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SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings.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 Vol.7, No.8; August 1994 FEATURES FEATURES NEED A DIMMER for a large domestic or stage application? This unit can dim incandescent or halogen lamp loads of up to 2400W or can be used for fan speed control. Details page 24.   4 Review: Philips Widescreen Colour TV Set by Leo Simpson Advanced set has picture-in-picture & Dolby sound 14 Electronic Engine Management, Pt.11 by Julian Edgar Fuel & air systems 80 Review: Philips P65 UHF CB Set by Marque Crozman Has user programmable scanning & up to 5W power output PROJECTS PROJECTS TO TO BUILD BUILD 24 High-Power Dimmer For Incandescent Lights by Marque Crozman Can dim lamp loads of up to 2400 watts 37 A Microprocessor Controlled Morse Keyer by Alexandre Zatsepin Lets you store & playback Morse messages THIS MICROPROCESSOR controlled Morse Keyer will really polish up your sending. It even has a memory that lets you record & replay a Morse message up to 64 characters long. Turn to page 37. 40 Dual Diversity Tuner For FM Microphones by John Clarke It automatically selects the best signal from two antennas 52 A Simple Go/No-Go Crystal Checker by Darren Yates Build it for just a few dollars 68 Build A Nicad Zapper by Darren Yates Zap the dendrites & give your cells a new lease of life SPECIAL SPECIAL COLUMNS COLUMNS 56 Serviceman’s Log by the TV Serviceman OLD NICAD BATTERIES can often be given a new lease of life by blasting away internal dendritic growths. And for that, you need this Nicad Zapper – see page 68. Time to talk about timers 65 Remote Control by Bob Young Modellers with dedication 84 Vintage Radio by John Hill Watch out for incorrect valve substitutions DEPARTMENTS DEPARTMENTS   2 23 50 79 80 Publisher’s Letter Mailbag Circuit Notebook Order Form Product Showcase 88 90 93 94 96 Back Issues Ask Silicon Chip Bookshop Market Centre Advertising Index THIS DUAL DIVERSITY TUNER automatically selects the best signal from two antennas to ensure a noise-free reception from FM wireless microphones. Deatails page 40. Cover concept: Marque Crozman August 1994  1 Publisher & Editor-in-Chief Leo Simpson, B.Bus. Editor Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Robert Flynn Darren Yates, B.Sc. Reader Services Ann Jenkinson Sharon Macdonald Advertising Enquiries Leo Simpson Phone (02) 979 5644 Regular Contributors Brendan Akhurst Garry Cratt, VK2YBX Marque Crozman, VK2ZLZ John Hill Jim Lawler, MTETIA Bryan Maher, M.E., B.Sc. Philip Watson, MIREE, VK2ZPW Jim Yalden, VK2YGY Bob Young Photography Stuart Bryce SILICON CHIP is published 12 times a year by Silicon Chip Publications Pty Ltd. A.C.N. 003 205 490. All material copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Macquarie Print, Dubbo, NSW. Distribution: Network Distribution Company. Subscription rates: $49 per year in Australia. For overseas rates, see the subscription page in this issue. Editorial & advertising offices: Unit 34, 1-3 Jubilee Avenue, Warrie­ wood, NSW 2102. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 979 5644. Fax (02) 979 6503. PUBLISHER'S LETTER Trivialising science & technology will not help to promote it These days, the products of science and technology surround us and we enjoy the benefits to the full. Paradoxically though, science and technology appear to be becoming less popular in schools and universities. Students appear to be taking the softer options of humanities-based courses rather than the more rigorous courses required for science and engineering. This is a serious problem and one which is occurring in most western economies. The lack of interest in science and technology can be attributed to a number of factors. For a start, there is a disenchantment with science and technology since it is now recognised that it does not have the cures and solutions for all the world’s problems. Second, with the loss of much tradi­tional manufacturing to the oriental and developing countries, it is perceived that there are less job opportunities for engineers and technicians. That second point is arguable but it is a per­ception nonetheless. While this problem is serious, it does not have an easy solution. Certainly, it will not be helped by the efforts of some organisations to popularise science and technology. I am thinking particularly of museums and the makers of science programs for television. When you visit museums these days, the emphasis seems to be on “hands-on” or interactive displays. Hence, museums have a tendency to become vast video games parlours where all sorts of science is supposed to be illustrated but not much is learnt. Now I agree that museums with working exhibits are more interesting than those where all displays are static but this all out effort to make everything interactive is counterproductive. But if museums are on the wrong tack, some science program makers are completely off course as they have a strong tendency to trivialise their material. Prime examples of this are “Beyond 2000”, which has degenerated into little more than a showcase of fairly boring products from overseas, and the current ABC program “Hot Chips”. I suppose the name says it all – it is the “fast food” approach to science and technology. The ABC program “Quan­ tum” is far better and its presenter Karina Kelly at least gives the impression that she is interested and committed to the fea­tured topics. Let’s face it, there is no easy way to promote science and technology. The sooner museums and other would-be promoters realise that, the better. Most people are interested and eager to take advantage of the latest developments in science and technology. It is sad to see that interest dissipated by halfbaked efforts to capitalise upon it. Leo Simpson ISSN 1030-2662 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. 2  Silicon Chip Consumer Product Review By LEO SIMPSON Philips’ revolutionary wide-screen TV receiver Recently, Philips released their newest wide format TV receiver onto the Australian market. Called the Matchline 76cm, it has every conceivable feature that could be crammed into a TV receiv­er, including Dolby Surround Sound, Picture-inPicture, Teletext and 100Hz digital flicker reduction. We borrowed a sample unit & watched it long & hard to bring you this report. 4  Silicon Chip T HIS IS NOT THE FIRST WIDE-SCREEN TV receiver from Philips, as they released their first model in Australia about two years ago. However, this 76cm Matchline is a completely new model with many more features and a lower price. So why would you want a TV set in the new 16:9 format? Given that there is not much program material at present, Philips has worked hard to make the new set as enticing as possible. If you have a laser disc player with movies recorded in the wide screen 16:9 format you will immediately appreciate the benefits of the new Philips receiver. The wide screen has a more dramatic presentation so that when you come to view a convention­al TV set with its 4:3 screen it seems to lose a great deal of visual impact. Before we go much further, we should explain these formats of 4:3 and 16:9 for the benefit of readers not familiar with these terms. Conventional TV sets have a screen which is four units wide and three units high. For a 63cm set (diagonal measurement), the screen will be nominally 50cm wide and 38cm high. Movies on the other hand, and the new HDTV standard, call for a 16:9 screen format and so the screen is 1.77 times as wide as it is high – much wider than a normal TV. When movies are broadcast by TV stations they have several options. They can aim a conventional camera at the movie screen and thereby clip off the edges of the screen; they can pan the camera to take in the action on the screen or they can broadcast in “letter box” format which results in a black strip at the top and bottom of the screen. This latter option is used quite often these days on SBS television and also by commercial TV networks when they are rolling the credits at the start of movies. Whichever way they do it though, the result is hardly what the movie producer intended. In producing this widescreen set, Philips give the viewer the option of watching normal programs in wide-screen format – the “superwide” mode. This means that you do not have to watch 4:3 programs with a black band down each side of the screen – you can expand the picture to fill the screen and in doing so, you lose very little at the top and bottom. Contrary to what you might expect, this does not lead to grossly distorted pictures with balloon faced people, extra long cars and so on. Philips has been much more clever than that. But before we explain what they have done, let’s talk about the general details of the new set. The new set is big and heavy but not overly so. It is 836mm wide, 591mm high, 593mm deep and weighs close to 55kg. The main component of the weight and the reason for the consider­able depth of the set is the tube. Glass is heavy and the tube needs to be quite deep to provide for such a wide deflection. All of the cabinet is plastic with a dark matt finish, very much in the style of today’s TV sets which are quite subdued in appearance. Also as with most of today’s sets, the new Philips Matchline is designed to be controlled exclusively by the in­frared remote handpiece; very few Philips’ new 76cm Matchline TV receiver has a 16:9 format picture tube & this gives a much more dramatic presentation than a conventional TV set. Particular features are the 100Hz flicker reduction circuitry & the scan velocity modulation system to enhance picture highlights. functions can be controlled from the set itself. Those that can are in an array of buttons down the lefthand side of the set and are as follows: Power On (standby), Video (select), Install, Volume (up/down) and Channel (select). These are grouped with RCA sockets for video and stereo audio inputs and an S-video socket. In practice, apart from the Install button which would only be used at the time of installation, these buttons would never be used unless the remote control handpiece was temporarily out of order due to flat batteries. In fact, the only control on the set which is likely to be used on a regular basis is the main power switch which is on the lefthand side of the cabinet. Philips recommend that it be used to turn the set off at night, thus avoiding any standby power drain, and also because when the set is turned back on again, the picture tube will auto- matically be degaussed, to maintain good picture quality. As you might expect, the remote control handpiece has a myriad of buttons and these can be quite confusing and hard to follow for those who are not technically inclined. With that in mind, some genius at Philips has come up with the idea of provid­ing a second remote control which provides just the basic func­ tions. This is doubly handy when the main remote control gets wedged in behind the lounge cushions and one is desperate to mute the sound, for example. Many features Even in a very long and detailed review it would not be possible to cover all the technical and user features of the Philips set. After all, it comes with two owner’s manuals, a brief one and the comprehensive one. Two infrared remote controls are supplied with the receiver, one with all the bells & whistles & the other with just the basic functions. Both have a very good operating range. August 1994  5 This photo shows one of the many on-screen menus which are brought into operation with the remote control. This one is for picture features & shows CTI highlighted. CTI stands for colour transient improvement & this feature mainly enhances the red details in the picture. The comprehensive one has 78 pages and it is only in English, not multiple languages! There­fore we’ll just discuss the main features in broad detail. Apart from the wide screen, the Philips Matchline has a brace of features which are all linked together technically: 100Hz flicker reduction, picture in picture, digital noise reduc­ tion, colour transient improvement (CTI), multiple system compa­tibility and still (freeze frame). A big problem with television viewing in Australia (and other countries which use 50Hz AC mains supply) is picture flick­ er. This becomes much more noticeable in large screen sets and even more noticeable in wide screen sets because the peripheral vision of the eye is so sensitive to flicker. Clearly, a wide screen set without some sort of flicker reduction would be un­pleasant to watch. This set and others on the market combat the problem by scanning the picture at 100Hz instead of 50Hz. That one change requires an enormous increase in set com­ plexity because it immediately means that a digital field store is required. Just a few years ago, digital field stores were only to be found in TV studios and they cost immense amounts of money. In essence, the luminance and chrom­inance signals are digi­tised by an analog-to-digital converter (ADC). Conversion takes place at a sampling frequency of 16MHz which, by the Nyquist criterion, limits the video bandwidth to 8MHz. This is wider than the 7MHz bandwidth required in Australia but this is a world set, capable of receiving TV broadcasts in any of 27 different for­mats, covering all the variations of PAL, NTSC and SECAM. After sampling, the digitised This series of on-screen photographs shows the images produced from a crosshatch pattern. Above left is the 6  Silicon Chip picture information is written to a bank of video memory. It is then read out twice, with a clock frequen­cy two times that used to store it. The detail of this system is a great deal more complex but suffice to say that scanning the fields at 100Hz instead of 50Hz is not the complete solution. While it solves broad area flicker (which is noticeable even on VGA screens scanned at 70Hz), it does not solve alternate line flicker. This is often very noticeable when TV stations put pictures in small boxes on the screen. Philips has solved the line flicker problem by not just doubling the vertical scan frequency to 100Hz but by also doubling the scan frequency as well, to 31.5kHz. Note that this is not exactly twice the PAL scan frequency of 15.625kHz but it is twice the NTSC scan frequency of 15.75kHz and ties in with the world nature of this set. Not only that, but the set uses a complex algorithm whereby alternate lines may be scanned in ‘ABAB’ mode for stable parts of the picture where flicker would be noticeable and in ‘AABB’ mode where the picture is moving and so flicker is not perceptible (where A and B stand for alternate lines in an interlaced picture). The result is a picture on the screen which is so stable and flicker-free that it is uncanny. If the picture is stationary as well, it is absolutely still, just as if it came from a slide projector – it is that good. Digital noise reduction Digital noise reduction (DNR) is a feature which is only made possible because of the fact that there is actually enough video RAM to store two complete fields. The set uses an algorithm pattern produced in 4:3 mode, together with a PIP display. Superwide mode (above) expands the image horizontally to compare the video signals, line by line, with the previous field and thereby distinguish between random noise (snow) and legitimate variations in the video signal. DNR can be introduced in two stages with the remote control and it can make a worth­while improvement in signals which have a modest noise content. However, it also results in a minor loss of detail on less noisy signals and so it is often difficult to decide whether to switch it in or out. Colour transient improvement (CTI) is another byproduct of the digital video processing and gives sharper transitions for colour picture information. The remote control gives you the option of turning CTI on or off but unless you know what to look for, it is hard to tell the difference with it on or off. Its main effect is to sharpen up red signals which can otherwise be quite blurry. Once you have noted the effect, you will leave the CTI switched on because it is beneficial. Picture in picture Picture in picture (PIP) might be regarded by some as a gimmick but in practice it is a very useful feature which allows you watch one channel while keeping an eye for the start of a program on another channel. Not only does it require a digital field store so that the two pictures can be synchronised together but it also needs two complete video processing chains: two TV tuners (UHF & VHF), two IF strips and so on. Hence, you can watch any video channel on the main picture and any channel on the PIP. You can even display a Teletext picture on the full screen while continu­ing to watch (and listen to) the PIP. Finally, as a byproduct of the field The chassis of the new Philips set is essentially a large motherboard with quite a few smaller boards plugged into it. Not shown is the superwoofer enclosure which is attached to the rear cover. store, it is possible to independently freeze the main picture using the STILL button on the remote and the PIP using the FREEZE button. This is not a particularly useful feature but it can be amusing to freeze some TV personalities while they are talking. Other picture enhancements The new Philips set has two other picture enhancements, one of which is extremely worthwhile and one which is arguable. The first is the SCAVEM circuit while the other is “black level stretch”. SCAVEM stands for SCAn VElocity Modulation and is used to delay the scan voltage to compensate for the delay in large video signal transitions which are caused by the capacitance of the picture tube. Normally, this capaci- by about 25%. Wide Screen is used for showing 16:9 program material, while Movie Expand (right) is used tance causes blurring of black-to-white and white-to-black transitions and this is quite noticeable on captions, weath­ er maps and so on. This feature really does work and makes the picture so much sharper than on conventional sets. In fact, in my opinion, apart from the flicker reduction of this set, the SCAVEM circuit is the feature which makes the biggest contribution to the outstanding picture quality of this set. We are not so sure about the “black level stretch” feature. As with other sets on the market, the new Philips set has a picture tube with a black face which gives a much higher picture contrast and makes the picture much easier to see in brightly lit and sunny rooms. So compared with sets of seven or eight years ago, the pictures to fill the screen while showing movies which have been broadcast in letterbox format. August 1994  7 are watching movies that the sound system really comes into its own (all the bass included). The set is supplied with satellite speakers for the rear surround channels and also has audio outputs to drive external amplifiers. Nor is their any need to connect a centre channel speaker because the Philips set simulates a centre speaker with its “phantom” speaker setting, via the front speakers. Even if the movie you are watching does not have Dolby sound, you can have a very good surround effect by selecting “matrix” which includes acoustic delay for the rear speakers. Chassis design This photograph shows how Teletext pictures can be displayed in 4:3 format while you watch (& listen to) a large PIP image. Note that the barrel distortion of the picture is mainly due to the photographic technique & is not evident on the set. already have better blacks and better contrast range (ie, over the full range from white to black, with all the greys in between). What the “black level stretch” is supposed to do is to increase the picture contrast of the dark parts of the picture. As I understand it, it pushes the black level down towards the blanking level so that the blacks are “blacker than black”. In my opinion though, it merely makes the picture too dark. I was able to make a direct comparison between this set and another Philips set which is 9 years old. The older set revealed more detail in the greys of the picture, simply because they weren’t so black. In effect, the black level extension seems to compress the bottom of the grey scale so that dark greys become black. Picture preferences Being something of a “video hifi enthusiast” I believe there is only one setting of contrast, brightness and colour temperature (picture white) which gives the best overall picture. However, Philips has provided for a number of picture preferenc­es which are entitled Rich, Soft, Natural and Personal. In my opinion, the Rich picture is much to dark, the Soft picture is blurred and the Natural picture is not too far away from being right although it still loses detail in the dark greys. Thankful­ly, you can set up your own personal preference and when that it done, it is excellent. 