exploring the technology that powers the sun · 4/10/1991 · to universal programming system the...

[PRACTICAL

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December 1991 £1.50

Exploring the technology that powers the Sun

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This month...

PE has gone through something ofa transformation this month. Due topopular demand, we are looking atmore new products and fewer projects- anyone who wants the final detailsof PE Chronos should send in a largeSAE.

This month's cover feature is anexamination of the JET JointUndertaking. This atomic fusionexperiment is probing the frontiers ofresearch that will lead the way tovirtually unlimited cheap electricalpower for the future. My thanks go toeveryone who showed me around thefaciity and helped with the variousdetails and pictures.

Our project this month is a follow-up to Jeff Macauley's power valveamplifier. For those who don't havethe space or lack of neighbours toblast away with 100W of raw power,this valve based system uses the sametechnology but is designed to be usedwith headphones.

Kenn Garroch, Editor

Next month...

We examine the latest craze thatinvolves the combination of computers,

video, sound and presentation,Multi -media.

Out On 5 December

December 1991 Volume 27 No. 12

Christmas Presents 16PE gets its requests off to Santa

The Making Of A Sun 20Atomic Fusion, the power source of the future

Electronics Under The Hammer 30Flogging the history of electronics

PE's Trivia Quiz 45How much do you really know about electronics?

Pure Sound For Your Ears 47Build a top quality headphone valve amplifier

Reviews

Wide Imaging Sound 38Canon's speakers break the mould

Animated Circuits 40See those electrons move with ACE

Scanning The Radio Waves 43Listening in on all bands

The Way Of The Universe 44Book reviews looks at The Matter Myth

Regulars

Wavelengths 5Are flat screen TVs here at last?

Innovations 6Intel's latest chips and an innovation competition

What's New 9Palmtops, video recorders and ISDN

Silicon Valley 14Converting from analogue to digital

Show Report 25Amstrad videophone, PC on a chip and the new Psion series 3 portable computers

How It Works 32Using the mains for an intercom

Practical Technology 35Image scanners, is this the way of the future?

Techniques 57

Three seasonal solutions to flashing those lights

Barry Fox 62BT makes excuses about its new numbers

Editor Kenn Garroch Advertisement Manager David Banner Production Manager: Richard Milner Production Assistant: Dino Digioacchino Office Manager Laura Esterman Office Secretary Wendy Rhodes Publisher: Angelo Zgorelec

Practical Electronics Intra House 193 Uxbridge Road London W12 9RA Tel: 081-743 8888 Fax: 081-743 3062 Telecom Gold: 87: 500567 Advertisements The Publishers ofPE take reasonable precautions to

ensure that advertisements published in the magazine are genuine, but cannot take any responsibility in respect of statements or claims made by advertisers. The Publishers also cannot accept any liability in respect of goods not being

delivered or not working properly. © Infra Press 1991. Copyright in all drawings, photographs and articles published in PRACTICAL ELECTRONICS is fully protected, andreproduction or imitations in whole or in pan are expressly

forbidden. All reasonable precautions are taken by PRACTICAL ELECTRONICS to ensure that the advice and data given to readers is reliable. We cannot, however, guarantee it, and we cannot accept legal responsibility for it. Prices quoted are

those current as we go to press. All material is accepted for publication on the express understanding that the contributor has the authority to permitus to do so. Practical Electronics is typeset at Intra Press on Macintoshcomputers using Quark Xpress. Reproduction by Circle Rule Ltd. Printing by Andover Press, St Ives plc. Distribution by Seymour Press 1.4911 0032-6372

December 1991 Practical Electronics 3

1

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4 Practical Electronics December 1991

Letters

WavelengthsIf you have any comments, suggestions, subjects you think shoul d be aired, write to PE

/have been a keen reader ofPractical Electronics since yourvery first issue and it has always

fascinated me to read over oldcopies and marvel over the changesover the years.However, not untilnow have I been moved to makeany criticism.

In the September issue, Mr. IanBurley writes about new items seenat the Chicago US ConsumerElectronics Show. His comments onthe Sharp active -matrix LCDscreens infuriated me and I am suremany others are positively longingfor these screens to becomeavailable in reasonable sizes and atreasonable prices so that we maysee the end of the ugly, bulky CRT -dominated boxes. So there is"apparently" a sizeable market forthese in Japan. And I expect therewould be in England, too, werethey available. And why his snidecomment "So what?". I don't care ifthe frames are ugly or tasteless.There have been plenty of tastelessTV cabinets designed. Why couldwe not have had a few details onthe sizes being manufactured, thecurrent costs and a projection offuture costs should these become

popular - as they must. Or it isperhaps that we, the consumers -and maybe the critics - are to bedominated by the great CRT -manufacturing industry?

Ray M BoormanMadridSpain

Sticking Sharp's world-beatingactive -matrix screen technology intothose horrid picture frames was aninsult to that technology. It was anunnecessary marketing gimmick, whichI hope Sharp thinks twice about infuture. Of course I keep a close eye onscreen developments and I'm convincedflat panel LCD -based screens willquickly replace CRTs in all but thelarger screen sizes once the technologyhas been honed.

Ian Burley

Viewing TroublesI look forward to the PDC systemdiscussed by Barry Fox inSeptember 1991 PE. It should solvesome problems but does not seemable to avoid the major weakness,already present but ignored, in thePanasonic bar code system.

What happens when timing

The offending screens

changes causes unexpectedprogramme overlap? TVbroadcasters apparently assumethat we are still in the 1940s withonly one TV channel. We watch thissingle channel 24 hours per day andare always fully aware of all thevariation announcements!

Programme clashing is treatedas being completely irrelevant.Despite the wonders of modernmicrosecond timekeeping andprerecording of most programmes,it seems impossible for publishedtimes to be achieved on a regularbasis.

A recent attempt to record twoseries, on separate channels, overseveral weeks failed. The first ranlate every week and up to tenminutes was lost at everychangeover. Even with a VCR it isimpossible to go out for theevening.

R G SilsonTringHerts

Why MultiMedia?What is all the fuss aboutmultimedia? I can't see that it hasany real applications. If you wantsound you get a HiFi with LPs,cassettes or CD. For vision, the VHSvideo recorder seems to havesettled down as the main system forimage recording and playback.Video cameras are also available forthose who want to record their ownmoving images. For a mixture ofboth sound and vision, try TV withNicam stereo from either thestandard terrestrial stations (BBC1and 2 and ITV 3 and 4) or satellite.These cover all the possibilities,apart from smelly -vision whichnever got off the ground.

Why would anyone wantpresentation graphics and soundinterfaced to a computer systemunless, of course, they are giving aseminar.

A StanleyBrighton

December 1991 Practical Electronics

Innovations

InnovationsThis month, Intel's latest chips, BT's new premium rate number and a boost for the hometaping campaign.

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Test Vector 1 Vector 2

Cache Memory Human interface

CPU1 CPU2 CPU3 CPU4

Intel's Micro -2000 shows what could be in the i586.

Towards The 588A recent report from Intelpointed the way towardsthe next generation ofmicroprocessors.Following on from itssuccessful i386 machinesthe i586 should have fourCPUs each rated at 700million instructions persecond, two vectorprocessing units thatwould speed upnumerical calculations,cache memory forfrequently used programsand data and a humaninterface providinginteractive video andvoice recognition. All ofthis would be squashedinto one chip using 100million transistors in onesquare inch of silicon.With a total throughput of2 billion instructions persecond and completecompatibility with thei386 range, it shouldprove a worthy opponentto the IBM/Motorola chipdestined to power thenext generation of IBMPCs.

Intel has been makingmicroprocessors since theearly days of 1970 whenthere were only about1000 transistors per chip.The co-founder of the

company Gordon Mooremade the observationsome time ago that thenumber of transistors on achip doubles every twoyears and that by the year2000 there should easilybe over 100 million perchip.

Intel's currentmicroprocessors are thei386 range. The 386SX isthe bottom of the rangeand has a 16 -bit data busrather than the 32 -bitstandard. The 386DX isthe mid range memberwhich conforms to the fullstandard and is availablein speeds from 16 to33MHz. At the top of therange is the i486. Thisuses a 386 microprocessor

and incorporates a 387maths co -processor, 385cache controller and8kbytes of static RAM onthe same chip.

Taping SupportA recent report publishedby the Consumer'sAssociation( Which?magazine October 1991)gave a boost to the HomeTaping Rights Campaign(HTRC). It vindicated thelong held suspicion thatmost people whorecorded copyrightmaterial onto cassettesdid so from records orCDs that they alreadyowned. This does notreally cause a loss to therecord industry and itseffect on sales has beenexaggerated. TheConsumer's Associationalso concluded that, "thecase for a levy onvideotapes is non-existent", since only 4% ofpeople survey copyingvideos.

The HTRC has beencampaigning since 1986 todefend home taping andoppose any levies

Will DAT be hit by tape levies?

imposed on blank tapes.These would go to therecord industry whichclaims that it is losingsales as a result of thisflouting of the copyrightlaws. Legislation iscurrently being preparedby the EuropeanCommission to imposelevies on recordingequipment as well asblank tapes.

CAD On A PCWNow CAD systems arenot only available on IBMPCs, Amstrad PCWs aregetting in on the act.CADsoft Systems recentlyannounced the release ofits Schematic DrawingPackage for the AmstradCPC6128 andPCW8256/8512 machines.Running under CP/M+,the package consists of aschematic editor, a printprogram and a symbollibrary. The latter suppliesmost of the morecommonly usedcomponent symbols suchas capacitors, resistors,transistors and logic gatesand an editor is providedso that more can beadded. Diagrams of up to50in x 50in can be drawnwith around 5000 objectsper drawing. The printingpackage provides outputon even the most basicdot-matrix printer.

Costing £29.99 with a£5 discount for registeredusers of other CADsoftproducts, it is avialblefrom CADsoft Systems, 18Ley Crescent, Tyldesley,ManchesterM29 7BD.


Innovations

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Example output from CADsoft's Schematic Drawing Package.

£1000 To Be WonAfter sawing through achair thirty years ago, RonHickman developed aflexible bench known asthe Workmate. Now acompetition has beenlaunched, sponsored byBritish Fuels, to "find thenext brilliant idea thatwill revolutionise outlives".

The first prize is £1000and British Fuels, thecountry's leading supplierof coal and oil, will alsogive free practical advicefor the development andmarketing of the newproduct as well as legalprotection andsuggestions on where toget the appropriatefunding. The second andthird prizes are £500 and£250 respectively and apanel of experts,including Sir Cyril SMithMBE MP will examine allentries in strictconfidence. Anyone whothinks they have a worldbeating idea and wouldlike to have a stab atwinning the prize shouldwrite to:BFL Innovations AwardFreepostThe BRAHM BuildingAlma RoadLeedsLS6 2AHortelephone 0532 304000and ask for an entry pack.

0898 SolutionAfter catching so muchflak from the media aswell as those who had topay some pretty hugetelephone bills, BT hasannounced a newpremium rate prefixnumber.

Under the old systemthe, now notorious, 0898number was used toaccess a wide variety oftelephone services fromchatlines to heavybreathers (adults onlylines). The callers had topay a higher rate for theseservices and there were a

number of situationswhere parents had had topay BT for the telephoneabuse committed by theirgregarious offspring.From BT's point ofview,the numbers wererented out to companieswho provided the actualservices and controllingthe situation proved to bedifficult.

There was so muchtrouble over the telephoneabuse that theIndependent Committeefor the Supervision ofStandards of TelephoneInformation Services

(ICSTIS) had to draw up acode of practice foranyone wanting toprovide a premium rateservice. BT has nowannounced that it willbeing doing its bit to helpwith the problem byproviding anotherpremium rate number,0891, to be operated alongside the 0898, which willconform to the ICSTISstandard.

The ICSTIS codeforbids the provision ofadult, chatline and mostlive conversation servicesover lines using the 0891prefix. Customers on thenew digital exchangeswill be able to stop theirtelephones accessing anyor all of the premium ratenumbers - 0898, 08364,0839 and 0881 - so thathuge unforeseen billsshould no longer arise.There is no charge for thecall barring service, theonly problem is that justunder half of thepopulation won't be ableto use it - BT has, as yet,only converted just overhalf its exchanges todigital operation.


SIMV14.11LLANCEPROFESSIONAL MAIM KITS

r No. I for Kits'Whether your requirement for surveillance equipment is amateur, professional or you are just fascinated by this unique area ofelectronics SUMA DESIGNS has a kit to fit the bill. We have been designing electronic surveillance equipment for over 12 yearsand you can be sure that all of our kits are very well tried, tested and proven and come complete with full instructions, circuitdiagrams, assembly details and all high quality components including fibreglass PCB. Unless otherwise stated all transmittersare tuneable and can be received on an ordinary VHF FM radio.

UTX Ultra -miniature Room TransmitterSmallest room transmitter kit in the world! Incredible 10mm x 20mm including mic. 3-12V operation. 500m range £16.45

MTX Micro -miniature Room TransmitterBest-selling micro -miniature Room TransmitterJust 17mm x 17mm including mic. 3-12V operation. 1000m range £13.45

STX High-performance Room TransmitterHi performance transmitter with a buffered output stage for greater stability and range.Measures 22mm x 22mm including mic. 6-12V operation, 1500m range £15.45

VT500 High -power Room TransmitterPowerful 250mW output providing excellent range and performance. Size 20mm x40mm. 9-12V operation. 3000m range £16.45

VXT Voice Activated TransmitterTriggers only when sounds are detected. Very low standby current. Variable sensitivityand delay with LED indicator. Size 20mm x 67mm. 9V operation. 1000m range £19.45

HVX400 Mains Powered Room TransmitterConnects directly to 240V AC supply for long-term monitoring. Size 30mm x 35mm.500m range £19.45

SCRX Subcarrier Scrambled Room TransmitterScrambled output from this transmitter cannot be monitored without the SCDM decoderconnected to the receiver. Size 20mm x 67mm. 9V operation. 1000rn range £22.95

SCLX Subcarrier Telephone TransmitterConnects to telephone line anywhere, requires no batteries. Output scrambled sorequires SCDM connected to receiver. Size 32mm x 37mm. 1000m range £23.95

SCDM Subcarrier Decoder Unit for SCRXConnects to receiver earphone socket and provides decoded audio output toheadphones. Size 32mm x 70mm. 9-12V operation £22.95

ATM Micro Size Telephone Recording InterfaceConnects between telephone line (anywhere) and cassette recorder. Switches tapeautomatically as phone is used. All conversations recorded. Size 16mm x 32mm.Powered from line £13.45

*** Specials ***DLTX/DLRX Radio Control SwitchRemote control anything around your home or garden, outside lights, alarms, pagingsystem etc. System consists of a small VHF transmitter with digital encoder and receiverunit with decoder and relay output, momentary or alternate, 8 -way dil switches on bothboards set your own unique security code. TX size 45mm x 45mm. RX size 35mm x90mm. Both 9V operation. Range up to 200m.Complete System (2 kits) £50.95Individual Transmitter DLTX £19.95Individual Receiver DLRX £37.95

MBX-1 HI -Fl Micro BroadcasterNot technically a surveillance device but a great idea! Connects to the headphone outputof your Hi-Fi, tape or CD and transmits Hi-Fi quality to a nearby radio. Listen to yourfavourite music anywhere around the house, garden, in the bath or in the garage andyou don't have to put up with the DJ's choice and boring waffle. Size 27mm x 60mm.9V operation. 250m range £20.95

UTLX Ultra -miniature Telephone TransmitterSmallest telephone transmitter kit available. Incredible size of 1mm x 20mm! Connectsto line (anywhere) and switches on and off with phone use. All conversation transmitted.Powered from line. 500m range £15.95

TLX700 Micro -miniature Telephone TransmitterBest-selling telephone transmitter. Being 20mm x 20mm it is easier to assemble thanUTLX. Connects to line (anywhere) and switches on and off with phone use. Allconversations transmitted. Powered from line. 1000m range £13.45

STLX High-performance Telephone TransmitterHigh performance transmitter with buffered output stage providing excellent stabilityand performance. Connects to line (anywhere) and switches on and off with phone use.All conversations transmitted. Powered from line. Size 22mm x 22mm.1500m range £16.45

TKX900 Signalling/Tracking TransmitterTransmits a continous stream of audio pulses with variable tone and rate. Ideal forsignalling or tracking purposes. High power output giving range up to 3000m. Size25mm x 63mm. 9V operation £22.95

CD400 Pocket Bug Detector/LocatorLED and piezo bleeper pulse slowly, rate of pulse and pitch of tome increase as youapproach signal. Gain control allows pinpointing of source. Size 45mm x 54mm, 9Voperation £30.95

CD600 Professional Bug Detector/LocatorMulticolour readout of signal strength with variable rate bleeper and variable sensitivityused to detect and locate hidden transmitters. Switch to AUDIO CONFORM mode todistinguish between localised bug transmission and normal legitimate signals such aspagers, cellular, taxis etc. Size 70mm x 100mm. 9V operation £50.95

QTX180 Crystal Controlled Room TransmitterNarrow band FM transmitter for the ultimate in privacy. Operates on 180 MHz andrequires the use of a scanner receiver or our QRX180 kit (see catlogue). Size 20mm x67mm. 9V operation. 1000m range £40.95

QLX180 Crystal Cointrolled Telephone TransmitterAs per OTX180 but connects to telephone line to monitor both sides of conversations.20mm x 67mm. 9V operation. 1000m range £40.95

QSX180 Line Powered Crystal Controlled Phone TransmitterAs per OLX180 but draws power requirements from line. No batteries required. Size32mm x 37mm. Range 500m £35.95

QRX180 Crystal Controlled FM ReceiverFor monitoring any of the '0' range transmitters. High sensitivity unit. All RF sectionsupplied as a pre -built and aligned module ready to connect on board so no difficultysetting up. Outpt to headphones. 60mm x 75mm. 9V operation £60.95

A build-up service is available on all our kits if required.UK customers please send cheques, POs or registered cash. Please add£1.50 per prder for P&P. Goods despatched ASAP allowing for chequeclearance. Overseas customers send sterling bank draft and add £5.00 perorder for shipment. Credit card orders welcomed on 0827 714476.

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New Products

What's NewA new section this month takes a quick look

at the latest electronic products.

