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A Video Distribution Amp to build SILICON CHIP NOVEMBER 2001 ISSN 1030-2662 6 $ 60* INC GST 11 NZ $ 7 50 INC GST PRINT POST APPROVED - PP255003/01272 9 771030 266001 siliconchip.com.au Aaand now, Ladeez ’n’ Genlemen For your listening pleasure . . . Presenting the STAR OF THE SHOW . . . SILICON CHIP’s AUDIOPHILE’S DREAM AMPLIFIER: 100W/channel! .002% Distortion! “Plug’n’play” assembly Superb new appearance! www.siliconchip.com.au How VAF designed their N 2001  1 HiFi Quality PA Speakers ovember soldering solutions FOR QUALITY TOOLS Non-contact voltage testing, 230-1000VAC Fully insulated body Low cost soldering station Safety hand guard TESTER VOLT STICK Light weight soldering pencil Distinguishes between active and neutral TEMPERATURE CONTROL SOLDERING STATION Tip glows bright red when voltage is sensed Fast tip temperature recovery WTCPTD Pocket sized TESTER VOLT STICK Butane gas powered soldering iron and hot air tool VS Temp. controlled from 15 to 60Watts AUTO IGNITION SOLDERING IRON / PYROPEN Diamond patterned nose grip 1000V insulated heavy plastic grips Handle contains approx.1 hour of butane Butane gas refill nozzle WSTA6 Extra long cutter blades Radiused chain grip Crimping die Nut turning hexagonal PLIERS HEAVY DUTY LINESMAN'S MA880 Safety insulated AC1000V conforming with DIN EN 60900, IEC standards Individually tested in water to 10000V Cold impact testing at -40ºC Single material polypropolene handle 620757 ROLA CASE BOX INCLUDING DIVIDERS RC001 This tone and probe kit is used by technicians to identify single conductors in multi pair cables at a cross-connect point or at remote ends The set comprises two main items, hand held volume adjustable probe and high power tone generator WIRE IDENTIFICATION SET 2  Silicon Chip FSET w h e r e quali t y c ou n t s Available with either solid or clear polycarbonate lids and with fixed or adjustable compartments Wattmaster SCREWDRIVER SET AND TEST DRIVER 12 PIECE COMBINATION SPANNER SET WITH HOLDER PRECISION DRILL GRINDER FBS230 Buy online at www.polykom.com, email us at info<at>polykom.com or call us on 1300 365 551 in Australia or 0508-POLYKOM (0508 765-9566) in New Zealand for more details. You may also fax your enquiries on 1300 365 559 in Australia or 0508-FAXPOLY (0508 329 7659) in New Zealand. Sizes: 6-7-8-9-10-11-12-13-14-1517 and 19 mm. Each spanner fits into its own space in the holder, which is provided with a hole for wall mounting. The clear size indications ease finding the right spanner. GERMAN QUALITY MINIATURE HAND TOOLS Environmentally friendly cardboard box with plastic tray for storage PROX-23820 The quiet power house with keyless chuck 0.5 - 3.2 mm. The maximum speed of 20.000 rpm is continuously variable down to 5.000. The spindle runs in a precision ball bearing and is fitted with a lock button. The 20 mm collar fits MICROMOT drill stands and vices. Fitted with a quiet, high quality, specially balanced permanent magnet motor.. Technical Data 5.000 - 20.000 rpm. Maximum power consumption 100 W, 230 V. Length 185 mm. Weight 450 g. Insulated according to class 2 require-ments. Supplied complete with 40 bits and cutters in a durable plastic case. PROX-28472 www.siliconchip.com.au Contents Vol.14, No.11; November 2001 www.siliconchip.com.au FEATURES 6 Defining The Ideal PA Loudspeaker Public address loudspeakers are usually the poor relations in sound reproduction but they don’t need to be – by Philip Vafiadis 12 Virtual Reality At DaimlerChrysler DaimlerChrysler’s unreal world – cutting manufacturing costs and improving car design PROJECTS TO BUILD 20 100W RMS/Channel Stereo Amplifier, Pt.1 This no-holds-barred audio amplifier is rated at 100W RMS per channel and has very low distortion – by Greg Swain & John Clarke 100W RMS/Channel Stereo Amplifier – Page 20. 32 A Neon Tube Modulator For Cars Simple circuit connects to the sub-woofer output and modulates a neon light to the beat of the bass – by Rick Walters 54 A Low-Cost Audio/Video Distribution Amplifier Easy-to-build unit can distribute six channels of composite video (& stereo audio) or three channels of S-video – by Jim Rowe 64 Short Message Recorder & Player You program it with a wave file up to 4s long via your PC’s parallel port and replay it at the press of a button – by Leon Williams Neon Tube Modulator For Cars – Page 32. COMPUTERS 38 Computer Tips AMD Processor Runs At The Wrong Speed; Video Cards & Shared IRQs; Checking Your Email From Another Computer; Getting Rid Of The Log-on Password; ICS & Thin Ethernet Networks; Internet Connection Sharing & Chat Programs; Freesco – A Simple Internet Gateway For Linux SPECIAL COLUMNS 40 Serviceman’s Log Ring every day until it’s fixed – by the TV Serviceman 80 Vintage Radio Video Distribution Amplifier – Page 54. Test instruments for vintage radio restoration, Pt.1 – by Rodney Champness DEPARTMENTS 2 3 53 74 77 Publisher’s Letter Mailbag Subscriptions Form Products Showcase Circuit Notebook www.siliconchip.com.au 88 91 94 96 Ask Silicon Chip Notes & Errata Market Centre Advertising Index Message Recorder/ Player – Page 64. November 2001  1 PUBLISHER’S LETTER www.siliconchip.com.au Publisher & Editor-in-Chief Leo Simpson, B.Bus., FAICD Production Manager Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Peter Smith Ross Tester Rick Walters Reader Services Ann Jenkinson Advertising Enquiries David Polkinghorne Phone (02) 9979 5644 Fax (02) 9979 6503 Regular Contributors Brendan Akhurst Rodney Champness, VK3UG Julian Edgar, Dip.T.(Sec.), B.Ed Jim Rowe, B.A., B.Sc, VK2ZLO Mike Sheriff, B.Sc, VK2YFK Philip Watson, MIREE, VK2ZPW Bob Young SILICON CHIP is published 12 times a year by Silicon Chip Publications Pty Ltd. ACN 003 205 490. ABN 49 003 205 490 All material copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Hannanprint, Dubbo, NSW. Distribution: Network Distribution Company. Subscription rates: $69.50 per year in Australia. For overseas rates, see the subscription page in this issue. Editorial & advertising offices: Unit 8, 101 Darley St, Mona Vale, NSW 2103. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 9979 5644. Fax (02) 9979 6503. E-mail: silchip<at>siliconchip.com.au ISSN 1030-2662 * Recommended and maximum price only. 2  Silicon Chip Kyoto protocols could be met In the campaign for the Federal election to be held on November 10th, Opposition Leader Kim Beazley has committed a future Australian Labor Government to ratifying the Kyoto proto­cols. If this occurred, Australia would be committed to reducing its greenhouse gas emissions to 8 percent above the levels exist­ing in 1990. Now whether you believe in the greenhouse effect and conse­quent global warming or not, Australia should be making a big effort to reduce its greenhouse gas emissions. Apart from any concern about greenhouse gases, Australia really is quite waste­ful in its overall use of energy. Nor do we have to be particularly clever in finding ways to reduce our energy use. In fact, while the USA is commonly thought of as a wasteful nation, in many ways they are much further down the track than Australia in reducing energy use. This is particularly the case with housing design to minimise heat loss and therefore, energy use. If you want instances of this, look at their widespread use of double-glazed and triple-glazed windows, low-E glass, super insulation of walls, roof and floors, air-to-air heat exchangers for central heating and so on. American householders have been forced down this path mainly because of their bitterly cold winters, far colder than anything most Australians could imagine. Even so, it is likely that many new American homes now use less energy over their winters than most Australian homes do in our comparatively mild winters. Nor is our energy wastage confined to the domestic scene. In transport and industry we are also very wasteful and there is lots of room for major improvements. Should we care about energy waste when overall we are doing quite well on the economic front? Well, that’s a stupid question really because energy waste costs each and everyone of us quite a lot of money every year. Overall, I am not sure whether Australia should ratify the Kyoto protocols or not but I am sure that we could get major economic benefits by improving our energy usage. It would not be hard for an incoming government to come up with cost-effective incentives for the housing, manufacturing and transport indus­tries to reduce energy usage. While we are at it, the Government should act to stop any more coal-burning power stations from being built. If any more thermal power stations need to be built, they should run on natural gas – such power stations have much higher thermal effi­ciency than coal-fired stations and they produce far less emis­sions. Gas-fired stations also can be brought on line very quick­ly and do not have to be left running to provide so-called “spinning reserve”. Apart from that, extraction of natural gas is far less environmentally damaging than any form of coal mining. And finally, it really is about time that the Government made a major push to develop large-scale solar power generation in this country. We have the sun and we have the know-how. Let’s push it hard because the future payoffs will be great. Leo Simpson www.siliconchip.com.au MAILBAG Thanks for prize I was delighted to win the WaveTek Meterman multimeter with my August Circuit Notebook item. It is a very welcome addition to my test equipment arsenal. My thanks to SILICON CHIP and Fluke Australia for this great prize. Andrew Partridge, Kuranda, Qld. The magic of PMPO With reference to J. R.’s letter in August’s “Ask Silicon Chip”, I recently noticed a Ghetto Blaster for sale in a discount store. It boasted 120W PMPO! Intrigued, I looked at the back of the machine to discover that it was powered by six D cells. My maths says that 120W from 9V DC (no power factor problems) means 13.3333A, not counting the motors or any losses. The loudest noise would have to be the squeals of pain coming from the D cells. To the manufacturer’s credit, the recommendation was to use alkaline cells but . . . Brian Wilson, Curtin, ACT. Sooper Snooper could be used illegally I am more than just a little disappointed at the lack of legal disclaimer associated with the article on the “Sooper Snooper” in the September 2001 issue. Reference to the Surveil­ lance Devices Act 1999 shows that your article incites, no less than three times, your readers in Victoria to break the law. Nowhere have you made mention that the use of a listening device may be illegal in some states. The three locations I have found are the first line of the introduction, paragraph two and para­graph ten. Specifically, the Surveillance Devices Act states that a person must not knowingly install, use or maintain a listening device to overhear, record, monitor or listen to a private con­versation to which the person is not a party, without the express or implied consent of each party to the conversation. www.siliconchip.com.au Normally a professional magazine, this uninhibited disre­ gard for the legislation of this country is unacceptable. I trust that you will issue a legal disclaimer in your next publication. Ian Stanley-Eyles, via email. Comment: readers building the Sooper Snooper project should be aware of the relevant clauses in the above Act. The full text of the Act can be accessed at: http://www.dms.dpc.vic.gov.au/ Electrical fatalities are not caused by homeowners I’m not sure whether you’ve published the following infor­ m ation before. I recently completed a TAFE course on electrical inspection and testing (course # 5661F – commonly known as the “tag & test” course) here in Wollongong. This entails a 2-day course, where the basic principles of AC power transmission and terminology are taught, along with basic concepts (voltage, current, resistance, etc) and workplace testing and safety pro­cedures were introduced. Part of the course is to learn how to use a ‘megger’ de­vice, in order to perform electrical tests on cables and exten­sion leads. Another part of the course is to actually make (under supervision) a 3-pin extension lead, test it and then ‘tag’ it as safe. The funny thing is, we were told by TAFE teachers several months ago, that once we had completed the course, we could be either licenced by WorkCover or Fair Trading, so that we could independently test equipment. When I recently approached both bodies however, I was told that neither of them had ever heard of any such arrangement. The only licences available in NSW are the full electrician’s licence, or the ‘restricted’ (because it’s still restricted to only the chosen few?) licence which allows certain people to connect/disconnect fixed wiring, as part of what they normally do (eg, plumbing, etc). It looks like the ‘old boys’ club strikes again. What’s the point of training someone to use a megger and a DVM, and then telling them that they can only use an approved test machine (eg, Safe-T-Check) and more to the point, why teach someone how to make up a 3-pin extension lead, if they’re not allowed to do it for a living? Perhaps another pertinent point is that of manufacturing. There must be literally hundreds of people on factory production lines around Australia, making up leads, power supplies and other high-voltage equipment and accessories, that eventually consumers will use. Just how “qualified” is a factory worker to make, inspect and test such equipment and what TAFE course have they done in order to prove their competency in this area? The issue is why can an unqualified factory hand manufacture equipment, that people with years of training and experience are forbidden to work on – even if it is just a part of their hobby? As a result of all of this, I believe that people are being trained to do what some electricians regard as their ‘dirty work’ (tag and test, etc) but those who gain the TAFE competency based ‘statement of attainment’ will in no way be rewarded with any­thing that looks like a licence or permit, that will allow them to operate as independent contractors. We were told very strictly in class, that this course does NOT make us into manufacturers or repairers (we probably can’t even legally repair the 3-pin cord that we made as a class exercise – what a farce!) There were several other startling developments that were revealed to the class during my brief time at TAFE. They were: (1) In 1999, of the 10 electrical fataliNovember 2001  3 ties reported to the NSW Department of Fair Trading, eight concerned licenced electrical contractors, who were careless when working on live power in­stallations (FT report B-15, for January 2000) while the other two concerned non-tradespeople who came into contact with damaged or unsafe equipment (an unearthed fridge and a broken light bulb). (2) The TAFE lecturers, themselves licensed tradespeople, let slip that the whole electrical industry will probably be deregulated over the next three to five years anyway. One of them also men­tioned the industry deregulation in New Zealand. Name supplied but withheld at writer’s request. High current is not problem 50 AMPS, run for the hills, Ma Baker. Peter Raffaelli, what a man! I just loved his letter in the September 2001 issue. Electricians love to tell you that they work with AMPS and that limp-wristed techs work with milli/micro amps. (squeak, squeak). As T. Bradley pointed out in the same issue, working on substa­tions or any other field where high voltages and currents are present doesn’t rate a mention when trying to get approval to do some house wiring. For the record, milliamps can kill you just as easily as amps can. As for Joe Bloggs getting the Active/ Neutral wires around the wrong way, this can be easily explained. People are told that their house wiring is AC. This is only partially true. The Active wire has an AC voltage on it while the Neutral is at the same potential as the Earth wire. If, indeed, your house received a true AC then both wires (active/neutral) would reverse polarity periodically. Then there would be no problems as to which side either wire was placed. This is why the consumer can come un­stuck, through misleading information. I do not think those who want change are for an open-slath­ er approach; just one that is fair. Nobody wants people dropping like flies from being electrocuted. If you looked up the statis­ tics, you would probably find that a large proportion were elec­ tricians. 4  Silicon Chip Peter mentioned the National Restricted Electrical Licence. This amounts to nothing more than being allowed to connect/dis­connect hot water systems. A lot of people, especially electri­cians think (quite wrong­ly) that the Licence gives you the right to put in power points. Just don’t try it as you will be in for a big shock. And a bigger fine. Changing laws can be a time-consuming business. It’s better and quicker just to add a few clauses to the Restricted Licence. They being; Clause 1: The holder can move or add power points, light fit­tings and switch­ es to existing wiring. Clause 2: Builders of kits or any design that incorporates the inclusion of transformers that need to be connected to mains power can do so. There needs to be a minimum amount of knowledge held by the person applying for the Licence; having done and passed Electri­cal Principles 1 and 2. This at least shows know­ledge on the subject. I. Moore, Port Macquarie, NSW. DVD picture quality can be very good I read with some astonishment the letters from Brad Shear­gold and John Richardson in the October 2001 issue. My experienc­es with a Grundig wide­screen (CRT) 100Hz set and an inexpensive Toshiba DVD player have been uniformly superb. Perhaps the Fujitsu plasma display mentioned was set up incorrectly or some experimentation with the DVD player setup menus was needed. I have been delighted with the video (and audio) quality of my reasonably modest setup, viewing 40 or 50 different DVD movies so far. Certainly it has been unnecessary to spend $10,000 on a posh player. I have also watched DVD movies on a large Philips plasma screen elsewhere and was very impressed. If my available budget had been large enough, I would have bought that screen on the spot. As for widescreen TV problems, I will agree that the digi­tal TV broadcasts can sometimes change format at frequent inter­vals but do not find this particularly disturbing as the TV is set to expand the picture to fill the screen. It does this in a nonlinear fashion, with 4:3 pictures expanded most at the left and right edges so that the resultant effect is almost unnotice­ able. The thought of returning to VHS fills me with horror, with its far worse picture quality, though passable sound. I am extremely conscious of picture quality as I regularly enlarge medium format colour negatives to 40 x 50cm and am used to critically assessing the results. It is certainly true that watching a widescreen DVD movie on a 4:3 set is not a fabulous experience. However, use a 16:9 set of even moderate size and the difference is huge. Perhaps I have been fortunate in my choice of TV, player and DVD movies, but it seems unlikely that I would never have encountered any of the problems mentioned in the above letters if such problems were as common as claimed. Ross F. Hall, via email. Videoscope a timely project Thanks for the VideoSCope in the October issue; just the project I’ve been looking for to get my sproutcam (webcam 2 at http://www.woa.com.au) back and operating again. It was a case of forehead slapping as to why I had never thought of that. I even have three old 50mm (1 x 28mm & 2 x 135mm) lens floating with bits of 50mm pipe. Could I put in a request for a PCM-controlled bicycle lighting system? My particular interest is long distance with recharging from hub generators. Terry Collins, via email. “Mantel” vs “Mantle” Thank you so much (once again) for providing us with a “real” Australian electronics magazine. It’s good to see that Jim Rowe and others have joined your team of authors. Sorry to be a bit nit-picky, but would you please tell Rodney Champness (in the nicest possible way, after a large thank-you for his articles on Vintage Radio), that the sort of radio he is referring to is spelled “mantel”, not” mantle”. www.siliconchip.com.au Like mantel clocks, they sit on a mantelpiece. David Pulford, Forestville, NSW. Refinement for Videoscope Thank you for another brilliant project in SILICON CHIP. I am referring to the VideoSCope in the October 2001 issue. I have built it and find new uses for it every day. However, one aspect which could be improved is the camera mounting plate or more specifically, how to fit it into the joiner and get the cable and gland all into position. It is very fiddly and I found I got very frustrated with it until I came up with a brilliant idea. Simply cut or file a groove in the round mounting plate the shape of the cable from the camera. This will allow the camera to be fitted to the plate, cable to be fitted to the camera and protruding from the hole in the mounting plate. This then allows the whole assembly to slip into the joiner with the groove allow­ing the cable to pass, then the gland is fitted and after that the retainer piece is fitted. The accompanying picture shows the modified plate I used. Colin Leonelli, via email. Watch out for fake power transistors I repair audio power amplifiers for a living and have had an unusual problem with five amplifiers over a period of the last six months. They either appear to be unrepairable or will bench test OK and then be returned by the owners with the inevitable comment “It’s the same fault (blown output transistors)”. Because I repair lots of amplifiers, I have a fairly sophisticated test setup which allows me to test them at less than full power to verify operation and to then test them at full power. Three of the five tested OK on the current-limited supply but when a sine wave test was performed with a full load and full power supply voltage, they almost immediately blew the output devices. The other two performed to spec but were later returned as being faulty. It finally clicked. All of these amplifiers used 2SA1302/2SC3281 transistors in the output stages. One of the amplifiers was a hifi unit rated at 50W per channel; considering that these devic­es are rated at 250V VCE, Icmax 15A Pd Max 200W, this is a case of overkill. Removing the previously replaced output devices from the amplifiers and carefully inspecting them found the problem. Even though they are marked with the Toshiba brand, they are not Toshiba devices. Using a straight-edge across the mounting surface it is imme­ www.siliconchip.com.au The Tiger comes to Australia The BASIC, Tiny and Economy Tigers are sold in Australia by JED, with W98/NT software and local single board systems. Tigers are modules running true compiled multitasking BASIC in a 16/32 bit core, with typically 512K bytes of FLASH (program and data) memory and 32/128/512 K bytes of RAM. The Tiny Tiger has four, 10 bit analog ins, lots of 2 digital I/O, two UARTs, SPI, I C, 1-wire, RTC and has low cost W98/NT compile, debug and download software. JED makes four Australian boards with up to 64 screw-terminal I/O, more UARTs & LCD/keyboard support. See JED's www site for data. TIG505 Single Board Computer diately obvious that the mounting base (collector) is concave. When the transistor is mounted to the heatsink, the area where the chip should be is not in contact with the heatsink, hence the failure. But it gets better. The accompanying photo shows two devices with the epoxy removed. The one on the right is the fake. The problem in all five amplifiers was fixed by importing the genuine Toshiba devic­es from the USA. Ian Rumbold, Sound Developments, Melbourne, Vic. Comment: these are the same devices as used in the Ultra-LD amplifier in this month’s issue, so readers should be warned. Use genuine transistors with the Toshiba or Motorola trademark. The TIG505 is an Australian SBC using the TCN1/4 or TCN4/4 Tiger processor with 512K FLASH and 128/512K RAM. It has 50 I/O lines, 2 RS232/485 ports, SPI, RTC, LCD, 4 ADC, 4 (opt.) DAC, and DataFLASH memory expansion. Various Xilinx FPGAs can add 3x 32bit quad shaft encoder, X10 or counter/timer functions. See www site for data. $330 PC-PROM Programmer This programmer plugs into a PC printer port and reads, writes and edits any 28 or 32-pin PROM. Comes with plug-pack, cable and software. Also available is a multi-PROM UV eraser with timer, and a 32/32 PLCC converter. JED Microprocessors Pty Ltd 173 Boronia Rd, Boronia, Victoria, 3155 Ph. 03 9762 3588, Fax 03 9762 5499 www.jedmicro.com.au November 2001  5 Recently Australian speaker designer and manufacturer VAF Research introduced a new high-performance Public Address speaker to its range of highly regarded hifi and home theatre speakers. And they’ve been run off their feet ever since! We asked Philip Vafiadis, of VAF Research, to explain the philosophy behind the design of the I-201 Public Address Speakers. Defining The Ideal Public Address Loudspeaker L OUDSPEAKERS play an impor tant role in a public address sys tem (or for that matter any sound reproduction system) as the final link in the signal processing chain. They convert electrical energy from the power amplifier into acoustic energy in air that travels as sound waves to the listeners. Regardless of the quality of the preceding signal processing chain, if the loudspeakers are of poor quality or incorrectly connected or operated, the result will be poor quality sound. Typically, the performance of loudspeakers is orders of magnitude (ie, multiples to the power of 10) worse than what we would accept from other 6  Silicon Chip audio processing devices. At some time or other, we have all struggled to understand a public speaker in a church or school hall amplified with the typical “column” or horn loaded public address loudspeaker system. In fact, most people have concluded that high-quality vocal reproduction in a reverberant environment is difficult, if not impossible. So what exactly are the requirements for a public address loudspeaker? Well, it must reproduce acoustically the electrical input signal at an adequate level to be heard, without introducing distortion or colouration. The loudspeaker must accurately match the ‘timbre’ of the voice or instrument it is reproducing. The sound should be clear and intelligible for each listener, even though the listeners may be widely dispersed in three dimensions. If used inside an enclosed space, it must do this with the added encumbrance of the superimposed room acoustics. The loudspeaker should not be prone to feedback or howl-around, when used with open microphones. From a practical point of view, it should be small, light and visually unobtrusive. It should be physically constructed in such a way that it can be installed in optimal positions, both www.siliconchip.com.au acoustically and aesthetically. Finally, it must connect and function reliably. There are many methods of converting electrical energy into acoustical energy (including some esoteric ones) but the overwhelming majority of loudspeakers use electrodynamic transducers constructed with voice coils in permanent magnet fields driving a moving diaphragm. Electrodynamic transducers have so far proven to offer the best balance of performance and ruggedness at an affordable price. To achieve the performance ideals listed above, the following areas of loudspeaker system performance are important: ♦ Time Alignment and Source     Coincidence, ♦ Controlled Directivity, and ♦ Stored Energy. Time Alignment and Source Coincidence Currently available electrodynamic transducer technology dictates that a full bandwidth response requires two or more drivers to handle high and low frequency ranges. Therefore, the acoustic output of a loudspeaker system is the sum of the outputs of its individual drivers, which are in physically different locations on the baffle. Because of the displacement between drivers, the acoustic transmission path distance from the listener to each driver’s acoustic centre will be different for each listening position. Therefore, in-phase arrivals of two driver’s outputs can only occur exactly at one point in space for one listener where the path distances are equal (or offset as necessary). Typically, this point will be along the www.siliconchip.com.au loudspeaker’s main axis. Thus, a typical loudspeaker can only be exactly “time aligned” at one point in space. At all other locations it will be time misaligned! This misalignment causes ripple in the frequency response for about an octave either side of the crossover frequency. Unfortunately, this is typically where the ear is most sensitive, in the region from 1-4kHz! The individual driver outputs from a 2-way horn-loaded system at best can only sum properly in one plane and at worst along only one axis. Above and below the vertical axis, the path distances vary significantly between the horn and bass driver and correct reconstruction of the audio signal can not, and does not, occur. Even side to side, the effective path length through the horn can vary enough to cause ripple in off-axis frequency responses. In order to prevent the problem of different path lengths to the listener from each driver in a multi-way system, the drivers’ effective acoustic centres must be coincident. This can be achieved either by coaxial drivers, or by a mirror image array, with appropriate signal processing delays if necessary. Note that either arrangement of drivers in itself does not guarantee coincidence or time alignment! The high-frequency driver in a coaxial design has its terminating acoustic load modulated by the position of the bass driver’s cone, which in turn leads to high levels of intermodulation distortion. Unlike coaxial designs, the high-frequency driver in a mirror image array is decoupled from displacement modulation effects caused by the bass drivers and has low levels of intermodulation distortion. Controlled Directivity So called “high Q” or Controlled Directivity loudspeaker systems are all the rage today. Unfortunately, there are a number of false premises on which this trend has been based. First is the notion of matching the loudspeaker coverage pattern to audience area. In fact, if we reverse engineer the ideal coverage pattern for a loudspeaker in a typical application using a CAD simulation program, it can be shown that normally a conical or slightly elliptical (“squashed” conical) polar November 2001  7 speaker systems is that by definition they have severe discontinuities in their power responses. In other words, they fail to deliver the promise of clearer, more articulate sound. The bottom line is that a “low Q” loudspeaker system will sound more musical and need less equalisation than a “high Q” system. Feedback Stability Margin The I-201 from VAF Research is ideal for live voice or music and works equally well as a front-of-house, foldback, monitor, installed, arrayed or portable system. pattern is normally the best fit. A second false premise is the notion of minimising reflections off nearby walls for improved intelligibility. In fact, reflections in the first 20 milliseconds or so enhance intelligibility and reflections from walls much further away are typically attenuated enough by inverse square law so as not to be significant. A third false premise is the notion of minimising the reverberant energy field in the room, to maximise intelligibility and articulation. In fact, it is generally more significant that the reverberant sound field has even energy against frequency. In other words, articulate, intelligible speech is possible in a highly reverberant room despite the long reverberation time. 8  Silicon Chip For musicality and intelligibility generally, it is important that a loudspeaker system delivers a smooth power response. Power response is defined as the total acoustic power output in all directions against frequency, as opposed to frequency response, which only considers one point in space. Of course, the frequency response is important too but in all directions! Power response can be considered like an average of frequency responses taken in all directions. A smooth power response will mean that the decaying reverberant sound field in a room will more closely match the direct sound field. This is important to achieve a natural sound quality for both voice and music, and actually makes speech easier to understand. The problem with horn loaded loud- It is a commonly held belief that feedback in a sound system is a result of excessive gain at one frequency and can be controlled by reducing the gain at that frequency. And yes, those two statements are true – but there’s more to it than that. Feedback is always occurring in a public address system with an open microphone, because sound reproduced by the loudspeakers will be picked up by the microphone and reproduced by the loudspeakers and around the loop it goes again. Normally the total gain or amplification around the loop is less than unity, so the system remains stable and useable. Essentially, this is because the rate at which sound energy is being added is less than the rate at which it is naturally decaying. If, however, the gain around the loop exceeds unity, then the sound level will build up rapidly, causing the squealing known as feedback. Because of the imperfections of typical sound equipment, there will be a small number of frequencies with more gain around the loop than general and these frequencies will be the ones which “take off” when the system goes into instability. Perhaps surprisingly, these frequencies do not necessarily relate to peaks in the frequency response. The time for www.siliconchip.com.au SPECIFICATIONS Frequency Range ����������������45Hz to 25kHz Frequency Response �����������65Hz to 20kHz (±2.5dB) with grilles Power Handling �������������������For amplifiers to 200W RMS Impedance (nominal) ����������4W Sensitivity ���������������������������95dB (1W <at> 1m) Enclosure type ��������������������35-litre, vented Drivers ��������������������������������2 x 210mm fibreglass cone woofers with 37.5mm aluminium voice coil and synthetic high compliance surround; 1 x 25mm impedance-matched soft dome tweeter with aluminium voice coil. Tweeter protection provided. Crossover ����������������������������Displaced pole third order Crossover Components �������2% tolerance air-cored heavy-gauge inductors; close-tolerance metallised polypropylene capacitors. Crossover Frequency ����������2700Hz Connectors ��������������������������2 x Neutrik Speakon™ 4-pin connectors (in/out). Enclosure ����������������������������Arrayable (90° arc) and stackable, 18mm MDF with internal bracing. Finished in textured black. Black perforated steel front grille. Finish ����������������������������������Matte black. Black perforated steel front grille. Mounting ����������������������������Top hat suitable for 35mm poles. (Other options on request). Dimensions (mm) ���������������640 (h) x 490 (widest point) x 320 (deepest point) Weight ��������������������������������18 kg sound to travel from the loudspeaker to the microphone is typically 5-25 milliseconds, which is a lot of cycles at voice frequencies. In other words, there is plenty of time for the sound energy level to decay during the propagation around the loop – unless a resonant mechanism is at play. Resonances cause energy to linger at specific frequencies, making the system prone to feedback at those frequencies. Sources of resonance (or energy storage) in loudspeakers include, but are not limited to, misaligned crossovers, cabinet panels, dust caps, diaphragm break-up modes, and cavities including those in the horns of horn-loaded systems. Unless well damped, these resonances will be the feedback break points in the system. Eliminating or at least severely attenuating system resonances improves the feedback stability margin to near the theoretical maximum. In practice, this provides more than enough gain before feedback for most applications, even in difficult acoustic environments such as churches, provided good quality microphones are used. Horn-loaded loudspeakers are at a distinct disadvantage in feedback stability margin because of the number of resonant modes supported in a typical horn. Often the assumed gain-before-feedback advantage of controlled directivity is more than traded off because of this. www.siliconchip.com.au Kits without compromise VAF Introducing the VAF Research I-201 Recognising that loudspeakers are by far the weakest link in the public address audio chain today, VAF Research has used CAD (Computer Aided Design) and CAM (Computer Aided Manufacture) techniques to develop a new high-performance public address loudspeaker system, the I-201. It is intended for use as a general purpose PA loudspeaker in small to medium-sized performance spaces. It is ideal for churches, hotels, restaurants, function centres and other live performance spaces. The I-201 can be used for live voice or music, foldback monitoring or recorded program reproduction. Multi-purpose cabinet design The unique cabinet geometry of the VAF Research I-201 lends itself to almost all applications. The ideal angle for a foldback wedge, the I-201 also sits up closer to a side-wall than a traditional trapezoidal design, minimising aesthetic and sight line problems in critical applications. Two I-201s will provide for 180° coverage from a side-wall position and four I-201s form a perfect circle for all-round coverage in a gymnasium, for example. Where additional reach is required, I-201s can be stacked vertically and/or “Sound quality to die for” Rolling Stone Magazine “..A new benchmark in every criteria” Best Buys Home Theatre Speaker Kits without compromise from $312 pr to $8,863 pr FreeCall 1800 818882 www.vaf.com.au vaf<at>vaf.com.au November 2001  9 I-201 HIGHLIGHTS ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ Affordable, multi-purpose arrayable, stackable cabinet design. Works equally well as Front-of-House, Foldback, Monitor, Installed, Arrayed or Portable system. Full-bandwidth design for music reproduction with reduced need for subwoofers. Breakthrough low stored energy design for high feedback-stability margin in reverberant environments. High internal acoustic damping, MDF cabinet construction – not a plastic box! Powder-coated, anti-resonant, dent resistant, curved metal grille. True acoustic time-aligned point source – no electronic processing required. Internal crossover with high-frequency driver protection. Flush, concealed carry handle positioned on centre of gravity for easy carrying. Recessed metal terminal plate with dual linked Speakon™ style connectors. Flush 38mm stand-mount adapter in base of cabinet. 