8  Silicon Chip Similarly, you can chose your colour temperature for the white areas of the picture and these are given as Normal, Warm and Cool. Warm makes the whites look pink while Cool makes them look blue. Normal is correct. Sound preferences In line with the concept of viewer democracy, Philips give the viewer a whole bunch of sound preferences which are listed as Voice, Music, Theatre and Personal. For most programs, the Phil­ips set just gives too much bass. In fact, it has a superwoofer enclosure intended to boost the bass and it does that very effi­ciently. Consequently, in order to make the sound as intelligible as possible, it is necessary to cut the bass right back and this became my “personal” setting. All of these adjustments are done via on-screen menus which appear superimposed on the picture every time your press a relevant button on the remote control. Even setting the volume is done to the accompaniment of a bargraph on the screen. And that brings me to another minor criticism. The avail­able increments in the volume setting are too big, so much so that with the volume setting at half way, the sound is at bellowing level. This could be easily fixed with some run­ning changes to the software in the microprocessor’s ROM. Dolby surround sound Philips has full Dolby Pro-Logic decoding in this set and it is when you We’ve included a photo which shows the general setup of the chassis. Actually, there is no chassis as such but there is a large mother­board with quite a few vertical boards plugged into it. Interestingly, the set has its own error message system via an array of seven LEDs on the main board and these are driven by the microprocessor. These will no doubt help in fault diagnosis should service be necessary. Picture evaluation To come back to the main feature of this set, throughout our evaluation we were intrigued by the various wide picture modes, their effects and how they were achieved. According to one explanation we had from the Philips technical people in Australia, when you switch to the “Superwide” mode, the major area of the picture is undistorted although it is magnified slightly, by about 10%; it is only the two vertical edges of the picture which are stretch­ed to fill the screen. The method used to stretch the picture is quite simple in theory; just vary the S-compensation applied to the picture tube yoke drive. Having been given the above explanation, we found it hard to understand. After all, it takes 52µs to scan one line on a normal picture and clearly the scanning voltages do have to be varied to provide the varying degrees of picture stretch. Note that the picture is also stretch­ ed vertically (although not as much as horizontally) in the Super­wide mode. This can cause a problem with pictures that have captions at the bottom of the screen or where the image is cropped at the top. To solve this problem, the When in Super-Wide mode, the 10% vertical expansion means that some of the top & bottom of the image will be lost & this can cause a problem with captions. The top image is in Super Wide mode, while the bottom image is in Movie Expand mode. We found Super Wide quite satisfying for 4:3 programs. remote control has two buttons to nudge the picture up or down by a small amount. This picture shift is brought into play by an additional deflection coil on the tube yoke. Thus, you can nudge the picture up to fully view the cap­tions or nudge it down if someone’s head is being scalped at the top of the screen. Other deflection trickery by the Philips set means that movies shown in “letter box” format can be expanded to fill the screen (which means that you lose the edges of the picture. To more precisely judge the effects of the various stretched picture modes, we took a series of off-screen photos displaying a crosshatch pattern provided by a TV pattern generator. Each mode is identified with an on- screen label such as NORMAL 4:3, SUPER­WIDE and so on. Note that the 4:3 screen photo has black strips on each side of the screen. We were also able to make direct comparisons between the Philips wide­screen set and a 9-year old Philips 63cm set (the KR683 chassis, one of the last Philips sets to be designed and manufactured in Australia). When these direct comparisons were made we noted the hori­zontal and vertical picture overscan present in the older set. This amounted to about 7% or 8% which does not sound like a lot but it is quite significant when you see a picture which is not overscanned. When you consider this factor, the amount of picture stretching in the SUPERWIDE mode is not as much as you might think. If you look at the 4:3 crosshatch picture you will see that it has 10 horizontal lines and 13 vertical lines while the SUPERWIDE picture has 9 horizontals and 12 verticals. Note that the squares are stretch­ed horizontally more than vertically. In fact, we judged that in SUPER­ WIDE mode, the horizontal stretch is about +25% while the vertical stretch is about 12%. Furthermore, the amount of horizontal stretch is pretty even across the screen. Having demonstrated the various picture modes, it occurred to us that if PIP was on the screen it would be stretched too. So we tried it. Guess what? The PIP stays virtually the same size and in the same position, regardless of which picture stretch mode is se­lected. This is very clever because it means that the synchronis­ing and sizing of the PIP image which is inserted into the main picture has to be digitally varied to suit the stretch mode! Having tried all the variations, we have to say that watch­ing normal programs in the Superwide format quickly become the norm. Even though there is some slight overall horizontal stretching of the image, it is hardly noticeable, particularly if you have been used to watching a conventional TV which is normal­ly overscanned more in the horizontal than vertical direction. The bigger image is simply more satisfying. And when applied to movies broadcast in “letter box” format, it also increases the satisfaction. All told, we were very impressed by this new wide format TV set from Philips. It contains a host of technological innovations which really do add to the viewing satisfaction. We certainly did not want to send the review set back! Such technology does not come cheaply although you have to admit that compared with any other consumer product, this set does have a lot to offer. It has a recommended retail price of $6299. An optional matching stand is also available. Finally, as an extra service, Philips will install, connect and tune the set in the new owner’s home and demonstrate most of the features. This home installation service will be available seven days a week and after hours, throughout Australia. Not only that, Philips will also remove all the packSC ing materials for recycling. August 1994  9 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 Electronic Engine Management Pt.11: Fuel & Air Systems – by Julian Edgar Electronic engine managed cars run fuel and air induction systems that are completely different from those in cars with carburettors. In an engine managed car, fuel is pumped in a circuit from the tank to the fuel injector supply rail and then back to the tank again. This continuous flow of fuel around the system keeps it cool to avoid vaporisation and means that a supply of high-pressure fuel is available whenever it’s needed. Fuel supply components The fuel supply system can be di- vided up into a number of sections, starting with the fuel pump: (1). Fuel Pump: fuel pumps in EFI systems are of the high pres­sure, roller-cell type. Because this type of pump works poorly without a head of fuel, it is located either below the fuel level or is primed by a second, low-pressure pump located in the tank. The pump’s electric motor is cooled by the fuel flowing through it and the pump is protected against outlet line blockage by a pressure release valve. Another valve, which is a non-return type, is located on the outlet side of the pump. Fuel injectors come in a variety of shapes & forms but are all basically electric solenoid valves. 14  Silicon Chip The fuel pressure in Bosch systems is usually held at 250kPa (36psi), although the pump is capable of up to 500kPa (72psi). (2). Fuel Damper: following the fuel pump in some cars is a small inline damper, comprising an internal chamber and a coil-spring diaphragm. As the pump operates, it generates a pulsing effect in the fuel pressure. High volume pulses will deflect the diaphragm in the fuel damper, temporarily increasing the size of the inter­nal chamber and so absorbing the pressure spike. Conversely, momentary drops in pressure cause the diaphragm to move into the chamber, thereby maintaining the output pressure at a constant value. As well as reducing minor pressure fluctuations, the damper can also lower pump noise. (3). Fuel Filter: a large, metal-encased fuel filter follows the fuel damper. This filter may be located close to the fuel tank or can be situated in the engine bay. Particles down to a size of 10 microns (.0001mm) are trapped by the filter to ensure that the fuel injector nozzles aren’t blocked. (4). Fuel Rail and Injectors: fuel flows from the filter to the fuel rail, where the individual injectors take their feed. The fuel rail is of a larger internal diameter than the fuel line from the tank. This is to ensure that as each injector operates, there is still sufficient fuel in reserve to prevent fuel pressure regulator con­trols the return flow to the tank and so maintains the fuel-rail pressure. As Fig.4 shows, this device is divided by a diaphragm into fuel and air chambers, and has a vacuum line to the manifold plenum chamber. Rather than maintain the fuel at a constant pressure above atmospheric pressure, the fuel is kept at a con­stant pressure above that found in the manifold. The injectors are located so that they squirt fuel immediately behind the inlet valves. Note the large volume square cross-section fuel rail above them. pressure variations occurring from injector to injector. The injec­tors can either be held in place by collars and bolts, or by the fuel rail itself. The role of the fuel injectors is critical – they have to be able to respond very quickly (1-1.5ms typical opening time), produce a well-atomised spray, and be durable in the extremes of tempera­ture and vibration under the bonnet. A fuel injector is basically an electrical solenoid valve. It consists of a gauze filter on the inlet, a solenoid winding around the armature, a needle valve and the electrical connec­ tion. The coil resistance varies with different designs, with four ohms resistance being typical. In general, the lower the coil resistance, the faster the response-time of the injector. (5). Cold-Start Injector: some cars, especially those with rela­tively early EFI systems, have an additional injector mounted on the plenum chamber. This injector is activated by the electronic control module during cold starts and enriches the mixture. More recent EFI systems simply run longer injector pulse widths to provide the extra fuel needed. (6). Fuel Pressure Regulator: the Because fuel injectors only have a very small opening lift, they can easily become blocked. To prevent this from happening, the fuel filter blocks particles down to .0001mm diameter. Fig.1: a typical multi-point fuel injection system. August 1994  15 A single cold start injector (see above) is used on some systems to ensure satisfactory running when the engine is cold. It fires into the plenum chamber to enrich the starting mixture. The fuel pressure regulator (right) maintains the fuel at a constant pressure relative to the manifold pressure. The actual fuel pressure constantly varies, however. This means that when an injector opens for a certain length of time, the same amount of fuel will flow irrespective of wheth­er the manifold pressure is high or low. If this weren’t the case, then manifold pressure variations would cause unwanted changes in the fuel injection quantity. Air induction systems Because fuel is added to the airstream just before the engine inlet Fig.2: this diagram shows the in-tank fuel pump & fuel level sender unit used in the Subaru Liberty. 16  Silicon Chip valves in the majority of EFI cars, the air induc­tion system can be designed almost solely for greatest airflow. In carburettor designs, the inlet manifold has to be kept short and sometimes heated to prevent fuel droplets from Fig.3: the fuel injectors are positioned so that they spray fuel into the intake port immediately behind the intake valves. This photo shows a modified Subaru Liberty Turbo air intake system. At the bottom left is a new fabricated intake duct to the air-filter box. The airflow meter is located just behind this box & the airflow then passes through a rightangled duct to the shiny section of pipe, which was made to replace a silencing resonator volume. The right-angled rubber bend then takes the induction air to the turbo inlet. These modifications reduced the pre-turbo intake pressure drop by 40%, with a commensurate in­crease in performance. forming on its walls. In addition, the throat size needs to be restricted so that intake gas velocities remain high Fig.4: a fuel pressure regulator consists of a fuel chamber & an air chamber with a vacuum line to the intake manifold. The manifold pressure controls a diaphragm that separates the two cham­bers (Holden VL Commodore). in all driving conditions. In EFI cars by contrast, resonant tuning of long intake runners is employed and the ducts can be sized to provide the lowest pressure drop at full load. (1). Intake Silencers: the combustion air is generally drawn from outside the engine bay to avoid the induction of hot air. In some cars, it then passes into a silencing volume, often comprising a plastic box located under the mudguard. A duct then carries the air to the air-filter box. (2). Air Filter: the air filters used in modern cars are general­ly flat corrugated paper element types. They are located in plastic boxes positioned to one side of the engine bay. The volume of the air-filter box is sometimes part of the intake resonant tuning which is employed to gain better cylinder fill­ing. In addition, the air-filter box also generally acts as an additional intake silencer. This intake air silencer volume is from a Subaru Liberty & is located inside the mudguard. (3). Airflow Meter: in cars not employing a MAP sensor, the air­flow meter follows the air filter. The airflow meter can be of the vane, vortex or hot-wire type. August 1994  17 Right: This view shows a typical 4-cylinder intake manifold. The plenum chamber is at the top, while below it are the individual cylinder runners. The throttle body is a simple butterfly valve which controls the airflow into the engine. Fig.5: the fuel pressure is typically regulated so that it is 250kPa greater than the manifold pressure. This ensures that the fuel injectors deliver a constant amount of fuel for a given pulse length, regardless of manifold pressure variations. This photo of a modified Mazda rotary engine clearly shows the throttle body, with the plenum chamber located behind it & the intake port runners in the foreground. Note that this racing engine does not use an air bypass valve & so the throttle blade is set so that it is slightly ajar at idle. 18  Silicon Chip (4). Throttle Body: the throttle body is the main butterfly controlling the airflow into the engine. The vast majority of throttle butterflies are controlled by a cable linkage to the accelerator pedal, although some exotic cars now run ‘drive-by-wire’ arrangements. A bypass passage is often built into the throttle body, with an adjustment screw to vary idle speed. (5). Auxiliary Air Valve: when the engine is cold it needs more fuel and air to idle satisfactorily than it does when warm. The extra fuel is supplied by either a wider injector pulse width or by a cold-start injector. The extra air is provided by the aux­iliary air control valve (sometimes called the bypass air control valve). Its function is to allow intake air to bypass the throt­tle body butterfly. These valves can be either controlled mechani­ cally by engine coolant temperature or can be electrically pulsed or otherwise controlled by the ECM. This valve can also be used – in conjunction with ignition timing control – to give a constant idle speed, irrespective of engine loads like the air-conditioner. In some cars, additional air-bypass valves perform the idle-speed control function, with the auxiliary air valve used only during warm-up. (6). Plenum Chamber and Inlet Runners: following the throttle body, the air enters a plenum (or surge) chamber, before flowing to the inlet valves through long runners. The res- The powerful Nissan Skyline GT-R twin turbo sports car uses a huge log-type intake manifold & six throttle butterflies. Fig.6: a typical air intake system for a fuel injected car. Fig.7: typical air intake flow diagram for a fuel-injected, turbocharged & intercooled engine (Subaru Liberty). onant intake tuning is related to the length and diameter of the individual cylinder runners and the volume of the plenum chamber. Tests have indicated that an increase in maximum engine torque of as much as 25% can be gained by appropriate tuning of this system. Some engines, notably those with four valves per cylinder, use two intake runners for each cylinder. The two sets of intake ducts are of different lengths and are activated by ECM-controlled butterfly valves located within the induction system. Sophisti­cated twin Helmholtz resonance intake systems SC are used on some cars. August 1994  19 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 MAILBAG Alternative probe for coolant alarm In relation to the Coolant Level Alarm project featured in the June 1994 issue of SILICON CHIP, our company is able to offer an expanding rubber probe as an alternative to the probes shown in the article. Installation of the rubber expansion probe re­quires only the drilling of a 3/8-inch hole in the radiator top tank, enabling fitting without removal of the radiator from the vehicle. These probes are constructed of high density rubber and stainless steel with a brass spade electrical tab connector and can be supplied for $16.85 each, including postage. We are also able to supply a screw-in plastic probe com­plete with a threaded brass bushing, that is soldered to the radiator tank, for $26.00, including postage. Contact Rob Sym­ mans at Monteck Electronics Pty Ltd, Phone (09) 330 6817 (BH) or (09) 457 0301 (AH); or write to 11 Portulaca St, Willetton, WA 6155. Coolant alarm too sensitive It’s been over three years now since the publication of my automotive coolant level alarm in the Circuit Notebook section, so it was fabulous to see the idea developed into a kit at long last. It should not only start to save a lot of Australians a lot of money, but it will help push the automo­ tive industry into providing such an alarm as a long overdue standard fitting. However, after reading the article through, I think the kit in its present form is doomed to be unreliable. The coolant sensor input is far too sensitive. In a new car it will work fine for a few months perhaps, but with dirty or old coolant and ageing cars and trucks, the scum in the coolant will coat a conductive layer over the sensor’s insulator which will conduct enough current to the stainless steel pin to give a false reading to the circuit. There will be no alarm when it is needed! In placing the sensor into the top radiator hose, you have possibly forgotten that the hose is fed by a reasonably strong water pump. Your circuit resets itself very quickly when coolant covers the sensor (assuming that the hose fitting is also im­mersed internally), so you could lose most of the coolant out of the system and have no coolant flow and yet the pump can splash and surge enough water onto the sensor to keep the alarm from sounding off. This is not as damaging as losing all water because the excess heat will dissipate by turning the water to steam but that will not encourage a lot of faith in the circuit. My notes on the test of the Ford Fairlane in 1990 are as follows. Its alarm would come on (visual only) if a resistor of 18kΩ or more ohms was fitted between the sensor lead and earth for more than 10 seconds. But at 15kΩ or less the alarm lamp would extinguish immediately. I do not have a record of the open circuit sensor voltage, but perhaps 5V as you have chosen is quite logical. For the Ford circuit to take 10 seconds to operate and yet clear immediately with a slight change in the sensor’s current indicates to me that their alarm timing section of the circuit is buffered from the sensor by a comparator. The Ford timing arrangement would also be useless with a sensor in the radiator hose but with the standard radiator nut fitting it is fine. Three of the cars at our house now have the correct radiator nut supplied from a radiator repair business. My suggestions are that the sensor input capacitor be in­creased to 1000µF and the 100kΩ resistor vertically above it in the schematic be replaced with a 10kΩ resistor. This is for the radiator nut version but the radiator hose will likely have higher normal resistance readings than that. Glen Host, Doubleview, WA. Comment: we did fairly extensive tests when we designed the coolant alarm and found that the value of 100kΩ used was about right. We also recommend that the radiator be regularly flushed & the correct inhibitor used to prevent false triggering. SILICON CHIP, PO Box 139, Collaroy, NSW 2097. Further comments on 12V battery charging The letter commenting on the solar regulator in the May 1994 edition suggested charging lead acid batteries at 14.2V and then reducing this to 13.8V. In my experience, 13.8V is a little low and you won’t get maximum use from your batteries, something that is important with a solar power system. On the other hand, 14.2V is a little high and will cause gassing and electrolyte loss. It’s a pain to have to keep topping up your batteries. I settled on a charging voltage of 14V. This will give a good charge with very little gassing. I have not had to top up my battery in almost two years and the battery is used daily with faultless performance so far. These figures could change slightly for different types and brands of batteries but the manufacturer told me 13.8V to 14.2V is the recommended range for my battery and that 14.4V is the maximum (anything above this and damage was likely). I recommend that people not sure of the best voltage should contact the head office of the manufacturer of their particular brand of battery and ask their advice. This way, maximum life is assured from your batteries. Now on to another matter: the Publisher’s Letter in the same edition, May 1994. It was said that with lower mains vol­tage, 230VAC instead of 240V, the picture on an old style tele­ vision would shrink. Not true – with lower voltage on the final anode of a picture tube, the picture actually blooms or gets bigger. I know it doesn’t sound logical but it’s true. Any TV serviceman will agree, and a detailed explanation would take many pages. Sorry to pick at an otherwise great magazine. D. Haddock, Kamerunga, Qld. Comment: our writer for the Serviceman pages has noted that with virtually all solid state TV sets, the reduction in mains voltage will make no difference. On old valve sets, a reduction in mains voltage will certainly cause the picture to bloom. August 1994  23 A high-power dimmer for incandescent lamps Need a dimmer for a large domestic or stage application? This unit will dim an incandescent or halogen lamp load of up to 2400 watts. It can also dim 12V transformer-driven halogen lamps or be used for fan speed control. Design by MARQUE CROZMAN 24  Silicon Chip Low power dimmers for loads up to 500 watts or so are readily available and quite cheap at around $20. But if you want to dim much larger loads than this the cost of a commercial dimmer becomes quite expensive and can range up to several hundred dollars. Why pay that much when you can save money by building this version and incorporate extra features as well? For example, this circuit can be remotely controlled by a 0-10V DC signal. This means that the dimmer itself can be in­stalled out of the way while three wires at low voltage can run to the dimmer potentiometer. This can then be placed in a con­venient location. Alternatively, you could incorporate a local/remote switch so that the dimmer could be directly con­trolled by the knob on its case or via the remote potentiometer. Furthermore, these options can always be incorporated later if you don’t need them right now. The dimmer is housed in a rugged diecast aluminium case measuring 170 x 121 x 55mm. The case provides heatsinking for the Triac as well as external protection for the circuit. As already noted, it can dim up to 2400 watts of lamps which may be made up in any combination. Minimum recommended lamp load is 40 watts. Let’s now have a look at the circuit diagram which is shown in Fig.1. This looks fairly complicated but is essentially a phase controlled Triac, similar to that in any commercial light dimmer. The major difference between this circuit and most 300-500W commercial 10 25VW A2 D3 24V CASE PIN2 IC1b E 4.7k 2 3 1 1 1k IC1b 2 2 3 4 5 6 D2 1N914 7 100  B 8 1k +15V ZD1 10V 400mW PIN14 IC2 +15V 100k SET MIN BRIGHTNESS VR2 10k 10k E 0.1 C 220  100k 100k +15V 5.6k IC2d 5 1 SET MAX BRIGHTNESS VR3 50k A N 240VAC F1 10A 820k IC2c 12 7 13 IC2b 6 10k 8 IC2a 10 LM324 11 4 9 D4 2x 1N4004 BR1 DB104 100 50VW IN GND REG1 7815 OUT CASE A1 I GO C E 7 13 14 11 IC1f IC1e 12 10 6 IC1d 5 VIEWED FROM BELOW B 2  4 IC3 MOC3021 A K .033 250VAC 6 1 4 14 3 10k 10k 2.4kW LAMP DIMMER G 0.1 L1 : 19T, 1mm DIA ENCU ON A PHILIPS 4330 030 60271 TOROID +15V A E CASE N GPO 2.4kW MAX 0.1 250VAC L1 G TR1 BTA41A A2 A1 0.1 250VAC 22  1W 240VAC 470  390  A LED1  K 2.2k 0.5W +4.6V DIMMMER VR1 50k LIN D1 1N914 Fig.1 (right): the full circuit of the dimmer. Most of the circuitry runs at low voltage & is isolated from the 240VAC mains via the transformer & the optocoupler IC3. 