The Refalo from Kyocera is a palm -top computer which,instead of a keyboard, uses a pen based system to recognisehandwriting. Measuring 190mm x144mm x42mm whenclosed, it weighs just 750g and is designed to take the placeof a Filofax - it even has ring binders so that filofax pagescan be attached.The computer side of things is based upon the wellknown 8086 (aka V30) which was at the heart of some ofthe early IBM PCs. Like these machines, its operatingsystem is MSDOS and is held in 256k bytes of ROM.On -board RAM is 256k, split into 192k user area and64k video RAM.Applications software will be loaded via an IC cardthat conforms to the Japan Electronic Industry

Development Association (JEIDA) standard. Built insoftware is planned to be of the usual organiser type, diary,

notebook, scheduler, and so on. The user interface is pen based usinga pressure sensitive LCD screen with a resolution of 240x320. For those who

can't manage without a keyboard, one is available as an optional extra - measuringthe same size as the Refalo itself. To connect to the outside world, an RS232 serialinterface is provided. The whole thing will cost around £1000 and should be available byApril next year.

Integrated Services Digital Network, better known asISDN could soon be available to many more people ifthe new Dataflex Pocket ISDN adapor takes off.Offering data transfer speeds of up to 64k bytes persecond, the device, which is smaller than an SonyWalkman, is fully BABT approved and compatiblewith ISDN-2. Initially aimed at reatil and financialinstitutions to speed up electronic funds tranfer, themodem, priced at £595+VAT, should broaden accessto the high speed communications network.

Callbox 2 is another gadget that should make communicating via thetelephone a lot easier. Designed to be linked to a PC, it allows completelyhands free operation of the phone with auto -dialling, voice -mail, light-weight headset plus numerous other applications. A programmers interface

is also available that uses the industry standard Hayes command set.Costing £825, the system is currently being designed into a number of telephoneapplications such as information response suystems, technical support and creditcontrol.


What's New

c016 The PC operating system competition is gathering

pace with DR DOS 6 being released at about thesame time as MS DOS 5.0. Offerring an alternative

operating system for PC users, Digital Research'sversionis better than Microsoft's by quite a wide margin.Improvements include a data compression utility thatallows up to twice a much data to be stored on a disk - filesare accessed in the normal way so operation is completelytransparent. Also available is a twenty -task switcher utilitythat allows up to 20 programs to be loaded at once. Thisallows the user to switch between them rather than having toquite from one application and then load up another as isgenerally the case with other versions of DOS.Anyone who uses PCs a lot should definately consider switchingor upgrading to DR DOS 6. The only drawback is that it isrelatively expensive at £79 or £24.99 as an upgrade for existingDR DOS users.

At 360dpi, Canon's BJC-800 colour bubble -jet printer offers some of thebest printing capabilities around. Four individual cartridges usingyellow, magenta, cyan and black feed their ink to a 64 nozzle print headto create the high resolution colour images. Unlike other colour printers,black printing quality is just as good as any other colour. The cartidgesare said to last for approximately 400 pages and can be replacesindividually.The printer will be available in the UK by March 1992 and will be pricedat around £1995.

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The new range of computers from Elonex all feature32 -bit microprocessors and range from the PC-

320XM to the PC -450B. The first comes with20MHz 386SX, 16kbyte cache, 1Mbyte of RAM,

40Mbyte hard disk and 512kbyte Super VGA andis the basic system. The top of the range has a

50MHz 486 microprocessor with 64kbyte cache,2Mbyte RAM, 40Mbyte hard disk and 512kbyte

Super VGA. Starting at £995 for the lower endmodel, the PC -450B costs £2195 with eight modelsbetween them offerring a wide election of platformsand prices to choose from.


What's New

Another printer offering laser quality colouroutput is the Hewlet Packard Deskwriter C -priced at £749. Boasting 300dpi resolution, ituses one ink cartridge which can be either a tri-chamber design incorporating cyan, magentaand yellow, allowing any colour to bereproduced, or a single chamber black formonochrome output. Aimed mainly at AppleMacintosh users, the printer has a number ofstandard fonts built in as well as an Appletalkinterface allowing it to be used on a network.

The Psion Series 3 is a new range of pocketcomputers featuring 80086 microprocessors,240x80 pixel double layer LCD, 640kbytes ofRAM and 385kbytes of ROM. A fullGraphical User Interface,wordprocessor, database,calendar, programming languageand calculator are bundled with thesystem and the basic model costsaround £200 including VAT.

Also new in the area of pocket portables is the GRiD M88.Featuring MSDOS 3.22 in ROM, the display is a CGAcompatible LCD screen offering either 8 lines by 20characters, 15 lines by 20 characters or 25 lines by 20characters. The 50 key keyboard, 80088 and 640kbytememory allow it to run virtually all DOS software. Connectionto the outside world is via RS232, a barcode reader orexpansion bu's. Priced at £999, GRiDs name for tough reliableportable computers should enable it to compete with thePsion and Poqet PC compatible palmtops.


What's New

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The Alba VCR2222 solves all of the problems that

4Iarise due to video tapes being too short. Because it4 has two video transports, it can record and playback up

to 20 hours of program material. Other features includerecording on both tapes at once, recording one tape whilewatching another, duplicating tapes, a four week/eightevent/99 channel memory and tape to tape editing.

The new V711B from Toshiba in the flagshipof the company's VCR range. FeaturingNICAM stereo, long play, on -screenprogramming, comprehensive searching andtiming facilities, picture quality enhancer, adynamic bass switch and simulcastrecording, its weighs in at a mere £499.99

Also from Toshiba is the 34in Super Screen NICAMDelux TITAN TV with Dolby Surround. Available fromOctober 1st, it features 100 channel tuning, unifiedremote control and on -screen display. Priced at£1999.99 it is the top of the Toshiba TV range.


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Silicon Valley

Data AcquisitionSystem On A ChipSilicon Valley this month looks at Nat Semi's new single chip DAS, the shrinking oftelecoms equipment and the fastest dual port RAM in the world.

The ease with which data canbe monitored has taken a stepforward with the introduction

of National Semiconductor'sLM12458 single chip dataacquisition system (DAS). Thisincorporates a 12 -bit self -calibratinganalogue to digital convertor(ADC), storage for up to 32conversions, internal RAM thatstores instructions on whichconversions should be performedwhen, an eight input multiplexer(MUX), watchdog facilities tocompare inputs against presetlimits, programmable conversionrates and built in referencevoltages, all powered from a single+5V supply.

Conversion times are rated at8.6us for 13 -bits and 4us for 9 -bitson the eight programmablechannels. The on -board digitalcontrol system consists of an 8x48instruction RAM that stores theacquisition instructions for up tofour differential or eight single -ended input channels. These can beused to specify the data gatheringchannels, their sequence, speed anddata output format resulting is ahighly flexible system.

Designed to be interfaceddirectly to a microprocessor, theLM12458 can take some of theprocessing load off the main systemby means of its programmability. Itis aimed at applications in datalogging, energy management,industrial process control,instrumentation, medical andportable systems, robotics andsignals analysis.

For more information contactNational Semiconductor,Industriestrasse 10, D-8080Furstenfeldbruck, Germany

More Portable CommsPortable communications systemssuch as cellular and cordlessphones are set to become evensmaller than they are now. A pair ofchips from Signetics offer advancedFM mixer -IF systems that shouldreduce the size of a PCB by 15%. Aswell as offering more facilities persquare centimeter, the NE606 andNE607 use lower supply currentand offer more facilities thancompetitive products.

Included on each chip is a mixeroscillator, two operationalamplifiers, IF amplifiers, limiteramp, voltage regulator andquadrature detector. All of thisallows the facilities of a portableFM communications system to besquashed into an even smallerspace.

More information can beobtained from Signetics, a

subsidiary of Philips on 071 5806633

Super Fast Dual -PortClaiming to be the densest dual -port SRAM available today, theIDT7M1002 offers 512k of memorywith an access time of 25ns. Thepackage is designed to be used with32 -bit RISC (reduced instruction setcomputer) or CISC (complexinstruction set computer) memorysystems to simplify design. Thehigh speed of the system makesthem ideal for use in applicationssuch as telecommunications,networking, digital signalprocessing, and image or graphicsprocessing.

Contact Integrated DeviceTechnology Europe, 21 TheCrescent, Leatherhead, Surrey,KT22 8DY, for more information.

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Telephone- 081-643 9568 or 041-221 2926 124 nours) IDecember 1991 Practical Electronics 15

Wishes

All I WantFor ChristmasBarry Fox and Ian Burley join the editor in getting their present lists off to Santa nice andearly so that a reply is assured

One of the best things aboutbeing editor of PE is that Iget to see, or at least hear

about, all the latest electronicgadgets. The problem with this ischoosing between them all forsomething I'd like. In the end, Idecided on some of the more recentpieces of kit that caught my eye.

Editor's ChoiceThe first is the Philips Scopemeter.This is, perhaps, the ultimateelectronic test instrument.Combining the features of asophisticated digital multi -meterwith those of a 50MHz oscilloscopeand a signal generator, this gadgetis also built into a super ruggd case- there aren't many oscillocscopesthat can be dropped one metre ontoconcrete without doing them somedamage. The top of the range

Kodak's digital camera system, a snip at $20,000.

model costs a mere £1095, wellbeyond my pocket but, if anybodyis looking to buy me a present...

Some say it is bad to combinebusiness with pleasure but one ofthe things that makes my job easierand is a lot of fun to use is theApple Macintosh used to put themag together. I have a huge one onmy desk (a IIcx plus 19in monitor)which is great for most things but isin no way portable. It would be niceto be able to work at locations otherthan the office and I have alwayshankered after a decent portablecomputer. The trouble is thatalthough there are a number oflaptop machines available, none arefully Apple Mac compatible -anyone who has used both PCs andMacs will know there is no goingback to a PC. Fortunately, there is arumour going around that Applewill be launching a full featurelaptop in the near future - thecompany denies all knowledge ofthis but stories in Mac User, the

Financial Times, plus third partysoftware houses boasting that theyare going to publish software for itcan't all be wrong. With any luck itwill be out by Christmas, in whichcase it will be at the top of my list.

One of the more fascinating andexpensive items covered recently inPE was Kodak's electronic camera.The Digital Camera Systemoperates in the same way as anormal Nikon 35mm but produces1280x1024 pixel images that can beloaded onto a computer for storage,display and editing. I may not bemuch of a photographer but one ofthese babies might make thedifference, especially when coupledto a high quality graphics machinelike a portable Mac...

Get AwayTrying to get away from it all is oneof my main hobbies. To help withthis I like to listen to the odd bit ofmusic and with this in mind, I


Wishes

would like to upgrade my CDsystem to a Philips Bitstream andmy speakers to Canon S50s (seereview this issue). With theseinstalled, I can sit back and enjoythe New Year in sonic comfort.

Barry FoxThe Japanese have grown rich onconsumer electronics. Massproduction is the key to low priceand high reliability; and digitalcircuitry is easier to integrate into afew chips. The main cost of acalculator or digital watch is now inthe packaging and distribution. Sostalls in Hong Kong sell them for50p and firms round the world cangive them away as free promotions,

even though the shop price isseveral pounds.

Now the Japanese majors, withsights set on the long-term future,are recognising that the world issaturating with electronic trinkets.They must think of new noveltiesthat people will buy on impulse, orelectronic equipment whichanswers a genuine need.

They know that what we DON'Twant for Christmas is anotherportable stereo, car radio or worldtime clock and calculator.

So what do I want?Having struggled with CD-

ROM, I have seen the potential ofthe medium but been driven todistraction by the lack ofcompatibility between CD-ROMdiscs, drives, computers and controlsoftware. What I want forChristmas is Sony's new DataDiscman, a table -top data bank thatis ready to read data from a CD-ROM at the flick of a single on/offswitch. They should be on sale thisChristmas in the USA at around$500.

No Mangled VHS For MeWalt Disney is releasing Fantasia onvideo for the first and final time thisChristmas. After that the originalversion will never be seen, onvideo, again. In the USA the releaseis on VHS tape and laser video disc.In Europe it looks like being onVHS tape only. I want it on laserdisc, because that way I should stillhave a good copy of Fantasia longafter other people have mangledtheir tapes.

Often I want a singlephotograph of something, or fewslides to project at a talk or lecture. I

also want to be able to photographsmall objects at close range. Mostmodern 35mm cameras have amacro facility which allows close-ups. But you have to shoot andprocess a whole reel of film. Sowhat I realy want is a sensiblypriced Polaroid camera, with amacro facility; better still I want onethat will shoot instant slides insteadof instant prints. But I fear there isnothing yet like that.

Likewise I fear I can't have thesimple gadget I would like thatcould plug into a TV set anddisplay on screen a positive imageof a photographic negative. I couldalready do this, by using a videocamera with neg/pos reversalswitch. But the camera would costthe best part of £1000 and I wouldhave to rig up some kind of adaptorin front of a macro lens to hold andilluminate the negative. What Iwant is a custom designed slideviewer which includes an imagesensor and negative/poitivesswitch.

I also want something that Ihave already got but others keepasking to borrow. It's a neat littleplug-in transformer which convertsUS and Japanese 110 volt mains upto 220 volts so that I can runEuropean electrical equipment inthose low voltage countries. Theshops are knee deep in dropperswhich reduce 220V to 110V, butwhat use are they to anyone inEurope? I bought my plug-in upconverter in America for $10, buthave never seen once since.

Finally I'd like a nagger. This is atelephone with a last number redialfacility which registers when thenumber is engaged, hangs up andkeeps on trying again, and again,and again every half minute or sountil the line is clear. The Britishauthorities won't let us have these,because they reckon it clogs up thetelephone system. But some foreignphones have them and anyone whohas tried using a nagger will knowwhat a boon it is.

Ian BurleyWhen I was first asked to write thisarticle, my immediate reaction wasto run riot with an imaginary creditcard endowed with an infinitecredit limit. To be asked what halfdozen bits of consumer electronicsone would like for Christmas,money no object guv


Wishes

visions of shiny new gadgets fromwide screen TVs, multi -standard hi -band videos, HiFi, phones, youname it! Actually settling on aselection of six proved much moredifficult. Not being related to PaulGetty, I am actually quite cautiousabout what I buy for myself in thereal world, despite what somefriends might say. It was difficult tojustify some of the more outrageousgadgets, even though I am self-confessed gadget -mad. So you may

be surprised to find that thefollowing electronics products are,on the whole, useful rather thanextravagant, though I still couldn'tafford half of them.

I would like an Amstrad 9600Fax. A fax machine? These marvelsof telephony are already consideredboring and utilitarian by most officeworkers; a fate of popular apatheticattitude which befell the personalcomputer some years back. In theStates, fax machines are rapidly

The security robot on show.

becoming established in asurprising number of homes. This isa trend which, like many others, wewill see over here sooner or later.As I do a fair amount of freelancewriting, I am constantly asked ifmaterial can be faxed to me. Untilnow, I have resisted the temptationto buy a fax - I use the TelecomGold Email service for sending text -only faxes directly from mycomputer. However, I will begiving in soon, and will take theopportunity to pension off my 8 -year old Binatone answeringmachine by buying a combined faxand answering machine. I can'tjustify the installation of a secondphone line, hence the combo unit.The Amstrad 9600 is excellentvalue, save one omission -a remotecontrol for the answering machinesection. I hear this due to beremedied quite soon. Now, didanybody mention discounts...?

. I joined the camcordergeneration earlier this year and nowfind I need a pocket -sized TV toview, in colour, footage I've shot onlocation. Until recently, miniatureportable TVs were sad gimmicks.Even Sony's first stab at the blackand white Watchman was neithertruly pocketable or much fun towatch. The quirky Sinclair flat -


Wishes

screen TV was a step in the rightdirection, though in my opinion theadvent of the first rather smearyand too -minute colour LCD TVsonly hinted at the futurepossibilities. With the arrival ofactive -matrix thin film transistortechnology, the better portable LCDTVs are now serious alternatives toconventional 14" portable tellys.Citizen, Sharp, Sony, Panasonic andothers have some very nice lookingmodels, but as a frequent-ishtraveller I'm disappointed not tohave found a world -standardmodel yet. Oh yes, at around £300for a 4" screen, they're ratherexpensive - but that doesn't matterhere, does it? Prices should dropnext year.

I get around quite a bit behindthe wheel of my car. Not only am Ia proponent of the paperless officebut I'd like a paperless car interioras well. No more fumbling with bitsof paper or maps at 70MPH on theM25, thankyou very much. TheBlaupunkt TravelPilot systemshows a remarkably detailed anddynamically updated map of thelocal vicinity you are travellingthrough, even taking into accountyour heading as you turn corners.Those who know me will leap at theopportunity of confirming howabysmal I am at finding my wayanywhere, so this would be anIDEAL Christmas present.

If there is one thing I have beenconvinced of totally in the last 18months, it's that interactive video ormultimedia is going to be asimportant to us as the printing

Blaupunkt's Travel Pilot should keep Ian on course.

REGENTSREGENTS PTRESTART BUILDRET

press was to Caxton in his day. Theadvantage Caxton had was that hedidn't have to fight to establish hishardware standard over a posse ofothers. I'd like a Kodak Photo CDcompatible CD -I player which Icould have permanently linked toboth my computer as a CD ROMdrive and the HiFi as a conventionalmusic CD player. OK, make thattwo of thek... Oh, and it would haveto have Bitstream digital soundshaping and if only it couldintegrate into the rest of my hifi likeSony's SIRCS II system.

Assuming it works as well as it'sexpected to do, Sony's newrecordable audio disc system, MiniDisc, should be a big commercialsuccess. Unfortunately, history tellsus that technical niceties in the

Everyone awaits DCC with baited breath.

league of random-access digitalsound recording at an affordableand pocketable price, aren'tguarantees of commercial success.74 minutes of audio on one disc isonly just adequate, though it doesbeat Philips' Digital CompactCassette which looks like onlyoffering 45 or 60 minutes per side.DCC will be out first and becheaper. I will almost certainly get aDCC deck anyway as I have asizeable collection of conventionalcassettes with which DCC remainscompatible and the old Aiwa deck Ihave is getting on a bit.

With DCC practically assured ofcommercial success, I still hopeSony makes it with the MDstandard, and I want one!

Although I've broken the rulesslightly with the last two selections,neither of which will be available byChristmas, here's a slightly moreoutrageous Christmas present ideawhich is scheduled for Christmasstockings in the US at least;Samsung's Scout -About domesticrobot. Launched at the big ChicagoConsumer Electronics Show back inthe Summer, this dinky dome -shaped intruder and fire detectorwill patrol your house withoutfalling down stairs (it can't climbthem either, alas) or bumping intothe furniture. If it needs to sound analarm it will even phone the police.Above all, it would be the idealgadget to stay that one step aheadof the Jones's! A snip at just $1,000(£590), even if it can't make the tea,just yet.


