A full RS232 implementation of a dual channelcomms port. It is IBM compatible using a 25way D connector.Uses 'FX and SYS calls.

INSTRUMENTATION.JOYSTICK PORT: A high speed A to Dconvertor which provides samples at up to 100 KHZ forversatile datalogging. As BBC B analogue port. uses the usualADVAL commands.

ROM SOCKETS: 3 ROM sockets for use through built in BBC B RFS_

MULTIPOD PROFESSIONAL

FILTER SET FOR VIDEO CAMERA (RGB)

10% VOUCHER ON CASH &CREDIT CARD SALES

Cash and credit caro purchasers of Archimedescomputers and complete systems will receive avoucher to the value of 10% of the purchaseprice. Vouchers will be valid for 90 days from thedare of issue.

TECHNO DTP PACKAGEArchimedes 410 1 Colour Systemupgraded to full 420 1 spec with2 Mb RAM and 20 Mb Hard disc

featuring our technoSCAN packageand either

Acorn DTP PackageFirst Word Plus Rel 2. Logistix

or

Impression and Pipedream 3

and a free mouse matfor only £1777 carr £12Finance available on chargeable basis.

Special Educational Subsidy on theTechno DTP package.

R140 UNIX SYSTEMLimited Period Offer

R140 Base Systemwith

Taxan 770- and PC EmulatorOr

Viking IIplus

Ethernet Card andAdministrators Guide

for only

£3000 + VATand it also includes on -site

maintenance contract.

F -This advertisement can only show an example of -Ithe range of products stocked by Technomatic Sosend for our latest BBC catalogue providingdetailed information and prices on BBC ComputerSystems. Peripherals. Software and Books.

NAME

ADDRESS

£117(b) Post Code

Retum to Technomatic Ltd, Techno House,

£15(d) L468 Church Lane. London NViI9 8UF. EE/3 90

TEL: 01 205 9558

C 0 \ \\T 1_,

April 1990Volume 16Number 177

ENTSIn next month's issue: LEADERImage segmentationHorn loudspeaker 11 Telephoning the world in the IL)9(l

1111000/1'Automatic power down COMPUTERS & MICROPROCESSORS 1) 'Four -sensor sunshinemeterExperimental all wave

14 PROJECT: RS -232 >plitterby A. Rigby

li 1

r.._..11 iiii-.:ki.,:111111 ,

.

1I I. a !Wit

band ferrite rod antennaTransistor characteristic

DESIGN IDEAS .. iiii.

,

plotting 54 Bridge rectifiers revisited --2ZNt2"';- --

* Intro scan for CD players (high -efficiency AC -DC converter/voltage multiplier[ Profile of Watford ElectronicsThe multi -MAC chipconceptAnalogue -to -digitalconverter

from an idea I_1. D.A.J. Harkema56 Digitally -controlled preamplifier

by K.J. Thouet

p. 50

DESIGN NOTES

Front cover60 Coded locking circuit for security systems

a Philips designAlthough MAC television pic- -

tures can not be received oncurrent PAL TV sets, thereare already two 02 -MAC

ELECTROPHONICS

21 PROJECT: BBD sound effects unit - final part

,--:,..--. .

- ,

channels on the Astra TVsatellite (which also transmitsthe Sky programmes). More-over, French (TDF-1), Ger-

by T. Giffard

GENERAL INTEREST

24 PROJECT: The digital model train - final part

'

-

man (TV-SAT2) and British by T. Wigmore Test box - p. 51(BSB) satellite TV pro-grammes will be in MAC:experimental or test pro-grammes from all three havealready been transmitted for

=5 PROJECT: Automatic mains isolating switchby R. Ernst and A. Wahr

INTERMEDIATE PROJECT51 Test box

...

some time. The signals from by D. Schijns , . ,.

all three are strong and totallynoise -free over most of west- RADIO & TELEVISION

,. : -,.

em Europe. tAlthough in Britain there are 46 PROJECT: Video mixer - final part

only four terrestrial channels by A. Rigby and G. Dam --and the Sky programmes. --- ----_-..."large parts of western Europehave a choice of over 20 dif-ferent TV channels either by

SCIENCE & TECHNOLOGY3s Parallel processing for faster computing

by Brian Kellock

-it-------:- ---%

cable or by dish aerial. -Oneday, British viewers will alsohave a choice of that manychannels, but it will take time.

ly Technological advances in crime detectionby David Pead

40 Robots for the rag trade

RS -232 splitter - p. 14

- --particularly since many arenot too interested in continen-

by Jim Kelsey

TEST & MEASUREMENT\\\\\ \\ \\\

:al programmes, or are they?-- s is in sad contrast to 27 PROJECT: Wiring allocation testerE urope. where both the BBCand the ITA channels are

an ELV design32 PROJECT: Video line selector

- , :II1

available and watched b;many.

by T. Giffard41 PROJECT: Q meter

__-- --

The TV pictures shown were by J. Bareford ---,

taken by a Dutch radio/TV 8I --

amateur early this year: theyclearly show the choice avail-

MISCELLANEOUS LNFORMATION a4.;

..

able to western Europeanviewers.

Electronics scene 12 &13: Events 57: Nev. books 57: Lett,f1 62: Switchboard 62: Readers services 63: Terms 64:Buyers guide 74: Classified ads 74: Index of advertisers 74 0 meter - p. 41

ELEKTOR ELECTRONICS APRIL 1990

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LI )R Fl Ft I lo pm' (w)i)

Produced and published by ELEKTORELECTRONICS (Publishing)

TELEPHONING THE WO N THE 1990SEditor,publisher: Len Seyrro'JrTechnical Editor: J. Bu,t.ngEditorial Offices:Down HouseBroomhill RoadLONDON SW18 4J0EnglandTelephone: 01-877 1688 (Nation..:'or +44 1877 1688 (International)Telex: 9170031.PC G)Fax: 01-874 9153 (National)or +44 1874 9153 (IntemationahAdvertising: PRB Limited3 'Noiseley TerraceCHELTENHAM GL50 1THTelephone: (0242) 510760Fax: (0242) 226626European Offices:Postbus 756190 AB BEEKThe NetherlandsTelephone: +31 4490 89444Telex: 56617 (eiekt nI)Fax: +31 4490 70161Managing Director: M.M.J. Landman

Overseas editions:FEDERAL GERMANYElektor Verlag GmbHSOsterfeld Simile 255100 AachenEditor: E.J.A. KrempeluerFRANCEElektor sariRoute Nationale: Le SeauB.P. 53; 59270 BailleulEditors: D.R.S. MeyerG.C.P. RaedersdorfGREECEElektor EPEKariskaki 1416673 Voula - AthenaEditor: E. XanthoulisINDIAElektor Electronics PVT LtdChhotani BuilrEng52C, Proctor Road, Grant Road (E)Bombay 400 007Editor. Surendra lyerNETHERLANDSElektuur BVPeter Treckpoetstraat 2-46191 VK BeekEditor: P.E.L. KersemakersPAKISTANElectra -shop35 Naseem PlazaLasbella ChawkKarachi 5Editor: Zain AhmedPORTUGALFerreira 8 Sento Lda.S.D. Estetani, 32-1°1000 LisboaEditor: Jeremias SequeiraSPAINIngelek S.A.Plaza Rep6blica Ecuador2-28016 MadridSWEDENElectronic Press ABBox 550514105 HuddingeEditor: Bill Cedrum

Distribution:SEYMOUR1270 London RoadLONDON SW16 4DH

Printed in the Netherlands by NDB,Zoetenvoude

Copyright 1990 Elektuur BV

ABCrry

Exciting developments in British electronicstechnology are about to open up a new hori-zon for personal communications. giving thecountry a leading role in Europe's telecommu-nications market in the 1990s.

A mould -breaking agreement. signed bymembers of the European Community last De-cember, will open the way for competition inthe provision of advanced telecommunicationsservices, such as electronic mail and access tocomputer databases, from the middle of thisyear. This is seen as a forerunner of further co-operation in the fast growing £54 billion Com-munity telecommunications' market.

Britain's current position reflects the Gov-ernment's policy of introducing competition inthe industry. British Telecom. which blazedthe privatization trail in 1984. and the smallerMercury Communications, have since beenwidening customers' choice in the provision oftelephone services.

For instance. Mercury's newly installedblue -and -white telephone booths. which ac-cept credit cards for calls, have been function-ing alongside British Telecom booths in manyparts of the country.

Perhaps the most important pioneeringBritish development is cellular communica-tions, allowing telephone conversations any-where in the world from cars. trains and air-craft by radio linked to fixed stations.

There are currently about 750.000 cellularphone users in Britain who pay an average of£300 for a handset. This compares, for exam-ple. with only 150.000 users in West Ger-many. who pay about £2.500 for their equip-ment.

Even more exciting prospects ahead are theTelepoint and Callpoint systems launched re-cently by the two British companies. Britonswill shortly be carrying these light -weight.folding phones. fitted with long-lasting batter-ies. and making and receiving calls fromwithin a distance of 100 metres from fixedpublic base stations.

In a hid to establish a lead in world tele-phone technology, three British consortia havealso been licensed by the Government to de-velop advanced personal communication net-works or portable phones to provide two-waydigital personal communications in the 1990s.

The new system offers the prospect ofusing the same handset at home, in the streetor in the office, to make calls with costs thatare not only competitive with those of the cel-lular operators. but possibly of the fixed tele-phone network as well. Small and easy to use.they would be the ultimate personal tele-phones.

The initiatives in Britain contrast sharplywith conditions in some European countrieswhere state-controlled telecommunication ser-vices use systems that are not compatible with

one another.France Telecom has been slow to develop

mobile telephone technology despite its othertechnological achievements in data switching,digital transmission and video text. The WestGerman Government has only recently li-censed that country's first private sector digitalmobile phone network that will compete withthe state -run Deutsche Bundespost Telekomfrom late 1991.

At present it costs several times as much tomake a call across Europe as it does to tele-phone a similar distance in the United States.It is hoped that liberalizing the EuropeanCommunity's telecommunication services willeventually lead to harmonization in costs.When that happens. Britain will be wellplaced to provide the expertise and experiencefor a competitive service.

The pan-European paging of travelling busi-ness people came a step nearer last Januarywith the signing of a memorandum of under-standing that involves stems operators from13 countries.

Under the European messaging system.known as MIES, due to start in late 1992. theinternational telephone system will be used tobleep executives on the move from as far

the use of pocket -sized pagers that alert peo-ple that someone wants to get in touch withthem is limited when travelling abroad.

Last January, British Telecom launched themost advanced automatic freephone serviceoutside North America.

Advanced Linkline is a highly versatileservice made possible by new technology inwhich British Telecom has invested more thanI: 100 million-the first non -American imple-mentation of the the "intelligent network"concept.

It will bring many extra facilities to thosecompanies that offer their customers 0800 and0345 numbers to call them free of charge. orat the cost of a local call. In consequence. nocall need go unanswered whatever the day ortime.

The new service differs from British Tele-com's existing automatic freephone service inharnessing the power of computers combinedwith digital electronic technology.

Readers are reminded that next month ourSTD code, together with that of 380.000 otherbusinesses in the Greater London area willchange. The code in the inner part of Londonwithin four miles of Charing Cross willchange from 01 to 071 at a minute past mid-night on Sunday 6 May-a Bank Holidayweekend-while that in the rest of the present01 area (ours included) will become 081.

ELEKTOR ELECTRONIC'S 1PRII. 1990

EFFICIENT COMPACT SATELLITETV ANTENNA

The D65S satellite TV antenna from Satel-lite Technology Systems Ltd in Bristolcombines high performance and a compet-itive price with a compact size; of 'off -set.design. it has a diameter of only 710 mm.An antenna with a diameter of 850 mm isalso available.

The three -strut antenna is made fromspecial steel. which is phosphate -treatedbefore being powder -coated in white asstandard, although other colours and fin-ishes are available.

The antenna is easily installed by boltsto a wall or by clamps to a mast. It pro-vides perfect reception within the 50 dBregion of the Astra satellite and has beentested successfully throughout Europe. Itsefficiency is quoted as not less than 65%.but it is said to out -perform antennas forwhich an efficiency of 75% is claimed.The quoted noise figure is 1.4 dB. Theminor diameter of the smaller antenna is650 mm with a focal length of 364 mm.

The world's first HF, electronically programmable,active filter. Type 32F8010, from Silicon Systems,Inc., is a low-pass design whose cut-off frequencycan be adjusted electronically from 510 13 MHz. For

more information contact Silicon Systems, 14351Myford Road, TUSTIN, CA (714) 731-7110, USA.

NEW TV AND VCR CHIPSA new set of ICs from Siemens is making amajor contribution to the simplified pro-gramming of video recorders. They allowthe user to mark the desired programme onthe teletext menu and enter it into therecording memory by pushing a button.

At present, the programming of videorecorders is often a tedious activity. Thevideo programme system-vPs-has facil-itated this task with the timely detection ofa late or early transmission. However.many numbers must be entered and con-firmed. and so far it has not been possibleto check with certainty whether errorswere made during the entry.

With the new tcs. the user simply callsthe programme page in the teletext menu.marks the desired program with a cursorand enters it into the recording memory of

c -j -f ra'

the VCR with all required data by a singlekeystroke. If desired, the system thenshows him the programmed transmission,thus ruling out errors.

(Readers may note that vcRs with tele-text programming are already available inBritain, but unfortunately, at the time ofwriting --late February-neither the BBCnor the independent TV stations in the UKtransmit the pulses necessary to operatethe vPs-Ed).

EUTELTRACS STARTS CUSTOMERDEMONSTRATIONS IN EUROPE

Customer demonstrations of the land mo-bile EUTELTRACS system began last Januaryvia two EUTELSAT satellites. EUTELTRACSthe first land mobile messaee-exchangeand position -locating facility via satellitein Europe.

EUTELTRACS is designed to enable com-panies to keep in permanent two-way datacontact with their vehicles throughout Eu-rope, and also to monitor their position.Countries launching customer demonstra-tions include the Netherlands and FederalGermany. Countries expected to launchdemonstrations soon include Austria. Fin-land. France, Italy and Spain.

The land mobile technology has beendeveloped by Qualcom Inc. a telecommu-nications and information-processing firmbased in San Diego. USA.

Satellite transmission to and from themobile terminals on the road are managedby an earth station operated at Lario. nearMilan, by Telespazio of Italy on behalf ofEUTELSAT. A number of Network Manage-ment Centres in several European coun-tries control access to the system.

-- SIFI-E filter has been designed speed-, c rejection of interference in the fre-

quency range below 100 kHz as experienced, for in-

stance. in switched -mode power supplies. It has atwo -stage circuit using ferrite and powder toroidalcore chokes and provides up to 30 dB rejection ofsymmetrical and asymmetrical interference at lessthan 50 kHz.

ENGINEERING INSTITUTIONSBEGIN MERGER DISCUSSIONS

The Institution of Electrical Engineers(iEE) and the Institution of Production En-gineers (IProdE) are to hold detailed talksleading to a possible merger.

Allowing for the support of the mem-bers of both institutions and the approvalof the Privy Council. the proposed mergeris likely to become effective in late 1991.

The IEE. founded in 1871. has 107,000members and the tprodE, founded in 1924,has a membership of 20.000.

The two institutions share many en-abling technologies. Developments inelectronics and information technology are

The new Siliconix S19910 power itosFer driver ic is the first in a range of 'adaptive' power -control circuits. This

single -channel, non -inverting driver adapts to the power mosFEr's operating conditions, thus providing protec-

tion for the mosFEr as well as optimizing gate drive when needed. Use of this adaptive technique eliminates

the need of designing motor drives for worst -case conditions or for adding external devices to guarantee safe

operation. The benefits are much improved system performance, greater efficiency and reduced costs.

ELEKTOR ELECTRONICS APRIL 1990

mtransforming the scope and nature of man-ufacturing engineering and thus wideningthe range of knowledge and skills neededby the production engineer. Moreover, agrowing proportion of manufactured prod-ucts involves electrical systems and. in-crea.singly, microprocessor -based controls.

Both institutions believe that themerger discussions could pave the way toa more integrated engineering profession.which would be of benefit both to thecountry and to the image and status of theengineer.

PC AT COMPATIBLE CHIP SETSIntel's new 82340 chip set is the only 16 -bit, two- to three -component solution thatsupports the entire price/performanceranee of the 32 -bit 386 microprocessor ar-chitecture, from the entry level 386 SXconfiguration to the higher performance33 MHz 386 DX microprocessor. PCs de-signed with fewer logic and TTL compo-nents are typically less expensive and usea smaller footprint than current modelswith the same performance.

CONFIGURABLE 4 -MEGABITEEPROM MEMORY MODULE

White Technology's new Model M4194E,a compact 4 -Megabit EEPROM MemoryModule. can be configured as 512 Kbyteby 8 bits. 256 Kbytes or 128Kbytes by 32 bits. The user makes the

choice because the hybrid is totally un-committed until it is soldered to the PC

board. Its design allows it to be used withvirtually any 8-. 16-. or 32 -bit micropro-cessor or system: Z8000. 8086, 80286,80386, MC68010, MC68020 and others.(Readers mar note that a more detaileddescription of this module will be given ina forthcoming issue-Ed.)

QUICKPULSE PROGRAMMERStack Ltd have developed solutions thatimprove existing data transfer formats togive higher transfer speeds, increase relia-bility and give confidence in the data in-

tegrity in the programming of EPROMS.

These solutions are incorporated in theType C289 programmer. The speed advan-tages gained by the use of Quick -Pulseprogramming over Intelligent program-ming arc shown above.

Details from Stack Ltd. WedgwoodRoad. BICESTER OX6 7UL.

TV STEREO DECODERS INA SINGLE CHIP

Stereo decoders for TV sets and videorecorders are now available as a singlechip: the Siemens TDA6610, TDA6611and TDA6620. These combine the func-tions previously provided by two chipswith a total of 52 pins in a single chip withonly 28 or 18 pins. Monitoring and controlof the ICs are achieved with the 12C bus.which has become established as the defacto standard for consumer electronicsequipment in Europe.

One of the most significant improve-ments offered by the new ICs is their ex-ceptionally high reliability in decoding thestereo pilot signals: a rapidly locking, non -adjusting PLL circuit uses the line fre-quency as a reference; this. in turn. formsthe reference for the pilot signals. Operat-ing almost like an audio spectrum anal-yser, the decoder uses a bandpass filterwith a very narrow bandwidth (<1 Hz) anda synchronous modulator to detect whetherthe transmitted signal is stereo or dual audio.

EXTRA -LONG-PLAYINGVCR TAPES ON RAY

Developments in vcg and tape technologyin Europe may result in VHS tapes provid-ing up to 3(1 hours of recording and playback time. The extra long playing videocassettes may become available during1991. according to BASF who are cur-rently testing the tape.

Meanwhile. Finland's Nokia has devel-oped a signal processing technology thatallows a vats recorder to run at about athird of its normal speed. That would ex-tend the playing time of an E-240 cassetteto 12 or 24 hours (on recorders that al-

ready have a long -play facility).

SATELLITE TV AUDIENCESDISAPPOINTING

According to Communications and Infor-mation Technology Research in London.European satellite TV attracts only 1.7%of European audiences. In early 1989, the40 European satellite stations had an audi-ence of only 16% of households equippedto receive them. But as only 11% of Euro-pean viewers can receive satellite stations,this means that they capture only 1.79i ofthe total European audience.

MATHCAD FOR ELECTRICAL/ELECTRONIC ENGINEERS

A MathCAD Application Pack for electri-cal/electronic engineers is available fromAdept Scientific Micro Systems. This willprovide engineers with a reservoir ofMathCAD formulas and methods for awide variety of electrical engineering cal-culations. incl. applications on antennasand waveguides. circuit analysis. transmis-sion lines. filter design, coding and signal

processing. and transfer functions for con-trol theory. Like other MathCAD packs(for mathematicians and statisticians). it isdesigned to work with version 2.0 up-wards of MathCAD running on IBM PC.PS/2 or compatible computers.

Tn,s new. low-cost 5 MHz Sweep Function Genera-tor is available from Flight Electronics. AscupartStreet. SOUTHAMPTON SO1 1LU.

ELEETOR ELECTRONICS APRIL 1990

In=232 S TIER

A. Rigby

Among the computer peripherals that are typically connected to an RS232 port aremice, plotters, tracker -balls. digitizers. printers, scanners and modems. Not

surprisingly, therefore, many computer users are forced to switch off their machineand perform the plug exchange trick when another peripheral is to be used. The

RS232 splitter eliminates this annoying problem by allowing up to 256 (yes) seriallycontrolled devices to be selected on 1 (yes) RS232 port. Switches and the like are

not required. since the selection of the peripherals is effected by software.

There is a clear discrepant -netween theserial interface -capabilities of the averagePC and the ever growing number of pe-ripherals purchased or built by computerusers. Most PCS offer only one RS232 port,while any extension beyond two of theseis relatively expensive. As result, tangledcable nests may be found behind many aPC, since a serial port may usually serveone peripheral only.

Not surprisingly, many PC userswould like to see a compact, inexpensiveand simple -to -use switching system for alarge number of peripherals. So-calledswitch -boxes offered commercially gener-ally allow two peripherals to share oneRS -232 port. Apart from the fact that anincrease from one to two peripherals is notexactly spectacular, these boxes must be

itched by hand, which requires thatthey are placed near the computer.

The RS -232 splitter has none of theseadvantages because:

it can handle many more than two pe-ripherals:it is controlled by the computer;it may be installed at a considerable dis-tance from the computer.

RS -232, a flexible interfacestandardThe RS -232 port has been in use for manyYears, mainly by virtue of its flexibility, itsability to cover long distances, its trans-mission speed options and good noise im-munity. The most practical boon is,

however, that data may be carried over a,single wire. In the most rudimentary con-figuration, a peripheral may be connectedto a computer by three wires only: TxD fortransmitted data, RxD for received data,and G\D (ground). 13v contrast, a parallelconnection requires at least 10 wires: 1 forground, 8 for the data signals and I for theSTROBE signal. At least 11 wires are re-quired if handshaking is used, since inthat case either Busi or ACI:NOWLEDGEmust be added. Although the 3 -wire seriallink mar use the XON \OFF protocol -i.e.,software - for handshaking, a hardwarealternative is often preferred in view ofspeed.and the use of simpler I/O routines.A hardware handshaking arrangementgenerally uses a number of control sig-nals, while software handshaking is basedon transmission and reception of certainwords that control the dataflow in accord-ance with the speed of the computer andthe peripheral,

Figure 1 shows the most commonlyUsed RS -232 link. A Computer is generallyclassified as DTE (data terminal equip-ment), and a peripheral as DCE (data com-munication equipment). A zero -modemconnection may be used in those caseswhere a number of control signals is notavailable. Control- and data -lines mayalso be crossed to enable two computers(both DTE) to communicate via a seriallink. The best known zero -modem con-nections are shown in -Fig. 2. The RING IN-DICATOR (RI) line is not shown in thesedrawings because it is used on some mod-ems only to signal to the computer that theauto -answer function has been actuated.The RI line is not normally used in appli-cations other -than with modems.

Switching by softwareTo guarantee compatibility with manyRS -232 peripherals, all eight control lineson the interface must be switched auto-matically. Obviously, the ground lineneed not be switched since it is commonto all equipment.

If, for instance, the computer is to beconnected to a particular printer with aserial input, all control and data signals ofa particular RS -232 outlet on the splitter

ELEK I UR ELECTRONICS APRIL 1990

RS -232 SPLITTER

Fig. 1. Standard RS -232 connections.

(to which the printer is connected) arepassed to the relevant pins of the com-puter's RS -232 port. All other equipmentconnected to the splitter is disconnectedfrom this port.

The passing of signals between thecomputer and the selected peripheralmust be done in the simplest way. In thecase of the RS -232 splitter, this has beenachieved by the use of software that trans-mits the peripheral selection code via theRS -232 port itself. Such a code is essen-tially a short trigger pulse which is sent bythe computer. It is not recognized as databy the peripherals since the TXD line isbriefly switched to a much higher trans-mission speed. The RS -232 splitter, how-ever, does recognize the trigger pulse andis switched to receive and process the da-tabyte that follows it. On reception of thetrigger pulse, the splitter prevents thesubsequent databvte being passed to theperipherals. Thus, channel selection hap-pens unnoticed by the peripherals.

There are several ways to generate thetrigger pulse. The actual method used de-pends on the computer type and your pro-gramming skills. Many computers allowthe RS -232 port lines to be controlled bymachine code or, say, a program languagelike C. A small program may be de-veloped, for instance, to make the TxD linelow for one clock pulse. If this does notwork out, an alternative method may beto briefly select the highest hit rate on theRS -232 port and transmit character FFH,which consists of a single low level (thestart bit). The disadvantages of this ap-proach are that the highest bit rate offeredby the computer is no longer available forthe peripherals, and that two R -C combi-nations must be changed in the RS -232splitter. Some computers, such as theCommodore Amiga 500, offer a maximumbit rate as high as 230 kbit/s, which re-sults in a single 4 -us long TXD pulse. Thissetting may be sacrificed to the above pur-pose of splitter channel control, since pe-ripherals operating at 250 kbaud are rare.

Users of IBM PCs and compatibles arein the fortunate position of being able toorder a disk which contains a simple pe-

ripheral channel selection program. Thepractical use of this program is simple:just enter the filename followed by thechannel number of the desired peripheral_

How it worksThe circuit in Fig. 3 contains the triggerpulse decoder and the channel selectionlogic. Every one serial channel requiresone extension circuit, which is shown inFig. 4. This is constructed on a small boardand connected to the main board by ashort length of dateable. The number ofextension boards may increase as the needfor more serial channels develops.