4.7k 9 IC1a 40106 As with any dimmer circuit, the power to the lamps is varied by Q1 BC547 Circuit principle 100k dimmers is that most of the circuit is isolated from the 240VAC mains supply by virtue of an optocoupler and a transformer. The heart of the circuit is the Triac, TR1. This is a BTA41A Triac, a 600 volt, 40 amp device which has been selected to cope with the high surge currents when switching on an incan­d­ escent lamp load totalling 2400 watts. Typically, the surge current at switchon can be 10 to 15 times the normal load cur­ rent; ie, the surge current could be 100-150 amps and last for several milliseconds. The Triac must also be able to cope with the high fault currents that flow when high power lamps blow their filaments. To explain, when a lamp blows its filament the now loose sections can flay around and come in contact with the stem supports. When that happens a high fault current can flow which is not extinguished until the stem fuse blows. Clearly, the Triac must be rugged to cope with this. 680  • • • • • IC1c • Features 2400W maximum lamp load 40W minimum lamp load Industry standard 0-10V dimming control Dims transformer-driven halogen lamps 10A mains supply fuse Adjustable maximum brightness Adjustable minimum brightness RF interference suppression 7.5kV optocoupler isolation between control circuitry and 240VAC mains for safety. +15V • • • August 1994  25 This view shows how the completed PC board is mounted in the case, along with the GPO & the mains terminal block. The front panel controls are connected to the board via a 7-way pin header. switching on the Triac early or late in each mains half-cycle. For high power operation, the Triac is triggered on late in each mains half-cycle so that the effective voltage fed to the lamp load is low. Similarly, for high power operation or full on, the Triac is triggered early in each mains half cycle so that virtually the full mains voltage is applied to the lamp load. This method of power control is referred to as “phase con­trol” because we vary the phase of the Triac trigger pulses with respect to the mains waveform. Most small dimmer circuits use a Diac or similar capacitor discharge device to trigger on the Triac but this circuit is more complex, mainly to provide isola­tion between the control circuitry and the 240VAC mains supply. Circuit description Before we dive into a full description of the circuit shown in Fig.1, let’s identify some of the key sections. First, at the top righthand corner is the Triac itself which feeds the lamp 26  Silicon Chip load via a standard 3-pin mains socket. In the lower right­hand corner is the low voltage supply which uses a 24V transformer feeding a bridge rectifier and 3-terminal regulator. In the top lefthand corner is the ramp generator (IC1a & IC2a) while below that, in the bottom lefthand corner, is the 0-10V DC control circuitry. Now that you are oriented, let’s start with the low voltage supply involving the 24V transformer. As already noted, this feeds a bridge rectifier (BR1) and a 100µF capacitor to drive a 3-terminal regulator REG1, which produces a 15V WARNING! While most of the circuitry operates at low vol­tage, this is a mains operated circuit and must be regarded as potentially lethal when power is applied to it. This project is not one for beginners and should only be attempted by construc­tors who have previous experience with mains powered circuits. DC supply. The reason for using the relatively high transform­er voltage of 24VAC has to do with the ramp synchronisation. Two diodes, D3 and D4, feed the rectified but unfiltered DC to a network at the input of IC1a which consists of a 4.7kΩ resistor, diode D1 and a 2.2kΩ resistor. As a result of this network, the voltage at the input of Schmitt trigger IC1a will be at +15V for most of the time but will drop to +4.6V at the beginning of each mains half-cycle. This waveform is inverted and squared up by IC1a to pro­duce a series of narrow positive pulses synchronised to the 50Hz mains supply. This pulse train drives the base of transistor Q1 which discharges the capacitor at its collector every 10ms. In between each discharge the capacitor is charged via the 100kΩ resistor connected to the +15V rail. The resulting sawtooth waveform is buffered by op amp IC2a and inverted by op amp IC2b and then fed to pin 13 of op amp IC2c which is connected as a comparator. Op amp IC2d is fed by the 50kΩ dimmer potentiometer VR1 which is fed with +10V from zener diode 7 D3 3 K 2 LED1  1 D1 Fig.2: this diagram shows the additional circuitry required for the remote dimming facility. It is connected to the main circuit via a 7-way header plug and socket on the PC board. ZD1 1 IC3 1k ZD1. Thus the input from VR1 can range anywhere from zero to 10V DC, depending on the desired lamp brightness. The DC voltage from VR1 is buffered by op amp IC2d which has an adjustable gain of less than unity (ie, it is an attenuator). The voltage from IC2d is fed to pin 12 of comparator IC2c which compares it with the 100Hz sawtooth voltage at pin 13. The result is a variable width pulse train corresponding to the dimmer setting; ie, wide pulses for a high brightness so that the Triac is triggered early in each 1k 100k VR3 100k 1 HEADER 22  1W 0.1 250VAC .033 250VAC 0.1 250VAC MOC3021 Fig.3 (right): the part layout diagram for the PC board. This should be used in conjunction with the wiring diagrams of Figs.4 & 5. Note the wire link between ZD1 and the adjacent 220Ω resistor. Note also that the two pads immediately above the 7-pin header are vacant. D2 1 4.7k 680  A 10uF 4.7k 2.2k 10k 5.6k 10k 1 100k VR2 D4 POWER TRANSFORMER IC2 LM324 820k Q1 10k 100  OPTIONAL REMOTE CONTROL 100uF BR1 4 10k 0.1 5 IC1 40106 1 S1 VR1 50k LIN 100k 24V 220W XLR 1 PLUG 6 390  3 470  2 REG1 (MOUNTED ON CASE) PRIMARY 50k LIN XLR 2 PANEL SOCKET 3 7 L1 F1 TRIAC1 ACTIVE NEUTRAL mains half-cycle and narrow pulses for a dim setting. The pulses from IC2c are then buffered by four paralleled inverters (IC1c,d,e & f) which drive the opto­ coupler IC3. In turn, the optocoupler triggers the Triac which drives the lamp. At this stage you have most of the picture of the circuit operation but there are some details yet to be discussed. For example, the remaining inverter in the 40106 hex Schmitt trigger package, IC1b, is connected to G A2 A1 LOAD the output of IC2c and is used to drive indicator LED1 via a 1kΩ resistor. This LED then provides a rough indication of the brightness setting of the dimmer since it is driven from the same pulses as are used to trigger the Triac. A 7-pin header socket on the board provides for local or remote operation. On the dimmer panel, a 50kΩ slider pot (VR1) provides the dimming control. Alternatively, switch S1, an addi­tional 50kΩ linear potentiometer and a 3-pin XLR socket can provide for remote dimming, as shown in Fig.2. RESISTOR COLOUR CODES ❏ No. ❏  1 ❏  4 ❏  4 ❏  1 ❏  2 ❏  1 ❏  2 ❏  1 ❏  1 ❏  1 ❏  1 ❏  1 ❏  1 Value 820kΩ 100kΩ 10kΩ 5.6kΩ 4.7kΩ 2.2kΩ 1kΩ 680Ω 470Ω 390Ω 220Ω 100Ω 22Ω 4-Band Code (1%) grey red yellow brown brown black yellow brown brown black orange brown green blue red brown yellow violet red brown red red red brown brown black red brown blue grey brown brown yellow violet brown brown orange white brown brown red red brown brown brown black brown brown red red black brown 5-Band Code (1%) grey red black orange brown brown black black orange brown brown black black red brown green blue black brown brown yellow violet black brown brown red red black brown brown brown black black brown brown blue grey black black brown yellow violet black black brown orange white black black brown red red black black brown brown black black black brown red red black gold brown August 1994  27 CORD GRIP GROMMET Fig.4: this diagram shows all the off-board wiring & the primary & secondary connections for the power transformer. Note that the earth leads from the power cord & power socket must be soldered to an earth lug which is securely bolted to chassis. MAINS CORD REG1 (MOUNTED ON CASE) 100k 10k 820k VR3 100k 100  IC1 40106 470  1 390  100k 1 1k ZD1 IC3 D2 4.7k 220  SECONDARY PRIMARY POWER TRANSFORMER 5.6k 10k 1 100k VR2 10uF 1k 100uF Q1 10k IC2 LM324 0.1 24V 1 HEADER 7 22  1W 0.1 250VAC .033 250VAC 0.1 250VAC MOC3021 L1 F1 A N G A2 A1 5 O/P 4 3 1 TRIAC1 2 A VR1 EARTH (GREEN/ YELLOW) K LED1 EARTH LUG NEUTRAL (BLUE) ACTIVE (BROWN) N E PANEL MOUNT POWER SOCKET A Note that the potentiometer must be a linear type otherwise the dimming charac­teristic will not be smooth and progressive. Brightness adjustments Adjustments are provided in the circuit for maximum and minimum 28  Silicon Chip brightness settings. First, VR2 provides the minimum brightness setting, when the main potentiometer VR1 is at is zero setting. VR3 sets the gain of op amp IC2d and thereby sets the maxi­mum brilliance setting. It is set by taking VR1 to its maximum setting and then noting the lamp brilliance. VR3 is then rotated clockwise to note if there is any increase in brilliance and then backed off slightly. The idea is to set it so that the maximum setting of VR1 does in fact give the maximum brilliance. The settings of VR2 and VR3 will interact so it will be necessary to adjust each XLR PANEL SOCKET ON/OFF SWITCH A (OUTPUT) A 2 7 3 240VAC 50k LIN LAMP DIMMER LOAD 1 N N E 5 Fig.6: this diagram shows how the dimmer could be wired up in a permanent installation. The dimmer itself could be installed in the ceiling, while the low voltage potentiometer connections & 10A switch could be on a standard architrave plate. Note that this installation can legally only be performed by a licensed electrician. 6 S1 4 3 1 2 A VR1 Fig.7: this diagram shows the mounting details for the insulated tab Triac. No mica washer or plastic bush is required. K LED1 Fig.5: this diagram shows the wiring of the remote control ver­sion with all connections made via a 150mm length of rainbow cable & a 7-way header plug. in turn several times to finalise the settings. High voltage circuitry So far, virtually all of the circuit description has ap­ plied to the low voltage portion but the components associated with the Triac need explanation. First, the 22Ω resistor and 0.1µF capacitor comprise a “snubber” circuit which allows the Triac to commutate correctly (ie, switch off reliably) at the end of each mains half-cycle when the load is inductive. This would be the case when dimming 12V transformer driven halogen lamps. The optocoupler is also provided with snubber protection and this takes the form of the 390Ω and 470Ω current feed resis­tors which are tapped off by the .033µF 250VAC capacitor. One of the drawbacks of this type of dimmer circuit is the very fast switching of the Triac. This produces switching transients which range up to 30MHz or more, resulting in a buzz­ ing sound when received by radios. To eliminate this problem, RF suppression is provided by inductor L1 which is in series with the load socket, together with the 0.1µF capacitor across the load. L1 and the 0.1µF capacitor comprise a low pass filter which is a very effective at reducing the amount of radiated interfer­ence. Note that a critical aspect of L1 is that it is wound onto an iron powder toroid. This gives an inductor with a relatively low Q-factor, ensuring that oscillations caused by the fast switching of the Triac are well damped. Construction The specified Triac is an insulated tab device which is mounted directly to the case for good heatsinking. Note the plastic cable tie which secures the interference suppression toroid (L1) to the PC board. The new dimmer is housed in a diecast aluminium case meas­ uring 171 x 120 x 55mm, as noted above. Most of the circuitry is mounted on a PC board measuring 96 x 79mm and coded 10107941. This also has the transformer mounted on it, as can be seen in the component overlay diagram of Fig.3. Note that this is slight­ly August 1994  29 This inside photo shows all the wiring, including the wired remote control facility. Note that there are slight differences between the board in this photo and the diagram of Fig.3. different from the PC board shown in the photos. Before you begin any soldering, check the board thoroughly for any shorts or breaks in the copper tracks. These should be repaired with a small artwork knife or a touch of the soldering iron where appropriate. Mount the diodes, resistors and wire links first. Note that one row of resistors is installed “end on” to save board space. You can use the clipped off resistor leads for the wire links. Now mount the 3AG fuse clips, the capacitors and the two trim­pots. Note that VR2 is 10kΩ while VR3 is 50kΩ; don’t inadvertent­ly swap them around. This done mount the transistor and the integrated circuits and make sure you install them with the correct orienta­tion which is shown by the notch at the pin 1 end. Fig.8: this is the full size etching pattern for the PC board. 30  Silicon Chip The transformer is bolted to the board using screws, nuts and lock­ washers and then its primary and secondary leads are soldered in. Note that the secondary wires are not depicted on the overlay diagram of Fig.3 but they are shown on the wiring diagram of Fig.4. This was done for clarity. The iron powder toroid (Philips 4330 030 60271) is wound with 19 turns of 1mm diameter enamelled copper wire. Strip the wire ends for soldering and space the turns evenly around the core. When soldered to the board, secure the toroid with a Nylon cable tie – see photos. Finally, you can mount the 3-terminal regulator and the Triac. The regulator is mounted on top of the board in the con­ventional way while the Triac leads are soldered to the underside of the board so that its metal tab can be bolted to the floor of the diecast case. Case assembly At the time of writing this article we do not know whether kits will be offered with pre-punched metalwork. If not, there will be quite a lot of drilling and filing to be done to prepare the case. You will need to drill and cut the holes for mounting the board, 3-terminal regulator and Triac, the Earth solder lug, the 2-way insulated terminal block for the mains cable, the hole for the cordgrip grommet, the flush-mount mains socket and the dimmer potentiometer. Note that all screw holes in the underside of the case and the lid should be countersunk. Four adhesive rubber feet should be fitted to the bottom of the case to avoid scratching table surfaces. The slider requires a slot 2mm wide and 50mm long. As well, if you require the optional remote facility, you will also need to drill or punch holes for the XLR socket and switch. The front panel artwork shown in Fig.9 shows how the front panel compon­ents are laid out. Use a photocopy of the artwork as a drill­ing template. The PC board is mounted on four 6mm pillars on the base of the case. Before installing it, you should attach the 250VAC 10A rated hook-up wires which will connect to the AC socket and to the insulated terminal block. Use brown for the Active lead and Blue for Neutral. Having mounted the board, the The 3-terminal regulator (REG1) is heatsinked by bolting it directly to one end of the case. Do not use an insulating washer here, as the tab of the regulator actually grounds the low voltage side of the circuit to the case. 3-terminal regulator and Triac can be bolted to the case. Note that the metal surface must be smooth and free of metal swarf. Use a light smear of heatsink compound under the metal tab to improve heat transfer. Note that mica washers are not required for either of these semiconductor devices. In fact, the tab of the 3-terminal regulator actual­ly grounds the low voltage side of the circuit to the case. The specified Triac, on the other hand, is an insulated tab device, so no mica insulation kit required. The mains cable should be secured in the case with a cordgrip grommet and its yellow/green wire should be attached to the earth solder lug. An earth wire from the mains socket runs to the same solder lug. All the wires to the lid of the case are run as a multi-strand (rainbow) cable to the 7-pin header socket on the PC board. If you require the optional remote facility, you will need to wire the front panel as shown in the diagram of Fig.5. The header plug comes un-assem­ bled as the plastic shroud together with a strip of pins. Carefully strip back and tin seven strands of a 150mm length of rainbow cable. With the pins still attached as a strip, crimp each pin onto the tinned wires before soldering. The pins can then be separated from the strip and pushed into the plastic shroud. Push until the locking spring on each pin becomes seated in the header. Once assembled, the rain­bow cable can be wired to the front panel components. When all the wiring is complete, check your work carefully against the circuit of Fig.1 and the wiring diagrams of Figs.3 & 4. Now you are ready to apply power but do not local remote input remote Max. load 2400W Fuse rating 10A (inside case) DANGER 240 VOLTS AC INSIDE lighting dimmer Fig.9: full size artwork for the front panel. August 1994  31 PARTS LIST 1 PC board, code 10107941, 96 x 79mm 1 sealed diecast aluminium case, 171 x 121 x 55mm 1 Philips toroid, Part No. 4330 030 60271 1 M2854 24V CT transformer 1 Clipsal 10A flush mount GPO socket 1 7-way single-in-line PCB header & socket (0.1-inch spacing) 1 female 3-pin XLR socket 1 SPDT round rocker switch 1 black slider pot knob 1 LED mounting bezel 1 self-adhesive front panel 1 earth lug 1 terminal block 4 adhesive rubber feet 1 1-metre length 1mm diameter enamelled copper wire 1 150mm-length 7-way rainbow cable 1 cordgrip grommet for mains cable 1 10A 240V AC 3-core mains cable & moulded plug 2 PCB mount 3AG fuse clips 1 10A 3AG fuse 9 3mm dia. x 10mm countersunk machine screws 3 3mm dia. x 25mm countersunk machine screws 12 3mm hex nuts & washers 4 6mm standoffs 1 50kΩ linear slider pot (60mm travel) (VR1) 1 10kΩ horizontal trimpot (VR2) connect a load at this stage. Fit the 10amp fuse, put the lid on the case and apply power. Move the slider up and down and observe the LED. It should brighten and dim in accordance with the control setting. If that happens, you are practically finished apart from setting the minimum and maximum brightness settings. To do this, you must connect a lamp load of 40 watts or more and take the lid off the case to do the adjustments. Warning: this circuit is potentially lethal due to the presence of 240VAC on the Triac and associated components. With the power on, set the dimmer pot to the minimum set­ting and adjust trimpot VR2 so that the lamp filament 32  Silicon Chip 1 50kΩ horizontal trimpot (VR3) Semiconductors 1 40106 hex Schmitt inverter (IC1) 1 LM324 quad op amp (IC2) 1 MOC3021 (IC3) 1 BTA41A Triac (TR1) 1 BC547 NPN transistor (Q1) 2 1N914 diodes (D1,D2) 2 1N4004 diodes (D3,D4) 1 10V 400mW or 1W zener diode (ZD1) 1 7815 15V regulator (REG1) 1 DB104 bridge rectifier (BR1) 1 5mm red LED (LED1) Capacitors 1 100µF 50VW electrolytic 1 10µF 25VW electrolytic 2 0.1µF MKT polyester 2 0.1µF 250VAC metallised polycarbonate (0.4-inch lead spacing) 1 .033µF 250VAC metallised polycarbonate (0.4-inch lead spacing) Resistors (0.25W,1%) 1 820kΩ 1 680Ω 4 100kΩ 1 470Ω 4 10kΩ 1 390Ω 1 5.6kΩ 1 220Ω 2 4.7kΩ 1 100Ω 1 2.2kΩ 1 22Ω 1W 2 1kΩ Scope photo 1 – ramp generator waveforms: top, waveform at pin 8 of IC1a; bottom, waveform at the collector of Q1. Scope photo 2 – comparator wave­ forms: top, waveform at pin 8 of IC2a; bottom, waveform from pin 14 of IC2c. Miscellaneous Heatsink compound, cable ties is at red heat. Now set the dimmer control to its maximum setting and adjust VR3 so that the lamp just gets to maximum brightness when VR1 is brought to its maximum. The settings of VR2 and VR3 will then have to be repeated because they do interact. Finally, attach the lid to the case and you are finished. What if it doesn’t work? The first point to check is the DC voltage as marked on parts of the circuit of Fig.1. You can use the case as the negative connection point for your multimeter. Note that the DC output of IC2d should vary in response to the setting of the potentiometer VR1. If you have an oscilloscope, you can check for the presence of the waveforms shown in Scope photo 3 – Triac waveforms: top, waveform at A2 of the Triac; bottom, waveform at pin 2 of IC3. Note that the mains waveform is flattened due to external causes. the accompanying scope photographs If not, you can still check for the presence of trigger pulses at the outputs of IC2c, IC2d and the paralleled outputs of IC1. This can be done because your multimeter can measure the average DC level of the pulses. At maximum setting, the pulsed DC output will measure close to +15V while at minimum it should be close to 0V. Failing that, check your soldering very carefully. The main cause of failure in SC projects is bad solder­ing. 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.jaycar.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.jaycar.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.jaycar.