Power Feature

Harnessing The PowerThat Drives The StarsThe JET fusion experiment operates at temperatures in excess of 300 Million °C. Is this thepower source of the future? Kenn Garroch investigates

Three minutes to go and 40mini -computers check andsynchronise the diagnostics

and control equipment. Signalstravel around the 19 fibre -opticloops at a rate of 25 Mega -bits persecond confirming that everythingis ready. A few seconds before zerothe toroidal magnetic field is turnedon and a small quantity ofDeutrium gas is let into theevacuated torus. As the countdownreaches zero, the current isswitched on rising swiftly to 1million Amps, ionising the gas andturning it into a plasma. MoreDeutrium gas is added followed,five seconds later, by a pellet of thesame material in solid form. Thetemperature of the plasma is nowaround 30 million degreesCentigrade. An additional 11MW ofheating increases this to over100M°C. A small sun will exist forjust two seconds in the heart ofEngland.

This process takes place every

twenty minutes between 6am and10pm six days a week at JET, theEuropean fusion research projectbased near Oxford. The JointEuropean Torus is the biggestexperiment of its kind anywhere inthe world. It aims to study thevarious methods of plasma heating,containment and density controlwith a view to using thermonuclearfusion as a practical form of energyproduction sometime in the nextcentury.

Fission And FusionThere are two main types of nuclearreaction that produce energy,fission and fusion. The first formsthe core of today's nuclear powerindustry and works by bombardinglarge atoms with neutrons causingthem to split up producing moreneutrons which split more atoms,thus forming a chain reaction. Thisprocess also produces a lot ofenergy which can be used to heat

steam and spin turbines to generateelectricity. A couple of undesirableaspects of the process are theconsiderable amounts of radiationproduced and the cost anddifficulty in handling the Uraniumor Plutonium fuel.

Nuclear fusion is an alternativereaction that also produces heat butuses abundant fuels and createsrelatively little long livedradioactive waste. Instead of usingheavy atoms, fusion smashestogether special forms of hydrogen,Deutrium (D) and Tritium (T). Thisreaction forms Helium (He) ionsand energetic neutrons. In a reactor,the neutrons are slowed down inthe surrounding "blanket" toprovide the heat source forelectricity production. By includingLithium in the blanket, Tritium willbe produced to refuel the reactor.Unfortunately, getting the reactionto take place requires a hugeamount of energy and theDeutrium and Tritium fuel must beheated to over 100 Million °C; in sodoing, the gas is turned into aplasma - the fourth state of matter,the other three being solid, liquidand gas. In a plasma, the encirclingelectrons of the atoms are soenergetic that they are forced out oftheir orbits to roam free.

The ParticipantsThe JET Joint Undertaking is thelargest project of the EuropeanAtomic Energy Community(EURATOM). Although it is basedin the UK, the technology,manpower, administration andscience are supplied by the 12members of the EC plusSwitzerland and Sweden. Createdin 1978 to run for 12 years, JET's


Power Feature

objectives were to construct andoperate a large Tokamak fusionexperiment in order to explorecontrolled thermonuclear fusion tothe stage where it could be used ina thermonuclear reactor. Threemain aspects of this experiment canbe expressed as the triple productof central plasma temperature (T),central plasma density (n) andenergy confinement time (t).Typical values of these required fora commercial reactor are:

T=10 to 20keV 100 to 200 M °Cn=2.5x102om-3t=1 to 2 secs

When JET was being designed inthe early 1970s, the best value of thetriple product ever achieved wasabout 20,000 times away from thissort of performance; in 1990/1JET isonly about six times away with atriple product of between 7 and 9 -the requirement being from 50 to100 (in the required units).

Some Like It HotTo bring the Deuterium gas up tooperating temperature a number ofmethods are used. The first appliesthe electrical transformer effect toinduce a large current into theplasma in the torus. The operationof a Tokamak (originally pioneeredin the USSR) is based upon adoughnut shaped containmentvessel in which the plasma formsthe single -turn secondary of atransformer. In JET there is a stackof eight primary coils with theability to induce up to 7.1 MillionAmps into the system. This ohmicheating heats the gas up to around50M°C at which point its centralresistance is so low that furthercurrent increase has little effect.

Because the induced currenttends to concentrate at the centrewhere the plasma is hottest, moreenergy can be put into the reactionby forcing the hot area to broaden.The Lower Hybrid Current Drivecouples 3MW of 3.7GHz microwavepower to the system and althoughstill experimental, it is hoped thatthis will shortly input an extra10MW of power giving a longerpulse length and increased stability.

The next heating method is toinject high velocity particles. Abeam of charged He or D atoms isaccelerated through 140,000V andthen neutralised. Because of themagnetic confinement of the

plasma within the vacuum vessel,charged atoms would not be able topenetrate the field. Removing thecharges allows them to enter thereaction, collide with the plasmaatoms and increase the overalltemperature. Two such systems areused in JET to give a total 20MW ofpower.

Another major energycontribution to the reaction isderived from radio frequencyheating. Because the ions andelectrons that make up the plasmaspiral around the magnetic fieldlines of the Tokamak at a set rate,radio waves beamed into the torusat the same frequency add to theoverall energy - up to 22MW ofheating is supplied by antennae onthe inner walls of the reactionvessel at a frequency of 25-55MHz.

Any He nuclei created by thefusion of D and T are charged andremain in the reaction. Theycontinue to heat the plasma andwhen there are enough of thesebeing created to maintain theplasma temperature, the ignitionpoint is reached and the plasmabecomes self heating.

Having reached the hightemperature required, the densityof the plasma is increased byinjecting pellets of Deuterium ice atspeeds of 1.2 to 1.5km/s. This caninstantaneously double the particledensity of the plasma bringing thesystem nearer to the ideal tripleproduct.

Holding Back The HeatHaving heated the plasma up to its

Atoms

Hydrogen Deutrium Tritium

Atoms of hydrogen are made up from one proton with one electron in orbitaround it. Adding a neutron to the central proton makes this atom into Deutriumwhich makes up about .002% of all water - which may not sound like a lot but theworld contains an awful lot of water. Adding another neutron makes Tritium. Thisdoesn't occur naturally in nature but is made in a fusion reaction. The reaction of1 Og of Deutrium, which can be extracted from 5001itres of water, with 30g ofLithium produces 15g of Tritium and enough power to last the average person alifetime.


Power Feature

D

The Deuterium, Tritium reaction produces Helium, a neutron and lots of energy.

+ T 4He + n(3.5 MeV) (14.1 MeV)

operating temperature, any energylosses must be minimised. Theconfinement time needs to bearound 1 to 2 sec and to achievethis, the plasma inside theevacuated torus is held away fromthe walls by magnetic fields. A setof coils around the minorcircumference produces a toroidalmagnetic field around the majoraxis of the machine. The currentflow through the plasma inducedby the transformer produces apoloidal field. These two interact toproduce a helical or spiral fieldwhich loops around the torus andprevents the plasma from rapidlyreaching the walls. An additional

set of coils is used to position theplasma within the reaction vessel.The resulting plasma shape is adoughnut with a D shaped cross-section.

The vacuum vessel is made upfrom eight D shaped identicalmodular pieces with built-in portsthrough which the reaction can beobserved and neutral beamsinjected. The advantage of themodularity means that if an octantfails, it can be replaced relativelyeasily.

Without all of these elaboraterestraining systems, the Plasmawould soon loose its heat and thefusion reaction would stop - an

aspect of fusion power that makes ita lot safer the fission.

Supplying JETTo get its reaction up and running,JET requires a great deal of power.One of the reasons for its location inOxfordshire, apart from beingadjacent to the Culham fusion labs,is its proximity to the Didcot powerstation. For each experimentalfusion pulse, around 700MW ofpower is needed. Only 550MW canbe drawn from the national grid,the rest comes from the on -sitestorage. This consists of two 9m 775tonne flywheels, each driven by an8.8MW motor. Between pulses theseare run up to between 225 and250rpm and on demand deliver400MW of pulsed power into theprimary of the transformer forohmic heating and the 32 magneticcoils of the containment system.The power supply of JET is a majorelectrical engineering achievementthat ranks alongside the rest of theexperimental fusion system interms of new technology.

Outside Looking InThe main objective of JET is toexperiment with different methodsof heating, power supply, fuelinjection, indeed, anything that canbe used to make future fusionreactors operate efficiently. Becauseof this, all of the reactions areobserved in the minutest detail. Thediagnostics use a number of


Power Feature

methods to examine the variousplasma parameters - from lasers toX-rays. All observations arecoordinated through thecomputerised control and dataacquisition system (CODAS) whichuses a network of 40mini-computers to handle the 27Mbytesof data produced from eachexperimental pulse. After beingcaptured directly from theTokamak, the data is transferred tothe main computers and then sentoff to a large IBM mainframe forfurther analysis. If JET gets the go-ahead to extend the research until1996 CODAS will be upgradedfrom its 1970's computertechnology to the latestworkstations, significantlyincreasing the analysis capabilities.

The Future Of JETOriginally envisioned as a 12 yearproject, JET, started in 1978, is nowreaching the end of its first two-yearextension. Another four years areunder consideration so that theeffects of impurities in a gas plasmacan be further studied.

Achievements to date include arecord plasma current of 7.1MA; theclosest to the required tripleproduct of any fusion experimentso far; the creation, in separateexperiments, of the required plasmatemperature, density andconfinement for a commercialreactor - JET is too small to achievethem all at the same time.

Following on from JET in theEURATOM program is the NextEuropean Torus (NET) orparticipation in a worl-wide projectITER (International ThermonuclearExperimental Reactor) incollaboration with the US, Japanand the Soviet Union. This will beused to establish the feasibility ofcommercial fusion power. It will beabout twice the size of JET with amagnetic field about 40% greater,be able to sustain a pulse for up toone hour and generate 1000MW offusion power. If all goes to plan,construction could start as soon as1997. By the beginning of 2030fusion power could be a realityproviding the world with cheap,clean and abundant electricalpower.

Magnetic FieldsTwo main magnetic fields are used in a Tokamak to hold the plasma in position.The toroidal field is generated by a ring of coils that encircle the torus generating aring -shaped field. The current induced in the plasma generates a poloidalmagnetic field that circles the tube of plasma. The combination of the toriodal andpoloidal fields make the characteristic magnetic field configuration of the Tokamakin which charged particles spiral around the field lines. Particles, therefore, onlyreach the walls by a relatively slow diffusion process.

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Side view showing the transformer and the D shaped plasma.

Toroidalmagnetic field

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Show Report

A Visit To The

Funkaulitellung FairThis month Ian Burley reports from Berlin and has a look at the latest Psion Organiser, asingle chip PC and a pair of domestically grown video telephones

The US holds two majorconsumer electronics fairs,admittedly trade -only, a year.

Europe's biggest fair, theInternationale FunkausstellungBerlin, is held once every two yearsand is open to both the trade andgeneral public. Comparing theEuropean event with its UScounterparts proved interesting andunderlined some fairly basicdifferences in taste and technologyemphasis.

Above all, the show was astrong showcase for Europeanfirms, many of whom wereshowing advanced technology notyet on sale, like HDTV (HD -MAC)for example. At the CES events inthe US, there has been muchconfident talk of US HDTVstandards but only the Japanesehave actually exhibited workingequipment there. In Berlin, wide-screen TV and HDTV and waseverywhere - even if there isn't yetfull agreement on which standardsto go for.

The show was an excellentopportunity for the public to seetomorrow's technology, like HDTV,first hand. Philips, Nokia,Thomson, Grundig and others allshowed HDTV sets working. Aspecial theatre was set up for video -projected HDTV demonstrationsand there was even an HDTVstudio built into the rather crampedexhibition complex.

There were two other kinds ofadvanced television on display aswell; standard 625 -line wide-screenD -MAC satellite broadcasting andPAL Plus, the proposedenhancement to terrestrialbroadcasting which will provideenhanced definition wide-screenbroadcasts on existing transmitter

equipment, but at the same timeremain compatible with theordinary broadcasts we enjoytoday.

D -MAC wide-screenbroadcasting is already availablefrom certain European satellites. Inthe UK, the demise of BSB has setback the introduction of wide-screen TV. HD -Mac high definitionwide screen satelite broadcastingcould start commercial service assoon as next year, though withsuitable TV sets still costing in theregion of £5000, widespreadadoption - EC policy or no policy -is some way off yet. PAL Plus isscheduled for as late as 1995. This isbecause the extremely complexpicture processing technologyrequired is still in an early stage ofdevelopment.

So what of audio and videoenhancements we can enjoy andafford in the shorter term?Attracting considerable attentionwas an interesting gimmick fromthe Finnish electronics giant, Nokia,

in the form of an AV remote controlwhich incorporates tilt switches.Nokia's so-called mouse -remote,which is now available in the UK, isdesigned for convenient one -handed operation; potentially acouch -potato's dream. Combinedwith on -screen indicators, the ideais that you select a function, volumefor example, by pressing one buttonand then make adjustments to thesetting by tilting the remotewithout releasing the button. Thefour-way tilt switch can facilitatesetting adjustments and menuselections on, for example, theenhanced teletext system, Top Text.I have to admit, I found the thingtricky to use, but that's a criticismof most remote controls. It was funthough.

Toshiba showed some enhancedcolour TVs which avoid moireinterference sometimes evident onfine patterns being displayed.100Hz refresh flicker -free TVs werealso evident.

Attracting rather more attention

1-9

NOKIA

The mouse remote.


Show Report

on the Toshiba stand were a pair ofprototype 10in portable colour LCDTVs, similar to ones shown at thelast two CES shows in the States,except these were European PALcompatible. Surely only price isholding back the introduction ofthese superb units.

Philips had a large presence atthe show. Its stand occupied mostof one hall and featured a verysurreal mix of present day productsand the products design students'futuristic imaginations. CD -Imultimedia was on show, as was abank of wide screen televisions.Sadly, DCC (digital compactcassette) was hidden away frompublic gaze, as was a novelapplication of the PostScript pagedescription language for teletextTVs. PostScript is used in the worldof computing for printing text andgraphics - like the pages of thismagazine for example. Philips isnow experimenting with the use ofPostScript for displaying highresolution information on a TVscreen, transmitting the data viateletext.

Over at Bosch/Blaupunkt thelatest RDS (Radio Data Service) carstereos were being put throughtheir paces. To be launched earlynext year, the latest iteration of RDSis called EON (Extended OtherNetwork) and introduces thefacility which allows the radio toswitch automatically to another

station when a traffic or newsreport is imminent. As one wag putit, it's ideal for classical musiclisteners who are apparentlydeprived of links with reality.

Pioneer had a recordable CDdeck, but this proved to be no threatto Sony's new Mini Disc recordableaudio -disc syste. Instead thePioneer deck is a write once(WORM) CD production deckdesigned for small volumemastering. Pioneer also revealed itis to introduce a similar deck forlaser video disc production soon.

On the camcorder front, theshow was a convenient place forSony to debut the world's first hi -band palmcorder, the Hi8 TR705.Capable of video recording qualitybordering on professionalstandards, the TR705 is no largerthan the already tiny TR75 standardresolution palmcorder it looks likereplacing. The TR705 will beintroduced at under £1,000 in theUK by the end of the year.

Canon introduced its new UC10and UC20 Video -8 palmcorders atthe show as well and demonstratedthat it was capable of coming upwith good designs which didn'tinvolve copying Sony. Replacingthe old (18 months!) novel, buthardly compact Canon A9 and A10camcorder models, the newversions are cleverly designed toacheive a very slim profile. Thestandard infra -red remote controller

even clips onto the top of eachcamera.

Finally, a few things spottedaround the exhibition; you've seendancing coke cans, now readyyourself for wobbling coke bottles.Take my word for it, they'rehilarious. Casio showed a Mercedestaxi with one of its LCD colour TVsinstalled for the benefit of thepassengers. AEG Telefunkenappeared to be stressing the abilityof its video recorders to be used atany angle, including upside down -a conveyor belt of the dozens of thethings was continuously rotating allday on their stand. Finally back toToshiba who had their solid statecamera on display. This uses highcapacity memory chip cards insteadof film or magnetic media. It islimited to comparatively lo-resdesktop publishing applications atpresent but the technology isgetting better all the time.

Overall, one comes away fromevents like these muttering thingslike, I wish we had shows like thesein the UK...

Videophones EverywhereTwo established UK companieshave announced plans to introducevideo phones some time next year.One of those firms, BT (previouslyknown as British Telecom), nosurprise. The second, Amstrad, iswell used to springing surprisesand this is no exception, though anAmstrad PR representative halfadmitted that the BT announcementforced a premature revelation of theAmstrad project in conjunction withGEC Marconi.

About the only thing the twoprojects have in common is thatthey're videophones. The BT oneuses ISDN (integrated servicesdigital network) lines and a 64K bitsper second image data transfer rateto feed its slow -scan black andwhite picture. Amstrad predictablyhas settled for conventional highspeed modem technology for ananalogue phone link and a colourLCD screen has been chosen. TheAmstrad incorporates chips capableof a 14.4K bits per second data rate,though undoubtedly datacompression techniques will beused to increase the throughput. It'squite likely Amstrad will enable itsvideo phone to be used as a modemlinked to a personal computer.

Although BT and then Amstrad


Show Report

announced they are developingvideophones, not much detail wasforthcoming. Both products aresome time from going on sale butestimates on price put them atopposite ends of the spectrum. TheBT phone is expected to cost wellover £1,000 and of course you willneed the special ISDN phone line -at both ends of the video -link ofcourse. Amstrad hinted that thetarget for its videophone wascomfortably under £1000 and, ofcourse, it could theoretically beused anywhere there's aconventional phone line. Whatwasn't quite clear was who exactlywould want to buy one of thesegadgets.

A PC on a chipThe US PC chip manufacturer,Chips & Technologies, hasannounced the latest developmentin its determined effort to integratePC -compatible chip technology.Last year the firm produced an IBMPC/XT (Intel 8088 -compatible)processor board not much largerthan a credit card. Now C&T hassqueezed the technology furtherand stuffed it all onto a single chip,the F8680 PC/CHIP. It contains an

Could there be a show like this in the UK?