The RS -232 interface of the circuit isshown to the left in Fig. 3. A total of tenbuffers is used: five for input and five foroutput. The buffers are needed for signallevel conversion since the circuit workswith TTL levels (max. 5 V), while the RS -:7: may swing between +12 V and

Note, however, that although agrov.-:-..; number of computers is capableof accepting TTL levels at the RS -232 port,there are good reasons to stick to positiveand negative levels with a maximum of12 V, mainly because these afford a largernoise margin.

Of all signals on the RS -232 connector,only mp of the computer is used by thecircuit -all other signals are simplyswitched through to the peripherals. TheTxD signal, called s -ix after level conver-sion, triggers monostable multivibrator(MNIV) IC With each falling pulse edge.External components R,-Ci give the NIMVa monotime of about 6 ps. If S -IN is still lowafter this monotime has lapsed, the pulseedge that triggered the NIN1V did not be-

long to a trigger pulse. The trigger pulsedetection is, therefore, based on pulse -width comparison with the monotime.This is achieved with bistable whoseclock input is connected to the Q output ofIC=, During the falling pulse edge, i.e., atthe end of the monotime, the bistable out-puts take on levels determined by the in-formation at the J- and K -inputs. TheK -input is tied to ground. When the J -input is low owing to pulses shorter than6 ps, the bistable output levels do notchange. If, however, the pulse is shorterthan 6 its, the J -input will be high at theend. Output Q goes high to signal that thetrigger pulse has been detected.

The MMV monotime is set to 6 us toallow a safety margin of about 1.5 timesbetween the pulse time (max. 4 ps) and thepulse !frne.

Gatc:C ., in combination withICT.s, IC t=-_- keep the trigger pulsefrom bein,,z to the peripheral(s).Bistable IC- :,,..eives a clock pulse viaIC0,--1C,J at every level change of t; -IN.This clock pulse has a length of about60 ns owing to the propagation delays ofthe HCT gates. Exactly 6 us after the clockpulse, the Q output of iC5r goes tow again,so that J -K bistable leb latches the levelspresent at its J- and _K -input. Pulses shor-ter than 41.ts are not noted since they havebeen eliminated already and can not,therefore, appear in the serial output sig-nal.

All other pulses that foim serial dataon the S -IN line are passed by the bistable.From the Q output, the s -IN signal is sup-plied to the peripherals via ICio,. Since theQ output of IC-., goes high on every triggerpulse. prevents the subsequent data-

DTE DTE DTE DTE

'ND 2 2 TxD 2

Rzo 3 R4D 33 p 3

RTS 4 RTS 44 4

CTS 5 CTS 5 t o 5

DSR 6 DSR 66 fl (-I' 67SG 7 SG 77

8 613.7.0 B DCD B

DTR 22 DTR 22.22 20

two -wireDTE - DTE- link

DTE

TxD 2

DCE

2

D 3

RTS 4

Cis 5 4 1 ---*DSR 6 4SG 7

DCD 8 4DTR n

IWO - wire DTE - DCE- link

900017-12

DTE DTE zero modem

DTE = computer DCE = modern

Fig. 2. In many cases.a full-blown RS -232 connection is not required. Shown here are threesimple links between DTE and DCE. and between DTE and DTE (zero -modem).

ELEKTOR ELECTRONICS APRIL 1991)

5V

16 COMPI FERS AND NIICROPROCESSORS

K1

O 22

RI 132 94'

34

3

1

0-6

O B

IC1d12

13

41

0

ROC

FLOC

CTSC

DSRC

13:12C

RTSC

OTRC

IBC

ICI

0

o rf12V

IC3b

22

K2

-0 RS

O 808

CTSB

1:GFL9

Pr 87' 83 RA 95

10

RS232Connector

0,0 1C2

5V

0

16

0

12V

5V

IC4

J2

IC3ca 14

e8.6

3

OOOO

01.3

RCert CeltCLR 0

IC5a

2

V

5V

341 1

CS C,to

RDAV

3537

39

ICi

1182

551

EPS

G4 ,4=-05-a 0 RCP

AY -3-101512

4060

42 TCPPt

RIO

X1

11

99

C2

1111_. Z456714/13

I -C3

391. arTn1

V

0 URI RD1

8D2t.725 8.03

.1-.. C63b34804

CS5

_31 DSO

"3 067

805

RIX,PDT

133 tea R33-Arda

*C5 97

142a 7

EOM

10

9

O

cut 1C7b

a

CLR19 0, 01

ir3 02

1C8034... OA

a

7

6

t6 t4C9

14

105 106 = &CT IC9 IC10

T °

14 0, 7405, HCT 05

13 273 07

3 9:CLK

19

5V

9

5V

C12

47EV

12V

0

to

2

012V

25

O

0

DCDS

PISS

D385

-rev

TD3

0 VAUD

0 .129

0 12V

O

26

2

16

9

'5

6

12

11

13

15

17

ICI = 1488IC2 =14881C3 = 1489

ICS = 74HCTI23IC8= 741-1C1-26

tO7 =74HCT73

IC9 = 74HCT041010 = 74HCT32

IC3d

11

121

13 4 5 9

O EM

o0 Al

0 820 4.3

o Al

O AS

0 A6-0.

*iee test

909017 - 13

Fig. 3. Circuit diagram of the motherboard, which contains the trigger pulse decoder and channel selection logic to address individualextension boards.

ELEKTOR ELECTRONICS APRIL 1990

liRS -232 SPLITTER

4

word reaching the peripherals. This con-dition is ended as 1C7a is reset.

The channel number that follows thetrigger pulse is decoded by a CART(universal asynchronous receiver/trans-mitter) Type AY -3-1013, which is an in-dustry standard chip. After IC7a has beenset by the trigger pulse, the CART, ICii, isreset via network R11 -C4 and inverter [Ow.This is done to ensure that it is cleared andready for the reception of the datawordwhich determines the channel selection.The bit rate at which the dataword is sentby the computer is set with jumper J1.Three bit rates, 2400 baud, 4800 baud and9600 baud, are available from a quartz -crystal controlled oscillator/divider, IC;.In practice, it will be convenient to use thesame data rate for the channel selectioncode and the normal communication withthe peripheral(s).

The DAN' (data available) output of theUART goes high on reception of the chan-nel selection code. The positive pulse edgecauses the code available in parallel formto be latched into ICs. The Q output of IC-,prevents error pulses from the DAv outputreaching ICs. Error pulses may occur sincethe CART receives all serial data, whetherthese are channel selection codes or not.The high level at the Q output of bistableIC7. prevents ICiod blocking the P pul-ses. A valid DAY pulse resets =,, thatthe next pulses on the saw line are sent asnormal data to the peripheral(s).

On power -up, network Rs -Ch resets bi-stables IC -a, 101,, register ICs and CARTICI i. This is done to make sure that thecomputer is connected to the peripheralon channel 0 when the system is switchedon. The peripherals and the computer arenot reset, however, so that the splitter maybe switched on the moment it is required.

The circuit diagram of an extensionboard is given in Fig. 4. Every peripheralconnected to the RS -232 splitter has itsown extension board. Word comparatorIC2p forms the channel code detector. ItsP -inputs accept the decoded datawordfrom the computer, while its Q -inputs ac-cept the pre-set channel number to be as-signed to the associated peripheral. If thewords match, pin 19 goes low. The chan-nel preset is defined as a binary value withthe aid of jumpers. Channel code 0(0000 0000z)is achieved by connecting alljumpers to ground, and channel code 253(1111 11112) by connecting all jumpers to+3 V.

The actuated P= -Q output of the 8 -bitword comparator enables buffers IC2; andlena-b-c to establish the connection be-tween the computer and the selected pe-ripheral.

Level converters IC22a-bc, IC24..b., andIC25 ensure the correct voltage levels onthe RS -232 output lines.

ConstructionThe track lay -outs and the componentmounting plan of the main board areshown in Fig. 5. This board is double -sided, but not through -plated. On the

ELEKTOR ELECTRONICS APRIL 1990

VALID

AC

AIA2

A3

A4AL,

A7

TDB

RTSB

DTRB

+12V

-12V

ROB

CTSB

DS RB

DCDB

RIB

K4

C

2

5V

2(0?

O

0

17

4

O000-0

11 6

13 13

15 8

17 1

10

+)5V

0PO 00

p2PI 01

IC20 02P3 03p4 74 04

P5 HCT 05P6 688 06

p7 07?=7;

5V

12V.23

18

5

00

15

70

1-

9

12

19 10

O

O

5

9

O

0

012V

OO

6

12V

10

IC21c

5V

01.71; 20

18 18

OOO

20 5

22 16

24 14

7

12

9

4

O

26

1G 2G a1Y1 Al1Y2 A2

1Y3 IC23 A3

1Y.. 1A474

2Y1 2A1HCT2A2

2Y3244

2A32Y4 2A4

2

0O3

3

IC22a

IC22b

12V

K3

ast)-ID

IC24c

O

0

O

IC24a

2

15

2

4

6

11

IC24 b

131C24d

O

12

IC25a

TOO

RTSO

DTRO

coo

CTS0

03140

0000

RIC

c231 0 0221 ° C20=IC21 IC24 milmi

.1170n

0 C21

IC25 aima

I1:47e.,

T/-------70IC21 = 74HCT32

IC25b IC25c IC25d IC22 =148811 11

81 11 IC24 = 148912 IC25 = 1489

12

900017. 14

Fig. 4. Circuit diagram of extension board.

ready-made printed -circuit board, the lo-cations where a short piece of wire mustbe soldered as a through contact are indi-cated by silver -coloured pads at the com-ponent side. A few of these throughcontacts are made by soldering resistorterminals at the track side and the compo-nent side. If ICs are soldered direct on tothe board, the white print on a few padshas to be removed. Fortunately, this isachieved almost automatically as a resultof the heat developed during the solde-ring operation. The advantage of solde-ring the ICs direct is that the pins form thethrough -contacts, so that wires near thepins are not required. These holes must,

however, have through -wires if IC socketsare used.

Do not start fitting parts on to theboard before all through -contacts havebeen checked and found to be in order.The actual population of the main PCB isstraightforward.

The extension board is shown in Fig. 6.It is single -sided and has 17 wire links,which must be fitted first. As with themain board, the decision whether or notto use IC sockets is up to you. The pinheader block for the channel address set-ting is made either from three single -rowpin headers or one dual -row and onesingle -row type. The extension board is

18 COMPUTERS AND MICROPROCESSORS

C10

013

14

0

Cl

RE oi010

+J2 -

CSR7 C7

2 CER11

(1).001 2

0000000000K2 000000-Cla 00,000000

cii 25 2600-11-00 0 0 00 + ++

Fig. 5. Double -sided printed -circuit board for the central unit. Note that this board is not through -plated.

ELEKTOR ELECTRONICS APRIL 1990

RS -232 SPLITTER 19

COMPONENTS LIST

MAIN BOARD

Resistors:2 10k3 470o.4 10k1 'IMO

1 lk0

;F12

R3:R4; R5

RI°

Capacitors:1 1n21 39p C21 27p C3

1 ion C4

1n2 C51 407 16 V radial C5

5 100n C7 --C11

1 47u 16 V radial C12

Semiconductors:2 1488 IC1:1C2

1 1489 IC31 4060 IC4

1 74HCT123 (Cs1 74HCT86 IC6

1 74HCT73 IC71 74HCT273 !Cs1 74HCT04 ICs1 74HCT32 Ida1 AY -3-1015 ICsi

Miscellaneous:1 quartz crystal 2.4576 MHz XI1 25 -way angled sub -D

connector (female) K!1 26 -way angled pin header K21 6 -way pin header Ji1 pin header block: 3 off

4 -pin contact strips J2

8 jumper1 PCB 900017.1

COMPONENTS LIST

EXTENSION BOARD(one required for each RS -232 peripheral)

Capacitors:3 100n CmC21:C2-21 47i 16 V tantalum C

Semiconductors:1 74HCT688 1C20

1 74HCT32 1(>1

1 1488 iC221 74HCT244 1C23

2 1489 IC24:1C25

Miscellaneous:1 25 -way angled sub -D

connector (male) K31 26 -way angled PCB header K41 pin header block; 3 oft

8 -pin contact strips Ja1 PCB 900017-2

ELEKTOR ELECTRONICS APRIL 1990

Fig. 6. Printed -circuit board for the extension (one required for each RS -232 peripheral).

20 COMPUTERS AND MICROPROCESSORS

connected to the main board via K4, andto the peripheral via

Power supply and serialdata formatThe power supply tor the circuit musthave +5-V, +12-V and -12-V outputs_ Thecurrent required by the circuit depends onthe number of extension boards installed.In some cases, the supply voltages may beobtained from the PC.

The serial data format (start/stop bits.and parity bit) is set with jumpers J2b, J:.and J2d. The most widely used format, onestartbit, eight databits, no parity and 1stopbit, is set with jumpers J2b, J2c and J2dto +5 V, and .12.1 to ground.

Software and componentvaluesThe hardware is not complete without acomputer program that provides the re-quired trigger pulse and the channel selec-tion code to actuate a particular channel(0-255). Since the control of the -rxo line isspecific to the type of computer and itsRS -232 interface, the model programgiven in Fig. 8 is based on the use of thehighest baud rate for the generation of thetrigger pulse. The BASIC program issimple by almost any standard, andshould not be too difficult to adapt for aparticular type of computer or interpreter.The bit rate for the trigger pulse is set to9,600, so that the highest possible bit ratefor normal use of the peripheral(s) is 4,800at the highest.

If bit rates other than the ones men-tioned above are used, networks R7-0,and Rh-Cr must be modified accordingly.The values shown in the circuit diagramare for a trigger pulse shorter than 4 its. Ifa longer trigger pulse is used, the new R -C

values may be calculated on the basis ofthe monotime, t, obtained from

r=0.45RC (ns)

where R is in kilo -ohms and C in pico-fa-rads. Remember that C must be greaterthan 10,000 pF (10 TO. Also note that the

UART SETTINGS

data format J2b5 bit and6 bit gnd7 bit8 bit

parity bit J2denabledisable gnd

parity J2aevenodd gnd

J2cgad

gnd

O_P $7511,

Fig. 7. Basic connections between the PC,RS -232 peripherals (example).

calculation is valid for a 74HCT123 only,not for a 74123 or 74LS123, which mustnot be used here.

lf, for example, a bit rate of 9,600 ischosen, the associated pulse time is

1/9600 s = 104 !is

To ensure a safe margin between the pulsetime and the monotime, the latter is maderoughly 1.5 times longer, i.e., 150 is. Theshortest pulse time that can occur in adatastream of 4,800 bits/s is 210 us, i.e.,

ggO 00-0-0000

-1 i S rag 0.gitO

ot_si g coo

the motherboard, the extension cards and the

much longer than the monotime of 150 its.Starting from a capacitor value of 12 nF(12,000 pF), an associated resistance of

150,000/(0.45 x 12,000)

or roughly 27 kil should give adequateresults.

In conclusion, for a system in which thetrigger pulse is transmitted at 9,600 baud,and the peripheral data at 4,800 baud,both networks R6-0 and R7-05 consist of

.27-ki2 resistors and 12-nF capacitors.

100 CLOSE110 REM 9600 baud, no parity, 8 bits,1 stopbit120 OPEN "com1:9600,N,8,1" AS #1130 INPUT "RS232 address" ,J140 PRINT #1 ,CHRS( 255 ): : REM SEND PULSE150 PRINT #1 ,CHR$(J ) : REM SEND ADDRESS160 CLOSE170 REM 4800 baud, no parity,180 OPEN "COM1 :4800 ,N,8 ,1" AS190 FOR I .,SH20 TO 80200 PRINT 41 ,CHRS( I ) ; : REM PRINT CHARACTER210 NEXT220 PRINT #1 ,CHRS( 13 ) ,CHRS( 10 ) : REM230 GOTO 100

8 bits, 1 stopbit#1

END OF LINE900017-15

Fig. 8. Model BASIC control program to control the serial port of an IBM PC or compatible.

ELEKTOR ELECTRONICS APRIL 1990

t))3DD so ND EFF

FINAL PART

In this second and final instalment of the article we deal with the operation of thecircuit as well as with the construction and alignment.

Circuit descriptionFigure 8 shows the BBD chip and the as-sociated clock driver as the central partsin the circuit diagram of the sound effectsunit. The basic internal structure of thePanasonic BBD chip is given in the blockdiagram in Fig. 7.

Each output of the BBD chip, 10, has apull-up load resistor and a coupling capa-citor (CI i-Cm) that feeds the delayed sig-nal to a potentiometer (P3 -P6) to allow theindividual delay levels to be set. Invertingopamp A3 adds the delay signals at unitygain.

Identical low-pass filters with steepslopes are connected to the input and theoutput of the BBD chip. Each low-passconsists of an active part (A4/As) and anL -C rr-filter (Li-C6-C9/L2-Cis-C21). The fil-ters are eighth -order types for a band-width of about 4 kHz. This value allowsthe maximum delay time of the BBD chipto be used at a clock frequency of 10 kHz.The filter attenuation at 10 kHz is 60 dB.A larger bandwidth may be achieved byscaling the capacitor values in the low-pass filters. For a bandwidth of 8 kHz, forinstance, the values of these capacitors aresimply halved. Bear in mind, however,that this also requires the clock frequencyto be increased to 20 kHz.

Opamp Ai at the input of the circuit isa non -inverting buffer which provides arelatively low output impedance. Thenext opamp, A:, is configured as an inver-ter with an amplification of 10. Opamp A3is also set up as an inverter, so that thereis no phase reversal between A 1 and A3.Opamp A6 inverts the signal at the output,

T. Giffard

OJT.? 02TE ojTE

0 0 0 0

3326 stage BBD

10

900010-12

Fig. 7. Block diagram of the MN3101 bucket brigade delay line (courtesy Panasonic).

and at the same time mixes the input sig-nal (from P9 -R1) with the delayed signal(from R2.). The simulated sound reflec-tions (echoes) are created with the aid ofpotentiometer P2 which feeds the longestdelay (from ICI pin 6) back to the non -in-verting input of A2.

The clock frequency is determined bythe components at pins OX1, OX2 andOX3 of the clock driver chip, IC2. The com-ponents network contains two frequency -determining elements: potentiometer P:and varicap 132. If Pio is set to its maximumvalue (500 kil), the varicap control volt-age allows a frequency range of 12.5 kHzto 18 kHz (maximum delay). If Pie is set tominimum resistance, the dock frequencymay be varied between 65 kHz and96 kHz (minimum delay).

The varicap voltage is provided by amodulation oscillator, A7 -As, which sup-plies a low -frequency triangular sweepsignal. The frequency may be set with Pit,and the modulation depth with P12.

The power supply of the circuit is sym-

metrical. The optimum direct voltage set-ting for the BBD chip is achieved by crea-ting a slight unbalance between thepositive and negative rail. This setting iseffected with preset P13.

Practical notesThe 4 -kHz bandwidth of the delayed sig-nals may appear too small. In practice,however, it is hardly a problem sincehigher frequencies are also attenuatedwith natural reverberation. Some applica-tions of the sound effects unit may, how-ever, require a higher bandwidth (see thenotes in Part 1 on redimensioning of thetwo low-pass filters). Whatever band-width is used, the clock frequency must beat least 2.5 times the roll -off frequency ofthe low-pass filters. The use of the maxi-mum clock frequency of 100 kHz resultsin a bandwidth of 40 kHz, which is amplefor hi-fi applications.

If difficult to obtain, the B13204 varicapmay be replaced by similar types withsufficiently high C,,:,,/Gs ratio, e.g., theBB104, BB204B or BB304. It is also possibleto use a parallel combination of two vari-caps, such as the 1313130 or BB2I 2.

The printed -circuit board has no provi-sion for the signal feedback arrangementshown in Fig. 4. Fortunately, this is simpleto implement by a few changes:

connect R3 to the output of A3 instead ofto pin 4 of ICI;connect the wiper of P2 to pin 6 of IC3 viaa 10-1S2 resistor;connect pin 5 of IC3 to ground.

Another interesting sound effect may beobtained by mixing the input signal ininverted form with the output signal. This

ELEKTOR ELECTRONICS APRIL 1990

F.I.F.CTROPHON1CS

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Fig. 8. Circuit diagram of the bucket -brigade sound effects unit.

may be achieved by connecting Pg to theoutput of .A2 instead of Ai.

Wire links A and B are provided toallow a compander (compressor/expan-der) to be inserted into the signal path. ifused, the compressor circuit replaces wirelink A, and the expander replaces wirelink B. Wire link C is removed to allow anexternal modulation voltage to be appliedto I'12.

Construction and alignmentAlthough a fairly complex circuit, the BBDsound effects unit should not present dif-ficulties in the construction. The popula-tion of the single -sided printed circuitboard shown in Fig. 9 is straightforward.

The Panasonic ICs must be treatedwith care as they may be damaged bystatic discharges. Play it safe and leavethese chips in conductive foam until theyare due for fitting in the circuit (as the verylast components). Never solder them di-rect on to the PCB.

Note that Cio is a bipolar electrolyticcapacitor. If difficult to obtain, it may bereplaced by two standard 22-µF types ofwhich the negative terminals are intercon-nected.

Use screened wire to connect thepotentiometers on the front panel to therespective terminals on the PCB. Poten-tiometers P3 -Ps max, share a single cablescreen. Their wipers are connected to thenumbered terminals on the PCB, while

their fixed connections (the ones with thesignals on them) go to the terminals at thesides of capacitors

Leave the Panasonic ICs out of the cir-cuit as vet. Provisionally fit wires betweenpin 12 (IN) and pins 4-9 of the socket forICI. Turn P2 and P4 to their minimum vol-ume settings, an apply power.

Set P3 for equal positive and negativevoltages (±8 V). Check the supply volt-ages at a number of points. Next, checkthat all opamp outputs, with the exceptionof A7 and As, are at about 0 V (all poten-tiometers must be connected for this test).The output of AT should supply a voltagewhich toggles between +8 V and -8 V (thetoggle rate is adjustable with Pii). OpampA, should supply a slowly varying signal.

With P2 and Pg set to minimum volumeand with a signal applied to the input, theeffects unit should supply an output sig-nal whose bandwidth is clearly limited(i.e., it lacks high -frequency components).Check that the volume of this signal isadjustable with P3 -Ps. Turn up P,) -thesignal must become louder and containmore treble. Turn up P2 and check that thevolume increases further at a slight soundchange. If these tests check out so far, thepower may be switched off and the Pana-sonic ICs fitted.

Switch the power on again. The BBDchips work if the effects unit producesoutput sound with P2 and PQ set to mini-mum volume. Turn up P3 -Ps in successionto test the single -reflection function. In-

crease the input level until the output sig-nal is distorted. Next, adjust P13 for mini-mum distortion, and increase the inputlevel for a second adjustment. Optimizethe drive margin in this way until no fur-ther improvement is noted.

Adjust Pio to check that it changes theecho distances. Turn up P12 -the vibratoeffect becomes audible. Set a short delaytime (signal from Ps only; Pio set to highclock rate) and slowly turn up MO to checkthat the vibrato effect changes into phas-ing.

Finally, test the reverberation function.Turn Pi2 fully counter -clockwise and turnup P2 carefully. Next, turn up the delaycontrols in succession to obtain differentreverberation effects.

CONTROLS OVERVIEW

Pi: input signal level

P2: feedback (=reverberation time)

P3-138: individual reflection levels

P9: input signal level at output

Pio: clock frequency (=delay in IC;)

Pii: vibrato phasing modulationfrequency

P12: vibratolphasing modulation depth

P13: distortion adjustment (IC

ELEKTOR ELECTRONICS APRIL1990

BBD SOUND EFFECTS UNIT FINAL PART

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COMPONENTS LIST

Resistors: 1 10k logarithmic Semiconductors:6 10k Ri;R4;Rs;R2s:R2e: potentiometer Pa 1 1N4148 Di

Ras 1 500k linear BE3204G 0210 100k R24R3;R16-R22;f33a potentiometer Pie 880C1500 E3.1

2 3k3 Fts;R7 1 -IMO linear 1 MN3011 lel2 5k6 R7;R2s potentiometer Pis

1 MN3101 1C2

4 1k05 1:15:139;R23;R24 1 Ik0 preset H P131 TL074 1C3

6 56k Rio -R15 1 TL072 1C4

2 470k R29:1131 Capacitors:1 TLC272 105

1 47k Rso 3 11.10; MKT CI;C10:C261 LM317 ICe

1 1000. Fb2 10 100n C2;C3:C24;C25;C31;1 LM337 1C7

1 68k R33 62 ;014;C:033;

2 1 MO R34;Fia5 Miscellaneous:1 6k8 R37

4 3n3 CI:CS;C;CM4 100 mH radial choke

2 3301? 1139:R428 22n Gs-C3:CIS-C21 Toko 181LY-104 1_1;L2;1.3;L:.

2 1k2 R4s;F1417 220n C11 -C17

1 printed -circuit board 900010.1 50k linear 1 22g: 25 V radial C27

potentiometer P1 2 470p C2a;C2a

2 10k linearpotentiometer R2;P:2

1 10p; 40 V; bipolar(radial) Coo

6 100k logarithmic 2 470p; 25 V (radial) C33:C37

potentiometer Ps -Ps 2 1g0; 16 V C35;C'39

ELENTOR ELECTRONICS APRIL 1990

24

THE DIGITAL MODEL TRAIN

CONCLUDING PARTby T. \Vigmore

The concluding part of the article discusses an alternative to thetwo -rail locomotive decoder, a coach lighting decoder

and front and tail lights

Parts 2 and 3 of this article described the designand construction of the locomotive decoder andtwo -rail adaptor. There will, no doubt, be somemodellers who do not want to build those unitsand rather buy the ready-made Marklin de-coder.