25mm dome high-power tweeter with acoustic dispersion control. Dual 200mm fibreglass long-throw precision bass drivers. the angle between pairs reduced from 90° to as little as 0°. Full bandwidth audiophile quality Unlike other small public address loudspeakers, the VAF Research I-201’s have been engineered to provide strong usable bass for full-range music reproduction. What’s more, the high frequency response extends well past 20kHz in a typical PA loudspeaker fashion! True point source time alignment The I-201’s Vertical Mirror Image Array with time-aligned drivers behaves as a true point source at all frequencies in all directions. The effective acoustical centre of the two bass drivers always remains at the same point as the effective acoustical centre of the tweeter for waves radiated in any di- 10  Silicon Chip rection. Acoustical reconstruction is accurate regardless of polar direction, giving the I-201 the smoothest total power response possible. Feedback The I-201’s are an ideal choice for a very reverberant hall, in spite of their “low Q” design. Combined with reasonable condenser microphones, there will be plenty of loop gain available, even for a quiet talker standing behind a lectern. There are three secrets to this success. First, I-201’s are a low stored energy system, much lower than typical PA designs. Second, typically only one cabinet a side is needed for coverage, which eliminates phasing between boxes and the consequent side lobes. And third, the polar response of the I-201 is very smooth, thanks to unique diffraction control incorporated into the baffle. Pricing The new VAF I-201 is available only direct from VAF Research, in the following forms: ♦ Fully assembled and tested: $1100 each. ♦ Ready to assemble kits where the cabinets are fully built and finished leaving only the final assembly: $940 each. ♦ Ready to assemble kits without cabinets but including cabinet plans: $599 each. Insured freight to most of Australia $30 each. If you buy the I-201 as a kit including cabinets, rather than fully assembled, you will get the same high level of performance as the factory finished version. VAF research can be contacted on FreeCall 1800 818882 or vaf<at>vaf.com.au More information on the new I-201 or other VAF models can be found at www.vaf.com.au SC www.siliconchip.com.au IT'S TRUE. I T ' S H E R E . the one you've always needed. IT'S FAST the most efficient and affordable personal analyser charger from the charger specialist IQ PAC www.siliconchip.com.au  Charges and analyses with capacity display at the same time.  NO overheating.  NO overcharging. IT'S VERSATILE  Three charging rates.  Three discharge rates.  Constant current or pulse charging. IT'S FLEXIBLE  Charge adaptor plate for different battery types. IT'S EASY TO USE  Charges automatically.  Press one button to analyse PREMIER BATTERIES PTY LTD ABN 12 003 149 013 Syd  (02) 9755 1845 Fax: (02) 9755 1354 Mel  (03) 9886 3432 Email: info<at>premierbatteries.com.au Internet: www.premierbatteries.com.au November 2001  11 How DaimlerChrysler is interfacing the real and the unreal VIRTUAL REALITIES Virtual Reality is being used more and more to not only design vehicles but to find the possible pitfalls in manufacture and minimise assembly time and costs. DaimlerChrysler has built a specialist VR facility in Ulm, Germany, where designers and engineers use VR tools to make their work more efficient. 12  Silicon Chip T he Virtual Reality Cometence Centre (VRCC) makes VR tools available to developers at their workstations. Depending on the task at hand, employees can select the required degree of immersion in the visual world they wish to enter. Not only that, they can mix “real” and “virtual” worlds! State-of-the-art facilities at Ulm include:  a PC-operated holobench;  a holostage, a new semi-circular projection which has recently been successfully patented;  a fully-equipped mixed and augmented reality laboratory. Holobench – the technology The holobench, a virtual workbench, comprises a vertical and a horizontal surface onto which projectors display images from behind and from below. The holobench in Ulm is the first of its kind in the world to be operated using “Infitec technology”, which enables stereo-vision through the separate control of the left and right eyes using interference filter technology. The result is a bright, three-dimensional image. It also uses DLP projectors, which give much greater luminous intensity than do tube projectors. The computer filters out the ambient light in the room so that the user can work on the holobench in daylight rather than in a dimmed setting. The VRCC holobench is operated by four PCs, with two more functioning as servers. The latter also carry out collision calculations and determining the position of the user. Research on the virtual workbench Long before the first physical model of a newly developed product is tested, designers need to know whether the individual components can be installed easily and cost-effectively. Such construction feasibility studies can now be simulated to a great extent on the holobench. The engineer puts on a data glove with sensors that measure the movewww.siliconchip.com.au ments of his or her hand. A corresponding virtual hand, which can install or remove virtual components, appears on the holobench surface. Sensors calculate the exact position of the hand in the virtual space. If the electronic hand touches any components, it does not move on any further but a wire-grid hand passes through the part and the point of collision is highlighted in color. As an example of the many investigations the VRCC has carried out, they examined the removal of the alternator from the Chrysler PT Cruiser. The research revealed that in order to remove the alternator quickly and easily, it was necessary to move another component by just a few centimetres. The practical aspect in investigations like this one is that the computer “feels” when contact takes place with another component, even in places where the point of contact is obscured by the image of the component. The software makes the components behave “realistically” by simulating their physical and dynamic properties. This means they can even slip along obstacles, altering their position in the space. In the past, it was only possible to research rigid objects in installation and removal studies. Now, however, DBView — visualisation software developed by DaimlerChrysler — is able www.siliconchip.com.au to automatically calculate the amount of space required for flexible objects such as cables or tubing. One example is vehicle seating that has four different axes of movement. Each variant means that a different amount of space is available in the vehicle. The data comes directly from the CATIA construction system onto the holobench surface. Whereas it was previously only possible to visualise the components, they can now also be altered directly and in real-time. When the collision detection system is in operation, the relevant components are marked – or the virtual seat adjustment does not function to the intended degree. Even a complicated mechanism, such as a moveable steering column, can be manipulated to estimate its behavior when construction alterations are made. Engineers are particularly interested in how much space the steering column can take up in extreme situations. DBView can make this calculation. Another typical use of the holobench is the interactive simulation of deep-drawing processes. The settings of the virtual equipment are controlled via a three-dimensional menu, which is operated by a so-called flying mouse. The sheet metal thickness is represented by different colors before, during and after processing. It is thereby easier to check the stresses acting on the metal sheet during the stamping process. Semi-circular projection + CAVE = HoloStage The VRCC has combined the advantages of semi-circular projection with the advantage of the CAVE. This is a room where the floor can also be used as a projection surface but where only one person has good-quality 3D vision. A semi-circular floor was built into the semi-circular projection area. Projection onto the floor is by means of two projectors and mirrors on the ceiling. The result is a stereo-capable holostage, which was recently successfully registered as a patent. Another feature of the holostage is the tracking system, which allows the observer to see an extremely realistic picture, depending on the angle. No cables or wires are necessary. Six cameras monitor the position of the user. The boundaries between the horizontal floor and the vertical, semi-circular wall are blurred by the computer, which “softly” masks the edges. The observer sees an edgeless, three-dimensional picture on the holostage. HoloStage – factory planning In factory planning it is just as important to consider the movements November 2001  13 people make, as is the correct positioning of the assembly line or the storage of materials. Researchers use a virtual model of a person, which moves around independently within the data field of the semi-circular projection. The starting and finishing positions of a particular route are already given but the number of steps taken or the movements made on the way are generated directly by the computer. Being able to represent or measure routes and distances is only one important factor in factory planning. Another is calculating stresses acting on the spine when an employee has to lift or install a component into a vehicle. These calculations, based on a large amount of medical data, are made on a virtual model to simulate real conditions. HoloStage – robot teaching VR technologies serve not only as output media (ie, to represent computer-generated data) but can also be used to input data. In the case of a robot that installs components or works on a car body in the semi-circular projection area, movements can be planned to the millimetre. To achieve this feat, the robot is taken by the hand, so to speak, by the engineer wearing a data glove. It is then led to the point where a component or tool is to be picked up and then to the point of contact with the vehicle. Carrying out robot teaching in this way is quicker and easier than entering the complex coordinates step-by-step on a computer. The information gained from using virtual models of humans for ergonom14  Silicon Chip ic studies, teaching robots and calculating likely component collisions on the assembly lines helps planners select the optimal factory layout. It is hardly possible to imagine modern, process-optimised factory planning without VR technologies today. Mixed reality/augmented reality The “Mixed-Reality Laboratory” at the VRCC is used to study applications in which it makes sense to combine elements from the real world with images from virtual reality. In this way, it is possible to teach company employees how to undertake complex manufacturing processes long before the launch of a new production series. The user wears a special head-mounted display fitted with a tiny video camera, which supplies images of what is actually happening. These video images are then exactly combined with a virtual image of the part or component under investigation. This perfect “fit” between the video images and the computer-generated image of the virtual component is made possible by the fact that all the real components have been given socalled markers. Markers consist of symbols or numbers on a flat surface, which are registered by the video camera and then transmitted to the computer. They tell the computer the precise angle at which the virtual image has to be positioned. In addition to this combination of images, the user is also provided with further information — in the form of text, graphics or video images — on how to install a component. This might include information on which tool should be used, as well as where to start. It is also conceivable that live images of an instructor could be superimposed. The new technology also has numerous applications in the fields of maintenance, vehicle diagnostics and service. For example, a mechanic is faced with a defect. Equipped with a semi-transparent head-mounted display, he or she is provided with the relevant information about the state of the vehicle. To guide the mechanic, an instructor establishes the precise nature of the problem through a natural language dialog. Images, graphics or arrows pointing to specific vehicle components indicate where the problem might lie. Even in a normal workshop situation, the use of mixed and augmented reality could help combine the usual toing-and-froing between reading the manual and actually working on the vehicle into a single activity and, as such, help cut repair times. Such a system would be particularly www.siliconchip.com.au attractive in remote regions where the workshop may not have a lot of experience on a particular make or model. In such a case, the mechanic or even the driver would be able to obtain direct advice on the nature of the problem. Mobile VR To increase the flexibility of maintenance and inspection routines for large fleets of vehicles, VR technology is also set to become increasingly mobile. A portable video unit strapped to an engineer’s belt will be able to transmit images to the computer. Once there, virtual reality images will be integrated and then sent back to the engineer’s head-mounted display. In such a context, the navigation aids — including hints about the source of the problem or tips on how it could be remedied — are once again set to play a major role. Text information could be superimposed on the images at the appropriate point. Such procedures are likely to result in substantial time savings as well a considerable improvement in quality. On the one hand, there will no longer be any need to consult technical manuals and on the other, the quality of the work can be checked as it occurs. Cockpit ergonomics Although virtual reality can be seen, it cannot be touched or felt. In certain situations, it makes sense to use relatively simple elements in order to create real mock-ups containing all the basic physical components that the user needs to establish a tactile contact with reality. As soon as it is possible to harmonise the virtual and the real worlds in this way, the user is able not only to see objects but also to “grasp” them – ie, touch and manipulate them. As a result, immersion in the world of virtual reality is made all the more realistic. Another task at the VRCC is to examine various vehicle cockpit designs from an ergonomic point of view. This is also an example of what is known as collaborative rapid prototyping. Here, the designer and user work hand in hand. The user sits in a wooden cockpit mock-up, containing instruments positioned according to the designer’s specifications (who sits close by). Via a head-mounted display, the user is supplied with images of both the planned cockpit and the road or www.siliconchip.com.au landscape through which the vehicle is virtually travelling – similar to an aircraft simulator. At the same time, the user can also try out the various arrangements of cockpit instrumentation and displays. With the aid of a data glove, the controls can be moved around or reformed into a different shape. The wooden surface of the cockpit mock-up provides the user with the necessary tactile sensations. The designer is also able to make immediate changes to the cockpit layout during the testing process. As a result, optimal cockpit ergonomics can be achieved more quickly and efficiently. Flow visualisation CAD models are made up of an agglomeration of surfaces. However, the process of vehicle design also makes substantial use of aerodynamic flow data and the flow of air inside the vehicle cockpit. As a rule, flow data is three-dimensional. Here, the complex challenge facing the VRCC researchers was to combine flow data with surface data in one single representation. The idea was to be able to see the effect of various flow patterns, the data for which had been processed in advance by mainframe computers working in overnight shifts. This visualised flow data is mixed with “real” images superimposed via video as well as VR data relating to the vehicle interior. In this way, various design alternatives can be tested. This might involve the impact that the size and shape of headrests have on the supply of fresh air to rear-seat passengers or the effect that the shape and settings of the air vents have on temperature control in the vehicle. VR meetings If VR truly is the intuitive, fully immersive man-machine interface of the future, then it certainly makes sense to extend its scope beyond the current dialog between engineer and computer. In the future, the aim is to use VR in a group context. All the information relevant to product development must be made available over and beyond system and even company boundaries. Indeed, such availability must function along the entire length of the chain. In this way, virtual reality could well help bring the twin processes of product planning and product development together even more. For a graphic example as to what the VRCC researchers have in mind for this exciting new technology, consider the following scenario: Designers and engineers seated around a conference table are discussing the latest version of a component under development. Each person is wearing a special head-mounted display. In the middle of the conference table is a turntable marked with a range of symbols. Each participant sees a virtual image of the component from exactly the same perspective as he or she would were it a real visual experience. The 3D model can therefore be fully visualised, with participants able to discuss the latest stage of component development. Participants do not even need to be in the same room, or even the same country. SC Acknowledgement: Text and photos courtesy of DaimlerChrysler. November 2001  15 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au Special Feature Project . . . Ultra-LD 2 x 100W stereo amplifier Finally, we have produced a rack-mounting version of our ground-breaking Ultra-LD amplifier. It’s taken many months but now it is here. It is rated at 100 watts RMS per channel, at vanishingly low levels of distortion – typically below .002%. It is ultra quiet too and it looks the part. Part 1: By GREG SWAIN & JOHN CLARKE 20  Silicon Chip www.siliconchip.com.au T HE NEW ULTRA-LD Stereo Amplifier incorporates a preampli­fier stage, LED bargraph power meters, fan-forced cooling, gold-plated heavy-duty speaker terminals and a host of internal engi­neering features that make it easy to build. The external finish and presentation Fig.1: the block diagram for the Ultra-LD Stereo Amplifier (one channel shown only). IC1 amplifies the selected input signal and drives a 100W power amplifier stage via volume control VR1. It also drives the LED bargraph circuitry (IC2 & IC3). www.siliconchip.com.au is to a professional standard. This is an ampli­fier that you will be proud to say, “I built this one myself!” If you could buy the equivalent of this amplifier from one of the big name brands you would have to pay lots more dollars and even then you wouldn’t get the extremely low dis- tortion and noise, very high damping factor and so on. Oh, and just a word about overall performance – these days there are lots of Dolby surround sound amplifiers and surround systems which are available at relatively low prices and some have quite high power outputs, up to 100W per channel from five channels. Are these comparable to the Ultra-LD? Let’s just put it nicely. For home theatre they are great value but most are not hifi. The Ultra-LD is a purist’s hifi amplifier. It’s an amplifier for audiophiles; it has no tone controls, no loudness control, no balance control and no switch­ing for multiple speaker systems, all of which can add to distor­ tion and noise. By the way, we’re not alone in adopting this purist con­cept. Take a look at some of the really expensive “audio­phile” amplifiers. Many don’t include tone controls or balance controls, or any other unnecessary features. Instead, the aim is to offer the best possible performance for your dollar and that’s what we’ve done with this unit. It also makes the amplifier delightfully easy to operate – you just switch it on, select the signal source and adjust the volume control to your liking. Design concept The original version of this amplifier was published in the March, May & August 2000 issues of SILICON CHIP. To save kit buyers a lot of money, we presented that version in standard PC tower case. This had the virtues of low cost, plenty of internal space for all the modules, different levels for the power supply and amplifier modules, and even inbuilt shielding for signal wires. All told, it was an effective although bulky package. So why are we now presenting this conventional rack-mounting version? There are several reasons but perhaps the main one is that many readers just did not like the amplifier-in-a-PC-case concept. They reckoned it was ugly, too bulky and pushed the recycling angle too far. Furthermore, the styling clashed with their existing hifi equipment. Still, we were not keen to revisit the Ultra-LD amplifier concept until Altronics recently indicated that they were seriously interested in producing a rack-mounting version. They weren’t so much interested in November 2001  21 the project as a kit but more as an addition to their existing professional equipment. And since it was to be a “professional amplifier” it would need to be substan­tially redesigned to meet new criteria. In essence, the new version of the amplifier would have to be easier to assemble. That meant that all soldered wire connec­ tions to the PC boards would have to go. Instead, all connections were to be made via crimped “quick connects” and board-mounted spade lugs. In addition, Altronics wanted LED bargraphs to match the styling of other amplifiers in their range and wanted us to adapt the design to a custom-made rack chassis which features an integral tunnel heatsink with fan cooling, slotted front panel and so on. All of that meant that we had to redesign the PC boards for the amplifier modules and the loudspeaker muting and protection module, as well as design a PC board for the power supply. In addition, we have incorporated a very low distortion preamplifier based on the Philips 5534 op amp and this incorporates the LED bargraph display circuitry. So there is a new board for the preamplifier, plus another board for the stereo RCA socket pairs on the back panel. The RCA input board and the pre­ amplifier board are connect­ed together using a flat 26-way ribbon cable fitted with header sockets at either end. This eliminates messy wiring to the source switch – you just plug the header sockets at each end of the cable into the matching pin headers on the PC boards and the job is done. All told then, this version of the Ultra-LD has had to be completely re-engineered to suit the rack case and it is now a lot easier to assemble. Even so, this is not a project for anyone new to electron­ics. Apart from having six PC boards to assemble, there is a lot of wiring to run in the chassis. We expect that the average construc­ tor, working carefully, will take around 50-60 hours to build and test it completely. The result will be an amplifier that you can be proud of and one which will deliver superb sound quality for many years to come. Operating features As already noted, the Ultra-LD is a very simple amplifier. On the front panel, it has just two knobs, one for 22  Silicon Chip the input selector and the other for the volume control. Apart from the On/Off rocker switch, the only other features are the LED bar­graphs for both channels and the headphone socket. Plugging in your headphones mutes the speakers via the relays on the muting and protection board. As well as being pretty, the LED bargraphs in this amplifi­er do serve a useful purpose. They display a signal range of 30dB so that as each extra LED lights, it indicates a signal increase of 3dB. When the orange 0dB LED lights, the amplifier is on the verge of clipping and so if the topmost red +3dB LED lights, you know the amplifier is clipping and the volume control should be reduced to give the best sound quality and also to protect your speakers against possible damage. On the rear panel, there are six pairs of RCA sockets, to cater for five stereo inputs (CD, DVD, tuner, etc) and a tape monitor output. The heavy-duty gold-plated loudspeaker terminals can accept the heaviest speaker cables available and while they may look a bit over the top, they are essential in keeping the distortion as low as possible. As in all high-power amplifiers, ventilation and cooling are important. This is achieved using a fan-cooled internal tunnel heatsink for the output transistors. Air flows in through slots in the base of the case and is blown out through slots in the sides – these must be kept clear. By the way, the fan only kicks in for heatsink temperatures above 60°C, so most of the time it will not be operating, keeping noise to an absolute minimum. After all, there’s not much point in having only the smallest whisper of residual noise from the speakers if the fan is noisy. Block diagram Let’s take a look now at the block diagram of the new stereo amplifier – see Fig.1. To keep things simple, this shows only one channel – the other channel is identical. S1 is a 5-position rotary switch and this selects the audio input signal – either CD, DVD, Tuner, Auxiliary or Tape. From there, the signal is fed to a non-inverting op amp stage (IC1) which operates with a gain of 3.6. Its output is fed to the Tape Out socket via a stopper resistor and is also fed to volume control VR1. The output from the volume control has two signal paths. First, the signal on the wiper is fed to a power amplifier which operates with a gain of 16. This then drives the loudspeaker via a loudspeaker protection/muting circuit. It is also fed directly to one side www.siliconchip.com.au of the headphones socket. Second, the signal from VR1 is also fed to IC2 which is a precision halfwave rectifier. It’s output is filtered and then fed to a display driver circuit based on IC3. IC3 in turn drives a 10LED bargraph display. This display operates over a 30dB range and is set www.siliconchip.com.au Above: the Preamplifier & LED Display module mounts vertically on the front panel while behind it are the two Power Amplifier modules, attached to a large tunnel heatsink. On the other side of the heatsink are the Power Supply module, the Loudspeaker Protector & Fan Controller module (mounted on the rear panel), and an RCA input-socket module (mounted upside down at top, left). up so that the top LED in the bargraph indicates signal clipping. OK, so much for the basics. We’ll now look at each of the main circuit modules and describe its operation in some detail. November 2001  23 How It Works: Preamp & LED Display Module This is the prototype Preamplifier & LED Display module. The LED displays operate over a 30dB range and are set up so that the topmost LED (red) indicates clipping. F IG.2 SHOWS the circuit for the Preamplifier & LED Display module. For the sake of simplicity, only one channel is shown – the other channel is identical. The preamplifier section uses a single 5534 low-noise op amp (IC1). As shown on Fig.2, the incoming audio source signals (CD, DVD, Tuner, Auxiliary & Tape) are selected by rotary switch S1 and fed to pin 3 of IC1 via a 150Ω “stopper” resistor and a 10µF bipolar capacitor. Note that the CD input is attenuated by feeding it through a voltage divider before it is fed to S1, so that it more or less matches the perceived levels from other sources. The 150Ω stopper resistor and the 10pF capacitor together form a lowpass filter to eliminate RF interference. Additional RF suppression is provided by a ferrite bead which is slipped over one of the leads of the 150Ω resistor. The 100kΩ resistor on pin 3 of IC1 sets the input impedance and also sets the input bias current for the op amp. IC1 is wired as a non-inverting amplifier and operates with a gain of 3.6, as set by the 4.7kΩ and 1.8kΩ feedback resistors (ie, Gain = 1 + 4.7/1.8 = 3.6). The 10pF compensation capacitor between pins 5 & 8 ensures stability, while the 390pF feedback capacitor rolls off the response above 100kHz. IC1’s output appears at pin 6 and is fed to volume control VR1 via a 10µF capacitor and 100Ω stopper resistor. In 24  Silicon Chip addition, the pin 6 output is fed to the TAPE OUT sockets via a 10µF bipolar capacitor and another stopper resistor (150Ω). The stopper resistors prevent instability by decoupling the output of IC1 from the capaci­tive effects of long cables. Following the volume control, the audio signal is fed di­rectly to the corresponding power amplifier. It’s also fed to pin 2 of IC2 (TL072) via a 220kΩ resistor and 0.22µF capacitor. LED display circuit IC2, D3 & D4 together form a precision half-wave rectifi­er. It works like this: when the input signal swings negative, pin 1 of IC2 goes high and forward biases D3. As a result, the op amp operates with a gain of -1.5 as set by the ratio of the 330kΩ feedback resistor to the 220kΩ input resistor. Conversely, when the input swings positive, pin 1 goes low. D4 is now forward biased and clamps pin 1 to 0.6V (ie, one diode drop) above ground. This effectively disables IC2. As a result, IC2 half-wave rectifies and inverts the nega­tive portion of the audio signal applied to its pin 2. This half-wave rectified signal is then filtered using a 680kΩ resistor and .01µF capacitor and applied to pin 5 of IC3. IC3 is an LM3915 display driver. As wired here, it operates here in bargraph mode (pin 9 tied high) and drives the 10 LEDs in 3dB steps. The 1.2kΩ resistor between pins 7 & 8 sets the display brightness, while the full-scale reading is set to 1.25V by connecting pin 8 to ground. This display circuit operates with a 30dB range and the gain of the precision rectifier is set so that the last LED (+3dB) lights at the point of clipping. Inevitably, this leads to some compromises in the display, since most of the action takes place over the second half of the volume control. At low-to-moderate listening levels, only the bottom two or three LEDs will flash on and off according to the signal peaks. Howev­er, that’s the way it has to be if you want the last LED to accurately indicate clipping. Alternatively, by increasing the gain of the precision rectifier (IC2), we could get more LEDs lighting up at “normal” listening levels. However, the last LED in the bargraph would then come on before the onset of clipping, so the display wouldn’t mean much – it would just look pretty. Power supply The preamplifier and precision rectifier circuits (IC1 & IC2) are powered from ±15V DC supply rails. As shown on Fig.2, half-wave rectifiers D1 & D2 are fed with 15V AC from the power transformer to derive unregulated supply rails of about ±20V DC. These rails are then filtered using 1000µF electrolytic capacitors and fed to 3-terminal regulators REG1 and REG2 to obtain the +15V DC and -15V DC rails respectively. Two 100µF 25VW capacitors are www.siliconchip.com.au Fig.2: the preamplifier and LED display circuit. S1 selects the signal source, while IC1 amplifies the selected signal and feeds volume control VR1. The signal then goes direct to the corresponding power amplifier stage. It also goes to precision half-wave rectifier IC2 which in turn drives an LM3915 LED display driver (IC3). used to filter the outputs of REG1 & REG2. In addition, two 10µF 35VW capacitors are connected between the +15V and -15V rails. These two capacitors provide additional supply www.siliconchip.com.au line filtering and are installed close to the supply pins of IC1 and IC2. IC3 is powered from a 12V rail derived from the Loudspeaker Protector & Fan Controller board (see Fig.5). Note that the LM3915 display circuitry is earthed via a 10Ω resistor, as is the Loudspeaker Protector circuit. This is a precaution to stop induced hum currents flowing in the earth path. November 2001  25 How It Works: Power Amplifier Module The power amplifier modules now feature heavy-duty quick connect terminals, as do all the other modules in the amplifier. Each amplifier module delivers up to 100W RMS with very low distortion. F IG.3 SHOWS the circuit for the two power amplifier mod­ules. It’s virtually identical to the “Ultra-LD 100W Amplifier” published in the March 2000 issue of SILICON CHIP. The input signal is coupled via a 2.2µF capacitor and 1kΩ resistor to the base of Q1 which together with Q2 makes up a differential pair. Q3 & Q4 act as a constant current tail to set the current through Q1 & Q2 and this makes the amplifier insensi­tive to variations in the power supply rails. The collector loads of Q1 & Q2 are provided by current mirror transistors Q5 & Q6. Commonly used in operational amplifi­er ICs, current mirrors provide increased gain and improved linearity in differential amplifier stages. In a conventional direct-coupled amplifier, the signal from the collector of Q1 would be fed directly to the base of the following class-A driver stage transistor (Q8). In our circuit though, the signal from Q1’s collector is fed to 26  Silicon Chip the base of Q7 which forms a cascode stage with Q8. Q9 provides a constant current load to Q8. Q4 does double-duty, providing the base voltage reference for constant current sources Q3 & Q9. A 3.3V zener diode, ZD1, provides the reference bias to the base of Q8. In effect, Q8 acts like an emitter follower and applies a constant voltage (+2.7V) to the collector of Q7 and this improves its linearity. The output signal from the cascode stage appears at Q8’s collector. Note the 100pF capacitor between Q8’s collector and Q7’s base. This rolls off the open-loop gain of the amplifier to ensure a good margin of stability. The output signal from the Q7-Q8 cascode stage is direct-coupled to the output stage. This comprises driver transistors Q11 & Q12 and the four output transistors, Q13-Q16. Actually, it may look as though Q9’s collector drives Q11 and that Q8 drives Q12 but in reality Q8 drives both; the signals to the bases of Q11 and Q12 are identical, apart from the DC voltage offset provided by Q10. Vbe multiplier Q10 is a “Vbe multiplier”. It can be thought of as a tem­ p eraturecompensated floating voltage source of about 1V. Q10 “multiplies” the voltage between its base and emitter, as set by trimpot VR1, by the ratio of the total resistance between its collector and emitter (330Ω + 390Ω + VR1) to the resistance between its base and emitter (390Ω + VR1). In a typical setting, if VR1 is 100Ω (note: VR1 is wired as a variable resistor), the voltage between collector and emitter will be: Vce = Vbe x 820/490 = (0.6 x 820)/490 = 1.004V In practice, VR1 is adjusted not to produce a particular voltage across Q10 but to set the quiescent current through the output stage transistors. Because Q10 is mounted on the same heatsink as the driver and output www.siliconchip.com.au Fig.3: the power amplifier circuit uses differential input pair Q1 & Q2 to drive cascode pair Q7 & Q8. This stage in turn feeds driver stages Q11 & Q12 which then drive the output stages (Q13 & Q14 and Q15 & Q16). transistors, its temperature is much the same as the output devices. This means that its base-emitter voltage drops as the temperature of the output devices rises and so it throttles back the quiescent current if the devices become very hot and vice versa. Driver & output stages Q11 & Q12 are the driver stages and they, like the output transistors, operate in class-AB mode (ie, class B with a small quiescent current). Note the 100Ω resistors connected in series with the bases of these transistors. These act as “stoppers” and they reduce any tendency for the output stages to oscillate supersonically. The output stages are connected www.siliconchip.com.au as compound current feed­back (CFB) transistors. This configuration acts like a very linear power transistor but with only one base-emitter junction rather than two as in a Darlington-connected power transistor. In this circuit, two paralleled power transistors, Q13 & Q14, are connected to NPN driver transistor Q11, while power transistors Q15 & Q16 are connected to PNP driver transistor Q12. The four paralleled 1.5Ω emitter resistors for each CFB transis­tor pair are there to help to stabilise the quiescent current. They also slightly improve the frequency response of the output stage by adding local current feedback. Note, however, that there is no in- trinsic means in the circuit for ensuring even current sharing between Q13 & Q14 and between Q15 & Q16. What current sharing there is will depend on the inherent matching (or lack of it) between the transistors. By the way, we did try the effect of small emitter resis­tors for each of the power transistors but these had the effect of worsening the distortion performance – so we left them out. Note that the current and power ratings of the output transistors are such that even if the current sharing is quite poor, it won’t cause problems. Feedback Negative feedback is applied from the output stage to the base of Q2 via an 18kΩ resistor. The amount of feedback – and therefore the gain – is set by the ratio of this 18kΩ resistor to the 1.2kΩ resistor at the base of Q2. This gives November 2001  27 a gain of 16 (ie, for a non-inverting amplifier, gain = 1 + 18kΩ/1.2kΩ). This means that an input signal of close to 1.8V RMS is required for full power. The low frequency rolloff of the amplifier is partly set by the ratio of the 1.2kΩ feedback resistor to the impedance of the associated 100µF capacitor. This has a -3dB point of about 1.3Hz. The 2.2µF input capacitor and 18kΩ base bias resistor feeding Q1 have a more important effect, with a -3dB point at about 4Hz. The two time-constants combined give an overall rolloff of -3dB at about 5Hz. At the high frequency end, the .0012µF capacitor and the 1kΩ resistor feeding the base of Q1 form a low pass filter which rolls off frequencies above 130kHz (-3dB). An output RLC filter comprising a 6.8µH choke, a 6.8Ω resistor and a 0.15µF capacitor couples the output signal of the amplifier to the loudspeaker (via the relay contacts in the Loud­speaker Protector). It isolates the amplifier from any large capacitive reactances in the load and thus ensures stability. It also helps attenuate EMI (electromagnetic interference) signals picked up by the loudspeaker leads How It Works: Power Supply Module and stops them being fed back to the early stages of the amplifier where they could cause RF breakthrough. The low-pass filter at the input is also there to prevent RF signal breakthrough. Finally, the output of the amplifier is attenuated using a 330Ω 1W resistor and fed to the headphone socket. The loudspeak­ ers are automatically switched off when the headphones are plugged in, by using the headphone switch to disconnect the drive to the relay driver transistors on the Loudspeaker Protector & Fan Controller module – see Fig.5. fully-regulated supply improves the separation between channels. Second, with a class-AB amplifier such as this, the very high asymmetrical signal currents flowing in each half of the output stage cause a distorted signal voltage to be superimposed on the supply rails. By using a fully regulated supply, we avoid the possibility of these signals being fed back into the input stages. Circuit details This easy-to-assemble module provides the ±52.5V and ±55V rails to the power amplifiers. The power transformer leads plug straight into the quick connect terminals on this board. T HE POWER SUPPLY is based on a 300VA toroidal transformer that’s been specially sourced for this amplifier by Altronics. This transformer has six windings: 2 x 35V; 2 x 50V; and 2 x 15V. Fig.4 shows the circuit of the power supply for the ampli­fier modules. There are two sets of supply rails: ±52.5V (nomi­nal) and fully-regulated ±55V. The unregulated ±52.5V rails 28  Silicon Chip feed the class-AB output stages and nothing else. The fully-regulated ±55V rails feed the input stages and the class-A driver stages of the amplifier. So why have we used these regulated supply rails when just about every commercial domestic stereo amplifier uses unregulated supply rails for the whole power amplifier circuit? The reasons are twofold. First, the The power supply circuit for the amplifier modules can be split into two parts. First, the two 35V windings are connected together and drive bridge rectifier BR1. This then feeds four 8000µF 63VW electrolytic capacitors to provide unregulated supply rails of around ±52.5V (at no signal) to power the output stages of the amplifier. The two 8.2kΩ 1W resistors are there to discharge the filter capacitors when the amplifier is switched off. The two 50V windings are also connected together (to give 100V AC centre-tapped) and these drive bridge rectifier BR2 and two 470µF capacitors to derive unregulated supplies of about ±71V. These rails are then fed to positive and negative 3-terminal regulators REG1 & REG2 to derive the ±55V rails. It’s not what it seems At first sight, this may appear like a conventional 3-terminal regulator plus booster transistor arrangement, with the power transistor being slaved to the regulator. But that’s not how this circuit works. www.siliconchip.com.au Fig.4: the power supply module produces ±52.5V (nominal) rails for the class-AB output stages of the power amplifiers, plus regulated ±55V rails for the input and class-A driver stages. Looking at the positive regulator for the moment, REG1 in fact carries all the current, which is only around 40mA, so there is no need for a booster transistor. However, the 3-terminal regulator cannot do the whole job. That’s because its input voltage is about 71V and when the power is first ap­plied, this would appear directly across the regulator, causing it to blow (its maximum input-output differential is only 40V). This is where power transistor Q1 comes into play. When the voltage www.siliconchip.com.au across REG1 exceeds 33V, zener diode ZD2 is biased on via the associated 47Ω resistor. This causes Q17 to turn on and this limits the voltage across REG1 to around 35V or so. The current through Q17 is limited to around 6.5A peak by the three paralleled 15Ω resistors in its emitter circuit. This peak current is very brief and occurs only while the 100µF ca­ pacitor at the output of REG1 is charged up to around 40V. From there on, the LM317 takes over and Q17 switches off. The same process occurs for the negative regulator REG2, with NPN transistor Q18 taking care of the charging current for the associated 100µF output capacitor. Low voltage windings As shown on Fig.4, the transformer also includes two 15V secondary windings. One of these windings feeds two half-wave rectifier circuits on the preamplifier module (see Fig.2), while the other feeds a full-wave bridge rectifier on the loudspeaker protector module (see Fig.5). The rectifier outputs in turn feed 3-terminal regulators to derive ±15V & +12V rails. November 2001  29 How It Works: Loudspeaker Protector & Fan Controller The Loudspeaker Protector module protects the loudspeakers in the event of a catastrophic amplifier failure. It also mutes the loudspeakers at switch-off & switch-on to prevent thumps and controls the heatsink fan. F IG.5 SHOWS the Loudspeaker Protec­tor & Fan Controller circuit. This has several functions: (1) it provides muting at switch-on and switch-off, to prevent thumps from the loudspeakers; (2) it protects the speakers against catastrophic failure in the amplifier; and (3) it provides temperature control for the fan-cooled heatsink, switching the fan on if the heatsink temperature rises above 60°C. The main reason for incorporating speaker protection into an amplifier is to prevent further damage in the case of a serious amplifier fault. In the Ultra-LD amplifier, the main supply rails are ±55V DC. This means that if one of the output transistors fails and there’s no loudspeaker protection, more than 50V DC would be applied to the speak­er’s voice coil. In a nominal 8Ω speaker, the voice coil has a DC resistance of around 6Ω and so the power dissipa­tion would be around 400W until the supply fuse blew. In the meantime, this amount of applied DC power is likely to push the voice coil out of its gap, damaging the voice coil and suspension in the process. And if the on-board supply fuse didn’t blow fairly quickly (a strong possibility since a current of around 8.5A may not blow a 5A fuse straight away), the voice coil would quickly become red-hot and could set fire to the speaker cone material. 30  Silicon Chip This risk applies to any audio power amplifier of more than about 40W per channel. So a loudspeaker protection circuit is a good idea. Circuit details As shown in Fig.5, each channel of the amplifier is con­nected to the NC & NO (normally closed & normally open) con­tacts of a relay. The relay wipers and NC contacts then each respectively connect to the positive and negative loudspeaker terminals. Each channel of the amplifier is monitored for DC faults by a triplet of transistors – Q1, Q2 & Q3 for the left channel and Q4, Q5 & Q6 for the right channel. We’ll just talk about the left channel here, since the circuit for the right channel is identi­cal. In operation, the active signal from the amplifier’s left channel is fed to a low-pass filter consisting of three 22kΩ resistors and two 47µF bipolar (BP or NP) electrolytic capaci­tors. This filter network removes any audio frequencies and just leaves DC to be monitored by the three transistors. This is done because we don’t want audio signals to trip the protection cir­cuit. The low-pass filter output is connected to the emitter of Q1 and to the base of Q3. Q1 monitors the amplifi­er output for negative DC signals while Q3 monitors for positive DC signals. Q3 turns on if a DC signal of more than +0.6V is present. Similarly, Q1 turns on if a DC signal of more than -0.6V is present on its emitter. This, in turn, pulls Q2’s base low and so Q2 also turns on. Q2 & Q3 have a common 56kΩ collector load resistor (R1) which normally feeds base current to Q7. If the headphone socket switch is closed, this means that Q7 normally is on. And that means that LED1, Q8 and relays RLY1 & RLY2 are also on. However, if Q1 or Q3 is turned on by an amplifier fault condition, Q7’s base is pulled low and so Q7, Q8 and the relays all turn off, disconnecting the speakers. Diodes D5 & D6 protect Q8 by quenching any back-EMF spikes that are generated when the relays are switched off. Q4, Q5 and Q6 monitor the right channel of the amplifier and they switch Q7, Q8 and the relays in exactly the same manner. The relays selected for the job have contacts rated at 10A and there are two reasons for this. First, we want the contact resistance in the relays to be as low as possible so that it has negligible effect on the amplifier’s per­formance, in respect of distortion, damping factor and so on. Second, the relay contacts have to pass and break the heavy DC currents which would otherwise flow through the loudspeaker if a fault occurs in the amplifier. Note that we don’t merely use the relays to disconnect the ampliwww.siliconchip.com.au Fig.5: each channel of the amplifier is monitored for DC faults by three transistors – Q1, Q2 & Q3 for the left channel and Q4, Q5 & Q6 for the right channel. If a DC signal is detected, Q7’s base is pulled low and this turns off Q8 and the relays. Another function of this circuit is to turn off the loudspeakers when the headphones are plugged into the head­phone socket. When this happens, the normally closed contacts (pins 6 & 7) in the headphone socket are opened and this removes the drive to Q8. As a result, Q8 turns off and so the relays also turn off and disconnect the speakers. open and Q9’s base is pulled high by a 2.2kΩ resistor. This turns Q9 on to run the fan. The fan is fed via a 22Ω 5W resistor so that it does not run at full speed. This makes it quieter but it still pumps a fair amount of air through the tunnel heatsink. When the heatsink subsequently cools down to around 40°C, the thermal cutout closes again and the fan is switched off. Note that 40°C is relatively cool, so the fan will usually run for a long time after it comes on. At normal listening levels, the heatsink only rises a few degrees above ambient and so the fan should rarely (if ever) come on. And even if it does, it operates so quietly that you won’t be aware that it is running. Fan control Power supply Temperature sensing for the fan control is based on a 60°C thermal cutout which is bolted to the centre of the main heat­sink, between the two power amplifiers. This thermal cutout controls transistor Q9 which in turn switches the fan on and off. The thermal cutout has a set of normal­ly closed contacts and so Q9’s base is normally low. This means that both Q9 and the fan are normally off. However, if the heatsink temperature rises above 60°C, TH1’s contacts Power for the Loudspeaker Protection circuit is derived from a 15V AC winding on the power transformer. This feeds a bridge rectifier (D1-D4) and the resulting 20V DC rail is then filtered using a 1000µF capacitor and fed to 12V 3-terminal regulator REG1. Finally, the regulated +12V rail from REG1 is filtered using a 10µF capacitor. This rail powers the Loudspeaker Protector board, as well as the LM3915 display drivers and the LED bargraphs SC on the preamplifier board. fier’s output from the loud­speakers. If we simply did this, it’s possible that the contacts would just arc across and so the heavy DC current would continue to flow through the loudspeaker. That might seem unlikely but when you have a heavy DC cur­rent and a high DC voltage pushing it along, it can be quite hard to break the circuit. This problem is solved by shorting the moving relay contacts to the loudspeaker ground lines (via the otherwise unused NC contacts) when the relays turn off. This diverts the arc current to chassis and ensures that the fuses blow on the amplifier. tection circuit, the relay opens within less than 0.5s and this prevents any turn-off thump from being heard. Muting delay The muting function is achieved using resistors R1 & R3 and capacitor C1 (220µF). When power is first applied, C1 is discharged and so no base current can flow to Q7 via R1. C1 then charges via resistor R3 (220kΩ) until, after about three seconds, enough voltage is present to allow base current to pass via R1 to Q7. This turns on Q7 which then turns on Q8 and the relay to connect the loudspeakers. If power is removed from the prowww.siliconchip.com.au Loudspeaker switching November 2001  31 A New Neon T for your nex O ur last neon tube modulator for cars (SILICON CHIP May 1997) proved quite popular, but what do you do if you don’t have a sub-woofer output from your stereo system to drive it? This latest version solves that problem. As well, the original unit turned off the neon tube for each bass beat but some readers wanted the neon to fire on the beat. This unit can do both. Oh! You do have a sub output on your system but you’d like to use this updated circuit? No worries, just omit three capacitors and off you go. How it works As you can see from the circuit (Fig.1) and photograph of the PC board there isn’t a lot to it. One IC, three transistors, a couple of diodes and a small handful of resistors and capacitors and its done. The Left and Right channel inputs are fed via a 0.47µF electrolytic capacitor to the inverting input of IC1a and they appear at the output, pin 1, as a summed inverted signal. The 0.47µF capacitor along with the 10kΩ input resistor value form 32  Silicon Chip a single-pole high-pass filter; the response will roll off at 6dB/octave below 33Hz. Trimpot VR1 controls the gain of IC1a over a 16:1 range from 0.33 to 5.3. The non-inverting input, pin 3, is connected to the 6V rail and this voltage is propagated through IC1b to the base of Q1. IC1b is configured as a 2-pole lowpass filter set to roll off at 150Hz. Its response, together with the 33kΩ resistor at its output and the .047µF capacitor, give a flat response from by Rick Walters very low frequencies up to 150Hz where the output is 3dB down. The response falls at 18dB per octave above this frequency. Thus the frequencies at the base of Q1 are predominantly those above 20Hz and below 200Hz (see filter response Fig.5). If you wish to use the circuit in conjunction with a subwoofer, you do not need the low-pass filter based on IC1b. The easiest way to eliminate this filter is to simply leave out the three capacitors (0.1µF, .047µF and .022µF) associated with it, although it will make very little difference to the display either way. With the DC level at the base of Q1 being in the vicinity of +6V and its emitter also at +6V, it will normally be turned off, but any signal with an amplitude above 6.6V will turn it on. Our bass beat note does just that for us. IC1c and IC1d are wired as a monostable (one stable state). With no input signal, pin 13, the inverting input of IC1d, sits at about 5V due to the voltage divider action of the 120kΩ resistor to 6V and the 470kΩ resistor to ground. As the inverting input is at a lower voltage than the non-inverting input (pin 12), the output, pin 14, will be near 12V. The 47kΩ and 82kΩ resistors hold the inverting input of IC1c at +7V which ensures that its output, pin 8, is near ground. Each of these outputs is connected to the base of an N-channel FET (Field Effect Transistor) via a www.siliconchip.com.au Tube display xt soundoff! soundoff! 4.7kΩ resistor to hold it either normally on (Q2) or normally off (Q3). Thus the neon tubes connected to pin 2 on the output connector will normally be illuminated and those connected to pin 3 will normally be extinguished. When the base of Q1 is taken more positive than the emitter it will turn on and the collector voltage will fall from 12V to 6V. This 6V negative step will be transferred to pin 9 of IC1c, via the .01µF capacitor, and pull it down from 7V to 1V, thus causing pin 8 to rise to near 12V. This will turn Q3 on and also raise pin 13 of IC1d from 5V to around +17V, via the .082µF capacitor. Thus its output will fall to ground and Q2 will turn off. The capacitor at the collector of Q1 will rapidly discharge but the potential at pin 9 will remain near 0V as pin 14 is now also close to 0V. The outputs will stay in their triggered (unstable) states while the .082µF capacitor slowly discharges. When the voltage at pin 13 falls below 6V pin 14 will revert to its high state (12V), causwww.siliconchip.com.au ing pin 9 to revert to 7V and thus pin 8 will fall to 0V (the original stable state). This time delay is set by the .082µF capacitor and the parallel value of the 120kΩ and 470kΩ resistors. Diode D2 and the 68kΩ resistor hold the base of Q1 high, keeping it turned on and preventing any audio signals from re-triggering the monostable. To enable you to test the PC board without any neon tube being connected we have provided a LED to mimic the tube’s response. It is wired in parallel with the normally on neon The unit doesn’t have a case: we left that part up to you because every installation will be different. Some may simply heatshrink the PC board and conceal it under the dash with some cable ties to hold it in place. November 2001  33 Fig.1: the complete circuit has just one IC, three transistors, a couple of diodes and a small handful of resistors and capacitors. LED1 is not shown on this circuit: see the wiring diagram. tube and it should light when power is applied to the PC board. A small terminal strip has also been fitted to the board edge to allow easy connection of the battery, the LED and the neon tube leads. Putting it together The first step is to check the copper pattern on the PC board against the magazine artwork, looking for bridges between tracks or cuts in the tracks. While such defects are unusual in commercially made boards it is easier to check for such before the PC board is assembled. The next step is to fit and solder the resistors and diodes. Use a multimeter to check the resistor values as sometimes, depending on the body colour, the band colours can be very difficult to identify. Follow with the IC socket (if used) or the IC. Ensure pin 1 faces towards the Zener diode. Now add the trimpot, the capacitors and lastly, the terminal strips and FETs. Solder three wires, two for the audio inputs and one for the earth, to the PC stakes. That completes the PC board assembly. We have deliberately not mounted the PC board in a case because every installation will be different. In most cases, we imagine the board will be “hard wired” into the car’s electrical system, in which case the board could simply be heat-shrunk and secured up under the dash with a cable tie. On the other hand, some constructors may wish to mount the board in a case (perhaps for portability), complete with RCA or similar sockets for the input. We’ll leave this side of it completely up to you. Testing it. Connect the LED anode (longer lead) and cathode to the second and fifth terminals on the terminal strip. Connect the positive 12V lead either from a power supply or car battery to the seventh terminal and the negative lead to the first. Connect an audio source to the input – just one channel is fine for testing. The best source of audio is a tape recorder or CD player because when you (shortly!) connect the neons up, you’ll probably find the RF interference they generate will obliterate any nearby radio signal! 34  Silicon Chip www.siliconchip.com.au Fig.2: the component layout on the PC board. The position of the LED shown here is in the “normally off” position – moving the cathode to terminal 2 should make it normally on. While listening to the music adjust the trimpot until the LED flickers off in time with the beat. You’ll need a reasonable amount of level to make the circuit work – if the LED stays on (ie, doesn’t flicker) wind the wick up on your stereo and/or set the pot at its maximum. You may have to reset this control to accommodate the different input level when you fit it in your vehicle. For comparison, here’s a same-size pic of the completed PC board, with the pattern shown below. If you swap the LED over to the fourth and fifth terminals, the LED should be flickering on (as distinct from flickering off) in time with the beat. Finally, the LED can be removed or it can be left in circuit – it doesn’t matter either way. If you wish to dress it up with a bezel, it Parts List – Neon Tube Modulator 1 1 2 1 2 1 PC board coded 05111011, 75mm x 46mm plastic box 59 x 109 x 34 (Jaycar HB-6025 or equivalent) RCA chassis mounting sockets 3-way terminal strips (Jaycar HM-3173 or equivalent) 2-way terminal strips (Jaycar HM-3172 or equivalent) neon tube (pair), Jaycar ST-3130 (red) or ST-3134 (blue) and/or ST-3138 bicolour neon tube 2 5mm x 3mm threaded spacers 2 3mm x 8mm countersunk bolts 2 3mm nuts Semiconductors 1 LM324 quad op amp (IC1) 1 BC338 NPN small signal transistor (Q1) 2 MPT3055E N-channel MOSFETs (Q2, Q3) 1 1N5404 3A diode (D1) 1 1N914 small signal diode (D2) 1 3mm or 5mm red LED (LED1) Capacitors 2 100µF 25VW PC mounting electrolytic 1 0.47µF 25VW PC mounting electrolytic 1 0.1µF MKT polyester 1 .082µF MKT polyester 1 .047µF MKT polyester 1 .022µF MKT polyester 1 .01µF MKT polyester Resistors (0.25W, 1%) 1 470kΩ 1 120kΩ 1 82kΩ 2 33kΩ 2 10kΩ 1 6.8kΩ 1 1kΩ 1 50kΩ trimpot (VR1) www.siliconchip.com.au 1 68kΩ 2 47kΩ 1 36kΩ 2 4.7kΩ1 3.3kΩ1 2.2kΩ could make a neat dashboard indicator, showing the pulses the neons are working to! Won’t work! If it doesn’t appear to work, the first check is to make sure that you actually fitted the LED with the correct polarity. The LED should be lit when across terminals two and five. Shorting the drain of Q2 to its source should cause the LED to light. If it does not, either the LED is faulty or in backwards. Once you get the LED to light with the short it should stay lit with the short removed. Check that the voltages on pins 9 and 13 are as shown on the circuit. If this is not the case, check each resistor value around IC1c and IC1d and check your soldering. Once the monostable is working you can check the audio with a multimeter set to read AC volts. Table 1: CAPACITOR CODES Value IEC Code EIA Code 0.1µF   100n   104 .082µF  82n  823 .047µF  47n  473 .022µF  22n  223 .01µF  10n  103 November 2001  35 The circuit was originally designed to run with this Neon Tube set from Jaycar. Its wiring is shown below (fig.3). Again, moving the black lead from the No 3 terminal to the No 2 terminal turns the neons from normally on to normally off. If you wish to use the Jaycar ST-3138 Neon (photographed below), you’ll need to open up the case and make a modification – adding an extra wire, as shown in the photo at the bottom of the page. Fig.4 shows the wiring to the PC board. Starting at the audio input and tracing through the circuit, pin 1 of IC1a should typically have a signal of around 1VAC with a normal input and VR1 fully clockwise and depending on the program material, a slightly lower voltage at pin 5. The same voltage should be measured at pin 7 of IC2b and a little less at the junction of the 33kΩ resistor and the .047µF capacitor. As long as you get a reading at each point you need not worry too much about the exact value. Careful checking of your work should show up the problem. The board is capable of driving 8-10 ST-3130/4 neon tubes so you can wire some normally on and others normally off to get the exact effect you want. Go out and knock them out at your next sound-off. For the serious car buff! While browsing the Jaycar catalog looking for the part number for the above tube we came across another one that intrigued us, the ST-3138. 36  Silicon Chip The extra wire (blue) is soldered to the switch in the position seen here. See the text for a more detailed explanation. It features a 3-position switch which can select colour 1 (C1), colour 2 (C2) or fade from colour 1 to colour 2 and back, on a continuous basis (CC). While the fade function didn’t work very well on our sample, our idea was to have one colour selected and let the beat change it to the other colour, then after the delay the tube would revert to the first colour. You will have to be a bit adventurous if you want this type of display as the tube’s electronics are in a sealed plastic case. A hobby knife www.siliconchip.com.au around the edge soon had the lid off. Our unit had two wires, one red, one white joining pads on the PC board to the switch. The red wire went to the position on the switch marked C2. By selecting C1 this red wire was grounded. Selecting C2 switches to the pink neon colour which changes to blue when the red wire is grounded. Just what we need! The cigarette lighter plug was chopped off and the striped black lead run to the battery supply (terminal 2). The plain black lead was connected to the battery negative (terminal 7) along with the battery lead. A wire was soldered to the red wire termination and taped to the black fig.8 lead. It was terminated on the normally off terminal (6). This is all shown clearly in the photograph. There is no reason why you can’t Table 2: RESISTOR COLOUR CODES    No.  1  1  1  1  2  1  2  2  1  2  1  1  1 Value 470kΩ 120kΩ 82kΩ 68kΩ 47kΩ 36kΩ 33kΩ 10kΩ 6.8kΩ 4.7kΩ 3.3kΩ 2.2kΩ 1kΩ 4-Band Code (1%) yellow purple yellow brown brown red yellow brown grey red orange brown blue grey orange brown yellow purple orange brown orange blue orange brown orange orange orange brown brown black orange brown blue grey red brown yellow purple red brown orange orange red brown red red red brown brown black red brown mix and match both types of neons. The main limitation is the current capacity of D1 (3A maximum). By AUDIO PRECISION 2HD-FREQ AMPL(dBr) & LEVEL(dBr) vs FREQ(Hz) 10.000 05 JUN 100 10:00:03 5.0000 0.0 -5.000 -10.00 -15.00 -20.00 -25.00 -30.00 20 100 1k 5-Band Code (1%) yellow purple black orange brown brown red black orange brown grey red black red brown blue grey black red brown yellow purple black red brown orange blue black red brown orange orange black red brown brown black black red brown blue grey black brown brown yellow purple black brown brown orange orange black brown brown red red black brown brown brown black black brown brown connecting the positive leads of the neons to the battery positive terminal instead of through the diode, the limitation becomes the voltage drop across each FET. With an on resistance (RDSon) of 0.15Ω you can safely draw 2-3A through each FET without a heatsink. With a decent heatsink you could probably double this. We measured the current consumption of the samples and found that the pair of ST-3134 tubes drew 250mA and the bicolour tube drew 130mA on pink and 90mA on blue. Armed with this information you can figure out your display requirements and how you will have to wire SC the tubes. Fig.5: The filter gives a flat response from very low frequencies up to 150Hz where the output is 4dB down. The response falls at 18dB per octave above this frequency. Thus the frequencies at the base of Q1 are predominantly those above 20Hz and below 200Hz. UM66 SERIES TO-92 SOUND GENERATOR . THESE LOW COST I.C.’S ARE USED IN MANY TOYS, DOORBELLS AND NOVELTY APPLICATIONS   1-9 $1.10 10-24 $0.99 25+ $0.88 EACH INC GST www.siliconchip.com.au November 2001  37 COMPUTER TIPS AMD 1GHz Processor Runs At The Wrong Speed Q I am building the “PC To Die For” as described in the June & July issues of SILICON CHIP and I have an AMD A1000AMT3C (1GHz) processor and an Asus A7V­133C Rev 1.05 motherboard with Rev 1005A BIOS. In jumper-free mode the BIOS is incorrectly reporting a 750MHz processor. I have visited the Asus website and have noted that numerous people are having the same problem but very few suggestions on how to rectify it. I was wondering if you were aware of this problem and/or any remedies. I am loathe to tackle the jumper settings as I do not know the FSB (front side bus) frequency, multiplier and core voltage settings for this processor. (N. E.) Your 1GHz Athlon processor has a 266MHz front side bus (FSB), as opposed to the lower-specced version which runs with a 200MHz front side bus This means that you have to change the “CPU Frequency” setting in the system BIOS from 100MHz to 133MHz. To do that, go to the “Advanced” menu screen in the system BIOS (see page 16 of the July 2001 issue) and change the “Operating Frequency Setting” entry from “Standard” to “User Define”. This done, you can then change the “CPU Frequency” A Video cards & shared IRQs Q I am experiencing problems with a Via chipset mother­board-based PC. When running programs that use the soundcard, it can crash. The TNT2 M64 video card and the soundcard both share IRQ11. I have IRQ 5 free and tried to reassign one of the cards to that IRQ. However, when I de-select “automatic settings” to allow me to edit the IRQs and memory addresses, Windows tells me that I cannot change the setting. If this IRQ “conflict” is the source of my problems, how can I get around it? On my other PC, a Gigabyte-based PC, IRQ 11 is shared with the same type of video card and a Realtek network card (install­ing the network card on the other PC is what started a whole raft of seemingly unresolvable problems). Any suggestions that can help me eliminate this problem will be appreciated. If the IRQ sharing is causing a conflict, how do I get around it? (M. T.) It sounds like you’re using the first PCI slot on both PCs (note: subsequent feedback indicated that this was indeed the case). Many motherboards force the AGP (video card) slot to share an IRQ with the first PCI slot but video cards often don’t like sharing an IRQ. If you have a soundcard or network A ICS & thin ethernet networks Q I have been following your articles on home networking for sometime and found them very helpful. The December 2000 issue covered shared internet connections for star topology home net­works. Is it possible to use Windows ICS for daisy-chain topolo­gy; ie, thin ethernet 75-ohm coax, BNC home networks? (G. M.) Yes, you can use ICS with a 75-ohm coax (10-Base200) network. You set it up in exactly the same way as for a star network. It’s the networking protocol (ie, TCP/IP) that’s important here, not the network topology. A 38  Silicon Chip from 100MHz to 133MHz. The “CPU Clock Multi­plier” setting should be 7.5 (ie, 7.5 x 133 = 1000, or there­abouts). That’s it – you can let the system auto-detect the Vcore (core voltage) for the processor. You don’t have to play around with jumpers on the motherboard and indeed it’s preferable not to unless you are very experienced. The reason your system is currently limited to 750MHz is because the Standard setting locks the bus frequency to 100MHz and, in addition, the CPU has its multiplier locked (to 7.5 in this case) – ie, 7.5 x 100 = 750MHz. card plugged into the first PCI slot, try moving it to another slot (eg, slot 3 or 4). That way, the card should grab one of the free IRQs. In fact, it’s always best to leave the first PCI slot free if you are using an AGP video card, to avoid IRQ conflicts. The first PCI slot is used only if you don’t have an AGP video card (or if the card is happy to share). If you are using Windows 98/Me, make sure that you have PnP OS enabled in your system BIOS. Also, don’t assign fixed IRQs to any of the PCI slots – set this to Auto instead and don’t reserve any IRQs for legacy devices (unless you have ISA cards). By the way, it’s standard practice under Windows 98/Me to remove the relevant drivers (in Device Manager) before removing an item of hardware, even if you are only moving it from one PCI slot to another. Don’t do too much at once. Get the system working with the video card first and make sure it’s stable. Then add the sound card and make sure this is working before installing the network card. It’s also a good idea to download and install the latest Via 4-In-1 drivers since your motherboard has a Via chipset, plus any driver updates for your sound card. www.siliconchip.com.au Checking your email from another PC Q I’m having trouble with my com puter and am unable to access my email. Therefore, I am trying a friend’s computer. Is it possible to access my email account from a remote computer and if so, how? (L.S.) Provided your ISP supports this facility, the easiest way to access your email from a remote computer is to point the web browser to www. mail2web.com (ie, using Internet Explorer, not the email client). Enter in your email address and password when prompted and the site will list all the emails in your POP3 mail­box. You can then down-load these, read your mail and even delete mail from the POP3 box. Another way is to create a new email account on your friend’s computer. By doing this, you will be able to dial into his/her ISP in the normal manner and retrieve mail from your ISP’s POP3 mailbox. Assuming that A you’re using Outlook Express, click Tools, Accounts, Mail, Add and follow the wizard to set up the account. You must enter your ISP’s mail server address for the POP3 server but the SMTP server and any other settings should be the same as that used by your friend. Of course, you must use your own name and email address where required. Another method is to set up an additional dial-up connec­ tion on your friend’s machine, so that you can connect to your own ISP. To do this, double-click My Computer, double-click Dial-Up Networking, double click Make A New Connection and follow the wizard to set up your Internet account and email exactly as you originally did for your own machine. When setup is completed, an additional dial-up icon will appear on the desktop and you can then choose which ISP you want to dial. Getting rid of the log-on password Q I recently decided to network my two computers so I bought two identical network cards at a computer swap meeting, together with the necessary cable and fittings. I fitted the cards, ran the cable, then installed the network on the Win95 machine. It worked like a charm – Windows 95 found the network card, installed the necessary drivers or whatever, then told me it was ready to go. Only prob­lem is that now I have to enter a *!<at>? password every time I boot the machine! (J. L.) No, you don’t have to do that. If you specified a pass­word when you set up the networking, simply change A it to no password by double-clicking the passwords icon in Control Panel, then clicking the “Change Windows Password” button. Enter your old password, leave the “New Password” and “Confirm New Password” fields blank and click OK, That done, double-click the Network icon in Control Panel to launch the Network configuration dialog box. Click the down button for the “Primary Network Logon” and choose “Windows Logon” from the list. When you reboot – voila! – no more *!