8086-compatibe CPU, an 8529 -compatible interrupt controller,8524 -compatible timer, memorycontroller, DMA emulator, CGAgraphics controller and a keyboardcontroller and a 6540 -compatibleUART for serial communications.All you need to add for a fullyworking PC is some memory, akeyboard and a display. The chip isa low power static device and ideal

for pocket PC applications. Theannouncement coincided withIBM's celebration of the PC's tenthanniversary. It's easy to be blaseabout ICs these days, but if you'veever peeked inside an early IBM PCand counted the staggering numberof chips which as required then,Chips & Technologies achievementcomes sharply into perspective.Next in line will be versions of the


Show Report

Is this the last we will see of Zonephones?

single chip PC incorporating morepowerful versions of the Intel 80xxprocessor series.

The Psion Series -3Another device which tends toremind me how old I am is thePsion Organiser. The short-livedMkI version was launched 8 yearsago. The Psion Organiser IIlaunched in 1985 looked outwardlythe same, but improvements to itsprogramming language, built inapplications and non-volatilememory cartridges and accessoriesmade the units far more useful.Over a million have been sold since.

Now, with the new Series -3Organiser, Psion has reacted to therising success of its Japanesecompetitors mainly in the form ofSharp, with its IQ range (known asthe Wizard in the States) and theCasio BOSS. The rise of pocket -PCcompatibles like the DIP/Atari

Portfolio and Hewlett-Packard'sHP95LX also needed to becountered.

Obvious differences between theold Organiser II and the new Series -3 include the latter's moreconventional 'clam -shell'configuration, opening up to reveala larger 240x80 pixel LCD screenand a conventional QWERTYlayout keyboard. The keys are easyenough to use but there's noclaiming this is a touch-typer'sparadise. A row of eight touch -sensitive icon -labelled function keysalong the top summon up theSeries -3's impressive line up of builtin applications which are stored in384K of internal ROM.

The applications include apersonal free -format database, timeand personal manager, wordprocessor, world information baseand an interesting calculator whichstoes the last ten calculations on ascrollable 'till -roll' for convenient

checking.The Series -3 borrows much of

the technology originally developedfor the much admired butcommercially unsuccessful PsionMC (Mobile Computer) laptoprange. The same tiny flash -EPROMor battery -backed RAM memorycartridges are used and they are filecompatible too. The sameproprietary programming languagecommon to all Psion's products,OPL, is used, as is a derivative ofthe MC200/400 multi -taskingoperating system. Also shared is thedisplay technology in the form ofthe very sharp retardation filmpassive matrix LCD which doesn'trequire a back -light. Just two AAbatteries are required to power theSeries -3 for 2-4 months typically.

Communication with the outsideworld is via a compact but very fast(1.54Mbits/second) proprietaryserial interface to which things likeconventional serial or paralleladapters or perhaps bar-codereaders can be attached. Softwarefor file exchange with PC -compatibles or Apple Macs isavailable. The built in piezo speakeralso acts as a DTMF tone dialer.

At £199 including VAT for the128K RAM version (up to 4Mb canbe fitted to the two cartridge slots),Psion's Series -3 is good value andan altogether more serious a beastthan the Sharp IQs and Casio BOSSsof the world.

The End Of TelepointHere's a topic not discussed in PEfor a while; Telepoint. The lasttelepoint digital public cordlessphone service operator, the BT -ledPhonepoint consortium, hadsuspended service and is offeringits customers refunds. ConsideringPhonepoint admitted it only had800 customers - each with just overfour public base stations at theirdisposal - you couldn't argue withtheir reason for pulling the plug.The eternal optimist in me notesthat the service has only beensuspended and the HutchisonGroup, which now operates thestill -to be launched Rabbit telepointservice, says it is determined topress ahead even though everybodyelse (Zonephone, Callpoint andPhonepoint) appear to have givenup the ghost.


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10 BAND COMMUNICATIONS RECEIVER.7 shortbands, FM, AM and LW DX/local switch, tuning 'eye' mains Enor battery Complete with shoulder strap and mans leadNOW ONLY £19.0011 REF 19P147.

WHISPER 2000 LISTENING AID.Enables you to hear soundsthat would otherwise be inaudible! Complete with headphones.Cased £5.00 ref 5P179TCAR STEREO AND FM RADIOLow cost stereo system givingS watts per channel. Signal to nose ratio better than 45db, wow andflutter less than 35% Neg earth. E.25.00 ref 25P21TLOW COST WALIKIE TALKIESPae of battery oper-ated units with a range of about 150' Our pnce £8.00 a _1 I

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Brand new units consisting of a camera, 14cm monitor, 70 metres ofcable, AC adapter, mounting bracket and owners manual 240v ACor 12v DC operation complete with built in 2 way intercom £99.00 ref99P2T1991 CATALOGUE AVAILABLE NOW IF YOU DO NOTHAVE A COPY PLEASE REQUEST ONE WHEN ORDERINGOR SEND US A 6"X9" SAE FOR A FREE COPY.GEIGER COUNTER KIT.Complete with tube, PCB and all compo-nents to build a battery operated gager ccunter. £39.00 rat 39P1TFM BUG KIT.New design with PCB embedded coil. Transmits toany FM radio 9v battery req'd £5.00 ref 5P1587FM BUG Built and tested superior 9v operation £14 00 ref 14P3TCOMPOSITE VIDEO KITS.These convert composite video intoseparate H sync, V sync and video. 12v DC. £8.00 ref 8P39TSINCLAIR C5 MOTORS 12v 29A (full load) 3300 rpm 6"x4" 1/4"

OP shaft New £20 00 ref 20P22TAs above but with fitted 4 to 1 mine reduction box (800rpm) andtoothed nylon belt drive cog £40.00 ref 40P8TSINCLAIR C5 WHEELS13" or 16" die including treaded tyre andinner tube. Wheels are black, spoked one piece poly carbonate. 13"wheel £6 00 ref 6P20, 16" wheel £6 00 ref 6P21TELECTRONIC SPEED CONTROL KIT1or c5 motor PCB and allcomponents to build a speed controller (0-95% ofspeed) Uses pulse width modulation £17.00 ref 17P3TSOLAR POWERED NICAD CHARGER.Charges 4AA nicads in 8 hours. Brand new and cased £6.00 ref6P3TMOSFETS FOR POWER AMPLIFIERS ETC.100 watt mostetpar 2SJ99 and 2SK343 £400 a pair with pin out info ref 4P51T Alsoavailable is a 2SK413 and a 2SJ118 at £400 ref 4P42T12 VOLT BRUSHLESS FAN4 1/2" square brand new ideal forboat, car, caravan etc £5 00 ref 5P206TACORN DATA RECORDER ALF503 Made for BBC computerbut suitable for others Includes mains adapter, leads and book£1500 ref 15P43TVIDEO TAPES. Three hour superior quality tapes made underlicence from the famous JVC company. Pack of 10 tapes £20.00 ref20P20TPHILIPS LASER. 2MW HELIUM NEON LASER TUBE.BRAND NEW FULL SPEC £40.00 REF 40P107. MAINSPOWER SUPPLY KIT £20.00 REF 20P337 READY BUILTAND TESTED LASER IN ONE CASE £75.00 REF 75P4T.SOLDER 22SWG resin cored solder on a 1/2kg reel Top quality£4 00 a reel ref 4P70T600 WATT HEATERS Ideal for air or liquid, will not corrode, lastsfor years coil type construction 3"x2" mounted on a 4" dia metal platefor easy fixing £3.00 ea ref 3P78T or 4 for moo ref 10P767.TIME AND TEMPERATURE MODULE A clock, digital ther-mometer (Celous and Farenheit (0-160 deg F) programmable toohot and too cold alarms. Runs for at least a year on one AA battery.E9.00 ref 9P5TRemote temperature probe for above unit £3.00 ref 3P60TGEARBOX KITS. Ideal for models etc. Contains 18 gears (2 ofeach size) 4 x5Omm axles and a powerful 9-t2v motor. All the gearsetc are push fit £3 00 for complete kit ref 3P937ELECTRONIC TICKET MACHINES These units contan amagnetic card reader, two matrix printers, motors, sensors andloads of electronic components etc (12"x12"x7") Good value atC12 00 ref 12P28T.JOYSTICKS Brand new with 2 fire buttons and suction feet theseunits can be modified for most computers by changing the connectoretc Pnce is 2 for £5 00 ref 5P174TGAS POWERED SOLDERING IRON AND BLOW TORCHTop quality tool with interchangeable heads and metal body. Fullyadjustable, runs on lighter gas.£10 00 ref 10P130T

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Ideal bedside light etc£4 00 each ref 4P82TELECTRONIC DIPSTICK KIT.Contains all you need to build anelectronic device to give a 10 level liquid indicator £5 00 (ex case)ref 5P1947UNIVERSAL BATTERY CHARGER.Takes AA's, C's, D's andPP3 nicads Holds up to 5 batteries at once. New and cased, mansoperated £6.00 ref 6P367ONE THOUSAND CABLE TIESI75mm x 2.4mm white nyloncable ties only £5.00 ref 5P1817PC MODEMS1200/75 baud modems designed to plug into aPC complete with manual but no software £18.00 ref 18P 12TASTEC SWITCHED MODE POWER SUPPLY8Omm x 165mm(PCB size) gives +5 at 3 75A, +12 at 1.6A, -12 at 0 4A Brand new£12.00 ref 12P397VENTILATED CASE FOR ABOVE PSUmth IEC filtered socketand power switch. £5.00 ref 5P190TIN CAR POWER SUPPLY. Plugs into cigar socket and gives3,4,5,6,7.5,9, and 12v outputs at 800mA. Complete with universalspider plug £5.00 ref 5P1677.CUSTOMER RETURNEDsvatched mode power supplies. Mixedtype, good for spares or repair £2.00 each ref 2P2927.DRILL OPERATED PUMP.Fits any drill and is self priming £300ref 3P140TPERSONAL ATTACK ALARM.Complete with built in torch andvanity mirror Pocket sized, req's 3 AA batteries £300 ref 3P1357POWERFUL SOLAR CELL 1AMP .45 VOLTbnly £500 ref5P192T (other sizes avahable in catalogue)SOLAR PROJECT KIT.Consists of a solar cell, special DC motor,plastic fan and turntables etc plus a 20 page book on solar energy!Price is £8 00 ref 8P51 TRESISTOR PACK.10 x 50 values (500 resistors) all 1/4 watt 2%metal film £5.00 ref 5P1707CAPACITOR PACK 1.100 assorted non electrolytic capacitors22 00 ref 2P286TCAPACITOR PACK 2. 40 assorted electrolytic capacitors £2 00ref 2P287TQUICK CUPPA? 12v immersion heater with lead and cigar lighterplug £3.00 ref 3P927LED PACK .50 red lads, 50 green leds and 50 yellow lads all 5mmE8.00 ref 8P527FERRARI TESTAROSSA. A true 2 channel radio controlled carwith forward, reverse, 2 gears plus turbo. Working headlights.£22.00 ref 22P6TULTRASONIC WIRELESS ALARM SYSTEMTwo units, onea sensor which plugs into a 13A socket in the area you wish toprated The other, a central alarm unit plugs into any other socketelsewere in the building When the sensor is triggered (by bodymovement etc) the alarm sounds Adjustable sensitivity Pnce perpair £20.00 ref 20P347. Additional sensors (max 5 per alarm unit)E1 1 00 ref 11P6TWASHING MACHINE PUMP.Mains operated new pump Not selfpriming £500 ref 5P187IBM PRINTER LEAD. (D25 to centronics plug) 2 metre parallel£500 ref 5P186TCOPPER CLAD STRIP BOARD17" x 4" of .1" pitch "vero" board£4 00 a sheet ref 4P627 or 2 sheets for £7 00 ref 7P227STRIP BOARD CUTTING TOOL£2 00 ref 2P352T3 1,2' disc dnve 720K capacity made by NEC £60.00 ref 60P2TTV LOUDSPEAKERS.S watt magnetically screened 4 ohm 55 a125mm. £3.00 a pair ref 3P109T.SPEAKER GRILLS set of 3 matching grills of different diameters2 packs for £2.00 (6 grills) ref 2P364T50 METRES OF MAINS CABLE £3.00 2 core black precut inconvenient 2 m lengths Ideal for repairs and protects ref 3P91T4 CORE SCREENED AUDIO CABLE 24 METRES £2.00Precut into convenient 1.2 m lengths Ref 2P3657TWEETERS 2 1/4" DIA 8 ohm mounted on a smart metal plate foreasy fixing £2.00 ref 2P3667COMPUTER MICE Ongmally made for Future PC's but can beadapted for other machines. Swiss made £8.00 ref 8P57T. Atari STconversion kit E2.00 ref 2P36276 1/2" 20 WATT SPEAKER Built in tweeter 4 ohm £5.00 ref5P205T5" X 3" 16 OHM SPEAKER 3 for £1.00!1 ref CD213TADJUSTABLE SPEAKER BRACKETS Ideal for mountingspeakers on internal or external corners, uneven surfaces etc 2 for£5 00 ref 5P207TPIR LIGHT SWITCH Replaces a standard light switch in secondslight operates when anybody comes within detection range (4m) andstays on for an adjustable tune (15 secs to 15 irons) Complete withdaylight sensor. Unit also functions as a dimmer switch! 200 wattmax. Not suitable for flourescents £14.00 ref 14P1OT2 MEG DISC DRIVES 3 1,7 disc drives made by Sony housed ina 5 1/4" frame 1 2 meg formatted £66.00 ref 66P1TCUSTOMER RETURNED 2 channel full function radio controlledcars only £8.00 ref 8P200TWINDUP SOLAR POWERED RADIO! FM/AM radio takes NICADbatteries complete with hand charger and solar panel 14P200T240 WATT RMS AMP KIT Stereo 30-0-30 psu required £40.00 ref40P200T300 WATT RMS MONO AMP KIT £55.00 Psu required ref 55P200TALARM PIR SENSORS Standard 12v alarm type sensor will inter-face to most alarm panels £16.00 ref 16P200TALARM PANELS 2 zone cased keypad entry, entry exit time delayetc. £18.00 ref 18P200T35MM CAMERAS Customer returned units with built in flash and28mm lens 2 for £8.00 ref 8P200TSTEAM ENGINE Standard Mamod 1332

SOME OF OUR PRODUCTS MAY BE UNLICENSABLE IN THE Ucngine0cozDletewith boiler pston etc £30


Old Technology

Electronics Goes UnderThe HammerOld experimental apparatus has now has great rarity value as Stephen Waddington foundout when he visited a recent Christies Sale.

Arecent sale at Christiesprovided a rare glimpse atsome of the apparatus,

machinery and instruments used bythe early electrical pioneers. TheNicholas Webster collection,auctioned in London recently,consisted of several hunderedpieces of scientific equipement,discharge tubes, philosophicalbooks and early electricalcomponents - including the mostcomplete collection of Geissler andCrookes discharge tubes ever seen.

Nicholas Webster was born inBirmingham and becamepreoccupied with science duringhis years at Bishop Vessey'sGrammar School in SuttonColdfield. Later employment withvarious electrical and scientificcompanies fuelled his interest inscientific and philosophicalinstruments and their use ineducation and research. Now 34, heoperates his own manufacturingcompany concentrating on thedesign and production of powersupplies.

Talking To The ExpertsChristies sale rooms is supportedby an impressive circle of dedicatedspecialists. Having decided that hiscollection was becoming a liabilityNicholas Webster sought theguidence from an authority onscientific instruments and Christiesspecialist, Jeremy Collins. Afterscrutinising, photographing andclassifying each iterm acomprehensive catalogue wasproduced and the whole collectionwas put under the hammer.

It was in the 16th century thatscientists first began to observeelectrical phenomena in a

Wimshurst pattern generator.

systematic andway - the production andstorage of static electricityprovided great interest.Early generating machinesconsisted of a glass barrelconnected to a handle andfriction pad severalexamples of which were inthe sale, the finest beingmounted on a finemahogany plinth. A brassconductor comb ensuredthat electricity could bedrawn when the handlewas turned. Electricitystorage took the form of aLeyden Jar - a primitivecapacitor.

More powerfulgenerators such as theWimshurst machineincorporating two contra -rotating glass plates withmounted brass fittings,

scientific

4/10*Crookes' Phosphorescent boquet tube.


Old Technology

Electrostatic friction barrel machine.

metallised brushes and Leydenstorage jars were also on show. Ofthe four examples in the sale, thehighest bid was realised by amachine with six rotating glassplates, copper brushes and brassconducting combs capable, it isesitamated, of generating a chargeof half a million volts.

Primitive Papendorff jarbatteries, graduated in pints,illustrated the operation of the firstchemical batteries. A myriad of

electrical meters showed thedevelopement of such instrumentsover the years. Encased inmahogany, two fine examplesincluded a voltmeter complete withmatching ammeter. Clearlyattention to detail was of majorimportance to the 19th centuryscientist.

The Early PioneersMention has alkready been made ofthe fact that the sale containedmany pieces of work from bothHeinrich Geissler (1832 - 1919) anWilliam Crookes (1814 - 1879).Geissler is a well known figure inthe history of scientific instrumentssince many of his creations remainin active service to this day.Influenced by his father, aninnovative glass blower, Geissler'scareer in instrument design gainedan international reputationproviding a service to chemists,medical doctors, physiologists andminerologists.

Crookes enjoys slightly lesspopularity despite the fact that hiswork led to the discovery of X-raysand later, the electron. Knighted in1897 and bestowed with the Orderoof the Mint in 1910 he studiedscience under Faraday, Wheatstoneand Stokes. An active physicist, heproduced a vacuum of onemillionth of an atmosphere andinvestigated the action of cathoderays within a glass tube vacuum.

He was responsible for much workwhich led to the development of thecathode ray tube used in modernday in televisions. He producedspecial tubes to examine cathoderays in various configurations andgas pressures and was one of thefirst to investigate the effect ofmagnetic fields on cathode rays.Exactly how Crookes manufacturedthe intricate tubes to such a highspecification is now a mystery andsurviving examples are extremelyrare.

Ranging in price from severalhundred to several thousands ofpounds, the tubes offered in the salevaried from the very practicalmaltese cross tube to the moreelegant phosphorescent tubescontaining intricate glass models -each carefully engineered todemonstrate a fundamentalphysical characteristic. To theindifferent observer, many of thetubes might be viewed as a piece ofart rather than an item of electricalscience. One pristine exampleconsisted of a flower painted with avariety of different mineral dusts,each of which flouresed differentlywhen bombarded with electrons,providing a beutiful shimmeringeffect.