Since the N.larklin decoder is intended foruse with three -rail systems only, a suitableadaptor is needed before it can be used with atwo -rail system. Fortunately, our two -rail adap-tor can be combined with the Nlarklin decodersto enable these to be used with two -rail tracks.

The adaptor monitors the logic level duringthe intervals between the data bytes. Depend-ing on this level, the incoming data are, or arenot, inverted by N4.

The adaptor has four terminals: input, out-put, positive supply and negative supply(earth). The supply is taken from across the47µF-, 6 V, capacitor on the PCB of the Marklindecoder.

The input is connected to the brown termi-nal of the decoder, while the output is taken topin 15 of the 16 -pin IC (Marklin or Zymos type)in the decoder.

The printed -circuit board for the adaptor isavailable in combination with our locomotivedecoder board, Code 87291-2/3 or with thecoach lighting decoder board described below,Code 87291-10. Note that the board is intendedfor surface mount components.

Coach lighting decoderThe coach lighting decoder is intended for all

Fig. 84. The completed alternative two -rail locomotive decoder.

Fig. 85. The printed -circuit board for the alternative two -rail locomotive decoder.

N1 -N4 = IC1 = 4030 (4070)MMV1 , MMV2 =1C2 = 4538

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PARTS LIST

All components must be suit-able for surface mounting.

Resistors:R1. R2 =1M0R3 = 10 kR4 = 270 k

Capacitors:C1 = 1n0C2 = 15 nC3 = 100 pC4 = 47 n

Semiconductors:ICI = 4030 or 40701C2 = 4538

Fig. 86. Circuit diagram of the alternative two -rail locomotive decoder.PCB 87291-2/3 or 87291.10

ELEKToR ELECTItuNICS APRIL 1990

THE DIGITAL MODEL. TRAIN - CONCLUDING PART

rolling stock and provides four independentswitching functions. It makes possible, for in-stance, the control of coach lighting, the givingof whistles or the operating of smoke genera-tors. It can be used only in conjunction with theElektor Electronics or Marklin Digital Train Sys-tem.

The circuit of the decoder-see Fig. 87-is acombination of the locomotive decoder (seeParts 2 and 3) and the universal signals andswitching decoder (see Part 4). The data on the

rails are decoded by ICt. When the address(Al -As) of the data byte on the rails corre-sponds to that set at pins 1-5 of ICI, the nextfour bits are compared internally with the pre-vious data and, if they agree, passed on to out-puts Db-D9. These outputs are connected to anumber of darlingtons that enable a particularfunction to be selected.

Because the first three outputs are each con-nected to two darlingtons in parallel, they canswitch somewhat higher currents (up to 1 A)

rails

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D1...D4 = 1N4935

Fig. 87. Circuit diagram of the coach lighting decoder.

than the fourth output. Note also that the fouroutputs can not all deliver their maximum cur-rent at the same time, since that would over-load 1C2 as well as rectifier bridge Dt-D4. It is,therefore, advisable to switch not more than 1 Aper decoder at any one time.

Since IC2 has internal freewheeling diodes,inductive loads (coils and solenoids) may beswitched without a problem.

The printed -circuit board Code 87291-10 is afour -fold design that enables two coach lightingdecoders and two two -rail adaptors to be con-structed. Part of the PCB is double -sided, butthrough -plated. It is, therefore, necessary to sol-der some components at both sides of theboard. For this reason it is not advisable to useIC holders.

Diodes 131-D4 should preferably be Type1N4935 (or -36 or -37), but Type 1N4001 mayalso be used, although this is slower than the

PARTS LIST(For ONE coach lighting decoder)

Resistors:R1 = 39 kR2 = 100 kR3 = 1k5R4 = 270 k

Capacitors:C1 = 1n0 (ceramic)C2 = 10 n (ceramic)C3 = 100 n(ceramic)C4 = 10µF, 25 V (tantalum)

Semiconductors:01-04 = 1N4935 or 1N4001D5 = 5V6, 400 mW zener diodeIC1 = MC145027IC2 = ULN2004

PCB 87291-10

Fig. 88. The four -fold printed -circuit board for the coach lighting decoder.

ELEKTOR ELECTRONICS APRIL 1990

26 GENERAL INTEREST

1N4935.The tantalum capacitor may be bent flat on

to the board after it has been soldered in place.Note that some components must be sol-

dered at the track (copper) side of the board.The outputs are switched to earth when

they are active. Loads must therefore be con-nected between an output and the positive sup-ply rail. The (common) positive rail is indicatedon the board by 'C'.

The output voltage is equal to the potentialprovided by the booster unit less the dropacross the bridge rectifier and the output tran-sistor. If the EEDTS booster is used, it is about15 V. The load must be matched to this voltageby connecting lamps in series or by using seriesresistors.

The decoder addresses must be set in thesame way as a locomotive decoder - see Table10 and Fig. 89. This is done by means of sol-dered wire bridges.

Bit 5-the function bit in the case of a loco-motive decoder-is here used as an address bit.To that end, the relevant input of ICI has al-ready been connected to earth on the PCB. Thismeans that the decoder must be accessed withthe additional function at 'on' (Nlarklin dataformat) or, as it were, a locomotive in the nextstate (EEDTS data format).

If desired, the connexion between ICI pin 3and earth may be cut and input Ds linked to thepositive supply rail. The decoder may then beaccessed with the additional function bit 'on' oras a locomotive in the previous position. Thisenables twice as many coach lighting decoders(162) to be accessed as locomotive decoders. Nocoach address should, of course, be the same asa locomotive address.

Coach lighting decoders may be controlledvia the locomotive controllers or via the RS232interface. Depending on the state of a controller,a certain combination of outputs will be active.

Note that instead of using potentiometersfor the locomotive controllers switches may beused. If, for instance, the input of a locomotivecontroller (pin 3 of the DIN connector) is con-nected to earth, all outputs will be active. How-ever, in order to use the relevant input, it is nec-essary, just as with potentiometer -type con -

Instruction Active outputs

<0><address> All

<1><address> 2

<2><address> 1 2

<3><address> 3

<4><address> 1 3

<5><address> 2 3

<6>eaddress> 1 2 3

<7><address> 4

<8><address> 1 4

<9><address> 2 4

<10><address> 1 2 4

<11><address> 3 4

<12><address> 3 4

<13><address> 2 3 4

<14<address> 2 3 4

<15><address>

Table 11. Summary of instructions for operatingthe coach lighting decoder via the RS232 inter-face. Note that if pin A5 of IC1 is linked to thepositive supply rail, all instructions must be in-creased by <16>.

numberof loco-motive

addressnumberof loco.motive

address

Al A2 A3 A4 Al A2 A3 A4

01 1 0 0 0 41 X 1 1 1

02 X 0 0 0 42 0 X 1 I

03 0 1 0 0 43 IX 1104 1 1 0 0 44 X X 1 1

05 X 1 0 0 45 0 0 X 1

06 0 X 0 0 46 1 0 X 1

07 1 X 0 0 47 X 0 X 1

08 X X 0 0 48 0 1 X 1

09 0 0 1 0 49 1 1 X 1

10 1 0 1 0 50 X 1 X 1

11 X 0 1 0 51 0 X X 1

12 0 1 1 0 52 1 X X 1

13 1 1 i 0 53 X X XI14 X 1 1 0 54 0 0 0 X15 0 X 1 0 55 1 0 0 X16 1 X 1 0 56 X 0 0 X17 X X 1 0 57 0 1 0 X18 0 0 X 0 58 1 1 0 X19 1 0 X 0 59 X 1 0 X20 X 0 X 0 60 0 X 0 X

21 0 1 X 0 61 1 X 0 X

22 1 1 X 0 62 X X 0 X23 X 1 X 0 63 0 0 1 X24 0 X X 0 64 1 0 1 X25 1 X X 0 65 X 0 1 X26 X X X 0 66 0 1 1 X27 0 0 0 1 67 1 1 1 X28 1 0 0 1 68 reserved29 X 0 0 1 69 0 X 1 X30 0 1 0 1 70 1 X 1 X31 1 1 0 1 71 X X 1 X32 X 1 0 1 72 0 0 X X33 0 X 0 1 73 1 0 X X34 1 X 0 1 74 X 0 X X

35 X X 0 1 75 0 1 X X

36 0 0 1 1 76 1 1 X X

37 1 0 1 1 77 X 1 X X38 X 0 1 1 78 OX X X39 0 1 1 1 79 1 X X X40 1 1 1 1 80 0 0 0 0

Table 10. Address settings for the lighting de-coder are identical to those for the Icomotive de-coder. Note that if the address of a locomotive is00, the adress settings A1 -A4 remain open (x).

open

' = can not be set digitally with Marklin decoder

trollers, to connect pin 4 or pin 3, or both, of theDIN connector to pin 2-see Fig. 90.

Control via theRS232 interface makesit rather easier to keepthe switching functionsindependent of one an-other. The relevant in-structions are summa-rized in Table 11.

Head and taillightsOne of the first thingsthat is omitted fromeconomically pricedmodel trains is anyform of lighting. Thecircuit in Fig. 91 en-ables any d.c. locomo-tive to be providedwith direction -depen-dent head and taillights. Since LEDs areused, a very long life isguaranteed.

The circuit is verysimple and is really

A4 A3 A2 AlExample 0 1 X 0 = Ice address 15

(see Table 10)

iC1

57251.X31.12

Fig. 89. How to set addresses(at pins A1 -A4 of ICI).

Eleklor Electronicsdata formal set

When S is closedall culpuls are active

Fig. 90. When pin 3 of the DIN connector islinked to earth, all outputs are active.

nothing more than a number of LEDs con-nected in a bridge. The FET in the centre of thebridge ensures a constant current as long as thesupply voltage remains above about 4.5 V. Thebrightness of the lights is, therefore, virtuallyindependent of the speed at which the traintravels.

The LEDs are connected in parallel pairs tokeep the minimum operating voltage as low aspossible. To ensure good current distribution, itis essential that only LEDs of the same type andcolour are used for each pair. Note that Di -D4should be yellow (head lights) and Ds -Dsshould be red (tail lights). If tail lights are notneeded, the relevant LEDs should be replacedby a wire bridge. Do not remove diodes D9 andDIO, however, as these are required at all timesfor the correct operation of the other LEDs.

Fig. 91. Circuit diagram of head and tail lights provision.

ELEKTOR ELECTRONICS APRIL 1990

vv A LOCA' 0\This set of handy test instruments, designed by ELV, takes the hassle out ofconductor identification and trouble -shooting during cable installation work.

Any one who has ever installed a multi -way cable between two locations in, say,a home or an office, is probably familiarwith the wire identification problem.Often, the connections must be made indifficult -to -reach places, and communica-tion with the 'other end' is difficult orimpossible. Multi -way cables are com-monly used in telephone systems, inter-coms and alarm systems.

Obviously, these problems do notoccur if the cable has only 2 conductors, orif each of its conductors has a unique col-our identification. In alarm systems, how-ever, cables with non -colouredconductors are in common use for reasonsof security. The wiring allocation problemmay also arise if a cable is extended byinserting a length of multi -way cable thathappens to be available.

In these cases, it is reassuring to be ableto check and record the function or num-ber of each conductor in the cable. Thewiring allocation tester described hereallows this to be done in a time -efficientmanner that eliminates the risk of wrongconnections. A code transmitter is used atone end of the cable, and a special receiverwith digital read-out at the other end.Both the transmitter and receiver arelight -weight, battery -powered units inrugged ABS enclosures.

Operation and controlsAs already stated, the wiring allocationtester consists of two units: one is a codetransmitter for use with up to 16 conduc-tors at a time, the other is a receiver witha digital read-out that indicates the num-ber of the conductor.

The transmitter is connected to the con-ductors in the cable by means of 16 smallcrocodile clips. If a cable has fewer than16 conductors, the remaining transmitterconnections are simply not used. If thereare more than 16 conductors in the cable,these are allocated in the respective num-ber of passes of 16 at a time.

It is important to make sure that theconductors to be allocated are potential -free and not connected at any point.

At the transmitter side, the conductorends are labelled with small adhesivesmarked 1-16, corresponding to the num-bers printed on the front panel of thetransmitter. The single lead at the oppo-site side of the transmitter enclosure ismarked REFERENCE and must be con-nected, for any test, to the correspondinglead on the receiver. In most cases, this ispossible by making use of the cablescreening braid, or a conductor with a

colour or thickness that makes it differentfrom the others. If neither of these possi-bilities is available, the REFERENCE leads onthe transmitter and the receiver may beclipped to a nearby earth connection, awater supply pipe, or a central heatingpipe.

The receiver has two leads, one for ground(REFERENCE), and one for the conductor tobe allocated at the far end of the cable.Both receiver leads have crocodile clips asused on the transmitter. The signal inputlead of the receiver is connected to any oneconductor in the cable. The instrumentindicates the conductor number definedat the transmitter side (1-16) on a liquid -crystal display (LCD). Short-circuits to theREFERENCE potential are indicated by a dis-play reading of '36'.

Both the transmitter and the receiver arepowered by a 9-V battery. The battery inthe transmitter may be installed by un-locking the cross -slotted screw at the backof the instrument, and removing the tophalf of the enclosure. The receiver has aseparate battery compartment that may beopened without unlocking a screw.

The transmitter battery will typicallylast for about 400, the receiver battery forabout 2,000, hours of operation, assumingthat a 9-V PP3-size Alkali -Manganesetype is used.

A red, flashing, LED is used on thetransmitter to indicate that the unit is on.The LED goes out if the battery voltagedrops below about 6.5 V, at which voltage

the instrument will, however, continue tooperate for a couple of hours.

The receiver's on/off slide switch islocated on the left-hand side panel of theinstrument. A conductor number is dis-played when the signal input receives avalid code from the transmitter. It is, inprinciple, possible to have the transmitterpower the receiver via the two conductorsin the cable. This option obviates the needfor a battery in the receiver, but does notenable the short-circuit tracing function('36' reading) to be used.

Transmitter circuitThe circuit diagram of the transmitter isgiven in Fig. 1. The 9-V supply voltage isapplied to buffer capacitor C3 via switchSi and resistor Rb. The voltage across C3 isused to power all transmitter circuits withthe exception of the LED. The actual cir-cuit supply voltage is of relatively littleimportance and lies between 5 V and 8 Vdepending on the number of conductorsconnected (remember that CMOS Itssuch as the ones used here can usuallyoperate from supplies between 3 V and15 V).

The oscillator in ICI operates at32.768 kHz as determined by quartz crys-tal Qi. The following dividers (bistables)in ICI provide a number of control signalswhich are used in the rest of the circuit.Output Q5 supplies a frequency of1,024 Hz. This signal clocks four shift reg-isters Type CD4015, IC2-1C3 (note thateach of these contains two shift registers).

ELEKTOR ELECTRONICS APRIL 1990

28 TEST AND MEASUREMENT

The data input of the top shift register istied to the positive supply voltage. Thisresults in output Q1 changing from low tohigh on the first clock pulse received fromthe Q5 output of ICI. Output Q2 changesfrom low to high on the second dockpulse. Similarly, Q3 and Q4 go high on thethird and fourth clock pulse respectively.

Output Q4 of the top shift register isconnected to the data input, pin 15, of thesecond shift register. Consequently, Q1 ofthe second shift register goes high on thefifth clock pulse applied to ICa. OutputsQ2, Q3 and Q4 go high on the sixth,seventh and eighth dock pulse respective-ly. The last shift register output that goeshigh is Q4 of IC3b. Shortly after, the low -to -high transition at Q10 of ICI causes allshift register outputs to go low again. Thisreset state has the same duration as thepreceding series of 16 clock pulses. WhenQ10 goes low again after 32 clock pulses,the shift registers are enabled again andaccept the clock pulses supplied by Q3 ofICI. The above sequence is repeated, start-ing with the low -to -high transition of Q1of ICzi. The on- (logic high) time of a shift

register output becomes shorter as it isfurther down the cascade. Hence, Q1 ofIC2. has the longest on -time of 16 clockperiods, while Q4 of is high for oneclock period only. These times are pro-cessed in the receiver to recognize the 16conductors that carry the associated sig-nals.

Inverters 1C4-IC3-ICb also act as buf-fers. Pin 2 of IC4 supplies a low signal witha duration of 16 clock pulses, while pin 10of ICE supplies a low signal with a dura-tion of one clock pulses.

A red LED, D4, functions as an on/offindicator on the transmitter. Its anode isconnected to the 9-V supply voltage di-rectly behind the contact of switch Si. Itscathode is connected to the collector oftransistor Ti via a 4.7 V zener diode, D.The transistor and associated partsR3 forms a 10-mA current source. The LEDwill light at constant brightness as long asthe battery voltage exceeds about 6.7 V.This value is obtained by subtracting thesum of the voltage drops across RI (0.7 V),D5 (4.7 V), and D4 (1.3 V) from the nomi-nal battery voltage of 9 V. The relatively

small current passed by Ti results in avirtually negligible voltage drop acrossthe collector -emitter junction. If the bat-tery voltage drops below 6.7 V, the bright-ness of the LED reduces rapidly, until itgoes out at about 6.0 V.

The current source around Ti is pulse -controlled to keep the overall current con-sumption of the LED low. The duty factorof the control signal, and with it the LEDcurrent, is about 0.14 (pulse/pause ratioof 1:7) as determined by diodes DI -D2 -Dawhich combine three counter output sig-nals of ICI to provide a LED flash rate ofabout 2 Hz. This arrangement results in apower saving of about 12.5c7c.

Receiver circuitThe circuit diagram of the receiver isgiven in Fig. 2. Like the transmitter, thereceiver is powered by a 9-V battery via aswitch and an R -C network, Rs -C.3. Resis-tor Rs has a relatively high value whichensures a circuit supply voltage of around5 V. Since the receiver circuit does notcontain current -hungry parts, the battery

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Fig. 1. Circuit diagram of the transmitter unit.

ELEKTOR ELECTRONICS APRIL 1990

WIRING ALLOCATION TESTER 29

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capacity will be sufficient for about2,000 hours of operation.

Like the transmitter, the receiver usesa Type CD4060 oscillator/divider as thecentral clock source. The clock pulse fre-quency at output Q5 is also 1,024 Hz asdetermined by quartz crystal Qt(32.768 KHz). The clock signal is appliedto the count input, pin 9, of IC4. The num-ber of clock pulses that can be counted isdetermined by the length of the counterenable signal applied to pin 10.

The following description of the re-ceiver timing sequence starts with the mo-ment output Q10 of IC2 supplies a resetpulse. This low -to -high transition is de-layed by network 14-C4 and subsequentlyapplied to the input of inverter IC3. As aresult, inverter ICac supplies a low -to -hightransition that resets the counters in IC4 aswell as the oscillator/divider, IC2. At thesame time, output Q10 of IC2 goes low,and the reset pulse supplied by ICk isended. The circuit is ready for a new countcycle.

Assuming that inputs ST3 and ST4 arenot connected, the inputs of gate IC3,1 arepulled high by lb. Since IC3,1 is an inverter,its output then supplies a low level thatkeeps IC4b disabled, although this counterreceives clock pulses. The display indi-cates '00' in this condition.

If inputs ST3 and ST4 are connected,iCza supplies a high level that enablescounter IC4b. The gate simultaneouslysupplies a pulse, via C5, to ICab, whichpasses it on to ICI,. The needle pulse atpin 11 of IC7 resets the two counters in 1C4,as well as the oscillator/divider, IC2. Sincethe pulse is very short, these circuits arere -enabled almost immediately after-wards, so that the clock pulses supplied

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Fig. 3. Timing diagrams to illustrate the operation of the code transmitter and receiver.

ELEKTOR ELECTRONICS APRIL 1990

30 TEST AND MEASUREMENT

by the Q5 output of IC2 may be counted byIC4a and IC4b.

After counter IC4b has reached state '9',a carry is effected to IC4a via the Q4 outputand the enable (EN) input of the respec-tive counters. In this manner, 16 clock pul-ses are counted until output Q10 of IC2changes from low to high.

When that happens, a high pulsereaches the strobe inputs of de-coders/LCD drivers ICs and IC6. Thisevent causes the current BCD countervalue (e.g., 16) to be latched and dis-played.

Since the most -significant counter,IC4., need discriminate only between 0and 1 (higher values than 16 are do notoccur), Q1 is connected to the least -signi-ficant input of the associateddecoder/LCD driver, 105. The next higherinput of ICs, pin 3, is driven by IC:. If ashort-circuit exists between a conductorand the reference potential, this gate sup-plies a permanent logic high level thatcauses the input value of IC5 to be in-creased by '2'. As a result, the value '1'determined by IC4 pin 3 changes into '3'.Hence, short-circuits in the cable are indi-cated by the value '36' on the display.

Shortly after the strobe pulse, ICkclears IC2 and counters 10.-1C4b with theaid of a delayed (Re -C4) reset pulse. Sincethe previously established counter statesare latched in ICs and ICa, the displayreading does not change. When the inputterminals, ST3-ST4, are disconnected, thedisplay changes to '00' after the next countcycle. Since the measurement rate is about30 per second, the display reading follows

the wire probe operations virtually imme-diately.

For the following description of theconductor decoding operation, it is as-sumed that the signal input, ST3, is con-nected to conductor number 8 in the cable.In the stand-by state, the transmitter sup-plies a high level, so that the output of IC3,1is low. As soon as the input signal goeslow, this output changes to high. Capaci-tor Cs supplies a reset pulse to IC2 and thecounters in 1C4. Next, the count cyclestarts. Counter IC4i counts the clock pul-ses supplied by the Q3 output of 1C2 untilthe output of IC -d goes high. In thisexample, input ST3 is low for 8 dock pul-ses, then reverts to high. The resultant lowlevel at the output of IC:ti disables IC4band so stops the counters at output state08.

After 16 clock cycles, Q10 of IC2changes to high and causes the counterstate to be latched in the LCD drivers. Thereadout is '08' in this case. Next, networkRe -C4 causes the counters to be reset, anda new measurement cycle to begin.

The input of ICm is protected by R4 -D2 -Ds.The latter is a zener diode because thecircuit has a relatively high series resistorin the power supply line to minimize thecurrent drain, and also because D2 alonewould not afford sufficient protectionagainst serious input overload conditions.

When the -receiver is used without abattery, the circuit is powered by thetransmitter, via the cable wires, the inputterminals ST3-5T4, R4 -D2 and C3. The lat-ter is a buffer device which retains suffi-

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cient charge to power the receiver circuitduring the low parts of the input signal.Obviously, the receiver can not workwithout a battery if its inputs are eitheropen or short-circuited.

A frequency of 128 kHz taken from Q8 ofIC: is applied to the DEN (display fre-quency in) terminals of the LCD drivers,ICC5-IC6, and to the backplane terminal,pin 2, of the 31/2 -digit LC display.

ConstructionTransmitterThe transmitter is constructed on a singleprinted -circuit board. Population of thisboard is straightforward with reference tothe parts list and the component overlayplus photograph in Fig. 3.

Start the construction by fitting thelow -profile parts such as the wire links,the diodes, ICs and resistors ([C socketsare not used).

Push the terminals of the miniatureswitch, Si, as far as possible into the rele-vant holes, then solder them at the trackside. Solder terminals are not required atany point during the construction of thetransmitter or the receiver.

Fit the LED such that the lower side ofits plastic body is about 15 mm above theboard surface.

Connect the battery clip wires to solderpoints ST18 (÷; red wire) and ST19 (-,black wire).

Seventeen crocodile clips and flexibleleads are provided with the kit for use inthe transmitter. Arrange the leads into a

COMPONENTS LIST

TRANSMITTER

Resistors:Rs = 68f2134;Rs = 10kR2 = 33kR3 = 100kRI = 20MQ

Capacitors:Cl ;C2 = 33p

C3 = 100u 16V

Semiconductors:ICi = CD40601C2;1C3 = CD4015IC4;105;103= CD4049Ti = BC548Ds = ZPD 4V7D1;02;D3:De;D7 = 1N4148D4 = LED; 3 mm; red

Miscellaneous:01 = 3a768 kHz miniature quartz crystal.Si = miniature toggle (SPOT) switch.Qty. 1: battery clip.Qty 17: flexible test lead with crocodile clip.23 cm silvered wire.

Fig. 4. Printed -circuit board for the transmitter.

ELEKTOR ELECTRONICS APRIL 1990

WIRING ALLOCATION TESTER

regular colour distribution, and use eitherblack or white for the separate referenceconnection. Insert the free end of each leadinto the respective hole in the side panelof the top half of the transmitter enclo-sure. Make a knot in each lead at the insideof the enclosure to provide a strain -relief.Leave a lead length of about 10 mm at theinside of the enclosure. Connect all 16 sig-nal input leads, and the single referencelead, to the respective points on the PCB.

Carefully fit the completed PCB intothe lower half of the enclosure. Install andconnect the battery.

Remove the nuts on the switch shaft.Place the top half of the enclosure on to thelower half while carefully drawing out the17 leads up to the strain -relief knots.

Secure the top and the bottom halvesof the enclosure with the self -tappingscrew provided. Make sure that the top ofthe LED is about level with the front panelsurface.

ReceiverThe construction of the receiver is also

straightforward. A few points should benoted, though.

The LC display is not fitted direct on tothe board. Instead, insert it into two 20 -way contact strips, which are previouslysoldered on to the board. These contactstrips raise the LC display a little so thatits face is at the correct height for the frontpanel of the enclosure.