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.jaycar.com.au A microprocessor controlled Morse keyer Here is a state-of-the-art Morse keyer which you can use to polish up your sending. It has a relay to control the keying of the transmitter & a loudspeaker so that you can listen to your sending. It also has a memory so that you can store a Morse message up to 64 characters long. Design by ALAEXANDRE ZATSEPIN It may seem like a contradiction in terms to have a “state-of-the-art” microprocessor controlled Morse keyer. After all, Morse code is the oldest method of sending messages over the air or along wires (telegraph) and many people probably think it is obsolete. However, without joining that debate and whether Morse should be used by amateur radio operators, this microprocessor controlled keyer is an elegant device to send your code. In fact, our photo shows it combined with an equally elegant Morse paddle; a highly desirable item to those who delight in CW (continuous wave) transmissions. Perhaps we should briefly mention that Morse code actually preceded radio transmissions by almost 50 years. Samual Morse patented his telegraph system in 1840 and it was not until 1898 that Guglielmo Marconi sent the first paid radiogram from the Isle of Wight. Even today, Morse code is used for radio messages and it is a method which can succeed in very difficult transmis­sion conditions where other more up-to-date methods fail. The Morse keyer is mounted on a small PC board which car­ries a Z8 microprocessor, a non-volatile mem­ ory chip, a miniature relay and not much else. The paddle is connected to a 4-way connector while the loudspeaker and relay output connections are made via 2-pin headers. A 2.1mm DC socket provides the power connection which can be to a 9V battery or to a 9V DC plugpack adaptor. Three buttons on the board control recording, speed and tone, while a August 1994  37 9x3.3k RESISTOR ARRAY P1 DOT 2 1 PADDLE +5V 1 430  3 4 5 6 7 2 8 9 15 16 3 DASH TONE S1 17 18 5 8 VCC P00 P22 P23 P02 5 D VIEWED FROM BELOW 12 100  Q1 VN0106 D G S 13 2 P25 3 P26 4 P27 QIN Q OUT P31 P32 P33 GND 7 X1 6 8 9 10 14 4MHz G O P01 IC1 Z86E08 11  K 4 D0 IC2 D1 3 93C46N SK 2 1 CS GND I LED1 STATUS P21 +5V PLAY S3 8 A VCC P20 1 P24 SPEED S2 G P3 S A K 100pF 9VDC INPUT P4 100pF RLY1 1 Q2 VN0106 D G S D1 1N4002 REG1 LM293-5 IN 100 16VW P2 2 GND OUT +5V 100 16VW MORSE KEYER Fig.1: the circuit is based on pre-programmed microcontroller IC1 (Z86E08) & non-volatile memory IC2. The non-volatile memory stores the message, tone, speed & cyclic redundancy code (CRC). setting is stored in the mem­ory buffer upon release of the key. LED indicates one of three possible states of the keyer. If power is applied and the LED is off, this indicates that the speed and tone settings are from the last operation and that there are no messages stored in the non-volatile memory. In this state, the keyer is in operating mode as described below. If the LED is on after power up, the speed and tone set­tings are from the last operation and there is a valid message in the memory. If the LED flashes after power up, the information in memory is invalid and is random. This condition may occur the first time the unit is powered up or if the non-volatile memory has been changed. To enter the operating mode, simply push the paddle key to the left or right; dot to the right and dash to the left, for example. The LED will stop flashing as soon as the key is operated and upon releasing the key, the circuit will enter the operating mode with a default speed of 70 characters per minute and a 1kHz tone (delivered via the loudspeaker). The relay operates in tandem with the loudspeaker. Record mode Sending speed To alter the sending speed, you press and hold down the SPEED button. To increase the speed, push the paddle 38  Silicon Chip key to the DOT position; to decrease the speed, push the paddle key to the DASH position. The Speed setting is stored in the non-volatile memory upon release of the key. To vary the tone from the loudspeaker, you press and hold down the TONE button and then push the paddle key to the DOT position to raise the frequency and to the DASH position to lower the frequency. Again, the Tone SPEAKER P3 Q1 BATTERY P3 100uF 100 100uF 1 D1 KEY P2 DOT 2x100pF Q2 PLAY S3 K Playback mode 430  X1 RELAY 1 REG1 IC1 Z86E08 1 GND SPEED S2 3.3k RES ARRAY 1 DASH IC2 936C46N TONE S1 The record mode allows you to store up to 64 characters in the memory. To enter the RECORD mode, press the SPEED and TONE buttons together. This will erase the existing message and the new message characters are loaded into the memory buffer. Pauses between characters are automatically set to one dash. Upon re­ ceiving 64 characters, the RECORD mode is terminated and after approximately 0.1 second, the keyer reverts to the normal operat­ing mode. To terminate the RECORD mode without entering all 64 characters, you press the PLAY button. After 0.1 second, the speaker will beep and the unit will revert to the normal operat­ing mode. After a message is stored, the LED will be on. A LED1 P1 Fig.2: install the parts on the PC board as shown here. Note particularly the orientation of the three switches. This is simple; just press the PLAY button. Any message in the buffer will start to play at the current speed and tone until the message is complete. To stop the message playback, you push the paddle key to either side. Circuit description The main element of the keyer is a Z86E08 microcontroller (IC1). This device incorporates a one-time programmable read-only memory (OTP ROM) PARTS LIST 1 PC board, 70 x 45mm 1 4MHz crystal (X1) 1 DIL relay (RLY1) 1 miniature 8-ohm loudspeaker 3 momentary contact PC-mount pushbutton switches 1 4-way PC mount male socket (P1) 2 2-pin headers and matching plugs (P2,P3) 1 2.1mm DC socket (P4) Semiconductors 1 Z86E08 programmed microcontroller (IC1) 1 93C46N non-volatile memory (IC2) 1 LM293-5 5V regulator (REG1) 2 VN0106 FETs (Q1, Q2) 1 green LED (LED1) 1 1N4002 rectifier diode (D1) which is loaded with the software. The Z86E08 has 14 input/output lines. Five are programmed as inputs (P20-P24), five are programmed as outputs (P26, P27, P00, P01 & P02) and one (P25) is programmed as bidirectional. Three of the input lines (P31, P32 & P33) are grounded. The internal oscillator of the micro­ controller runs at 4MHz, as set by the crystal connected to pins 6 & 7. A Capacitors 2 100µF 16VW electrolytic 2 100pF ceramic Resistors 1 9 x 3.3kΩ resistor array 1 430Ω 0.25W resistor 1 100Ω 0.25W resistor Kit availability A complete kit for the Morse Keyer is available from FLC Microdesign Pty Ltd, 28 Haugh­ton Rd, Oakleigh, Vic 3166. Phone (03)563 3096; Fax (03) 563 3017. Payment may be made by cheque or postal money order. Pricing is as follows: Complete kit (does not include DC plugpack) .....................$45.00 Optional DC plugpack ........$10.00 Postage & packing .............$10.00 9-way resistor network pulls all the inputs to +5V and when any of the buttons is pushed, the respective input is pulled to 0V. Of the three outputs, P00 drives the LED directly, P01 drives the loudspeaker via FET Q1, and P02 drives RLY1 via FET Q2. The non-volatile memory (IC2) (93C46N) has 1024 bits organ­ised as 64 x 16. It stores the message, tone, speed and cyclic redundancy code (CRC) in the absence of power. CRC is used for error detection, to prevent wrong messages, speeds or tones being accepted. Power is supplied via the DC input socket and then through the protective diode D1 to voltage regulator REG1 to provide the +5V supply rail. The total current consumption is less than 25mA with the optional relay. Assembly Construction of the Morse keyer is very straightforward since it is such a small board with few components. The PC board measures 70 x 45mm. Mount all the small components first, such as the diode, the voltage regulator, resistors, the two FETs and the capaci­tors. Make sure that these components are correctly polarised or oriented. This done, mount the two header sockets, the DC socket, the 4-way socket for the paddle keyer and the three button switches. Finally, you can mount the microcontroller (IC1), the memory chip (IC2) and the relay. After you have checked all your work carefully, you can apply power and check voltages on the board. The output of the 3-terminal regulator should be at +5V and this voltage should also be present at pin 5 of IC1 and pin 8 of IC2, as well as pin 1 of the resistor array. This being the case, connect a loudspeaker and a paddle and you can send SC Morse code. August 1994  39 Dual diversity tuner for FM microphones; Pt.1 Plagued by signal dropouts from FM wireless microphones? This Dual Diversity Tuner automatically selects the best signal from two antennas to ensure a drop-out free reception. By JOHN CLARKE FM wireless microphones are now commonly used for stage and public address work. They have the obvious benefit of allowing the performers (or speaker) to roam about the stage without being tied to a microphone cord. In its most basic form, an FM wireless microphone setup consists of a small FM transmitter (to transmit the signal from the microphone), a receiving antenna and a companion FM receiver. The receiver picks up the signals from the transmitter and feeds the demodulated signal to the stage amplifier or PA system. At least, that’s the way it’s supposed to work in theory. Unfortunately, this type of system is often plagued by bursts of noise due to signal drop-outs 40  Silicon Chip as the performer moves about on stage. That’s because the received signal strength can vary quite markedly as the wireless microphone moves from one position to another. These signal strength variations are caused both by ob­ structions in the signal path between the transmitter and the receiving antenna and by nulls due to signal reflections from various objects in the room. The most obvious sources of obstruc­tion are the performers’ bodies and other on-stage objects, with metallic objects causing the greatest problems (depending on size). Careful siting of the receiving antenna can help to mini­ mise this problem but the results are often far from satisfac­tory. The best way to dramatically improve reception is to use two receiving antennas which are separated by several wave­lengths. In this situation, the signal is usually good in at least one antenna and, by using a receiver which can automatical­ly choose the best signal, good reception can be maintained for virtually 100% of the time. This type of tuner is called a “diversity tuner”. While commercial diversity tuners are available, they are generally quite expensive. As a result, this design should appeal to those capable of building their own equipment. It will cost considerably less than a commercial unit but provides similar performance. The design is also easy to build and requires no special equipment for alignment, so you shouldn’t have any problems on that score. It can be used with any standard wireless microphone which operates in the commercial FM band (88-108MHz); eg, the microphone FM transmitter published in SILICON CHIP in October 1993. Alternatively, you can use one of the readily-available commercial FM wire­­less microphones. As can be seen in the photographs, the circuitry is housed in a slimline rack mounting case. On the front panel are a 10-LED signal strength bargraph, two LED indicators to show the active antenna (either A or B), a test switch to enable manual selection of either antenna, an audio level output control, and a power switch. The rear panel carries two 75Ω PAL sockets for the anten­nas, an RCA output socket (audio out) and a fuseholder. The audio output connects to your mixer or power amplifier. Performance Fig.1 and the accompanying specifications panel show that the FM tuner is an excellent performer. As shown, the sensitivity is very good, with -3dB limiting occurring with an input RF level of just 1.3µV, while the signal-to-noise ratio reaches 60dB at just 7µV input and is an excellent 75dB at 100µV. These figures ensure a good-quality, low-noise signal for a wide range of RF signal inputs. Note that the signal meter levels are useful for showing the relative noise level from the FM tuner. At level 5, the tuner has reached ultimate quieting (75dB), while at signal level 2, the signal to noise ratio is 60dB. At level 10, the AGC is coming into effect to prevent overload. While this tuner performs equally as well as a commercial hifi tuner, it differs in that it requires two antennas and has fixed tuning. And, of course, it only provides for mono recep­tion. The two antennas connect to the tuner via shielded RF cables and should be mounted several wavelengths apart. If the signal from the wireless microphone deteriorates in the active receiving antenna, the tuner automatically switches to the other antenna in an effort to maintain signal quality. It does this according to one of three modes of operation. • The first mode occurs when a good signal is always available from at least one antenna. In this mode, the tuner only switches between the two antennas when the signal level in the active antenna drops below a preset threshold. Provided that the signal level in the active antenna is above this threshold, then this antenna remains selected regardless of their relative signal strengths. If, however, the signal strength in the active antenna drops below the threshold, the second antenna is selected. This antenna now remains selected until its signal drops below the threshold, at which point the first antenna is selected again, and so the process continues. The preset threshold, by the way, is the signal strength at which the signal-to-noise ratio has reached its maximum. Fairly obviously, it is unnecessary to switch antennas in this situation. • The second mode of operation occurs when both antennas provide signal strengths below the threshold. In this situation, the tuner selects the antenna that provides the best signal strength but that’s not all it does. At intervals of about one second, it also briefly switches to the other antenna to check its signal strength. If it’s lower than the active antenna, it quickly switches back again but if it’s higher, it stays there and briefly monitors the previous antenna at regular intervals. This constant switching between antennas does cause a slight distur- Main Features • • • • • • • • • • • • • • Dual antenna inputs Fixed tuning – can be set anywhere in FM broadcast band (88-108MHz) Low distortion Excellent signal-to-noise ratio High sensitivity Typical open air range of 60 metres with dipole antennas 10-LED bargraph display for signal strength indication Active antenna indicator LEDs Test switch to manually select alternative antenna (useful for setting up) Adjustable audio level output AGC to prevent overloading of tuner input Three modes of antenna switching to minimise antenna switching disturbances Automatic muting if poor signals received from both antennas to minimise noise 50µs de-emphasis (can be easily altered to 75µs) August 1994  41 10 +10 AUDIO 9 -10 8 -20 7 -30 6 -40 5 MUTE THRESHOLD -50 4 -60 3 -70 2 -80 -90 AGC SET POINT 1 'S' METER AUDIO OUTPUT (dB) 0 10 100 RF LEVEL AT 98MHz (uV) 1k 1 0 10k Fig.1: this graph shows the performance of the FM tuner front end. The sensitivity is very good, with -3dB limiting occurring at an RF input level of just 1.3µV, while the signal-to-noise ratio reaches 60dB at just 7µV input & is an excellent 75dB at 100µV. ANTENNA 'A' FM TUNER ANTENNA 'B' IF OUTPUT 'A' SIGNAL STRENGTH DECISION CIRCUIT SIGNAL STRENGTH FM TUNER CONTROL COMBINER IF DEMODULATOR AUDIO OUTPUT IF OUTPUT 'B' TRADITIONAL DUAL DIVERSITY TUNER Fig.2: most dual diversity tuners use two FM tuner front ends to receive signals from separate antennas. The signal strength in each tuner is monitored by a decision circuit & this controls a combiner circuit so that the best signal from the FM tuner outputs is fed through to the demodulator. This scheme works well but the need for two FM tuner stages adds to the cost. ANTENNA 'A' FM TUNER ANTENNA 'B' IF DEMODULATOR AUDIO OUTPUT SIGNAL STRENGTH ANTENNA SWITCH CONTROL DECISION CIRCUIT SILICON CHIP DUAL DIVERSITY TUNER Fig.3: the SILICON CHIP Dual Diversity Tuner differs from the traditional approach by using a single FM tuner stage & an antenna switch to select between the two antennas. In this case, the decision circuit monitors the signal strength in the FM tuner & controls the antenna switch to ensure that the best signal is selected. 42  Silicon Chip bance in the audio signal but this is barely notice­able, particularly as the signal is already down in the noise. Of course, if the signal strength in one antenna rises above the threshold, then the tuner will maintain selection of that antenna until the signal drops again. • The third mode of operation occurs when the signal strength is very poor from both antennas. In this case, the audio is muted to prevent noise. The tuner then continuously assesses the signal strength in each antenna and, when one rises above the preset minimum, it immediately locks onto that antenna and re­leases the muting. Normally, the first mode is the one that operates since, with correct antenna arrangement, the signal can be expected to be good in at least one antenna virtually all of the time. Under these circumstances, the switching action will be inaudible. If due care is taken with antenna siting, the second and third modes should operate rarely (if at all). Basic arrangement Fig.2 shows the traditional arrangement of a dual diversity tuner. It uses two receiving antennas, with each antenna feeding a separate FM tuner. The signal strength from each tuner is monitored by a decision circuit which then controls a combiner stage. ANTENNA 'A' SIGNAL LEVEL AGC CONTROL IC1 ANTENNA 'B' AUDIO ANTENNA SWITCHER D1-D4 IF FILTER T2, X1 MIXER IC1 Q1 RF AMPLIFIER IF FILTER X2 IC1 IF AMPLIFIER AND LIMITER 10.7MHz IF AMPLIFIER LOCAL OSCILLATOR IC1, T1, D5 IC1 DEMODULATOR IC2, L10 AUDIO OUT MUTE IC7 AMPLIFIER IC6, VR3 AFC CONTROL MUTE COMPARATOR IC5a, VR2 'A' 'B' SIGNAL LEVEL INDICATORS LED11, LED12, IC8e,IC8f BUFFER IC4a LED1 LED10 VREF CONTROL MINIMUM SIGNAL COMPARATOR IC5b, VR3 ANTENNA R SWITCHING OSCILLATOR IC9 CE D-A CK CONVERTER IC11 R SIGNAL LEVEL INDICATOR IC3 ANTENNA SWITCHING LATCH IC10a MANUAL IC10b, S2 '0' OUT R TIMER IC12 Fig.4: this is the complete block diagram of the SILICON CHIP Dual Diversity Tuner. The signal level generated by the IF amplifier stage in the FM tuner (top of diagram) is monitored by comparators IC5a & IC5b & these then control the antenna switching logic (IC9-IC12). There are various ways of combining the IF signals from the two tuners. One way is to simply select the largest signal, while another method involves adding the two outputs together. A third method involves adding the outputs according to a weighting determined by the signal-to-noise ratio of each IF signal. The first method is the easiest and is the one most commonly used. Following the combiner stage, the resulting IF signal is demodulated to produce an audio output. The main drawback of this approach is that it requires two tuners and this adds to the cost. It also presents problems as far as the design is concerned, since each tuner must be able to lock onto the signal without being affected by the other’s local oscillator. This problem is usually cured by shielding each tuner in a separate metal case or by using a common local oscillator. By contrast, the SILICON CHIP Dual Diversity Tuner uses an entirely different approach that makes do with just one FM tuner stage – see Fig.3. In this design, the signals from the two antennas are fed to the tuner via an antenna switch. Only one antenna is selected at a time and a decision circuit, which monitors the signal strength from the FM tuner, selects the antenna which will provide the best results. The main advantage of this approach is that it eliminates the second tuner, thereby reducing the cost and simplifying construction. Only a few extra parts are needed for the antenna switch, although the decision circuit is slightly more complicat­ed than in the previous case. Block diagram Refer now to Fig.4 – this shows the full block diagram for the Dual Diversity Tuner. The antenna switch, FM tuner and demod­ulator make up the top half of the diagram, while the decision circuit occupies the bottom half. The antenna switcher uses low capacitance VHF diodes D1-D4 to switch the antennas and the selected antenna signal is ampli­fied by tuned RF amplifier stage Q1. This amplifier has AGC (automatic gain control) applied to it, the AGC level being set by the signal level from IF amplifier stage IC1 and by the signal level from the output of the RF amplifier itself. Nominally, the AGC only comes into effect when the RF signal is greater than 10mV. Its job is to prevent overload by reducing the gain of the RF amplifier at high signal levels. Following the RF amplifier, the signal is fed to balanced mixer stage IC1 where it is mixed with the local oscillator signal. This local oscillator stage (IC1, T1 & D5) operates at a frequency that’s nominally 10.7MHz below the RF signal. As a result, the mixer stage converts the incoming RF signal to a 10.7MHz FM signal (plus other sum and difference sign­als). This 10.7MHz signal is now filtered (T2, X1), amplified and filtered again August 1994  43 44  Silicon Chip .01 .01 D1 BA482 .01 .033 220k 3.3k 10  2.2k 2.2k .01 +12V 2.7k K A 7 14 6 5 6 8 K 4  7 4 4.7k 10  2.2k L4 L5 X2 10.7MHz .01 2.7k 0.1 IF AMPLIFIER AND DEMODULATOR 0.1 2.2k D4 BA482 .01 .01 ANTENNA B D3 BA482 IC8f .01 A IC4a LM358 2.7k 3  +12V .01 L3 .01 ANTENNA A LED11 RED TP1 IC8e 74C14 5 .01 ANTENNA B LED12 GREEN L1 L2 D2 .01 BA482 ANTENNA A 2 3 L6 10  8 IC5b LM393 0.1 0.1 300W 0.1 .01 1 47 16VW 16 17 15 2 1 390  10k 0.1 L10 IC2 TDA1576 4 560pF 1 6 750  L8 27pF 6 13 IC8a 5 7 ANTENNA SWITCHING TIMER 12 0.1 4 33pF 10  5V 11 SIG 12 14 METER ZERO VR1 10k 33pF 3 .01 S .001 .001 G1 D L7 Q1 BF981 .001 G2 +12V .001 10  .001 10  0.1 1.2M 220k VC1 8.550pF RF PREAMPLIFIER +12V 8 13 10 1 IC9 7555 18 2 22k .018 6 3 .001 10  IC8b 3.9k 0.33 3 2 11 10 11 10 5 5 4V REF 9 LO OUT 6 13 14 16 0.1 T1 6 15pF MIXER AND IF FILTER 2 3 4 4 47  3 390pF X1 10.7MHz 3.9pF 390pF 5 1 T2 D5 BB119 33pF 2 .01 .01 100k 10  1 8 16  D7 1N4148 1.5k 1.5k 17 18 7   10k 6   14 13  2 12  4 11  3 5 ANTENNA SWITCHING OUTPUT 1 D IC10aQ 4013 2 CK Q S R 6 4  10 SIGNAL STRENGTH METER IC3 LM3914 15  3 9 0.1 LED LED LED LED LED LED LED LED LED LED 82  1 2 3 4 5 6 7 8 9 10 5W 11 10 12 D6 1N4148 4 17 7 LO AGC 8 IN IC1 TDA1574 15 18 AGC OUT 1.8pF 6.8pF 6.8pF 100k 220k 220k .01 10  +12V .01 VC2 530pF .0068 8 9 33pF L9 33pF +12V +12V +12V I GO ANTENNA UPDATE TIMER 2 3 1 0 1 22k D-A CONVERTER 4.7k IN 0V 47 16VW 4 S1 CASE E N 240VAC F1 250mA A 10 10k 10k 10k 10k +12V 6.3V T1 M2852 10k 7 5 6 IC6b 8 7 220k 1 0.1 220k 4 IC7 4066 12 14 10 11 6.3V 2 47k D9-D12 4x1N4004 OUTPUT LEVEL VR4 100k 47pF IC6a LF353 3 6 IC5a 7 10k 4700 25VW 10 1 MUTE THRESHOLD VR2 10k +12V 5 330k +12V GND REG1 7812 AUDIO OUTPUT MINIMUM SIGNAL LEVEL VR3 10k 1 OUT 10k +12V 4 27k 33k 2 2 3 7 39k 2 IC4b 3 47k 56k 10 1 4 5 IC8c 8 IC11 4017 13 CE 4 1 IC12 R 7555 8 +12V 15 R 16 CK 14 10k 10k 2 10 100k 10k 6 3 +12V 0.1 D8 1N4148 D8 1N4048 9 DUAL DIVERSITY FM TUNER IC8d 0.1 8 S2 ANTENNA TEST 10k 10k D A K G2 VIEWED ON LABEL SIDE S D CK 11 9 R Q IC10b S 10 8 G1 7 12 0.1 14 (X2), after which it is applied to a limiter stage. The limiter restricts the signal level applied to the following demodulator stage (IC2, L10) and also improves the signal-to-noise ratio. The demodulator converts the FM IF signal into an audio signal and provides an automatic frequency control (AFC) line to the local oscillator. This line is used to control the local oscillator so that it always oscillates at a frequency that’s exactly 10.7MHz less than the tuned RF signal. Let’s return now to the IF amplifier/ limiter stage. As well as driving the demodulator, this stage also provides a signal level output and this is applied to the signal level indicator (IC3) and to buffer stage IC4a. As previously mentioned, the signal level indicator drives a 10-LED bargraph. Buffer stage IC4a drives the following mute comparator and minimum signal comparator stages (IC5a and IC5b, respectively). In operation, the mute comparator compares the signal level with a reference voltage and controls the mute circuit (IC7) at the output of the demodulator. When the signal level is very low (which would result in considerable noise in the audio output), the mute comparator activates the muting circuit so that no signal is fed to amplifier stage IC6. The minimum signal comparator (IC5b) compares the signal level from IC4a with a voltage set by a D-A converter (IC11). When a high signal level is applied to IC5b, the antenna switch­ing oscillator (IC9) is off and the output of the D-A converter is at a maximum. However, if the signal level drops below the output from the D-A converter, IC5b’s output toggles and releases the reset on the antenna switching oscillator. This oscillator now starts Fig.5 (left): the final circuit uses low capacitance VHF diodes D1-D4 to switch the antenna outputs to RF amplifier stage Q1. IC1 & IC2 form the heart of the FM tuner, while IC3 & LEDs 1-10 form the signal strength meter. Depending on the signal strength, comparator IC5b controls the antenna switching latch (IC10) via IC9 to select the appropriate antenna. IC5b & IC7 mute the audio output if the signals from both antennas fall below a preset threshold. August 1994  45 Specifications Preset frequency range ������������������������������������� 88-108MHz Audio output at 75kHz deviation ������������������������ 620mV RMS to 1.7V RMS (adjust­able) Frequency response into 4.7kΩ load ���������������� -0.4dB at 20Hz and 15kHz Signal-to-noise ratio at 75kHz deviation ������������ 75dB for >100µV RF input Total harmonic distortion at 50kHz deviation ����� Better than 0.15% at 1kHz De-emphasis ����������������������������������������������������� 50µs (75µs optional) RF input at -3dB before limiting (98MHz) ���������� 1.3µV RMS AM rejection ������������������������������������������������������ Typically 54dB (1kHz, 30% AM modulation) Isolation between antennas ������������������������������ 27dB Antenna switching response time ���������������������� <100µs and clocks the antenna switching latch (IC10a) to