The Nicholas Webster collectionrepresented a piece of history whichhas been sadly neglected. Itdepicted the intermediate stagebetween the discovery of electricityand its emerganece as an essentialpart of the twentieth century.


How It Works

How It Works...The Mains IntercomIt is often stated that the wood cannot be seen for the trees, in the case of the mainsintercom, it could be said that the link cannot be seen for the wiring. Jim Haskins explains.

All modern houses haveelectrical wiring used toprovide power to lighting,

heating, general mains appliancessuch as the washing machine andso on. Even though this may be ona number of "ring -mains", all ofthese are connected together at themains fusebox whefe the electricitysupply enters the house. Mainsintercom circuits take advantage ofthis to allow information, usually inthe form of speech, to betransmitted from place to placewithin a building. Most peoplewould probably manage this formof communication by shouting -this was certainly the way I wasbrought up. However, there areapplications such as baby alarms orwhere the building is very large orwhen there is a need to controlmains appliances at a distance,where the built in electricalconnection system of a house is anideal information conduit. Indeed, anumber of the latest home controlsystems use the technique to greateffect and there are now a numberof dedicated chips available thatmake the design and constructionof such a circuit much easier.

The example device shown overthe page is one of the originalsystems as can be seen from itsantique transistors and switches.

High VoltageThe most obvious drawback withusing the mains wiring fortransmitting information is that it isalready being used by a 240V 50Hzsignal. Mixing this directly withsound picked up from amicrophone which is usually atonly a few milli -volts, may seemlike a hopeless task. However, it is

easier than it may seem. The firststep is to isolate the unit completelyfrom the mains circuit using atransformer. Information can bepassed either way through thisdevice without having to dealdirectly with the mains itself. Theother advantage of this is that themains voltage can be stepped downto a level that is easy to managewith simple transistor circuitry, saybetween 3V and 15V.

ModulationThere are a number of ways inwhich information can be placedupon a wire. Probably the simplestis to modulate a high frequencycarrier, say around 200kHz, withthe speech signal. This removes anyproblems with 50Hz interferenceand works in much the same wayas radio communications. Ademodulator at the receiving unitrecovers the signal and amplifies itfor reproduction on the intercom -another advantage of this method isthat it allows a number of intercomsto operate on the same wiringsystem, all at different carrier

frequencies.

Things That Go BumpA big problem with using the mainswiring to transfer information isthat it can be a very noisy medium.All large household appliances,especially washing machines,tumble driers, drills - machine thatswitch fairly hefty voltage, cancause large spikes in the mainswhen the are switched on or off.This could cause havoc to a mainsintercom, even though it is isolatedfrom the direct mains wiring by atransformer. A large spike could,theoretically, be transferred into thecircuitry and overload it.

To come with noisy mains,powerful filters are used. Theseallow through only the frequencybeing used for the informationtransmission. Anything else isrejected so the system is protectedfrom mains interference that mightzap the circuitry as well as simplenoise that would make any voiceinformation incomprehensible.


Mains Intercom

Amplifiercircuitry

COntrolbuttons

On/Off and volume.

n>n

Loudspeaker/microphone

-----....._,...

Connection to mains

Mains connectioncircuit board

Mains isolatingtransformer


OMNI ELECTRONICSstock a wide range of

electronic components at

174 Dalkeith RoadEdinburgh EH16 5DX

Tel: 031 667 2611Open Mon-Thu 9.15am-6.00pm

Fri 9.15am-5.00pmSat 9.30am-5.00pm

1990/91 catalogue costs £1.50 TWAcontains vouchers to use against purchases

Do you have your copy yet?

D.V.M. Module Brand new full spec 3 1/2 Digit Voltmeter Module. Large 0.56 LED Display, FSR +/- 200mV.Supply required from 8 to 18V. Size 8cm x 5.5cm. Circuit supplied for multimeter £18.75

MEOAPROM Programs 2764/128/256/5120/010/020 (1 Meg/2 Meg 28/32 pin) HMOS. CMOS, NMOS typeEPROMs. Attractively cased and supplied with power unit. Powerful operating software includes full screenEditor, extensive file handling (Intel Hex, Binary, ASCII Hex), Byte/block or complete ROMprogram/verification/editing. Fast algorithm 1K x 8 Bit per 1.9 secs. Runs on IBM or compats via RS232 port(works on laptops) £128.95

Auto Tracks VS PCS Designer Produce professional printed cirsuit boards quickly and easily on you IBMPC/XT/AT or Amstrad 1640. Single/Double sided. Auto routing, rats nest or point to point entry, Zoom Editing,Various line/pad sizes. Library & User defined parts. Printer options for 9/24 pin include 1:1, 2A, Solder mask &Text. Too many features to list here, SAE for further details. Minimum system requirements IBM PC/XT with CGAgraphics, Epson printer, Mouse optional £59.95

Micro Engine Development board for MCS8031/51. Contains PLCC 8031, 24 pin EPROM socket, 6 MegXtal, address latch IC and 18 pin IDC header output Ports 1 & 3. Ideal for stand alone control applications.Size 7cn x 4.5cm approx. Full screen Editor assembler for IBM PC/XT/AT (downloads code to printer port ordisk) £39.95

EPROM/ROM Emulator Works on ANY computer with Centronics printer port. Emulates all ROMs from 1K(2758) to 32K (27256) over 50 types supported. Any file sent to printer port appears as ROM on targetmachine. Fast download. Ideal for MICRO ENGINE development £89.95

All prices inclusive, SAE for further details

John Morrison (Micros) Dept PE4 Rein Gardens, Tingley,

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TUTORKIT MICROELECTRONICS TUTORS

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Practical Technology

Putting You In

The PictureImage scanners are reaching the point where they are cheap enough and produce goodenough quality to make traditional methods redundant. Karl Levine looks into the matter.

The technology that allowsimages to be scanned andconverted to a digital format

is becoming cheaper and improvingin quality. It finds uses in thedesign of fax machines, the printingof magazines and newspapers,information storage and opticalcharacter readers, to name but afew. One industry that looks set tobe revolutionised by the technologyis small scale publishing.

Getting Into PrintAt the moment, transferringphotographs to the printed pageusually requires specialisedequipment which is expensive bothto buy and use. The photographsare scanned at a resolution of about1240 dots per inch (dpi - thenumber of dots or pixels in a squareinch) and the digitised informationsent to a computer for storage. Theimage is then combined with theimage of the text on the page andthe whole thing coded up, usuallyusing some form of computer pagedescription language (PDL) such asPostscript. It can then be sent to aprinter that is able to understandthe language and reproduce thepage. An advantage of using a PDLis that it is independent of theresolution of the output device. A300dpi laser printer can cope with itjust as well as a 1240dpi Linotron -the standard machine used to printonto the high quality film fromwhich the plates are made to put ona printing press.

To obtain apparent shades ofgrey, some of the resolution of theprinter is sacrificed and dots areclumped together to form blobs -squares, circles, lines - which canbe used to provide different grey

The picture used f

densities. This is most obvious innewspapers where quite coarsedots are used. The conversion of animage into these dots uses a half-tone screen. This is effectively agrid through which the image isviewed. Each square has a differentcolour or grey level and is assigneda blob whose size is dependentupon this level. The halftone screenis usually measured in lines perinch and has an angle at which thelines or dots are drawn.

Scanning In OperationAll of the lower end and mid -rangescanning systems, such as thePanasonic FX-RS307 used for thisarticle, operate in much the sameway. A bright light illuminates thepage and a set of horizontal sensorspick up a line of the reflectedimage. The sensor moves down thepicture taking in the informationand feeding it to the computer or

other capture device. The accuracyof the scan depends partly uponhow close the sensors are spacedand partly on how good themechanics of the system are.Obviously, the better these are, thehigher the cost.

The image being scanned caneither be straight black and white,in shades of grey, or colour. Mostmid -range systems sense thedifferent intensities of the imageand convert them to either 16 or 256shades of grey.

The ResultsThe Panasonic FX-RS307 offers600dpi resolution in 256 shades ofgrey. This is the maximumspecification with other, lesser,resolutions being used to speedthings up. To illustrate theoperation of the machine, a numberof scans were taken at differentresolutions and qualities. The


Image Scanner

software supplied with the systemallowed either grey scale (16 or 256levels), half tone screen or black andwhite. Additional controls allowedthe contrast, brightness andbackground level to be adjusted aswell as the gamma - it is possible tochange the equalisation of the greylevels in a similar way to adjustingthe levels of the various frequencieson a audio graphic equaliser, this is

known as the gamma setting.The first selection of scans

(below) uses the black and whiteline -art option. The results are notbrilliant but are certainly goodenough for inputting into artpackages and either tidying up ordrawing over. The second set (overpage) illustrate the half -tone screenspossible - these are actually appliedby the software and are

From left to right, line art quality at 75,300 and 600dpi.

*

Clockwise, 75dpi,150dpi, 300dpi and600dpi with 256 greylevels. The last pictureis at 600dpi bu usingonly 16 grey levels.Inset is a 1270dpi 256grey level image.

independent of the output device.Only systems that don't havePDLs that insert their own half-tone screen would normally needto use this option, alternatively,they can be used to reproducereasonable images on amonochrome computer screen.The next set of pictures (above) aregrey -scale. The advantage of these

is that software can be used to editthem or change their size, evenimprove the image by shrinking itdown and effectively making thedots closer together.

The difference between thevarious options as far as computerprocessing is concerned is one offile size. An A4 image at 75dpi inline -art form takes up about 68k


Image Scanner

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bytes. Increasing the resolution to300dpi ups this to 1059k. 600dpirequires 4231k - pretty large.Changing to 16 level grey -scaleincreases these values to 266k,4321k and 16920k. Moving up to256 grey levels creates some hugefiles, 530k, 8461k and 33839krespectively - the latter takes up agood third of the 100M drive usedto create and store PE andprocessing it takes quite a longtime.

By comparing the image withthat scanned in the conventionalway, the quality of the scanner canbe appreciated.

Moving Up To ColourA resolution of 600dpi and 256 greyscales is just about good enough forvery basic applications such asscanning black and whitephotographs. For higher qualitywork involving colour a moreadvanced machine must be used. Atthe moment, there are few mid-range machines that support 24 -bitcolour. To get some idea of whatthis means, 4 -bits is used to store 16grey levels, 8 -bits gives 256 greylevels. 24 -bits splits the colourimage into component parts, red,green and blue and sets aside 8 -bitsfor each. This gives 256 x 256 x 256or 16,777,216 possible colours.Unfortunately, the best of thesescanners only runs to 400dpi soalthough a wide range of coloursmay be available the resolution stillhas a little way to go to reach the2400dpi or so needed to produce animage good enough for a colourmagazine cover. The otherdrawback is the size of the imagefiles created by these scanners.

A solution to the size problem isto compress the files using dataencoding techniques. In manyimages, there is a great deal of

Half -tone images at 150dpi, clockwise:Horizontal, vertical, square, detail,chain, press, bayer and spiral.

Top, 300dpi detail half -toneBottom, 600dpi detail half -tone

redundant information, especiallywhere there are large areas of thesame colour. There are two mainapproaches to this. The first aims toproduce a smaller file which, whendecompressed, will result in anexact replica of the original.Alternatively, some of the data canbe discarded, usually with a loss ofdetail or a flattening of the colourranges. Many realistic images havequite subtle variations in colourwhich, although not always directlyvisible to the naked eye, affect thequality of the image. These minorvariations can make losslesscompression very difficult.Removing the variations allowsgreater compression and increasesthroughput.

The FutureAs the price falls and the qualityimproves, scanners should becomequite common, not only inpublishing but in all areas wherestatic images have to be convertedinto digital form, quickly andcheaply.


Speaker Review

A New WaveIn SoundCanon's new S-50 loudspeakers are set to challenge traditional design, taste and sound.James Smith checks them over to see how they measure up.

Loudspeakers have beenaround for a long time and inthat time have not really

changed a great deal. In the mainthey are still built into large orsmall square boxes with the soundbeing directed out of the front.Thenew Canon S -50s, apart fromlooking rather startling, are rather adeparture from normal loudspeakerdesign. Instead of directing thesound outward from single ormultiple cone speakers, they beamthe sound downwards and divert itinto the room via a reflectivesurface. The idea is to give a widerimage to the stereo and allow morethan one person to sit in the"perfect" listening position.

Old Style SpeakersMost high fidelity (HiFi)loudspeakers are actually made upfrom one or more speaker conesmounted inside a square woodenbox (Fig. 1). The aim is to reproducerecorded sounds as perfectly aspossible, that is, to make the soundjust like the original. Since thehuman ear is able to hear soundsfrom about 20Hz to 20,000Hz andassuming that the recording system

Are the S -50s really magio.nwhrooms?

is able to take in and store thisrange, a loudspeaker must be ableto reproduce it as accurately aspossible.

The next step is to give an imageof the sound. When listening to aconcert whether orchestral or pop,the sound doesn't come from onesource but is spread across thestage. To get the same effect with aHiFi system, two speakers are usedto give stereo. Because human

beings have twoears, a speakerplaying to each onefools the brain intobelieving that thesound is spread overa stage - feeding anequal sound intoeach speaker placesit in the centre,feeding it to just oneor the other moves tothe side of the stage.Of course, things arenot quite a simple asthis. Human hearing

Tweeter

Mid -range

Woofer

Side view (cutaway)

Fig. 1. Inside a normal loudspeaker.

Front view

is backed up by a great deal ofsound processing software in thebrain and modern speakerrefinements, including the S -50stake this into account. Sitting in thecentre of the speakers but a littleway back (Fig. 2 left) should giveoptimum stereo. However, mostpeople either don't sit still, don'thave the space, or simply likelistening to music with someoneelse. Unfortunately, this means thatthe optimum position cannot beachieved. A person sitting closer toone speaker than another will findthat the sound from that speaker islouder so the stereo effect isdiminished. To get around thisproblem, the Canon S -50s producea wide image effect.

Wider SoundThe construction of the Canon S-50speakers means that the sound isnot beamed directly to one spot butis spread out around the front ofthe speaker. Fig. 2 right shows thebasic idea and with two speakers, a


Speaker Review

Fig. 2. An exagerated illustration of old style speakers on theleft compared with the wide image on the right.

listener should be able to sitanywhere between them, even welloff to one side, and still hear goodstereo sound. Instead of thelistening area being single point it isa circle or oval. Because of this, anumber of people can listen tostereo sound from the same sourceand hear approximately the samething - more like being at a concert.

On The InsideOne look at the S -50s immediatelyreveals their differences fromordinary speakers. The mushroomshaped dome holds the single 5inspeaker in a reflex arrangement(Fig. 3). Under this is the conicalreflector which directs the soundout into the room. The speaker isactually aimed off-centre so that themain direction of the sound isforward. The supports which holdthe dome to the reflector alsoprevent sound being directed toofar back. Instead. the bass reflexhole is positioned between themdirecting the main bass soundsdirectly backward.

They have a very solid feel andeven when used at a relatively high

volume, there is virtually novibration of the domes. Thereflectors are solid castzinc/aluminium alloy - Canonboasts that they are the largestsingle zinc pressure die- castings inthe UK.

Another feature of the speakersare the magnets used to drive thecoils. An older technology, using anAluminium/Nickel/Cobalt slughas been revived that allows the S -50s to be placed next to TVs andmonitors without them affecting thepicture quality in any way.

Sounding OffNo matter how technologicallyadvanced they are, the true test of aloudspeaker system comes fromlistening to it. The wide image effectis definitely present and, apart fromone drawback, pretty good. Theproblem lies with positioning andthe height at which they should beplaced. Unfortunately, there is arelatively narrow angle at which thesound is really good and the wideimaging effect especially noticeable.Above this it diminishes so that ifthe speakers are positioned

relatively low down, appropriatefor a low slung sofa, standing uplooses the effect. Because of this itwas found that the best position forthem was on stands at least a metrehigh. Apart from this, everybodywho listened to them was quiteimpressed, not just with the wideimaging stereo, but with the overallsound. Considering the unusualway in which it is beamed into theroom, no noticeable colouring ordistortion cropped up.

How Good Are They?Whether a HiFi system, especiallyspeakers, is any good is largely amatter of taste and experience. Iwas favourably impressed withtheir performance. They were easyto install, sounded good from lowvolume to high over a wide varietyof music and the wide imagingworked well. They also attracted anumber of comments about theirshape - some puzzled, somecomplimentary. Although theywouldn't really suit victorian decoranything modern is enhanced bytheir unusual styling.

SpecificationsProduct:Canon S-50 Wide Imaging StereoSpeakersAnechoic frequency response:70Hz to 18kHz ±3d8Nominal impedance:8SIPower handling:50W - can be used with any amplifieror stereo TV with output power ratingsbetween 15 and 100W per channel.Price: £349.99 incl VAT£399.99 with standsAvailabilityCanon Audio Tel. 0483 740005


Software Review

Using Technology To

Teach TechnologyAlfred White loads up ACE and finds that learning about the operation of electronic circuitscan be fun.

Learning the basic concepts ofelectronics is the first step onthe way to understanding a

whole new world of technology.This educational process can behelped along with the addition ofdynamic teaching aides such asACE.

The package is designed to runon an IBM PC/AT (286, 386 or 486microprocessor) compatiblecomputer with a VGA graphicsdisplay plus mouse and hard diskdrive. Installation is simply amatter of inserting a disk andtyping INSTALL. This sets up adirectory on the hard disk andunpacks the relevent files into it.Typing ACE starts the software andthe title screen gives the user achoice of circuits to look at and playwith. The mouse is usedthroughout to point and click atthings to select them and get themmoving.

The use of a graphical userinterface (GUI) and standardisedcontrols similar to a cassetterecorder make ACE quite intuitiveto use. There is no need to refer tothe manual as far as basic operationis concerned -- a big plus for any

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computer program.

Moving CircuitsA wide variety of subjects arecovered by the system and selectingone, such as capacitors or resistors,from the title screen gives a newscreen with a selection of circuits --

these show the basic

Simple resistor circuit.

components and howthey are wired together.Pointing the mouse atone of these andclicking, loads it upready for operation.The controls at thebottom of the screennow allow the power tobe turned on (start), theoperation to be steppedthrough (step), reset(rewind), stopped andcleared (eject). Clickingthe start button

initialises the simulation and thebattery starts to move current. Thegraphical analogue is a series ofbuckets that lift current upwards togive the idea of creating a potentialdifference. In situations where thecircuit is incomplete, say when theswitch is open, the buckets areempty showing that no current isflowing. Different componentsaffect the current flow in differentways and colour is used to denotewhich parts of the circuit are athigher or lower potentials thanothers. A legend at the top of thescreen shows the colour variationand what it means.