Fit capacitor C3 and crystal Qi horizon-tally. Cut off three 10 -mm long pieces ofsilver-plated wire (provided in the kit)and fit these into the holes for the slideswitch, Si. Solder these wires at the trackside, making sure they remain vertical.Next, solder the terminals of the slideswitch to the free wire ends.

The receiver input leads are fitted andconnected as discussed with the transmit-ter. The red wire goes to PCB spot ST3, theblack (or white) one to PCB spot ST4. Thebattery clip is connected as with the trans-mitter -the red wire goes to ST1 (-0; theblack wire to ST2 (-).

Fit the PCB with the LC display facingdown into the top half of the enclosure

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A complete kit of parts for the wiringallocation tester is available from thedesigners' exclusive worldwide dis-tributors (regrettably not in the USAand Canada):

ELV FranceB.P. 40F-57480 Sierck-les-BainsFRANCETelephone: +33 82837213Fax: +33 82838180

Push the PCB down until the face of theLCD is about level with the front panelsurface. Secure the PCB with two self -tap-ping screws at the side of the battery com-partment. Apply a little glue at the side ofthe input terminals to secure the PCB lo-cally.

Remove the battery cover and place thebottom half of the enclosure on to the tophalf. At the same time, draw out the twoinput wires and guide the battery clipwires to the battery compartment,through the slot provided. If necessaryadjust the position of the battery clip inthe compartment.

Join the two enclosure halves with thescrews provided, and install the battery.

The wiring allocation tester is ready foruse at this stage. Alignment is not re-quired.

COILIPIPIMITS LIST

RECEIVER

Resistors:R4 = 10k

= 22kR2 = 33kR9 =82kRs;Rs = 100kRi = 20MO

Capacitors:CI;C2 = 33pCs =1n0C4:Cs = 10nC3 = 1110 16V

Semiconductors:102 = CD4060IC3 = CD40111C4 = CD4518ICs;ICs = C04056D3 = ZPD 8V2Di ;D2;04:Ds = 1N4148

Miscellaneous:Qi = 32.768 kHz miniature quartz crystal.LCD' = 3'.t -digit display.Si = SPOT slide switch.Qty. 1 :battery clip.Qty. 1: 40 -way IC socket (for LC display).Qty. 2: flexible test lead with crocodile clip.39 cm silvered wire.

Fig. 5. Printed -circuit board for the receiver.

EI.EKTOR ELECTRONICS APRIL 1990

VIDEO LINE SELECTORfrom an idea by C.J.A. Kuppens

This low-cost line selector is a must for any one working on television and videocircuits. The reason is plain: an oscilloscope, even when set to TV field or line

triggering, will not usually allow you to study the video content of one specific line inthe picture. This is simply because it is re -triggered by every next sync pulse instead

of a single, user -defined, one. The present instrument ends the hassle in keepingyour scope triggered on a video signal. Applications are manifold and interesting asyou will soon discover. In particular, the 'invisible' test lines transmitted as an extraservice by most TV stations are indispensable for aligning video circuits as well as

for bandwidth- and picture -quality assessment.

LEKTOR

ELECTRONIC:Although many oscilloscopes offer twotimebase settings and associated sync sep-arators for TV signals, these functions areoften difficult to master for the beginner.For simple TV signals like a monochromestaircase, the TV field and line triggermodes are usually sufficient to ensure areasonably stable scope display. For mov-ing pictures, however, triggering is a con-stant nuisance. Furthermore, the scopeuser often has no idea which picture linehe is monitoring.

The function of a video line selector isnot unlike that of a word comparator for,say, a logic analyzer. Both circuits allowthe user to define a certain trigger condi-tion for the displaying instrument(usually an oscilloscope). This condition isnecessary to extract only the wanted infor-mation from a composite signal, and toprevent all other information arriving atthe display, where it causes confusion anddisplay irregularity. In the case of thelogic analyzer, the trigger condition isdefined as a combination of logic levels. Inthe case of the video line selector, it isdefined as the number of a specific line inthe TV picture. The present circuit has ablock of thumbwheel or other switcheswith BCD outputs to set up a trigger con-dition for any one of 625 lines (PAL) in an

interlaced TV picture. As a result, the se-lected line is the first one displayed on theoscilloscope (depending on the timebasesetting, more lines may follow).

The TV pictureAlthough it is assumed here that thereader is familiar with the basic structureof a TV signal, a few essential points willbe covered briefly in the interest of thecircuit description. The discussion appliesmostly to the PAL I/B/G TV standards.

A moving TV picture is not a series ofstill images projected on the screen inrapid succession. Rather, it is produced bythe light emission of individual pixels(picture elements) at the inside of the pic-ture tube. These pixels are actuated by afast scanning electron beam. The intensityof this beam is accurately controlled toactuate certain pixels, while 'skipping' ad-jacent ones. In this way, the picture is builtup from many hundreds of thousands pix-els. Since the actuation and light emissiontimes of the pixels are finite, the picturemust be 'refreshed' at a sufficiently fastrate. This is achieved by haying the elec-tron beam perform a scanning movementas shown in Fig_ 1. The picture is, in fact,composed of two fields, which together

form a raster or picture. To allow suffi-cient time for the blanked beam to travelfrom the bottom of a raster to the top ofthe next one, and to prevent displayflicker, the scanning is interlaced, i.e., twofields are written in succession. After theblanking period (vertical flyback), thebeam starts to write, in a zig-zag manner,the first (or 'odd') field, starting at the topcentre of the picture. The number of com-plete pictures (rasters) is 25 per second,which is obtained by displaying 50 inter-laced fields per second.

Since a PAL picture consists of625 lines, each field must have 312.5 linesto maintain the correct relationship withthe other field due to the interlacing. Thesequence is, therefore, 1-314-2-315-3-316,etc. (see Fig. 1).

A number of lines at the top and thebottom of the picture shown in Fig. 1 fallinside the field blanking and are thereforenot normally visible on the TV. On manyolder TV sets they can be made visible,however, by reducing the vertical picturewidth. In practice, about 10% of the avail-able number of picture lines (625 for PAL)fall within the vertical flyback (blanking)period, which contains the verticalsynchronization pulse and a number ofother signals.

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Fig. 1. One TV picture (or raster) consistsof two interlaced fields.

EI.EKTOR ELECTRONICS APRIL 1990

VIDEO LINE SELECTOR

TV lines in a PAL picture have a dura-tion of 64 As, which corresponds to a linefrequency of 15,625 Hz. About 52 As ofeach line contains picture information -the rest (invisible to the left and the right)is allocated to the line blanking interval.One picture is built up in 20 ms, i.e., thevertical sync runs at 50 Hz.

Inside the field blankingperiodAt the end of each field (312.5 lines). thescanning beam has to be repositioned topoint to the top of the screen. The (simpli-fied) drawings in Fig. 2 show a staircasevideo signal in two successive fields. Theraster synchronization pulse starts at in-stant FDW, the field datum word, and lasts2.5H (H = one line period). A problemmay occur with the line synchronization,which must continue during the fieldsynchronization. Normally, in a compo-site video signal, the line synchronizationis detected as a pulse that goes lower thanthe reference black (or blanking) level.Since the field sync pulse already reachesthe lowest possible level, the TV wouldmiss out on at least 2 line sync pulses ifthey were not inserted 'upside-down' inthe field svnc interval. This can be donewith impunity since most line sync pro-cessors in TV sets and monitors use thenegative edge of the pulse (in Fig. 2, theseare marked with a small dot).

Since each raster consists of an oddnumber of lines, a field consists of.an evennumber of lines plus one half line. Thismeans that instant FDW coincides withthe start of a full line (number 1) in thefirst field, and with the centre of a line(number 313) in the second field. As a re-sult, the inverted line -sync pulses occur atdifferent instants in the odd and evenfields. Without special measures, this maylead to incomplete interlacing and, as aresult, a light display flicker.

The cause of this (possible) problemlies with the synchronization separatorcircuits in the TV. In general, the line- andfield -sync signals are obtained in twoways with the aid of different circuits. Theline -sync is obtained by differentiating thesync pulse train, whereas the field -sync isobtained by integrating the sync pulsetrain. Without going into details on theseoperations, it will be clear that the instantthe field -sync pulse for the first field ar-rives, it will be one line period (H) afterthe last line sync pulse. For the secondfield, however, it follows at only 32 As(0.51-1) after the last line sync pulse. Thissituation would lead to timing problemswith the regeneration of the field -syncpulses (obtained from integration, whichis a time -based operation) for the twofields, and, as a result, small, but visible,interlace imperfections.

The solution to this problem has beenfound in the use of equalizing pulseswhich precede and follow the field -syncpulse as shown in Fig. 3. These pulses,which are 2.35 -As long, are inserted into

FIRST FIELD

FIELD BLANKING INTERVAL291 -4-

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335 336 -iOne no.

Fig. 3. TV -field transition including equalizing pulses to ensure near -perfect interlacing(EBU PAL standard).

2.5H -long slots before and after the field -sync pulse. The frequency of the equali-zing pulses is 2 times that of the linefrequency, while their width is half that ofa line -sync pulse.

The beneficial effect of the equalizingpulses is that the integrator output volt-ages provided by the picture sync separ-

ator are made equal for both fields. Theresult is near -perfect interlaced scanning.

Although the first 20 lines after thefield -sync fall within the field blankingperiod, they are not normally empty (i.e.,black with no video content). Indeed, thelines in the blanking period are often themost interesting to the video technician.

ELEKTOR ELECTRONICS APRIL 1990

34 TEST AND MEASUREMENT

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1-00

11

01

14

71 6

C5-C14 = 100n

5 R6

47k

21 31 4

02tYa

08

K3

mss

000

5.00032..15

Fig. 4. Circuit diagram of the video line selector. The heart of the circuit is formed by an integrated synchronization separator,

Depending on the TV station and opera-ting authorities, lines 15-21 and 328-334usually contain special test signals Thesevideo insertion test (\'IT) signals may befed to an oscilloscope to assess the recep-tion quality or the response of certain sub-circuits in the receiver. In a number ofcases, these lines are also used for remotemonitoring of transmitter linearity andfor information exchange between a cen-tral microwave distribution tower and T\'relay stations. The use of these lines ap-pears to be little-known, which makesthem even more interesting (also for cer-tain satellite -TV transmissions).

In Europe, Teletext is normally carriedin lines 15, 16, 20, 21 328, 329.333333 and 334.

The circuitThe practical circuit of the video line se-lector is fairly simple -see Fig. 4. The cir-cuit may be divided in two parts: a syncseparator (IC: and IC:.) and a counter plusword comparator (IC: -ICs).

The circuit has two inputs and one out-put. One of the inputs is for the compositevideo signal (0 -Bs at connector KO, andthe other for the BCD switch block (ordiscrete switches) used for setting thevideo line number. The output supplies aCMOS-compatible, digital, signal with aswing of 5 V for connecting to the triggerinput of an oscilloscope.

The key component in the sync separ-ator is IC:, a Type L\11881 from National

Semiconductor. This chip contains every-thing that is necessary to extract thesynchronization pulses from a compositevideo signal applied to its input, pin 2. Inaddition, it is capable of identifying, onthe basis of their different sync -pulsestructures, the odd and even fields thatmake up a raster. Only the BURST andoDD EVEN outputs are used in the presentapplication. The BURST output goes lowfor about 4 us to mark the approximatelocation of the chrominance colour burst(4.43 \IHz for PAL; 3.58 MHz for NTSC)on the back porch of the line blankingperiod. The burst pulse is used here forline counting since the LNI1881 lacks aline -sync output. Provided the timing iscorrected, this can be done with impunity

ELEKTOR ELECTRONICS APRIL 1990

VIDEO LINE SELECTOR

BACKGROUND TO VIDEO INSERTION TEST (VIT) LINES

VIT lines enable the quality of TV reception as well as the quality of TV and video equipment to be checked and optimized.A number of test signals are available. and their function is discussed briefly. The contents of the VIT lines are in accordancewith the relevant EBU recommendtions for PAL G.131 transmissions (CCIR Specification 624-2).Attention: the use and function of VIT lines are recommendations. not standards. Differences may therefore occurdepending on the type of transmitter (terrestial,satellite: high1low power: TV -band: etc.). as well on services and broadcast-ing authority.

VIT lines 17 and 18

12 22 2626 34 4,2 41 43 52 56 62 64 76 84 33 91 423 1-24 112 113 124 123--+1141

le.4433

(a) Reference bar to establish max. black and white levels.Test: LF-response of receive system.

(b) 2T -pulse for picture resolution assessment. T is theshortest possible rise -time in a system in which the highestfrequency of a sinusoidal signal is fc. Hence. T=1:2fc. In aPAL TV system. fc=5 MHz so T=0.1 us. The 2T pulse hassinusoidal slopes and a width of 0.2 us. Test: amplitudereduction of the 2T pulse with respect to the reference barmeans loss of high frequencies in the system. For normalTV reception, a loss of 20% is acceptable.

(c) 20T -pulse for testing chroma- and luminance responseand possible interactions between these components. The20T pulse is actually a 20T -long chroma burst. Since20TE-0.5 MHz and the chroma frequency is 4.43 MHz.these components are affected differently by bandwidthlimiting factors in the transmission system. Test: the 20Tpulse serves to identify amplitude and phase distortion:

response (1):

- : 4-302-41Wer_27.1.

chroma amplitude reduced

response (2):

response (3):

different phase delays for chroma andluminance

combination of (1) and (2)

(d) Monochrome staircase for linearity assessment. Stepsare 140 -mV level increments. Test: irregular step sizemeans non -linearity.

(e) Multiburst for frequency response measurement. Thebursts have a nominal amplitude of 420 mV:za and arepreceded by a 8 -us long 125 kHz reference signal. Test:high -frequency loss is marked by reduced amplitude.which is first noted with the last three bursts.

VIT lines 330 and 331

11'

1

0 36

035

04403

_mg L1,4 11

0 8,11 21 -sr=su.'55 6341U1241 i). 330 44164 sr...,carrier 144syrc 331

84144440 5444.4.11

12 22 25 73 47 41 4032 566] 76 28 81 86 92 sa 124 123

(f) Staircase with colour subcarrier for differential gain orphase error detection. The subcarrier level is 280 mVc:).Ideally. the colour separator in the receiver removes theluminance component and supplies a 30-ps long 4.43 MHzburst of 280 mVcp. Test: phase or amplitude irregularitieson the step instants (40-44-48-52-56 us). Use an oscillos-cope for amplitude test. and a vectorscope for phase test.

(g) Colour subcarrier signals and extended colour burst formeasurement of intermodulation between chrominanceand luminance components. After filtering out the chromasubcarrier (4.43 MHz). the luminance level should be con-stant at 0.65 V. Test: amplitude irregularities occurringbetween 78-92 us indicate intermodulation caused bychroma changes (g1) or luminance changes (g2: subcar-rier level of 420 mV0p).

From theory to practice. Lett -hand oscillogram: lines 17-18. Right-hand oscillogram: lines 330-331. Scope used: Iwatsu 100 MHz.

ELEKTOR ELECTRONICS APRIL 1990

36 TEST AND NIEASURENIENT

-10

041

fDO

FS r NOCO 11, 003

1(00

00

TsO

O0

OOOOO

O

0

O

0

40) (/=;0;)

0-11-0 0 40 0-41-0 ° 3

010-1-1001

O 0 0-1-1-0 2

0

since every line blanking period has a rearporch (whether a burst is actually presentin the CVBS signal is irrelevant here).

Both the ODD/EVEN and the BURST sig-nals are lengthened by a non-retrigger-able monostable contained in ICz.

The ODD FAT output toggles on therising edge of the first equalizing pulse inthe field -sync pulse for the first field. Thecounters in the word comparator, how-ever, are preset on the falling edge of thispulse. Since that instance occurs half -waythrough the first line, a preset value of 2(0010) is loaded into IC: by tying its B -input to the +5-V line. The result, how-ever, would be that triggering occurs halfa line too early for the first 5 lines, whichrequires a correction at the end of the lastequalizing pulse. Timer 1C2.b is triggeredon the rising edge of the ODD/EVEN signal.The Q output of this timer is connected tothe LOAD inputs of the counters IC:, IC;and IC'. These are actuated on the risingedge of the clock signal, when the presetvalues are loaded.

The BURST/ BACK PORCH signal suppliedby the L.N11881 is not used direct for con-trolling the load operations in thecounters. Instead, a non-retriggerablemonostable, IC2., is used to prevent thecounters being advanced five lines toomany by the equalizing pulses_ The mono -time of ICI, is -set to about 48 its by R2 -C4.If the monostable triggers on a equalizingpulse, this monotime ensures that the nextone is 'skipped'. In principle, the mono -time could be made a little shorter, butalso a little longer, e.g, 62 us or so, to elimi-

COMPONENTS LIST

Resistors:1 680k1 68k1 27k

RiR2

R3

3 47k 4 -way SIL array RcRs:Rs

Capacitors:9 100n CI :C2;Cs-C141 100n ceramic C32 1n0 Ce:Cs1 100p 25V radial Ce1 101.1 10V radial C7

Semiconductors:4 1N4001 131;02;D3:1341 Lt111881 IC1

1 74HCT221 IC2

3 74HGT162 IC3;IC4:ICs3 74HCT85 IC6:1C7:ICs1 7805 !Cs

Miscellaneous:1 mains transformer. Options: VR1109

(Block) or 207-863 (RS components(see text).

1 PCB terminal block Ki1 BNC or phono socket Ks1 BNC socket K.3

1 PCB 900032Fig. 5. Track lay -out and component mounting plan of the single -sided printed -circuitboard for the line selector.

ELEKTOR ELECTRONICS APRIL 1990

VIDEO LINE SELECTOR

ABBREVIATIONS USED IN THISARTICLE

BCD binary coded decimalCCIR Comite Consultatif Inter-

national de RadioC V B S chroma-video-blanking-

synchronizationFDIV field datum wordPAL Phase Alternation LineVIT Video Insertion Test

nate the risk of IC2a being triggered bynoise in the blanking period.

The three -digit binary line numbersupplied by the three counters is com-pared to a three -digit number set on BCDswitches. The line number word andswitch word are applied in groups of4 bits to the An and Bn inputs of threecascaded 4 -bit comparators Type74HCT85. The A=B output of the last com-parator, ICs, goes high if the counted linenumber matches the number set on theBCD switches. This instant marks the trig-gering of the oscilloscope timebase. sothat the content of the relevant line is displayed. The actual trigger instant coin-cides with the end of the colour burst atabout 4 gs after the positive edge of theline -sync pulse.

The 5-V regulated power supply of thecircuit is standard and requires no furtherdiscussion. Provision is made to fit threedifferent mains transformers, as will bediscussed below.

ConstructionThe single -sided printed -circuit board forthis project is shown in Fig. 5. Dependingon the enclosure you intend to use, it mayhave to be cut into two to separate thepower supply section from the rest of thecircuit.

Start the construction of the mainboard by fitting all 14 wire links, followedby the passive parts. The components inpositions R4, Rs and Rn are preferably 4 -re-sistor, 5 -pin single -in -line (SIL) arrays.Discrete resistors may also be used if sucharrays are difficult to obtain. In that case,fit four 47-1:0 resistors upright on to theboard and cut their free terminals short.Join the free terminals with a horizontallyrunning wire that goes to the PCB holemarked with a dot.

Voltage regulator IC, can make dowithout a heat -sink as it dissipates littleheat.

IC sockets are not strictly required butyou may prefer to use them to make re-placement of an IC easier if a fault is sus-pected.

Three different types of transformermay be fitted on the power supply board.The choice between these depends onavailability and the mains voltage (UK:240 V; other European countries: 220 V).For operation from 240-V mains, fit a2x4.5 V (1.2 VA) transformer from RS

Prototype of the video line selector fitted in an ABS enclosure. BCD thumbwheel switchesare fitted on the front panel for easy line setting. The video output socket (second from theleft) enables the instrument to be hooked up in parallel with existing video connections.

Components. For 220-V mains, use eithera Block lx 9 V (13 VA) or a 2x6 V (1.5 VA)type. Install insulated wire links if necess-ary:

parallel with an e \1sting video link. Alter-natively, a single BNC input socket maybe fitted. In that case, a T -junction is usedto make the parallel connection. The trig-ger output of the circuit is a BNC socket toallow ready use of available test cables.

Practical useThe mains is connected to terminal block Since tile LN.11681 has a maximum inputKi. voltage rating of 3 Vrp, it is recommended

The choice of the BCD switches is all to provide the input of the circuit with ayours. Thurnbwheel switches with BCD 10 kil linear potentiometer as a level con-outputs are available from several sour- trol. Remember that the input impedanceces. Their only disadvantages are that of the LM1881 is about 10142, and the CYBSthey are usually relatively large and not signal must be negative -going, i.e. theas quickly to operate as rotary types. Be- sync pulses point down and represent thefore connecting the BCD switches to the lowest instantaneous voltage.circuit, be sure you know the pin assign- Connect the trigger output of the cir-ment (A -B -C -D and _/common). A mis- cult to the external trigger input of thetake here makes the selection of a oscilloscope. The composite video signalparticular video line a matter of chance. If is applied simultaneously to the line selec-in doubt, check out the pin functions of the tor, the oscilloscope input and a videoswitches you intend to use with a monitor to assist in tuning to a TV station.multimeter. The inputs marked '1' on the Set the scope to external triggering, andPCB must be connected to the least-signi- select the TX' El+ mode if available. Set theficant bit, i.e., the switch terminal whose timebase to 20 us. The scope should dis-output level changes every time the play three successive lines, starting withswitch is operated. Similarly, the termi- the number set on the line selector (line 17nals that change every second, fourth and is suitable for a start).eight switch turn are connected to the PCB Finally, in view of the relatively fastpins marked 2, 4, 8 respectively. signals that occur in TV pictures, particu-

The PCB(s) and the BCD switches are larlv in the VIT lines, it is recommendedfitted into a suitably sized ABS enclosure. to use an oscilloscope with a bandwidthThe type shown in the photographs has an of at least 20 MHz. You will notice that aoutside size of 165 ii:4 I (LxWxH). relatively high trace intensity setting isA mains socket with integral fuseholder is required for a close examination of the testfitted on the rear panel. Two video input line contents.sockets are fitted on the front panel toenable the line selector to be connected in

RS 2 x 4.5 V: B-F and A-CBlock 1 x 9 V: B-E and A-DBlock 2 x 4.5 V: A-C; B-F and D-E

ELEKTOR ELECTRONICS APRIL 1990

38

SCIENCE & TLC1J \ °LOGYPARALLEL PROCESSING FOR FASTER COMPUTING

Scientists and engineers at Hydraulics Re-search Ltd. a company based near Oxford.are involved in the massive task of con-structing a three-dimensional computermodel of the North Sea. The project aimsto simulate the movement of fine sedi-ments and heavy metals under the actionof tides and currents.

For time-consuming modelling of thiskind, increased use is being made in Britainof parallel -processing computers. Thesehave many processors operating in paral-lel, enabling many tasks to be carried outconcurrently. In this way. data needed forconstructing models can be obtained muchfaster than by conventional single -

processor serial computers.Among other uses of parallel pro-

cessing is the design of new genera-tions of aero engines whose develop-ment depends on the availability offast computing. At Derby. Rolls-Royce is exploring the potential ofparallel processing as a tool forspeeding up the study of airflowthrough engines as well as for pre-dicting stress and vibration of enginecomponents.

Expertise exploitedElsewhere, parallel processing isplaying a vital role in fundamentalscientific and medical research. Forthe Imperial Cancer Research Fund inLondon as part of an internationalcollaborative project to map thehuman genome. holder of the "blue-print of life-, parallel processingpromises to speed up the process ofcracking its code considerably.

In these applications and other,like them, it is the parallel computer,and processing expertise of Britishcompanies that are being exploited.Such applications represent the lead-ing edge in the industrial use of a technol-ogy for which the United Kingdom is pio-neering both hardware and software.

Parallel processing is developingmainly along two lines. These are deter-mined by the type of problems to be sol-ved and are reflected in the architecture ofthe computers. In both cases. the object isspeed with the one -operation -at -a -timeconcept of the conventional computerbeing replaced by architectures that makemultitudes of simultaneous operations

by Brian Kellock

possible.One form of architecture is the single

instruction multiple data stream (ststo) inwhich an array of simple processors islinked to enable many identical operationsto be done simuiltaneously. The other isthe multiple instruction multiple datastream (miNID) where many more powerfulnetworked processors carry out various re-lated operations at the same time.

The Distributed Array of Processors(DAP) from Active Memory Technology(AMT) is an established example of anSIMI) parallel computer. It is this make thatis used for both the Hydraulics Research and

Systems soldDAP technology was pioneered in Britainby International Computers Ltd (ICL) be-fore the product was taken over by AMTfor further development. Another Britishuser is Queen Mary College. London.which provides a DAP service to around1000 users world-wide.

Last September. .AMT had sold 69 DAPsystems to universities. government de-partment and industrial users. Of these, 25were in the United Kingdom. 37 in theUSA. six in Continental Europe. and onein Japan. Applications range from molecu-lar physics and medical imaging to fluid

dynamics and radar processing.One of the most recent contracts

has been from the US Army for a DAP610 (cost S360.000) for mounting in ahelicopter to process airborne scannerimagery for minefield detection.

As Britain's premier computermanufacturer. ICL has a continuinginterest in developing parallel -pro-cessing machines. It is currently theprime contractor in a consortium ofEuropean companies that work to-gether as part of an Esprit 2 project.EP 2025 (European Declarative Sys-tems ) to build an MIMI) type parallelcomputer that uses oft -the -shelf RISCcomputer chips.