<at>? password required (note: you may have to reboot twice – once for the changes to take effect). Freesco – A Simple Linux Internet Gateway Looking for a simple Internet gateway to share an Internet connection? Then take a look at Freesco available at http://www.freesco.org Freesco is a single diskette (1.44Mb) Linux Internet Gateway with all the necessary bells & whistles (runs in less than 6Mb RAM and includes DHCP, NAT, named and telnetd). I run it on an old Pentium P75 with 16Mb of RAM & 56Kb modem and it supports my five workstations running a variety of Internet application simultaneously – Stephen Wright, VK2KHA. www.siliconchip.com.au Connecting drives to the Asus A7V-133 motherboard Q I enjoyed the article on “A PC To Die For” but changed some of the components for my PC (although it’s basically the same). If I understand it right, the Asus A7V-133 motherboard has two IDE controllers: Via and Promise. Does this mean that I can run both of my CD drives as master units (one on each controller), rather than as master and slave? I currently have the burner drive as the master and the CD-R as the slave. The hard disk drives (HDDs) are master/slave. (N. L.) Yes, you can run both CD drives as masters – just put one as master on the primary IDE port and the other as master on the secondary IDE port. In fact, this is the way to go if you want to copy to a CD-ROM burn­er. The two hard disk drives can be run from the Promise Ultra ATA100 ports. You can either run them as master/slave as you have done or, better still, run them both as masters – one on each port. A Internet Connection Sharing and MIRC Q I have a network set up with Internet Connection Sharing, with the ICS computer connected to a cable modem. Everything works fine except when I try to send direct connect chats using MIRC or any other chat software. People can send me messages but I can not chat from the networked computers. However, I can do so OK from the ICS computer direct, or when I dial out from one of the workstations. Any ideas on how I can get these chats to work properly? (F. K.) Go to www.yahoo.com and search for “ICS AND mirc” (without the inverted commas). You’ll find lots of informa­ tion on working around your problem. No guarantees though – we haven’t tested the solutions offered. A November 2001  39 SERVICEMAN'S LOG Ring every day until it’s fixed Most customers are reasonably patient while an appliance is in dock. Some are even apologetic. But others, particularly when a new and expensive device is concerned, demand – almost hourly – that it be fixed yesterday. This story was contributed by a colleague working for a Sony Service Centre. In line with most modern service centres, field or home service nowadays consists of simple installation tasks, or just collection and delivery by apprentices. The weight and bulk of modern sets usually requires at least two men to handle them, though I have seen a TV trolley to do the job. This trolley is fitted with suction cups and a wind-up mechanism to raise and lower a set of up to 140kg. Unfortunate­ly, its biggest disadvantage is its cost; around $1400 but as the salesman said, it’s still probably a lot cheaper than a bad back. But that aside, the main complaint about warranty repairs is listening to a whingeing customer and trying to convince him that he is not really entitled to a new set. And understand­ ably, most cannot comprehend why their latest technological marvel has failed when it is barely out of the egg. The good side is having the ear of the manufacturer’s tech­nical officers and their ability to arrange for spare parts to arrive promptly. In addition, one is supplied with brand new original service manuals and can often attend courses on new models. Sony KV-ES34M31 TV set Anyway, this is my colleague’s story, as he tells it. It concerns an 80cm flat tube Sony KV-ES34M31, employing a AG3 chassis. The customer was annoyed when it failed within months of buying it. The 84kg set was gingerly 40  Silicon Chip placed in the middle of my bench by the delivery team and left for me to fix – with an instruction from the Sony Technical Officer to fix it urgently. The set, though dead, was able to indicate this via its Standby/Timer LED flashing an error code. In this case, it was flashing twice, which means “I’m dead”. Isn’t technology wonder­ ful? – a device designed to indicate the bleeding obvious. But to be truthful, it actually does offer worthwhile diagnostic clues – according to the service manual, the probable cause was that the horizontal output transistor Q6807 and Q6810 pin-out transistor, (both 2SC5480-01) were short circuit. I removed both and found that Q6807 was indeed short circuit but Q6810 was OK. Because the customer was making such a noise about his set, the Technical Officer was on the phone every few hours enquiring about my pro­ gress. Not having seen this set before, I asked him what was the likely cause of the transistor failure? He replied that it was usually the horizontal output transformer. In any event, he suggested I replace both transistors, in case the other one was weakened by the stress Items Covered This Month • Sony KV-ES34M31 TV set. • Pansonic TC-68P22A TV set. • Orion Triade 34 TV set. • Ryobi 12V cordless drill battery charger. of the failure. I had two new transistors by the next day and after fitting them and switching the set on, nothing happened except that the one-eyed beacon on the front of the set flashed six times. This suggested that the EHT was too high because capacitor C6831 was open circuit (or CN6101 on the D1 board is disconnected). This was puzzling, as there was no EHT at all. In fact, there was no horizontal drive (HD1) coming into the D board from CN6800 pin 13 or from CN4101 pin 4 from the E board (RGB out, deflection). However, all was revealed when I removed and examined the E board to find that a whole series of surface mounted transistors had been literally blown apart. I was onto the Technical Officer quick smart. The next day, after reassuring the client that his set was receiving attention, I fitted a new module which Sony had quickly supplied. And Sony weren’t messing about – they wanted it fixed as quickly as possible. And they weren’t interested at this stage in fixing it at component level, unless it was on a major assembly. Unfortunately, the horizontal output transistor blew up again when power was applied and the standby lamp was back to two flashes. The next day, after suffering another call from our custom­er, another two transistors and a new horizontal output trans­former (T6803) were fitted. Phew! – at last a picture and sound. The width was a little low, probably due to the new components, so I readjusted it by writing new values under GEO 044 HSZ in the Service Mode with the remote control. I thought that that would be the last of it – except that, with the brightness and contrast turned up more than 80%, the width would shrink 50mm on each side. There was obviously still something wrong, most likely in the automatic brightness limiter circuitry. www.siliconchip.com.au I traced the circuit back from pin 11 of the horizontal output transformer with a multimeter. Finally, I reached R6866, a 2.7kΩ resistor, which measured nearly 100kΩ. Replacing it fixed the problem but I now had to reset the horizontal size to where it was before. Though the fault proved to be an interesting exercise, the client’s tactic of ringing every morning was a bit annoying. It annoyed the Technical Service Officer too! Panasonic TC-68P22A TV set The next story concerns a Panasonic TC-68P22A using an MX-8 chassis. This set was just out of warran­ty and came in for a dark picture. As it was only slightly out, it could be readjusted in the Service CHK2 and CHK4 modes. This is done by simultaneously pressing the RECALL button on the remote control and the Volume Down button on the set’s front panel, to get into the “Market Mode”. The selection of the CHK mode is made using either button 1 or button 2 on the remote control. The sub-brightness level can be adjusted with buttons 3 or 4 and vol6 and memorised by www.siliconchip.com.au button 0. The typical value is 2DH and why it is in two different menus is beyond me. There is a more advanced technical procedure to set the sub-brightness to 2.3V on TPA1. This involves shorting TPA57 to TPA50 and J67 to TPA32. However, the service manual can’t quite make up its mind which CHK mode to be in. It suggests CH3 and the data to be 63, which contradicts what it says earlier. Anyway, I set it for the default value which was fine but I found it was unable to store this. There was nothing for it but to order and fit a new EEPROM IC (1102 24LC08BIPA22). I did this and then reprogrammed the option codes in the CHK1 menu. Fortunately, it all worked well. The fault was fixed and after a few days soak testing it was returned to the customer. Two weeks later, the same set was returned for a rework as there was now a new fault. The greyscale was out and it was again too dark. Going through the menus again, I found that the red cut-off data in the CHK4 white balance adjustment mode was corrupted. Again, it wasn’t difficult to reset these levels and soak test the set. Firware upgrade Another two weeks passed before an understandably upset customer brought the set back again with the same problem. At this stage, I decided to have a chat with the Panasonic Technical Officer who advised me of a CPU (microprocessor unit) firm­ware upgrade for this chassis. (Firm­ware is the program which carries the various settings – brightness, contrast, picture geometry, etc. Once set, it should not vary). Apparently, this modification is aimed at the firmware setting of early production sets (1999), whereby it is possible for the customer to access cutoff and sub-brightness settings without knowledge of doing so. What irony! We had only just fitted a brand new EEPROM, supplied by Panasonic, that was two years out of date. Basically, if a customer watches Channel 9 a lot, sooner or later he will press the combination of control buttons that will bring on this fault. Technical Information Sheet (Order November 2001  41 Serviceman’s Log – continued No. T0001MX8-2) gives a table for new data in the CHK1 Option Code menu which will over­come this. However, it is necessary to get into the Memory Edit mode (“vol -” and “mute” buttons) while in the CHK1 menu and then key in the new data. I soak tested the set for a week before letting it go back – especially testing the Channel 9 remote function. Two months later, a furious customer returned the set, let­ ting me know in no uncertain terms what a buffoon I was. This time the fault gave an effect similar to old fashioned brown photographs made on printing-out-paper. I spent a long time going over everything but finally con­cluded, with the Panasonic Technical Officer’s help, that the CPU (IC1101 MN1873284TF 42  Silicon Chip I) was corrupting the EEPROM data. Replacing the microprocessor has, hopefully, finally fixed the problem – at least, I haven’t seen the set for three months now! Conflicting technology With so much technology in the home these days, it is inevitable that conflicts between technologies would start to arise. At present, our biggest headache is digital transmissions. It is very difficult to explain to Mrs Brown that the new VCR she bought to replace her previous Jurassic model can’t tune the stations clearly because of digital co-channel interference. The other inevitable area of conflict is the remote con­trol. Nowadays, every­thing has a remote control function. Anyway, because of the huge number of types of remote control systems out there, sooner or later you get one that controls something you don’t want it to. One friend has a brand new Nokia 6210 mobile phone which, with certain buttons depressed, will lock his Toyota Landcruiser doors. Thieves these days use digital scanners and when someone uses a keyless lock it stores the digital pattern and frequency and then can use this to unlock the device later when it is unattended. Some of these crooks cruise around industrial and housing estates using broadband transmitters and see which remote roller doors will open. All new remote systems now use a rolling code, as indeed they do with cars. Recalcitrant remotes Another of my friends (I have two!) had an old Philips KL9A1 TV set with remote control and a brand new Sanyo VX800 hifi VCR and kept complaining that the remote controls were intermit­ tently not working – especially the Sanyo. I called around one day but everything was in perfect work­ ing order. This fault continued for weeks and he was starting to get a bit fed up with it all. I took the remote controls to work and dismantled them to check for corrosion, faulty joints and anything else I could find – but everything was perfectly OK so I returned them. The fault was still there and sometimes he would complain that he couldn’t even change the controls manually on the Philips TV set. Every time I looked at them they all worked perfectly and only sometimes did they work for him. This went on for months and was only resolved when he decided to get on to Optus cable TV and they installed a set-top box and, of course, a remote control. When they left, it was all working but that night the new control wasn’t working and nor were any of the others. It took the Optus service engineer the next day to find the cause of all this trouble. The problem was due to a Condor Energy Saver 18W fluores­cent light. Apparently, it transmits harmonics that were affect­ ing all the remote control receivers. The reason I never saw the fault was that I called around in the daytime when the light was off. And the Philips TV set couldn’t operate manually because it was receiving www.siliconchip.com.au commands via its remote receiver that had priority. Ryobi charger I never cease to be surprised at the confusing problems that can arise in simple equipment. The other day, I was given a Ryobi 12V cordless drill battery charger to fix, the fault being that it wasn’t charging. “Piece of cake” I said, tempting fate. I took the thing to pieces and found that it consisted of no more than half a dozen components – a DC jack input from the AC power adapter and a small PC board which carried a diode, a transistor, a resistor and a LED. It’s all incredibly simple. I measured voltage coming in but none out. It didn’t take long to work out that, despite the polarity being clearly marked on the DC socket board and on the PC board, it could never have worked in this configuration. Reversing the wires produced a voltage output but the LED wouldn’t light. I checked the 2SC945 transistor to find it was open circuit. This was replaced and I then checked the remaining three compon­ents out of circuit and found that they were OK. The LED even lit OK when tested but it wouldn’t work in circuit. This was ridiculous. I work on complicated circuits all the time but this simple circuit had me stumped. It was totally frustrating. I reassembled and tried it once more with the battery in its receptacle. And would you believe it? – it was now working properly. I wasn’t about to set up a committee to investigate this apparent miracle. Instead, I just mentally thanked whoever it is that controls these things and left it at that. Thinking about it later, I concluded that the chrome-plated springs in the battery receptacle weren’t making proper contact with the battery before everything was reassembled. But really, in the scale of things, it’s not that important – far better to concentrate on the Big Bang theory and ask what happened before the bang and who set it off? Postscript: the customer returned this unit sometime later and I discovered that the reason that the battery holder was wired the wrong way was because the AC power pack originally supplied to me was the wrong one. I was given a 9V one, not the correct 12V one that comes with this unit. The tips of the DC plug are opposite for each voltage. This probably accounted for why the transistor was blown too.” Orion Triade TV set I was pleased to find that the Orion Triade 34 TV set was already on my bench because that meant I didn’t have to lift it. It’s bad enough getting old but to have a bad back as well would surely be the end. Fortunately, in my case it’s just sen­ ility and Alzheimer’s that are my only problems – I still have my looks! Back to reality. The Orion Triade is an Italian-made 79cm TV set, model 346A4 T8007PIP using the “Professional 7000” chas­sis. It is a large set with only one visible control (the on/off switch) and three other push­ MINI SUPER DRILL KIT IN HANDY CARRY CASE. SUPPLIED WITH DRILLBITS AND GRINDING ACCESSORIES $61.60 GST INC. www.siliconchip.com.au November 2001  43 to deserve this. I left the set on for the rest of the day and switched it off at going-home time. The next day, when I returned, the set was dead, as before. I carefully repeated what I had done the day before and managed once more to start the set. This went on for a couple of days but it was always dead the next day. The problem seemed to me was that it was intermit­tently unable to start when cold even though all the voltages were there in the standby mode but not in the ON mode. Four microprocessors buttons concealed behind a door on the righthand side. This one was dead and I had no remote control or instruc­tion booklet. The good news was that I did have a circuit dia­gram. Despite it being such a huge set, the chassis is small and one doesn’t have to remove the whole of the back to get to it. Undoing two screws removes a cover for the neck of the tube and the chassis. To say the set was dead was not totally accurate. When the power was switched on, the set was going into a standby mode with a small red LED illuminating on the front escutcheon. The three buttons on the side are marked “+”, “-” and “menu”. I pressed the top one and the set tried to fire up but failed and then went completely dead. All I could do was to switch the power off, wait a few minutes and power it all up again in the same way. The switchmode power supply is on a self-contained module on the righthand side of the chassis (looking at the rear) but access makes it difficult 44  Silicon Chip to measure all the voltage outputs. I removed the supply and connected a dummy load to the 150V rail and 240V AC to its input. The power supply worked OK, so I re­moved the main chassis and checked for faulty joints and shorts, especially in the horizontal output stage, but could find none. And yet with the set all back together, there were no vol­tage outputs in the full-on position. Suspecting the horizontal output transistor, I short­ed its base and emitter and checked the collector voltage. This time, the voltage was there. Because access was poor and I had used a piece of solder to join the two junctions together, I used a meter probe to break the link. To my surprise the set fired up and gave a magnificent picture and full sound. All the functions were working and when I switched the set off and on, it came back up perfectly. Well, this was all very exciting but I really didn’t know what I had done This set has no less than four microprocessors, the control one being ICR2 (uP83COSS SEI 7000). The set is switched on from pin 41 via transistor TR1 after a Power On Resetting interrupt sequence on pins 37, 33 and 42. This voltage is then applied to TP5, TP6 and ICP4, which then connects the 12V and 8V rails to the horizontal oscillator and deflection circuits. The horizontal sync pulses are sent back to the power supply via an optocoupler (FAP1) and TP4 to the control chip (IVP1 TEA2261, pin 10) to change the switchmode power supply frequency from 23kHz to the 14.5kHz operating condition. A second optocoupler (FAP2) feeds back the secondary vol­tage levels to pin 6 of comparator ICP1. This latter stage inter­ested me and the next time it was on, I measured the main 150V rail accurately with a digital meter. This was significantly high at 157V (5% error), possibly enough to trip the protection cir­cuit through FAP2. I reduced PP1 to set the correct voltage precisely. This indeed made the set easier to start in the mornings but there were still occasions when it wouldn’t start and it wasn’t good enough to send back to its owner. One thing I did notice was the timing of the various voltages from standby to on – in particular, there was a delay for the 12V to appear on pin 6 of ICP4 (TA8138A). This might be enough to make the horizontal sync pulses build up. I ordered a new one, making sure I specified one with an “A” suffix because without the A, this IC is a 7-pin in-line type, as opposed to the “Q” formation for which this set is drilled and punched. The new IC finally fixed the problem and after soak testing it SC for a week, it went back home. www.siliconchip.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au Order Form/Tax Invoice Silicon Chip Publications Pty Ltd ABN 49 003 205 490 PRICE GUIDE- Subscriptions YOUR DETAILS (all subscription prices INCLUDE P&P and GST) Your Name________________________________________________________ (PLEASE PRINT) Organisation (if applicable)___________________________________________ Please state month to start. 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Folded: $A5.95 inc p&p within Australia; elsewhere $A10 inc p&p. *BOOKSHOP TITLES: Please refer to current issue of SILICON CHIP for currently available titles and prices as these may vary from month to month. SUBSCRIBERS QUALIFY FOR 10% DISCOUNT ON ALL SILICON CHIP PRODUCTS AND SERVICES* *except subscriptions/renewals and Internet access Item Price Qty Item Description P&P if extra Total Price Spec i SUB al Offer SCR IBE & COM PUTE GET R OM FO N Aust R FREE! IBUS ralia Only* Total $A TO PLACE YOUR ORDER Phone (02) 9979 5644 9am-5pm Mon-Fri Please have your credit card details ready OR Fax this form to (02) 9979 6503 with your credit card details 24 hours 7 days a week OR Mail this form, with your cheque/money order, to: Silicon Chip Publications Pty Ltd, PO Box 139, Collaroy, NSW, Australia 2097 * Special offer applies while stocks last. 11-01 Low-Cost Audio/Video Distribution Amplifier Do you need to distribute video and audio signals to a bunch of monitors or VCRs, without any loss in quality? This easy-tobuild Audio/Video Distribution Amplifier can split normal composite video (plus stereo audio) signals six ways, or you can use it to split S-video signals three ways. By JIM ROWE T HERE ARE LOT’S of situations where an AV Distribution Amplifier is necessary. For example, let’s say that you want to set up an audio-video (AV) system for a college classroom, where half-a-dozen monitors are to be fed with video and audio signals from a single VCR. Or perhaps you want to set up a small video duplication facility, with a “master” VCR or VCD (video CD) player feeding up to five recording VCRs plus a video 54  Silicon Chip monitor (so that you can keep an eye on recording quality). Another possibility is that you want to set up a stand at a trade show, with the output from a DVD player fed to a video projector, three or four monitors and a sound system. In situations like these, there’s more to it than just hooking everything up with the necessary cables and some multi-way connectors. Distributing video and audio signals to multiple destinations has to be done properly, or signal losses and cor­ruption can make the results very disappointing. Blurred pictures with “ringing” and colour “bleed”, together with weak and muffled sound, are inevitable unless the system is properly set up. In general, the way to prevent these problems is to use an “audio-video distribution amplifier”. This provides enough gain (or amplification) to compensate for the losses involved in “splitting” the video and audio signals to feed multiple loads. It also ensures that the video cables can all be terminated in the right impedance, to prevent ringing and other distortion. Commercial AV distribution amplifiers are available but they’re not exactly cheap. That’s why you might like to consider this design. The kit costs less than half as much as a comparable commercial unit. What it does Our AV Distribution Amplifier accepts a standard composite video www.siliconchip.com.au All the parts are mounted on a large double-sided PC board, so building the unit is really easy. This is the composite video version – only a few minor changes are required to distribute S-video signals. signal (PAL or NTSC) from a VCR, camcorder, VCD or DVD player and provides six “clone” signals to drive the same number of monitors, projectors, VCRs or whatever. The video output signals are all virtually identical to the input signal, because the video amplifier stages inside the unit have a frequency response flat to within 0.1dB to over 100MHz. They also operate with very low distortion, noise and phase shift. Any line-level mono or stereo audio signals which accompany the video can also be split six ways, again without any signifi­cant reduction in frequency response or signal-to-noise ratio. The audio stages also operate with very low distortion and chan­nel crosstalk. What’s more, the unit is very easy to build. It’s built inside a standard low-profile plastic instrument case, with all parts mounted directly on a PC board so there’s no off-board wiring to worry about. And it all runs from a nominal 12V DC supply, which can be either a low-cost plugpack supply www.siliconchip.com.au or a battery. The total current drain is less than 60mA. By the way, although the video side of the unit is mainly intended for distributing normal composite video to six loads, the circuit and PC board pattern also allow it to be wired to distribute S-video or “Y/C” signals to three loads, instead. So if you need an S-video distribution amplifier, we’ll explain how this can be done later in the article. Amplifier chip The video side of the project is based on a very impressive wideband buffer amplifier chip made by Maxim Integrated Products. Designated the MAX­497, it includes four closed-loop buffer ampli­fiers, each with a voltage gain of 2.0 and the kind of perfor­ mance we could only dream about a few years ago. As you can see from Fig.1, its buffers have a rated fre­quency response for small signals of about 120MHz (-0.1dB) and the response is still rated to extend to around 215MHz (-3dB) at full power output. Each buffer amplifier inside the MAX497 offers a typical input impedance of 1MΩ shunted by 2pF, an output impedance of only 1.5Ω at 10MHz, an output slew rate of better than 1100V/ Where To Buy The Kit The copyright on this project is owned by Jaycar Electronics who will have complete kits available shortly after publication. These kits will include pre-punched front and rear panels with screened lettering. Prices are as follows: (1) Complete kit for composite video version ..........................................$139.95 (2) Complete kit for S-video version.........................................................$139.95 Kits can be purchased from you nearest Jaycar store or via mail order. November 2001  55 Parts List 1 PC board, code 02111011, 198 x 158mm 1 plastic instrument case, 225 x 165 x 40mm 3 RCA sockets, PC-mounting 9 dual RCA sockets, vertical PC-mount 1 2.5mm PC-mount DC power connector (J22) 8 PC board terminal pins, 1mm diameter 3 10mm x M3 machine screws with M3 nuts 15 small self-tapping screws, 6mm-long Semiconductors 1 MAX497 quad video amp (IC1) 1 LM833 dual low-noise audio amplifier (IC2) 1 LM555 timer (IC3) 1 7809 +9V regulator (REG1) 1 7805 +5V regulator (REG2) 1 7905 -5V regulator (REG3) 1 3mm red LED (LED1) 1 zener diode, 9V 400mW (ZD1) 3 1N4001 diodes (D1-D3) Capacitors 1 1000µF 25VW RB electrolytic 2 220µF 25VW RB electrolytic 2 100µF 16VW RB electrolytic 2 10µF 16VW TAG tantalum 2 2.2µF 16VW TAG tantalum 2 0.39µF MKT polyester 2 0.22µF MKT polyester 4 0.1µF monolithic ceramic 1 0.1µF MKT polyester 1 0.01µF MKT polyester Resistors (0.25W, 1%) 4 100kΩ 4 150Ω 14 47kΩ 5 75Ω 1 10kΩ 1 22Ω 1 2.2kΩ 2 10Ω Changes for S-video version 6 dual RCA sockets, PC board mounting (not 9) 2 single RCA sockets, PC board mounting (not 3) 4 4-pin mini DIN sockets 9 additional 1mm PC board terminal pins 6 75Ω resistors (not 5) 8 additional 10mm x M3 machine screws with M3 nuts WHERE TO BUY A KIT Kits for this project will be available from Jaycar Electronics – see panel. 56  Silicon Chip µs for a 4V step and an output THD (total harmonic distortion) of better than -58dBc for a 2Vp-p output swing at 10MHz. The overall device also offers adjacent-channel crosstalk of better than -72dB, “all hostile” crosstalk of better than -65dB, and differ­ ential gain/phase errors of less than .01%. So it’s a very im­pressive device. But why a gain of 2.0? Simply because the MAX497 is de­signed specifically for driving “back terminated” coaxial cables – where the source end of the cable is presented with its match­ing impedance as well as the load end. This is done by using a series resistor, normally 75Ω for driving video cables. However this means that a 2:1 voltage divider is formed by the back termina­ tion resistor and the cable’s termination resistor at the load end. So by giving the buffer amplifier a gain of 2.0, we restore the overall gain to unity and ensure that each load receives a full-amplitude replica of the input signal. Circuit details As shown on Fig.2, a single MAX497 (IC1) forms the heart of the distribution amplifier’s video circuitry. To use the chip’s four internal amplifiers to provide six output channels, we pull a small trick. This relies on the fact that each of the four channels in the MAX497 can actually drive a total load as small as 100Ω (ie, a back-terminated 50Ω cable and load), rather than the 150Ω presented by a back-terminated 75Ω cable and load. The inputs of all the amplifiers are tied together, so that they produce exactly the same output signal. Then as well as using each output to drive its own specific load via a 75Ω back-termination resistor, we also use each output to provide half the drive to a third output, via 150Ω resistors. This means that the third output from each pair is still driven with an identical signal to the other two and with the same effective back termina­tion resistance (150Ω/2 = 75Ω). Thus, when the inputs of the two pairs are also tied togeth­er, this provides a total of six buffered outputs from a single composite video input. By separating the two pairs we’re also able to use them for handling the separate Y (luminance) and C (chrom­ inance) signals of S-video and split each of them three ways. That’s how Fig.1: the gain of each amplifier in the MAX497 chip is 2.0 (6dB), and remains virtually ruler flat until beyond 100MHz! the video side of the unit is changed from 1:6 distribution for composite video to 1:3 distribution for S-video. The audio side is just as straightforward as the video side, being based on a single LM833 low-noise dual op amp IC (IC2). The two op amps in IC2 are used in identical cir­cuits, one for each of the stereo audio channels. Each op amp is configured as a buffer, with the 100kΩ resistor pairs applying negative feedback to give a voltage gain of (you guessed it) 2.0. This allows their inputs to be provided with the usual “line level” terminating impedance of 47kΩ and their outputs to be connected to splitter resistors of the same value – so that the overall gain is unity when the outputs are connected to audio equipment inputs with an impedance of 47kΩ. In this case coupling resistors are used to protect both the inputs and outputs of the op amps from any possible DC levels, but the capacitor values are chosen to minimise any change in frequency response. Power supply That’s really all there is to it in terms of the distribu­tion amplifiers. The rest of the circuitry is for the unit’s power supply, to provide the correct supply voltages which are derived from a nominal 12V DC source. The MAX497 operates from supply rails of ±5V, while the LM833 needs rails of at least ±9V to handle typical line level audio signals. So the power supply circuitry is designed to provide all four of these voltages from the www.siliconchip.com.au S-VIDEO IN *LINK 150 15 11 13 9 2 16 4 14 6 12 8 10 75 75 75 75 150 75 1 5 3 7 150 10 1k 2.2F 16V 0.22F LEFT AUDIO INPUT 1k 3 47k 2 1k 8 IC2a LM833 1 1F 1k 100k 1k -9V 0.1F LEFT AUDIO OUTPUTS +9V 1k 0.1F LED K 10 -9V 1k A 2.2F 16V 0.22F RIGHT AUDIO INPUT 1k 5 47k 6 IC2b LM833 1k 4 7 1F 1k 100k 1k LED1 POWER  A K 1k 2.2k D1 1N4001 12V DC INPUT DC SOCKET + 1000F 25V _ +9V REG1 7809 IN OUT GND REG2 7805 IN OUT GND 10F 16V +5V 2x 0.1F 100F 16V 10k 7 0.1F 6 www.siliconchip.com.au 150 VIDEO OUTPUTS 75 2 Fig.2 (right): the circuit for the video distribution amplifier. IC1 handles the video signals, while IC2 handles the stereo audio. The circuit can be wired to output six composite video channels or three S-video channels. IC1 MAX497 VIDEO IN Construction Fig.3 shows the wiring details for the Video Distribution Amplifier. Note that this is for the composite video version – we’ll cover the S-video version later. All the parts are mounted on a single PC board coded 02111011 and measuring 198 x 158mm. This board needs to be dou­ ble-sided to allow correct configuration of the MAX497 video chip but there’s no need for plated-through holes. Instead, the con­ nections between the top and bottom copper layers are made via PC terminal pins and by soldering the component leads on both sides of the board where necessary. We also make use of the top copper layer to provide signal shielding. Why does the PC board have to be the size it is, when there’s not all that much circuitry inside? Well, it’s simply to allow all of those output connectors to be fitted directly to the board, along its back edge. This reduces the off-board wiring to zero, making -5V +5V *INSTALL LINK FOR COMPOSITE VIDEO RIGHT AUDIO OUTPUTS incoming “raw” 12V DC input, at the modest current levels needed. As shown in Fig.2, series diode D1 is used to protect the supply from reverse-polarity damage. The 1000µF capacitor provides smoothing before the input is fed to REG1, a 7809 regu­ lator which provides the +9V rail. This, in turn, also feeds REG2, a 7805 regulator which provides the +5V rail. We generate the negative supply rails by using a 555 timer (IC3). This is wired as a high-speed commutator switch and drives a charge-pump voltage inverter circuit based on diodes D2 & D3 and two 220µF capacitors. This produces an output voltage of about -10V across the second capacitor, which drops to around -9V across zener diode ZD1. The zener thus establishes the -9V supply rail and also drives REG3 to produce the -5V rail. Finally, we also use the raw DC input to operate the pilot LED, via a 2.2kΩ series resistor. SC 2001 8 4 VCC RES TRIG OUT DIS IC3 555 CV THR GND 1 3 5 220F 25V D2 1N4001 D3 1N4001 220F 25V -9V 22 100F 16V -5V REG3 7905 IN OUT GND ZD1 9V 10F 16V .01F 6 CHANNEL A/V DISTRIBUTION AMP November 2001  57 This is the completed PC board assembly. Note that some component leads must be soldered on both sides of the board – see text. the unit easy to build and eliminating potential wiring errors. RCA connectors The video and audio outputs are all made via nine double board-mounting Capacitor Codes      Value   IEC Code EIA Code 0.39µF   390n  394 0.22µF   220n  224 0.1µF   100n  104 .01µF    10n  103 RCA connectors. The three directly behind the MAX497 chip provide the six video outputs, while the remaining six each provide one pair of stereo audio outputs. At the front, the inputs are made via three single board-mounting RCA sockets. A 2.5mm concentric power connector is used for the 12V DC input and this too is at the front because there was no room at the rear. The only other item on the front panel is the pilot LED, at the lefthand end. As shown in Fig.3, everything is laid out fairly spacious­ly, with the signal flow from front to rear for both video and audio signals. PC board assembly Before fitting any components to the PC board, position it in the bottom half of the case and check that it has been trimmed to the correct size. The board has to fit quite snugly between the front and rear panels and if it’s too large, you won’t be able to assemble everything later. It’s better to check this out now and if necessary file it down to size, as it’s much harder to do if all the components have been mounted Resistor Colour Codes   No.    4  14    1    1    4    5    1    2 58  Silicon Chip Value 100kΩ 47kΩ 10kΩ 2.2kΩ 150Ω 75Ω 22Ω 10Ω 4-Band Code (1%) brown black yellow brown yellow violet orange brown brown black orange brown red red red brown brown green brown brown violet green black brown red red black brown brown black black brown 5-Band Code (1%) brown black black orange brown yellow violet black red brown brown black black red brown red red black brown brown brown green black black brown violet green black gold brown red red black gold brown brown black black gold brown www.siliconchip.com.au K 1k AUDIO OUT LED1 A 1k AUDIO OUT 1k 1k 220F 10k 1F +9V 10 ZD1 10 D2 1k 1F P2 100F 75 COMPONENTS MARKED WITH ( ) MOUNT ON BOTTOM SIDE OF PC BOARD * 0.1F IC1 MAX497 AUDIO OUT 150 * 75 0.1F 1 * -5V 75 *+ RIGHT AUDIO IN 10F + P5 -5V REG3 7905 INSTALL FOR COMPOSITE VIDEO ONLY 75 + 10F LINK 100k 1k VIDEO OUT REG2 7805 100F +5V VIDEO IN 47k 100k P4 47k +9V 100k -9V 1k 0.1F LEFT AUDIO IN P1 1k + 0.22F P3 + + 12V DC INPUT 2.2F DC SOCKET IC2 LM833 + D1 1k 2.2F 1 220F 100k + 1000F 22 AUDIO OUT .01F 0.22F AUDIO OUT 1k D3 0.1F 0.1F INSTALL FOR S-VIDEO ONLY 150 VIDEO OUT IC3 555 1k REG1 7809 150 150 75 VIDEO OUT 1 AUDIO OUT 1k + 2.2k 75 P6 GND = PC BOARD PIN = TOP SIDE Fig.3: install the parts on the PC board as shown here to build the composite video version. Note that the capacitors shown in blue are installed on the underside of the PC board – see text and photo. on the board. Next, it’s a good idea to check the board’s patterns (top and bottom) for any possible defects – bridges or hairline cracks, etc. Fix these if you find them, then fit the six PC terminal pins www.siliconchip.com.au (P1-P6) used to make the layer-to-layer connections and the video input linking. P6 is in the bottom righthand corner of the board, while pins P1-P5 are fitted near REG2 and the two 100µF = BOTTOM SIDE capacitors. These pins also provide convenient places to check the +9V, -9V and -5V supply rails. Note that all six pins (P1-P6) should be soldered to both the top and bottom copper pads, to ensure they act as through-hole vias. Install the link near the video input socket if you’re building the unit to distribute normal composite video but November 2001  59 The composite video version has no less than 18 RCA output sockets – six for the video outputs and 12 for the stereo audio output pairs. The S-video version substitutes three 4-pin mini DIN sockets for the video outputs, plus another 4-pin mini DIN socket for the video input. leave it out for S-video. The next step is to fit the double RCA connectors along the rear of the board and the other connectors along the front. The double RCA connectors have plastic locating lugs on each side, which mate with matching 3mm holes in the board. You push each connector’s three connection pins through their holes until the barbs on the plastic lugs clip into position, then you solder the pins to the pads below. With the single RCA connectors, the connection tails them­selves hold the connectors in place but you may need to enlarge the holes in the board to take them because the tails are rec­ tangular in cross-section (about 0.5 x 2.5mm). This is also true for the DC power connector. A round jeweller’s file can be used to convert the drilled holes into slots. This view shows the mounting details for the two 0.1µF monolithic ceramic capacitors and the 10µF tantalum capacitor on the underside of the PC board. 