The whole simulation isgraphical with the current flowbeing denoted by small dotsmoving through the wires. As themanual is at pains to point out,these do not represent electrons andtheir speed doesn't represent thedrift velocity, they just represent


ACE Review

the flow and how it varies when itreacts with components.

Circuit ChoiceThe circuits siumlated by ACE areshown in table 2. Starting off withsimple bulb and batteryexperiments, they move on to coverresistors, capacitors, diodes andtransistors as well as relays andoscillators. A number of interactivecomponents are also provided inthe form of variable, light and heatdependent resistors and switches. Acouple of good examples of theoperation are shown in the relaycircuits and the oscillators. The firstallows a variable resistor to beturned up until enough current isflowing through the relay coils sothat the magnetic field closes theswitch and an additional circuitwith a bulb in it turns on. This

Relay demonstration.

Light dependent resistor and relay.

Oscillation in operation.

Astable Multivibrator.

7

I-rJJ-

A selection o circuits.

illustrates graphically how suchcircuits operate. The oscillators areeven better since they show thebuild up of charge on capacitorsand the change of field in inductorsand how this shuttles backwardsand forwards to give oscillations.

Teaching AidThere are three ways in which ACEcan be used. The first is as dynamicblackboard where the teacher canuse the circuits to show studentswhat is going on. In the electronicbook format, the software allowsindividual students to experimentwith various circuits or performcourse work as specified by theteacher. The third area of operationis as a revision system wherestudents can check their ownunderstanding.

ACE is designed to demonstratecircuits in a predefied way. All ofthe circuits are preset and will onlyperform in the way the softwareauthors designed them to. It wouldhave been nice to be able to take thevarious comonents available anddesign new circuits -- this is, afterall, what electronics is all about. Insome ways the variety of circuits inACE allows all of the possibilities tobe seen, perhaps future productswill allow these changes to bemade.

On the whole the animatedgraphics are excellent and,especially in the oscillator circuits,show the operation of theelectronics with great clarity. Foranyone who is an absolutebeginner, ACE is definately a goodway to begin understanding

Circuits simulatedAlternating currentBulbs in series and parallel

Ilt pacitorsnductors and insulatorsdes and rectification

usesInternal resistanceInductors and relaysMeasuring voltage, current and

livistanceMediators

Potentiometers and current -voltagecharacteristicsResistors in series and parallelTransistor circuitsVariable resistorsThere are 78 circuits in total

Components simulatedAC generatorAmmeterBatteryBulbCapacitorDiodeFuseInductorLight dependent resistorPotentiometerRelayResistorThermistorTransistorVoltmeter

SpecsProduct: ACEPrice £199Available from:Bradford Technology LtdRipley StreetBradfordWest Yorks, BD5 7RR


Q&A

TechniquesWith Christmas well and truly on the horizon, Andrew looks at 3 ways to flash your lights.

This techniques column has aseasonal bias: three ways toflash your Christmas Tree

lights. The first method is intendedto be used with one or two chainsof lights, the second with threechains and the third with four.

The circuit shown in Fig. 1 willflash one or two chains of lights bymeans of triacs. The circuit ispowered by a mains -dropper andseries diode, to avoid the cost andspace associated with a mainstransformer. To make this means ofderiving power practical, it isnecessary to minimise the currentconsumption of the unit. Becausemost of the current is used totrigger the triacs, the triac-triggering is designed to supplyshort pulses at around the mainszero crossing, minimising theaverage current consumption.

Power SupplyThe reservoir capacitor, Cl, ischarged on positive going half

01 1N4006

RV1470kSensitivity

cycles of the mains via R1 and Dl.To minimise the ripple on thepower supply, a second stage ofsmoothing is supplied by R2 andC2. The zener diode D2 regulatesthe supply to approximately 12volts, and because the current in R2is continuous, the ripple on thesupply is very low.

The clock for the flashing cycleis provided by ICla and b, which isconnected as a conventional CMOSclock generator. The componentvalues here have been chosen togive an output frequency ofapproximately 2Hz. This can bechanged is required by changingthe values of R4 and/or C3.

An optional light -level detectorcircuit disables the clock and thesecond output during the hours ofdaylight, switching the lights on atdusk and off at dawn. If thisfunction is not required, the ICinputs controlled by it should beconnected to the positive supply. Alight -dependent resistor is shownas the photosensitive element in the

R6470k

ICI a IC1b

IC3a

R9100k

02 BC212

R161k

T

-1N1177U-

T2TIC206D

R1122k

IC1d

light detector, but a phototransistoror photodiode could be used ifavailable.

IC2a and IC2b form a triggerpulse generator whose output isactive while the mains waveform iswithin the range -50V to +50V.Triac triggering occurs when theoutput of IC2b is at logic 0. Whenthe mains is more negative than50V, pin 5 of IC2b is below its logic0 threshold, so that pin 4 is forcedto logic 1. When the mains is above+50V, pin 2 of ICla is above itslogic 1 threshold, so that pin 6 ofIC2b is at logic 0 and therefore pin 4is at logic 1. Only in between thesetwo extremes can pin 4 go to logic0.

The negative gain trigger pulsesare inverted by IC1c, and gatedtogether with the flashing clocksignal by IC1d. When both inputsof IC1d are at logic 1, Q1 isswitched on triggering triac Tl. Ifthe light level is sufficient to raisethe input voltage of IC2c above its

Continued on page 57

01BC212

R121k

T1

L

R131000

0 L00

Lights 1

C4100n

class x

R171000

C51000

"" class x

ON

0Lights 2

0

Fig. 1.

Radio Scanner Review

Sifting ThroughThe Air WavesAlan Black examines the Tandy Pro -41 radio scanner and, apart from attempting to breakthe law, finds a new hobby.

It must be said first of all that it isquite easy to break the law witha radio scanner. It is able to

listen in on all of the radio channelsthat normal 'tuners can't. Thisincludes those used by the Police,armed forces, ambulances, firebrigades as well as taxi companiesand, believe it or not, baby alarms.

Unlike commercial broadcastingwhere radio channels are on the airpretty well all of the time, mostother forms of radiocommunications are on a strictlystop/start basis. This means thatthere may well be long periodswhere nothing happens at all -hence the use of a scanner to listento them. Instead of having a tuningknob, a scanner allows particularfrequencies to be entered directlyinto each of the channels. It thenscans them, stopping only whensomething interesting is happening.The hassle with this is findingsomething to listen to - huntingaround wavebands by typingfrequencies in is rather boring,especially when there is so muchradio space. On the plus side, whenan active channel has been found,

Specifications

Product: Tandy Pro -41 ScannerFrequency ranges66-68MHz in 5kHz steps137-174MHz in 5kHz steps406-512MHz in 12.5kHz stepsScanning rate:10 channels/secPower requirements:5 -AA batteries 7.5VDC or 5 -AA NiCdbatteries 6VDC or an AC adaptor12VDCPrice £99.95Available from Tandy Stores

all the effort of finding itmakes listening isworthwhile. Altern-atively, there are books offrequencies available forthose who want to takean easier route.

The Pro -41 looks alittle like a pose phonewith its LCD readout,pushbutton controls andblack flexible aerial - thiscan be removed and anexternal aerial attached tothe BNC connector. Thenumeric keypad is usedto enter the frequenciesand select the channels inmanual mode. There areten channels in all andeach can be programmedwith a particularfrequency (see specstable). Other controlsinclude a lock -outfunction which allows thescanner to ignore certain channels -useful when a known channel istransmitting something useless andother channels are to be searched.From the opposite viewpoint, thesquelch control sets the minimumlevel at which a signal should beaccepted and cuts out any noise orhiss. At minimum, all channels areaccepted, turning it up only allowsthrough those that are transmittingclearly.

The scan button tells the internalelectronics to scan through the 10channels until somethinginteresting crops up. On finding abusy chanel, it is switched on andcan be listened to via the integralloudspeaker or a earphone, thevolume control-on/off switch setsthe output up to abound 260mW.When the channel goes quiet or

returns to hiss, it is turned off andthe system waits for three secondsbefore resuming the scan. Thisallows any replies to a particularmessage to be heard beforescanning sets in again.

Listening in to the radio waves,especially forbidden ones, is quiteappealing to the more enquiring(nosy) amongst us. The Pro -41 is abottom of the range model withonly 10 channels and limitedfrequency ranges but is notparticularly expensive. It getsthrough batteries rather rapidly butthe ability to charge NiCdsinternally from an external powersupply helps a bit - the batteriesand external supply will cost extra.For around £100 it should prove tobe a good starter for the buddingaudeur.


Books

New Paradigms InPhysicsThis month's books range from the a description of how attitudes to physics are changingto home security.

The Matter Myth: Towards 21stCentury SciencePaul Davies and John GribbinPrice £16.99 (hardcover)Publisher VikingISBN 0-670-83585-4

There can't be too muchpopularisation of science especiallyof the more complex ideas such aschaos and relativity. Davies andGribbin explore the change fromNewtonian and Einsteinian physicsto a holistic view of the Universewith all of its inherent randomnessand uncertainty.

Although it is sometimesirritating and often contentious, thebook is a good read and often un-put-downable. It should appeal toboth the knowledgeable and thenewcomer to science and goes someway to explaining why the world isthe way it is.

Perhaps it will even followHawkings' A Brief History Of Time,into the best seller charts.

towards 21st - century science

ELECTRONICPROJECTS

HOME SECURITYOwen

Electronic Projects For HomeSecurityOwen BishopPrice £6.95 (paperback)Publisher PC PublishingISBN 1-870775-12-0

Regular readers of PE will knowthe work of Owen Bishop from old.His projects and articles havegraced these pages for a number ofyears.

This book gives practicalguidance for building intruderdetection systems from simple lightbeam and pressure mat detectorsthrough to fire detectors andtamper -proof multi -channel alarmsystems.

Circuits and construction detailsare given throughout as arecomponent listings. All of thesystems are designed to be built onstripboard so anyone who is afraidof PCBs need not take fright. Theexplanations are straightforwardthough at times a little technical.

Newnes Electronic Circuits PocketBookRay MarstonPrice £12.50 (hardcover)Publisher NewnesISBN 0-7506-0132-9

The number and variety ofintegrated circuits available to theelectronics constructor is growingall the time. This book bringstogether information from a wideselection of popular linear circuits.The approach taken is to give asmuch information as possible.Diagrams and tables abound as doapplication circuits and copiousbackground information. Startingoff with transistor arrays, theauthor progresses through op -amps, audio amps, displays, timersphase locked loops waveformgenerators, voltage regulators,radio ICs and sensors. This is theideal book for anyone whoregularly designs and buildselectronic circuits using linear ICs.M

mammimm

ELECTRONICCIRCUITS

ammeamom

111821111111111111

11111111111111111111111111111111111111111111111111


Quiz

The Great ElectronicTrivia QuizHow much do you know about electronics? Is your background theoretical, practical ortrivial? Find out by answering the following questions.

History1 In what year did James ClerkMaxwell write A Dynamical TheoryOf The Electromagnetic Field?

a - 1864b - 1891c - 1925

2 The first practical thermionicvalve was produced by

a - Thomas Alva Edisonb - John Ambrose Flemmingc - Lee De Forest

3 To what new science did Karl GJansky give birth?

a - radio astronomyb - electron microscopyc - the study of atomic radiation

4 For what were Brattain, Bardeenand Shockley awarded a NobelPrize in 1956?

a - their work onsuperconductorsb - designing computersc - their work on semiconductors

5 Lasers have been around for along time. Who made the first trueruby laser?

a - Theodore Harold Maimanb - Donald Arthur Glaserc - Michael Faraday

6 When did colour TV first startregular broadcasts in the UK?

a - 1954b - 1967c - 1969

7 The first practical tape recorderable to record and playback soundwas exhibited in 1900 at

a - the Paris Exhibitionb - the Berlin Trade Fairc - the Albert Hall

Science8 The formula V=RI is morecommonly known as

a -Fleming's Right Hnad Ruleb - Fleming's Left Hand Rulec - Ohm's Law

9 Which of the following is not aconductor

a - Copperb - Magnesiumc - Sulphur

10 The Ionosphere starts at analtitude of about

a - 50kmb - 50 milesc - 500km

11 In a cathode ray tube, electronsare produced from

a - the heaterb - the cathodec - the anode

12 Who is this?

a - Allessandro Voltab - John Ambrose Flemingc - Sir Humphrey Davy

13 X-rays have a frequency range ofapproximately:

a- 106 to 108 Hzb- 1016 to 1022 Hzc - 1022 to 1024 Hz

14 The element gold (Au) is notsilver coloured because of:

a - densityb - conductivityc - relativistic electrons

Technology15 Which of the following is not apart of a transistor?

a - the gridb - the drainc - the base

16 A thyristor is made up from anumber of P -N junctions, howmany?

a -2b -3c -4

17 The word modem is in commonuse. What does it stand for?

a - modulator demodulatorb - modular demonstrationmodelc - morphological operationaldata encryption machine

18 NTSC is a colour TVtransmitting system used in theUSA. What does it stand for:

a - Never Twice the Same Colourb - National Television SystemsCommitteec - New Technology for SendingColour


Trivia Quiz

19 What is this?a - variable inductanceb - atomic power stationschematicc - Van De Graff machine

20 Which of the following colours isnot used in resistor coding

a - redb - pinkc - violet

21 Which of the following is not aform of computer memory?

a - RAM

b - flashc - fractal

Products22 The 80x86 range ofmicroprocessors was originallymanufacturerd by:

a - Motorolab - Fairchildc - Intel

23 Bitstream technology ismarketed by:

a - Philipsb - Sonyc - Ford

24 C-QUAM is a technology fora - Stereo FM radiob - Ham radioc - Stereo AM radio

25 Digital Compact Cassettes wererecently launched where?

a - Las Vegasb - Frankfurtc - San Francisco

26 Which of the following is a CADsystem:

a - Ranger 2

b - Explorer 1c - Pagemaker

PA3 0 0' PIA...PAX In 0 PA5

PM la 0 PrA8

PAO 0 En PAn

FTD ocs MI E3 RESET

GND In E3 DO

o Ea DI

AO 0 E3 D2

PC, mi 8255 PPI ED D

PCS al E3 Do

PC5 0 0 DPC5 M 0 CSPCO 9 Ea 07

PC1 in III V55

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PC.3 n30 Pe,Ea sss

1130 in El PS5

Pei lin 0 PIN

xim 0 Ea Pea

27 What is this?a - an analogue to digitalconvertorb -a microprocessorc - an interface chip

28 Practical Electronics is howmany years old this issue:

a - 25b - 28c - 30

To see how well you did, turn topage 60.

NATIONALCOLLEGE OFTECHNOLOGYDISTANCE LEARNING COURSES

The National College of Technology offer a range of packagedlearning short courses for study at home or in an industrialtraining environment which carry national BTEC awards. Studycan commence at any time and at any level, enabling you tocreate a study routine to fit around existing commitments.Courses on offer include:

Analogue ElectronicsDigital Electronics

Fibre/OptoelectronicsProgrammable Logic Controllers

Tutor support and BTEC certification are available as optionswith no travelling or college attendance required. These verypopular courses which are ideal for vocational training containworkbooks, audio cassette lecturettes, PCBs, instruments,tools, components and leads as necessary to support thetheoretical and practical training. Whether you are anewcomer to electronics or have some experience and simplyneed an update or certifications, there is probably a distancelearning course for you. Write or telephone for details to:

National College of TechnologyNCT Ltd. PO Box 11, Wendover, Bucks

Tel: (0296) 624270

Interak 1BUILD YOUR OWN COMPUTER

1 1 I 1__t El

liU

INT E R AK can be commenced with the minimum of outlay Bare boards'tom E10 95 beg borrow or steal the components or buy from us - allparts available separately No special or custom chips tie PALs ULAsASICs etc, used - no secrets

Go as fast or as s,owlv as your funds and enthusiasm permit

Made tor thOlitt.nO must know wnat goes inside circuit diagramsand, descriptions are provided And honestly can yOU really use acomputer effectively if you don I know what s msde and nobody win'ON you'

Solid engineering construction something to be proud of 19' 3U rackmounting plug in circuit boards and modular construction keepsobsolescence at bay

nourishing Independent Users Group and newsletter Hundreds ofprograms on disk at little or no cost from the Users Group

Program in machine code lAssembler) Basic C Forth etc DatabaseWord Processing. Scientific applications

Cassette tape operation or disk t up to 4 drives Megabyte 3 5- availablefrom us Out you can add 3" 5 25- 8' if you want, Disk operatingsystem CP M Plus

64K RAM Z80 based at present with potential for expansion to a 16Megabytes address space and Zilog s latest Z80280 in the future

Needs no specialised knowledge to construct and we will happily getyou Out of a jam if you get into one

Availactility of personal and individual after sales service. impossible toobtain from large companies whO are only after your money

Security of supply - from Greenbank Electronics establishedin 1970

GreenbankFor more details write or phone us:

Greenbank Electronics. Dept PE 12 460 New Chester Road.Rock Ferry, Birkenhead. Merseyside L42 2AE Tel 051-645 3391


Constructional Project

The Purest AudioSound AroundIn a quest for audio superiority, Jeff Macauley follows up his recent power amplifier designwith a high quality headphone amplifier which ranks alongside best you can buy.

Despite the fact that stereoheadphones offer a farhigher degree of fidelity

than the best speaker systemscurrently available they havealways been a poor relation. Inmany ways this is a pity since whendriven from a high qualityamplifier, which need not beexpensive, the results can besuperb. Herein lies the rub.Although most stereo amplifierscome equipped with a headphonesocket, this has usually been addedin as an afterthought on themanufacturer's part.

Optimum ResultsThe conventional HiFi ampoperates in Class B mode. At thekind of level that headphonesoperate the distortion generated byclass B amplifiers is at a maximumdue to the non-linear crossovercharacteristics of their outputtransistors.

To make matters worse theheadphones are usually fed viaresistors to avoid overload. Thisremoves any damping that the ampcould provide. The result isincreased distortion. As with allengineering problems the only wayto obtain optimum performance isto study the facts and design acircuit to suit. Headphones havecome a long way since the bulky 8Qunits of the seventies. Today's cansuse thin mylar diaphragms andhave a typical impedance of 3252.