Britain has been responsible fordeveloping the key component usedWay in several NIINID parallel-pro-

,,ing computers. This is the trans-puter. a British invention developedby Inmos.

In 1985. six members of the teamthat developed the Inmos transputerset up Meiko Scientific to exploit itfor parallel processing.

Meiko has developed a computercalled Computing Surface. a reconlig-urable and expandable machine in

which the application software is used toalter the geometry of connexions betweenprocessors to suit the problem. Because itcontains a large number of networkedtransputers. each one a computer with itsown processor and memory. this will carryout a variety of different operation simul-taneously. Rolls-Royce is currently experi-menting with such a computer.

To date. more than 200 Computing Sur-face machines have been sold to industrial.military and research customers. Meiko's

The DAP 610 parallel processing computer contains 4096single -bit processors and will perform up to 40 billion

operations per second.

Imperial Cancer Research Fund projects.There are two versions of DAP: the

DAP 610 with an array of 4096 one -bit pro-cessors. each with up to 64 kbits of localmemory: and the DAP 510. which has 1024processors.

In operation. all of a DAP'S one -bit pro-cessors will do the same task. but eachuses different data. Large amounts of inputdata can be split into parallel streams forsimultaneous processing at up to 40 billionoperations per second.

ELEKTOR ELECTRONICS APRIL 1990

PARALLEL PROCESSING FOR FASTER COMPUTING 39largest one is at Edinburgh University.where the Edinburgh Concurrent SuperComputer Project now operates the largestparallel computer in Europe. With 400processors. this can perform 400 millionarithmetic calculations per second.

World leaderInmos's Type T800 transputer is the basiccomponent of a parallel -processing com-puter developed by Southampton Univer-

sity and its co-partners of the now com-pleted Esprit 1 Reconfigurable TransputerProject 1085.

What began in 1985 as a research pro-ject resulted in 100 man-years in a com-mercially available reconfig.urable com-puter. With the use of architecture devel-oped at Southampton. up to 1024 trans-puters can be linked in a single machine.

Southampton University is continuingto help maintain the country's position as

-ECHNOI,OGICA .AD\ ANC

When robbers hijacked a lorry carrying£300,000 worth of cigarettes in London.they thought the police had been left farbehind as they lost themselves in thecity's busy rush-hour traffic. They did notrealize that the lorry contained a low -fre-quency transmitter that broadcast its posi-tion wherever it went. The thieves weresoon arrested.

The system, called Datatrak, was de-veloped by Securicor-Wimpey. the privatesecurity firm. and the speedy tracking ofthe hijacked cigarette lorry was soimpressive that police forces aroundBritain are studying other possibleuses.

Vehicles are fitted with a computerthat picks tip signals from transmit-ters all over the country. The com-puter uses these to plot the vehicle'sposition against a grid reference mapand then relays it to a network of basestations. The base stations determinethe position of the vehicle within sec-onds to an accuracy of 50 metres.

The innovation is just one of themany crime prevention techniquesdeveloped by British experts that aremaking life much harder for criminals.

Perhaps the most important ad-vance of the past five years is the ge-netic fingerprinting technique that isnow used all over the world. This en-ables any individual to be identifiedfrom a drop of blood or saliva asuniquely as if his fingerprints hadbeen taken. When the technique v. :1'first used by British officers on a dif-ficult case involving the murder oftwo teenage girls. it immediatel.showed that their prime suspect v.in fact innocent.

a world leader in the development and ap-plication of parallel processing.

It is especially active in working on newcommunications architectures aimed at en-hancing communication between proces-sors at large bandwidths. Poor communica-tion is a weakness currently limiting thenumber of processors that can be put to-gether. In this work the university believesitself to be ahead of the rest of the world.

S IN CRIME DETECTION

by David Pead

would volunteer to take the genetic test tohelp narrow the inquiry.

Eventually. 5000 men provided smallsamples of blood for analysis. The mur-derer was discovered when one of the vol-unteers told police that a work colleaguehad tried to persuade him to take the testfor him. Tests on the colleague provedpositive and he is now serving a life sen-tence in prison.

The technique was developed by DrAlex Jeffries at Leicester University and

are unique to every individual. Dr Jeffriesand his team discovered a segment of ge-netic material that can be used to probe forthese mini -satellites. The probe splits upthe genes and eenerates a pattern of bandsthat can be printed on x-ray film.

Identifying criminals has always beenone of the most difficult parts of policework, and genetic fingerprintine has nowgiven officers another effective tool thatcan be used in a completely new area.

The pattern of chemical signals in the DNA molecule is uniqueto every individual and it can be represented graphically.

British police can now use these patterns to take bodily traces,such as blood or saliva, and connect them to one person.

Murderer caughtAs the murders had taken place in a nor-mally quiet country area in Leicestershire.police officers asked local people if they

depends on hyper -variable mini -satellitesof deoxyribonucleic acid (DNA) that occurin the chromosomes of every body cell.

These small segments of DNA are dot-ted about the chromosomes in patterns that

Visual memoryMany crimes are solved through wit-nesses identifying those responsible.Traditionally. this has meant witnessesporing over albums of photographs ofknow criminals or attempting to de-scribe the suspect's features frommemory to a police artist. who at-tempts to draw a likeness based on thedescription or build an image with theaid of identikit equipment.

Witnesses looking through photo-graph albums can soon become con-fused by the sheer mass of faces thatthey see. ldentikit systems. where wit-nesses build up faces from pre -drawnsegments. can also prove confusingand police artists are always depen-dent on hog.- good the witness is at ar-ticulating visual memories.

Researchers at the Government'sscientific and research branch of theHome Office have now come up witha system called E -Fit that appears toovercome some of these problems.

Working with a psychology teamfrom Aberdeen University, they havedesigned the system so that witnesses'memories are actually enhanced ratherthan put under pressure. Witnesses de-

scribe the most striking thing they remem-ber about the criminal. From a computerlibrary of all the main variations of facialfeatures that are possible, equivalent fea-tures are shown on screen one at a time.

ELEKTOR ELECTRONICS APRIL 1990

40 SCIENCE & TECHNOLOGY

When the witness is happy with a par-ticular feature (such as a curly moustacheor a cauliflower ear), the next feature heor she remembers is subjected to the sameprocess of identification.

Features libraryEventually, the computer presents all thechosen features together in a suggestedface likeness on the screen. and the wit-ness can then alter it in any way to get itright. The face can be widened, flattened.or stretched in any conceivable way tomake the likeness conform as accuratelyas possible to the witness's memory.

When the system was put on trial in anumber of British police forces. arrestssoon followed. In one force. a man whohad committed a sexual assault wascaught by a uniformed officer referring tothe E -Fit likeness the very first time thesystem was used.

In another force, the E -Fit compiled bya policewoman in a murder case was di-rectly responsible for the murderer's even-tual arrest.

The system's developers at first con-centrated only on building a library of thefacial features of white males. They be-lieve that good likenesses of 99.9i- of theBritish population of white males can nowbe made in E -Fit. As the system seems tobe operating well in police forces, workhas now begun on building libraries cov-ering white women and ethnic minori-ties, as well as making up whole -bodycomposites.

The system will eventually link in toFACES, another development from the re-search group. This is an updating of the oldphotographic albums of known criminalsand is proving very successful.

Photos of known criminals are stored ina computer. but before a witness looks at

any he gives the police officer as good adescription as possible. This description isfed into the computer. which breaks downthe key elements. such as "big nose and amole on his cheek-.

Likely suspectsThe computer then sorts all its photographsand will only offer known criminals withbig noses and moles on their cheeks. Itpresents them on a screen in small groups,starting with the criminals with the closestlikeness to the witness's description.

If the witness says none of them is thecriminal. the computer will offer the nextclosest possibilities-perhaps those with aslightly smaller nose. but still with a moleon the cheek.

This cuts down by an enormous amountthe number of photographs witnesses haveto look at. as well as quickly offering upthe most likely suspects.

ROBOTS FOR THE RAG TRADE

Robots with built-in sewing machines areabout to revolutionize the garment indus-try in Britain-known traditionally as therag trade-by producing made -to -measureclothes within 24 hours of order.

Manufacturers predict that by the year2000 clothes shops will be stocked withsample garments only. The customer willbe measured, the data transmitted to thefactory. and the clothes tailored by robotsto the customer's needs. bank balance andbody shape.

This radical change in the world of theseamstress is already being introduced bywholesale clothing manufacturers, butthere is still one garment the robot findsdifficult to make. Ask it. for instance. tomake a pair of underpants and, to coin apopular phrase, it definitely gets its knick-ers in a twist.

However, this problem will soon havebeen resolved by a £171.000 project atHull University where 15 robots, linked tosewing machines. have been programmedto make a pair of underpants for men orknickers for women every 30 seconds.

Sponsored by Corah, a garment manu-facturer from Leicester. who suppliesbriefs to large retailers such as Marks &Spencer, the project is backed by theClothing Technology Centre. responsiblefor promoting good design in the industry.

Problematical productionThe research team is led by Dr AntonyWilkinson and Professor Paul Taylor. Ithas long been possible to provide auto -

by Jim Kelse2,-

mated production lines for clothing, pro-vided they are dedicated to a particular de-sign of garment.

Briefs and knickers present great prob-lems to a labour-intensive industry. A typi-cal pair of briefs is made from four piecesof cloth. two of which are roughly triangu-lar for the front and back. Two squares arerequired to make up the gusset. At the startof the production line are stacks of cloth.cut in bulk and the robot has to pick upone for every garment made.

Inititally. this task proved impossible.The robot dropped the piece and could notpick it up with his pincers. Howe er. someyears ago for another project, Hull Univer-sity researchers developed the Kemp grip-per, which blew air on to the top of thestack of material to be sewn, causing thefabric edges to lift. A thin pincer couldthen slide in and pick up the top piece.

This technique was taken up in the lat-est project and now enables the robot tohandle the fabric.

In the manufacture of underpants, thefirst two sewing operations create a pieceof cloth shaped like an hour -glass. with adouble thickness gusset sewn to the twotriangles. At this stage it is still two-di-mensional and can be laid flat on a con-veyor belt.

After the next stage. where on of thewaist seams is sewn and elastic run alongthe leg hole. the half -completed briefs turninto a tangle of cloth and elastic which is acomplex shape difficult to describe incomputerized modelling programs.

Central computerThe Hull team has had to overcome nu-merous problems. The double-knit cottonused for briefs has a good deal of lint onits surface which causes nicking in align-ment and the fabric tends to stretch. Suchdifficulties have had to be overcome increating the hardware and software tomake underwear.

The technicians are using a centralcomputer to control a number of personalcomputers. each responsible for a single.complex operation, such as destacking orstitching a gusset. The computers takedata from sensors and send commands tothe robots which then begin production.

The researchers are using RTX robotsbuilt by one of Britain's largest manufac-turers. UMI. This firm specializes in edu-cational robotics, producing thousands ofrobots for research purposes and de-signed to perform boring and dirty jobsin industry.

At Hull. an electrostatic gripper hasbeen designed that can lift not only fab-ric. but paper. leather. nylon and carbonfibre. It makes the fabric stick to a flatplate with the aid of only a 9 V battery.

There is practically no such thing as astandard body shape. so. for the cus-tomer, robot production is good news.

In shops. purchasing staff will be ableto see the latest trousers. hats or socksbefore a manufacturer begins makingprototypes. The same data will be fedinto the bulk cutting machine and usedfor costings.

ELEKTOR ELECTRONICS APRIL 1990

Q METER41

J. Bareford

\ \ \ \\ \\ \

Among the main electrical properties of an inductor are its self-inductance, itsquality (Q) factor and its self -resonance frequency. An instrument to measure the

Q factor is described here. Based on resonance frequency measurement, theinstrument can be used for testing inductors at frequencies up to about 50 MHz.

Many electronics experimentalists shyaway from the design and use of inductorsbecause they feel that these componentsare difficult to test and measure. Also,often owing to lack of experience and suit-able test instruments, these constructorsare not always aware of the relative im-portance and meaning of inductor proper-ties like the self-inductance and thequality factor. Instruments for measuringself-inductance have been described forlow -frequency and high -frequency induc-tors in Ref. 1 and Ref. 2 respectively. TheQ -factor, which is equally important formany applications, may be measured atreasonable accuracy with the present in-strument. The Q meter discussed is notintended for laboratory use where highaccuracy and repeatability are prime con-siderations. Rather, it is a low-cost testinstrument for comparative Q measure -

o ments with an accuracy of about 10%. Itsusable frequency range extends from70 kHz to about 50 MHz, while Q factorsup to about 200 can be measured withreasonable accuracy.

The principleSince Q factor measurement is covered indetail in many electronics textbooks, arecap may suffice to explain the basicoperation of the instrument -see Fig. 1.

A generator, G, with an internal resist-ance RG is connected to an inductor and avariable capacitor. The voltage across thecapacitor, LL, is measured. The inductor,L., is actually a combination of an induct-ance and a series resistance, The vari-able capacitor is adjusted until the L -C

Fig. 1. Principle of Q factor measurement.

tuned circuit resonates at the frequencyset on the generator. At the resonant fre-quency, co (= 210, the voltages on the ca-pacitor and the inductor are in oppositephase, so that

111_,)/ = cot., /(Rc+Rs) = Qi,

In other words, the loaded Q factor, QL, isthe inverse of the loss factor of the induc-tor. The higher its Q, the better the induc-tor, or in more practical terms, the moreselective the parallel- or a series -tuned cir-cuit that can he made by connecting it to acapacitor.

From the above formula, the internalresistance of the generator, RG, deter-mines the Q factor along with the self-in-ductance, the resonant frequency arid the

inductor's internal resistance_ Assumingthat RG«R the real (or unloaded) Q fac-tor may be calculated from

Q = col,/ R.

The unloaded Q factor exists in theoryonly since there is always a generator re-sistance, however small.

.A few points should be noted here_ Theloss resistance, R-, is not simply the resist-ance measured by, say, an ohmmeter. Formost small inductors, the cl.c_ resistance isformed by the wire turns and remainssmaller than 1 S2 or so. The actual value of

however, is a function of frequencybecause it is determined by the skin -effectwhich forces high -frequency currents tobe 'pushed' towards the surface of thewire. The skin effect thus reduces the ef-fective wire diameter and increases ohmiclosses in the inductor owing to dissipa-tion. As a result, R- of an inductor is oftenmuch higher than the ohmic resistance.

The second point to note is evidentfrom the equations: the internal resistanceof the generator must be as low as possibleto prevent large deviations of themeasured Q factor of inductors with arelatively small R.

Finally, losses in the tuning capacitorand stray capacitance in the test circuitmay lower the measured Q factor. In prac-tice, deviations of up to 10% must beallowed for, hit these are not usually aproblem in practical electronics work.

A more practical approach to Q factormeasurement is illustrated in Fig. 2_ Thevoltage across an 1.-C tuned circuit is

ELEKTOR ELECTRONICS APRIL 1990

42 TEST AND MEASUREMENT

Fig. 2 3 -dB bandwidth test method for establishing the Q factor of an inductor in atuned circuit.

measured at the resonant frequency. Thisoltage is called the reference level, Ur-,

Next, the generator is tuned up and downto determine the frequencies at which thevoltage drops to 0.71 These two fre-quencies are the -3-dB roll -off points, andthe range between them is the 3 -dB band-width, B. A parallel combination of anideal capacitor and inductor would resultin a tuned circuit with an infinitely smallbandwidth. In practice. however, thereare small losses, so that

Q B

This test method may be applied in prac-tice with the aid of an RF signal generatorto supply the required signal at the reson-ant frequency, and an oscilloscope to findthe -3 dB points. Care should be taken,however, to couple these instruments aslightly as possible to the tuned circuit.Also, the previously mentioned loss fac-tors in L and C, as well as stray inductanceand capacitance, must be taken into ac-count.

Practical circuitAll the i..ngrej tent mentioned in the con-text of theoretical Q measurement arefound back in the circuit diagram in Fig. 3.

The RF signal generator is realized byan amplitude -controlled oscillator, T.with six frequency ranges. The oscillatoris tuned by a variable capacitor C:3, at thepole of the range selector, Si. Amplitudestabilization is achieved by rectifying theoscillator output signal and using the di-rect voltage so obtained to control the cur-rent sunk by differential amplifier TI -T2.The RF rectifier for this purpose is formedby C; and Di -D2. The latter are two Schott-ky -harrier diodes Type HP2800 fromHewlett Packard. The voltage at the gateof FET T4 goes more negative as the oscil-lator amplitude increases. Since the am-plification of Ti is inversely related to thenegative control voltage, a tendency of theoscillator to produce a higher output volt-age is counteracted by a smaller gain of Ti.When the oscillator starts, C5 is rapidlycharged and causes the gain control cir-

cuit to reduce the output amplitude untila stable level is achieved.

The function of the amplitude stabili-zation circuit is, of course, bound by prac-tical limits. The actual oscillator outputvoltage varies between 0.9 Vpp and 1.6 Vppat the lowest frequency in am, range (Ci3set to maximum capacitance). This vari-ation may be greater in the highest fre-quency range as stray capacitance andinductance in the circuit become signifi-cant.

FETs T, and T7 form a complementarypower output amplifier capable of drivingthe 5042 RF test output, Kt, and imped-ance transformer L. The quiescent cur-rent of the power output stage isdetermined by Pi, which is adjusted forminimum distortion of the oscillator out-put signal.

Switch 52 selects between the rectifiedoscillator output voltage (position B) andthe rectified voltage developed acrosstuning control C24 (position A). Both volt-ages are obtained with the aid of virtuallyidentical MOSFET buffers, Ts/T., whichare followed by signal rectifiers 1-134-C23/ D5-D,Cr. The ratio of the resonantvoltage to the reference voltage (= oscilla-tor output voltage) is a direct measure ofthe Q factor of the inductor, L..

Inductor Ls forms a wideband imped-ance transformer to ensure a low gener-ator series resistance and straycapacitance. The importance of thesecharacteristics is evident from the earlierdiscussion on basic Q measurement.

Opamp ICI forms the meter outputdriver. The maximum output voltage of2 V corresponds to a Q of about 200. Theactual read-out may be digital on a ready-made 3 -digit LCD module, or analogue ona small moving -coil meter with a full-scaledeflection of 2 V.

The circuit is powered by a symmetri-cal ±5 V supply obtained in a conventionalmanner by creating a virtual ground withthe aid of an opamp, IC3. The input volt-age to the circuit may he unregulated be-tween 12 VDC and about 18 VDCsupplied by a low -power mains adapter.The current consumption of the circuit issmaller than 30 mA.

If used, the LCD must be powered bya separate battery, which will provideample power for at least 200 hours ofoperation.

ConstructionThe first and foremost consideration thatmust be given to the construction of theinstrument is to keep the connections be-tween the inductor under test and the ter-minals marked Lx as short as possible.This is the reason that the printed -circuithoard (see Fig. 4) is fitted vertically be-hind the front panel of the enclosure, aType LC830 from Telet, which has beenused for previous instruments in thisseries.

Inductor LsStart the construction by winding Ls as

shown in Fig. 5. Use 0.5 mm dia. ena-melled copper wire. Winding A is simpleto make because it consists of 40 turns onthe ferrite ring core_ Spread the turnsevenly along the core, and at the sametime ensure that the connections end updose together.

The low -impedance winding, B, con-sists of ten parallel -connected sub -wind-ings on the ring core. Each of thesesub -windings is formed by e3/4 wire turn,the top and lower connection of which areconnected to others by common wires thatrun round the outside of the ring core.First, make the ten sub -windings from 20 -mm long pieces of enamelled copper wire,of which the enamel must be carefullyremoved over a length of about 1 mm atboth ends. Next, cut off two 65 -mm longpieces of the same wire, and remove theenamel at the ends as well as at ten loca-tions at 6 -mm intervals. Clamp the tensub -windings on to the ring core; the con-nections are at the outside. Run the firstcommon wire around the outside of thecore and join the ten top connections of thesub -windings. Next, do the same with thesecond common wire and the lower con-nections of the sub -windings. Press thecommon wires in place and bring theirfree ends together. Connect the B termi-nals to the respective points on the PCB-the wire that joins the top connectionsof the sub -windings goes to ground on thePCB. Solder the A terminals to the respec-tive PCB connections.

The Type G.2-3 /FT16 ring core fromNficrometals may be hard to find locally.To enable constructors to find equival-ents, the main electrical characteristics ofit are given below.

outside diameter: 16 mminside diameter: 9.6 mmheight: 6.3 mmrelative permeability (p): 4300At. value: 3280-5500frequency range: 0.1- 50 MHz

Printed -circuit boardThe printed -circuit board for the Q meteris double -sided but not through -plated.The large copper surface at the componentside forms an earth plane to assist in RFdecoupling.

Mount the six trimmer capacitors on tothe board, making sure that they are sol-dered rapidly to prevent deformation ofthe PTFE material by overheating. Next,fit the associated six inductors. Note thatthese are mounted alternately verticallyand horizontally to prevent inductivecoupling. As a further precaution, reversethe orientation of every second inductor.This is easiest done by noting the positionof the coloured tolerance ring at one of thesides of the body.

The remainder of the passive parts onthe printed -circuit board are fitted in theusual manner. Voltage regulator IC2 isfitted upright (like all resistors) and doesnot need a heat -sink as it dissipates littleheat under normal circumstances. Partterminals not shown with a small circle on

ELEKTOR ELECTRONICS APRIL 1990

Q METER 43

C14BF494 BF256

C 1BE S

5V

L2 L3 IA L5I L6 L7I C15 1 CI6 1 = C17 1 C18 1 1if. ,1 g i E. 1 a 1 : a

_C191= 1

40p 1 40p 1 40p 1 40p 11 40p 1 40p 1

lb ...

$ C13

2xBF494

5009

=C20

137n

5V

RI

fl

BC550C

77n

T3

D

147n

C41Nene

47nT5

R4

075V1BF

Tr256A

R2

-E

270n

IZEIM

QUI

02

61 R7

10n

BF R6

982 z

0

1-05V1

C8-lOon

T4

NEIR3 Cs

IN=

2xH P2800

01

180n

C7

R C9

em m l100n

LI11

1 4700560p

PI

85170

RIE6

-2"" I KEEI

EllR22 0T7

R8

25k

Ic7n

R9

BS250

R10

C11=NM

47n

C12 O 5V

BF981

BS170B S250

BF982D iS

C

LB

1

40W40T 1 11T

1

G2.3/FT16

*see text

C24

10n

5V O C25

BF981

R13

5005

47n

C26

10n D5

5V0

D3-D6=AA119

5V C2I

47n

C22

BF981

I0n D3

5Ve

D6

C27 P2

100n

MEI

Operate52

cal.

B

C23

:On

5V

OC31

trndRII

IEZ1271C1

5

105bOV

C32

lop1M bov

5V

,. R20III31

P3

R14

9

100k

C28 RIB

IOn 9

TLC271

1C2

K1 RF

1 0

C29

10425V

2V 20=200

- 0

900631 - 13

Fig. 3. Circuit diagram of the Q meter. The read-out is either digital in the form of an LCD module. or analogue in the form of a moving -coilmeter -the choice between these is entirely up to the constructor.

the component overlay are soldered directto the copper surface at the componentside of the board.

Solder rotary switch Si direct on to theboard (do not use a type with wire connec-tions; these, however short, introduce un-acceptable stray inductance). Only onesection of a dual -pole b -way switch isused.

The FETs are static sensitive and theirterminals must remain short-circuited bya small piece of aluminium foil until they

have been soldered on to the board. Theactual solder operation should be as briefas possible, and take place with the soldertip connected to the ground surface of thePCB.

Finally, fit solder terminals for all ex-ternal connections.

Mechanical work and connectionsStudy the lay -out of the front -panel(Fig. 6) and determine the location of thePCB to the right. Drill the front panel,

using the ready-made adhesive as a tem-plate. At this stage, you have to choosebetween a digital read-out and a moving -coil meter before cutting the requiredclearance. If used, the moving -coil metermust be provided with a scale of 0-200.The 1.54_ voltage must be 2 V (if necessaryfit the required series resistors to makethis voltage correspond to the f.s.d. cur-rent of the meter).

Provisionally fit all controls and soc-kets on the front panel. Mark the location

ELEKTOR ELECTRONICS APRIL 1990

44 TEST AND MEASUREMENT

of the four holes in the PCB corners at theoutside of the front -panel, to the rightwhere the PCB is to be fitted vertically.Drill holes for M3x50 screws withcountersunk heads. Insert these screwsfrom the outside of the aluminium frontpanel. Secure them at the inside with a nutand a locking ring. Next, slide approxi-mately 30 -mm long plastic PCB spacersover the screws and install the hoard withthe components facing the inside of thefront panel. Determine how much spaceyou need for the tuning capacitors, theFREQ. BNC socket and the Lx terminals,then cut the PCB spacers to the minimumrequired length. The Lx terminals are me-dium -duty binding posts for panelmounting.

Remove all controls and terminalsfrom the front panel and apply the self-ad-hesive, two-colour, front panel foil.Mount all controls and sockets andtighten them without damaging the foil.Cut the spindle of the CAL. potentiometer,P5, to enable the knob to be fitted. Do thesame with the spindle of the rotary switchon the PCB. Solder wires to the terminalsof all controls and the meter (or LC dis-play): those to the tuning capacitors, theFREQ. socket and the Lx terminals must bekept as short as possible. Their length,inclusive of the cable connector, must notexceed 30 mm. Coax cable (RG174 L-)may be used for the FREQ. output, hutgiven the short length ordinary screenedcable is also suitable_

OPERATION AND CONTROLS

POWER switch: switch instrument onand off.