select the alternative antenna. If the signal from this antenna is suffi­ciently high (ie, above the level from the D-A converter), IC5b immediately resets the switch­ing oscillator so that the antenna selection is maintained. However, if the signal from both antennas is low, the antenna switching oscillator remains on and the two antennas (A & B) are alternatively switched in and out by IC10a at a rapid rate. During this time, the switching oscillator also clocks the D-A converter, which reduces its output voltage on each clock cycle. When this voltage eventually drops below the signal level, IC5b stops the antenna switching oscillator and IC10a latches the currently selected antenna. At this point, timer IC12 is activated and, after about 1s, resets the D-A converter so that its output is again at maximum. As previously described, the minimum signal comparator (IC5b) now compares the D-A output with the signal voltage and so the above process is repeated indefinitely. Finally, a manual switching circuit (IC10b and S2) enables either antenna to be selected at the press of a switch. Each time S2 is pressed, the alternative antenna is selected and this selection can be maintained by holding the switch in. This is a useful feature for testing and setting-up purposes, since it enables the antennas to be sited for best signal strength. Circuit details Fig.5 shows the final circuit of the Dual Diversity Tuner. It uses 12 ICs, 46  Silicon Chip a dual gate Mosfet (Q1), several coils and nu­merous minor components to perform all the functions described above. Despite the apparent complexity of the FM tuner from the block diagram, it really is quite straightforward. It’s based on a Philips chip set consisting of two ICs (IC1 and IC2) and these only require the addition of suitable coils, a varicap tuning diode and sundry minor parts to give a basic high-quality mono­phonic FM tuner. IC1, a TDA1574 Integrated FM Tuner IC, forms the front end of the tuner. It contains a balanced mixer, local oscillator, linear IF amplifier and AGC circuitry. Its companion, IC2 (a TDA1576 FM IF Limiter), provides a limiting IF amplifier, a quadra­ture demodulator, AFC output and field strength indicator output. An RF amplifier based on dual-gate Mosfet Q1 increases the sensitivity by about 28dB. The signal for the RF amplifier is supplied from either antenna A or antenna B via the antenna switcher. Let’s take a closer look at how this switcher works. Diodes D1-D4, along with coils L1-L4, form the basis of the antenna switcher. D1-D4 are actually Philips Silicon Planar Diodes. These have a very low capacitance of 0.65pF at a reverse voltage of 12V, and a forward resistance of about 0.6Ω at a for­ward current of 5mA. These specifications are for 100-200MHz operation, which makes them ideal for switching FM broadcast band antennas. The DC control lines for the antenna switcher are driven by the Q and Q-bar outputs of flipflop IC10a via 10Ω resistors. For example, when Q is at +12V, Q-bar is at ground. D2 is thus for­ward biased via its 2.2kΩ anode resistor and L2, while D4 is forward biased via L4 and its 2.2kΩ cathode resistor. At the same time, D1 and D3 are reverse biased at +12V and are therefore non-conducting. In this situation, the signal from antenna A can pass via D2 and the associated .01µF capacitors to the input of the RF amplifier at L5. The signal from antenna B, however, is blocked by diode D3 and is instead shunted to ground via D4 to ensure maximum isolation from the RF amplifier input. Conversely, when Q-bar of IC10a switches to +12V and Q goes to ground, the situation is reversed. D1 and D3 are now forward biased, while D2 and D4 are reverse biased. The signal from antenna B is now coupled to the RF amplifier input (via D3), while the signal from antenna A is blocked by D2 and shunted to ground via D1. Note that all the diodes are AC-coupled using .01µF capaci­tors. This is done to isolate the DC voltages which switch the diodes from the antenna. Inductors L1-L4 complete the DC paths through the diodes; they act as short circuits at DC but provide a high impedance at 100MHz to avoid loading the antenna signals. The signal from the antenna switcher is amplified by the RF preamplifier stage, as described previously. This stage consists of dual-gate VHF Mosfet Q1 and inductors L5-L7. L5 inductively couples the signal to L6 which forms a tuned circuit with trimmer capacitor VC1. VC1 is adjusted to tune the circuit to the wireless microphone frequency, so that out-of-band fre­ quencies are rejected. The signal at the bottom of L6 is AC-coupled to ground via a .01µF capacitor, while the top end of L6 connects to gate G1 of Q1. This gate is DC biased to 4V from pin 5 of IC1 via a 220kΩ resistor which also serves to dampen the very high Q of the L6-VC1 resonant circuit. Note that this line is decoupled using a .001µF feedthrough capacitor, two .01µF capacitors and a 10Ω resistor, to shunt any RF signal to ground. Gate G2 of Q1 is used as the AGC input and the control voltage is derived from the AGC output (pin 18) of IC1 via a 10Ω resistor. The .001µF Most of the parts for the Dual Diversity Tuner are installed on two PC boards: a main board & a much smaller board which holds the RF amplifier components. The full assembly details will be published in Pt.2. feedthrough capacitor and .001µF capacitor on either side of the resistor ensure that RF signal is not fed back to the AGC pin of IC1. Normally, the voltage on G2 is about 10V and this biases Q1 so that it provides full gain. However, at very high signal levels, the AGC voltage goes down. When it drops below 8V, the gain of Q1 is reduced by about 6dB/volt. Q1 is connected in a common source configuration with the amplified signal appearing at its drain. The quiescent current through Q1 is set by a 390Ω source resistor and this is bypassed by a .001µF capacitor to ensure maximum AC gain. The supply to Q1 (via L7) is filtered using a 10Ω resistor and .001µF feedthrough capacitor. The amplified RF signal is fed to L8 via a 27pF capacitor. L8 then inductively couples this signal into a tuned circuit consisting of L9, two 33pF capacitors and trimmer VC2. A 220kΩ resistor is connected in parallel with VC2 to damp out the high Q of the LC resonance, to make the circuit easier to align. Balanced mixer Following this tuned circuit, the signal is AC-coupled to the balanced mixer inputs of IC1 (pins 1 & 2). In addition, some of the signal is coupled via a 1.8pF capacitor to pin 3, which is the wideband input for the AGC circuit. The local oscillator inputs are at pins 7 and 8 of IC1, while the output appears at pin 6. Its frequency is set by the tuned circuit formed by the primary winding of local oscillator coil T1 (pins 4 & 6), the associated 15pF and 33pF capacitors, and varicap diode D5. The capacitance of D5 is set by a control voltage from the AFC (automatic frequency control) output of IC2. Feedback for the local oscillator is developed via the secondary winding between pins 2 and 3 of T1. Note that the dots on pins 2 and 4 indicate the winding phase required to obtain oscilla­tion. Pins 16 and 17 of IC1 are the balanced mixer outputs and these are fed to the primary winding of IF transformer T2. This winding and the two associated 390pF capacitors form a 10.7MHz tuned circuit, while the centre tap of the winding connects to the +12V supply to provide a load for the open collector outputs of the mixer. The secondary of T2, at pins 4 and 5, drives 10.7MHz ceramic filter (X1) via a 47Ω resistor. This resistor, together with the impedance of T2’s secondary, provides the correct 300Ω load for the ceramic filter. Following X1, the signal is fed to the IF amplifier input at pin 14 of IC1. The output from this stage then appears at pin 10 and is further filtered by 10.7MHz ceramic filter X2 before being coupled to pin 15 of IC2. Limiting & demodulation IC2 includes a 4-stage limiter amplifier which amplifies the signal from X2 and limits the signal once it reaches about 30µV at the pin 15 input. The limiter amplifier also provides a signal strength output voltage at pin 13 and this voltage is fed to the to the AGC input (pin 12) of IC1. IC1 monitors both this narrowband signal level and the wideband signal level at pin 3 and initiates AGC at its pin 18 output whenever the signal level exceeds a predetermined level. Following the limiter amplifier, the signal is converted to an audio signal using a quadrature demodulator. Inductor L10 across pins 4 and 6 forms the quadrature coil and this is driven from pins 3 and 7 via 33pF capacitors. The 560pF capacitor across the quad­ rature coil provides tuning, while the parallel 750Ω resistor damps the Q to ensure minimum distortion in the recov­ered audio signal. The resulting audio outputs appear at pins 8 and 9 of IC2 and are identical except that they are 180 degrees out of phase. Note that a .0068µF capacitor is wired between pin 8 and 9 to provide the required 50µs de-emphasis, to compensate for the pre-emphasis in the wireless microphone. If the wireless microphone has a 75µs pre-emphasis, this capacitor should be changed to .01µF. August 1994  47 Both audio outputs have a DC offset of 5.5-9.8V, the exact value depending on the frequency of the local oscillator. As previously mentioned, the DC output at pin 9 is used to provide AFC for the local oscillator by applying the offset voltage to varicap diode D5. This voltage is applied to D5 via two series 100kΩ resistors, while the associated 0.33µF and .01µF capacitors filter out unwanted RF and audio signals from this line. As well as driving the AGC input of IC1, the signal strength voltage at pin 13 of IC2 is also fed to pin 5 of IC3, an LM3914 linear dot/bar LED driver. This device, in company with a 10-LED bargraph display, forms the signal strength meter. Inside IC3 is a string of 10 comparators and a voltage reference. As the signal level rises, these internal comparators progressively switch their outputs low to light the corresponding LEDs. The two 1.5kΩ resistors set the LED brightness and the display range. Note that the supply to IC3 is decoupled using a 0.1µF capacitor, while the supply to the LEDs is decoupled using a 10µF capacitor and an 82Ω 5W resistor. This resistor ensures that most of the power dissipation takes place outside the IC so that its ratings are not exceeded. Audio muting The signal strength voltage at pin 13 of IC2 is also fil­tered using a 3.3kΩ resistor and a .033µF capacitor and applied to unity gain op amp IC4a. The output from this buffer stage then drives pin 5 of mute threshold comparator IC5a and pin 3 of minimum signal level comparator IC5b. IC5a compares the signal level on its pin 5 input with a preset voltage from VR2. In practice, VR2 is set so that the output from IC5b is normally high. This high output closes CMOS analog switch IC7 so that the audio signal from pin 8 of IC2 is fed to IC6a. However, if the signal level falls below the threshold set by VR2, pin 7 of IC5a goes low and IC7 opens to mute the audio signal. IC6a is the output audio amplifier. It is wired in non-inverting mode and its gain can be varied from 5.7 to 15.7 using VR4. The 47pF capacitor in the feedback path reduces high frequency noise in the audio output. Pin 2 of IC6a is biased at half supply 48  Silicon Chip using buffer stage IC6b. This stage is itself biased at half supply using two 10kΩ resistors, while the 10µF capacitor at the non-inverting input provides decoupling. Antenna switching IC5b (the minimum signal level comparator) has two control functions. First, it controls the clock enable (CE) input of D-A converter IC11. Second, it controls antenna switching oscillator IC9 via inverter IC8a. If the signal level on pin 3 of IC5b is greater than the level set by VR3 on pin 2, pin 1 of the comparator will be high. IC9’s reset input will thus be low and so this oscillator (a 7555 timer) will be off. At the same time, the high on CE of IC11 will also prevent clocking of this counter. In practice, this means that the currently selected antenna will be maintained. However, if the signal level drops below the threshold set by VR3, IC5b’s output switches low and releases the reset on IC9. When this happens, pin 3 of IC9 immediately goes high and clocks IC10a, a 4013 D-type flipflop, which toggles its Q and Q-bar outputs. These outputs, in turn, control the antenna switcher (D1-D4) in the manner described previously. They also drive inverter stages IC8e and IC8f which activate the antenna LED indicators (LEDs 11 & 12) to show which antenna has been select­ed. If the signal level from the new antenna is now higher than the reference voltage set by VR3, IC5b’s output immediately goes high again and IC9 is held reset to maintain the selection. However, if the signal level is lower than the threshold, IC9 will continue clocking IC10a and so the antennas will be alter­nately switched at about 2.8kHz (ie, once about every 360µs). Each time an antenna is selected, IC9 clocks decade counter IC11 via inverter IC8b (ie, IC11 is clocked at 2.8kHz). As shown on Fig.5, IC11’s “0” to “5” outputs are connected to resistors which range in value from 22kΩ up to 56kΩ. IC11 and its associated resistors form the D-A converter. Initially, output “0” of IC11 is high and the maximum voltage is applied to pin 3 of IC4b. As the counter now counts up, this voltage steps down as each output goes high in turn, finally reducing to 0V when output “6” (not shown) goes high (since outputs “0” to “5” are now all low). This voltage remains at 0V when outputs “7”, “8” and “9” go high. IC4b amplifies the applied voltage by about three times and provides a buffered output for VR3. As the voltage falls, it is continually compared by IC5b against the incoming signal level (selected from each antenna in turn), until it falls below the signal level. At this point, IC5b’s output goes high again, IC9 is held reset and the current antenna is held. IC11 also stops counting due to the high on its CE input (pin 13). In this way, the circuit selects the antenna with the high­est signal strength. Counter reset IC12, together with inverters IC8c and Ic8d, is used to reset the counter (IC11). As soon as the “0” output of IC11 goes low (ie, on the first clock cycle from IC9), pin 2 of IC8c goes high and releases the reset on oscillator stage IC12. Pin 3 of IC12 now goes high for about 1s and then switches low again. This low is inverted by IC8d and applied to the reset input (pin 15) of IC11 via a 0.1µF capacitor. IC11’s “0” output now immediately switches high again and so IC12 is once again held reset via IC8c (ie, pin 3 of IC12 remains low). Diode D8 protects the reset input of IC11 by clamp­ing this input to ground when the output of IC8d goes low. At this point (ie, following reset), the output from the D-A converter is at its maximum and so the threshold voltage set by VR3 is also at maximum. IC5b now compares the signal strength from the selected antenna against this new threshold and so the selection process begins again. Manual antenna switching IC10b is the other half of the 4013 dual-D flipflop. It basically operates as a debouncing circuit for the antenna test switch (S2). Each time S2 is pressed (ie, pin 10 is pulled high), Q-bar toggles high and clocks IC10a via isolating diode D7 to select the alternative antenna. This antenna selection is maintained while ever the switch is held down. When the switch is released, Q-bar of IC10 goes low again and the circuit returns to normal mode. Power for the circuit is derived from the mains via a 12.6V transformer. This secondary AC voltage is rectified PARTS LIST 1 1-unit high black anodised rackmounting case with screen printed front & rear panels 1 PC board, code 06307941, 207 x 161mm 1 PC board, code 06307942, 28 x 49mm 2 pieces of blank single-sided PC board, 53 x 15mm 2 pieces of blank single-sided PC board, 38mm x 15mm 1 piece of blank single-sided PC board, 38 x 12mm 1 Altronics M-2852 12.6V 3.78VA mains transformer 1 DPST illuminated rocker switch with red Neon indicator (S1), Altronics Cat. S-3217 or equivalent 1 M205 safety fuse holder (F1) 1 M205 250mA fuse 1 TO-220 mini U heatsink, 26 x 30 x 12mm 1 100kΩ log pot (VR4) 1 16mm OD black anodised knob 1 SPDT momentary pushbutton switch (S2) 2 insulated panel mount PAL sockets 1 insulated RCA panel socket 4 rubber feet 6 cable ties 17 PC stakes 1 solder lug 4 5mm standoffs 6 2mm screws & nuts for panel sockets 4 3mm screws & nuts for standoffs 3 4mm screws & nuts to secure mains transformer & earth solder lug 1 3mm star washer for earth solder lug 3 10kΩ horizontal trimpots (VR1VR3) 1 700mm length of 0.8mm tinned copper wire 1 400mm length of 0.6mm enamelled copper wire (ECW) 1 250mm length of 0.5mm ECW 1 200mm length of 0.25mm ECW 1 piece of large diameter heatshrink tubing (to insulate contacts of S1 and F1) Coils and filters 4 balun formers, Philips 4313 020 4003 1 (L1-L4) 3 Neosid type ‘A’ adjustable inductance assemblies, type # 99-007-96 (base, former, can & F29 screw core) (T1,T2 & L10) 2 matched Murata SFE10.7ML 10.7MHz ceramic filters (X1,X2) Wire & cable 1 7.5A mains cord & plug 1 300mm length of 3-way rainbow cable 1 400mm length of single core shielded audio cable Semiconductors 1 10-segment LED bargraph (LEDs1-10) 1 3mm red LED (LED11) 1 3mm green LED (LED12) 1 TDA1574 Integrated FM Tuner (IC1) 1 TDA1576 FM/IF Amplifier (IC2) 1 LM3914 linear LED dot/ bargraph driver (IC3) 1 LM358 dual op amp (IC4) 1 LM393 dual comparator (IC5) 1 LF351 dual op amp (IC6) 1 4066 quad CMOS analog switch (IC7) 1 74C14, 40106 hex Schmitt trigger (IC8) 2 7555, LMC555CN CMOS timers (IC9,IC12) 1 4013 dual D-flipflop (IC10) 1 4017 decade counter decoder (IC11) 1 7812 1A 12V 3-terminal regulator (REG1) 1 BF981 dual gate Mosfet (Q1) 4 BA482 low capacitance VHF silicon planar diodes (D1-D4) 1 BB119 VHF varicap diode (D5) 3 1N4148, 1N914 switching diodes (D6-D8) 4 1N4004 1A rectifier diodes (D9D12) using diodes D9-D12 and filtered with a 4700µF capacitor to derive an 18V (approx.) DC rail. A 3-terminal regulator (REG1) then provides a stable +12V supply for the circuitry. The 47µF capacitor at the output of the regulator is in­cluded to ensure regulator stability. Capacitors 1 4700µF 25VW PC electrolytic 2 47µF 16VW PC electrolytic 4 10µF 16VW PC electrolytic 1 1µF 16VW PC electrolytic 1 0.33µF MKT polyester 5 0.1µF ceramic 9 0.1µF MKT polyester 1 .033µF MKT polyester 1 .018µF MKT polyester 19 .01µF ceramic 1 .0068µF MKT polyester for 50µs de-emphasis (use .01µF for 75µs) 2 .001µF ceramic 4 .001µF feedthrough ceramic 1 560pF ceramic 2 390pF ceramic 1 47pF ceramic 5 33pF NPO ceramic 1 27pF NPO ceramic 1 15pF NPO ceramic 2 6.8pF NPO ceramic 1 3.9pF NPO ceramic 1 1.8pF NPO ceramic 1 8.5-50pF miniature trimmer capacitor (VC1), Altronics Cat. R-4009 Green 1 5-30pF miniature trimmer capacitor (VC2), Altronics Cat. R-4007 Yellow Resistors (0.25W, 1%) 1 1.2MΩ 1 3.9kΩ 1 330kΩ 1 3.3kΩ 6 220kΩ 3 2.7kΩ 3 100kΩ 4 2.2kΩ 1 56kΩ 2 1.5kΩ 2 47kΩ 1 750Ω 1 39kΩ 1 390Ω 1 33kΩ 1 300Ω 1 27kΩ 1 47Ω 2 22kΩ 9 10Ω 10 10kΩ 1 82Ω 5W 2 4.7kΩ Miscellaneous 1 plastic alignment tool (to adjust slugs & trim­mer capacitors) 1 plastic tuning wand with a brass screw on one end and an F29 ferrite slug on the other (joined by plastic tubing – see Pt.2). That completes the circuit description. Next month, we will continue with the complete construction and SC alignment details. August 1994  49 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. Theft protection for automatic cars N/C Preventing engine cranking rather than killing the COM KEYPAD D1 COMBINATION LOCK 1N4004 ignition or fuel injection as SILICON CHIP a means of theft protection JULY 1990 has the advan­tage that the device is only operative while the vehicle is stationary. This simple device prevents crank­ing by making use of the lock is wired to operate a relay (RLY1) switch circuit on the drive selector which has heavy duty con­tacts to carry of an automatic transmission. This the starter solenoid current. prevents engine cranking unless the Note that the relay contacts are in transmission is in Neutral or Park. It series with the switch on the transmismakes use of the combination lock sion drive selector. The lock circuit is keypad featured in the July 1990 issue wired for mono­stable operation which of SILICON CHIP. This is available as a means that the cranking circuit is enkit from Dick Smith Electronics (Cat abled for 20 seconds after the correct K-8403). The relay in the combination code is entered to the keypad. To use A sensitive lightmeter for the darkroom Photographic printing papers have increased in sensitivity and some require light of the order of 0.1 Lux for exposures of 10 seconds. A lightmeter for the darkroom must therefore be capable of measuring reliably to better than .01 Lux and have a small sensitive area to permit spot measurements. It should have no hysteresis effect so that it is ready for measurements imme­diately after the room light is switched off. A desirable feature would be to have direct reading of time required for correct exposure in a range of 5-20 seconds and a direct reading of relative paper sensitivity so that when paper from the same batch is used at a later date, the controls can be set immediately and printing started. This meter circuit meets all the above criteria and is PD1  easy to use. It uses an eye reBPW21 sponse photodiode from RS Components, part num­ ber 303-719, with an active area 50  Silicon Chip L2 TO SWITCH ON DRIVE SELECTOR L1 FROM "CRANK" CONNECTION ON IGNITION SWITCH. (REMOVED FROM SWITCH ON DRIVE SELECTOR) N/O less than 3mm squared. The photocell is sealed, has no hysteresis and covers a light range from less than .01 Lux to greater than 100,000 Lux. It is used in the open circuit voltage mode which gives a logarithmic re­sponse and covers the whole range with an output ranging from 40-550mV. Doubling the incident light increases the output by about 20mV and this is pretty consistent across the range. The photocell anode is connected directly to the gate of the FET rather than via a PC board to maximise the input resistance. VR1 is adjusted so that increasing the light by one stop on the enlarger lens increases the reading by 10mV. The reading on the meter can be balanced to zero by setting VR3 and VR4 in the gate of the balancing FET, 470 16VW Q1 2N5486 G S1 D S VR1 10k 10T DVM 200mV 25 16VW 25 16VW RLY1 TO IGNITION CONNECTION ON IGN. SW. TO CHASSIS the system, the ignition is turned on, the code is entered and the engine can be started. There is no need for a secret switch although the device should be disabled when the vehicle is being serviced, to avoid the need to divulge the keypad code. Ron Searle, Bundaberg, Qld. ($20) Q2. VR4 is adjusted for the expo­sure time of 5-20 seconds. Calibration is performed by the following steps: (1) Use switch S2 to short out the gate of FET Q2; (2) Adjust VR1 for a change of reading of 10mV for each one-stop change in the enlarger lens setting; (3) Use switch S1 to short the photocell and adjust VR2 to obtain a zero reading on the digital voltmeter (DVM); (4) By trial and error, produce a good print with the usual adjustment of enlarger aperture and printing exposure time; (5) set trimpot VR4 to the corresponding exposure time; (6) Open switches S1 & S2;. (7) Select the spot to be measured (or use a diffuser in front of the enlarger lens to measure average) and adjust VR3 (paper sensitivity) to read 0mV Q2 2N5486 D G S VR2 10k 10T S2 PAPER SENSITIVITY VR3 10k EXPOSURE TIME VR4 1k 1k 100k 470 10VW ZD1 5.6V 1W 9V Low-cost LED level display There are many audio LED