Furthermore, the requiredpower for a given sound pressurelevel (SPL) is desirably low. Asurvey of 25 types shows that thesensitivity for 1mW input variesbetween 86 and 97dB SPL. Thisimplies that even the most

insensitive types will provide 96dB,the accepted bench mark for aspeaker systems with an input of10mW or less.

Given this information it is clearthat as far as output power isconcerned the requirements aremodest. At the other end of thescale all the headphones examinedhave a maximum input of 100mW.The ideal amplifier would have anoutput between these extremes. Asfar as other parameters areconcerned the performance needsto be on par with a normal amp.That is to say, as little distortion aspossible combined with asatisfactory bandwidth and signalto noise ratio.

Top Of The ClassesWith the small output power comesthe possibility of operating theoutput stage in Class A, thusavoiding distortion generated byconventional amps at low output.

The finished product (artists impression)

With the requirements definedthe next stage is to produce asuitable circuit. A solid state designcould be produced but I havealways preferred the sound ofvalves. Apart from personalpreferences, however, there aregood technical reasons for usingthem. These devices have adistortion level nearly ten timeslower than a transistor circuit.Furthermore the high inputimpedance of valves ensures thatthe individual stages don't load oneanother. There is an old audioadage about feeding lowimpedances into high impedances.Any amplifier stage, regardless ofthe technology used, will operatewith less distortion as the load intowhich is operates is increased invalue.

Valves though are inherentlyhigh impedance devices and aconventional valve amp can onlyfeed a speaker system of lowimpedance via a step down


Headphone Amp

How It WorksFig. 1 shows the circuit diagram. For the purposes ofdescription it breaks down into three parts. First theoutput stage. This uses an output pentode of ratherspecial design configured as a triode. This can bedone simply by connecting the screen grid to theanode. Using this valve in cathode follower modeensures a low output impedance, high inputimpedance and extremely good linearity. The correctoperating current is drawn from the valve by theconstant current source formed by the darlington Q3and the control transistor Q2. At switch on Q3 is turnedhard on by the base current provided through R6. As aconsequence Q2's base goes positive untilapproximately 0.6V is dropped across R9. Q2 thensinks any excess current through R6 and the circuitstabilises. The current is equal to 0.6V/R9,

Turning now to the input part of the circuit. This isbased on the well known TL072 dual low noise op -amp. The reasons for choosing this device include itsexceptionally good slew rate, a total harmonicdistortion (THD) of less than 0.005% at 1kHz and lownoise. To operate from a voltage high enough to powera valve the IC's supply voltage must be reduced to lessthan 35V. This is the function of 01. This is a highvoltage darlington. R7 and R8 produce a suitably lowvoltage on the base which appears at a low impedanceon the transistor's emitter. There is a hidden function inthis circuit which concerns the use of C7. This smoothsthe voltage on 01's base. In conjunction with 01 thecircuit acts as a gyrator providing 70dB of ripplerejection. To this can be added the 60dB ripplerejection ratio of IC1. the result being that the circuiteffectively ignores any supply voltage variations.

The most unusual feature of this circuit is the directcoupling between op -amp and valve and the latter'sinclusion in the negative feedback loop. This allows thebest of all possible world's to be obtained. First the op -amp sees an almost infinite impedance looking into thevalves grid. This means that the op -amp's output stagewill operate in pure push-pull class A so that the op -amp is generating the minimum distortion. Negativefeedback which is applied from the cathode to the op -amp's inverting input via R5 is driven from the

Fig. 1 Circuit diagram showing one channel.

Cl

blO

4--1VR1

2

R1

R3

R2

R

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cathode's low impedance.Applying feedback from a low impedance into a

high impedance is the situation which favours lowestTHD figures.

Voltage gain is set by the ratio of R5 to R4. Q3looks like a short circuit at signal frequencies and anopen circuit at DC. C3 this sets the DC gain at unityand the voltage that appears on the non -inverting inputis maintained identical to that on the output. Inputsignals are fed into the circuit via the volume controlVR1. C1 couples these signals into the non -invertinginput. R1 and R3 provide bias voltage leaving anexceptionally smooth bias voltage.

Finally, the power supply. T1 is the high tension(HT) transformer, the secondary is doubled by D1 andD2 and C6 smooths this voltage, The circuit is fed fromthe doubled voltage. Heater voltage is pure AC in thisdesign. The overall negative feedback reduces anyinduced hum over a thousandfold. Since the hum -levelproduced by AC heating is about 5j.tV in the first placeand a typical signal will be in the order of a volt, it'spretty obvious that the use of DC doesn't produce anyaudible benefits and thus cannot be justified oneconomic grounds. The heater voltage is fairlysubstantial at about 750mA per channel and so aseparate transformer is used to supply the requiredpower. Note that a 6-0-6VAC secondary is used. Thestandard heater voltage is 6.3VAC. However, the useof a slightly lower voltage extends the valve life withoutmaterially affecting the device's design characteristics.

Indeed, one of the major advantages of using avalve in a hybrid circuit of this kind is that the overallAC and DC feedback makes the circuit immune tovalve aging and the consequent changes that occur inits parameters duriong its operating life. One of themost dramatic illustrations of this is to try tapping thevalve with a screwdriver blade, gently of course. Thefeedback system reduces the microphony of the valveto such an extent that no sound will be heard throughthe phones.

Microphony is due to the fact that we are dealingwith a mechanical structure. when tapped smallmovements of the internal electrodes are turned intocurrent variations which are then applied to the output.

+C4

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Headphone Amp

20

57

25

25

63 63

70

40

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Back Panel

2 x 10mm diamholes for thephonos

Note:This drawing is not to scaleHoles marked A are 10mm dia fitted with grommetsAll unmarked holes are 3mm dia

A

v

25

33

33

20

Fig. 5. The case construction.

transformer. This componentultimately limits the quality ofsignal that can be produced by avalve design. If this component canbe removed then the quality can besubstantially improved. As for lowimpedance drive, this dependsmainly on device selection. What isrequired is a low impedance valvecapable of delivering fairlysubstantial current swings,preferably with a low voltage

power supply.A low impedance drive can be

obtained by operating the outputvalve as a cathode follower. Thiscircuit configuration acts like anemitter follower with a high inputimpedance, low output impedanceand less than unity gain. Like theemitter follower, the circuit possesvery low distortion levels. Less that0.1% at full output. Much searchingthrough tube manuals produced

two possibilities for the outputvalve. One of these is no longeravailable which lead to the selectionof a 6CW5.

Without negative feedback theoutput impedance of the amplifieris 68g. Too high for our purposesbut very low for a valve. By using adual op -amp as a voltage amplifierand applying negative feedbackaround the whole circuit, the outputimpedance can be reduced to less


Headphone Amp

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The construction of the circuit falls naturally into twoparts, the mechanical and the electronic. It is best totackle the electronics first. Most of the components aremounted on a stripboard panel, the layout of which canbe seen on the facing page. Note that the valveholdersare mounted upon the top panel. These require 19mmdiameter mounting holes. The best way to make theseis to drill them out with a suitable drill.

Having done this, mark out and drill the smallerscrew fixing holes and mount he valve holders intoposition. Next, attention can be turned to to mountingand soldering the remaining components. Little needsto be said about this. Ensure that all the polarisedcomponents are mounted the right way around. Alsocheck your work to ensure that the breaks have beenmade in the correct positions in the tracks. Also thatthere are no unwanted blobs of solder across tracks.When all the components have been successfully

From i/psocket

V16

W16

The volume controls

The output socket.

EE11 EE24 DD2

than an Ohm which is ideal. Withthis low output impedance there isno need for an output transformer,the signal is simply fed to thephones through a large electrolytic.A low ESR component is used hereto ensure even frequency responseand to avoid DC being applied tothe phones.

There is no setting up procedureto be followed with this circuit.Provided the wiring has been doneas shown, it will work first time. Tocheck it out connect yourheadphones, a suitable signalsource and apply power. After afew seconds the heaters should startto glow and a slight hum will be

V19

W1

FromFrom i/psocket

mounted, connect the valveholder pins to the tracindicated using hookup wire. Also attach the otherflying leads leaving these about 12in long to facilitateeasy connection. On the input phono sockets, ensurethat the earthed pin doesn't come into contact with thechassis as this creates a hum loop.

Having built the electronics, attention can now beturned toward the box. Drilling details of this are shownin Fig. 3. Again, this is quite straightforward. Havingattached the various pots, sockets and transformers,the last task is to interwire these following theschematic. After checking everything thoroughly theunit can be assembled making sure that enough spaceis left between the chassis and stripboard. Finishing isa matter of personal preference, the prototype wasspayed matt back with legends applied and coatedwith varnish.

heard. The hum will subside after afew more seconds and the music illappear. This hum is simply a resultof the DC conditions in the circuitstabilising. The signal to noiseration in the circuit is excellent andcomplete silence will be heard inthe absence of a signal.

If anything else happens whenthe amp is tested, there is a fault.The solution is to check the boardfor error, correct it and try again.The only other problem that mightcrop up is a hum loop. This iscaused by earthing the unit whenthe device feeding the signal in isalso earthed. The solution is toremove the earth lead from themains plug.

After all the struggle, will theresults be worth it? Definitely. I canhear nuances in my collection ofCDs and records that I neverrealised were there before. Mostimportantly of all, on the very bestrecordings one can tell how theinstruments are being played, notjust what the are playing. For mymoney, this is the test of a good

Components

Resistors, 1% metal oxideR1 47kR2, R3, R5, R6, R7 100kR4 10kR8 27kR9 12ohmsVR1 47k logpotentiometer

CapacitorsC1 10uF 25VC2, C3, C7 100uF 25VC4 1000uF 25VC5, C6 1000uF 63V

Semiconductors/valvesQl, Q3 BDT65CQ2 AT5058V1 6CW5D1, D2 1N4007MiscellaneousT1 20 - 0 - 20, 20VAtransformerT2 6 - 0 - 6 12VAtransformer2 B9A valve holdersCaseVeropanel1/4in stereo socketdual phono socket

A full kit of designerapproved parts is availablefrom Hobtek,The Cottage8 BartholomewsBrightonSussexThe cost is £69.95 includingpost and packaging.

4


Index 1991

IndexVolume 27 January 91 to December 91.

Features100 Years Of ElectromedicineA Closer Look At The Missing LinkA New Radio Licence From The DTIA Second Look At CADAll I want for ChristmasAmateur Radio ExplainedAn A to Z of Digital DevicesBasic ElectronicsBasic ElectronicsBasic ElectronicsBreathing Life Into The Medium WaveCharges On The MoveComputers Comms And Cock -upsComputer controlled serial multiplexerConverting Ideas Into CashD. I. Y. Printed Circuit BoardsDoes Office automation mean alienationEconomy And The Electronics IndustryFrom paper tape to laser beamGetting The Message AcrossHistory Of TechnologyHistory Of TechnologyImage ScanningIn The Beginning Was The TelephoneLasersLooking Towards The FutureMicro -controllers: A Buyers's GuideNicam Stereo TVNotebook ComputerOptical Fibres TechnologyPhilips Set To Storm The HiFi WorldPhilips To Break The Sound BarrierPractical Electronic Neural NetworksProbing The InterfaceRefreshing The Silver ScreenResistance CalculatorSynchronous Logic DesignTaking To The Air In New York CityTalking To The SkiesTechnology Under. The HammerThe Facsimile MachineThe Great Electronic Trivia QuizThe History Of TelevisionThe Integrated Circuit StoryThe Merest Flick Of A SwitchThe Power That Drives The starsThe Transistor StoryUnderstanding Private Radio PagingWhen The Dream Comes True

Constructional ProjectsA Surface Mount Signal TracerAt The Lower End Of The RangeBike ComputerCar positioning aidCounting The Rain Drops As They FallDealing With Very High FrequenciesDigital CompassFrequency MasterGetting It All Down On SiliconIs Anybody There?

The advances in medical electronics over the years AprilAll about the RS232 AugustGetting a radio licence becomes easier NovemberSome of the problems of computer aided design NovemberBarry Fox, Ian Burley and Kenn Garroch have desires DecemberHistory of amateur radio MarchNames and functions and diagrams for digital ICs February

FebruaryMarchJanuaryOctoberAugustNovemberFebruaryMarch

Inductors, capacitor coupling, active filtersLC tuned circuitTime and frequencyAM stereo is now a possibility with C QUAMCCDs and how they workBarry Fox on portable communicationsLinking more than one RS232 to the BBC microHow to get a patent and the pitfalls of inventingHow to make a PCB or printed circuit board JulyThe effect of technology on our lives JulyHow is the recession affecting the electronics industry AugustThe history of computer memories AugustOptical fibre transmission and how it works JuneAmbrose Fleming JanuaryThe life and times of Alessandro Volta FebruaryHow images are transferred into print DecemberOffice technology SeptemberAll about lasers JanuarySolar cells, Optical discs, transistor technology NovemberA look around the various micro -controllers MayWhat is Nicam, how it works, JanuaryWhat's in a laptop AugustHow optical fibres work FebruaryDigital Compact Cassette May 19Winter CES report AprilSimulating the brain JulyInterfacing the BBC, ST, Amiga, CM, Spectrum, IBM AprilA look at screen technology NovemberA gadget for working out parallel resistances FebruaryUsing state machines FebruaryAmateur radio in New York OctoberAll about satellites JulyChristies Sale features old electronic equipment DecemberA closer look at the fax SeptemberA test to tax your mind DecemberTV history from Baird to satellite JuneHistory of ICs from Tinkertoy to microprocessors MarchAll you ever need to know about switches AprilA visit to the Joint European Torus DecemberHistory of the transistor MayHow radio pagers work JanuarySuperconductors from their origins to their future May

Surface mount components make a simple sig tracerLow frequency meter 0.5 to 20Hz6502 microprocessor controlled sensor systemUltrasonic distance sensorMeasuring rainfallPE Chronos high frequency inputs and scalingHow to sense magnetic fields with a hall effect deviceA digitally controlled frequency generatorPROM programmerThe phantom phone rings when you put it down

OctoberJulyJanuaryMarchNovemberOctoberFebruaryMarchAprilJune


Index 1991

LCD Rev CounterListening To The LandscapeLooking At It LogicallyLow cost car alarmMicrocontrolling the robot carPE Chronos Building The DisplayPE Chronos V The Main BoardPE Chronos: Getting Into ConditionPE Chronos: Putting On WeightPE Chronos: The first boardSamfex, A digital sound sampling systemShoot Your TV With A PCThe Box That Bites BackThe Purest Audio Sound AroundThe Time Has Come For Many Things...Thermal WarningTripping The Light FantasticWe Have The PowerWho Said the Valve Was DeadYou Can Stop The Music

Data SheetThe 2716 EPROM, the 8212 I/O portHitachi H8/330UART 6402 transmitter receiverLH2426, LM 1201NS32CG160 microprocessor

How It WorksIR Intruder DetectorMain IntercomSupersonic HeterodyneThe Dot Matric PrinterThe MacintoshThe MultimeterThe VCRThe Video Camera

Practical ComponentsThe resistorCables And Wires

The Junction DiodeSurface Mount Devices

Techniques

LCD frequency counter, convertorUltrasonic scannerVisual data code convertor simplifies logic circuitsFull featured car alarmMachine code programs for controlling the carSome output for the counter timerPE Chronos gets its main boardSignal conditioning circuitsMore circuitryBuilding the first PCBSound sampling onto a computerTV screen capture to computerPersonal alarm system built on stripboadA valve headphone amplifierPE Chronos project basic specsUsing a thermistor in an electronic switchAmazing Light DisplayDual power supply using battery eliminatorsHigh quality valve stereo amplifierMidi Analyser

April ML928/9, SL490, M375 remote controlJuly 8255 PPI interface chipMarch The 6522 VIA interface chipSeptember UAF42 active filterNovember

Passive infra -red intruder detectorSending messages down household wiringSuperhet radio receiverInside a dot matrix printerThe MacintoshHow the multimeter worksHow the video cassette recorder worksThe insides of a video camera

AprilAugustJuneOctober

The CapacitorThe BatteryThe TransistorThe Inductor

Cheap circuit design, balanced audio circuitsFinishing up the humidity machine A battery level monitorFluorescent Light Dimmer switchesHumidity machineLight activate switchesSimple ADC, voltage controlled volume control with reduced distortionSolar heating panel temperature sensor Guitar pickup constructionStanding Wave Ratio measurement, train controllerThe operation of antennae, frequency response, solar power

ReviewsACECanon S-50 SpeakersComputer Aided DesignCounting The PulsesElectronics Made Easy?Measuring Up Digital Multi -MetersOn The Right TracksPhilips Crosses a DMM with a ScopeTandy Pry41VIP A Virtual Instrument

Animated Circuits For EducationWide imaging soundReview of Boardmaker 1 and 2 CADPulsar logic circuit simulator software for the PCProtolab analogue electronic circuit simulatorA look at a selection of multimetersSeetrax Ranger review CAD system for PCA look at the new Philips Scopemeter10 channel radio scannerA software DMM for a PC

Dry JointsReprints of PE Chronos Diagrams from JulyLCD rev counter Midi analyser Car positioning aid Frequency Master Eprom ProgrammerPE Chronos July 91 PE Chronos August 91 Talking to the skies July 91

JanuaryJuneJulyJanuaryJanuaryNovemberSeptemberJuneJulyAugustOctoberMayAprilDecemberMayFebruaryAugustMaySeptemberMarch

AugustJuneMayOctober

OctoberDecemberNovemberJuneAprilAugustMaySeptember

MaySeptemberJulyNovember

AprilAugustSeptemberJuneNovemberMarchJulyMayOctober

DecemberDecemberMarchSeptemberSeptemberSeptemberJuneOctoberDecemberNovember

AugustMay 91October 91


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54 Practical Electronics

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UNIVERSAL PROGRAMMERHi -Lo ALL -03 £295

Take advantage of Asian low labour cost!* Texas Instrument approved. Good quality.* PC based, programs stored into 5 diskettes.* Program most MPU, PLD, EPROM, EEPROM, BPROM.* Adaptors for PLCC devices are available.* 1 year guarantee. Money back if not satisfied.* Price includes postage but not VAT.

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Special OffersComputer Grade Capacitors with screw terminals 38000of 20V... £2.5087,0000f 10V £1.95, 68.000of I5V £2.95, 10,000of 16V £1.507 segment Common anode led display 12mm £0.45

LM293I AT5.0 Low drop out 5V regulator 10220 package £0.85

BS250 P channel MOSFET £0.45, BC559 transistor £3.95 per 10074LS05 hex inserter £10.00 per 100, used 8748 Microcontroller ........£3.50

TV Main switcth 4A double pole with momentary contacts for remote controlpack of 10 £3.95 box of 60 £19.95.