FREQ. socket: oscillator output for testpurposes.

Lx sockets: connect to inductor to betested. Do not use test leads.

METER: digital (LCD) or analogue(moving -coil); max. scale indication:200.

CAL. control (P3): adjust to set meterreading of 100 in celibate mode.

CAL./OPERATE switch (S2): select be-tween calibrate and Q measurementmodes.

TUNING COARSE switch (Si): selecttest frequency range. Always startmeasurement in 20-70 MHz range,switch to next lower ranges if no reson-ance is found.

INDUCTANCE ADJUSTMENT control(C24): turn to find resonant frequency inselected range. Use before FINE TUN-ING control.

TUNING FINE control (C13): peak res-onant voltage indication on meter ordisplay.

C3 0 =,=C4'L.

n2'1

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CA A00092J R13 C23

92

ELEKTOR ELECTRONICS APRIL 1990

Fig. 4. Double -sided printed -circuit board for the 0 meter.

Q NILTER 45Finally, drill a suitably sized hole in the

back panel of the enclosure to enable theadapter (d.c. input) socket to be fitted. Ifyou use an LC display, install a batteryholder for a single 9-V PP3 size battery,and use a double -pole (DPDT) on /offswitch to power the display and the in-strument simultaneously but separately.

Ready for testingProvisionally connect the PCB to the wiresfrom the controls, the meter, the FREQ. out-put socket and the binding posts. Set alltrimmers, P2, and the front panel controlsto the centre of their travel. Only Pt is setto minimum resistance (fully clock -wise).

Setting upAlthough the meter may be set up withoutthe help of an oscilloscope and a fre-quency meter, it is recommended to usethese instruments to achieve the best oper-ation.

Set the coarse tuning control to the lo-west range (70 kHz). Switch on and usethe scope to check the presence of a signalat the FREQ. output on the front panel.Adjust Pt for minimum distortion of thesine -wave. Do this for all ranges. In thehighest range, a compromise will have tobe reached between an acceptable outputlevel and minimum distortion. If vou do

Fig. 5. Construction of the wideband transformer. Ls (left), and practical version (right).

not have an oscilloscope, use the meter onthe instrument to adjust Pi: set Cu tomaximum capacitance (fully cw) and ad-just Pi until the amplitude in the highestrange (70 MHz) is not more than half thatin the lowest ranges.

The calibration preset, P2, is adjustedwith the aid of an inductor whose Q factoris accurately known (read the section onpractical use below to find out how the Qfactor is measured). Unfortunately, thereis practically no other way to calibrate theinstrument. Owners of an oscilloscopeand an RF signal generator may, however,use the previously discussed 3 -dB band-width method to approximate the Q factorof a particular inductor. If this method can

COMPONENTS LIST

Resistors:1 560U R1

1 1k0 R21 4M7 R3

1 1k5 R4

1 47012 As1 IMO Rs2 10k R7;R82 100 Ra;Rio1 47Q Rif2 6k8 1312;1113

2 100k R14;R181 820Q R15

2 4k7 R16;R171 150k R19

1 82k R2o2 won R21;R22

25k preset H PtIMO preset H P2

100k lin. potentiometer P3

Capacitors:8 47n

1 270n1 180n4 10n1 560p6 100n

Cl :C2;C4',C10;C 1;C20;C21;C25

C3

CsC6;C12;C22 ;C26

C7

CS;C9;C23:C27;C25;C30

2 500p mica -foil tuningcapacitor C13;C24

6 40p PTFE foil trimmer C14-C191 101.1 25V axial C29

2 10n 10V axial C31;C32

Semiconductors:2 BF494 Ti;T21 BC550C T31 BF256A T41 BF982 Ts1 BS170 Ts1 BS250 T72 BF981 Ts;Ts2 HP2800 D1;D24 AA119 D3-Ds1 LED 071 TLC271 ICI1 7810 1C2

1 LM741 IC3

Inductors:1 470pH1 10mH radial1 1mH1 100gH L.1 101.1H L5

1 1111-3 Le

1 100nH 1.7

1 G.2-3:FT16 ferritetorpid Ls

Enamelled copper wire 0.5 mm dia.

Miscellaneous:1 6 -way rotary switch for

PCB mounting: 2 poles Si1 miniature SPDT switch S21 BNC socket Kt2 binding post1 PCB 9000311 front -panel foil 900031-F1 enclosure LC -850 (Telet)

not be used, or if a reference inductor isnot available, P2 is simply left at the centreof its travel.

Some manufacturers of small chokesand other inductors, e.g., Siemens andToko, state the approximate Q factor oftheir products in the related datasheets,extracts of which are often reproduced incatalogues of electronics mail-order firms.These values may be used as a guidanceto verify the correct operation of themeter, and to provide the best possiblesetting of P2 in the absence of a referenceinductor.

The frequency ranges may be cali-brated, although this is not strictly necess-ary. If desired, connect a frequency meterto the FREQ. output, and adjust trimmersC14-Clq in the respective ranges for themaximum frequency indicated on thefront panel. Fine tuning control Cu is setto minimum capacitance (hilly ccw) forthis adjustment.

Practical useThe meter is simple to operate: connect theinductor to be tested to the terminals Lxand set S2 to OPERATE. Starting in the hig-hest range, find the resonant frequency byoperating the FINE TUNING and INDUCT.ANCE ADJUSTMENT controls. Step down tothe next lower range if you do not find aclear resonance indication, which ismarked by a sudden increase in the meterreading.

When the resonant frequency has beenfound, the two tuning controls are ad-justed for a maximum meter indication.Switch S2 to CAL. and adjust P3 (CAL.) for

f.s.d. on the meter (indication '100').Switch S2 back to OPERATE and check thatthe resonance is still there by carefullyturning the FINE TUNING control. The Qfactor of the inductor can be read from themeter.

In the highest frequency range, it maybe impossible to make the meter indicate100 in the calibrate mode. In that case,adjust the CAL. control to set a reading of'50' and multiply the meter reading in theOPERATE mode by a factor of two.

References:1. Self-inductance meter. Elektor Electro-nics September 1988.2. RF inductance meter. Elektor ElectronicsOctober 1989.

ELEKTOR ELECTRONICS APRIL 1990

VIDEO Ai

FINAL PART: CONSTRUCTION, ALIGNMENT AND PRACTICA

A. Rigby & G. Dam

USE

In this final instalment of the article we deal with the connecting -up of the completedprinted -circuit boards, and the assembly into the enclosure. Also, a detailed

setting -up procedure is given, which is no luxury given the complexity of the videomixer. Notes on the practical use of the unit round off the article.

Mechanical work on the ESM enclosuremay be started when the three modulesdescribed in previous instalments(switching board, remodulator board,keyboard and power supply), are com-plete and ready for interconnecting.

The sloping panel of the ESM enclosureprobably requires most mechanical work.Fortunately, the drilling template sup-plied with the front -panel foil for themixer allows the panel to be cut anddrilled in a straightforward manner. Tobegin with, fix the template to the insideof the front panel with the aid of a fewdrops of glue. Next, use a jig -saw to cutout the slots for the slide potentiometersand the holes for the switches. Work care-fully and take your time to reposition theworkpiece if required for a particular saw-ing angle.

Determine the locations of the holes inthe rear side of the enclosure throughwhich the video in/out sockets are ac-cessed. Drill these holes at a relativelysmall diameter, then use a reamer to pro-vide the necessary clearance. The use of areamer is preferred over a larger drill be-cause its larger cutting surface results inless vibration of the workpiece and, as aresult, better holes.

The screw holes in the front panel aredrilled and carefully enlarged to acceptcountersunk M3 screws. The heads ofthese screws must be flush with the sur-face of the front panel to prevent the self-adhesive foil being damaged. Secure eachM3 screw at the inside of the front panelwith a drop of glue or Lock-tite (if you canget hold of it). Next, turn 10 -mm longmetal PCB spacers with internal M3threading on to the screws. The spacershold the keyboard PCB, and allow this tobe removed without the need of looseningthe screws underneath the front -panelfoil, which is likely to be damaged by suchan operation.

The photograph in Fig. 16 illustratesthe way in which the printed -circuitboards are arranged in the enclosure. Pro-visionally install the boards in the case toobtain a like arrangement. Mark and drillthe holes in the bottom plate to enable theswitching board and the transformerboard to be secured on it. Next, mark and

cut a rectangular clearance in the left sidepanel of the enclosure to accept the mainssocket with its integral switch and fuse.

First testFor a first test, install the switching boardand the transformer board in the enclo-sure. Connect the input terminals of thetransformer board to the mains socket,and the output terminals to the switchingboard. The complete wiring diagram ofthe video mixer is given in Fig. 17. Pointswhere the supply voltage may bemeasured are indicated to assist in check-ing and fault-finding.

After powering up, it will be foundthat the NIAX452s on the switching boardrun fairly warm. This is perfectly normal,however, and no cause for alarm.

First, the presence of thesynchronization signals is checked withthe aid of an oscilloscope. Apply a compo-site video signal to socket K3 (vIDEo-Iinput), and adjust P2 until the signal atpin 13 of ICs is high for 60 ps. Similarly,adjust Ps for a 'low' duration of 11 Its.

Testing the keyboard PCBA global test is carried out on the key-board PCB before it is secured to the in-side of the front panel. First, connect thekeyboard to the switching board by meansof the short flatcables mentioned in therelevant parts list. Next, make a cable treeto connect Pi, P4 and the power supply ofthe keyboard to the switching board. Theconnections of Pi and P4 must be made inscreened wire. The screening braid is con-nected at the side of the switching boardonly. The cable trees should have a lengththat obviates the need of disconnectingthem when the video mixer is disassem-bled for tests and adjustments.

After switching on, it will be noted thatmost keyboard controls are inactive if novideo signal is applied, since this ensuresthe presence of the centralsynchronization. With a signal applied, itmust be possible to control each LED byactuating the associated key. Effects are,however, not achieved at this stage sincethe modulation board is not yet con-

nected. \one the less, the passing of thevideo signal from K, K4 and K to outputsK,, K7 and Ks may be verified by actuatingS;-.S1:. The KEYLocK function may also bechecked. When actuated, it should negateany effect of S14-S29 being pressed. If thesetests check out so far, mount the modula-tion board at the rear side of the switchingboard (their copper sides face one an-other). Ensure sufficient distance betweenthe boards by using 10 -mm long PCB spa-cers.

Potentiometers 1):,. and Pis may be con-nected to the modulation board by nor-mal, light -duty wire without screening.

The construction of the video mixer is,in principle, complete after connecting thepower supply lines. Figure 18 showssome of the pre -folded flatcables that in-terconnect the boards.

AlignmentHaving got this far you are probablyanxious to see the first effects from yourvideo mixer. Start the alignment by con-necting a composite video source to theVIDEO -I input, and a monitor to the output.Neither INPUT -2 nor INPUT -3 is providedwith a video signal so as to achieve a black

Fig. 16. Inside view of the completedprototype.

)R ELECTRONICS APRIL 1990

VIDEO MIXER FINAL PART 47background when these inputs are se-lected. The black background is requiredinitially to adjust the effects.

The effects shown in the pictogramswith potentiometers Pis and Plo may betested already. Very likely, however, theyare not as they should be because the PCBhas not yet been aligned. Run a quickcheck on the other video inputs by ap-plying the video signal and selecting themwith the functions SEL I, SEL 2 and SEL 3. Tomake the effects visible at output Kb, K7 orKs, switches Ss and S12 must be actuated.

Modulation boardThe adjustment of the modulation boardis fairly extensive. For clarity's sake, it is,therefore, listed in Table 2. Before startingthe adjustment procedure, set all presetson the modulation board to the centre oftheir travel.

Initially, switches Si, Ss, Sit, Si -1 andS30-S34 are actuated. Only Si -S4 are usedduring the adjustment -all other swit-ches are left at the above settings.

Apply the video signal to socket K.First, the span of Pi; and P2o is optimized.This is achieved when the extreme valuesof the control voltages correspond to thepeak values of the horizontal amd verticalramp voltages. The effects used for theadjustments are, therefore, the verticaland horizontal curtain -type wipe, both ofwhich make use of the associated rampvoltages.

Switches Si and 514 select the horizon-tal wipe effect with video -I to the left andvideo -2 (black) to the right. Actuate slidepotentiometer Pis to check that a verticalline moves across the screen. The linemarks the transition between two videosignals. Adjust Pis and P2o until the ex-treme positions of Pi= correspond to theextreme left and right side of the screenrespectively. These adjustments interactto some extent and must be repeated a fewtimes for best results. Presets Pi. and P21are adjusted similarly for the vertical wipeeffect. They set the lower and upper limitsthat can be reached by P20.

The above adjustments should be car-ried out with some precision as they areimportant for a number of other effects. Ifnecessary, reduce the vertical and /orhorizontal picture width on the monitor toensure that the whole of the picture isvisible. After the adjustments, these con-trols are returned to their original settingsto move the blanking transitions out of thevisible area.

First, the triangular voltages are ad-justed. Initially, select the double horizon-tal wipe effect and concentrate onsymmetry. The wipe is opened to the ex-tent that the disappearing video signal isjust about visible to the left of the horizon-tal curtain (Si or SI). Adjust Ps until thenarrow area with the video signal in it isequally wide at both sides of the curtain.Move P15 to the other extreme setting andadjust P- until the curtain just about closes(look at the top of the triangle).

The vertical double wipe (52 or S4) isadjusted in a similar manner. Preset Pin is

Presets Effects selection

P14: P16

P19; P21

S14, S1 or S3

S14, S2 or S4

Adjustment of

span of P15

span of P20

P6; P7

P10; P11

S15, S1 or S3

S15. S2 or S4

symmety and amplitude of H- triangle

symmetry and amplitude of V- triangle

P17: P18: P22

S16; Si or S3

S17, S1 or S3

S18, S1 or S3

S28, S1 or S3

unity -gain amplifier

P23

S16. S2 or S4

S17. S2 or S4

S18. S2 or S4

S26. S2 or S4

P5; P8, P9

P12; P13

S21: Si or S3

S20. S2 or S4

inverter

shape, amplitude and d.c. setting of H- parabola

amplitude and d.c. setting of V- parabola

P17; P18; P22

S19, S2 or S4

S20. S2 or S4

S21. S1 or S3

S27. S2 or S4

S28. S2 or S4

S29. S2 or S4

unity -gain amplifier

S20, S1 or S3

P23 S21. S2 or S4 inverter

S27. S1 or S4

S29. S1 or S3

Table 2. Overview of adjustments.

adjusted until one picture line only isvisible at the top as well as at the bottomof the picture. Slide P2o to the other ex-treme setting and adjust Pit until the cur-tain just does not open.

The next step in the adjustment in-volves the unity -gain amplifier_ Select thediagonal curtain (Sit, and Si or S3). AdjustPis until the video signal applied coversthe whole of the picture area. During thisadjustment, Pis must be set such that thecurtain is not, or practically not, visible.Presets Piz and P22 are adjusted until thecurtain can be moved just off both sides ofthe screen (both with Si and S3). Next,complete the adjustments listed inTable 2. Small corrections may be effectedby P--, Pis and P22.

Next, set up the inverter. Once moreuse the diagonal curtain (Sin), but this timewith the other two selections (S2 or S4).Adjust P23 until the curtain disappearsfrom the screen at the extreme settings ofPi... As with the unity -gain amplifier, theother effects may be used to check thecorrect setting of P.

The parabolic voltage is the last adjust-ment on this board. Use either S21 andS2 /S4 (horizontal parabola), or Szo and52 /S4 (vertical parabola). Preset P5 definesthe symmetry of the horizonal parabola;Ps the amplitude; and P. the d.c. setting.

These presets must be adjusted to preventunwanted side -effects in the picture as Pris operated. Presets P12 and Pi_ are ad-justed likewise to shape the vertical para-bola.

This completes the adjustment proce-dure and the video mixer should now pro-vide all functions. If small corrections arerequired for particular effects, consultTable 2 to see which presets are involved.Since a number of adjustments interact, itmay be necessary to repeat the entire set-ting -up procedure a few times. Alwaysremember, however, that any change inany one setting affects the following ad-justments.

For scope ownersThe adjustment of the video mixer isgreatly facilitated if an oscilloscope isavailable. The adjustment of Pis and Pin,for instance, merely entails matching themaximum voltage at the potentiometerwith the peak value of the ramp at pin 6of IC2s (Pis) and pin 6 of IClo (Pis). Similar-ly, the minimum value of the poten-tiometer voltage is made to correspond tothe minimum value of the relevant ramp.These levels are simple to observe and setwith the aid of an oscilloscope. The adjust-ment of the remaining waveforms is

ELEKTOR ELECTRONICS APRIL 1990

48 RADIO AND TELEVISION

y: T:

O.41--0

915.513135

cr

.910/,10,-C-1044.4.6.1 0 o

:.:IF---0.,-..,.,...:,,- =11-'-- - iko=;Ale. 0..e .re -:-=-, =-11-%-= .=.1.3 GtE---'-*e

o_z

=or,

. E aO .., ;6-'CI:7)'0 olfoo.4..Pz,-i

Io--0o=-.,0 o-,

Fig. 17. Wiring diagram of the video mixer. Supply voltages and waveforms are shown inset to assist in fault-finding, if necessary.

ELEKTOR ELECTRONICS APRIL 11)90

VIDEO AIIXER FINAL PART 49

Fig. 18. Flatcables with IDC sockets usedfor interconnecting the boards.

equally simple: the signal levels mustcorrespond to the effective span of poten-tiometers Pi3 and PD. Presets Ph, P7, Pieand Pii define the level of the triangularvoltage, while P5, PS, P.., PI2 and PL; areused for the calibration of the parabolicvoltages.

The scope is used to give P P:- andP22 settings that results in identical signalsat pin 9 of Ns4 and pin 7 of IC7.313, inde-pendent of the setting of Pis. Finally, P23 isadjusted until the direct voltages of thesignals at pin 7 of ICs;e and pin 6 of Ic.16are at an equal level_

Let's use itTo close the article, some hints are givenas regards the practical use of the manyfunctions offered by the mixer.

To begin with, we make a short touraround the keyboard areas. The sourceselection is effected in the top right-handcorner. Here, the user selects the videosignals which are sent to the recorder ormonitor. If, for instance, video signal 1 (55selected) is being recorded, the previewoutput may be connected to a monitor towatch the signals at inputs VIDEO -1 (Sid)and /or VIDEO -3 (Sit). Also, the previewmode (Si:) allows a particular picture ef-fect to be pre -selected. This is useful inmany cases to 'practice', i.e., to get theeffect right beforehand so as to prevent itgiving the wrong results once actually ap-plied.

The fading controls effectively causethe mixer to switch between two videosources. These sources are selected withthe aid of keys SEL-I /SEL-2 (Ss: and 5:;3) aswell as with SEL-2/SEI.-3 (S and S;;).

The superimpose switches, 530 andare located at the left-hand bottom cornerof the front panel. The superimpose effectis obtained by first wiping to a doublepicture with Pi, followed by swapping thesuperimpose selection with S21 and usingPi again for the fade-out. In this way, thesuperimpose function is used to changebetween two video signals. FunctionsSINIP-1 and SIMP-2 therefore correspond to

the SEL-I/2 and SEL-2 3 keys, 57,2-S35, so thatthe superimpose function may be used toswitch between all possible video sources.

The function of effects switches Si -Siwill be evident after having followed thesetting -up procedure. A few additionalpoints should be noted, however. Swit-ches 514 -Sal are fitted along a blue line onthe front panel, and switches Sao -S:; alonga white line. The effects along the blue lineare grouped such that the selected videosources are switched When changing fromthe top options (5., or 54) to the loweroptions (Si or 5:). For the 'mixed out' func-tion (Ss and/or Si:) this means that a'hard' transition, or cut, can be made. An-other advantage of the arrangement ingroups is that effects may be changed inthe 'mixed out' mode without problemswith fading controls Pis and P:o set to theirextreme positions. Since these settings donot affect the mixed -out signal, it ispossible to switch from video source 1 tovideo source 2 via effect A. Both A and Bare effects found along the blue line.

The effects joined by the white line donot offer the above possibilities. The useof 'white. effects first requires the curren-tly displayed video source to be selectedvia the output function (so, apparentlynothing happens). Next, the desired effectalong the white line is selected, and therelevant potentiometers are set such thatthe signal at the preview mix output is anexact copy of that at the recorder output_Next, the mix output is re -enabled (noth-ing happens so far) and, finally, thedesired effect selected. This may loOkcomplicated on paper, but is really quitestraightforward in practice. Most dif-ferences in the operation arise from thedifferences between the two types of ef-fect.

Switch S:: allows externally defined ef-fects to be selected. The range of theseeffects is practically without limits andinvites the use of experimental circuits.

Among the possible external effects is,for instance, the placing of a particularvideo signal inside a frame, with anothersignal in the background. This may beachieved by providing K4 (VIDEO -2) with asignal that consists of maximum black -to -white transitions, e.g., a rectangularwave. Further, connect the KEY -OUT out-put of the switching board to the HKEYinput of the modulation board. This ar-rangement allows the signals at inputsVIDEO -I and VIDEO -3 to be combined underthe control of the signal at input VIDEO -2.Slide control Pts is used in this mode tocontrol, depending on the signal suppliedby source 2, the grey level at which theswitching between sources 1 and 3 takesplace. This option may be made perma-nently available on the mixer by fitting apair of extra connectors at the rear panel.The horizontal and vertical effects may beextended in a similar manner.

Figure 19 shows the circuit diagram ofan experimental effects generator which isintended to get you started with your ownexperiments with the video mixer (re -Member that external effects are selected

C

?IC

0

a

MIM

.5V

(2)7) ,0 ItICIc ICU

ICI 0 ill0 ..

ICI4093

Fig. 19. Experimentalgenerator.

rectangular-wve

by S22). The generator consists of two os-dilators whose output frequencies aredetermined with the aid of presets. Thehorizontal and vertical synchronizationpulses stop the oscillators and enable thediodes to discharge the timing capacitors.This is done to ensure correctsynchronization as with mixed video sig-nals.

The outputs of the NAND gates areconnected to the H -KEY and V -KEY inputs tocreate bars and rectangles in the picture(depending on the selection made by Si -Si). The number of rectangles is deter-mined by the oscillator frequencysettings. The generator is, of course, in-tended as guidance only for the design ofmore complex external effects generators,which should give the user of the videomixer even more possibilities to use hiscreative power.

Video Mi \er -publications overview:

Part 1 (switching board): January 1990Part 2 (modulation board): February1990Part 3 (keyboard): March 1990Part 4 (construction; alignment; practicaluse): April 1990

ELEKTOR ELECTRONICS APRIL 1990

50

PROFILE:WATFORD _ I CT RONICS

by Bernard Hubbard

Speedy response, quality of components. and competitivepricing are the ingredients that have transformed a home -based business supplying electronic components to thehobbyist into a multi -million pound operation.

Watford Electronics began life in the home of Nazir Jessain 1972 when the former NHS optician went into businesswith a qualified electrical engineer. Today. the direct mailand retail electronic component and computer businesshas an annual turnover in excess of £10 million and is oneof the best known suppliers of Acorn and BBC microcom-puters in the United Kingdom.

The story behind the determination to build a successfulbusiness goes back to Nazir's roots. Son of awealthy Indian trading family. Nazir grew upin Tanzania where. at the age of 11. he wassent to work in one of the family's factoriesafter school instead of being able to go out toplay with his school chums. "We were taughtthat business comes first". states Nazir as ifhe was recounting something akin to the Hip-pocratic oath.

Perhaps more than any other. one incidenthad a marked effect on the young Nazir. Atthe age of 15. he had just failed to complete adeal on behalf of his family at the local mar-ket when a callous uncle said: "We are not abusinessman. are we?". Despite his assuredfuture. Nazir knew that one clay he would notbe able to contain his resentment at this un-fair treatment and that sooner or later he would have tomake his own way in the world without having to rely onthe Jessa business empire.

That day came during a particularly hot spell when.driving his uncle's pick-up truck in Dar es Salaam. Nazirsuddenly made up his mind to go to England and qualify asan optician. To the complete astonishment of the Jessafamily. Nazir had flown to England and enrolled on acourse only a few days later. His office is still decoratedwith the certificates stating his qualifications as an opti-cian.

In spite of his qualifications. Nazir found that his salaryworking for the NHS only just about covered his living ex-penses. so that when an opportunity arose for a qualifiedoptician in Libya. he applied and got the job.

During his two -and -a -half year spell abroad. Nazir bud-geted carefully and, although by the time his contract hadcome to an end he had not saved a fortune, he was able tobuy a house in England and still had £2500 left to start asmall business.

Shrewdly. Nazir managed an optician's practice duringthe day to keep his drawings on the fledgling Watford Elec-tronics to a minimum and worked in the electronics busi-ness during the evening. "I would rush home from workand begin processing the orders so that we could get themin the post by 9 p.m. in order for them to be delivered thenext day. At weekends, we would hang a sign in the windowof the front room and people would call for their orders.Often. there would be customers waiting in the lounge. thehall and even in the chive for their components."

In spite of his lack of knowledge of electronics and hispartner leaving the business after a while. Nazir managedto earn a reputation for Watford Electronics. He confesses:"I didn't have a clue. When I ordered transistors. I was ex-

Nazir Jessa

petting something like radios instead of those three-leggedbeasties to appear."