level circuits and kits on the market for use in preamplifiers and amplifiers, or as standalone units, and these work well. However, most are built on a large PC board and are generally quite expensive. This circuit uses only eight components and one IC to perform the same operation and can be built for about $15. The circuit is designed to connect to the line out of a CD player or tape deck but, by changing the input resistor to a higher value, it could also be connected to the speaker output of any amplifier or hifi system. An LM3914 LED bar/dot driver IC forms the basis of the circuit. This IC contains a series of 10 op amp comparators which compare the incoming signal with a divided reference signal (about 1.2V). Each op amp then drives a LED (LEDs 1-10) and this produces a moving display which fluctuates according the level of the audio signal. In operation, the incoming audio signal is fed through a 470Ω limiting resistor and into a 100kΩ on the DVM; (8) Short the photocell with switch S1 and adjust time to 10 seconds and note the reading on the DVM. This becomes the relative paper sensitivity and any time you want to use this batch of paper short the cell, set VR4 to 10 seconds and adjust VR3 to give this reading on the DVM; (9) Open switch S1 and proceed with your measurement of any negative at any magnification by adjusting enlarger aperture and time dial to achieve 0mV. This gives you the correct conditions for printing. The cell output has a temperature coefficient of -2mV/°C; this becomes about -1mV/°C on the meter. Therefore note the temperature at the time of measurement of the paper sensitivity and correct this value by the difference in ambient temperature during printing; ie, reduce paper sensitivity by 1mV for every 1°C increase. Victor Erdstein, Highett, Vic. ($45) +5V INPUT GND 470  VR1 100k 3 D1 1N914 9 LED1-10 1 1 Q1 BC558 18 5 17 2.2 1k 15 6 14 7 13 680  11 3  4  5  6  7  12 2 2  16 IC1 LM3914 1  8  9  10 10  4 trimpot (VR1) which acts as a level control. From there, the signal passes through a 1µF electrolytic capacitor which acts as a high pass filter. Because Q1 (BC558) is a PNP transistor, positive going excursions of the audio signal are ignored and are clamped by D1 (1N914) to the positive rail. Negative going signals, however, cause Q1 to conduct and the output is 8 taken from the collector and fed into pin 5 of IC1. The 680Ω resistor on pins 6 & 7 sets the internal reference voltage and the LED brightness, while the 2.2µF capacitor sets the LED “fallback” time. Pin 9 may be connected to the positive rail to produce a bar display, or left open circuit to produce a dot display. L. Trengove, Sawtell, NSW. ($25) 27  4.7k 6 270  2 IC1 ZD1901 4 8 IC2 555 Q1 MJE340 3 270  +12V OUTPUT 100 16VW ZD1 9.1V 1  0V Optoelectronic pickup for ignition systems This circuit has been designed as an optoelectronic trigger for the High Energy Ignition System featured in the May 1988 issue of SILICON CHIP. It uses a readily available photo-interrupter, IC1, from Jaycar Electronics (Cat. ZD- 1901). This is used to drive IC2, a 555 timer which is used simply as a Schmitt trigger. IC2 in turn drives switching transistor Q1 which connects to the points input on the ignition circuit, as shown on page 34 of the May 1998 issue. Des Logan, Ingle Farm, SA. ($20) August 1994  51 This photo shows the completed Crystal Checker. If the crystal is working, the LED will light. A Simple Go/No-Go Crystal Checker This simple circuit will help you sort through that pile of crystals lying on your workbench. If the crystal works, the LED lights. Best of all, it can use parts which you probably already have in your junkbox. By DARREN YATES If you’ve had a go at building any RF projects in the past you’ll probably have a couple or maybe quite a few crystals lying around. Crystals are quite fragile components because of their construction. Unlike a resistor or capacitor, if you drop one on the ground from a decent height, it’s a 50-50 bet whether it will work again. Testing them is not a breeze either. You just can’t take out your trusty multimeter and plug the crystal in. In fact, the only real way is to try it in an oscillator circuit. And that’s exactly what this little Crystal Checker does. The crystal is placed in the feedback network of a transistor oscillator. If it oscillates, meaning that the crystal works, a LED lights up. If the crystal 52  Silicon Chip doesn’t work, the LED stays off. You can’t get much simpler than that. Note that if you have overtone crystals, the circuit will not tell you whether or not the crystal is operating at the designated frequency, just whether or not it will oscillate at its fundamental frequency. Circuit description Let’s take a look at the circuit in Fig.1. As you can see, there are only two transistors, a couple of diodes, a LED and a few other components. Q1 is a BF199 RF transistor and with its associated components forms an untuned Colpitts oscillator. The crystal forms the main element of the circuit. Positive feedback comes from the emitter through the .001µF capacitor back to the crystal and base. If the crystal works, the circuit will begin oscillating immediately and a waveform will appear at the emitter of Q1. If you look at this on your oscilloscope, you could expect to see a rough sinewave with and an amplitude of about 2V peak-to-peak, depending on the frequency. Diodes D1 and D2 rectify the signal from the emitter of Q1 and the resulting DC voltage is fed to the base of transistor Q2. Once this voltage exceeds 0.6V, transistor Q2 turns on and lights LED 1. As soon as the crystal is removed, the circuit stops oscil­lating and the LED goes out. As a point of interest, if the crystals you have are less than 10MHz, then you could probably get away with a BC548 for Q1. The BC548-series transistors have a high FT (gain-bandwidth product) of about 100MHz or so but they don’t tend to work well in oscillator circuits above about 10MHz. FM microphones often get away with a BC548 but the output at the required 100MHz or so is quite Q1 BF199 47k B CRYSTAL UNDER TEST 10 16VW 2x1N914 .001 100pF B1 9V A C E .001 1k 2.2k LED1  Q2 K BC548 C B D1 D2 10k BF199 E B E 0.1 BC548 B C E VIEWED FROM BELOW C A Fig.1: the circuit of the Crystal Checker is shown with a BF199 for Q1 but a BC548 will work with many crystals under 10MHz. K Construction Construction of the Crystal Checker is a snap and shouldn’t take you any Resistors (0.25W, 1%) 1 47kΩ 1 2.2kΩ 1 10kΩ 1 1kΩ Fig.2: this sample waveform was taken from the emitter of Q1 with the scope probe set to 10:1 division. The crystal was an American TV intercarrier type with a frequency marking of 3.579545MHz. The onscreen measurement shows the frequency as 3.5MHz, well within the accuracy of most oscilloscopes. As you can see, the signal amplitude is about 2.4V peak-peak. more than an hour or so. All of the components except the 9V battery fit on a small PC board, coded 04106941, and measuring only 52 x 40mm. Before you begin any soldering, check the board thoroughly for any 10uF 1k 47k Q2 .001 0.1 10k LED1 Q1 .001 B1 K 2.2k CRYSTAL UNDER TEST A Semiconductors 1 BF199 RF NPN transistor (Q1) 1 BC548 NPN transistor (Q2) 2 1N914 signal diodes (D1,D2) 1 5mm green LED (LED1) Capacitors 1 10µF 16VW electrolytic 1 0.1µF 63VW MKT polyester 2 .001µF 63VW MKT polyester 1 100pF ceramic SIMPLE GO/NO-GO CRYSTAL CHECKER low – in the order of millivolts which is too low for our application. Below 10MHz, they work quite well with a good output voltage. Why not try one out and see what you get. You can’t damage the crystal and it’s always fun to experiment! Power is supplied by a 9V battery which is bypassed by a 10µF electrolytic capacitor. We haven’t specified a power switch mainly for the reason that it would double the cost of the parts! Besides, once you’ve checked all your crystals, you can unclip the battery and use it on something else. You could also experiment with different supply rails. The circuit should work well with any voltage between 6V and 15V although if you are using a BC548 for Q1 and a supply voltage of less than 9V, it may not like the higher crystal frequencies. Again, experiment and see for yourself! The quiescent current should be around 3mA, pushing up to 6-8mA with the LED on. PARTS LIST 1 PC board, code 04106941, 52 x 40mm 4 PC stakes 1 9V battery 1 battery clip D2 D1 100pF Fig.3: the component layout diagram for the PC board. We suggest connecting a pair of leads with crocodile clips to make connec­tions to the crystal. shorts or breaks in the copper tracks. These should be repaired with a small artwork knife or a touch of the soldering iron where appropriate. When you’re satisfied that the board is OK, start by in­stalling the resistors and diodes, followed by the capacitors and transistors. Be sure to follow the overlay diagram (Fig.3) carefully, as some of these components are polarised and won’t work if you install them the wrong way around. Finally, solder in the LED and the PC stakes for the battery and the crystal. You might like to make up a pair of short alligator clip leads to connect the crystal – see photo. Testimg Testing the circuit is pretty much the same as normal use. Find a crystal that you know works, preferably something between 32kHz to 4MHz, pop it in and connect the 9V battery. If the circuit works, you should see the LED light. If it doesn’t, check that the components are in their correct locations and check the orientation of components such as the LED, transistors and Fig.4: this is the full size artwork diodes. In addition, check for the PC board. Check your board the solder con­ nections carefully against this pattern before for dry joints or shorts mounting any of the parts. between tracks. SC August 1994  53 SPECIALS BY FAX If your fax has a polling function, dial (02) 579 3955 and press your POLLING button to get our latest specials, plus our item and kit listing. Updated at the start of each month. HF ELECTRONIC BALLASTS Brand new “slim line” cased electronic ballasts. They provide instant flicker free starting, extend tube life, reduce power consumption, eliminate flicker during operation (high frequency operation), and are “noise free” in operation. The design of these appears to be similar to the one published in the Oct. 94 SILICON CHIP magazine. One of the models even includes a DIMMING OPTION!! Needs external 100K potentiometer or a 0-10V DC source. We have a good but limited stock of these and are offering them at fraction of the cost of the parts used in them! Type A: Designed to power two 32W - 4’ tubes, will power two 40W - 4’ tubes with no noticeable change in light output, has provision for dimming: $26 Type B: Designed to power two 16W - 18" tubes, will power two 18W - 18" tubes with no noticeable change in light output: $18 MISCELLANEOUS FLAT NOSE PLIERS: $4 per pair. BATTERY CHARGER: S2 accessory set for Telecom Walkabout “Phones”. Includes cigarette lighter cable, fast rate charger, and desktop stand. Actually charges 6 series connected AA Nicad batteries: $27. BATTERY PACKS: Contain 6 AA Nicad batteries wired in series, can easily be pulled apart, used units, satisfaction guaranteed: $2 per pack. LITHIUM BATTERIES: Button shaped with pins, 20mm diameter, 3mm thick. A red led connected across one of these will produce light output for over 72 hours (3 days): 4 for $2. CIGARETTE LIGHTER LEADS: Cigarette lighter plug with 3 metres of heavy duty fig. 8 flex connected. Should suit load currents up to 20A: 5 for $5. SUPERCAPS: 0.047F/5.5V capacitors: 5 for $2. HOUR METER: Non resettable, mains powered (50HZ), WARBURTON FRANKI, 100,000 Hours maximum, 0.01Hr resolution: $15. PCB MOUNTED SWITCHES 90 deg. 3A-250V, SPDT: 4 for $2. AC POWER SUPPLY: Mains in, two separate 8.5V/3A outputs, in plastic case with mains power lead/plug and output leads/plugs: $15 Ea. MONITOR PCB’s: Complete PCB and yoke assembly for high resolution monochrome TV monitors (no tube). Operate from 12V DC, circuit and information provided: $15. MODEMS: Complete mains powered non standard 1200 baud Telecom approved modems. We should have brief information available. Limited stock at below the price of the high quality case that these are housed in: $30 for 2 modems. MEDICAL LASER One only water cooled medical laser with selectable outputs: Argon (7W multiline) or Dye laser (1W red). Large water cooled unit with a separate control box and accessories (350kg): $15,000 LEVEL RECORDER One only, Bruel & Kjaer level recorder type 2305, in good condition: $300 54  Silicon Chip DIE CAST BOXES These large (187 x 120 x 56mm) aluminium die cast boxes have several holes drilled in them and have a C&K toggle switch and a 6.25mm phono socket fitted. New units from an unfinished production project: $4 Ea. WELLER SOLDERING IRON TIPS New soldering iron for low voltage Weller soldering stations and mains operated Weller irons. Mixed popular sizes and temperatures. Specify mains or soldering station type: 5 for $10. NICAD BATTERY PACKS Brand new Toshiba 7.2V-2.2AHr Nicad Battery packs in a plastic assembly: $20 Ea. If you purchase three packs we will supply a matching fast charger (90min.) that can charge up to three of these batteries (one at a time). Modern unit that employs “delta V” voltage detection to terminate charge, needs an external 12V-2.2A unregulated supply: $60 for three battery packs and a three way charger. PLUGS/SOCKETS 3 pin chassis mounting socket and a matching covered three pin plug. Good quality components that will handle a few amperes at low voltage: $5 for 4 pairs. DYNAMIC MICROPHONES Low impedance dynamic microphones with separate switch wiring, 3.5mm mic. plug, 2.5mm switch plug, as used on most cassette recorders: $4 Ea. 40mW IR LASER DIODES New famous brand 40mW-830nM IR laser diodes, suit medical and other applications: $90 Ea. Constant current driver kit to suit: $10. HIGH POWER LED IR ILLUMINATOR This kit includes two PCBs, all on-board components plus casing: Switched mode power supply plus 60 high intensity 880nm IR (invisible) LEDs. Variable output power, 6-20VDC input, suitable for illuminating IR responsive CCD cameras, IR night viewers etc. Professional performance at a fraction of the price of the commercial product. COMPLETE KIT PRICE: $60 LOW COST 1-2 CHANNEL UHF REMOTE CONTROL Late in October we will have available a single channel 304MHz UHF remote control with over 1/2 million code combinations which also makes provision for a second channel expansion. The low cost design includes a complete compact keyring transmitter kit, which includes a case and battery, and a PCB and components kit for the receiver that has 2A relay contact output! Tx kit $10, Rx kit $20. Additional components to convert the receiver to 2 channel operation (extra decoder IC and relay) $6. INCREDIBLE PRICES: COMPLETE 1 CHANNEL TX-RX KIT: $30 COMPLETE 2 CHANNEL TX-RX KIT: $36 ADDITIONAL TRANSMITTERS: $10 FIBRE OPTIC TUBES These US made tubes are from used equipment but in excellent condition. Have 25/40 mm diameter, fibre-optically coupled input and output windows. The 25mm tube has an overall diameter of 57mm and is 60mm long, the 40mm tube has an overall diameter of 80mm and is 92mm long. The gain of these is such that they would produce a good image in approximately 1/2 moon illumination, when used with suitable “fast” lens, but they can also be IR assisted to see in total darkness. Our HIGH POWER LED IR ILLUMINATOR kit, and the IR filter are both suitable for use with these tubes. The superior resolution of these tubes would make them suitable for low light video preamplifiers, wild life observation, and astronomical use. Each of the tubes is supplied with an 9V-EHT power supply kit. INCREDIBLE PRICES: $120 for the 25mm intensifier tube and supply kit. $180 for the 40mm intensifier tube and supply kit. We also have a good supply of the same tubes that may have a small blemish which is not in the central viewing area!: $65 for a blemished 25mm intensifier tube and supply kit. $95 for the blemished 40mm intensifier tube and supply kit. SIEMENS VARISTORS 420VAC 20 joule varistors that are suitable for spike protection in Australian 3 phase systems: 10 for $5. TAA611C ICs TAA611C Audio power amplifier ICs, no more information: 5 for $5. INTENSIFIED NIGHT VIEWER KIT SC Sept. 94. See in the dark! Make your own night scope that will produce good vision in sub-starlight illumination! Has superior gain and resolution to all Russian viewers priced at under $1500. We supply a three stage fibre-optically coupled image intensifier tube, EHT power supply kit, and sufficient plastics to make a monocular scope. The three tubes are supplied already wired and bonded together. $290 for the 25mm version $390 for the 40mm version We can also supply the lens (100mm f2: $75) and the eyepiece ($18) which would be everything that is necessary to make an incredible viewer! MAINS POWERED GAS LASER Includes a professional potted mains power supply and a new 3mW red tube to suit. One catch, this supply requires a 4-6V (TTL) enable input which is optically isolated, to make the unit switch ON. Very low consumption from a 4.5V battery. $100 for a new 3mW tube plus a TTL mains power supply to suit. SUPER DIODE POINTERS - HEADS These pointers probably represent the best value when you compare them on a “brightness per dollar” basis. They are about 5 times brighter than 5mW/670nm pointers! They have an output of 2.5mW at 650nm, which is about equal in brightness to a 0.8mW HE-NE tube!! SPECIAL INTRODUCTORY PRICE: $150 We will also have available some of the 3V diode modules used in these pointers at approximately $125, and also some 2.5mW/635nm laser diode modules with special optics at approximately $280. VIDEO TRANSMITTERS Low power PAL standard UHF TV transmitters. Have audio and video inputs with adjustable levels, a power switch, and a power input socket: 10-14V DC/10mA operation. Enclosed in a small metal box with an attached telescopic antenna. Range is up to 10m with the telescopic antenna supplied, but can be increased to approximately 30m by the use of a small directional UHF antenna. INCREDIBLE PRICING: $25 TDA ICs/TRANSFORMERS We have a limited stock of some 20 Watt TDA1520 HI-FI quality monolithic power amplifier ICs, less than 0.01% THD and TIM distortion, at 10W RMS output! With the transformer we supply we guarantee an output of greater than 20W RMS per channel into an 8ohm load, with both channels driven. We supply a far overrated 240V-28V/80W transformer, two TDA1520 ICs, and two suitable PCBs which also include an optional preamplifier section (only one additional IC), and a circuit and layout diagram. The combination can be used as a high quality HI-FI Stereo/Guitar/P.A., amplifier. Only a handful of additional components are required to complete this excellent stereo/twin amplifier! Incredible pricing: $25 for one 240V-28V (80W!) transformer, two TDA1520 monolithic HI-FI amplifier ICs, two PCBs to suit, circuit diagram/layout. Some additional components and a heatsink are required. LIGHT MOTION DETECTORS Small PCB assembly based on a ULN2232 IC. This device has a built in light detector, filters, timer, narrow angle lens, and even a siren driver circuit that can drive an external speaker. Will detect humans crossing a narrow corridor at distances up to 3 metres. Much higher ranges are possible if the detector is illuminated by a remote visible or IR light source. Can be used at very low light levels, and even in total darkness: with IR LED. Full information provided. The IC only, is worth $16! OUR SPECIAL PRICE FOR THE ASSEMBLY IS: $5 Ea. or 5 for $20 GAS LASER SPECIAL We have a good supply of some He-Ne laser heads that were removed from new or near new equipment, and have a power output of 2.5-5mW: very bright! With each head we will supply a 12V universal laser power supply kit for a ridiculous TOTAL PRICE of: $89 AA NICADS Brand new AA size Saft brand (made in France) 500mA Hr. batteries, also have solder connections (can be removed): $2 Ea. or 10 for $ 16. TWO STEPPER MOTORS PLUS A DRIVER KIT This kit will drive two stepper motors: 4, 5, 6 or 8 eight wire stepper motors from an IBM computer parallel port. Motors require separate power supply. A detailed manual on the COMPUTER CONTROL OF MOTORS plus circuit diagrams/descriptions are provided. We also provide the necessary software on a 5.25" disc. Great “low cost” educational kit. We provide the kit, manual, disc, plus TWO 5V/6 WIRE/7.5 Deg. STEPPER MOTORS FOR A SPECIAL PRICE OF: $42 CAMERA FLASH UNITS Electronic flash units out of disposable cameras. Include PCB/components and Xenon tube/reflector assembly. Requires a 1.5V battery. $2.50 IR LASER DIODE KIT auto iris lens. It can work with illumination of as little as 0.1Lux and it is IR responsive. Can be used in total darkness with Infra Red illumination. Overall dimensions of camera are 24 x 46 x 70mm and it weighs less than 40 grams! Can be connected to any standard monitor, or the video input on a Video cassette recorder. NEW LOW PRICE: $199 IR “TANK SET” A set of components that can be used to make a very responsive Infra Red night viewer. The matching lens tube and eyepiece sets were removed from working military quality tank viewers. We also supply a very small EHT power supply kit that enables the tube to be operated from a small 9V battery. The tube employed is probably the most sensitive IR responsive tube we ever supplied. The resultant viewer requires low level IR illumination. Basic instructions provided. $140 BRAND NEW 780nm LASER DIODES (barely visible), mounted in a professional adjustable collimator-heatsink assembly. Each of these assemblies is supplied with a CONSTANT CURRENT DRIVER kit and a suitable PIN DIODE that can serve as a detector, plus some INSTRUCTIONS. Suitable for medical use, perimeter protection, data transmission, IR illumination, etc. For the tube, lens, eyepiece and the power supply kit. 5mW VISIBLE LASER DIODE KIT We include a basic diagram-circuit showing how to make a small refrigerator-heater. The major additional items required will be an insulated container such as an old “Esky”, two heatsinks, and a small block of aluminium. $40 Includes a Hitachi 6711G 5mW-670nm visible laser diode, an APC driver kit, a collimating lens - heatsink assembly, a case and battery holder. That’s a complete 3mW collimated laser diode kit for a TOTAL PRICE OF: $75 BIGGER LASER We have a good, but LIMITED QUANTITY of some “as new” red 6mW+ laser heads that were removed from new equipment. Head dimensions: 45mm diameter by 380mm long. With each of the heads we will include our 12V Universal Laser power supply. BARGAIN AT: $170 6mW+ head/supply. ITEM No. 0225B We can also supply a 240V-12V/4A-5V/4A switched mode power supply to suit for $30. 