60  Silicon Chip Once the connectors are all fitted and their leads soldered to the board underneath, you’re ready for the final stages of the assembly. This simply involves fitting the resistors, capacitors, diodes, ICs and regulators, mainly in that order. Most of this wiring is very straightforward and shouldn’t pose any problems. But be especially careful around the video chip (IC1), because many of its pins have to be soldered to pads on both the top and bottom of the board. Two of the 0.1µF mono­lithic ceramic bypass capacitors for this chip (the “centre” pair) also have to be mounted on the bottom of the board and soldered on the top. By contrast, the “end” pair are mounted on the top of the board. It’s best to leave all four of these monolithic capacitors until after you have fitted IC1, because they’re easier to fit afterwards without damaging them. When you fit IC1, all of its pins should first be soldered to the pads on the bottom of the board. Then after allowing the chip to cool down for a minute or so, turn the board over and solder pins 1, 3, 5, 7, 9, 11, 13 and 15 to their top pads as well. This done you can then fit the two end bypass capaci­ tors, soldering their leads underneath, and finally the two centre capacitors from below with their leads soldered on the top. Note that it will be necessary to bend the leads of these two “underneath” capacitors by about 45°, so that they don’t foul the bottom of the case later www.siliconchip.com.au on – see photograph. By the way, DO NOT use an IC socket for the MAX497 chip. While it’s a fairly pricey chip, it needs to be soldered directly to the board to minimise lead inductance (otherwise it won’t operate properly). It’s a fairly rugged device though, so don’t be too nervous. Just use a clean, well-tinned fine bit on your soldering iron and make the soldered joints quickly to avoid overheating. The only other part that’s mounted underneath the board is one of the two 10µF tantalum bypass capacitors adjacent to IC1. This capacitor bypasses the -5V rail. Again, it may be necessary to bend its leads by about 45° before you fit it, so its body won’t hit the bottom of the case when the board is mounted. Note that all three TO-220 regulator chips are mounted flat on the top of the board. This means that their leads all need to be bent down by 90° about 5mm from the body, before each device is fitted. This done, it’s a good idea to fit an M3 ma­chine screw and nut to hold each device down to the board, before soldering the leads on the bottom. Don’t fit the second 75Ω input terminating resistor (near the link) if you’re building the unit for distributing normal com­posite video. This resistor is only needed when the board is used for S-video. The power indicator LED (LED1) should be fitted with its body about 15mm above the board. Make sure Fig.4: if you want to build the project to distribute S-video signals, here’s how to modify the 4-pin mini DIN sockets to fit inside the low profile case. that it’s correctly orientated before soldering its leads – the anode lead is the longer of the two. Once it’s in, bend its leads at right angles about 8mm above the board, so that it will later mate with its hole on the front panel. Final assembly If you’re assembling the unit from a complete kit, the front and rear panels will be supplied punched and silk-screened. Alternatively, if you’re building from scratch, you’ll have to drill and ream the various holes for the connectors, using photo­copies of the front and rear panel artworks as templates. Note that most of the RCA socket clearance holes should be 10mm or 10.5mm in diameter, while that for the DC input socket should be 7.5mm and that for the LED 3mm. As you can see from the rear panel artwork, there’s also a 3mm hole alongside each double RCA connector position. These holes are used for the small self-tapping screws which attach each connector to the rear panel, to strength­en the complete assembly. Once all the holes have been drilled in the panels, you’re ready for the final assembly. This is easiest if you first offer both panels up to the board assembly so that they mate with the connectors and attach the rear panel using the small self-tappers. The complete assembly can then be fitted into the bottom half of the case and secured by fitting self-tapping screws into the matching integral plastic standoffs – one in each corner, and two more along the front to add strength and rigidity. Quick checkout Now for the smoke test. Connect the board to a 12V DC supply (eg, a plugpack) and check the various supply rail voltag­es using a multimeter (or Fig.5: here’s how to wire the mini DIN sockets to the Distribution Amplifier PC board for the S-video version. www.siliconchip.com.au November 2001  61 eo Distribution Ampli­fier is probably working correctly. If you don’t get the correct voltages, remove power immediately and look for the problem. It’ll probably be a faulty solder joint or a component mounted incorrectly. Assuming everything checks out correctly, you can com­plete the assembly by attaching the top of the case. The unit is now ready for business. S-video version Now let’s look at building the unit for 1:3 distribution of S-video. Figs.4 & 5 show the details. First of all, you don’t fit the video input RCA socket to the front of the board. Nor do you link the two PC terminal pins just behind the 75Ω input resistor (ie, near the video input socket). However, you do fit the second 75Ω resistor, just behind these pins. Also, at the rear of the board, you leave off the three double RCA sockets used for the video outputs. Instead, you fit PC terminal pins into the holes where the three pins of each socket normally go and solder them to the pads underneath – ie, nine more terminal pins in all. These changes allow you to fit the unit with the usual 4-pin “mini DIN” sockets used for S-video connections, with the sockets mounted directly on the front and rear panels and the board connections made via very short wires to the terminal pins – see Fig.5. Modifying the S-video sockets Fig.6: here are the full-size artworks for the front panel and the two rear panel versions (composite video and S-video). DMM). P1 and P2 should both be at +9V (relative to board earth, eg, P6). Similarly you should find -9V at P3 or P4 and -5V at P5. 62  Silicon Chip You should also be able to measure +5V at the output termi­nal of REG2 – ie, the lead nearest REG3. If all four voltages are OK, your Vid- Because of the limited panel space of this low-profile case, the commonly available S-video sockets have be modified to fit in – see Fig.4. This involves drilling new mounting holes in their flang­es and then cutting the flanges somewhat shorter – about 24mm end-to-end. Note that although the unit has only three video output channels in the S-video version, there are still six audio output RCA socket pairs on the rear panel. Only three stereo pairs are required, of course, but you can still fit all six so that there are no holes in the rear panel. 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PROGRAMMING AND CUSTOMISING THE BASIC STAMP 2nd edition Edwards 0071371923 ARP$89.95 This guide gives you a comprehensive tutorial on the easy to use BASIC Stamp single-board computer, which runs a PIC Microcontroller, and doesn't require you to do any assembly language programming. Second edition contains a new section on Stamp-specific and Stampfriendly peripheral devices and a new chapter on Applying the BS2-SX. All prices include GST McGraw Hill books are available N 2001  63 from Dick Smith, Jaycar, Altronics, Technical Books Melbourne and all good bookstores www.siliconchip.com.au ovember Download WAV files from your PC and play them at will! short Message RECORDER AND Player by Leon Williams Got a need for a short audio message player? Been tempted to build or buy a voice recorder? Well, here’s a voice recorder with a muchimproved recording technique. No longer limited by the shortcomings of built in microphones, you edit and enhance your messages as WAVE files on your PC and then download them direct to the Message Player. 64  Silicon Chip www.siliconchip.com.au W to-female 25-way cable. The download used in PCs and the Internet because hile there have been many software is started and the required file there is plenty of software to generate projects for voice recorder/ opened, the shunt on the PC board is and play them. They don’t employ playback boards, they all moved from PLAY to PROGRAM and complicated compression algorithms suffer from one major drawback. the file is then downloaded. It is very but instead just have a header block They can only record and playeasy and takes about 15 seconds to followed by the raw audio data. back sounds (usually voice) that are complete. recorded by a little onboard electret WAVE files come in a number of microphone. You push a button and The message player is built on a formats providing varying levels of speak into the microphone and that’s single-sided PC board, with all the sound quality from basic to CD qualabout all you can do. You can’t really components on-board except for the ity. add any exciting sound effects or enloudspeaker and the power and D To keep the Message Player inexhance your voice in any way. connectors. pensive, it has been designed to only With the Message Player all that’s All the components are standard work with 8-bit mono 8kHz files. changed. Now you can record, mix types available from most electronThis means that we don’t need a lot and edit sophisticated sound files ics shops. The exception may be the of memory to hold the files and so with your PC and download them to SRAM chip. These have been used by we can get away with a single SRAM be played when and where you want. the millions over the years, so you may chip. be able to locate one from a disposal OK, so where would you use the While the Message Player sound source. Failing this, you can get them Message Player? The answer is any output is not exactly hifi, it is entirely new from places like Farnell and RS place that you want short audible adequate for the purpose. messages to be heard. Let’s have a closer look at the WAVE What about a personfile format we are alised front door bell or a using. warm message to welcome  The start of the Stores standard WAVE (.WAV) file format shoppers, or maybe a talk-  file contains a header Battery back-up for me ing car alarm to tell you block, a block of data mory  Quick PC file downloa your lights are on? that provides inford A unique application  mation about the file Simple logic control int erfacing could be to replace your including things such Built in 250mW audio telephone ring sound with  as the sampling rate amplifier a voice message like “Hey  and the size of the file. Easy to use companion software you, answer the phone”! We won’t go into Runs from 9V plug pa All you would need to do  it in depth here but if ck at low power is detect the ring signal you are interested, a and trigger the Message search on the Internet Player to play the message. will uncover plenty of Components. The Message Player has a replay information about the While a 62256 is specified for the time of four seconds and in replay different WAVE file formats, including storage SRAM, manufacturers somemode has only two controls. These are full descriptions of the header block. times use different labelling, such as a logic level negative pulse to start the Mono obviously refers to the fact 43256. This should be fine, rememreplay (“GO”) and a similar pulse to that there is only one channel of aubering that the majority of 32K SRAM stop the replay (“STOP”). dio, hence the reason we only use one chips have the same pin outs and funcIf the message is not stopped speaker! The frequency of 8kHz refers tionality. Don’t worry about the access during the four seconds it will stop to the rate at which each byte of data is time, usually written as a couple of automatically at the end. If you want converted from digital to analog to prodigits at the end of the part number, the message to continue, it’s simply a duce sound. At 8kHz (8000 bytes per perhaps preceded with a dash. matter of holding the GO input low second), we can reproduce voice quite This is not a critical issue with the until you want it to stop. well but reproducing high frequencies Message Player, so if you are purchassuch as 15kHz is not possible. At this These pulses can be derived from ing a new one, select the slowest to rate we can get four seconds of replay simple pushbutton switches or other save some money. from a 32Kbyte file. more elaborate interfacing circuits. The Message Player is housed in a Each byte of audio data is held as If you think that the Message Player plastic case but there is no reason why eight bits, which gives us a maximum memory is not big enough, just time it couldn’t go into an existing piece of 256 different bit combinations. The yourself speaking for four seconds and of equipment if you have the space. reproduced audio waveform is comyou will see that you can get a lot said The normal power supply would be prised of 255 equal voltage steps and in that time. The Message Player is a 9V plugpack but any regulated DC will be at minimum amplitude when only intended for short message applisource between 8V and 12V will also all the bits are zero (00 Hex) and at cations and anyway, who needs a 60 be suitable. maximum amplitude when all the second message every time a wanted bits are a one (FF Hex). A feature of event happens? Wave files the WAVE format is that when there To download the sound files into WAVE (“.WAV”) files are probably is silence (no sound), the amplitude the player, you connect it up to your the most common audio file format rests at midway (7F Hex). PC printer port with a standard male- MESSAGE PLAYER F EATURES www.siliconchip.com.au November 2001  65 66  Silicon Chip www.siliconchip.com.au Fig.1: it might look complicated but in reality there’s not much to the circuit. Its operation is described in the text. Note that the two jumpers were brought out to a DPDT slide switch in our final prototype. Perhaps a more correct way of looking at a WAVE file is that it swings negative and positive about a central resting point. Circuit description The circuit is shown in Fig.1. The audio file is stored in IC1 which is a 32K (32768) by 8-bit wide SRAM (Static Random Access Memory) chip. As this is the heart of the design, let’s have a close look at how it operates. An SRAM chip looks like any other logic chip with a black plastic body and pins. The difference is that it can hold lots and lots of bytes (eight bits) of data, which can be entered (written), stored and read back very quickly. Each location (memory cell) within the SRAM is selected by the bit pattern on the address pins. When all the address lines are low we select the first memory cell. As they increment in binary they select the next byte and so on, until they are all high when the last memory cell is selected. The SRAM chip we are using is a 62256, where the sequence 256 refers to the fact that it can store 32K x 8 bits (32 x 8 = 256). A 6264 would store 8K x 8 bits, etc. Our chip has 15 address lines to address a maximum of 32,768 locations, and eight data lines. Those who have access to a 32K SRAM data sheet will notice that the address and data line labelling is different to that shown in Fig.1. This was changed in this instance to simplify the PC board layout, however changing the notations does not cause a problem. The term random in SRAM refers to the fact that any memory cell within the chip can be accessed (written or read) in any sequence. The data lines can also be interchanged, as long as we read and write the data with the same bit pattern. That is, if we write a bit to a line we label D7, then we must also read back the bit as D7. Because we do not need to access the memory cells in any particular sequence and because all the data bits can be treated equally, we can label the address and data lines as we wish. As well as the address and data lines, the SRAM has three control lines that must be used correctly to write and read the SRAM. Pin 27 is the Write (WR) pin and is normally high. It is taken low when writing www.siliconchip.com.au This shot of the inside of the message recorder was taken before we decided to add the two pushbuttons switches (“GO” and “STOP”) on the end panel, as well as bringing the “PROGRAM” and “PLAY” headers out to a slider switch on the front panel. These switches make the unit much easier to use: you don’t have to whip the front panel off every time you want to change the message! eight bits of data into a cell selected by the address lines. To read data back from the chip, the write line must be high. Pin 22 is the Output Enable (OE) pin and controls the output buffers. When high the output is disabled and placed in a high impedance state, while taking it low enables the output buffers. Pin 20 is the Chip Select (CS) input and when it is high the chip is de-selected. In this state, read and write requests are ignored and the chip is placed in standby mode. When the chip select pin is low, the chip operates normally and data can be read and written. In contrast to memory devices such as EPROMs and EEPROMs, IC1 is a volatile memory. This means that it will only hold the data in its memory cells while power is applied. Luckily, the memory can be maintained when the main power is removed, through a secondary battery backup, as long as pin 20 is held high. The backup supply can be as low as 2V, needing a current of only a few microamps. This can be easily supplied by a couple of AA cells which under these conditions should last a long time, probably as long as they would left on the shelf. Addressing and control IC2, a 4040 12-stage binary counter, is used to address the first eight lines of the SRAM. The clock input is on pin 10 of IC2, and a high on pin 11 resets all outputs to zero. IC3, a 4024 7-stage binary counter, addresses the remaining seven lines of the SRAM and is clocked when pin 13 of IC2 goes low. The reset line of IC3 is connected to the reset line of IC2, so that both are reset simultaneously. IC4d is configured as a Schmitt trigger clock oscillator with a frequency of 8kHz, set by the .022µF capacitor and VR1. With the clock operating at 8kHz, we address 8000 memory locations per second. The memory size is 32,768 bytes, so the time taken to address all the memory, and hence the replay time is 32,768/8000 = 4.096 seconds. The clock is enabled when pin 13 November 2001  67 Fig.2: almost all the components mount on one PC board, as shown here. The two “jumpers” (for programming and playing) can be moved to a front panel DPDT switch to save opening the case every time you want to change the message. Likewise, the “GO” and “STOP” PC stakes can be brought outside the case. is taken high and stops when pin 13 is low. Pin 8 of IC4c is normally held high by a 10kΩ resistor, so clock pulses can pass through via pin 9 and onto the address counters. When the clock is stopped, IC4d pin 11 is forced high, which allows the write pulses through IC4c in program mode. More on this later. Starting and stopping of the clock and hence the replay is controlled by IC4a and IC4b. This crossover configuration is called a set-reset flipflop, and toggles between two states. Pin 1 of IC4a and pin 6 of IC4b are normally held high by 100kΩ resistors. Assuming pin 3 of IC4a is low, pin 4 of IC4b and hence pin 2 of IC4a will be high. When the GO input is pulled low, pin 1 of IC4a is pulled low, forcing pin 3 to go high. This enables the clock and forces pin 4 of IC4b to go low. Even when the GO input is taken high again, the flipflop stays in Compare this picture with the component overlay above when assembling the PC board and you shouldn’t have any problems. 68  Silicon Chip www.siliconchip.com.au Parts List – Message Player 1 PC board, code 01111011 1 plastic case, 197mm x 113mm x 63mm (Jaycar HB6012 or equivalent) 19 PC board stakes 2 2-pin headers with shunts, OR 1 DPDT mini slider switch 1 2-pin header shunt 1 25-pin male D connector with mounting hardware 1 76mm 8Ω speaker 1 DC panel-mount socket to match plug pack 1 28-pin IC socket 1 Twin AA battery holder 4 12mm x 3mm screws and nuts 4 Self adhesive feet Light duty hook up wire, tinned copper wire,10-way ribbon cable Double-sided tape pads (for securing battery holder) Fig.3: here’s how to wire the 25-pin “D” socket which connects to your PC via a standard parallel cable. Pins 18-25 would normally be soldered together with a straight length of tinned copper wire. the same state. The flipflop will only change state when pin 6 of IC4b is pulled low. This can occur in one of two ways: (1) by pulling the STOP input low; pin 3 of IC4a then goes low, disabling the clock and forcing pin 4 of IC4b high. (2) when pin 6 is pulled momentarily low by the negative pulse generated after the last memory cell has been addressed. This is accomplished by differentiating the negative edge of IC3 pin 3 with a .01µF capacitor and a 100kΩ resistor. In a similar way, the rising edge of IC4b pin 4 is differentiated by a .01µF capacitor and a 100kΩ resistor, creating a high-going pulse to reset the address counters. Diode D5 is employed to limit negative spikes which could damage the ICs when IC4b switches from high to low. Because the GO and STOP inputs may be controlled from external control circuits, diodes D1-D4 and the 10kΩ resistors are included to protect the inputs from excessive current and voltages. In summary, the start/stop operation works like this. Pulsing the GO line low starts the clock and the replay. www.siliconchip.com.au Semiconductors 1 32K x 8 SRAM 62256 or equivalent (IC1) 1 4040 12-stage binary counter (IC2) 1 4024 7-stage binary counter (IC3) 1 4093 quad NAND gate (IC4) 1 LM358 dual opamp (IC5) 1 LM386 audio power amp (IC6) 1 BC547 NPN transistor (Q1) 5 1N4148 signal diodes (D1-D5) 3 1N4004 power diodes (D6-D8) 1 1N5819 Schottky diode (D9) 1 7805 positive 5V regulator (REG1) Capacitors 2 470µF 25VW PC electrolytic 1 470µF 16VW PC electrolytic 1 100µF 16VW PC electrolytic 1 10µF 16VW PC electrolytic 5 0.1µF MKT polyester 1 .047µF MKT polyester 1 .022µF MKT polyester 4 .010µF MKT polyester 1 .0022µF MKT polyester Resistors (0.5W, 1%) 1 4.7Ω 1 10Ω 9 1kΩ 1 5.1kΩ   1 6.2kΩ 1 12kΩ 7 15kΩ 10 30kΩ 3 100kΩ 2 20kΩ horizontal trimpots (VR1, VR2) Pulsing the STOP input low during a replay will stop the clock and the replay. Replay will also stop automatically when the last address line goes from high to low. It is also possible to replay continuously by holding the GO input permanently low. In this case, there will be a small gap in the replay as the address counters go from maximum count to zero at the end of the message but it is hardly noticeable. Sound generation To read data from the SRAM, the 6 10kΩ shunt must be in the Play position. As each memory cell is addressed, the respective data will appear at the data pins. The array of 15kΩ and 30kΩ resistors connected to the data pins forms what is referred to as an R/2R digital-to-analog converter. This type was chosen because it is much cheaper than a dedicated D-to-A converter IC, and in any case does an excellent job in this circuit. The voltage at the D-to-A output is buffered and appears at pin 1 of IC5a. It has a resolution of 256 equal steps November 2001  69 ranging from around 0V to 5V. 0V represents the minimum level of the audio waveform and 5V the maximum of the audio waveform, while 2.5V is the rest or silence level. IC5a is wired as a non-inverting buffer and has a very high input impedance. This is necessary to stop the low impedance of the following circuits loading the D-to-A converter and reducing its accuracy. Due to the low sampling rate used (8kHz), the audio waveform needs to be low-pass filtered to remove high frequency components and improve the listening quality. IC5b is configured as a 2-pole lowpass filter with a cut-off frequency of 4kHz. The output level is quite high at this point, so a 10kΩ resistor is included between the output of IC5b and the volume control to avoid overloading the audio power amp stage. The signal from the volume control is capacitively coupled to the audio power amp IC6. This is a well-proven circuit using an LM386 in its basic form, driving an 8Ω speaker. A 4.7Ω resistor and a 470µF capacitor provide supply decoupling, while the .047µF capacitor and 10Ω resistor connected to pin 5 help to prevent instability in the output stage. Power supply The power supply is a standard 7805 3-terminal voltage regulator fed from a 9V plugpack. The circuit draws minimal current, so one rated at say, 150-300mA, will be ample. Avoid using a plugpack with a higher voltage rating, because the LM386 is not designed to withstand a supply voltage much greater than 12V. Of course, you can use a 9V regulated supply if you prefer. Diode D6 is used to prevent damage to the circuit from supplies connected with reverse polarity and a 470µF capacitor smoothes the usually unregulated plugpack output. The regulator is ‘jacked up’ with a diode (D7) in the ground lead, giving an output voltage of 5.6V. A 0.1µF capacitor is included at the output of REG1 to help prevent instability. The output voltage is reduced back to 5V by diode D8 which feeds the main circuit. The audio sections are powered from the unregulated supply and consequently do not operate when the main DC power is removed. When the main power is disconnected and the output of the regulator goes below 4V, Q1 turns off and CS is pulled high. When CS is high the SRAM is placed in standby mode and consumes very little power. The CS lead must be high before the battery backup supply switches in otherwise the data retention will not work. The keen-eyed will notice that the battery backup supply is also connected to the remainder of the logic ICs. These are CMOS chips with minimal current drain and so do not significantly degrade the expected battery life. Battery backup Programming Diode D9 is used to connect the battery backup supply when the main supply is removed. With the main supply connected, D9 is reverse-biased because the cathode is more positive than the anode, so no current flows from the batteries. However, when the main supply is missing, D9 conducts and the batteries supply power to the SRAM. D9 is a Schottky diode, which has a much lower forward voltage drop (about 0.3V) than a normal diode and is used to maximise the SRAM data retention time as the battery ages. A typical SRAM will hold its memory with a supply as low as 2V. With 3V or more from a pair of new AA cells, minus the 0.3V drop in the Schottky diode (D9), around 2.7V is available for the SRAM. Transistor Q1 is normally biased on due to the base resistor connected to the output of REG1. The collector of Q1 is connected to the Chip Select line of IC1, s o when main power is connected, CS is pulled low, enabling normal chip operation. Programming is done by connecting to the 25-pin parallel or printer port of a PC operating under DOS or a DOS box in Windows 95 or Windows 98 (Windows NT, Me and 2000 use the parallel port differently and may not work properly). The data to be programmed into the SRAM is output in parallel on pins 2-9, and the negative going programming clock pulses are output on pin 1. The ground connection is made through paralleled pins 18-25. To place the board into program mode, the shunt must be moved from the Play header onto the Program header pins. This causes pin 22 (Output Enable) to go high, disabling the output buffers, and connects the PC clock signal to IC4c and pin 27 (Write) of IC1. Before programming starts, the replay must be stopped so that the address counters are reset and addressing the first memory location. The 1kΩ resistors couple the data leads from the PC into the data pins of IC1 and also protect the inputs from damage from surge currents. The resistors associated with the D-to-A converter are much higher in value than 1kΩ and so do not interfere with the programming process. A 1kΩ resistor and a .01µF capacitor Table 1: RESISTOR COLOUR CODES              No. 3 10 7 1 6 1 1 9 1 1 Value 100kΩ 30kΩ 15kΩ 12kΩ 10kΩ 6.2kΩ 5.1kΩ 1kΩ 10Ω 4.7Ω 70  Silicon Chip 4-Band Code (1%) brown black yellow brown orange black orange brown brown green orange brown brown red orange brown brown black orange brown blue red red brown green brown red brown brown black red brown brown black black brown yellow violet gold brown 5-Band Code (1%) brown black black orange brown orange black black red brown brown green black red brown brown red black red brown brown black black red brown blue red black brown brown green brown black brown brown brown black black brown brown brown black black gold brown yellow violet black silver brown Table 2: CAPACITOR CODES Value IEC code EIA code 0.1µF   100n   104 .047µF  47n  473 .022µF  22n  223 .01µF  10n  103 .0022µF  2n2  222 www.siliconchip.com.au Fig.4: the full-size PC board pattern, ready for you to make your own or to check commercial boards for any defects. This pattern can also be downloaded from the SILICON CHIP website. filter the programming clock input, to eliminate unwanted noise from providing false write pulses. Before programming starts, pin 9 of IC4c will be high and as the programming pulse is also high, pin 10 of IC4c will be low. Programming starts with the PC outputting eight bits of data onto the data leads. The programming clock line is pulsed low, pulling the Write pin of IC1 low and writing the data into the addressed memory cell. When the programming pulse goes high again, pin 10 of IC4c goes low, clocking the address counters onto the next location. It is important when programming memory that the address and data lines are steady while the Write line is pulsed low and returns high. At first glance, the circuit may seem at odds to this requirement. However, the address counters will not change state until well after the Write line has been taken high due to the propagation delay in IC4c, IC2 and IC3. The software repeats this process until all the memory locations have been programmed. The rate that the programming pulses are generated and hence the total programming time could have been much faster but it has been purposely slowed down. This has been done to avoid any problems that might arise with long cable lengths and different PC printer ports. In any case, the whole process only takes about 15 seconds on an average PC. www.siliconchip.com.au At the conclusion of programming the shunt is moved back to the Play position. A 10kΩ resistor holds the Write pin high when the shunt is removed, avoiding unwanted writes to the SRAM. Construction Start construction by assembling the PC board. There are seven wire links to be installed, so do these first. Ensure they are straight and lay flat on the PC board. Follow this with the smaller components, such as the PC stakes, IC socket, trimpots, resistors and diodes. Next, install the capacitors, ensuring that the electrolytics are installed with correct polarity. Follow this with the transistor and ICs but leave the SRAM chip until later. Note that not all the ICs face the same way, so check the component overlay diagram before soldering them in. Take care with the CMOS chips, by trying to avoid touching the pins, earthing yourself before holding them and soldering the power supply pins first. The 5V regulator (REG1) is installed with its metal tab facing into the PC board. It runs cool and won’t need a heatsink. Once the PC board is loaded you can prepare the case which needs to have a number of holes made in it. See the photographs as a guide. Start with a hole to mount the DC socket at the righthand end of the case. The D connector is mounted on the side of the case near the programming PC stakes. The rectangular cutout for the D connector is easily made by drilling a number of large holes and finishing to shape with a small file. You will also need to drill two holes on either side of the cutout to secure the connector with the mounting hardware. Place the PC board on the bottom of the case, locating it so that there is enough room at the lefthand end to sit the battery holder. Mark the positions of the holes, remove the PC board and drill with a 3mm drill. Drill a pattern of holes in the middle of the lid to allow sound to escape from the speaker. If you use the specified case you’ll find dimples on the underside of the lid which make drilling neat, evenly-spaced holes relatively easy. Once the case has been prepared, install the DC socket and D connector and mount the PC board in the case with 3mm screws and nuts. An extra nut is placed on each screw between the case and the PC board to act as a spacer. Mount the speaker on the inside of the lid with a bead of silicone adhesive placed around the edge and leave to cure. The DC socket and the speaker are wired to the PC board stakes with hookup wire. Ensure that the speaker wires are long enough to allow the lid to be removed and placed alongside the case. The D connector is wired to the PC board using a short length November 2001  71 MESSAGE RECORDER/PLAYER 9V DC PLAY SILICON CHIP GO www.siliconchip.com.au PROGRAM STOP PC PARALLEL PORT Fig. 5: here’s the full-size artwork for the front panel. You can photocopy this or if you want it in colour, download it from www.siliconchip.com.au. As you can see, this panel incorporates a switch for the Play/Program function and also brings the “GO” and “STOP” pins outside the case. Exactly how you do this is up to you! of multi-coloured ribbon cable, with pins 18-25 of the D connector soldered together with a piece of bare tinned copper wire. The battery holder is placed at the end of the case and soldered to the battery PC stakes using the wires that come with the holder. Apply four self-adhesive feet to the bottom of the case when finished. Initial testing Once construction is complete, check your component placement and soldering carefully. Remember that the SRAM chip should not be in place yet. If all appears OK, connect the plug pack to the DC socket and measure the voltage at the power supply socket with a multimeter. This should be somewhere around 9-12V, depending on the plugpack used. Next, measure the voltage at REG1’s input, which should be around 0.6V less. Then check the voltage at the junction of D8 and D9, which should be close to 5V. If not, disconnect power quickly and look for errors, especially with the power wiring 72  Silicon Chip and the installation of the polarised components. When you are satisfied that the power supply is working, remove the supply and adjust the two trimpots to mid-position. Now plug the SRAM chip into its socket (with pin 1 closest to IC2) and place the shunt in the Play position. Apply power again, and briefly ground the GO input. A raucous noise should come from the speaker for about four seconds as the SRAM outputs its random data. Ground the GO input again and then momentarily ground the STOP input to check that the replay stops before the 4-second period elapses. Now permanently ground the GO input and measure the frequency of the clock at pin 11 of IC4d. Adjust VR1 until it is as close as you can get to 8kHz. In the unlikely event that no sound comes out, check firstly that VR2 is turned from the ground position. If this appears OK then you will have to check out the other parts of the circuit, such as the oscillator and the audio stages. Fault finding will be a lot easier if you have access to an oscilloscope, however with the foregoing description of the circuit you should be able to find most problems with just a multimeter and monitor amplifier. The software To download files into your Message Player, you will need to load the companion software file called MSGPLAY.EXE. This is available from the SILICON CHIP website and comes as a zipped up file. Once you have downloaded the file, unzip it using WinZip and copy it to a new folder on your PC. Use this folder to store all your generated sound files, as it makes them easier to find if they are all together. MSGPLAY is a DOS program, and is obviously designed to work with a PC running DOS. However, it runs quite happily in a DOS window under Win95 or Win98. As previously mentioned, Win NT, Me and 2000 operate differently and will not work properly with MSGPLAY. (Everything appears to be working but the WAV file doesn’t download). When you run MSGPLAY you will www.siliconchip.com.au be greeted with an opening menu screen. On this menu you have four options, which you highlight with the Up and Down arrows keys and then choose by pressing Enter. The program is easy to drive and provides lots of on-screen messages to help you through. The Open file menu allows you to enter a file name for opening, the Download menu steps you through the download process and choosing the final option exits you from the program. The Setup menu is the third option and allows you to select the printer port that you have the board connected to (usually LPT1) and also provides two test files for downloading. These files can be used if you think you have troubles with the hardware, or you simply can’t wait to hear something other than noise come out the speaker. The first file is four seconds of 1000Hz sinewave, which you can use to