But Nazir is a quick learner. Monitoring the activities ofhis competitors in the specialist trade magazines, hebought and sold accordingly. Very soon he was advertisingin his own right under the Watford Electronics banner.Within a short time. he was also able to take on his firstemployee: his brother Raza. who is still his right-hand mantoday. After two _rears trading, the turnover of Watford Elec-tronics had risen to .£10.000.

Then came several boosts to the young company. In con-junction with a trade magazine. Watford Electronics ran a

project that involved presets. In no time at all.the company had sold 150.000 units. Thenfollowed a TV game: Watford sold 25.000 in amatter of weeks. Perhaps the biggest sellerwas a drum rhythm machine based on an scschip that was featured in Practical Wireless. '1used to groan when I heard the postman ar-rive with yet another bagload of orders. In fact.at one stage. I was working until 3 a.m. everyday in a bid to clear the backlog."

Almost by accident. Nazir and Raza stum-bled on another lucrative market-that for theBBC micro. Watford suddenly found Acorndealers buying printer cables from them. "Wecould not get enough of them, because we hadto be careful: if our supplier had found outwho our customers were, he might have de-

cided to cut us out and sell direct."The Jessa brothers found a way around this tricky prob-

lem. They began to buy single -ended cable from one source.connectors from another and fit the two together on theirown premises. For months. they sold 100 a day without ei-ther of their suppliers getting a hint of the lucrative market.

Helping owners of the BBC Model A computer upgradeto a Model B was another high -growth area for WatfordElectronics. The Jessa brothers began marketing their ownkit in direct competition with Acorn. Needless to say. thecomputer manufacturer was not too pleased with Watfordundercutting the hardware makers by quite a margin.Soon, dealers from all over the UK were comming to Wat-ford Electronics. especially since the company had simpli-fied the marketing by giving them an option of kit 1, 2. 3. or 4.

Today. Watford Electronics has grown to generate an an-nual turnover of more than £10 million with a staff of 45.Eighty per cent of the business comes from mail order sales,which means processing an average of 500 orders a day. Evenso, during the writer's visit (on a Thursday). there were cus-tomers queuing to buy computer -related products in the re-tail shop that forms the ground floor frontage of the compa-ny's headquarters in Watford High Street.

As to the future. Nazir said: 1 don't see people spendinghours on electronic projects and building their own computerswhen they can buy them so cheaply: instead. they will belooking for add-on boards for their computers and tailoringsoftware to suit their own requirements."

Despite his running a Mercedes as well as a Rolls-Royceand the fact that his 9000 sq. ft. business property is worthabout 12 times what he paid for it a few years ago. Nazir findsone of the greatest sources of satisfaction his being a re-spected member of the Watford business community. Hisroots, he says. "are firmly here-in Watford."

ELEKTOR ELECTRONICS APRIL 1990

INTERMEDIATE 0A series of projects for the not -so -experienced constructor. Although each article

will describe in detail the operation, use, construction and, where relevant, theunderlying theory of the project, constructors will, none the less, require an

elementary knowledge of electronic engineering. Each project in the series will bebased on inexpensive and commonly available parts.

TEST BOX

D. Schijns

Test equipment, however simple, is essential at almost any level in practicalelectronics. In many cases, one grows fond of certain test gear of which all the

shortcomings and inaccuracies are thoroughly familiar. In not a few cases, the goodold continuity tester or the battered multimeter remains in use for years for no other

reason than that it is there and easy to use. The instrument described as thismonth's intermediate -level project has so many uses that it may well become one of

your favourites on the test equipment shelf.

Although the multimeter is without doubtthe best instrument for many tests andmeasurements in practical electronics,there are also situations in which acheaper, less sophisticated tester/indica-tor is equally useful. This is particularlyso for quick fault-finding where thepresence or polarity of a voltage is of moreimmediate importance than the actualvalue.

The second application of the presenttest box, LED (light -emitting diode) test-ing, is not often found even on top -grademultimeters. An ohmmeter is, of course,the thing for accurate resistance measure-ments. The test box, however, by virtue ofits built-in buzzer, is eminently suited torough resistance indications, testingdiodes, tracing short-circuits in multi -wire cables, and checking the operation ofall sorts of contacts. The test box may alsobe used as a flooding indicator in a bath-room, in a cellar, or near the washing ma-chine. A further application incombination with an LDR (light -depend-ent resistor) is a light detector as part of analarm system. Finally, a PTC or NTC resis-tor may turn the test box into a tempera-ture alarm.

Circuit descriptionThe circuit diagram shown in Fig. 1 con-sists of three parts, each with its own func-tion.

The simplest part consists of batteryBt; and series resistor R4. These two com-ponents form a LED tester. The battery

supplies the required voltage, while R4limits the LED current to a safe value.Because the polarity of modern LEDs canno longer be determined by lookingthrough the device and spotting the ca-thode as the larger surface, the LED undertest must be reversed if it does not lightwhen connected to the test box. If it stilldoes not light, it is almost certainly faulty.

The second part of the test box consistsof three components, D2, D3 and R;-, whichform a voltage indicator. Like R4, R7 is aseries resistor to prevent the diodes being

overloaded. Both LEDs light when an al-ternating voltage is applied to the inputterminals. Direct voltages cause either 11!or D3 to light, depending on the polarity.The use of a particular colour for the LEDsas well as the input terminals may assistin determining the polarity quickly (agood colour selection is red for the +). TheLEDs do not light at input voltages lowerthan about 3 V (the actual level dependson the type of LED used).

ELEKTOR ELECTRONICS APRIL 1990

ElINTERMEDIATE PROJECT

The third part of the circuit is a littlemore complicated than the previous twobecause it contains an amplifier whichfunctions not unlike a comparator_ Thispart is for resistance indications, diodetests and conductance tests_ The compo-nent marked Bzi is an active buzzer thatproduces a loud beep if the resistancevalue of the component connected to theinput terminals is below a certain pre-defined value. Components that may betested in this manner include resistors,diodes, switches and relays. The activityof the buzzer may be verified by short-cir-cuiting the input terminals. In that condi-tion, transistor T2 conducts and powersthe buzzer.

T', a pnp transistor, is normally offbecause its base is connected to the posi-tive supply voltage via R3 and R2, whichprevent base current flow. This situationdoes not change until T1, a field-effecttransistor (FET), starts to conduct. Thiscauses the left-hand terminal of R3 to beheld at virtually 0 V (ground potentialthat T2 receives base current. The result isthat the buzzer is actuated.

FET Ti is switched on and off by thevoltage at its gate, which is connected to apotential divider. This consists of Ri andthe resistance at the input terminals on theone hand, and either R5 -P1 or on theother hand. The selection between thecombination of the resistor -preset combi-nation and the single resistor is made withswitch Si. The voltage across the potentialdivider is supplied by a second 9-V bat-tery, Bt2. Diode Di protects the gate of Ti,which is extremely sensitive because of itshigh input resistance, against static dis-charges.

When the input terminals are not con-nected to a component, the FET can notconduct because of the negative voltage atits gate. When the test inputs are short-cir-cuited, however, the gate voltage rises toa level just below 0 V. As a result, the FETstarts to conduct and causes the buzzer tobe actuated.

The resistance (at the input terminals)at which the FET starts to conduct is deter-mined by the settings of potentiometer Pi

0 R4

® 0 I

I

0...100VAC/DC

L

esR1

0

4700

1W

R2

BF245C

D1 R6

BAT85

0

0

D2 D3

RR-

AC/DC

0

R7

2W

R5

p,c-0St

Oa

P11M

T1

Cli

110p16V

R3

39k

BC557BBz1

T2

0

Bt119V

0

0C2

Bt29V

16V

906018X -11

Fig. 1. Circuit diagram of the test box, which is a combination of three useful test circuits.

and range switch Si. When Si is set toposition A-C, the buzzer is actuated atresistance values smaller than 10 Mil(mega -ohm). This position is, therefore,suitable for finding short-circuits in low -voltage cables (e.g., a length of coaxcable). Switch position A-B (indication0-1M on the front panel) reduces the sen-sitivity of the circuit so that the buzzersounds at resistance values lower than

1 Mn (with Pi set to maximum resist-ance).

Potentiometer Pt may be providedwith a resistance scale which is 'cali-brated' by connecting, in succession, anumber of resistors of different valuesfrom the E12 series. The positions of Pi atwhich the buzzer sounds are marked withthe value of the resistor connected to thetest terminals.

Fig. 2. Views of the completed printed -circuit board before it is fitted into the enclosure. Note the way in which the wander sockets andthe potentiometer are fitted.

ELERTOR ELECTRONICS APRIL 1990

TEST BOX

eroaoe ks

0

.-1Z

es_Ad17

70/

\ananti

o 4=

4

Fig. 3. Track lay -out (mirror image) and component mounting plan of the printed -circuitboard for the test box.

906018-F

Fig. 4. Suggested lay -out and lettering of the front -panel.

COMPONENTS LIST

Resistors:1 10k 1V11 390k R2

1 39k R'3

1 47062 R4

10k Rs

1 10M Rc1 4k7 2W R7

MO lin. potentiometer

Capacitors:2 10pF 16V C,:C2

Semiconductors:1 BAT852 LED 02:02.1 BF245C Ts

1 BC55713 T2

Miscellaneous:1 miniature on:off switch S:1 12-V active buzzer BzI

PCB 906018

The test box does not have an on/offswitch because neither Ti nor T2 conductuntil a component is connected to theinput terminals. When the circuit is notused, Ti and T2 draw a negligible current.The voltage/polarity indicator does notconsume battery current, while the LEDtester consumes battery current onlywhen a LED is connected.

ConstructionThe printed -circuit board for the test -boxis shown in Fig. 3. The mirror image of thetrack lay -out is shown to make the pro-duction of this board as simple as possibleby photocopying and transferring to afilm.

All components, with the possible ex-ception of the BAT85, are fairly standardand should be available from varioussources. The buzzer must be an active orself -oscillating type, which means that itproduces a tone when connected to a di-rect voltage.

The photographs in Fig. 2 illustrate thearrangement of the range switch, thebinding posts and the resistance controlpotentiometer on the board. These parts,and the LEDs, protrude from the frontpanel, to which they are attached.

As already mentioned, the use of col-oured components is recommended. Redis particularly suited to 'positive', whileblue, black or green are typically associ-ated with 'negative' or ground.

The application as a flooding indicatorrequires a kind of sensor made from apiece of printed -circuit board onto whichpairs of parallel copper traces are etched.This sensor is connected to the resistanceinputs of the test box. Any drop of wateror increased humidity that forms a resist-ance lower than the value set on the testbox will set off the alarm.

1-1.1-:KTOR LI.ECTRONICS APRIL 1990

54

DESKThe contents of this column are based solely on information supplied by the author

and do not imply practical experience by Elektor Electronics

[3IMGE RECAPOR

HIGH -EFFICIENCY AC DC CONVERTER/VOLTAGE MULTIPLIER

From an idea by D. A. J. Harkema

This article discusses an extension of the well-knownsingle-phase, full -wave bridge rectifier to provide a high -efficiency

voltage multiplier. The extension is based on a circuit developed byDip.Eng. Th. Gisper, a Swiss engineer, who described his design in

a paper entitled CIF-DC-Converter-Schaltung in der passivenTelemetrie (Eidgenossische Technische Hochschule-ETH-

Zurich 26 February 1988)

A conventional bridge rectifier is shown inFie. 1. When terminal a of the transformeris positive, diodes D, and D3 conduct andcurrent flows through load RL. When ter-minal b becomes positive, on the alternatehalf cycles of the transformer voltage. D4and Di conduct and current flows in RL inthe same direction and at the same level asbefore. The voltage across the load isequal to the peak value of the voltageacross the transformer secondary less thepotential drops across the diodes.

There are various ways of increasing theoutput of the rectifier and some of these areshown in Fie. 2. Fig. 3 and Fig. 4: a single -ended, a balanced and a bridge voltagedoubler respectively. The circuit of Fig. 3 isused when a balanced d.c. output (with re-spect to earth) is required.

In Fie.. 2. when a is positive, DI con-ducts and capacitor C1 charges to the peak

value of the a.c. input voltage. On the re-verse half -cycle. D, conducts and C, alsocharges to the peak value of the input volt-age. The charge on C1 is retained, since Diis reverse -biased. Therefore. both capaci-tors charge to the peak value of the inputvoltage, so that the d.c. output voltage isequal to twice the peak input voltage. Thisis only true. however. when no load isconnected across the output terminals.

With a load connected across the out-put. current is supplied to it by the dis-charge of the capacitors. On alternate halfcycles, the capacitors are recharged. Thismeans that the output voltage is a directvoltage with an a.c. ripple superimposedon it. This ripple is minimized by makingthe capacitors as large as is practicallypossible, taking into account the currentdrain and the frequency of the a.c. inputvoltage.

The circuit in Fig. 4 is a better type ofvoltage doubler. It has two important ad-vantages over that of Fig. 3. The first isthat the frequency at which the capacitorsare charged is twice as high. so that theripple voltage is reduced. The second isthat the load on the transformer remainsthe same even when the loads on the twod.c. outputs are different.

The Gisper development is basically acombination of the bridge rectifier of Fie.Iand the voltage doubler of Fi2. 2 as shownin Fig. 5a. or a synthesis of the circuits ofFie. 3 and Fie. 4. as shown in Fig. 5b.

Briefly. the circuit of Fig. 5a works asfollows. It will be assumed that the a.c.input is sinusoidal and has a peak value of20 V. During the first quarter of a period.capacitors C, and C3 are charged viadiodes D4 and Dr, to a potential of +20 V.When the a.c. input decreases. D, is re -

Fig. 1. Conventional bridge rectifier. Fig. 2. Singleended voltage doubler. Fig. 3. Balanced voltage doubler. Fig. 4. Bridge voltage doubler.

LLENTOR ELECTRONICS APRIL 1990

Fig. 5. The Gisper design is a combination of thebridge rectifier of Fig. 1 and the voltage doublerof Fig. 2 as shown in (a) or a synthesis of therectifier in Fig. 3 and the voltage doubler of Fig.4 as shown in (b).

verse biased and the voltages across C,and C3 are maintained at +20 V.

When the a.c. input passes throughzero. Ds conducts and C1 is charged to+20 V. At the same time, C, dischargesvia Do and C3 via D1 to a value of +10 V.The voltage at the junction D1 -C1 changesfrom +20 V to -20 V. This causes Cs to becharged to +30 V. The potential acrossDri-D, is then -20 V.

.As soon as the a.c. input rises. D1 is re-verse biased. The voltage across capaci-tors CI and C, remains +10 V and +20 Vrespectively. This causes the potential atjunction CI -D3-135 to rise and reach avalue of +30 V when the input reaches+10V. When the input rises to -20 V, the

Protecting electronic circuits

The protection of electronic circuitsagainst the effects of hostile environ-ments, a frequent cause of malfunction.is made easier by the Prelude Concoat-ing System' from Concoat Ltd. who spe-cialize in the application of conformalcoatings.

The system is intended for small to

Fig. 6. The Gisper bridge may be extended asshown. The addition of each pair of diodes andcapacitors raises the d.c. output voltage by avalue equal to that across one half of the basicbridge rectifier.

potential across C3 rises to +34 V.At the moment the input exceeds

+10 V. the voltage across C, rises from+10 V to +20 V. while that across CI de-creases to +16 V.

When the input decreases, D5 is re-verse biased. The voltage across C, re-mains +20 V and that across C/. +16 V.As soon as the a.c. input becomes morenegative than -16 V. C1 is charged via D3to +20 V. At the same time, the potentialacross C, -D6 -C3 -D1 attains a value of-20 V, that across C, drops to +17 V. andthat across C3 rises to +37 V.

When the a.c. input increases again.the process described repeats itself.Within a few cycles, the voltage across C3has risen to +40 V and that across C, to+20 V.

It appears that the Gisper bridge can beextended as shown in Fig. 6 and Fig. 7.The addition of each pair of diodes andcapacitors raises the output voltage by avalue equal to that across one half of thebridge rectifier. It is also possible whenfurther extending the circuit of Fie. 6 totap voltages at various points of the diodenetwork as shown by the dotted lines inFig. 7.

medium-sized companies and incorpo-rates all the equipment needed for the ini-tial cleaning. masking. automatic dipcoating and inspection: a two -stagecleaning system: a dip -coating unit: anUV inspection boot and a drying cabinet;a portable viscometer for monitoring theliquid coatings: and a microdot precisiondispenser to mask out non-coatable partswith an impermeable latex compound.

DESIGN IDEAS

Fig. 7. `'then further extending the circuit ofFig. 6, it becomes possible to take off voltage atvarious points in the circuit as shown here bythe dashed lines.

Sources:

Th. Gisper: HF-DC-Converter-Sehaltun-gen in der passive'? Telemetric,: Semester-arbeit an der Professur fiir elektrotechnis-che Entwickelungen and Konstruktionen.ETH Ziirich. 26 February 1988.

Elektronica, 17 November 1989. "Span-ningsverdubbelaar met hoop rendement-.

The process uses 'Humiseal. confor-mal coatings: a plastic film of acrylics.epoxies, polyurethanes. etc.. which con-forms to the profile of the PCB. Thespeed of the process is such that Euro-cards can be treated in batches of 10 at anoveral rate of more than 120 per hour.Concoat Ltd, Alasan House. Albany Park.Frimley Road. CAMBERLEY GI215 2PL.Englund.

ELEKTOR ELECTRONICS APRIL 1990

LTAL Y Co PREAMPLIFby K. J. Thouet

The idea presented here concerns the combination of digital andanalogue techniques to produce an intelligent preamplifier

with integral time switch

The digital section of the preamp is basedon a standard Pc motherboard that has ade-quate RAM. place for a Rom. and two orthree expansion slots. A keyboard inter-face, and often a V24 interface, is nor-mally supplied free of charge with theboard and these are all that's needed toconnect the board to a personal computer.

The unit must be provided with a goodbut not too expensive small screen. Mod-em one- or two -row LCDs with driver areideal for this purpose.

Because of the available loudspeakerinterface, the preamp can be made to alertthe user audibly to any operating error.

Also needed is a timer if that is not al-ready available on the motherboard.

To enable the control unit to operatecorrectly in the stand-by mode. a largerCMOS RAM and higher capacity battery arenot a luxury in some cases.

Last but not least, an interface isneeded to the analogue section and thismay consist of a couple of 8 -bit ports.

Since the unit has no on -off switch. thestand-by timer is switched off by software.This happens in a well-defined sequence:the loudspeakers are switched off first andthen the equipment connected to the sys-tem. When that is done. the PC ascertainsfrom stored time sw itch data when the sys-tem should be switched on again.

At a pre -determined time, the timerswitches the power supply on again andrestores the states of input level. volume.outputs used. and so on. to what thesewere before the system was switched off.

Both the remote control and the key-board on the proposed unit have 28 keys sothat a normal infra -red Rc stem is per-fectly suitable. The many keys add to theease of operation. The soft'.'. are must besufficiently tolerant for the control circuitsto provide the exact action that is required.A possible layout of the front panel of theremote control unit is shown in Fig. 2.

The interface to the analogue sectionshould have special consideration since ithas to deal with latches on the one hand(PC) and relays and Upto-isolators on theother. A stepper -motor -controlled poten-tiometer would be eminently suitable here.If that is used. it is only necessary. in orderto set a specific level. that the zero posi-tion is easily detected (in a similar way as

in a disk drive unit). From the zero posi-tion. the potentiometer may be set manu-ally without upsetting the automatic con-trol.

A few points regarding the software. Itis clear that the quality of a unit of this na-ture is directly dependent on the quality ofthe software.

As programming language, Pascal. C.or any other high-level language may beused.

It is, of course. an advantage if the in-terface cards could first be used in a nor-

mal Pc, as this would enable the softwareto be checked without the need of havingto program a PROM. If difficult to clearfaults arc experienced, it may help to usethe EPROM simulator published somemonths ago

Finally, there is also the possibility ofdownloading the program and timer datavia a V24 interface for testing the com-pleted Rc unit or for further development.II

'''Elektor Electronic.% . Dec. 1989. p.14.

Digital section

RTC CMOSRAM

16 -segment LCDincl. driver

StandbyTimer

Standbymainssupply

NiCdbattery

PC - I/0 Bus I

Standard XT mother board withRAM and special ROM software

V24 connexions keyboard connexions

Digitalmainssupply

110 driver forrelay/opto-coupter

Analogue section

8

Analogue input socket

A

1

Input selector (relay)

Recording selector (relay)

1

Preamp and level amplifier

Volume and tone control

A Output selector(loudspeaker, headphone

Analogue mains supply

Mains power switched

Fig. 1. Block diagram of the proposed digitally controlled preamplifier.

DO

TUMOMMI DI

MCI Ml

CDI FR

CA TBII SA III SO

AUX C I

3

Bass Input

I I 6ConL

7Lin.

I0VoLI

BILI 2

Treb.I

Rec.

DateSp 1Time

8 II pm.

9 111Headp.1Disp.

I Sp 2 IWeek

Sp3Day rower -0-11- +I ON OFF

/

90D035 12

Fig. 2. Possible layout of the front panel of the RC unit.

EI.EKTOR ELECTRONICS APRIL 1990

MANAGING CREATIVITY INSCIENCE AND HI -TECHby Ronald KayISBN 3-540-51375-2221 pages - 220x140 mmPrice £17.50 (hardcover)This is one of those books that you cannotput down once you have started to look init. It is a book that I wish had been avail-able many years ago when, as a youngnewly appointed scientific manager, I wasstruggling with a mass of new ideas, rules,procedures, etc.: it would have saved me(and, no doubt, some of those I was manag-ing) a great many headaches.

Since those days, not much has changedin scientific and technological manage-ment: when elevated to 'management',scientists and engineers continue to befaced with having to develop a split per-sonality. On the one hand they are drawninto one direction by their training gearedtowards fostering their creativity and onthe other into a 'red tape area' by their needto 'manage'.

Ronald Kay is well aware of theseproblems: he started his career as a re-search physicist and then moved on tomanagement in a number of hi -tech orga-nizations, teaching on the subjects of man-agement, information technology andcomputing, and then as an independentconsultant to the hi -tech industry.

Managing Creativity in Science andIli -Tech bears proof of his vast experiencein managing scientific and technologicalresearch and development. Many of hisideas will cause not a few eyebrows to be

IEE MEETINGS1-6 April - Software engineering for

electronic system designers (Vacationschool at University of Warwick)

9-12 April - Automated test and diagno-sis (Bournemouth International Centre)

23-26 April - Video, audio and datarecording (University of Birmingham)

Information on these, and many other,events may be obtained from the IEE,Savoy Place, LONDON WC2R OBL,Telephone 01-240 1871.

BRITISH ELECTRONICS WEEK isbeing held at Olympia, London, from 24to 26 April. Exhibitions incorporated inthe British Electronics Week include theAll Electronics/ECIF Show; ATE; Cir-cuit Technology; Electronic ProductDesign; Interface; Miltest; PowerSources and Supplies; Surface MountVillage; Fibre Optics and Optical Tech-nology; and Custom Electrical andDesign Techniques.

C) 0 X

raised: "Employees have a right to knowwhere they stand"; "In the world of hi -tech, women are underrepresented"; "Theneed for praise and recognition is neverfully satisfied"; "Don't compete with thepeople you manage".

Some other findings in the book mightwith advantage be adopted by many an or-ganization: "Bureaucracy is the antithesisof creativity. In a hi -tech environmentwhere creativity is to be nurtured, intro-duction or change of any administrativeprocedure should be subject to line man-agement concurrence" and "Be adamantin rejection of procedures that are defendedpurely on the basis of their long-lived ex-istence. Creativity can only flourish in anenvironment that allows for change".

The book is an absolute must for allengaged in the hi -tech industry, universityand government laboratories, and engi-neers and scientists in, or moving to, ad-ministrative positions.Springer-Verlag (London) Ltd,Springer House, 8 Alexandra Road,LONDON SW19 7JZ.

THE NEW HEAT TRANSFER

436 pages - 235x157 mmPrice $29.95This is the second edition of this fascinat-ing work; the first edition was published

;'J P' -r

Further information from The EvanSteadman Communications Group Ltd,The Hub, Emson Close, SAFFRONWALDEN CB10 1HL; Telephone(0799) 26699.

VISION Audio International '90 will beheld at Earls Court, London, from 22 to25 April. Details from EMAP MaclarenExhibitions Ltd, Beech House, 849,Brighton Road, PURLEY CR2 2BH,Telephone 01-660 8008.

COMMUNICATIONS and The WhichComputer? Show will be held at theNEC, Birmingham on 24-26 April. De-tails from Reed Exhibition CompaniesLtd, Oriel House, 26, The Quadrant.RICHMOND TW9 1DL, Telephone01-948 9900.

in English in 1974 and in Russian in 1977.

It is dedicated to "all who stand up forfreedom"-particularly freedom ofthought.

The main thrust of the book is a newheat transfer science that abandons theconcept of the 'heat transfer coefficient',and replaces it with the concept of 'ther-mal behaviour'. The particular advantageof the new heat transfer is that it greatlysimplifies the solution of problems involv-ing non-linear behaviour.

The book also presents a new electricalscience that abandons Ohm's Law and theconcept of 'resistance', and replaces thelatter with the concept of 'electrical be-haviour'. The particular advantage of thenew electrical science is that it deals withlinear and non-linear devices in the samesimple way, that is, it replaces both 'Ohm'sLaw science' and 'non -Ohm's Law sci-ence' with one science that is both logicaland simple.

The application of both new sciences isdemonstrated in numerous practical prob-lems that are solved in the text.

A fascinating book that should be readby all interested in science and particularlyin new thoughts in science.Ventuno Press, 6792 TimberwoodDrive, West Chester, Ohio 45069, USA.