12V-2.5 WATT SOLAR PANEL SPECIAL These US made amorphous glass solar panels only need terminating and weather proofing. We provide terminating clips and a slightly larger sheet of glass. The terminated panel is glued to the backing glass, around the edges only. To make the final weatherproof panel look very attractive some inexpensive plastic “L” angle could also be glued to the edges with some silicone. Very easy to make. Dimensions: 305 x 228mm, Vo-c: 18-20V, Is-c: 250mA. SPECIAL REDUCED PRICE until the end of 94!: $20 Ea. or 4 for $60 Each panel is provided with a sheet of backing glass, terminating clips, an isolating diode, and the instructions. A very efficient switching regulator kit is available: Suits 12-24V batteries, 0.1-16A panels, $27. Also available is a simple and efficient shunt regulator kit, $5. CCD CAMERA Monochrome CCD camera which is totally assembled on a small PCB and includes an SOLID STATE “PELTIER EFFECT” COOLER-HEATER These are the major parts needed to make a solid state thermoelectric cooler-heater. We can provide a large 12V-4.5A Peltier effect semiconductor, two thermal cutout switches, and a 12V DC fan for a total price of: $45. ITEM No. 0231 RUSSIAN NIGHT VIEWER We have a limited quantity of some passive monocular Russian made night viewers that employ a 1st generation image intensifier tube, and are prefocussed to infinity. CLEARANCE: $180 INFRA RED FILTER A very high quality IR filter and a RUBBER lens cover that would fit over most torches including MAGLITEs, and convert them to a good source of IR. The filter material withstands high temperatures and produces an output which would not be visible from a few metres away and in total darkness. Suitable for use with passive and active viewers. The filter and a rubber lens cover is priced at: $11 DOME TWEETERS Small (70mm diam., 15mm deep) dynamic 8ohm tweeters, as used in very compact high quality speaker systems: $5 Ea. We also have some 4" woofers: $5 Ea. VIDEO ZOOM LENSES Wire antenna - attached, Microphone: Electret condenser, Battery: One 1.5V silver oxide LR44/G13, Battery life: 60 hours, Weight: 15g, Dimensions: 1.3" x 0.9" x 0.4". $25 REEL TO REEL TAPES New studio quality 13cm-5" “Agfa” (German) 1/4" reel to reel tapes in original box, 180m-600ft: $8 Ea. MORE KITS-ITEMS Single Channel UHF Remote Control, SC Dec. 92 1 x Tx plus 1 x Rx $45, extra Tx $15. 4 Channel UHF Remote Control Kit: two transmitters and one receiver, $96. Garage/Door/Gate Remote Control Kit: Tx $18, Rx $79. 1.5-9V Converter Kit: $6 Ea. or 3 for $15. Laser Beam Communicator Kit: Tx, Rx, plus IR Laser, $60. Magnetic Card Reader: professional assembled and cased unit that will read information from plastic cards, needs low current 12VDC supply-plugpack, $70. Switched Mode Power Supplies: mains in (240V), new assembled units with 12V-4A and 5V-4ADC outputs, $32. Electric Fence Kit: PCB and components, includes prewound transformer, $28 High Power IR LEDs: 880nm/30mW/12deg. <at> 100mA, 10 for $9 Plasma Ball Kit: PCB and components kit, needs any bulb, $25. Masthead Amplifier Kit: two PCBs plus all on board components: low noise (uses MAR-6 IC), covers VHF-UHF, $18. Inductive Proximity Switches: detect ferrous and non-ferrous metals at close proximity, AC or DC powered types, three wire connection for connecting into circuitry: two for the supply, and one for switching the load. These also make excellent sensors for rotating shafts etc. $22 Ea. or 6 for $100. Brake Light Indicator Kit: 60 LEDs, two PCBs and ten Rs, makes for a very bright 600mm long high intensity Red display, $30. IEC Leads: heavy duty 3 core (10A) 3M LEADS with IEC plug on one end and an European plug at the other, $1.50 Ea. or 10 for $10. IEC Extension Leads: 2M long, IEC plug at one end, IEC socket at other end, $5. Motor Special: these motors can also double up as generators. Type M9: 12V, I No load = 0.52A-15,800 RPM at 12V, 36mm Diam.-67mm long, $5. Type M14: made for slot cars, 4-8V, I No load = 0.84A at 6V, at max efficiency I = 5.7A-7500 RPM, 30mm Diam-57mm long, $5. EPROMS: 27C512, 512K (64K x 8), 150ns access CMOS EPROMS. Removed from new equipment, need to be erased, guaranteed, $4. Green Laser Tubes: Back in stock! The luminous output of these 1-1.5mW GREEN laser diode heads compares with a 5mW red tube!: $490 for a 1-1.5mW green head and a 12V operated universal laser inverter kit. 40 x 2 LCD Display: brand new 40 character by 2 line LCD displays with built in driver circuitry that uses Hitachi ICs, easy to drive “standard” displays, brief information provided, $30 Ea. or 4 for $100. RS232 Interface PCB: brand new PCB assembly, amongst many parts contains two INTERSIL ICL232 ICs: RS232 Tx - Rx ICs, $8. Modular Telephone Cables: 4-way modular curled cable with plugs fitted at each end, also a 4m long 8-way modular flat cable with plugs fitted at each end, one of each for $2. 12V Fans: brand new 80mm 12V-1.6W DC fans. These are IC controlled and have four different approval stamps, $10 Ea. or 5 for $40. Lenses: a pair of lens assemblies that were removed from brand new laser printers. They contain a total of 4 lenses which by different combinations - placement in a laser beam can diverge, collimate, make a small line, make an ellipse etc., $ 8. Polygon Scanners: precision motor with 8 sided mirror, plus a matching PCB driver assembly. Will deflect a laser beam and generate a line. Needs a clock pulse and DC supply to operate, information supplied, $25. PCB With AD7581LN IC: PCB assembly that amongst many other components contains a MAXIM AD7581LN IC: 8 bit, 8 channel memory buffered data acquisition system designed to interface with microprocessors, $29. EHT Power Supply: out of new laser printers, deliver -600V, -7.5KV and +7kV when powered from a 24V-800mA DC supply, enclosed in a plastic case, $16. Mains Contactor Relay: has a 24V-250ohm relay coil, and four separate SPST switch outputs, 2 x 10A and 2 x 20A, new Omron brand, mounting bracket and spade connectors provided, $8. FM Transmitter Kit - Mk.II: high quality high stability, suit radio microphones and instruments, 9V operation, the kit includes a PCB and all the on-board components, an electret microphone, and a 9V battery clip, $11. FM Transmitter Kit - Mk.I: this complete transmitter kit (miniature microphone included) is the size of a “AA” battery, and it is powered by a single “AA” battery. We use a two “AA” battery holder (provided) for the case, and a battery clip (shorted) for the switch. Estimated battery life is over 500 hours!!: $11. High Power Argons: the real thing! Draw pictures on clouds, big buildings etc., with a multiline water-cooled Argon laser with a few watts of output. “Ring” for more details. Argon-Ion Heads: used Argon-Ion heads with 30-100mW output in the blue-green spectrum, will be back in stock soon, priced at around $400 for the “head” only, power supply circuit and information supplied. Two only 10:1 video zoom lenses, f=15150mm, 1:1.8, have provision for remote focus aperture and zoom control: three motors, one has a “C” mount adaptor, 150mm diam. by 180mm long: OATLEY ELECTRONICS MINIATURE FM TRANSMITTER Phone (02) 579 4985. Fax (02) 570 7910 $390 Ea. Not a kit, but a very small ready made self contained FM transmitter enclosed in a small black metal case. It is powered by a single small 1.5V silver oxide battery, and has an inbuilt electret microphone. SPECIFICATIONS: Tuning range: 88-108MHz, Antenna: PO Box 89, Oatley, NSW 2223 Bankcard, Master Card, Visa Card & Amex accepted with phone & fax orders. P & P for most mixed orders: Aust. $6; NZ (airmail) $10. August 1994  55 SERVICEMAN'S LOG Time to talk about timers Why is there such an unbridgeable gap between one of the video recorder’s main features & the way the public reacts to it. I refer to the program timer, which allows the VCR to record programs in our absence. They can cope with almost any timing requirement, yet hardly anyone uses them. The story is really about the mechanics of a tricky VCR timer problem which, I suspect, may be more widespread than is realised. It may, just possibly, also be age dependent. But it set me thinking about the public’s response to timers. The particular case involved a National NV-370 machine; a very popular model which first appeared some 10 or 12 years ago. And it says something for the quality of these machines that most of them are still giving excellent service. Serious faults have been minimal, with most service work being simply routine; eg, cleaning, replacing worn belts and the occasional head replace­ment for well-used units. In this case, the owner was an elderly lady and her com­plaint was that the timer function was giving trouble, but “only sometimes”. I didn’t like the sound of it because of all the intermittent faults one can think of, a timer function intermit­tent is about the worst imaginable. And had it been anyone else, I would have immediately sus­pected finger trouble; the inability of the user to set up the timer function correctly. For the truth is that the majority of VCR owners are incapable of using this facility – and readily admit it. Some have never even tried. Others have tried a couple of times, fouled it up and given the idea away. And that’s a pity, because it is one of the most valuable features of a VCR, allowing users to capture programs they would not otherwise enjoy. I’m not sure why this is such a problem. Customers often complain that these devices are, to use a glib “in” phrase, not “user-friendly”. In response, the makers have responded by pro­ducing new models which are claimed to be “more user-friendly”. Yet, in reality, the more they try, the more complicated they seem to make them and the more the public shies away. Conversely, many early machines like the NV-370 were relatively simple to set up and most had a good instruction book. Even so, few of my customers seemed to have mastered the simple procedures involved. There are probably many factors involved but I do suspect one: the 24-hour clock which most makers now use but which is foreign to most users. Not that I blame the makers for using it. It is far more logical than the clumsy AM/PM arrangement which is CLOCK ON OFF CLOCK NORMAL PROGRAMME ON OFF DAY HOUR MIN TIMER REC Fig.1: the clock and timer controls for the National NV-370 VCR. The 24-hour clock used in most VCRs confuses many users. 56  Silicon Chip itself wide open to confusion. Unfortunately, program guides are invariably set out in 12-hour times. Perhaps it would help if they could include both time systems with the 24-hour figures in brackets. Well, it’s just an idea. Back to the VCR But I digress – back to the lady’s NV370. I suppose it goes without saying that when I put it up on the bench and checked the timer function, it worked perfectly. But I know the lady well enough to rule out finger trouble. She’s been using this timer function for years and, in a sense, is more familiar with it than I am. So I proceeded on the assumption that there really was a fault. And in order that those not familiar with this machine can follow the story, it will help if I set out the various controls involved and how they are used. The clock and timer controls occupy the right-hand half of the front panel and are normally concealed by a small fold-down flap. And, from the left, they are: Timer Selector, On, Off, Day, Hour, Min-, Min+ and Timer Rec (the latter coloured orange). The Timer Selector is a 3-position slide switch, the three positions being designated (from left) Clock, Normal and Program­me. The other controls are pushbuttons; toggle, hold down or lock, as appropriate. Setting the Timer Selector to the Clock position (left) allows the clock to be set to the correct day and time, simply by holding down the Day, Hour and Min buttons in turn, until the appropriate reading is obtained for each. In practice, the clock is set so that it is slightly ahead of the real time and this reading is held until the real time coincides with it. Then, when the Timer Selector is switched to Normal, the clock will start and keep time. Normally, of course, the clock doesn’t need resetting unless the power has been turned off at the mains. When the Timer selector is set to the Programme position (right), the timer function can be set up. Pressing the On button brings up the clock display, which is then programmed by holding down the Day, Hour and Min buttons, until the required starting time is displayed. The Off button is then pressed, so that the required finishing time can be similarly set up. Finally, the Timer Rec (orange) button is pressed and locks into the On position. At the same time a small clock symbol appears to confirm that the timer function is set. The Timer Select button is then reset to Normal. It’s not a particularly complex procedure really but mis­takes can still all too easily occur. Common mistakes include setting the wrong 24-hour time, the wrong day or the wrong chan­nel, neglecting to press the orange button, and forgetting to rewind the cassette, to name just a few. Anyway, those were the steps I went through to test the timer, normally setting the starting time a minute or so ahead and the finish time a minute after that. Even so, it takes time, and I tried to fit the tests in during natural breaks. Initially, I couldn’t fault it but persistence eventually paid off. I had set the Timer Selector button to Program, then pressed the On button. But the normal On function did not re­spond. I fiddled with the On button and, after several tries, it came good and I was able to set an On time. I then went to the Off button, only to find that it was reluctant also. At this point, more or less by chance, I happened to touch the Timer Select button, whereupon the clock display flashed off and on again. I wiped that setting and went through the procedure again. And again the On button did not respond but this time I fiddled the Timer Select slide switch button and was rewarded with a most erratic flashing clock display. So, a faulty slide switch? Dirty contacts? Worn contacts? Well, it was something like that. Access requires removal of the top and bottom covers, which then allows the front panel to be unclipped. By then undoing one screw, the timer board can be lifted out for examination. And a point to note here is that the Timer Select slide switch is soldered directly to the underside of this board but is not supported in any other way. The first thing I did was squirt some CRC into the switch and flick it back and forth a couple of times. I then went through the timer sequence again but there appeared to be no improvement and so I turned the machine over to check the under­ side of the board. In particular, I wanted to take a closer look at the soldered joints that secured the switch. At first glance they appeared to be OK but the jeweller’s loupe told a different story. Two of the joints were cracked – not dry joints, but definite fractures. I was puzzled as to what might have caused this but, for the moment, I was more interested in having found a fault (hope­ fully, the fault). Some careful attention with a good hot iron and solder effectively remedied the cracks and proved to be a complete cure. Prolonged testing on the bench and follow up checks with the owner have proved the point; it hasn’t missed a beat since. More to come Well, that was the end of that particular episode but there was more to come. It was the first time I had encountered or heard of such a fault and thus alerted, I decided to make some routine checks as any NV-370s came through the workshop. I have handled several since then, mainly for routine checks and cleaning, and have found one more with the same fault. Which brings me back to the question as to why it happens, remem­bering that we are talking about fractures and not dry joints. The best theory that I can advance is that the soldered joints are not quite adequate, the solder layer being quite thin. While they are undoubtedly adequate electrically, they are simply not strong enough mechanically to with­stand the stresses as the switch is actuated during regular use. And that conclusion leads to a August 1994  57 SERVICEMAN’S LOG – CTD somewhat contradictory thought. For those people who don’t use the timer facility – which, as I have already implied, is the majority – such a weak­ness is not a problem. So the facility will not cause problems, as long as you don’t use it. (There must be something wrong with that line of reasoning some­where)! More realistically, it probably explains why this problem has not surfaced to any extent before this; it has probably taken this long, with regular use, to find the weakness. Colour TV set The “worn-out” VCR And there is one more incident worth relating. One of my customers is a local electrician and, while on a job one day, his customer asked him if he had any use for an old video recorder, adding that it was destined for the tip because, as far as he was concerned, it was “worn out”. The electrician already had a VCR but it so happened that he did have a use for another one – “worn out” or not. His need was for a UHF/VHF down-converter, for use with an old, but still good, VHF-only TV set. And he knew enough to know that the down-converter function should still work, even if the rest of the machine really was “worn out”. So he grabbed it with both hands. I first learned about this when his wife brought their main VCR in for a minor service. After relating the story, she asked whether I thought it would be worthwhile checking it out and possibly restoring it to full operation (they had not even tried it in this role). I suggested she bring it in so I could make some preliminary checks. The machine turned out to be an NV-600, an up-market ver­sion of the NV-370. A preliminary check proved quite promising. I found only one serious mechanical fault – failure of a back ten­sion brake, due to loss of its felt pad. I replaced that, then put the machine through its paces, checking out both the record and replay functions. Would you believe it? – it turned in a first class performance. And it was on its way to the tip! That left only one more test – and I’ll bet you’re way ahead of me. That’s 58  Silicon Chip then the original owner of the NV-600 may not have been far wrong when he used the term, “worn out”, much as I dislike the expression. Personally, I’ve always regard­ed it as a convenient don’t-know, couldn’t-care-less, copout phrase, but in this case, wear may have been a significant fac­tor. Fig.2: this diagram from the Hitachi Fujian 1425B colour TV set shows the tuner (vertical block at top right) & the V164 zener diode (bottom, centre) that’s connected to the collector of transistor V105. right, the timer function. And you’ve prob­ ably also guessed that it was faulty. Right again but more to the point, the symptoms were virtually identical with those on the original NV-370. So it was into the works for a look at the same board. The only snag was that, in this machine, it is a proper swine to get at. But when I did reach the board the jeweller’s loupe told the same story; two fractured joints. Once these had been remade, the timer worked perfectly. So the electrician had scored an up-market recorder, in excellent condition, for no cost other than my routine service charge. It was smiles all round. But one final thought. If my theory as to the cause of these failures is correct, My next story is on quite a different theme. It concerns a Hitachi Fujian colour TV set, model HFC-1425B, which is in many ways similar to the HFC-1421B dealt with in my June 1994 notes. Initially, the exercise seemed like a fairly routine one; so much so that I was not sure whether the story was worth the telling. I finally decided that it was, mainly because the exact nature of the fault was new to me and I thought that it was worth passing on for someone else’s benefit. In the event, it turned out to have an unusual twist. But first I will detail the service exercise just as it happened. The set came in with the complaint that “there’s no picture and no sound”. I interpreted this as meaning a completely dead set, which could mean anything from a blown fuse to an obscure fault in the switchmode power supply. Well, the description was literally true. There was no picture and no sound but the set was still very much alive. It was scanning normally and displaying a beautiful off-channel snow­storm, indicating that the fault was somewhere in the front end. Of course, this kind of fault would normally produce plenty of noise in the speaker but I had momentarily forgotten that this chassis features a muting circuit which kills the sound if there is no signal. This set employs a search and program system for channel selection and this was the first thing I tried. I began by check­ing for any channels that may have already been programmed into it and then, when this revealed nothing, I initiated the search function. But this didn’t work either and, more to the point, there was no change of any kind to the screen image during these checks. Normally, there is some variation as the system searches and encounters odd patches of interference but, in this case, there was just a steady snowstorm. Fortunately, the set is fairly easy to work on, for which I give due credit to the manufacturer. I went first to the tuner, which is shown on the right- had side of the accompanying circuit as a small vertical block with nine terminals – see Fig.2. The IF output terminal is at the bottom, with the +12V supply terminal above it. This was the first one to check and this was OK. The next ones to check were the three marked, re­spectively, BL, BH and BU. These are +12V supply rail terminals for the low (BL) portion of the VHF band, the high (BH) portion of the VHF band, and the UHF (BU) band. These are energised individually, according to the selected channel. So, as the set is put through its programming procedure, each of these terminals should, in turn, go to +12V. Which, in fact, is exactly what happened. So that cleared that part of the system. That didn’t leave much, except terminal VT. This carries the tuning voltage – a variable voltage developed at the collec­tor of transistor V105 in response to the signal fed to its base from pin 1 of IC101. So I should have been able to detect a voltage on this pin, ranging from about 0V to (typically) about 30V during a search function. Alternatively, it should show a fixed voltage if a particular channel is selected. However, there was no voltage of any kind on this pin, regardless of which tuning function was initiated. Well that seemed fairly straightforward. Pin VT connects to the collector of transistor V105 via three resistors: R167, R168, and R169. These were easily checked and cleared. From the collec­ tor of V105, the circuit goes (down) to a voltage regulator cir­cuit; the kind of setup commonly found in tuner supply systems and designed to minimise any drift in tuning voltage. It consist­ ed of R182 (15kΩ), C175 (270pF) and zener diode V164 which, I assumed from its type number, operated at around 33V. This cir­cuit is fed, in turn, from the main 113V rail. And the solution was simple; resistor R182 was open cir­cuit. Well, that was a new one in a Hitachi Fujian, although I have had trouble with a similar resistor in a Samsung and also in a Philips. In the latter two sets, the resistor went high resist­ance, which restricted the tuning range to the low end of each band. Anyway I fitted a new resistor and the set came back to life. Nevertheless, it was necessary to check that the full tuning voltage range was available and that all three bands could be programmed correctly. In fact, everything checked out 100% and, after a routine check of overall performance and a few minor adjustments, the job was finished. Never-ending story End of story? Not quite. And I wonder if any reader has spotted what appears to be a contradiction in the circuit as I described it above. Well, take heart if you didn’t because I didn’t either; at least, not initially. The truth is that, in practical servicing, one cannot afford the luxury of analysing every part of a circuit as one works on it, particularly when it is a simple operation like looking for a lost voltage. So, initially, I simply took the circuit at face value. But then I decided to write this story; and I began making notes and mentally organising how I should present it. And, of course, it August 1994  59 SERVICEMAN’S LOG – CTD was obvious that, in order to put the reader in the picture, I would have to describe the circuit, just as I have done. Then suddenly it struck me. How can we have a variable voltage developed at the collector of V105, when that collector is fed directly from a zener diode voltage regulator circuit? And the simple answer is, we can’t. So how does the system work? I pondered over this at some length and was still pondering over it in the workshop when a colleague walked in. Glad of an opportunity to pick someone else’s brains, I immediately buttonholed him. When I filled him in, he readily agreed that it didn’t seem to make sense. His suggestion was that there was an error in the circuit; that there should be a collector load resistor between the regulator circuit and V105’s collector. In fact, he felt sure he had seen such an arrangement in another circuit for a differ­ ent model of the On Sale Now At Selected Newsagents Or buy direct from SILICON CHIP Price: $7.95 (plus $3 for postage if ordering from Silicon Chip). Order today by phoning (02) 979 5644 & quoting your credit card number; or fax the details to (02) 979 6503; or send cheque, money order or credit card details to PO Box 139, Collaroy, NSW 2097. 