test that the whole board and the PC connection is working. The second test file is a 31Hz sawtooth wave with 256 steps. If you download this file and run it, you will be able to check the linearity of the D-to-A converter with an oscilloscope connected to pin 1 of IC5a. Making files and downloading Producing your own WAVE files is quite easy. Every PC that has a sound card and a sound recorder program can make WAVE files. To make advanced ones, through editing, mixing and adding special effects, you really need a special sound file editor. Don’t think that you have to rush out and spend a fortune on software, because you can download shareware or freeware from the Internet. They may not give you all the features of a professional sound file editing program but you’ll still be able to produce exciting results. Just get on the Internet, use your favourite search engine and start searching. The file that you create must be mono, 8kHz and 8-bit. If you have created it under another format, you need to convert it first. Just to make sure, the download software inspects the file when it is opened and informs you if it is not suitable. If your final file is large, you will only be able to store the first 32KB. If your file is smaller than 32KB, the download software will fill the remainder of the SRAM with silence (7F Hex). So let’s download and play a file. Firstly, run the download program, select the Setup option and choose the connected printer port. Then select the File open option and enter the file name. Select the Download option and follow the instructions. Place the shunt in the Program position and connect the cable. Start the download and you will see the counter showing you the progressive count as the bytes are written to the SRAM. You will also notice, as the download is progressing, that you can hear in slow time the file that you have created. This is quite normal as the data being downloaded to the SRAM is also fed to the D-to-A converter and audio amplifier but at a much slower rate than normal. Once the downloading is finished, move the shunt to the Play position and disconnect the cable. Pulse the GO input low (eg, short it to 0V) and you will hear your creation being played. To change the playback volume, adjust volume trimpot VR2 with a small screwdriver. Now is a good time to check the battery backup operation. Insert two new AA cells into the battery holder and disconnect the plugpack. Wait a few minutes and then re-connect the plugpack. Ground the GO input and if the file is still in the SRAM, you will hear it being played. If not, it may be that the batteries are in the wrong way or that diode D9 was installed with the incorrect polarity. Or the batteries could be flat! Interfacing The Message Player requires inputs to start and stop the replay. We’ll leave it up to you to work out an interface for your particular application. The robust GO and STOP input circuits allow a wide range of control possibilities. The simplest way is to use two pushbutton switches wired between the inputs and ground for manual control. However, if you have external inputs they can be either 5V negative-going pulses from logic circuits or a set of normally-open relay contacts or even open-collector transistor switches. Remember that the GO input must be normally high and grounded momentarily to start replay but you only need a similar STOP pulse if you don’t want the full 4-second replay. If you build a small interface board, you’ll find plenty of space within the case to mount it and you’ll probably be able to power it from the existing plugpack supply as well. SC K&W HEATSINK EXTRUSION. SEE OUR WEBSITE FOR THE COMPLETE OFF THE SHELF RANGE. www.siliconchip.com.au November 2001  73 PRODUCT SHOWCASE Need a new battery for your cordless drill? Here’s one! “Speedskins” convert keyboards for learning If you’ve ever had to buy a replacement battery for a cordless drill, you’ll know just how much they cost: usually the original price of the drill PLUS an arm and a leg. $70-$100 is common! Dick Smith Electronics have come up with the perfect solution. Don’t replace the battery: replace the whole thing! For less than forty bucks, you’ll get a 14.4V cordless drill with a 10mm keyless chuck, electronically-controlled variable speed (0 to 550rpm), forward and reverse switching and six-torque settings. It also has a 3-5 hour charger and It is considered very difficult to learn to touch type when you can see the keyboard letters – the temptation to “peek” is simply too great, slowing the learning process signficantly. If you’re in the position of teaching computer skills – or want to learn better – a Speedskin could be the answer. It is a flexible but opaque keyboard cover which doesn’t stop the keyboard being used, it simply hides the letters. It doesn’t cover the whole keyboard, only the alpha and numeric keys. And because keyboards are virtuallty all made to the same size, they’ll fit notebooks and laptops as well as conventional keyboards. They can even be separated for ergonomic keyboards. They are also available in DVORAK layout for those who want to learn this supposedly more efficient system. Speedskins should be available from most computer and stationery stores for around $19.00 to $24.00. even a screwdriver bit and a plastic carry case! Compare that with what you’d pay for just a new battery. Available at all DSE stores and through mail orders. Contact: Dick Smith Electronics 2 Davidson St, Chullora NSW 2190 Phone: (02) 9642 9100 Fax (02) 9642 9153 Website: www.dse.com.au Small business UPS American Power Conversion (APC) have available 350W or 500W unin-terruptible power supplies (UPS) designed to give small offices time to properly close files and shut down systems when power fails. “Power disturbances account for 45% of all computer availability problems,” said Leanne Cunnold, APC Managing Director (Aust & NZ). Depending on the computer type, the Back-Up CPS can give up to 20 minutes or so operation from its own battery after mains power fails. It also protects against power surges, including phones, faxes, modems, etc within its guard, including RJ-45 and USB ports for connection with the work- 74  Silicon Chip station. Filesaving, autoshutdown software for both Windows and Mac is included with with each UPS. Recommended retail price of the 350VA model is $221.00, while the 500VA model is $315.00. Contact: American Power Conversion Phone: (02) 9955 9366 Website: www.apcc.com Contact: Divisible by Zero PO Box 25, East Brunswick Vic 3057 Phone: (03) 9388 9902 Fax (02) 9388 9923 Website: www.dbz.com.au www.siliconchip.com.au SILICON CHIP WebLINK How many times have you wanted to access a company’s website but cannot remember their site name? Here's an exciting new concept from SILICON CHIP: you can access any of these organisations instantly by going to the SILICON CHIP website (www.siliconchip.com.au), clicking on WebLINK and then on the website graphic of the company you’re looking for. It’s that simple. No longer do you have to wade through search engines or look through pages of indexes – just point’n’click and the site you want will open! Your company or business can be a part of SILICON CHIP’s WebLINK. For one low rate you receive a printed entry each month on the SILICON CHIP WebLINK page with your home page graphic, company name, phone, fax and site details plus up to 50 words of description– and this is repeated on the WebLINK page on the SILICON CHIP website with the link of your choice active. Get those extra hits on your site from the right people in the electronics industry – the people who make decisions to buy your products. Call David Polkinghorne today on (02) 9979 5644 Based in Perth, WA, RobotOz carries an extensive range of Robots and Robotic Products from the world’s leading suppliers. Update: HOT NEWS!! NEW RANGE of Lynx-motion Robot Kits - Laser Cut Acrylic and Fluoro Colours!! Have a look! RobotOz Tel:(08) 9370 3456 Fax: (08) 9370 2323 WebLINK: www.robotoz.com.au A 100% Australian owned company supplying frequency control products to the highest international standards: filters, DIL’s, voltage, temperature compensated and oven controlled oscillators, monolithic and discrete filters and ceramic filters and resonators. Hy-Q International Pty Ltd Tel:(03) 9562-8222 Fax: (03) 9562 9009 WebLINK: www.hy-q.com.au For everything in radio control for aircraft, model boats and planes, etc. We also carry an extensive range of model flight control modules including GPS, altitude and speed, interfaces, autopilot and groundstation controllers. More info on our website! Silvertone Electronics Tel:(07) 4639 1100 Av-COMM Pty Ltd Tel:(02) 9939 4377 Fax: (02) 9939 4376 WebLINK: www.silvertone.com.au WebLINK: www.avcomm.com.au Looking for GENUINE Stamp products from Parallax . . . or Scott Edwards Electronics, microEngineering Labs & others? Easy to learn, easy to use, sophisticated CPU based controllers & peripherals. These and a huge range of components available now! VAF Research offers Speakers for the Audiophile Purist or Home Theatre Extremist. Home Entertainment Equipment and Accessories. They have ready-to-assemble loudspeaker kits along with quality drivers from the world's leading suppliers. MicroZed Computers Tel: (02) 6772 2777 Fax: (02) 6772 8987 WebLINK: www.microzed.com.au For broadcast, audiovisual and film industries. Wide bandwidth, high output and unconditional stability with hum-cancelling circuitry, front-panel video gain and cable eq adjustments. 240V AC, 120V AC or 24V DC VAF Research Pty Ltd Tel: 1800 818 882 Fax: (08) 8363 9997 NEW! HC-5 hi-res Vid eo Distribution Amplifier DVS5 Video & Audio Distribution Amplifier Five identical Video and Stereo outputs plus h/phone & monitor out. S-Video & Composite versions available. Professional quality. Fax: (07)4639 1275 International satellite TV reception in your home is now affordable. Send for your free info pack containing equipment catalog, satellite lists, etc or call for appointment to view. We can display all satellites from 76.5° to 180° WebLINK: www.vaf.com.au When it comes to purchasing quality products over the Web, you can count on the Wiltronics team to provide you with the best value for money. For over 25 years, Wiltronics has supplied the needs of the Electronics Industry, and look forward to continuing this service. Wiltronics Pty Ltd Tel: (03) 9762 3588 Fax: (03) 9762 5499 WebLINK: www.wiltronics.com.au JED designs and manufactures a range of single board computers (based on Wilke Tiger and Atmel AVR), as well as LCD displays and analog and digital I/O for PCs and controllers. JED also makes a PC PROM programmer and RS232/RS485 converters. Jed Microprocessors Pty Ltd Tel: (03) 9762 3588 Fax: (03) 9762 5499 WebLINK: www.jedmicro.com.au VGS2 Graphics Splitter High resolution 1in/2out VGA splitter. Comes with 1.5m HQ cable and 12V supply. Custom-length HQ VGA cables also available. Check our NEW website for latest prices and MONTHLY SPECIALS www.questronix.com.au Email: questav<at>questronix.com.au Video Processors, Colour Correctors, Stabilisers, TBC’s, Converters, etc. QUESTRONIX www.siliconchip.com.au www.siliconchip.com.au All mail: PO Box 548, Wahroonga NSW 2076 Ph (02) 9477 3596 Fax (02) 9477 3681 Visitors by appointment only NN ovember ovember2001  75 2001  75 Jaycar’s smallest-yet CMOS Colour Pinhole Camera with Audio This colour video camera measures just 20 x 20 x 16mm and is ideal for remote surveillance situations where a more-expensive CCD camera is not required. It is ideal for checking visitors at the front door, monitoring a sleeping baby or keeping an eye on the swimming pool. The camera has a composite video output so it can be voice operated recording. Software is included to enable messages to be downloaded to a PC via the printer port and e-mailed to friends or business colleagues. Accessories include an 2 x AAA batteries, earphone, microphone, line-out cable and a tele-phone adaptor. However, the telephone adaptor is NOT approved for use in Australia. Price at all Jaycar Electronics stores is $ 449.95 (Cat. XC-0280 ). Contact: Jaycar Electronics 100 Silverwater Rd, Silverwater NSW 2128 Phone: (02) 9741 8555 Fax (02) 9741 8500 Website: www.jaycar.com.au How to Do Everything With Your Scanner If you own a scanner – and more than one third of homes with Internet access also have scanners – do you get the most from it? If you’re typical of most users you’re probably only using a fraction of its capabilities. Many people use their scanners only to send photos to their friends, not realising there’s so much more they could do. Now there’s a new book from McGraw-Hill which can really answer all those scanner questions for you: “How to Do Everything with Your Scanner” by Jill Gilbert, describes not only how to use a scanner to capture a wide variety of images, it offers advice and tips on image and color correction and provides details on using photo editing software to edit, repair and modify scanned images There are also scanning projects for all members of the family, including creating a logo, stationery, adding 76  Silicon Chip broadcast quality connected directly to a video recorder or the A/V input of a normal TV. It sells for $159.95 (Cat. QC-3459). . . . and an 810 minute Digital Voice Recorder A new Samsung digital voice recorder from Jaycar will store up to 810 minutes (Yes, that’s 13.5 hours) of digital voice quality audio in a neat, slim hand-held unit. Four separate message groups are available and each group can have up to 100 messages. The recorder has an integrated LCD to show the status of various functions including battery condition, rec/playback level, message number & length, message group, etc. Also included is a VOX function and variable microphone sensitivity for AUDIO MODULES images to a web page or e-mail and there is even an 8-page colour insert that shows step by step progress for repair/ restoration of damaged photos and several of the included sample projects. With a recommended retail price of $44.95, this book (along with many others in the McGraw-Hill Technical range) is available from Dick Smith Electronics, Jaycar Electronics, Altron-ics, Technical Books (Melbourne) and all good bookstores. Contact: McGraw-Hill Book Co Aust Pty Ltd 4 Barcoo St, East Roseville NSW 2069 Phone (02) 9415 9899 Website: www.mcgraw-hill.com.au Manufactured in Australia Harbuch Electronics Pty Ltd 9/40 Leighton Pl. HORNSBY 2077 Ph (02) 9476-5854 Fx (02) 9476-3231 CAN BUS Analyser from Yokogawa The Controller Area Network (CAN) bus is widely used for automotive, factory automation and other applications, The Yokogawa DL7200 CAN BUS signal analyser captures and analyses the waveforms of bus signals that previously proved difficult with conventional protocol analysers. It comprises a multichannel digital oscilloscope with four analog channels and 16-bit logic input channel (optional) as its base unit. Users can analyse the CAN bus in synchronisation not only with its signal but also with other signals, such as a signal from a sensor or a control signal sent to a module. Using this feature along with the CAN bus trigger and analysis functions, users can efficiently evaluate and debug the overall range of a system. The CAN Bus Analysis Functions analyse waveform data existing on the CAN bus and acquire into long-recordlength memory with a maximum of 16 megawords (MW) in a time-series SC manner. Contact: Yokogawa Australia Pty Ltd Private Mail Bag 24 Nth Ryde NSW 1670 Phone: (02) 9805 0699 Fax: (02) 9888 1844 Website: www.yokogawa.com.au www.siliconchip.com.au CIRCUIT NOTEBOOK Interesting circuit ideas which we have checked but not built and tested. Contributions from readers are welcome and will be paid for at standard rates. Alternative circuit for a white LED torch This is an alternative approach to the circuit for the White LED Torch in the December 2000 issue. It will give a usable light from a battery with an open circuit terminal voltage of 0.5V (that’s so flat that it will not run anything else at all). The circuit will drive an 8000mcd high intensity white LED to 20mA at 3.6V from a single 1.5V cell or, by changing a resis­tor, from a single 1.2V rechargeable cell. The LED used for the prototype was from Dick Smith Electronics (Cat Z-3982). The circuit is a blocking oscillator type and the compon­ ents are not critical – it is almost guaranteed to oscillate. L1 and L2 are wound on an “H” shaped ferrite bobbin which measured 3.25mm inside diameter, 4.25mm inside length. These bobbins are in abundance in switchmode power supplies from old computers, monitors, colour TVs, etc. The precise dimensions are not critical although if the size is too different you may have to alter the value of R1 to compensate. Central locking interface Some cheap car alarms do not have a connection for the central locking system. However, in most it should be possible to find a point www.siliconchip.com.au L1 is wound by first stripping the enamel from one end of 0.25mm enamelled copper wire (not critical but physical size needs to be considered) and soldering it to one of the mounting pins of the bobbin. This done, wind 100 turns and strip and solder the other end to the other pin. L2 is wound straight on top of L1 and consists of 30 turns of the same wire. The ends of this winding are left floating and held in place by hot glue or wax. The reason for such a close turns ratio is to keep the circuit oscillating at very low vol­tages and very heavy loads. R1 is 22Ω for a 1.5V battery or 10Ω for a 1.2V battery. For different LEDs or multiple LEDs you may wish to experiment with other values. Instead of risking your expensive white LED you can temporarily use two red LEDs in series. If the LED is out of circuit in the alarm circuit which is high when the alarm is activated and low when it is off. This signal can then be used to drive this relay circuit to operate the central lock­ing system. The interface circuit converts when the oscillator starts the voltage across C1 (output) quickly rises above 9V. Connecting this to the LED would result in its immediate destruction. Switch off and discharge the capacitor before connecting the LED or make sure the LED is never out of circuit. L1 measures 300µH. The transistor used is not critical as long as it can handle the input current. The 1.5V circuit draws 130mA for the full 20mA output at 3.6V. If the unit fails to oscillate, as indicated by no or little voltage across C1, re­verse either (not both) L1 or L2. Philip Chugg, Rocherlea, Tas. ($40) each toggle of the alarm signal to a brief pulse to operate the two relays which then are then connected in parallel with appropriate contacts on the master solenoid in the central locking system. Frank Keller, via email. ($40) November 2001  77 Temperature-controlled soldering iron One reason why commercial soldering stations are expensive is that, in general, they require the use of soldering irons with inbuilt temperature sensors, such as thermocouples. This circuit eliminates the need for a special sensor because it senses the temperature of a soldering iron heating element di­rectly from its resistance. Thus this circuit will, in principle, work with any iron with a resistance which varies predictably and in the right direction with temperature (ie, positive temperature coefficient). A soldering iron that’s ideally suited for use with this controller is available from Dick Smith Electronics (Cat T-2100). This circuit runs from a 12V battery or a mains-operated DC source. It works as follows: a DC-DC converter (IC1, Q1, D1, Q2, T1, D2, L1, etc) steps up the 12V DC input to about 16V. The higher voltage boosts the power to the iron and reduces warm-up time. This output voltage is applied to a resistance bridge in which the heating element of the iron forms one leg. The other components of the bridge include resistors R7-R9 and pots VR2VR4. When the iron reaches a preset temperature, as set by VR4, the output of IC2a goes high, sending a signal to switching regulator IC1. This forces the output of the converter to a relatively low voltage. A bi-colour LED indicates that the iron has reached the preset temperature by changing from red to green. The iron now begins to cool until it drops below the preset temperature, at which point the output voltage from the DC-DC converter goes high again and the cycle repeats. A degree of hysteresis built into the circuit makes the LED flicker between red and green while the iron is maintained at its preset temperature. Calibrate the circuit as follows: while the iron is still relatively cold, monitor the input voltage and current and adjust VR1 so that the input power (Volts x Amps) is about 50W. When you have done that, set VR4 to maximum and adjust VR2 so that the LED flickers between red and green when the iron has reached the desired maximum temperature. Finally, set VR4 to mid-position and adjust VR3 so that the LED flickers when the iron reaches the desired midrange operat­ing temperature. As an 78  Silicon Chip www.siliconchip.com.au example, you might choose to set the maximum temperature to about 400°C and the Herman Nacinovich this month’s wi mid-range operat­ing is nner of the Wav etek temperature to about Meterman 85XT 350°C. The overall true RMS digita l multimeter. temperature range, in that case, should be approximately 280°C to 400°C. Check that the calibration is correct and repeat the ad­ justment procedure if necessary. Use a temperature probe, prefer­ably one designed especially for soldering irons, rather than guesswork, when making the adjustment. Note: VR4 should have a logarithmic taper to compensate for non-linearity in the temperature-resistance characteristic of the soldering iron. Herman Nacinovich, Gulgong, NSW. $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ As you can see, we pay good money for $ $ $ each of the “Circuit Notebook” contributions $ $ $ $ $ published. But now $ $ $ $ there’s an even better $ $ reason to send in $ $ $ $ your circuit idea: $ $ $ $ each month, the $ $ $ $ best contribution $ $ published will $ $ $ $ win oneof of $ $ winone $ $ these superb $ $ $ $ Wavetek Meterman $ $ $ $ 85XT true RMS $ $ $ $ multimeters - valued $ $ at around $380! $ $ $ $ So don’t keep that $ $ $ $ brilliant circuit secret $ $ $ $ any more: send it to $ $ $ $ SILICON CHIP and $ $ you could be a winner! $ $ $ $ $ Contributions must be your own original work or a major $ $ adaptation and not published elsewhere nor submitted for $ $ $ publication elsewhere. SILICON CHIP’s decision is final. $ $ $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ CONTRIBUTE AND WIN! 1 meter to win every month! www.siliconchip.com.au • • • • • • • • If you need: P.C.B. High Speed Drill 3M Scotchmark Laser Labels P.C.B. Material – Negative or Positive acting Light Box – Single or Double Sided – Large or Small Etch Tank – Bubble Electronic Components and Equipment for TAFEs, Colleges and Schools Prompt and Economical Delivery FREE ADVICE ON ANY OF OUR PRODUCTS FROM DEDICATED PEOPLE WITH HANDS-ON EXPERIENCE We now stock Hawera Carbide Tool Bits KALEX 40 Wallis Ave E. Ivanhoe 3079 Using a LED as a light sensor This circuit shows how to use an ordinary LED as a light sensor. It makes use of the photovoltaic voltage developed across the LED when it is exposed to light. LEDs are cheaper than photo­ diodes and come with a built-in filter, which is useful when the application involves colour discrimination. The photo-voltage of a red LED (its bandgap voltage) is typically about 2V. The source impedance of this voltage is about 800MΩ in daylight, rising to infinity in darkness. A TL071 JFET input op amp is used to amplify and buffer this extremely high impedance signal. Resistor R1 ensures that the op amp “sees” a 0V input when the LED is in total darkness. To avoid undue loading of the signal, R1 would ideally be a 100MΩ or larger resistor but since such high values are rare and expensive I used a smaller value and increased the gain of the op amp to compensate for the voltage loss. To avoid the need for a second variable resistor to set the op amp’s input offset to zero, R1 must be large P.C.B. Makers ! Ph (03) 9497 3422 FAX (03) 9499 2381 ALL MAJOR CREDIT CARDS ACCEPTED Silicon Chip Binders enough for the reduced voltage across the LED to swamp the op amp’s input offset voltage. With a 30MΩ resistor for R1, the voltage at the op amp input when the LED is exposed to bright light is reduced to about 60mV. This is just over four times the 13mV maximum input offset of the TL071 op amp. R1 can be three 10MΩ resistors in series. Alternatively, I have found that a reverse-biased 1N4148 diode has an impedance of about 30MΩ (connect it in the circuit with the anode to ground). The output of the circuit is about 0V when the LED is in darkness. VR1 sets the gain of the op amp and it should be ad­justed to give the required output voltage when the LED is ex­posed to bright light. Andrew Partridge, Kuranda, Qld. ($30) REAL VALUE AT $12.95 PLUS P&P  Heavy board covers with 2-tone green vinyl covering  Buy five & get them postage free Price: $A12.95 plus $A5.50 p&p each (Australia only) Just fill in & mail the handy order form in this issue; or fax (02) 9979 6503; or ring (02) 9979 5644 & quote your credit card number. November 2001  79 VINTAGE RADIO By RODNEY CHAMPNESS, VK3UG Test Instruments For Vintage Radio Restoration; Pt.1 The restoration of vintage radios requires a range of skills, from cabinet restoration to fault finding. Fault finding and fine tuning the performance of a piece of equipment is a skill that is developed over time. It is dramatically enhanced by the use of test instruments. A considerable number of vintage radio buffs don’t have a technical background in radio and electronics and may therefore have problems restoring the electronics of their radios. Run-of-the-mill faults can be found fairly easily found with quite basic instruments. In most cases, if a set hasn’t been butchered and is in reasonable condition, it is probable that the set can be restored to working order without the use of instru­ments. This does not mean plugging the set into the mains or connecting batteries and expecting the set to work properly. Sometimes this is all that is required – but rarely so and I never recommend this approach. Why is this so? The question has to be asked: “why was the radio taken out of service?” Usually, it was because it had developed some fault. If the aim is to get the set going without any test instru­ ments, it is often possible to achieve this by replacing compon­ents that are known to be particularly troublesome. The key components to be replaced are the automatic gain control (AGC) bypass capacitors, the audio interstage coupling capacitor(s) and the output valve plate bypass capacitor. In addition, the elec­trolytic filter capacitors in the power supply should be replaced in case they have become short circuit or excessively leaky. With these components replaced, the set may work and work well but you cannot be sure if all faulty components have been replaced. It’s a bit like working blindfolded. On the other hand, the set may still not work and it could have some serious fault that could cause more damage when power is applied and to anyone who may touch the chassis. Some people are comfortable with this approach but I’m not, although it is less risky that the first method. However, all is not lost, as with the use of a few common test instruments most faults will be found in receivers. This month, we’ll start with the humble multimeter. The multimeter This photo shows two typical 20,000 ohm/volt moving-coil multimeters. Analog meters have an advantage if the measured reading is fluctuating. 80  Silicon Chip An analog moving coil multimeter or a digital multimeter (DMM) will find most faults where voltage, current or resistance can be measured. It is very helpful to have a circuit when con­ducting measurements on a piece of radio equipment, or any other electronic gear for that matter. A good circuit diagram will list the voltages www.siliconchip.com.au that can be expected at various points throughout a receiver. In older circuits, it will even specify the character­istics of the multimeter, usually 1000 ohms per volt. Measuring voltages Until the early 50s, most multimeters had a rating of 1000 ohms per volt. This meant that if the meter was set on the 250V range, it had a total resistance between the two probes of 250,000 ohms (250kΩ), while on the 50V range it had a resistance of 50,000 ohms (50kΩ). It is most important to know this when making measurements. For example, the first audio stage may have a 250kΩ plate resistor connected to the 250V supply rail – see Fig.1. In order to measure the plate voltage, the multimeter can be switched to the 250V range and the probes connected between the plate of the valve and earth/chassis. However, the maximum reading that can be obtained would be 125V, even if the valve drew no current. This is because of the “loading” effect of the multimeter’s internal resistance. In effect, this internal resistance forms a voltage divider with the 250kΩ resistor connected to the +250V rail, so the read­ing is much lower than expected – in this case, half the expected reading. Similarly, if the multimeter was switched to the 50V range, the maximum reading would be 42V. And if the 10V range were selected, the meter would read a maximum of 9.6V. That’s because the internal resistance Because of their much higher input impedance, digital multimeters (DMMs) are much more accurate than moving coil types for making voltage measurements. They also often include capacitance measurement, transistor gain and diode check ranges. of the meter would be 50kΩ and 10kΩ respectively, and so the loading effects are much greater. However, when reading from the high tension (HT) line to earth, the voltage reading on the meter will be correct as the circuit has virtually no resistance in series with the HT line. To overcome the loading problem it is most desirable that the meter used have a rating of at least 20,000 ohms per volt, which most moving-coil multimeters have. The readings will still be a bit low in high-impedance circuits such as the first audio plate circuit but not drastically so. Remember that on circuits with voltages shown as measured with a 1000 ohm per volt meter, the actual voltage measured with either a 20,000 ohms per volt meter or a DMM will be higher than the pub­lished figures. A moving-coil multimeter of 20,000 ohms per volt rating cannot measure the AGC voltage in a receiver as it acts as a near short circuit on the AGC line. On the 10V range, it has a resist­ance of only 200kΩ between the probe points, whereas the AGC filter resistor may be 2MΩ (two megohms). In this case, the indicated AGC voltage reading will be a tenth of normal. Meterman. The Working Man’s Meter. Meters that fit your job. Meters that fit your wallet. Introducing Meterman, a hot new brand of test and measurement tools that gives you the performance you need at a price you can afford. Meterman is a line of more than 60 meters, clamps, and testers. Each one designed with the right combination of features, functions and accuracy to fit your application. You work hard on the job. Get the tool that’s easy on your wallet. Ask your local test and measurement supplier for the Meterman products or contact Meterman on Locked Bag 5004 Baulkham Hills NSW 2153, phone 02 8853 8812 or fax 02 8850 3300, or visit metermantesttools.com TM www.siliconchip.com.au November 2001  81 Silicon Chip Binders REAL VALUE AT $12.95 PLUS P&P These binders will protect your copies of SILICON CHIP. They feature heavy-board covers & are made from a dis­ tinctive 2-tone green vinyl. They hold up to 14 issues & will look great on your bookshelf. Having looked at the deficiency of the moving coil multi­meter in making measurements in high impedance circuits, it is time to look at ways of overcoming this. A DMM with an input resistance of 10MΩ or more can be used to accurately measure voltages in all but the highest impedance circuits. For normal valve receivers, it can be used to measure all voltages up to around 1000V. Note that some cheap DMMs, such as the one in the centre of the accompanying photograph, have an input resistance of just 1MΩ which isn’t good enough for some circuit measurements in valve receivers. Pay that little bit extra; it’s worth it. I use both digital and moving coil multimeters, as each have their strong points. Measuring current Or fax (02) 9979 6503; or ring (02) 9979 5644 & quote your credit card number. Measuring current with a DMM or a moving coil multimeter is not a problem with either type. You will need to break into the circuit so that the meter leads can be placed in series with the circuit. When making measurements, make sure that you start with a high current range and then go lower. Meters do not take kindly to currents or voltages that send the needle or DMM well over range. After you have finished, always make sure that the meter is set back onto a high voltage range (and the meter probes connected to the voltage inputs), otherwise an expensive mistake could be made by connecting a meter that’s still on a current range across the power supply. Unfortunately, I’ve managed to do this a few times. Use this handy form Measuring resistance  80mm internal width  SILICON CHIP logo printed in gold-coloured lettering on spine & cover  Buy five and get them postage free! Price: $A12.95 plus $A5.50 p&p. Available only in Australia. Silicon Chip Publications PO Box 139 Collaroy Beach 2097 Enclosed is my cheque/money order for $________ or please debit my ❏ Bankcard ❏ Visa   ❏ Mastercard Card No: _________________________________ Card Expiry Date ____/____ Signature ________________________ Name ____________________________ Address__________________________ __________________ P/code_______ 82  Silicon Chip To accurately measure a resistance, one end of the compon­ent to be checked should be lifted out of circuit and then the meter probes placed across the component (usually a coil or a resistor). No adjustment of a DMM is necessary to accomplish this task (other than setting the unit to the “ohms” range) but a moving coil meter should be “zeroed” before trying to measure a resistance. Moving coil meters have very cramped and rather inaccurate meter readings at the higher resistance readings on each range. By comparison, a DMM is much easier to read. Always make sure that there are no charged capacitors in circuit when measuring ohms. Not only will the readings be inaccurate but damage to the meter may occur. Return the meter to a high voltage range after measuring resist­ a nces so that no meter damage occurs when voltages are next measured. Selecting a multimeter (1) Analog multimeters: the AC and DC voltage ranges need to extend to 1000V. The lowest range with fullscale deflection is likely to be 10V for AC and 2.5V for DC. DC current only can be measured with these units and can start from as low as 50µA full scale deflection (FSD) and go to as high as 10A FSD. The resistance ranges should start at around one ohm per division and measure as low as 1Ω. The maximum resistance that can be measured (or, more accurately, estimated), is in the region of 10-20 megohms. They are quite inaccurate at the high end of the measurement ranges. The meter movement needs to be rated at 20,000 ohms/volt (or higher). An analog meter shines particularly when the parameter being measured is varying, as the trend of adjustments can easily be seen. The claimed accuracy of most of these meters is around ±4% FSD. Examples of units that meet the above criteria are the Altronics Q1025, the Dick Smith Electronics Q1025 and the Jaycar QM-1020. The Altronics and DSE models appear to be identical units. There will be similar units Fig.1: this diagram shows a 1000 ohm per volt meter measuring the plate voltage in a circuit with a 250kΩ plate load resistor. It shows 125V on the 250V range (ie, 50% the correct value), 42V on the 50V range and 9.6V on the 10V range. By contrast, a DMM with an input impedance of 10MΩ gives a reading of 244V – 97.6% the correct value). www.siliconchip.com.au Photo Gallery: Music Masters Mozart Looking for an old valve? or a new valve? BUYING - SELLING - TRADING Australasia's biggest selection Also valve audio & guitar amp. books SSAE DL size for CATALOGUE ELECTRONIC VALVE & TUBE COMPANY Music Masters Radio Company, Brisbane, produced the “Mozart” in 1940. The set is a superhet with the following valves: 6A8-G frequency changer; 6U7-G IF amplifier; 6B6-G first-audio/detector/AVC rectifier; 6V6-G output and 80 rectifier. Photo & information courtesy of the Historical Radio Society of Australia. from other suppliers too, so have a good look around to find a meter that satisfies your needs. Digital multimeters The selection of a suitable DMM is not as simple as select­ing an analog meter as there are just so many more to choose from, with a myriad of features. The first thing I look at is the input resistance and this should be at least 10MΩ or even higher, so that high impedance circuits are not loaded excessively when measurements are being made. Most meters costing more than about $45 are likely to be suitable. The voltage ranges should start at about 200-400mV AC & DC and extend to 700V AC and 1000V DC. On AC, the maximum frequency that can be applied to the meter without affecting the measure­ ment accuracy varies. A couple of mine will still read the cor­rect voltage at frequencies up to a least 2kHz. The current ranges should start at around 200µA on AC & DC and extend www.siliconchip.com.au to 10A or maybe even 20A AC and DC. The resistance ranges should be able to measure to below 1Ω and up to at least 10MΩ or 20MΩ. One facility I find very handy are capacitance measurement ranges. However, not all meters with such ranges will accurately measure low capacitance values. It is desirable to be able to accurately measure values down to 10pF and up to around 20µF or more. Meters with a range of 4nF (.004µF) or lower will usually measure down to around 10pF with reasonable accuracy. Always make sure that a capacitor is discharged before trying to measure it, otherwise damage to the meter may occur. With some capacitors, it is necessary to use clip leads to con­nect them to the meter. If this is done, note the reading of the meter before the capacitor is connected and subtract this from the total reading to compensate for the lead capacitance (note: this only applies when measuring very small value capacitors). Sometimes, when measuring a capacitor in a receiver, such as a tun- PO Box 487 Drysdale, Victoria 3222. Tel: (03) 5257 2297; Fax: (03) 5257 1773 Mob: 0417 143 167; email: evatco<at>mira.net Premises at: 76 Bluff Road, St Leonards, Vic 3223 SMART FASTCHARGERS® 2 NEW MODELS WITH OPTIONS TO SUIT YOUR NEEDS & BUDGET Now with 240V AC + 12V DC operation PLUS fully automatic voltage detection Use these REFLEX® chargers for all your Nicads and NIMH batteries: Power tools  Torches  Radio equip.  