DC -DC converter Reliability model V I2P5 I2v in 5v 200ma out 300v input to

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Hour counter (used) 7 digit mains 240V AC 50Hz £1.45Resistor pack 2500 resistors I/8 -2W 50 different values £8.95Qwerty keyboard 58 key good quality switches new £5.00

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Components

High Stability ResistorsCarbon Film Resistors 0.568 to 10M0 E24 series 1/4W - 1p100 off per value - 75p 1000 off in even hundreds per value - MOOMetal Film 114W 1080 to 1 MO E12 series 5%- 2p. 1% E24 series - 3pMixed metal/carbon film 1/2W E24 series 1R0 to 10M0 - 1 1/2pMixed metal/carbon film 1W 487 to 10M0 E12 series - 5pBC107/8/9 - 12p. BC182, BC183,13C1134, BC212 & L versions - 10pBFV50.51 & 52 - 20p 283055 - Sop TIP31A,32A 25p. TIP. 41.42 - 40p

Tantalum bead etectrolytics subminiature (MfdsNolts)0-1/35, 022/35, 0.47/35, 1.0/35, 2.2/35. 3.3/16, 3.3/20, 4.7/16 -14p. 3.3/35 4.7/25,4.7/35 - 15p. 6.8/16, 6.8/35 - 16p. 10/16, 20/25 - 20p. 10/35, 22/16, 33/10, 47/10- 30p.100/6 - 30p 100/16 - 50p. 220/6 - sop

Aluminium Electrolytics (Mfds/Voitsi1,50. 2.2/50.4.7/50, 10/16, 10/25, 10/50- 5p 22/16, 22/25, 22/50, 47/16. 47/25. 47i5O

6p. 100/16, 100/25 - 7p. 100/50 , 12p. 220/16 - 8p. 220/25, 220/50 - 10p. 470/16470/25 - 11p. 1000/16 15p, 1000/25 - 18p. 2200/25 - 22p

Miniature Polyester Capacitors 250V Wkg. Vertical Mounting01..015..022. 033.047. 068 - 4, 0/ 5p 0.15, 22 6p

Mylar Capacitors 100V Wkg. Vertical Mounting E12 Series1000p to 8200p 3p. Doll to .068 - 4p. 0.1 -5p.0.15. 0.22 6p

Subm. Ceramic Plate 100)/ Wkg. E12 Series Vertical MountingIP8 to 47P - 30 56P to 330P - 4p. 10%390P to 4700P - 4p

Plate/disc ceramic 50V. Wkg. Vertical Mount. E12 series 1P0 to 1000P &E6 series 1500P to 47000P - 2p. 0.1 - 3p

Polystyrene Capacitors 63V Wkg. E12 Series Axial Mounting1OP to 620P 4p. 1000P to 10,000 - 5p. 12,000P -

DiodesZener diodes E24 series 3V3 to 33V 400mW - 8p. 1 watt - 12p. 184148 - 2p. 1N4001 -3p. 1N4002 - 3.5p. 1N4007 -5p.1N5404 - 14p. 00,91 - Bp. M143 -10p. W005 - 20p.WO1 -25p. IMMO - 6p.L.E.D's Red. Green & Yellow 3mm & 5mm - 10p 8mm - 35p2055 fuses 0.15410 106 quick blow - 5p 0.1A to 5A Anti Surge - 8pHigh Speed dolls 0,8mm, 1,0mm, 1.3mm. 1.5mm, 2mm 30p"Expo" "Reliant' drilling machines 12V d.c. with improved 3 -jaw chuck - £7.00Nicads AA - 90p. HP11 - £2. HP2 - £2.20. PP3 C5 Universal chargers for all abovebatteries £6.50Glass reed switches with single pole make contacts - 8p. Magnets - 12p. 0.1" stripboatd2.5' X 1" B rows 27 holes - 25p. 3.75' X 2.5" 24 rows 37 holes - 70p. Ionisers list price06.95 7 year guarantee -Elmo. Jack plugs 2.5mm 5 3.5mm - 14p. Sockets panelmtg. - 10pAll prices VAT inclusive. Postage 30P (free over £51

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Practical Electronics 55

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tuneable 80-135 MHz, 500 metrerange, sensitive electret microphone,high quality PCB. SPECIAL OFFERcomplete kit ONLY £5.95, assembledand ready to use £9.95 post free.Access orders telephone 021 411 1821.Cheques/ P.O.'s to: QuantekElectronics Ltd, (Dept P.E.), 45aStation Road, Northfield,Birmingham, B31 3TE

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PE 100w/ch Moscode Amp. designerapproved kit for £194 inclusive dittowith drilled top panel add £10matching all valve preamp, DCcoupled, passive R.I.A.A., £110inclusive. Hobtek dept P.E.,TheCottage, 8 Bartholomews,Brighton,Sussex,BN1 1HG

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NASDA, Japan's NationalSpace Development AgencyExhibition is on show at theScience Museum, Exhibition Road,London, until the 28th February1992. The exhibition is located onthe Ground Floor in the Explorationof Space Gallery.

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L J56 Practical Electronics

Techniques

R5470k

IC5c.

IC2a 4013 IC2b 4013S

0

k--251 3- Cr.

-R QD

R8100k

IC50 IC5c

+12V

R1410k

lC4a

Continued from page 42switching threshold, the outputgoes to logic 0 forcing the output ofICla to logic 1 and the output ofIC1b to logic 0. This preventstrigger impulses from reaching Ql.

If two chains of lights are to beused the part of the circuitincorporating IC3, Q2 and T2should be added. IC3a is fed fromthe opposite flashing clock phase,so that it produces trigger pulseswhen IC1d does not, and vice -versa.Because it is fed from the oppositeclock phase, the light sensing signalwould hold this output on ratherthan off, if a two -input gate wereused. If preferred, anotherquadruple two -input gate could beused to produce this function byusing several parts of the IC. This isleft as an exercise for the readerwho wants to experiment with it.

Note that a Schmitt trigger gateis needed for IC2c in order toprovide clean switching as the light -level changes. The Schmitt trigger

IC3a

*-DIC4b

gates are used with advantage inthe zero -crossing detector, but if thelight level detector is not required,then ordinary two -input nand gates(4011s)can be used in the zero -crossing detector.

Three -Way SequencerThe circuit shown in Fig. 2 employsmany of the principles of the circuitin Fig. 1. The power supply and thezero crossing triggering of the triacsneed no further explanation. Thesignificant part of this circuit is thesequencer itself, formed from ICI,IC2, IC3a, and IC4. IC1a and b areconnected as a conventional cmosclock generator, as described before.IC2 and IC1c and d are connected toform a two-bit counter whichcounts from 0 to 2. The action ofthis counter is illustrated by thewaveforms in Fig. 3. Also shown onthis waveform diagram are thethree output signals, two of whichcorrespond with the Q(bar) outputs

Fig. 3.

Clock

IC2 pin 2 Qo

IC2 pin 12 Qi

ICI Pin11 Do

IC3 pin 3 (output 3)

L__

1 --

(output 1)(output 2)

10k

V

a

T T

C3

Output 3

0

N

from the 4013.The outputs as shown would

switch each string of lights on fortwo clock pulses out of three. If thewaveforms are inverted, they willswitch each output on for oneclockpulse out of three, giving twooptions for the flashing regime.Exclusive OR gates are used toinvert the signal or simply buffer it,as required, allowing a singleswitch to control the sequence.

A light -level detector is notshown in this design, but one couldeasily be incorporated if desired. Todo this use a 4093 instead of a 4011for IC5, and use the remaining partof IC5 as the light -level detectoritself. Then, use three -input NANDgates (4023s) instead of the 4011sused to control Q1, Q2 and Q3. Thethird input of each gate should beconnected to the light -level detectorto gate off the output.

PipelightThe circuit of Fig. 4 shows a four-way sequencer of a type whichcould be used for a pipelight. It isdesigned to sequence with eitherone output on at a time, or twooutputs at a time. It gives a goodeffect with several strings ofordinary Christmas tree lights,which can be run separately, ortwisted together to give a pipelight-effect. This is much cheaper than acommercial pipelight, looks more


Techniques

0RI10k,

y

SW20

I915

470k

-12V

4

IDOk

R7470k

I00k

-D

+12V

112

104

IC4

104

Dz'

IC5115

attractive as the individual lampsare not obscured by the piping, andis effective mounted in or over awindow, as well as around a tree.

Once again, the power supplyand zero level triggering circuitry isthe same as the other designs. Theoptional light -level detector gatesoff the outputs via an extra set oftwo -input NAND gates which drivethe triggering transistors. It isconvenient to gate off the outputs inthis way because the logic signalfrom the previous stage requires tobe inverted in order to be of thecorrect polarity to drive the outputtransistors. If the light -level detectoris not required, then the commonedinputs of IC9 should be connectedto +12V.

Of course, if the final NANDgates are omitted altogether, thenthe output sequence will consist ofone light or two lights off, ratherthan one light or two lights on. Thismight be preferred if you want thetree brilliantly lit up all the time, butstill with a moving effect.

The heart of the circuit is abinary counter made from two JKflipflops. The signal to the J and Kinputs of the second flipflop can beinverted, either manually orautomatically with a fixed period,via IC2. This makes the countercount down rather than up, toreverse the movement of the

IC4

1C7

108

109

108 109IC8

sequence.The counter is clocked by a

different design of clock generator,using one Schmitt trigger gate. Thisdesign is less widely used than thetwo -gate design, because itsoperating frequency depends moreon the characteristics of the gate. Ifthe switching levels of the gate arenot symmetrical, then the mark tospace ratio of the output will not beeven, either. This effect may beobserved in some units whenautomatic sequence reversing isused. It may be apparent that moretime is spent in one direction thanin the other, though this is not likelyto be considered a seriousdrawback.

Looking at the top row, eitherpin 1 or pin 5 of IC5 is held at logic1, forcing the corresponding outputto logic 0, while the other gatesimply inverts the logic signal fed toits other input. This is re -invertedby IC5c, which has a signal on oneinput and logic 0 on the other, andis then gated together with the zero -crossing signal by IC5d. Thechannels incorporating IC6, 7 and 8work in just the same way.

For the two -light -on sequence,the four counter outputs correspondwith the four channels required. Forthe one -light -on sequence, IC4 gatestogether pairs of outputs to providea signal which goes to logic 0 for

6131k

412V

02

R16jjtk

412V

/5L T17102060

1400t

100n

T21102060

-()Output

010061

100n

Output

L -0Output

one clock pulse out of four. Theselector system described aboveselects either the outputs from IC4or one of the Q or Q(bar) counteroutputs directly.

General CommentsAll of these units are powereddirectly from the mains, so specialcare should be taken when buildingand testing them. Some aspects oftesting can be carried out using alow -voltage power supply, but thezero crossing detector only workswhen the unit is connected to themains.

Note that the zero crossingdetectors have two resistors inseries, going to the live of the mains.This is to avoid damage in case oneresistor momentarily breaks downunder a mains spike.

All the triacs are shown withsnubber networks to protect them.In many cases these will not berequired, but if they are not fittedyou may find that a sequencerwhich has worked very well forsome time will fail soon after beingplugged in at another location. Forexample, though my own mainssupply is normally clean, switchingon and off the fluorescent light in afriend's kitchen will kill anyunprotected triac which happens tobe plugged in at the time.


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SCIENCE AND TECHNOLOGY

Every month we bring you thel_best coverage of the moderntechnical world.

Innovations has all the news of the latestdevelopments, technical features explainthe detail behind the glittering facade oftechnology, while writers such as Barry Fox,Technology Journalist of the Year and Ian Burley, Editorof BT's Prestel Micronet consumer section, analysethe growing role of electronics in everyday life.Finally, for those of you who want personal hands-on experience of design and construction, ourprojects offer entry level designs and advancedchallenges.

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Quiz Results

Barry Fox continued from page 62

Wasted Money?Last year BT spent over £30 million educating thepublic on the last change, with advertisements and over75 million printed leaflets. Brian Haigh, BT's Director ofOperations, wrote to all London subscribers reassuringthem that the change would "anticipate your needswell into the future". Bryan Carsberg said the changewould "provide the extra numbering capacity that isneeded". Despite full knowledge of the 10 digit plan,neither BT nor OFTEL warned that there would beanother change within four years.

Within months of the London change BT hadsecretly scheduled a national change for April 1994 andwas confident that OFTEL would endorse it.

OFTEL acknowledges that the 10 digit scheme wasmade possible by the London change in May 1990,which ended the use of the digit 1 as the first digit ofany national number. The key issue is why BT did notmake a one-step change in London in May 1990,splitting London's 01 code into 0171 and 0181, insteadof 071 and 081 - and why OFTEL did not insist on BTdoing it.

Technically Flawed ExcusesBoth BT and OFTEL claim that there were "technicalreasons" why the London numbers could not beswitched from 01 to 0171 and 0181 in May 1990. Butneither BT nor OFTEL has been able to explain whatthese reasons are. When I asked BT I got a string oftechnically flawed excuses about not being able tointercept wrongly dialled calls.

On the day when the 10 digit scheme wasannounced BT's new Helpline, set up to advise thepublic on the number change, was blaming OFTEL,saying that BT could not make the one-step changebecause OFTEL "had not agreed the ten digit scheme".Earlier this year OFTEL had blamed BT, for not beingsufficiently advanced in its exchange modernisationprogramme to cope with the extra digit.

Everything points to the simple fact that they justdid not think it through. It is now too late to undo thedamage.

Personalised NumbersBut it is not too late to solve a future problem on whichneither British Telecom nor OFTEL has yet formulateda plan. If Lord Young's dream becomes true andeveryone in the UK gets their own personalizedtelephone number, callers will not know whether theyare making a local call to someone just round the corneror at the other end of the country or elsewhere inEurope. They will thus not know how much a call iscosting them until they get their bill.

Answers to Trivia Quiz

la, 2b, 3a, 4c, 5a, 6b, 7a, 8c, 9c, 10a, 11b, 12b, 13b, 14c, 15a,16b, 17a, 186, 19a, 20b, 21c, 22c, 23a, 24c, 25a, 26a, 27c, 28b

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London

Speakers Include:Doctor Patrick Moore,

CBE. Editor -in -Chief. Astronomy Now

Professor Arnold Wolfendale,Astronomer Royal

Professor Sir Bernard Lovell,Jodrell Bank. University of Manchester

Professor Malcolm Longair,Cavendish Laboratory. Cambridge University

Professor Peter Willmore,Department of Space Sciences. Birmingham University

Professor Tony McDonnell,Head of Unit for Space Sciences. University ofKent at Canterbury

Professor Andrew Lyne,University of Manchester

Doctor Heather CouperLeif Robinson,

Editor. Sky & Telescope

Doctor John Mason,Deputy Editor. Astronomy Now

The Venue:Royal Borough of Kensington Town HallHornton Street. London W8 7NX ENGLANDFriday 14th - Saturday 15th February 1992

For details of how to exhibit contact the organisers:Peter Haill & Associates LimitedSuite 75.49 Hallam Street, London.W1N 5LN ENGLANDTelephone: 071-580 2104Fax: 071-323 3891

Sponsored by:

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For a copy of the Conferenceof special accommodationand how to apply for tickets. write to:

The 1992 European AstroFest (Tickets)Intra House. 193 Uxbridge Road.

London W12 9RA ENGLAND

Barry Fox

The Change-overTo Ten DigitsBarry's bug -bear this month concerns the change over in London from 01 to 081/071 andthe predicted change in 1994 for the rest of the country.

If you are one of the 4.5 millionLondon telephone subscriberswho now have to spend money

on changing their stationery orrepainting shop and vehicle signs,for the second time in four years,you will almost certainly be askingthe same question. Why couldn'tthe telephone numbers in Londonhave been changed in May 1990 in away which left them unchanged inApril 1994, when the rest of thecountry changes?

I have been asking that simplequestion for more than a year nowand neither BT nor OFTEL, thegovernment's Office ofTelecommunications, can give me astraight answer. They have comeup with various excuses, but nonehold water.

More Numbers NeededNo-one disputes the need for moretelephone numbers. That is theprice we must pay for the glorious

hen I askedBT I got a stringof technicallyflawed excusesabout not beingable to interceptwrongly dialledcalls."

liberalistion of the last decade. Justtry remembering what it was like inthose dark days before the PostOffice/British Telecom lost itsgovernment monopoly. You couldonly rent a phone, usually with adial; you could only rent ananswering machine, at exhorbitantcost and extension sockets were anoverpriced luxury.

What many people question isthe way the new numbers havebeen liberated. It is apparently withshortsight by both BT and OFTEL.

Even before all telephonenumbers in London were changedin May 1990, British Telecom hadproposed a quite differentnationwide change. Mercurybacked the idea. Now OFTEL hasapproved it. Over the Easterweekend in 1994, 9 digit numberswill become 10 digit numbers.

Going Up To NineAdding an extra digit at thebeginning of all 26 million numbersin the UK (eg 0171 and 0181 in

London) increases the reservoir ofnumbers tenfold and letscompeting services identifythemsleves by the change of justone digit. Initially everyone will getan extra 1, with the digits 2-9available (eg 0271 and 0281) forother services, such as mobile andpaging, in the future.

Giving people closely relatednumbers for home, mobile andpaging equipment comes close torealising the dream of Lord Young.When Secretary of State forIndustry he proposed that everyoneshould have their own personalnumber. Incoming calls would thenfind them anywhere in the UK orEurope.

OFTEL took on responsibilityfor telephone numbering from BTon 1 April 1989. But OFTEL hadbeen aware of the 10 digit plansince 1988 and Professor Sir BryanCarsberg, Director General ofTelecommunications, comissionedOvum Ltd to study it. Ovumreported to Carsberg in July 1989and gave "overwhelming support"for the 10 digit scheme.

Despite this OFTEL let BTdouble its pool of London numbersin May 1990 by changing all the 01codes, to 071 in the inner city to 071and to 081 in the outer half. BTurgently needed extra numbersbecause it was close to the practicallimit of 4.5 million numbersavailable from 01 codes. There arenow nearly 5 million subscribers inLondon. BT could have got enoughnew numbers by changing only halfLondon from 01, but judged itbetter to inconvenience everybodythan be seen to favour subscriberson one side of the Thames or theother.Continued on page 60


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exploring the technology that powers the sun · 4/10/1991 · to universal programming system the...

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