The Fourth International Cable &Satellite Exhibition and Conference willtake place at the National Hall, Olympia,London from 9 to 11 April. Details fromCable & Satellite 90, 11 ManchesterSquare, LONDON W1M 5AB, Tele-phone 01-486 1951.

The European CASE Conference will beheld at the Tara Hotel, London, on 2-3

April. Details from Blenheim Online,Blenheim House, Ash Hill Drive, PIN-NER HA5 2AE, Telephone 01-868 4466.

A number of seminars on InformationTechnology, Data Communications andElectronic Engineering has been orga-nized for this month by Frost & Sullivan.Details from Frost & Sullivan, SullivanHouse, 4 Grosvenor Gardens, LON-DON SW1W ODH, Telephone 01-7303438.

ELEKTOR ELECTRONICS APRIL 1990

N AL C MAINS ISOLA \G SWPTCby R. Ernst and A. Wahr

It is an undeniable fact that electric and magnetic fields affect livingorganisms. How strong a field the human body can withstand

without ill effects is a matter of argument between scientists andenvironmentalists. We leave it for the reader to decide whether he

deems it of benefit to fit the mains switch described here in anumber of (to him) critical locations in his home or to dismiss the

whole idea as scare -mongering.

Man lives in an electro-magnetic environ-ment: the surface of the earth is surrounded by innumerable electrical and mag-netic fields, from static to very high fre-quency ones. Although virtually everyoneknows of the earth's magnetic field. few ofus are aware of the 250 kV potential thatexists between the earth and the iono-sphere or of the cosmic radiation between300 MHz and 350 Gllz that bombards theearth unceasingly. Through centuries ofevolution, life on earth has learned to livewith those natural phenomena, but whatabout the artificial electro-magnetic fieldsthat man has been creating for the past 150years?

Some scientists and physiologists haveworked out the recommended maximumperiods that we can remain within thefields created by electrical installationswithout suffering long-term ill effects. Forinstance, the German medical scientist DrHubert Palm has drawn up a formula ac-cording to which we should not stay toolong within a distance of 1.20 m to thesouth and 30 cm to the north, east andwest of mains wiring or electrical equip-ment.

Most of us spend the larger part of ourlives at work and in bed. In most bedroomsthere are a number of mains outlets. somequite close to the headboard. If. like us.you believe that the electro-magnetic fieldaround the mains wiring affects your well-being adversely. the automatic mains iso-lating switch described here should be ofinterest to you.

The isolating switch, the circuit dia-gram of which is shown in Fie. I. is in-tended primarily to be inserted into themains wiring where it enters the room.When. with the switch fitted, all mains -op-erated equipment in the room is switchedoff. only a small. biologiCally acceptable.direct voltage remains on the wiring.When a light or other apparatus is switchedon. the mains voltage is immediately re-connected to the bedroom wiring.

Since the maximum allowable currrentthrough the switch is limited. the unit is

provided with a plug and a socket outletthat enable it to be bypassed when re-quired.

Circuit descriptionIn Fig. 1., diodes DI and D2 form a

full -wave rectifier for the alternating volt-age at the secondary of transformer Trl.When there is no load on output socketK2. that is, all connected equipment isswitched off. the potential across CI isabout 12 V. This voltage is applied to allequipment connected to K2 via R5 and thecontacts of relay Re 1. Resistor R5 limitsthe current to a safe value in case of ashort-circuit at K2. As long as this situa-tion pertains. no current flows and the cir-cuit remains in its quiescent state.

When any of the loads, rated at not lessthan 3.5 W. is switched on, a direct currentflows through it and this causes a forwarddrop of about 2.4 V across diodes D -1--D6.

This results in a current through R3 andthe transmit diode of opto-isolator IC2.The ensuing light emitted by that diode re-sults in the receive transistor in IC2 to beswitched on and this in turn gives rise toC2 being discharged via R2 to a potentialof about 2Ub/3. The ensuing output at pinQ of timer ICI is amplified by emitter fol-lower TI to a value sufficient to energizerelay Re 1.

The relay contacts then change overand output socket K2 is connected directto the mains via plug K1, so that the rele-vant load is powered.

Diode D3 ensures that both half cyclesof the mains voltage can pass. althoughIC2 is driven during one half cycle only.Capacitor C2. however. buffers the voltageto the trigger input of the timer.

When the relevant load is switched off,the current through D5 -D4 -D6 and thetransmit diode in 1C2 ceases. The receivetransistor in the opto-isolator switches off

C

C

of

F3

ZENZVA2

R5

01

IN400I

r 02

011N4004

co

03

i:2

00

9

1

'Fief

D71N41104

1t CC3

DS 413x 1tIrs11Cc.:

P31C2

2

BC557A

+4

T1L111

CR1C1

555TF-

TR

c2 =163VT

893153

Fig. 1. Circuit diagram of the automatic mains isolating switch.

EI.EKTOR ELECTRON ICS APRIL 1990

AUTOMATIC MAINS ISOLATING SWITCH

ft' 0 0

Fl0

a

0 0F3

0

F2

Ki

lap k [0 0 0]121_-

LI

Fig. 2. Printed -circuit board for the automatic mains isolating switch.

and capacitor C2 discharges slow is RI(the high -impedance inputs of ICI havevirtually no effect). .After about 100 ms.the potential across Cl drops below thelower voltage threshold of the input com-parator: the output of IC1 is then insuffi-cient to energize the relay and the circuitreturns to its quiescent state.

Diode D7 protects T1 and the inte-grated switching circuit against voltagepeaks caused by the back-emf of the relaycoil.

Diodes D3-D6 have a maximum cur -

HIGHER FUNDAMENTALFREQUENCY CRYSTALS

Euroquartz has introduced a range of crys-tals that operate at up to 350 MHz in thefundamental mode.

Manufactured by Hi -Q Crystals of theUSA. the new range of crystals have a bet-ter temperature coefficient, a higher Q andlower insertion losses than surface acous-

rent rating of 1 A. They and the relay con-tacts are protected against overloads byanti-surg.e fuses Fl and F2 at the mainsinput. The primary of Trl is protected byquick -blow fuse F3.

Inductor L I is intended as an h.f. de -coupling element, since spurious signals inthe 100 MHz band, resulting from the on/off switching of all kinds of electricalhousehold equipment, are propagated bycapacitive or inductive coupling over theearth line in the mains wiring.

tic wave (SAw) devices.Frequency calibration at 25 °C is typi-

cally within ±50 ppm with better toler-ances available on request. The tempera-ture coefficient is ±50 ppm over the range-55 'C to +105 °C, or ±-25 ppm over thesame range to special order. Euroquartzclaims a TC of just -±5 ppm over the range-5 T to +60 'C and almost zero between

PARTS LISTResistors:R1 = 33 kR2 = 4k7R3 = 82 RR4 = 120 kR5 = 12 R

Capacitors:C1 = 1000 pF, 50 V, radialC2 = 41t7, 63 V

Semiconductors:D1-D7 = 1N4004T1 = BC557ASIC1 = TLC555IC2 = TIL111

Miscellaneous:Fl, F2 = fuse, 1 A, anti -surgeF3 = fuse, 250 mA, quick -blow3 PCB type fuseholdersTr1 = PCB type mains transformer,

9V. 3.2 VAK1 = mains plug outlet for panel mtgK2 = mains socket outlet for panel mtg2 three-way terminal block for PCB mtgRe1 = relay, 12 V, with 2 change- over

contacts rated at 1 A (e.g. SiemensType V23037 -A0002 -A101)

L1 = decoupling coil, 40 gH, 1 AMains noise/pulse suppression filterSuitable metal housing

ConstructionThe isolating s\'. itch is best constructed onthe primed -circuit board shown in Fig. 2:the construction should then not presentany undue problems.

Inductor LI is a low -resistance, 40 gHdecoupling coil. rated at 1 A. If a propri-etary type is not readily available, it maybe made as follows.

Using cardboard. make a 50 mm longtube with an outside diameter of 25 mm.On this. lay three layers of 15 turns each ofinsulated (yellow/green) equipment wire of1.5 mm2 cross-sectional area. Leave theends of the wire about 20 cm long (untilthe coil is wired in). Use insulating tape tofix the windings in place.

The switch unit must be housed in aproperly earthed metal case.

Finally. it is advisable to use a propri-etary mains filter at the input to the unit. II

+25 'C and +100 'C.The new crystals are designed for use

in applications where fundamental fre-quency operation is essential, such as fil-ters and oscillators.

Euroquartz Ltd, Blacknell Lane Indus-trial Estate, CREWKERNE TA18 7HE,England.

ELEKTOR ELECTRONICS APRIL 1990

60

DESIGN NOTESThe contents of this column are based on information obtained frommanufacturers in the electrical/electronics industry and do not imply

practical experience by Elektor Electronics or its consultants.

CODED LOCKING CIRCUIT FOR SECURITY SYSTEMS

General descriptionThe TEA5500 from Philips is a coder/de-coder circuit for security systems. TheTEA5500 is housed in a 16 -lead DIL case(SOT38) and the TEA5500T in a 16 -leadmini -pack (S016L: SOT162A).

The system has the ability to transmit acomplex code between a coding and de-coding unit by infra -red radiation. The de-vice can operate as coder or decoder de-pending on the external circuitry con-nected to the data input. The code is madeby the ten input pins El -E10 by connect-ing them either to ground (LOW) or to thepositive supply (HIGH), or leaving themfloating (co). This allows 310-2 combina-tions. Two combinations are prohibited:El-E10=HIGH and E 1-E9=HIGH,EIO=LOW.

CodingIn the coding mode. the data input is con-nected to Vp and both outputs (S1. S2) areconnected to a p -n -p output transistorwhich drives an infra -red radiation emit-ting diode.

After every start the coder completesthree coding runs and then stops automati-cally.

The code consists of 24 bits. Each bit isrepresented by presence or absence of adata pulse following a clock pulse. Thefirst four bits form the recognition code.The following ten pairs of bits are deter-mined by the connexions of the input pins(EI-E10). For the corresponding code inthe decoding mode, the order of the inputpins is reversed and connexions L (low)and so (floating are interchanged.

DecodingIn the decoding mode, an infra -red sensi-tive diode is connected to the data inputvia an amplifier. If the input data is recog-nized. the data input of the decoder isclosed temporarily (disregarding immedi-ately following data) and one of the out-puts is actuated for a predetermined time,after which the following start will actuatethe other output.

If the data input is not recognized, nei-

CHARACTERISTICSTamb = 25 °C; voltages with respect to pin 1; unless otherwise specified

parameter conditions symbol min. WP. max. unit

Supply

Supply voltage (pin 16) Vp 3 4.5 6.5 V

Supply current Vp = 4.5 V Ip 1.8 2.5 3.2 mAOutput current (pins 3 and 4) Vp = 4.5 V 10 25 - - mA

Inputs El to EIO

Input voltage HIGH VIH Vp -0.3 - - V

Input voltage LOW VIL - - 0.3 V

Input voltage floating VIE; L 1 - Vp -1 V

Input current HIGHI I H 2 7 12 µA

Input current LOW II L -4 -9 -15 AAInput current floating IIFL - - 2 µA

Data input

Input voltagefor decoding mode HIGH VdH Vp -0.6 Vp Vp + 0.3 Vfor decoding mode LOW VdL - - 0.5 V

Input currentin coding mode Idc 8 16 25 pAin decoding mode HIGH Vp = 4.5 V IddH - - 2 pAin decoding mode LOW Vp = 4.5 V IddL -8 -16 -25 PA

Minimum pulse width of DATAinput signal rdp 2 - - Ps

.051352-13

parameter conditions symbol min. ryp. max. unit

Oscillator characteristics Vp = 4.5 VSwitching voltage thresholds

high level Vth 3.10 3.32 3.50 Vlow level Vti 0.65 0.71 0.90 V

Input currentafter switching high level Ith 27 36 45 pAafter switching low level 10 -6.7 -9 -11.3 pA

Ratio Ith/Iti Alosc 3 4 5

Duration of oscillator pulsein coding mode note 1 rc 20 0.4Cd(pF) - psin decoding mode rd 3-rc 0.4Cdsc(pF) 5.7c ps

Oscillator capacitorin coding mode notes 1 and 2 Cdsc 56 - - pF

Duration ofoutput active status rd - 384 -rd -data input disabled status rx - 576.7d -

Influence of temperature onduration of oscillator Arcirc

0.002 oc -1pulse

Influence of supply voltage onduration of oscillator

AT

Arc/7c

-

0.16pulseAV P

- V-1

Zener diode voltage across supply Vz 6 - 8 V

Notes to the oscillator characteristics

1. Minimum value coder - capacitor must provide minimum pulse width of DATA pulse rdp (= 1/5 rc).2. Ratio coderidecoder capacitor 1:3.

930052-14

ELEKTOR ELECTRONICS APRIL 1990

61DESIGN NOTES

.73

1,2

Cot:

:O&33 Inputs

El E2 93 95 E6 E7 E9 E113

OSCILLATOR/L401,21STABLE

1 4 puT

IA 13 12 it 9 7 5

INTERFACE

TEA5503TEA55-0317

-10- SWl.TLOGIC

COLCOL PARATOR

24

SHIFT REGISTER

COOERIDECOOERDRIVE

52

OUTPUT ORivE

St

9,7..X52

Outputs

Fig. 1. Block diagram of the TEA5500 TEA5500T.

E1

5 A 9

912

A El

3, I C, C3 114 -S07 I

Cost ;Ljse5,:11.

.fi_.ransuutruutanana_r_

coding El E2 E3 ES E9 E 10 = L H

4 : 4 # a 4 4 4 4I / V i I 'I T Idecoding E 10 E9 E8 - E3 E2 E I L = H

E A B OA CIB

L I 0 0 1

1 1 0

1-1 I 1 0 0R.X.2152 15

023 023

Fig. 2. Timing diagram of the TEA5500 TEA5500T.

ther of the outputs is actuated: after thethird coding run has been completed. thedata input of the decoder is closed tern-poraril .

Soldering (by hand)Plastic mini -packsFix the device by first soldering two diag-onally opposite end leads. Apply the ironto the flat part of the lead only. Contacttime must be limited to 10 seconds at up to300 °C. When proper tools are used, allother leads can be soldered in one opera-tion within 2-5 seconds at 270-320 'C.(Pulse -heated soldering is not recom-mended for SO packages).

Plastic DIL packagesApply the soldering iron below the seatingplane (or not more than 2 mm above it). Ifits temperature is below 300 T. it mustnot be in contact for more than 10 sec-onds: if between 300 0C and 400 'C. fornot more than 5 seconds.

(Philips Data Sheet TEA5.50aTE.455007)

0ATA

I 7 -r

!E ErE Et ES

Ts 13 72 IT ta

5 5T 93aND 1E10 1E2 1ES 1E7

IL

S2

y

Ca -751A ICY

90X62-19

El -E 10: Code (H. L.

Fig. 3. Application diagram - coding mode.

Ear.__

AMPLIFIER

PULSESHAPER

T

13.3 nF

VP TCosc I15 2 14

r. :IVA 3L = Cala 7

3 1 El I E5

13 12 11 10SI4-

TEA5500 . open caflectursiTEA5590T S2 lo luau

3

6 7 9 9

Es I

E10 - El: code (H, L).

900052. 17

GNO

SiT

EIO

E9 1E

E8 EE71-8-

TEA550CTEA550,7,7

i61vp

7E I DATA

E1

131E2

11 E4

TO1 ES

1 ES

Fig. 4. Application diagram - decoding mode. Fig. 5. Pinout of the TEA5500 TEA5500T.

ELEKTOR ELECTRONICS APRIL 19911

flr) EALlr Erlr) !IA.) Sri H

1.1j

LETTERS

Letters of a general nature, or ex-pressing an opinion. or concerning amatter of common interest in thefield of electronics (in its widestsense), should be addressed to TheEditor at our London offices. Theirpublication in Elektor Electronics kat the discretion of the Editor.

Dear Sir-I agree with the letter from G.Clements (January 1990). A lot of the pro-jects in Elektor Electronics contain com-ponents which are difficult, if not impossi-ble to get here in the UK. I also feel thatover the last twelve months the magazineappears to be biased towards computeruser. We are not all computer freaks andhence there are those of us who have nointerest whatsoever in hardware. inter-faces. and programmers. I would like tosee more novel projects in Elektor Elec-tronics and below I have listed some sug-gestions and ideas.

A professional high -quality radio mikeand receiver:

Electronic spirit level with audible andvisual indication:

A proximity detector that works: I haveyet to see one:

Telephone scrambler for private phoneconversation:

Field strength meter for mobile trans-mitters;

Underground pressure sensitive detec-tor using a piezo transducer:

A wideband FM RF signal tracer. Theunit could use a frequency -to -voltage con-verter in order to extract the audio contentfrom a strong FM signal in the region 40MHz to 500 MHz. The unit could have ahigh sensiti ity so that it would only haveto be in close proximity to a transmitter inorder to hear audio content;

A device for detecting a signal tone ina cable without making physical contact orpicking tip AM RF energy. Such a deviceis useful for tracing a particular cableamong a bunch of cables as found. e.g.. insecurity control panels.

In the mean time, I am looking forwardto the February issue which contains aproject for modulating the mains voltage.These are the types of project/idea that Iconsider to interest the majority of readers.P. Male. Pershore, Worcs.

Thank You for your letter into which you

have obviously put a lot of thought.Equal/v. we need to spend some time onlooking into your ideas. some of whichlook rather daunting at first sight. Nonethe less. we'll have a go. Any readers whothink they ,nay be able to contribute.please write with details.

As far as the comment on computersgoes. I do not quite agree. I am not a com-puter freak by any means: to me a com-puter is nothing hut a tool. Unfortunately.although we hare a good in-house designdepartment. this can not cope with all therequirements of the maga.:ine. Therefore.like other maga:hies. we buy from free-lance designers; authors, but. regrettablyfor you and me. 8 out of every 10 submis-sions deal with computer software or pe-ripherals.

None the less. in 1989 we have suc-ceeded in publishing the following mainarticles:Audio & hill: II articles (5 projects):Computers: 22 (15 projects):Electrophonics: 6 (6 projects):General interest: 19 (19 projects):Intermediate project: 7:Radio &TV: 20 (20 projects):Test & measurement: 13 (12 projects).

From this, you will see that there were69 projects of noncomputer subjectsagainst 15 computer projects_ This is tosome too low a ratio, but I feel that for amaga:ine that tries to deal with all thingselectronic that is not a bad proportion.None the less. all these points will not hejOrgonen, so keep tip the comments. par-ticularly if they are as constructive as inthis letter. [Ed]

SWITCHBOARD

Switchboard allows all PRIVATE READERSElektor Electronics one FREE advertisement ofup to 10S characters. including spaces, commas.numerals. etc_ per month.

Write the advertisement, which must relateto electronics, in the coupon on this page:MUST INCLUDE a private telephone numberor name and address: post office boxes are notacceptable_

Elektor Electronics 41'ublishing) can not ac-cept responsibility for any correspondence ortransaction as a result of a free advertisementor of any -inaccuracy in the text of such an ad-vertisement.

Advertisements will he placed in the orderin which they are received.

Elektor Electronic,, Fliblishingr reserve theright to refu,- t -s .nents without givingreasons. or v. them.

WANTED. Canal Plus decoder (FrenchTV programme) building instructionswanted (to be bought). Phone +45 98573785.

FOR SALE. Heathkit SW7800 generalcoverage receiver plus auto transformer£175. Evenings: (0428) 713326.

PSST! Wanna buy an Amstrad DMP2000printer? Reliab le workhorse. Make me anoffer. Andy at (0367) 20788.

FOR SALE. Philips colour monitorCM8833: works on IBM/Atari/Amiga.£150 incl. manual, leads and postage.Telephone (0638) 663326.

HOBBY CLEARANCE! All must go!PSUs. CPUs. chips. capacitors and resis-tors. Dragon corn puter £35. Hard disk£125. Eight -inch drives: sae for list. NicSpiers. 20 Eaton Way, Gt Tatham,N1ALDON CM9 8EE; phone (0621)892512.

FOR SALE. Coax relays 24 V. SPCO.

150 W at 500 MHz c/w: 50 12 BNC plugs.

£5. Sim. Cirkit CX 120 p. Fmax = 2.5GHz. Phone Nev on (0273) 694347.

WANTED. S/H 5.25 -inch disk drives.Gemini keyboard. 80 -bus software. Isanyone still into 80 -bus?? Richard Smith(07292) 3051.

FOR SALE. Tek 50 + 'SE Labs 100 MHzscopes. Racal 9081 synthesizer, signalgenerator. mod analyser. Phone for detailsat (0206) 42147.

WANTED. Man ual and or circuit dia-gram for Hewlett Packard 3311A FunctionGenerator. Phone Bruce at (0272) 556151.

Send this coupon to: Elektor Electronicsi Publishing). Down House, BroomhillRoad. LONDON SW18 -1JQ.

EDck cabals ease-meW character to each box

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ELEKTOR ELECTRONICS MARCH 1990

Hams and addfass MUST ti : . r- r

ELEKTOR ELECTRONICS APRIL 19911

Please mention ELEKTOR ELECTRONICS when contacting advertisers

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GRAN DATA LTD.. Opt II.P.. K.P HOUSE, UNIT 15. POP -IN COMMERCIAL CENTRE, SOUTHY/AY, WEMBLEY, MIDDLESEX, HA9 OHE.ENGLAND.Telephone: 01 900 2329 Telex No: 932885 (SUNMIT) Fax: 01 903 6126

rA ....ess 577 4-5..1 C.: b .s:repted Open MC -.::3)' r.r. SI!...rcay.

ELEKTOR ELECTRONICS APRIL 1990

Cross Band Full Duplex4 Scanning Modes10 Function Memory ChannelsHighly Visible Colour LCD DisplayIlluminated Front Panel Controls5 Channel Spacing StepsBuilt-in DuplexerFunction Keys have UniqueAudible ToneBell FunctionCompact & Lightweight

Accessories Included:Hand-held microphoneMobile mounting bracketMounting hardwarePower cable

This very high quality 2m 70cm FM dual band mobile transceiver has beenspecialty designed to provide maximum performance and operatingconvenience in an ultra compact package. An impressive array of featuresgives maximum flexibility in mobile installations. The transceiver has anoutput power of 45W (VHF) 35W (UHF) and incorporates a high low powerswitch. Tne unit is provided with 10 programmable memories. Channelspacing is in 5, 10, 12.5, 20 and 25kHz steps. There are four scanningmodes:

1. VFO scanning of the entire band. 2. Memory scanning of selectedmemories. 3. Programmed band scanning of a selected segment ofthe band. 4. Priority scanning allows selection of a frequency, in VFOor memory, to serve as a priority frequency.

A duplexer is built-in so that when an antenna for both bands is in use,only one feeder cable for the transceiver is necessary.

The unit is supplied with a comprehensive instruction manualit isillegal to transmit with this unit unless you hold a Radio Amateur'sClass B (or A) licence.Quote Reference DBT40 £499.95

Ultra compact, lightweight design- 6.5W Output Power

(with optional 12V battery pack) Simple Operation< Easy to See LCD Display< 10 Channel Memories

Battery Save Function Lock= Tone Burst= Amazing Compact Size Only 3x6x17 cm approx.

A very high quality, lightweight. 2m handheldtransceiver. incorporating many useful features.This transceiver is extremely simple to operate,most functions can be performed with one hand!

Quote Reference AHT40 £219.9512V Ni-Cad Battery Pack

For use *eh ether above handheld rarscaieraA 1211700mAh bay peck a intogra4CCAC comparterIllicit aloes the transceiver b be rowed tun a car

ccaretse Wier socket.A dtyper e atm a:alai* kr we a.27 scoot

Bari-! HBP40 559,95 NBC40 C14.95

psALINCO

from MAPLINthe authorised

distributor

;;;;; 11111 /111111 lllll 1/rni O11111,1 ti/ .,01 ..11

6W VHF 5W UHF Output Power(with optional 12V battery pack)

Cross Band Full Duplex Operation- Frequency selection by Direct

Keyboard Entry or Step Upltep Down< Automatic Battery Save Function< 20 Memory Channels< Built-in DTMF Keypad and Encoder< Amazing Compact Size Only

3x 6x 19 cm approx.This unit is very compact and is one of the smallestdual band transceivers currently available. Withthe battery pack supplied output power is 2.5W forVHF and 2W for UHF. Frequency selection iseither by direct keypad entry of the requiredfrequency or by using step up step down buttons inincrements decrements of 5kHz, 100kHz and1MHz. An automatic battery save (ABS) functionwill extend battery life considerably. There are 20memories (10 VHF and 10 UHF) for storingoperating. offset and tone frequencies. Thescanning facility has a priority function which hasthe ability to scan between chosen VHF and UHFfrequencies. Al OdB RF attenuator is switchselectable and can be used in areas of high RFsaturation.

Quote Reference DHT40 £369.95

J/11 e _A, ELECTRONICSP.O. Box 3, Rayleigh, Essex SS6 SLR.

CREW V CARD LA_CDVLIIKE

0702 554161 c ==". . 54

PHONE BEFORE 5PM FOR SAME DAY DESPATCHa cat m al a PAO-in bye el arm:: -.YE:" E,ag. Marcebe,. Ncr-tbra.7,.

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SEE THE COMPLETE RANGE Of TRANSCEIMIS AND LOTS MORE IN OURBUMPER 080 -PAGE CATALOGUE

ON SALE NOW AT ALL BRANCHES Of WHSMITH -PRICE £2.25!