Mobile phones  Video cameras  Field test instruments  RC models incl. indoor flight  Laptops  Photographic equip.  Toys  Others  Rugged, compact and very portable. Designed for maximum battery capacity and longest battery life. AVOIDS THE WELL KNOWN MEMORY EFFECT. SAVES MONEY & TIME: Restore most Nicads with memory effect to capacity. Recover batteries with very low remaining voltage. CHARGES VERY FAST plus ELIMINATES THE NEED TO DISCHARGE: charge standard batteries in minimum 3 min., max. 1 to 4 hrs, depending on mA/h rating. Partially empty batteries are just topped up. Batteries always remain cool; this increases the total battery life and also the battery’s reliability. DESIGNED AND MADE IN AUSTRALIA For a FREE, detailed technical description please Ph (03) 6492 1368; Fax (03) 6492 1329; or email smartfastchargers<at>bigpond.com 2567 Wilmot Rd., Devonport, TAS 7310 November 2001  83 Photo Gallery: Stromberg-Carlson Model A22 3-Valve TRF Receiver An auto-ranging facility is also useful in some circumstances but can be confusing where a range changes unexpectedly. If you believe auto-ranging is for you, make sure that you can manually select the range that you want as well. Just about a all units these days have a claimed accuracy on the voltage ranges of 0.5% (or better) ±1 count. Of course, this applies only if the meter has not been abused in any way. Accuracy greater than this is not necessary for routine work. Analog or digital? Made by Stromberg-Carlson, Sydney, in 1930, the Model A22 is a 3-valve TRF receiver housed in an elegant long-legged wooden cabinet. It was fitted with an 8-inch (200mm) loudspeaker and used the following valves: B443 detector, E415 output and UX280 rectifier. Photo & information courtesy of the Historical Radio Society of Australia. ing capacitor, it is desirable to swap the test leads over to get the correct reading. The actual capacity of the meter circuitry may cause erroneous readings if near the receiver chassis. An audible continuity facility is another useful feature, as this makes it unnecessary to watch the meter when making continuity tests. A diode test 84  Silicon Chip range is a handy range too – this will measure the forward voltage drop in a solid state junction, whether it be in a diode or a transistor. It’s also handy for checking that there is no conductivity in the reverse direction and for determining whether a transistor is PNP or NPN type and whether a diode is a silicon or germanium type. This is really your personal choice. Analog units are more suitable if a reading is varying and some people prefer to see a needle moving across a meter scale. That said, digital multi­ met­ers (DMMs) are much better value for money, are more accurate and have a greater selection of measurement facilities. What’s more, it doesn’t matter which way around you connect the probes when making measurements on a DMM. Analog meters, on the other hand, must be connected with their positive (red) lead to the more positive voltage point when measuring a DC voltage. The same applies when measuring current. Which ever meter you select, make sure that there is an insulated collar around each probe shaft just above the probe tip. These collars are designed so that if your fingers slip along the probe (eg, in humid weather), they will not come in contact with the metal part of the probe (which could give you a shock). What do I use? I use both digital and analog meters, although most of the time I prefer a digital meter. A multimeter, whether it is an analog or digital model, is by far the most important test instrument that you will use for fault-finding and testing vintage radios. Select wisely and you will have a versatile instrument that will last you for years. However, while a multimeter will allow you to find most faults in a receiver, there are some problems that a multi­meter will not be able to detect. Under these circumstances, other test instruments are needed. We’ll look at some of these instruments in future columns, including signal generators, signal injectors, signal tracers, transSC former testers and so on. www.siliconchip.com.au (USED) OLYMPUS SZ SERIES STEREO-SCOPIC MICROSCOPES WITH ZOOM: In as new condition, less than one year old. Supplied with twin fibre-optic illuminator ideal for commercial, industrial and educational use. Worth around $4500, We have just a few of these priced at around $1500.For more info check our web-stite or call Branko 02 95843563. AS NEW AT 1/3 OF THE PRICE MORE! MORE! MORE! (NEW) MULTI FUNCTION BATTERY CHARGER / DISCHARGER: WITH A FREE BONUS (NEW) SANYO CADNICA 6 CELL AA NiCad PACK 7.2V/ 740mAh, (Cells easily spilt )(shown here without outside heat-shrink) New in original box with instructions. This unit was designed to charge NI-CD & NIMH mobile phone batteries of 4.8V, 6.0V and 7.2V. Operates from 12-24V DC input. Features include processor control & multi stage charge indicator. By changing the value of one resistor it can charge higher voltages, although a higher voltage plugpack is required for 9.4V or higher. Includes cigarette lighter lead, 12V / 1A DC plugpack & instructions for modifications for higher voltages. The unit has battery charging terminals but the user will have to make their own adaptor to interface to a battery. The plugpack supplied alone is worth around $30 retail. Weight is 0.9kg. . (ZA0100) $29 (NEW) SANYO CADNICA 6 CELL AA NiCad PACK 7.2V/ 740mAh, (Cells easily spilt )$7ea NEW 80mm 12V FANS Ideal replacement for computer power supply fans. 12V <at> 0.15A..$4 or 4 for $12 SOUND CODE HOPPING UHF MINI TX / RX PAIR: High Security in a very small transmitter & receiver pre-built package. Crystal locked 433MHz, with approx.100M range. Indicator flash relays, boot release and immobiliser output. Two TX & 1 RXunits (RTXC2): $99 We have more used test HAND HELD BAR-CODE SCANNERS equipment. we need to clear some Used SYMBOL brand. These units use a to make way for the next lot. But small 1mW helium-neon tube and a you may have already missed it. scanning motor and columnating optics. Has The only way to make sure you its own internal 12V power supply to scan don’t is to subscribe to our bargain bar-codes. Comes with suitable plug-pack corner and receive advanced and cables.$66 notice Just send us a blank E-Mail to.... DESK TOP BARb a r g a i n c o r n e r - s u b s c r i b e CODE SCANNERS <at> o a t l e y e l e c t r o n i c s . c o m Used desk-top scanners uses a $5 BARGAIN BUSINESS SPEAKERPHONE: BACK AGAIN! We have managed to get a small quantity of these phones again. PANASONIC model KX-TS85ALW telephones were used during the 2000 Olympics. Lots of features inc. speed dialler, Hands Free Volume Control, Call Waiting, Ringer Indicator, Call Forward immediate, Dial lock, Redial, Recall. You will find these as a newly introduced product in a Major Australian Electronics dealers' catalogue for $161. Manual is not supplied but can be downloaded from our web-site(KXTS85) Soon to be published in RADIOMAG magazine LOW COST 5 GEARED AC MOTORS Brand new small mains operated geared motors, very strong, made for rotating microwave turntables, 240V/ 50Hz/3W/5RPM., $4Ea. or or 4 for $12. (NEW) 24V BATTERY CHARGER: Denison brand (Aust.) Computer Charger, Model 12/160/8. This is a 3 phase, 24V, 12cell lead acid battery charger. 750mm(H) x 500mm(W) x 400mm(D). : (ZB0204) $440 (4 only) 36V: Model 18/160/8, 36V, 18cell charger. 750mm(H) x 500mm(W) x 400mm (D). (ZB0205) $390 (2 only) 36V: Model 18/100/8. This is a 3 phase, 36V, 18cell 750mm(H) x 500mm(W) x 400mm(D). These are very heavy, we can definitely not send them by Post: (ZB0202) $370 (2 only) See web-site for more info. Valve amplifier A genuine 4 valve amplifier that can drive a pair of headphones. Uses subminiature pentode valves that wire directly to the PCB. Includes Bass, Treble and Volume controls and has transformer and line output connections. The HT volltage is derived by a voltage multiplier and Filament voltage is derived from a voltage regulator. The whole is powered from a 9V AC-1A plug-pack. This plugpack can power two of these kits: two are WARM needed for Stereo sound. This kit will RICH be released within six weeks. 2.4GHz AUDIO / VIDEO TRANSMITTER / RECEIVER KIT: Most transmitters on the market promise 100 to 200m range and deliver only 50m on open ground with line of site. We tested this kit it in an urban area, in a less than ideal environment, under power lines, over metal fences and through houses at 200m. At 200m we had a perfect picture, no lines or snow etc. We are working on a dipole antenna that should give more than 1km range. Easy to build using prebuilt Transmitter & Receiver modules. KIT PRICE: (K171) $159 laser diode.Contains four rotating and about 10 fixed front surfaced mirrors plus control electronics $55 USED) IBM NETWORK LASER PRINTER 17 (4317): Dual bin unit. 17 pages per minute print speed, 600 dpi resolution. This printer does double sided printing. These units do not include a toner cartridge or a network card (parallel port only). Weight is 23kg: (ZA0314) $300 (10 only) 20 x 2 LCD BACKLIT CHARACTER DISPLAY: Made by Optrex model #DMC2059, (data is available for similar 20 x 2 displays). 6mm x 8mm characters, 122mm wide x 30mm high. PCB dimensions 151mm wide x 56mm high. Uses standard Hitachi chipset (HD44780) with LED backlight (DL8) $11 each or 3 for $27 (USED) PRO QUALITY CCD CAMERAS: We have a variety of used cameras with a variety of different lenses from $180- check out our website for more info. CLEARANCE AUSTRALIAN MADE BARGAIN NEW.... EVAPORATIVE WATER COOLERS. GEARED STEPPER Some boxes may be a little dirty or slightly damaged. Features inc. economic running. MOTORS... These Safe 6VDC operation (Plugpack supplied), Small geared stepper motors would be ideal internal stainless steel reservoir, Can be for telescope tracking used with commercially delivered water etc And include a bottles or with a large soft-drink bottle... 1350:1 Reduction. $25...(Bottle not supplied) www.oatleyelectronics.com Orders: Ph ( 02 ) 9584 3563, Fax 9584 3561, sales<at>oatleyelectronics.com, PO BoxN89 Oatley NSW 2223 www.siliconchip.com.au ovember 2001  85 major cards with ph. & fax orders, Post & Pack typically $7 Prices subject to change without notice ACN 068 740 081 ABN18068 740 081 $16 limited stock $25 SC_NOV_01 Silicon Chip Back Issues April 1989: Auxiliary Brake Light Flasher; What You Need to Know About Capacitors; 32-Band Graphic Equaliser, Pt.2. May 1989: Build A Synthesised Tom-Tom; Biofeedback Monitor For Your PC; Simple Stub Filter For Suppressing TV Interference. July 1989: Exhaust Gas Monitor; Experimental Mains Hum Sniffers; Compact Ultrasonic Car Alarm; The NSW 86 Class Electrics. September 1989: 2-Chip Portable AM Stereo Radio (Uses MC13024 and TX7376P) Pt.1; High Or Low Fluid Level Detector; Studio Series 20-Band Stereo Equaliser, Pt.2. November 1993: High Efficiency Inverter For Fluorescent Tubes; Stereo Preamplifier With IR Remote Control, Pt.3; Siren Sound Generator; Engine Management, Pt.2; Experiments For Games Cards. December 1993: Remote Controller For Garage Doors; Build A LED Stroboscope; Build A 25W Audio Amplifier Module; A 1-Chip Melody Generator; Engine Management, Pt.3; Index To Volume 6. May 1991: 13.5V 25A Power Supply For Transceivers; Stereo Audio Expander; Fluorescent Light Simulator For Model Railways; How To Install Multiple TV Outlets, Pt.1. July 1991: Loudspeaker Protector For Stereo Amplifiers; 4-Channel Lighting Desk, Pt.2; How To Install Multiple TV Outlets, Pt.2; Tuning In To Satellite TV, Pt.2. September 1991: Digital Altimeter For Gliders & Ultralights; Ultrasonic Switch For Mains Appliances; The Basics Of A/D & D/A Conversion; Plotting The Course Of Thunderstorms. January 1994: 3A 40V Variable Power Supply; Solar Panel Switching Regulator; Printer Status Indicator; Mini Drill Speed Controller; Stepper Motor Controller; Active Filter Design; Engine Management, Pt.4. February 1994: Build A 90-Second Message Recorder; 12-240VAC 200W Inverter; 0.5W Audio Amplifier; 3A 40V Adjustable Power Supply; Engine Management, Pt.5; Airbags In Cars – How They Work. March 1994: Intelligent IR Remote Controller; 50W (LM3876) Audio Amplifier Module; Level Crossing Detector For Model Railways; Voice Activated Switch For FM Microphones; Engine Management, Pt.6. April 1994: Sound & Lights For Model Railway Level Crossings; Discrete Dual Supply Voltage Regulator; Universal Stereo Preamplifier; Digital Water Tank Gauge; Engine Management, Pt.7. October 1989: FM Radio Intercom For Motorbikes Pt.1; GaAsFet Preamplifier For Amateur TV; 2-Chip Portable AM Stereo Radio, Pt.2. October 1991: Build A Talking Voltmeter For Your PC, Pt.1; SteamSound Simulator For Model Railways Mk.II; Magnetic Field Strength Meter; Digital Altimeter For Gliders, Pt.2; Military Applications Of R/C Aircraft. November 1989: Radfax Decoder For Your PC (Displays Fax, RTTY & Morse); FM Radio Intercom For Motorbikes, Pt.2; 2-Chip Portable AM Stereo Radio, Pt.3; Floppy Disk Drive Formats & Options. November 1991: Colour TV Pattern Generator, Pt.1; A Junkbox 2-Valve Receiver; Flashing Alarm Light For Cars; Digital Altimeter For Gliders, Pt.3; Build A Talking Voltmeter For Your PC, Pt.2. January 1990: High Quality Sine/Square Oscillator; Service Tips For Your VCR; Phone Patch For Radio Amateurs; Active Antenna Kit; Designing UHF Transmitter Stages. December 1991: TV Transmitter For VCRs With UHF Modulators; Infrared Light Beam Relay; Colour TV Pattern Generator, Pt.2; Index To Volume 4. February 1990: A 16-Channel Mixing Desk; Build A High Quality Audio Oscillator, Pt.2; The Incredible Hot Canaries; Random Wire Antenna Tuner For 6 Metres; Phone Patch For Radio Amateurs, Pt.2. March 1992: TV Transmitter For VHF VCRs; Thermostatic Switch For Car Radiator Fans; Coping With Damaged Computer Directories; Valve Substitution In Vintage Radios. March 1990: Delay Unit For Automatic Antennas; Workout Timer For Aerobics Classes; 16-Channel Mixing Desk, Pt.2; Using The UC3906 SLA Battery Charger IC. April 1992: IR Remote Control For Model Railroads; Differential Input Buffer For CROs; Understanding Computer Memory; Aligning Vintage Radio Receivers, Pt.1. April 1990: Dual Tracking ±50V Power Supply; Voice-Operated Switch (VOX) With Delayed Audio; 16-Channel Mixing Desk, Pt.3; Active CW Filter; Servicing Your Microwave Oven. June 1992: Multi-Station Headset Intercom, Pt.1; Video Switcher For Camcorders & VCRs; IR Remote Control For Model Railroads, Pt.3; 15-Watt 12-240V Inverter; A Look At Hard Disk Drives. September 1994: Automatic Discharger For Nicad Battery Packs; MiniVox Voice Operated Relay; Image Intensified Night Viewer; AM Radio For Weather Beacons; Dual Diversity Tuner For FM Microphones, Pt.2; Electronic Engine Management, Pt.12. June 1990: Multi-Sector Home Burglar Alarm; Build A Low-Noise Universal Stereo Preamplifier; Load Protector For Power Supplies. August 1992: Automatic SLA Battery Charger; Miniature 1.5V To 9V DC Converter; 1kW Dummy Load Box For Audio Amplifiers; Troubleshooting Vintage Radio Receivers; The MIDI Interface Explained. October 1994: How Dolby Surround Sound Works; Dual Rail Variable Power Supply; Build A Talking Headlight Reminder; Electronic Ballast For Fluorescent Lights; Electronic Engine Management, Pt.13. October 1992: 2kW 24VDC - 240VAC Sinewave Inverter; Multi-Sector Home Burglar Alarm, Pt.2; Mini Amplifier For Personal Stereos; A Regulated Lead-Acid Battery Charger. November 1994: Dry Cell Battery Rejuvenator; Novel Alphanumeric Clock; 80-Metre DSB Amateur Transmitter; Twin-Cell Nicad Discharger (See May 1993); How To Plot Patterns Direct to PC Boards. February 1993: Three Projects For Model Railroads; Low Fuel Indicator For Cars; Audio Level/VU Meter (LED Readout); An Electronic Cockroach; 2kW 24VDC To 240VAC Sinewave Inverter, Pt.5. December 1994: Easy-To-Build Car Burglar Alarm; Three-Spot Low Distortion Sinewave Oscillator; Clifford – A Pesky Electronic Cricket; Remote Control System for Models, Pt.1; Index to Vol.7. March 1993: Solar Charger For 12V Batteries; Alarm-Triggered Security Camera; Reaction Trainer; Audio Mixer for Camcorders; A 24-Hour Sidereal Clock For Astronomers. January 1995: Sun Tracker For Solar Panels; Battery Saver For Torches; Dolby Pro-Logic Surround Sound Decoder, Pt.2; Dual Channel UHF Remote Control; Stereo Microphone Pre­amp­lifier. April 1993: Solar-Powered Electric Fence; Audio Power Meter; Three-Function Home Weather Station; 12VDC To 70VDC Converter; Digital Clock With Battery Back-Up. February 1995: 50-Watt/Channel Stereo Amplifier Module; Digital Effects Unit For Musicians; 6-Channel Thermometer With LCD Readout; Wide Range Electrostatic Loudspeakers, Pt.1; Oil Change Timer For Cars; Remote Control System For Models, Pt.2. July 1990: Digital Sine/Square Generator, Pt.1 (covers 0-500kHz); Burglar Alarm Keypad & Combination Lock; Build A Simple Electronic Die; A Low-Cost Dual Power Supply. August 1990: High Stability UHF Remote Transmitter; Universal Safety Timer For Mains Appliances (9 Minutes); Horace The Electronic Cricket; Digital Sine/Square Generator, Pt.2. September 1990: A Low-Cost 3-Digit Counter Module; Build A Simple Shortwave Converter For The 2-Metre Band; The Care & Feeding Of Nicad Battery Packs (Getting The Most From Nicad Batteries). October 1990: The Dangers of PCBs; Low-Cost Siren For Burglar Alarms; Dimming Controls For The Discolight; Surfsound Simulator; DC Offset For DMMs; NE602 Converter Circuits. November 1990: Connecting Two TV Sets To One VCR; Build An Egg Timer; Low-Cost Model Train Controller; 1.5V To 9V DC Converter; Introduction To Digital Electronics; A 6-Metre Amateur Transmitter. June 1993: AM Radio Trainer, Pt.1; Remote Control For The Woofer Stopper; Digital Voltmeter For Cars; Windows-Based Logic Analyser. May 1994: Fast Charger For Nicad Batteries; Induction Balance Metal Locator; Multi-Channel Infrared Remote Control; Dual Electronic Dice; Simple Servo Driver Circuits; Engine Management, Pt.8. June 1994: 200W/350W Mosfet Amplifier Module; A Coolant Level Alarm For Your Car; 80-Metre AM/CW Transmitter For Amateurs; Converting Phono Inputs To Line Inputs; PC-Based Nicad Battery Monitor; Engine Management, Pt.9. July 1994: Build A 4-Bay Bow-Tie UHF TV Antenna; PreChamp 2-Transistor Preamplifier; Steam Train Whistle & Diesel Horn Simulator; 6V SLA Battery Charger; Electronic Engine Management, Pt.10. August 1994: High-Power Dimmer For Incandescent Lights; Microprocessor-Controlled Morse Keyer; Dual Diversity Tuner For FM Microphones, Pt.1; Nicad Zapper (For Resurrecting Nicad Batteries); Electronic Engine Management, Pt.11. March 1995: 50 Watt Per Channel Stereo Amplifier, Pt.1; Subcarrier Decoder For FM Receivers; Wide Range Electrostatic Loudspeakers, Pt.2; IR Illuminator For CCD Cameras; Remote Control System For Models, Pt.3; Simple CW Filter. December 1990: 100W DC-DC Converter For Car Amplifiers; Wiper Pulser For Rear Windows; 4-Digit Combination Lock; 5W Power Amplifier For The 6-Metre Amateur Transmitter; Index To Volume 3. July 1993: Single Chip Message Recorder; Light Beam Relay Extender; AM Radio Trainer, Pt.2; Quiz Game Adjudicator; Windows-Based Logic Analyser, Pt.2; Antenna Tuners – Why They Are Useful. \January 1991: Fast Charger For Nicad Batteries, Pt.1; Have Fun With The Fruit Machine (Simple Poker Machine); Build A Two-Tone Alarm Module; The Dangers of Servicing Microwave Ovens. August 1993: Low-Cost Colour Video Fader; 60-LED Brake Light Array; Microprocessor-Based Sidereal Clock; A Look At Satellites & Their Orbits. April 1995: FM Radio Trainer, Pt.1; Photographic Timer For Dark­ rooms; Balanced Microphone Preamp. & Line Filter; 50W/Channel Stereo Amplifier, Pt.2; Wide Range Electrostatic Loudspeakers, Pt.3; 8-Channel Decoder For Radio Remote Control. March 1991: Transistor Beta Tester Mk.2; A Synthesised AM Stereo Tuner, Pt.2; Multi-Purpose I/O Board For PC-Compatibles; Universal Wideband RF Preamplifier For Amateur Radio & TV. September 1993: Automatic Nicad Battery Charger/Discharger; Stereo Preamplifier With IR Remote Control, Pt.1; In-Circuit Transistor Tester; +5V to ±15V DC Converter; Remote-Controlled Cockroach. May 1995: Build A Guitar Headphone Amplifier; FM Radio Trainer, Pt.2; Transistor/Mosfet Tester For DMMs; A 16-Channel Decoder For Radio Remote Control; Introduction to Satellite TV. April 1991: Steam Sound Simulator For Model Railroads; Simple 12/24V Light Chaser; Synthesised AM Stereo Tuner, Pt.3; A Practical Approach To Amplifier Design, Pt.2. October 1993: Courtesy Light Switch-Off Timer For Cars; Wireless Microphone For Musicians; Stereo Preamplifier With IR Remote Control, Pt.2; Electronic Engine Management, Pt.1. June 1995: Build A Satellite TV Receiver; Train Detector For Model Railways; 1W Audio Amplifier Trainer; Low-Cost Video Security System; Multi-Channel Radio Control Transmitter For Models, Pt.1. ORDER FORM Pleasesend send the followingback backissues: issues: Please the following      ____________________________________________________________ Enclosed is my cheque/money order for $­______or please debit my: ❏ Bankcard ❏ Visa Card ❏ Master Card Card No. Signature ___________________________ Card expiry date_____ /______ Name ______________________________ Phone No (___) ____________ PLEASE PRINT Street ______________________________________________________ Suburb/town _______________________________ Postcode ___________ 86  Silicon Chip 10% OF F SUBSCR TO IB OR IF Y ERS OU 10 OR M BUY ORE Note: prices include postage & packing Australia ....................... $A7.70 (incl. GST) Overseas (airmail) ............................ $A10 Detach and mail to: Silicon Chip Publications, PO Box 139, Collaroy, NSW, Australia 2097. Or call (02) 9979 5644 & quote your credit card details or fax the details to (02) 9979 6503. Email: silchip<at>siliconchip.com.au www.siliconchip.com.au January 1998: Build Your Own 4-Channel Lightshow, Pt.1 (runs off 12VDC or 12VAC); Command Control System For Model Railways, Pt.1; Pan Controller For CCD Cameras; Build A One Or Two-Lamp Flasher; Understanding Electric Lighting, Pt.3. February 2000: Multi-Sector Sprinkler Controller; A Digital Voltmeter For Your Car; An Ultrasonic Parking Radar; Build A Safety Switch Checker; Build A Sine/Square Wave Oscillator; Marantz SR-18 Home Theatre Receiver (Review); The “Hot Chip” Starter Kit (Review). February 1998: Multi-Purpose Fast Battery Charger, Pt.1; Telephone Exchange Simulator For Testing; Command Control System For Model Railways, Pt.2; Build Your Own 4-Channel Lightshow, Pt.2; Understanding Electric Lighting, Pt.4. March 2000: Doing A Lazarus On An Old Computer; Ultra Low Distortion 100W Amplifier Module, Pt.1; Electronic Wind Vane With 16-LED Display; Glowplug Driver For Powered Models; The OzTrip Car Computer, Pt.1; Multisim Circuit Design & Simulation Package (Review). April 1998: Automatic Garage Door Opener, Pt.1; 40V 8A Adjustable Power Supply, Pt.1; PC-Controlled 0-30kHz Sinewave Generator; Build A Laser Light Show; Understanding Electric Lighting; Pt.6. May 2000: Ultra-LD Stereo Amplifier, Pt.2; Build A LED Dice (With PIC Microcontroller); Low-Cost AT Keyboard Translator (Converts IBM Scan-Codes To ASCII); 50A Motor Speed Controller For Models. May 1998: Troubleshooting Your PC, Pt.1; Build A 3-LED Logic Probe; Automatic Garage Door Opener, Pt.2; Command Control For Model Railways, Pt.4; 40V 8A Adjustable Power Supply, Pt.2. June 2000: Automatic Rain Gauge With Digital Readout; Parallel Port VHF FM Receiver; Li’l Powerhouse Switchmode Power Supply (1.23V to 40V) Pt.1; CD Compressor For Cars Or The Home. June 1998: Troubleshooting Your PC, Pt.2; Understanding Electric Lighting, Pt.7; Universal High Energy Ignition System; The Roadies’ Friend Cable Tester; Universal Stepper Motor Controller; Command Control For Model Railways, Pt.5. July 2000: A Moving Message Display; Compact Fluorescent Lamp Driver; El-Cheapo Musicians’ Lead Tester; Li’l Powerhouse Switchmode Power Supply (1.23V to 40V) Pt.2; Say Bye-Bye To Your 12V Car Battery. January 1996: Surround Sound Mixer & Decoder, Pt.1; Magnetic Card Reader; Build An Automatic Sprinkler Controller; IR Remote Control For The Railpower Mk.2; Recharging Nicad Batteries For Long Life. July 1998: Troubleshooting Your PC, Pt.3 (Installing A Modem And Solving Problems); Build A Heat Controller; 15-Watt Class-A Audio Amplifier Module; Simple Charger For 6V & 12V SLA Batteries; Automatic Semiconductor Analyser; Understanding Electric Lighting, Pt.8. August 2000: Build A Theremin For Really Eeerie Sounds; Come In Spinner (writes messages in “thin-air”); Loudspeaker Protector & Fan Controller For The Ultra-LD Stereo Amplifier; Proximity Switch For 240VAC Lamps; Structured Cabling For Computer Networks. April 1996: Cheap Battery Refills For Mobile Telephones; 125W Audio Amplifier Module; Knock Indicator For Leaded Petrol Engines; Multi-Channel Radio Control Transmitter; Pt.3; Cathode Ray Oscilloscopes, Pt.2. August 1998: Troubleshooting Your PC, Pt.4 (Adding Extra Memory); Build The Opus One Loudspeaker System; Simple I/O Card With Automatic Data Logging; Build A Beat Triggered Strobe; A 15-Watt Per Channel Class-A Stereo Amplifier. September 2000: Build A Swimming Pool Alarm; An 8-Channel PC Relay Board; Fuel Mixture Display For Cars, Pt.1; Protoboards – The Easy Way Into Electronics, Pt.1; Cybug The Solar Fly. July 1995: Electric Fence Controller; How To Run Two Trains On A Single Track (Incl. Lights & Sound); Setting Up A Satellite TV Ground Station; Build A Reliable Door Minder. August 1995: Fuel Injector Monitor For Cars; Gain Controlled Microphone Preamp; Audio Lab PC-Controlled Test Instrument, Pt.1; How To Identify IDE Hard Disk Drive Parameters. September 1995: Railpower Mk.2 Walkaround Throttle For Model Railways, Pt.1; Keypad Combination Lock; The Vader Voice; Jacob’s Ladder Display; Audio Lab PC-Controlled Test Instrument, Pt.2. October 1995: 3-Way Bass Reflex Loudspeaker System; Railpower Mk.2 Walkaround Throttle For Model Railways, Pt.2; Fast Charger For Nicad Batteries; Digital Speedometer & Fuel Gauge For Cars, Pt.1. November 1995: Mixture Display For Fuel Injected Cars; CB Trans­verter For The 80M Amateur Band, Pt.1; PIR Movement Detector; Digital Speedometer & Fuel Gauge For Cars, Pt.2. December 1995: Engine Immobiliser; 5-Band Equaliser; CB Transverter For The 80M Amateur Band, Pt.2; Subwoofer Controller; Knock Sensing In Cars; Index To Volume 8. May 1996: Upgrading The CPU In Your PC; High Voltage Insulation Tester; Knightrider Bi-Directional LED Chaser; Simple Duplex Intercom Using Fibre Optic Cable; Cathode Ray Oscilloscopes, Pt.3. June 1996: BassBox CAD Loudspeaker Software Reviewed; Stereo Simulator (uses delay chip); Rope Light Chaser; Low Ohms Tester For Your DMM; Automatic 10A Battery Charger. July 1996: Build A VGA Digital Oscilloscope, Pt.1; Remote Control Extender For VCRs; 2A SLA Battery Charger; 3-Band Parametric Equaliser; Single Channel 8-Bit Data Logger. August 1996: Introduction to IGBTs; Electronic Starter For Fluores­cent Lamps; VGA Oscilloscope, Pt.2; 350W Amplifier Module; Masthead Amplifier For TV & FM; Cathode Ray Oscilloscopes, Pt.4. September 1998: Troubleshooting Your PC, Pt.5 (Software Problems & DOS Games); A Blocked Air-Filter Alarm; A Waa-Waa Pedal For Your Guitar; Build A Plasma Display Or Jacob’s Ladder; Gear Change Indicator For Cars; Capacity Indicator For Rechargeable Batteries. October 1998: Lab Quality AC Millivoltmeter, Pt.1; PC-Controlled Stress-O-Meter; Versatile Electronic Guitar Limiter; 12V Trickle Charger For Float Conditions; Adding An External Battery Pack To Your Flashgun. November 1998: The Christmas Star; A Turbo Timer For Cars; Build A Poker Machine, Pt.1; FM Transmitter For Musicians; Lab Quality AC Millivoltmeter, Pt.2; Setting Up A LAN Using TCP/IP; Understanding Electric Lighting, Pt.9; Improving AM Radio Reception, Pt.1. September 1996: VGA Oscilloscope, Pt.3; IR Stereo Headphone Link, Pt.1; High Quality PA Loudspeaker; 3-Band HF Amateur Radio Receiver; Cathode Ray Oscilloscopes, Pt.5. December 1998: Protect Your Car With The Engine Immobiliser Mk.2; Thermocouple Adaptor For DMMs; A Regulated 12V DC Plugpack; Build Your Own Poker Machine, Pt.2; Improving AM Radio Reception, Pt.2; Mixer Module For F3B Glider Operations. October 1996: Send Video Signals Over Twisted Pair Cable; Power Control With A Light Dimmer; 600W DC-DC Converter For Car Hifi Systems, Pt.1; IR Stereo Headphone Link, Pt.2; Build A Multi-Media Sound System, Pt.1; Multi-Channel Radio Control Transmitter, Pt.8. January 1999: High-Voltage Megohm Tester; Getting Started With BASIC Stamp; LED Bargraph Ammeter For Cars; Keypad Engine Immobiliser; Improving AM Radio Reception, Pt.3; Electric Lighting, Pt.10. November 1996: Adding A Parallel Port To Your Computer; 8-Channel Stereo Mixer, Pt.1; Low-Cost Fluorescent Light Inverter; How To Repair Light Dimmers; 600W DC-DC Converter For Car Hifi Systems, Pt.2. February 1999: Installing A Computer Network; Making Front Panels For Your Projects; Low Distortion Audio Signal Generator, Pt.1; Command Control Decoder For Model Railways; Build A Digital Capacitance Meter; Build A Remote Control Tester; Electric Lighting, Pt.11. December 1996: Active Filter Cleans Up Your CW Reception; A Fast Clock For Railway Modellers; Laser Pistol & Electronic Target; Build A Sound Level Meter; 8-Channel Stereo Mixer, Pt.2; Index To Volume 9. January 1997: How To Network Your PC; Control Panel For Multiple Smoke Alarms, Pt.1; Build A Pink Noise Source; Computer Controlled Dual Power Supply, Pt.1; Digi-Temp Monitors Eight Temperatures. February 1997: Cathode Ray Oscilloscopes, Pt.6; PC-Con­trolled Moving Message Display; Computer Controlled Dual Power Supply, Pt.2; Loud Sounding Telephone Alarm; Control Panel For Multiple Smoke Alarms, Pt.2. March 1997: Driving A Computer By Remote Control; Plastic Power PA Amplifier (175W); Signalling & Lighting For Model Railways; Build A Jumbo LED Clock; Cathode Ray Oscilloscopes, Pt.7. April 1997: Simple Timer With No ICs; Digital Voltmeter For Cars; Loudspeaker Protector For Stereo Amplifiers; Model Train Controller; A Look At Signal Tracing; Pt.1; Cathode Ray Oscilloscopes, Pt.8. May 1997: Neon Tube Modulator For Light Systems; Traffic Lights For A Model Intersection; The Spacewriter – It Writes Messages In Thin Air; A Look At Signal Tracing; Pt.2; Cathode Ray Oscilloscopes, Pt.9. June 1997: PC-Controlled Thermometer/Thermostat; Colour TV Pattern Generator, Pt.1; Audio/RF Signal Tracer; High-Current Speed Controller For 12V/24V Motors; Manual Control Circuit For A Stepper Motor. March 1999: Getting Started With Linux; Pt.1; Build A Digital Anemometer; 3-Channel Current Monitor With Data Logging; Simple DIY PIC Programmer; Easy-To-Build Audio Compressor; Low Distortion Audio Signal Generator, Pt.2; Electric Lighting, Pt.12. April 1999: Getting Started With Linux; Pt.2; High-Power Electric Fence Controller; Bass Cube Subwoofer; Programmable Thermostat/ Thermometer; Build An Infrared Sentry; Rev Limiter For Cars; Electric Lighting, Pt.13; Autopilots For Radio-Controlled Model Aircraft. May 1999: The Line Dancer Robot; An X-Y Table With Stepper Motor Control, Pt.1; Three Electric Fence Testers; Heart Of LEDs; Build A Carbon Monoxide Alarm; Getting Started With Linux; Pt.3. June 1999: FM Radio Tuner Card For PCs; X-Y Table With Stepper Motor Control, Pt.2; Programmable Ignition Timing Module For Cars, Pt.1; Hard Disk Drive Upgrades Without Reinstalling Software? July 1999: Build A Dog Silencer; 10µH to 19.99mH Inductance Meter; Build An Audio-Video Transmitter; Programmable Ignition Timing Module For Cars, Pt.2; XYZ Table With Stepper Motor Control, Pt.3. August 1999: Remote Modem Controller; Daytime Running Lights For Cars; Build A PC Monitor Checker; Switching Temperature Controller; XYZ Table With Stepper Motor Control, Pt.4; Electric Lighting, Pt.14. July 1997: Infrared Remote Volume Control; A Flexible Interface Card For PCs; Points Controller For Model Railways; Colour TV Pattern Generator, Pt.2; An In-Line Mixer For Radio Control Receivers. September 1999: Automatic Addressing On TCP/IP Networks; Autonomouse The Robot, Pt.1; Voice Direct Speech Recognition Module; Digital Electrolytic Capacitance Meter; XYZ Table With Stepper Motor Control, Pt.5; Peltier-Powered Can Cooler. August 1997: The Bass Barrel Subwoofer; 500 Watt Audio Power Amplifier Module; A TENs Unit For Pain Relief; Addressable PC Card For Stepper Motor Control; Remote Controlled Gates For Your Home. October 1999: Sharing A Modem For Internet & Email Access (WinGate); Build The Railpower Model Train Controller, Pt.1; Semiconductor Curve Tracer; Autonomouse The Robot, Pt.2; XYZ Table With Stepper Motor Control, Pt.6; Introducing Home Theatre. September 1997: Multi-Spark Capacitor Discharge Ignition; 500W Audio Power Amplifier, Pt.2; A Video Security System For Your Home; PC Card For Controlling Two Stepper Motors; HiFi On A Budget. October 1997: Build A 5-Digit Tachometer; Add Central Locking To Your Car; PC-Controlled 6-Channel Voltmeter; 500W Audio Power Amplifier, Pt.3; Customising The Windows 95 Start Menu. November 1997: Heavy Duty 10A 240VAC Motor Speed Controller; Easy-To-Use Cable & Wiring Tester; Build A Musical Doorbell; Replacing Foam Speaker Surrounds; Understanding Electric Lighting Pt.1. December 1997: Speed Alarm For Cars; 2-Axis Robot w/Gripper; Loudness Control For Car Hifi Systems; Stepper Motor Driver With Buffer; Power Supply For Stepper Motor Cards; Understanding Electric Lighting Pt.2. www.siliconchip.com.au November 1999: Electric Lighting, Pt.15; Setting Up An Email Server; Speed Alarm For Cars, Pt.1; Multi-Colour LED Christmas Tree; Build An Intercom Station Expander; Foldback Loudspeaker System For Musicians; Railpower Model Train Controller, Pt.2. December 1999: Electric Lighting, Pt.16; Build A Solar Panel Regulator; The PC Powerhouse (gives fixed +12V, +9V, +6V & +5V rails); The Fortune Finder Metal Locator; Speed Alarm For Cars, Pt.2; Railpower Model Train Controller, Pt.3; Index To Volume 12. January 2000: Spring Reverberation Module; An Audio-Video Test Generator; Build The Picman Programmable Robot; A Parallel Port Interface Card; Off-Hook Indicator For Telephone Lines. October 2000: Guitar Jammer For Practice & Jam Sessions; Booze Buster Breath Tester; A Wand-Mounted Inspection Camera); Installing A Free-Air Subwoofer In Your Car; Fuel Mixture Display For Cars, Pt.2; Protoboards – The Easy Way Into Electronics, Pt.2. November 2000: Santa & Rudolf Chrissie Display; 2-Channel Guitar Preamplifier, Pt.1; Message Bank & Missed Call Alert; Electronic Thermostat; Protoboards – The Easy Way Into Electronics, Pt.3. December 2000: Home Networking For Shared Internet Access; Build A Bright-White LED Torch; 2-Channel Guitar Preamplifier, Pt.2 (Digital Reverb); Driving An LCD From The Parallel Port; Build A morse Clock; Protoboards – The Easy Way Into Electronics, Pt.4; Index To Vol.13. January 2001: LP Resurrection – Transferring LPs & Tapes To CD; The LP Doctor – Clean Up Clicks & Pops, Pt.1; Arbitrary Waveform Generator; 2-Channel Guitar Preamplifier, Pt.3; PIC Programmer & TestBed; Wireless Networking. February 2001: How To Observe Meteors Using Junked Gear; An Easy Way To Make PC Boards; L’il Pulser Train Controller; Midi-Mate – A MIDI Interface For PCs; Build The Bass Blazer; 2-Metre Elevated Groundplane Antenna; The LP Doctor – Clean Up Clicks & Pops, Pt.2. March 2001: Driving Your Phone From A PC; Making Photo Resist PC Boards At Home; Big-Digit 12/24 Hour Clock; Parallel Port PIC Programmer & Checkerboard; Protoboards – The Easy Way Into Electronics, Pt.5; More MIDI – A Simple MIDI Expansion Box. April 2001: A GPS Module For Your PC; Dr Video – An Easy-To-Build Video Stabiliser; A Tremolo Unit For Musicians; Minimitter FM Stereo Transmitter; Intelligent Nicad Battery Charger; Computer Tips – Tweaking Internet Connection Sharing. May 2001: Powerful 12V Mini Stereo Amplifier; Microcontroller-Based 4-Digit Counter Modules; Two White-LED Torches To Build; A Servo With Lots Of Grunt; PowerPak – A Multi-Voltage Power Supply; Using Linux To Share An Internet Connection, Pt.1; Computer Tips – Tweaking Windows With TweakUI. June 2001: Fast Universal Battery Charger, Pt.1; Phonome – Call, Listen In & Switch Devices On & Off; L’il Snooper – A low-Cost Automatic Camera Switcher; Build a PC Games Port Tester; Using Linux To Share An Internet Connection, Pt.2; A PC To Die For, Pt.1. July 2001: The HeartMate Heart Rate Monitor; Do Not Disturb Tele­ phone Timer; Pic-Toc – A Simple Alarm Clock; Fast Universal Battery Charger, Pt.2; A PC To Die For, Pt.2; Computer Tips – Backing Up Your Email; Digital Amplifiers Are Here (Feature). August 2001: Direct Injection Box For Musicians; Build A 200W Mosfet Amplifier Module; Headlight Reminder For Cars; 40MHz 6-Digit Frequency Counter Module; A PC To Die For, Pt.3; Using Linux To Share An Internet Connection, Pt.3. September 2001: MP3 – Changing The Way You Listen To Music; Making MP3s – Rippers & Encoders; Build Your Own MP3 Jukebox; PC-Controlled Mains Switch; Personal Noise Source For Tinnitus Sufferers; The Sooper Snooper Directional Microphone; Using Linux To Share An Internet Connection, Pt.3; Newgroups – Common Terms & Abbreviations. October 2001: A Video Microscope From Scrounged Parts; Build Your Own MP3 Jukebox, Pt.2; Super-Sensitive Body Detector; An automotive Thermometer; Programming Adapter For Atmel Microcomputers; Building Your Own PC – One Man’s Approach. PLEASE NOTE: November 1987 to March 1989, June 1989, August 1989, December 1989, May 1990, February 1991, June 1991, August 1991, January 1992, February 1992, July 1992, September 1992, November 1992, December 1992, January 1993, May 1993, February 1996, March 1998 and february 1999 are now sold out. All other issues are presently in stock. For readers wanting articles from sold-out issues, we can supply photostat copies (or tear sheets) at $7.70 per article (includes p&p). When supplying photostat articles or back copies, we automatically supply any relevant notes & errata at no extra charge. A complete index to all articles published to date is available on floppy disk for $11 including p&p, or can be downloaded free from our web site: www.siliconchip.com.au November 2001  87 ASK SILICON CHIP Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line and we’ll answer your question. Write to: Ask Silicon Chip, PO Box 139, Collaroy Beach, NSW 2097; or send an email to silchip<at>siliconchip.com.au Fence tester does not flash I was wondering if there was a modification to the Maxi Electric Fence Tester described in the May 1999 issue. I pur­chased it to monitor the performance of a mini electric fence module. We are failing to keep the cats off a balcony and have been losing fish. The electric fence tester is not flashing. I can measure 500V+ from the anode to the cathode, which I suspect should just about fire the tube without any triggering pulses. I don’t have a means of measuring a trigger pulse. The 220kΩ resistor reads correctly. Any suggestions or advice would be appreciated. (J. G., via email). • It seems possible that the electric fence tester is not delivering a suitable pulse to fire the Xenon tube even though it has enough voltage across it to fire. Try connecting the tester with the opposite polarity; ie, connect the HT end to the ground stake and the ground end to the HT of the fence. This will re­verse the trigger pulse polarity and may be all that is needed to fire the Xenon tube. It will not reverse the voltage across the Xenon tube as this is rectified using diodes D1-D4. If this does not work, try connecting the 220kΩ resistor to a point further up Charging smaller Nicads I have a query about the Multipurpose Fast Battery Charger as described in your June 2001 issue. The charge and discharge rates for Nicads seem more suited to larger capacity cells. I use a lot of AA Nicads, most of which are 500mA.h. Is it possible to provide lower charge and discharge rates for these smaller cells? (J. B., via email). • The design is not easily changed to provide lower charging and discharging rates. These changes would be best done by rede­signing 88  Silicon Chip the 820Ω resistor string; ie, connect it a few resistors further toward the fence high-tension end of the string. This should give more trigger voltage to the Xenon tube. Again, try both fence connection polarities. Thermostat not needed for Turbo Timer I’ve have just recently bought the Turbo Timer kit (de­ scribed in November 1998) from Jaycar Electronics. While putting it together, I decided that I would not use the thermostat as it is too much trouble to install it. So what needs to be altered in order to bypass the thermostat in order for the Turbo Timer to always be activated when the car keys are taken out? Is there even a need to alter the thermostat? (L. T., via email). • If you do not wish to use the thermostat, then simply leave this connection open-circuit. In other words, do not make a connection to the thermostat terminal on the PC board. Query on transformer VA ratings In the 1978 edition of the ARRL handbook it says that for both a full-wave bridge (four diode) and a the project with smaller and cheap­ er mains and switching transformers. However, without changing the design too much, the charge and discharge currents can be effectively halved by using only one instead of two 0.1Ω 5W resistors for current sensing. This will mean that the setting for 1.2Ah cells will now be 600mA.h. Switching could be incorporated to select a charge current of 6A or 3A. Keep the leads to the switch short. The best posi­ tion for the switch would be directly on the PC board, adjacent to the 0.1Ω resistor. two-diode centre-tapped full-wave rectifier, the diodes can to be rated at half the DC current being drawn by the load. It also says that for a full-wave bridge, the transformer VA needs to be calculated based on the DC current being drawn but for a two-diode centre-tapped arrangement, the VA needs to be calculated based on 0.7 (ie, root 2) of the DC current. For a non-filtered load is this correct? It would mean that the centre-tapped transformer would have to be 1.4 times the VA of one that used a bridge diode setup. • In practice, you would take a much more conservative ap­ proach in the ratings of the diodes, allowing for transient voltages and initial surge currents. Either way, the VA rating on the transformer would be the same since the total power supplied would be the same. Charger for AAA cells wanted I have a Kodak MC3 digital camera and MP3 player and it uses three AAA batteries. Buying new disposable batteries all the time is impractical and expensive. I need a charger that can fast-charge two sets of three AAA batteries at a time. Could you suggest a kit or a product I could buy? (A. T., Wagga Wagga, NSW). • Our Fast Universal Charger published in the June & July 2001 issues will charge 3.6V Nicads or NiMH batteries (ie, it can do 3 AAA nicads in series) but it could not do two sets at one time because it could not properly monitor the “end-point” voltage of both sets. Computer video signals are different to PAL I’d like some advice on combining the y/c signals from a computer video card so that the signal can be recorded on a VCR with composite video input terminals. Can this be done as simply as audio signals can be combined with a virtual www.siliconchip.com.au earth mixer or is it more complex than that? (S. B., via email). • It is not possible to record the video signals for a comput­er monitor on a VCR because the video standards are quite differ­ ent. The horizontal and vertical sweep frequencies are faster than for PAL or NTSC and there is no colour burst signal. While there are VGA to PAL adaptors, they are quite complex. Coil for ignition system What sort of coil do you have to use with the High Energy Ignition kit? Do you use a coil that needs a ballast resistor or one without, eg, Bosch GT40R? (M. K., via email). • Definitely do not use a high-current coil like the Bosch GT40/r series. Use the standard coil intended for your car. Failing that, use a 12V coil. Setting up a CCTV system I have been wondering for some time now how I may be able to install a home closed circuit video security system that is simple and avoids the high expense associated with the profes­sionally installed systems. I do not want the computer-based models as the computer is often the first item stolen or damaged and besides, I do not want one running perpetually while I am away. A 12V supply for cameras etc I can handle. All of the equipment I have seen/ read about to date re­quires a timelapse video recorder. These are expensive and no doubt have been developed for shopping centres and banks. I can buy three or four normal VCRs Fuel mixture display shows lean I bought the Jaycar fuel mixture display kit and hooked it to my 1994 Holden Barina GSi but the only LEDs that come on are the red ones. When I start the engine the last LED comes on but as I turn the trimpot fully to the left, only the second last LED lights. As the car warms up, the last LED comes on and it stays that way. Is the Barina designed differently and do I need to replace the resistor with ones with different values. There are no solder bridges and all the LEDs are correctly positioned. What for the price of a time-lapse model and all I need it to do is to switch it on in record mode. I want this mode so that I can operate the VCR from a PIR detector when the house is unoccupied. PIR on, the VCR records, PIR off, the VCR stops – simple? My enquiries to service people would seem as if I was asking for a trip to the moon! Surely someone can develop a circuit/device that would allow a home VCR to be so modified, even if the VCR has to be taken to a technician to have the work done. What do you think? (G. E., via email). • We have done exactly that project (camera, PIR, VCR etc) in the September 1997 issue. Tacho display too bright I recently made the Digital Tacho from the August 1991 issue. Everything went well and it worked as it should. In the daytime you can see the num- can I do? (G. E., via email). • We are not sure what you mean by “only the red LEDs come on” as all the LEDs are red. We assume you mean that the display always shows lean mixture with the lower two LEDs lighting. Possibly the problem is with the adjustments of both VR2 and VR3. You need to set them as described in the adjustment section of the article. Also check that the connection to the EGO has a good ground. Differences between the ground connection for the power supply on the fuel mixture display unit and the sensor ground can cause the display to show lean. bers well but at night-time, boy are the numbers bright; they are so bright that I have to pull the plug on it. Is there a way to dim the numbers to a readable brightness, which would not require a great deal of change to the circuit, using an LDR or something like that? (D. C., via email). • The only way to reduce the brightness of the displays would be to reduce the 9V rail by replacing the 150Ω resistor in the GND pin of the 7805 with a 200Ω wirewound pot. These are avail­able from DSE, Cat R-6911. However, if you reduce the supply much below 6V it is likely that the circuit itself may malfunction. Hall Effect sensor for ignition system Could you please advise me if I can use the UGN3503u Hall Effect sensor instead of the HKZ101 Hall sensor with: (1) a distributor ring magnet assembly, similar to the Sparkrite ring PARALLAX BS2-IC BASIC STAMP $112.00 INC GST WE STOCK THE COMPLETE DEVELOPMENT SYSTEM www.siliconchip.com.au November 2001  89 Li’L Pulser Train Controller is full on My son and I have enjoyed putting the kit for the Li’L Pulser Train Controller together but there are a couple of problems we have been unable to resolve. First, the speed adjustment does­ n’t work; ie, the train either goes forward at full speed or back at full speed. The Track LED (#3) shows green when switched to reverse and red when switched to forward, and its intensity doesn’t vary with the position of the potentiometer (VR1). It does not appear that the LED was fitted the wrong way round, as the flattened (K) side of the light base is in the correct orientation (the ends, of course, have been trimmed). It is possible that these problems are related. I have been through the suggested checks: the voltages across the ICs are correct but I have not adjusted the trimpots yet. The shorting siren magnet sold by Jaycar some years ago; (2) a crankshaft-mounted notched trigger wheel or (3) a crankshaft-mounted trigger wheel with magnets? (K. W., via email). • You can use a magnet assembly to drive the UGN3503 Hall effect unit. It comprises a Hall effect unit biased to produce a 2.5V output with a 5V supply. The voltage swings above or below 2.5V, depending on the polarity of the magnet. You will need to capacitively couple the Hall effect output to the reluctor input circuit of the High Energy Ignition. Use a large bipolar electrolytic such as a 47µF for coupling. Also note works and potentiometer (VR1) seems to work. I am assuming that there is a problem with the delivery of the sawtooth signal to IC2 but really I have no idea where the problem lies. (J. W., Nedlands, WA). • The circuit appears to have a problem driving the Mosfet with a switchmode signal. This could be due to any number of causes including: the pin 7 output of IC2a is tied to pin 8 via a solder bridge; the 6.8kΩ resistor at VR1 is either the wrong value or it is not connecting to ground; IC1b is not producing a triangle waveform which should show about 6V at pin 1 when meas­ uring DC volts; or error amplifier IC1a has pin 7 set low because of incorrect setting of VR2. The colour of the LED is not important. Some bi-colour LEDs have the anode terminal for a red LED while other LEDs may have the anode for a green LED. To change the colour for forward or reverse simply swap the leads. that the UGN3503 needs a 5V supply (see the Dick Smith Electron­ics catalog data section). A 5.1V zener can be used in conjunc­tion with the 12V supply and a 330Ω series resistor to provide this. Decouple the 5.1V supply with a 100µF electrolytic capaci­tor. A toothed crankshaft wheel will work if it has magnets attached. Keyboard amplifier wanted I propose to use your 100W class AB amplifier – ie, the one using the Motorola plastic power devices – as a keyboard performance ampli­fier. I’d prefer to dispense with the regulated rails and just use one unregulated plus & minus supply for the sake of simplicity. Ob­viously, in this application, I’m prepared to sacrifice a degree of fidelity. Would you mind giving me your opinion on whether this would be OK? (B. V., via email). • Yes, you can do that but you are wasting the design. You would be better off building the much cheaper (and more powerful) Plastic Power amplifier module described in the April 1996 issue. New remote control for alarm I have a Repeller alarm in my car. Is it possible to get another remote (preferably smaller) for it? (A. S., via email). • There are couple of problems here. You cannot just replace the remote handpiece because the new transmitter must have exact­ly the same coding as the original. Unless the substitute trans­ mitter uses the same encoder chip as the original, then the chances of matching codes are zero. Another approach is that you may be able to replace the transmitter and the receiver/decoder in the alarm itself. If this is possible, you could look at one of the remote controls featured in our February 1996 issue. Alternatively, you could purchase a learning UHF remote such as the Cat LA-8990 from Jaycar Electronics. Using 4-ohm loads with the class-A amplifier I have built the class-A amplifier from the July & August 1998 issues and am pleased with its performance. The specs state that it is rated at 15W into 8Ω. Can you tell me what it is likely to achieve into 4Ω? Also, is it possible to increase the output by WARNING! SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of SILICON CHIP magazine. Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. SILICON CHIP also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Trade Practices Act 1974 or as subsequently amended and to any governmental regulations which are applicable. 90  Silicon Chip www.siliconchip.com.au CD burners with 200 MMX Pentiums I loved the September issue, especially the article that allows me to turn my old computer into an MP3 music machine. Unfortunately, I am stuck with a 200MHz MMX Pentium VX mother­ board for the present. I recently upgraded to a 40GB Seagate 7200 RPM hard-drive (only 8GB is for­ mattable), with Windows 98SE as my operating system. This allows me to do many things but best of all I can connect USB items. I want to connect a CD burner but get conflicting informa­tion from salesmen. None of the burnproof units seem to be com­patible with a 200MMX Pentium. Can you tell me why these units will not work with my system? (M. T., Donvale, Vic). • Manufacturers seem to allow paralleling the output transistors and the power sup­ply? (S. F., Lake District, UK). • You can operate the class-A amplifier with 4-ohm loads and it will probably deliver about 25 to 30 watts maximum. The only problem is that once the load current exceeds about 1.9A peak, the amplifier will no longer be in class A. Instead, it will be in class AB (albeit with exceedingly low crossover distortion arte­facts) for pow­ er levels above 7.5 watts. While we have not looked closely at the biasing, if you wanted to run in class-A up to full power for 4-ohm loads, you would need to double the quiescent current. You would not need Notes & Errata Multi-Purpose Fast Battery Charger II, June & July 2001: this charger is not suitable for charging cells and batteries with capacities below 1.2AH and voltages below 6V. AA and AAA Nicad and NiMH cells should not be connected to this charger as the “No Batt” LED will light due to the cell voltage rising above 2V with initial charging. However, the charger will charge a 6V AA Nicad battery pack successfully. LED Number Display, September 2001: the circuit on page 69 shows the www.siliconchip.com.au quite a big performance margin in their spec list. There is every chance that these drives will indeed run on your machine. Our guess is that you’ll need at least 48MB of memory and you may not be able to run other applications while burning CDs (this can be risky even on fast machines!). The specs are pushed up somewhat in order to include sup­port for on-the-fly CD audio track ripping and encoding. Even if your machine isn’t fast enough to do this on-the-fly, it’s not a major problem; just save to hard disk first in .WAV format and then convert to MP3. It will be necessary to upgrade the motherboard BIOS to format all 40GB of your new hard disk drive. Alternatively, you can use Seagate’s Disk Manager utility. You’ll find it at: www.seagate.com/support/disc/ drivers/discwiz.html to double up on the output transistors but you would need a fan-cooled heatsink to cope with the 80W dissipation and you would need a bigger power supply. Boosting the remote control extender Is it possible to run more than one IRLED on the remote control extender (July 1996)? If so, what do I have to do so it still works because I have two units in different places? (R. S., via email). • You can run another IRLED via a separate 220Ω resistor connected to transistor Q1. 4511 7-segment decoder pins correctly but the labels for LE (latch enable) and LT (lamp test) have been swapped. Synchronous Clock Driver, October 2001: the circuit on page 37 has a number of errors. IC1 should have the positive rail to pin 14 and 0V to pin 4, while pins 4 & 6 have been transposed. On IC4, pins 3 & 11 have been transposed. In the text, the last line of the second last paragraph should read “with the clock signal to IC4”. The second line of the last paragraph should read “pins 4 & 10 of IC1. And the reference to R1 should be R2, in the last paragraph. SC Small Manufacturers Prototypers TAFEs and Colleges Introducing: THE MINI NC PC Board Drilling Machine Here’s the answer for “in-house” prototyping, small production runs, education, etc. Much lower in cost than larger machines, easy to use and comes complete with software. Also drills plastic components such as covers or patterns. IT’S JUST A FRACTION OF THE PRICE AND ON-GOING COST OF A LARGER NC DRILLING MACHINE! P&E PTY LTD FOR INFORMATION PH: CALL: (03) 9545 3722 FAX: (03) 5971 1040 WHAT’S THAT SEMI? Don’t know what it is? Number rubbed off? Can’t identify leads? Need to match gain? The PEAK ATLAS ANALYSER will tell you -Automatically and in just a few seconds! FO? MORE INit vis c.co.uk peakele DIODES JFETS TRANSISTORS TRIACS SCRS LEDS MOSFETS      Auto identifies semis Auto identifies leads Auto identifies faults Checks transistor gain Matches semis Indispensable aid for technicians - designers engineers - laboratories - hobbyists - everyone! Available now from: PAVIKA MANAGEMENT 15 Gilda Ave, Penrith Sth NSW 2750 Ph (02) 4732 4813 Fax (02) 4732 4836 email: pavika<at>bigpond.com November 2001  91 REFERENCE GREAT BOOKS FOR DIGITAL ELECTRONICS – A PRACTICAL APPROACH AUDIO POWER AMP DESIGN HANDBOOK By Douglas Self. 2nd Edition Published 2000 By Richard Monk. Published 1998. From one of the world’s most respected audio authorities. The new 2nd edition is even more comprehensive, includes sections on load-invariant power amps, distortion residuals and diagnosis of amplifier problems.368 pages in paperback. 85 $$ $$ 65 With this book you can learn the principles and practice of digital electronics without leaving your desk, through the popular simulation applications, EASY-PC Pro XM and Pulsar. Alternatively, if you want to discover the applications through a thoroughly practical exploration of digital electronics, this is the book for you. A free floppy disk is included, featuring limited function versions of EASY-PC Professional XM and Pulsar. 249 pages, in paperback. VIDEO SCRAMBLING AND DESCRAMBLING for Satellite & Cable AUDIO ELECTRONICS If you've ever wondered how they scramble video on cable and satellite TV, this book tells you! Encoding/decoding systems (analog and digital systems), encryption, even schematics and details of several encoder and decoder circuits for experimentation. Intended for both the hobbyist and the professional. 290 pages in paperback. This book is for anyone involved in designing, adapting and using analog and digital audio equipment. It covers tape recording, tuners and radio receivers, preamplifiers, voltage amplifiers, audio power amplifiers, compact disc technology and digital audio, test and measurement, loudspeaker crossover systems, power supplies and noise reduction systems. 375 pages in soft cover. By John Linsley Hood. First published 1995. Second edition 1999. TV by Graf & Sheets 75 $ NEW 2nd Edition 1998 3rd W 3rd NE NEW ON:: ITION ED EDITI ME SA SAME ICE!! PR PRICE UNDERSTANDING TELEPHONE ELECTRONICS By Stephen J. Bigelow. Fourth edition published 2001 In keeping With the distinguished tradition of its .. predecessors, Understanding Telephone Electronics, FOURTH EDITION, covers conventional telephone fundamentals, including both analog and modern digital communication techniques. It provides basic information on the functions of each telephone system component, how electronic circuits general dial tones, and how the latest digital transmission techniques work. 59 $$ GUIDE TO TV & VIDEO TECHNOLOGY By Eugene Trundle. First pub­­lished 1988. Second edition 1996. Eugene Trundle has written for many years in Television magazine and his latest book is right up to date on TV and video technology. The book includes both theory and practical servicing information and is ideal for both students and technicians. 382 pages, in paperback. 59 $$ 92  Silicon Chip 99 $ 85 $ EMC FOR PRODUCT DESIGNERS By Tim Williams. First pub­­lished 1992. 3rd edition 2000. Widely regarded as the standard text on EMC, this book provides all the information necessary to meet the requirements of the EMC Directive. It includes chapters on standards, measurement techniques and design principles, including layout and grounding, digital and analog circuit design, filtering and shielding and interference sources. The four appendices give a design checklist and include useful tables, data and formulae. 299 pages, in soft cover. ELECTRIC MOTORS AND DRIVES By Austin Hughes. Second edition published 1993 (reprinted 1997). For non-specialist users – explores most of the widely-used modern types of motor and drive, including conventional and brushless DC, induction, stepping, synchronous and reluctance motors. 339 pages, in paperback. 65 $ www.siliconchip.com.au BOOKSHOP WANT TO SAVE 10%? SILICON CHIP SUBSCRIBERS AUTOMATICALLY QUALIFY FOR A 10% DISCOUNT ON ALL BOOK PURCHASES! ENQUIRING MINDS! (To subscribe, see page 53) ALL PRICES INCLUDE GST PIC Your Personal Introductory Course ANALOG ELECTRONICS NEW NEW NEW NEW NEW NEW by John Morton – 2nd edition 2001 By Ian Hickman. 2nd edition1999. Essential reading for electronics designers and students alike. It will answer nagging questions about core analog theory and design principles as well as offering practical design ideas. With concise design implementations, with many of the circuits taken from Ian Hickman’s magazine articles. 294 pages in soft cover. 85 $ $ TELEPHONE INSTALLATION HANDBOOK by Steve Roberts $ 67 The definitive guide to home and small business installation - extensions, modems and telephone systems. Provides a practical guide to installation of telephone wiring. Ranges from the single extension socket to the Private Automatic Branch Exchange (PABX), with the necessary tools, test equipment and materials needed by installers. 178 pages in soft cover. NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW 43 Concise and practical guide to getting up and running with the PIC Microcontroller. Assumes no NEW prior knowledge of microcon-trollers, introduces the PIC’s cpabilities through NEW simple projects. Ideal introduction for NEW students, teachers, technicians and electronics enthusiasts – perfect for NEW use in schools and colleges. NEW 270 pages in soft cover. NEW VIDEO & CAMCORDER SERVICING AND TECHNOLOGY by Steve Beeching (First published 2001) Provides fully up-to-date coverage of the whole range of current home video equipment, analog and digital. Information for repair and troubleshooting, with explanations of the technology of video equipment. 318 pages in soft cover. SILICON CHIP'S COMPUTER OMNIBUS First published 1999 SILICON CHIP'S ELECTRONICS TEST BENCH First published 2000 Hints, tips, Upgrades and Fixes for your computer from articles published in SILICON CHIP in recent years. Covers DOS, Windows 3.1, 95, 98 and NT. A must for the computer user. $12.50 (Aust); $A15.95 NZ (prices include P&P) O R D E R H E R E P&P A collection of the “most asked for” Test Equipment projects and features from the pages of Australia’s “most asked for” electronics magazine. Exceptional value at $13.20 (Aust); $A15.95 NZ (prices include p&p).  ANALOG ELECTRONICS..................................................$85.00  AUDIO POWER AMPLIFIER DESIGN...............................$85.00  AUDIO ELECTRONICS.....................................................$85.00  DIGITAL ELECTRONICS ..................................................$65.00  ELECTRIC MOTORS AND DRIVES (2ND EDIT)................$65.00  EMC FOR PRODUCT DESIGNERS...................................$99.00  GUIDE TO TV & VIDEO TECHNOLOGY............................$59.00  PIC - YOUR PERSONAL INTRODUCTORY COURSE........$43.00  TELEPHONE INSTALLATION HANDBOOK........................$67.00  UNDERSTANDING TELEPHONE ELECTRONICS.................$65.00  VIDEO & CAMCORDER SERVICING/TECHNOLOGY........$67.00  VIDEO SCRAMBLING/DESCRAMBLING..........................$75.00  SILICON CHIP TEST BENCH.................................... (see above)  SILICON CHIP COMPUTER OMNIBUS.................... (see above)               ORDER TOTAL: $...................... Orders over $100 P&P free in Australia. AUST: Add $A5.50 per book NZ: Add $A10 per book, $A15 elsewhere www.siliconchip.com.au 67 $$ TAX INVOICE Your Name__________________________________________________________ PLEASE PRINT Address ____________________________________________________________ ___________________________________ Postcode_______________ Daytime Phone No. (______) __________________________________ STD Email___________________<at>_________________________________  Cheque/Money Order enclosed OR  Charge my credit card –  Bankcard  Visa Card  MasterCard No: Signature______________________Card expiry date PLUS P&P (if applic): $........................... TOTAL$ AU.............................. POST TO: SILICON CHIP Publications, PO Box 139, Collaroy NSW, Australia 2097. OR CALL (02) 9979 5644 & quote your credit card details; or FAX TO (02) 9979 6503 November 2001  93 ALL TITLES SUBJECT TO AVAILABILITY. 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Satellite TV Reception International satellite TV reception in your home is now affordable. Send for your free info pack containing equipment catalog, satellite lists, etc or call for appointment to view. We can display all satellites from 76.5° to 180°. AV-COMM P/L, 24/9 Powells Rd, Brookvale, NSW 2100. Tel: 02 9939 4377 or 9939 4378. Fax: 9939 4376; www.avcomm.com.au Need prototype PC boards? We have the solutions – we print electronics! Four-day turnaround, less if urgent; Artwork from your own positive or file; Through hole plating; Prompt postal service; 29 years technical experience; Inexpensive; Superb quality. Printed Electronics, 12A Aristoc Rd, Glen Waverley, Vic 3150. Phone: (03) 9545 3722; Fax: (03) 9545 3561 Call Mike Lynch and check us out! We are the best for low cost, small runs. NEED A PCB FOR YOUR IDEA? Supply us with your schematic. We can design and supply you with a PCB. www.elcomtel.com.au CCTV Quads from $168 / $303 Mono / Colour 4 pixs 1 screen www.allthings.com.au UNIVERSAL DEVICE PROGRAMMER: Low cost, high performance, 48-pin, works in DOS or Windows inc NT/2000. $1320. Universal EPROM programmer $429. Also adaptors, (E) EPROM, PIC, 8051 programmers, EPROM simulator and eraser. Dunfield C Compilers: Everything you need to develop C and ASM software for 68HC08, 6809, 68HC11, 68HC12, 68HC16, 8051/52, 8080/85, 8086, 8096 or AVR: $198 each. Demo disk available. ImageCraft C Compilers: 32-bit Windows IDE and compiler. For AVR, 68HC11, 68HC12. $396. Atmel Flash CPU Programmer: Handles the 89Cx051, 89C5x, 89Sxx in both DIP and PLCC44 and some AVR’s, most www.siliconchip.com.au Mark22-SM Slimline Mini FM R/C Receiver • • • • • 6 Channels 10kHz frequency separation Size: 55 x 23 x 20mm Weight: 25gm Modular Construction Price: $A129.50 with crystal Electronics PO Box 580, Riverwood, NSW 2210. Ph/Fax (02) 9533 3517 email: youngbob<at>silvertone.com.au Website: www.silvertone.com.au E.A. 1973-1997; S.C. Vol. 1 No. 1 to 1997. Some issues missing both sets. Offers: phone Keith (02) 9997 1051. MINI Cameras with Microphone only $44 ! COLOUR only $79 ! www.allthings.com.au New New New 8-pin EEPROMS. Includes socket for serial ISP cable. $220, $11 p&p. SOIC adaptors: 20 pin $99, 14 pin $93.50, 8 pin $88. Full details on web site. Credit cards accepted. GRANTRONICS PTY LTD, PO Box 275, Wentworthville 2145. (02) 9896 7150 or http://www.grantronics.com.au SEE-in-the-DARK Camera in-built IR LEDs in Water Resistant Case for disturbance-free Baby – Bird – Animal – Porch observation from $147 * NEW Wireless Version available NOW ! * www.allthings.com.au PCBs MADE, ONE OR MANY. Low prices, hobbyists welcome. Sesame Elec­tronics (02) 9586 4771. sesame<at>internetezy.com.au; http:// members.tripod.com/~sesame_elec NEED A SPARE WHICH IS NO LONGER AVAILABLE OR TOO EXPENSIVE? We can design and supply a replacement. www.elcomtel.com.au MULTIMEDIA BEGINNERS PIC TOOLS. Popular world wide for private and educational use. Hours of interac- tive learning fun. Includes programmer, animated simulators, interactive tutorials, real world interface, projects and utilities. Additional experimenter parts include PIC16F628, LCD, EEPROM, LEDs, relay and driver plus more. All explained in detail with working code. www.bubblesoftonline.com DIY CCTV PAKS 4 Cameras Mikes & Switcher..... $265 4 COLOUR & Switcher............... $385 4 Cameras Mikes & PC DVR...... $311 4 COLOUR & PC DVR............... $431 4 Cams Mikes & QUAD .............. $360 4 COLOUR & QUAD ................... $637 Time-Lapse 24 hr VCR only $449 with CCTV PAK ! DIY INSTALL-PAKS Plug-In Cables – Power Supply – etc www.allthings.com.au A COLLECTION OF ELECTRONICS MAGAZINES AND BOOKS from early 60’s to late 90’s, largely complete. Best offer watgully<at>wizard.teksupport.net.au or 0408 339410. Multiplexers CCTV Full-Screen Full-Resolution Recording FOUR TIMES MORE DATA than a Quad from $597/$944 Mono/Colour. www.allthings.com.au continued next page November 2001  95 G.S. & W.M. MILLAR ELECTRONICS SUPPORT SOLUTIONS Electro-mechanical/Electronic repairs, rebuilds, maintenance, calibrations etc. Quality service at your site/s or in our workshop. PH: 0416 278-775 Positions At Jaycar We are often looking for enthusiastic staff for positions in our retail stores and head office at Silverwater in Sydney. A genuine interest in electronics is a necessity. Phone 02 9741 8555 for current vacancies. Advertising Index Altronics.......................Loose Insert Allthings Sales & Services..... 94-96 Av-Comm Pty Ltd.........................95 Dick Smith Electronics........... 16-19 RCS HAS MOVED to 41 Arlewis St, Chester Hill 2162 and is now open, with full production. Tel (02) 9738 0330; Fax 9738 0334. rcsradio<at>cia.com.au; www.cia.com.au/rcsradio HOME SOHO PAKS DIY only ! $82 / $109 ! Mono / COLOUR Camera & MICROPHONE + Plug-In 20 metre AV Cable Set + Plug Pack ! www.allthings.com.au CCTV Equipment * BLEMISH FREE & LOW BLEMISH CCDs * up to 5 YEARS WARRANTY * OVERNIGHT DELIVERY * www.allthings.com.au DESIGN DEADLINES? If you have more work than you can cope with, then we can assist you with the design. www.elcomtel.com.au DIGITAL OSCILLOSCOPE, USB, VHF Receiver; temperature/voltage measurement via phone kits. www.ar.com.au/~softmark VIDEO amplifiers, Stabilisers, TBCs, Converters, Mixers, etc. QUESTRONIX (02) 9477 3596. NEW SUPER MICROPHONE. Point and listen in up to 500 metres away $95. Spy KITS-R-US 08-82703175 More at www.bettanet.net.au/GTD $2 PACKS Buy 10 packs, get the 11th one free #001 20 x quality USA nylon cable ties #002 10 x 14-pin IC sockets #003 20 x 16-pin dip 8 x 47k resistor array #004 20 x 7408 quad 2 input and gate #005 10 x 1.5uF 6VW SMD chip capacitor #006 10 x 0.47uF 20VW SMD chip capacitor #007 10 x 2.2uF 2VW SMD chip capacitor #008 2 x 8MHz ceralock for PIC CPU chips #009 4 x Murata UHF 3pF trimmer cap #010 2 metres 40-way IDC cable #011 2 x 52-pin PLCC IC sockets #012 6 x BF86 no brand RF transistors #013 40 x 1N4148 signal diode ($5/100) #014 2 x DB series connectors your choice of any 9 to 50 pin M/F plugs and sockets, limited stocks. 96  Silicon Chip bug 1.2km range $49. Match box size spy camera transmits clear picture to TV up to 200m $195. Pan tilt wireless remote control dome camera complete $750. GCS Electronics (02) 4227 9933 or 0410 739 317. Evatco..........................................83 DOME CCTV Cameras from $49 / $75 Mono / Colour www.allthings.com.au IRH Components.....................OBC www.procontechnology.com.au fischertechnik robotic kits, interfaces and software. Industrial I/O boards and microcontroller boards. Programming and design service available. Credit cards accepted. Phone 03 9830 6288. Fax 03 9830 6481 for a free catalogue. JED Microprocessors...............5,75 VCR Controller use your home VCR to Record Events Wireless IR Learning Remote from $30. www.allthings.com.au Grantronics..................................95 Harbuch Electronics....................76 Hy-Q International.......................75 Instant PCBs................................95 Jaycar ................................... 45-52 Kalex............................................79 Meterman....................................81 McGraw Hill.................................63 MicroZed Computers...................75 Oatley Electronics........................85 P & E Pty Ltd...............................91 Pavika Management....................91 PolyKom....................................IFC GEM * COLOUR Video Camera * 600 + H-Line Resolution * High 0.007 lux Sensitivity * Extraordinary 58 + dB Signal : Noise Ratio * SUPER WIDE 275 + Dynamic Range * Incredible 150 + dB Smear Rejection * www.allthings.com.au Printed Electronics...................... 95 KIT ASSEMBLY RobotOz.................................11,75 NEVILLE WALKER KIT ASSEMBLY & REPAIR: • Australia wide service • Small production runs • Specialist “one-off” applications Phone Neville Walker (07) 3857 2752 Email flashdog<at>optusnet.com.au Silicon Chip Back Issues....... 86-87 WANTED Smart Fastchargers.....................83 PERSON WITH EXPERIENCE/APTITUDE to fault find & repair PCBs – without diagrams. GENEROUS PKG NEG. Tel John<at>AER (03) 9482 4958 or 0415 305 470. CIRCUIT IDEAS: Do you have a good circuit idea? If so, sketch it out, write a brief description of its operation & send it to SILICON CHIP. We pay up to $60 for a good circuit but your idea must workable & original. Questronix..............................75,96 RCS Radio...................................96 RTN.............................................74 RF Probes...................................75 Robotic Education Products..........7 Silicon Chip Binders....................82 Silicon Chip Bookshop........... 92-93 SC Electronics Testbench..........IBC Silicon Chip Subscriptions...........53 Silvertone Electronics..................95 Solar Flair/Ecowatch....................94 VAF Research..........................9,75 Wiltronics.................37,43,73,75,89 _____________________________ PC Boards Printed circuit boards for SILICON CHIP projects are made by: • RCS Radio Pty Ltd. Phone (02) 9738 0330. Fax (02) 9738 0334. www.siliconchip.com.au