60  Silicon Chip same make of set, only he wasn’t sure which one. At that point, he left me to ponder some more. But I was through pondering. If his theory was correct, it was easy enough to prove. The set was still in the workshop, the owner having left it with me before going on holidays. At the first opportunity, I pulled the back off and traced out the circuit. But there was no sign of any extra resistor; the set was exactly the same as the circuit. So what’s the explanation? I made some more careful meas­urements of the voltages appearing on terminal VT and, while they can range up into the 20V plus range, they went nowhere near the 30V or so of the zener rating. So, in fact, the zener wasn’t functioning. So why is it there? The best explanation I can offer is that the 15kΩ resistor, R182, is the collector load resistor and the 113V rail, from which it operates, is regarded as being sufficiently well regu­ l ated as not to need further regulation. But that still doesn’t explain the role of the dormant zener, V164. My guess is that it is purely a protective device, designed to protect the tuner in the event of a failure of, say, V105. It this went open circuit, or ceased to draw current for any other reason, then close to the full 113V of the main HT rail would be applied to the VT terminal – and I imagine the tuner may not like that. Well, that’s my theory, and it looks like I’m stuck with it. That is, unless someone out there is on better terms with Hitachi Fujian sets and can come SC up with another explana­tion. 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.jaycar.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.jaycar.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.jaycar.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.jaycar.com.au REMOTE CONTROL BY BOB YOUNG Modellers with dedication In this & the following column, we will be looking at the work of two modellers who richly deserve the above descrip­tion. For those who have complained about such things in the past, here you will find no flying sandshoes, high speed model aircraft or radio controlled machinery – just good solid R/C modelling of the most excellent kind. The first of the two is Keith Mealey, one of my oldest and most loyal customers. He specialises in R/C boats and, in particular, Murray River paddle steamers. Keith’s fleet of paddle steamers include the P.S. Adelaide, the P.S. Canberra and, for good measure, two models of the P.S. Pevensey, one in 1:16 scale and the other in a smaller scale. Just for a change I will allow Keith to tell his own story in his own matter-of-fact way. By the way, all the dimensions are Imperial, for which Keith makes no apology. The P.S. Pevensey “The first of these models is the P.S. Pevensey which is a 1:16 scale replica of this notable paddle steam- er and measures about 84 inches (2.1 metres) in length and 27 inches (686mm) across the paddleboxes. It has been scratch built using plans available from the Port of Echuca and additional measurements taken from the actual vessel. Construction commenced in 1991 and only a few details are required to complete the model. The materials used in construction were 3/8" x 7-ply timber for the hull frames and 3/32" x 3-ply for the hull sides and bottom, overlaid with 1/16" thick Obechi planks below the water-line. Obechi is also used for the superstructure. The internal keelsons are made of 3/4" x 1-1/2" square section aluminium with a 1/8" wall thickness. The engine is a twin cylinder type (built from castings — the cylinders being machined by the late Reg Wood) of 3/4" bore and 1-1/2" stroke and fitted with Stephenson reversing gear. Steam is provided by a 6" diameter 10" long copper Scotch Return boiler with Inglis modification (certificated to 100 psi). The boiler is fired by bottled propane gas. Radio control This photo shows the 1:16 scale model of the P.S. Pevensey paddle steamer. A 6-channel FM transmitter & receiver control the following functions: throttle, rudder, reversing gear, whistle, steam-operated cylin­der drain-cocks & an onboard automotive cassette player. The model is controlled by a custom-built Silvertone FM 6-channel transmitter and receiver. The functions controlled are throttle, rudder, reversing gear, whistle, steam-operated cylin­der drain-cocks and an on-board automotive cassette player. Power to the electronics system is provided through a Silvertone cus­tom-built 12V to 6V voltage regulator, connected to the same 12V, 6A.hr gel-cell battery as the cassette player. The regulator has a high current capacity to power the high-torque servos used.” One of the reasons I have chosen to present this series of articles apart August 1994  65 from the obvious very interesting content of these articles, is that each of these modellers approached me for custom built transmitters and receivers. Models such as those built by Keith require a special type of transmitter. This is in order to gain full operational advan­tage of the very spectacular models they turn out. This past development work has made it possible to present a design for a transmitter and receiver in SILICON CHIP. The receiver will be presented first, in a few months’ time. Now you may well ask, “Why present an R/C kit when there is so much cheap, high quality gear available on the market?” The answer is that apart from the obvious pleasure and knowledge obtained from building your own R/C system, one of the advantages of the system to be presented is the builtin flexibility. Our system will be capable of expansion from 2 to 32 channels, will use AM or FM, and will have many features not commonly found on commercial systems. Most importantly, it will be done with readi­ly obtainable components, thus making servicing easy. However I digress. Let us allow Keith to continue his story with an account of his second paddle steamer, the P.S. Adelaide. The P.S. Adelaide is a 1:16 scale replica of the original & measures about five feet in length. The radio control system is a JR FM 4-channel unit which operates the throttle, rudder, forward/reverse & whistle. The P.S. Adelaide “This model is a 1:16 scale replica of the P.S. Adelaide and measures about five feet in length. It has been scratch built from measurements taken from the actual vessel and has taken over 1000 hours to complete (excluding the machining of the engines). Construction commenced in 1987. The materials used in the construction of the model were; 3/8" x 7-ply timber for the hull frames, 1/8" x 3/8" Spruce planks for the hull and 1/16" Obechi planks for the superstruc­ture. The internal keelsons are of 1" x 1" square box section aluminium. This model is driven by two Stuart 10H 3/4" bore and stroke engines coupled and mounted above the boiler. They are fitted with Stephenson reversing gear. Steam is provide by a gas-fired Stuart centre-flue marine boiler (commercially built) which is certificated to 50 psi. The radio control system is a JR FM 4-channel unit which operates 66  Silicon Chip The P.S. Canberra radio control system is a commercial JR FM 5 channel radio control unit which operates the rudder, throttle, forward/reverse & a cassette player. Motor control is via a fully proportional electronic speed con­troller which incorporates a 12V to 6V voltage regulator (to power the radio receiver). the throttle, rudder, forward/reverse and whistle. The P.S. Canberra Finally, there is P.S. Canberra. “This is a 1:16 scale replica of the P.S. Canberra and measures about five feet in length. It has been scratch built from measurements taken from the actual vessel. Materials used in the construction of the model were 1/4" x 5-ply timber for the hull frames, 1/16" x 3/8" Obechi for plank­ing the hull (laid over 1/16" plywood) and 1/16" Obechi planks for the superstructure. The internal keelsons are of 1" x 1" square section aluminium. This model is driven by a 12V Marx decaperm motor with reduction gearbox, the final drive to the paddleshaft being by toothed belt. Motor control is via a Frank Brown (Maritime Model Club of NSW Inc) fully proportional electronic speed con­ troller which incorporates a 12V to 6V voltage regulator (to power the radio receiver), forward/reverse control, neutral point adjustment and maximum speed adjustment. back to the interesting conversations, the endless quest for perfection and, most of all, the enthusiasm which permeated every aspect of their lives and compare those days with the money-centred conversations of today, I am sad to the extreme. Custom radio This close-up view shows the 6-inch diameter x 10-inch long boiler in the P.S. Pevensey. Also visible in the foreground is the propane gas bottle that’s used to fire the boiler. The engine is a twin cylinder type of 3/4-inch bore & 11/2-inch stroke & is fitted with Stephenson reversing gear. The R/C system is a commercial JR FM 5-channel control unit which operates the rudder, throttle, forward/ reverse and cassette player.” The above is a bare bones description which does little justice to the exquisite workmanship that has gone into these models. From the joggling of the deck planking to the attention paid to the steam plumbing, Keith has spared no effort in his quest for excellence. Many people have great difficulty in coming to terms with this type of modelling and typical comments when viewing this superb workmanship range from “I could not spend that amount of time on a project that does not earn any money” to “I just simply would not have the patience!” What these comments reveal is a complete lack of understanding of the personality of the dedicat­ed modeller. The true, dedicated modeller is on his own Quest of the Holy Grail and in the case of modellers like Keith the Grail becomes the perfect model. Every joint in the framework or the tiniest of details become mini adventures in their own right, to be carried through in a spirit of excellence. In the end, the fact that onlookers may gasp at the finished product is only icing on the cake. The true satisfaction comes from the inside but sadly this is a spirit which is dying in our increasingly materialistic society. When I was young, there were thousands of these people and they were my heroes. They built models of all kinds of things but most of all they glowed with an internal fire fuelled by an increasingly rare commodity these days; they were content! They were great people to keep company with and I mourn their passing. When I think The transmitter for the P.S. Pevensey is a built around standard Silvertone RF (FM) & encoder modules. The unusual steering wheel was hand made & is fitted to a standard Futaba 2-channel wheel type steering unit But enough of the philosophising. Let us return to Keith’s radio. The transmitter is a built around standard Silvertone RF (FM) and encoder modules. There is nothing fancy about the RF section but the encoder features some interesting techniques. It is basically a multiplexed output type with a single tuning control to set the 1.5ms neutral. This is sent to each control pot in turn, with the extremes being the usual 1-2ms. Symmetri­cal balanced reference voltages are used which allow servo re­versing. The servo reversing is achieved by bringing the three wires from the control pot to a 3-pin header socket (positive, signal, negative). Each channel output has its own 3-pin header plug. This allows some interesting features: (1) Servo reversing is simply a matter of turning the plug through 180°. (2) Channel shuffling can be achiev­ ed by rearranging the order of the control pots on the header pins. Thus, different receivers can be used with the correct servo outputs. (3) Servo reversing is locked away inside the Tx case and is not easily switched into reverse by accident or by fiddlers. (4) The encoder PC board becomes a true module and may be re­placed easily and quickly for servicing. The photo of Keith’s Tx shows that it is fitted with an unusual steering wheel. This was hand made by Keith and is fitted to a standard Futaba 2-channel wheel type steering unit. The lever to the left of the case (throttle) is a standard single axis Silvertone stick unit, fitted with a mechanical trim lever. There are two slide controls one above the steering wheel and one on the left hand side of the case. Two toggle switches and a momen­ tary switch complete the control complement. There is one spare, unused channel built into the transmitter in case of future expansion. The receiver is a standard Silvertone FM 8-channel unit. Next month, I will describe some models by another dedSC icated enthusiast. August 1994  67 Bring your old nicad batteries back to life. Blast them with this: r e p p a Z d a c Ni Do you have a few suspect nicad batteries lying around in your kitchen drawer? Why not try bringing them back to life with this Nicad Zapper? It zaps the cell with a highvol­tage, high-current burst to blast away any internal shorts caused by dendrites. By DARREN YATES Nicad batteries are one of the few items in electronics that everyone has an opinion on – you either love ‘em or hate ‘em! They can make life a lot easier but they can also be a right royal pain if you don’t treat them with “kid gloves”. The reason for most of the hate mail they receive is the well-known “mem­ory effect”. This effect occurs if the cell is not completely discharged before being recharged. After numerous cycles, it “remembers” the 68  Silicon Chip partially charged state to which it is repeatedly discharged and thereafter only discharges as far as this point. The battery then behaves as though it has gone “flat”. When that happens, many people assume that the cell has “had it” and a new cell is substituted. It doesn’t have to end this way though. Nicad cells that suffer from memory effects can often be restored to full health by subjecting them to several complete discharge/recharge cycles. The better approach, of course, is to avoid the memory effect in the first place. This can be done by completely dis­charging the cell to its end-point voltage (usually 1.1V) before placing it in the charger. An automatic nicad battery discharger was described in the November 1992 issue of SILICON CHIP, while a complete charger with automatic inbuilt discharging circuitry was featured in the September 1993 issue. Another frequent cause of nicad failure is dendritic growth within the cell as it ages. Because they have a fairly low im­pedance, these tiny dendritic growths create shorts across the internal cell structure and so the cell can no longer deliver its rated power. Once again, the approach for most people is to replace the cell with a new one. However, it’s amazing how often we keep these crook cells rather than discarding them. Often, they are thrown into a drawer or placed on a shelf in the garage, perhaps in the D1 1N4004 +9-20V 4.7k 68k .01 Q1 BC548 C B 68k D2 1N4004 Q3 BC558 E B 4.7k .001 18k C B E E B 5.6k ZD1 33V 400mW C 1M 100 35VW ZAP S1 Q7 MTP3055 D 1k G S 100k A Q6 READY BC557 LED1 C  K 10k 10k B C L1 : 2 LAYERS OF 0.4mm DIA. ENCU ON NEOSID L-5110 TOROIDAL CORE Q8 BC548 E 1000 35VW 1000 35VW NICAD CELL 1k 1k 0V 390  +V Q5 BC557 E D3 FR104 E 1k C E B 2.7k Q4 BD139 C470  B Q2 BC548 0.1 L1 100 35VW PLASTIC SIDE B E C A VIEWED FROM BELOW K E C B GD S NICAD ZAPPER Fig.1: the circuit uses multivibrator stage Q1 & Q2 to switch transistors Q3 & Q4 on & off. Q4, L1 & D3 form a step-up converter circuit; it charges the 100µF reservoir capacitor at its output to 33V & so the two 1000µF output capacitors also charge to 33V. The output capacitors are then discharged through the nicad cell via MOSFET Q7 which is turned on by pressing S1. Q5 & ZD1 provide output voltage regulation, while Q6 & Q8 drive the ready indicator LED. forlorn hope that they’ll somehow, magically, “get better”. The cure If you’ve got any crook nicads in your home, its quite possible that many of them can be resurrected using this Nicad Zapper. Just as fuse wire “blows” when you push too much current through it, it’s also possible to “fuse” (or blast away) the dendritic growths by zapping the cell with a brief high-voltage, high-current pulse. Because the pulse is kept very brief, no damage is done the cell itself. However, the dendrites disinte­ grate and the cell can now be recharged to full capacity, thus effectively bringing it back to life. As a result, the Nicad Zapper can save you lots of dollars. Nicad batteries aren’t exactly cheap; at least, not when you have to keep constantly replacing them. Well, that’s how it works in theory, anyway. And while we can’t guarantee that the idea will work for every nicad cell (or battery pack), it should work for at least some. In operation, the Nicad Zapper provides a 5ms burst of charge at 33V from two 1000µF capacitors. It operates from a 9-20V DC plugpack (or battery) supply and is easy to use. You simply connect it to the battery and push a single switch to deliver the required “zap”. One zap should generally be enough, but you can deliver several zaps to the battery if you want to be really sure of getting rid of all the nasties. The circuit Let’s now have a look at the circuit for the Nicad Zapper – see Fig.1. As you can see, discrete transistors do all the work, from waveform generation to charging and zapping. Transistors Q1 and Q2 form a standard multivibrator cir­cuit. It works as follows. When power is initially applied, both transistors are for­ward biased and are in a race situation. If Q1 turns on first (for example), its collector pulls the base of Q2 low via a .01µF capacitor and so Q2 will be biased off. The .01µF capacitor now charges via its associated 68kΩ resistor and, when it reaches 0.65V, Q2 turns on and turns off Q1 via the .001µF capacitor, and so the process continues indefinitely. The ratio of the two cross-coupled capacitors sets the duty cycle of the output waveform to 1:10, while the frequency of operation is set by the two capacitors and their associated 68kΩ resistors to about 3kHz. As a result, the circuit generates a train of brief negative going pulses at Q2’s collector and these pulses are fed to Q3 via an 18kΩ resistor. Transistor Q3 functions as a driver stage for NPN power transistor Q4. Thus, each time a negative-going pulse appears at Q2’s collector, Q3 and Q4 turn on. Transistor Q4, inductor L1 and diode D3 together form a simple step-up switching converter. It works like this: each time Q4 switches on, current flows through L1 and so energy is stored in this inductor. During this time, D3 is reverse biased since its anode is effectively connected (via Q4) to ground. When Q4 subsequently switches off, the collapsing magnetic field around the inductor tries to maintain the current through it and so the voltage across the inductor rises. D3 is now for­ward biased and so the inductor dumps its stored energy into a 100µF reservoir capacitor. The output from this stage in turn charges two parallel 1000µF capacitors via a 390Ω current limit­ing resistor. Regulating circuitry Left to its own devices, the output voltage (ie, the vol­tage across the two 1000µF capacitors) could rise to over 70V, which is far too high. To prevent August 1994  69 switch charges via the 100kΩ resistor to ground and the 1kΩ gate resistor. When it reaches full charge (after about 10ms), Q7’s gate is at 0V and so it no longer conducts. This prevents the user from holding the circuit on (by keeping S1 pressed) and allows the main reservoir capacitors to recharge again. This arrangement ensures that the circuit can deliver only a one brief zap to the nicad cell each time S1 is pressed. When S1 is released, the associated 1MΩ resistor discharges the 0.1µF capacitor and so the switch circuit is effectively re-armed. LED1 A S1 D1 0.1 L1 18k 68k 4.7k .01 68k Q3 100uF +9-20V Q8 Q6 0V Q7 B 1k 100uF Q4 2.7k 10k D3 100k Q5 1k 5.6k 10k 1k Q2 470  Q1 390  1k .001 4.7k D2 1M K E 1000uF TO NICAD CELL Ready LED 1000uF Because we want the output capacitors to charge to the maximum voltage (ie, 33V) in order blast away any internal shorts in the cell, we need some sort of indicator to tell us when the circuit is ready. This is because it takes a few seconds for the output capacitors to fully recharge each time S1 is pressed. The ready indicator circuit is based on LED 1, Q6 and Q8. If the output voltage is less than 33V, then ZD1 is non-conduct­ing and Q6 is off. However, as soon as the output reaches 33V, ZD1 conducts and Q6 turns on. This then turns on Q8 which lights LED 1. Power for the Nicad Zapper can come from any 9-20VDC source capable of supplying around 200mA; eg, a plugpack supply or the cigarette lighter socket in your car. Diode D1 provides reverse polarity protection, while the 100µF capacitor provides C ZD1 Fig.2: several different transistor types are used on the board, so check their type numbers carefully against the circuit diagram (or parts list) before mounting them in position. this from happening, a voltage regulator circuit based on transistor Q5 and zener diode ZD1 is employed. It monitors the voltage on D3’s cathode and controls Q3 accordingly. While ever the voltage on D3’s cathode is below 33V, ZD1 is non-conducting and Q5 is off since its emitter and base voltages are equal. However, when the output voltage rises above 33V, ZD1 conducts and Q5 turns on and pulls Q3’s base voltage above its emitter voltage. Q3 now turns off and so Q4 also turns off, effectively shutting down the step-up converter circuit. The output voltage now falls again and when it drops below 33V, Q5 turns off and the step-up converter starts again. As a result, the output voltage is maintained at about 33V. Q7, an N-channel MOSFET, is used to discharge the output capacitors into the cell. This transistor is controlled by momen­ tary pushbutton switch S1. When S1 is pressed, Q7 turns on (since its gate if pulled high) and so the charge in the two 1000µF ca­pacitors is dumped into the nicad cell to provide the required “zap”. What happens now is that the 0.1µF capacitor connected to one end of the TABLE 1: RESISTOR COLOUR CODES ❏ No. ❏  1 ❏  1 ❏  2 ❏  1 ❏  2 ❏  1 ❏  2 ❏  1 ❏  4 ❏  1 ❏  1 ❏  1 70  Silicon Chip Value 1MΩ 100kΩ 68kΩ 18kΩ 10kΩ 5.6kΩ 4.7kΩ 2.7kΩ 1kΩ 470Ω 390Ω 2.2Ω 4-Band Code (1%) brown black green brown brown black yellow brown blue grey orange brown brown grey orange brown brown black orange brown green blue red brown yellow violet red brown red violet red brown brown black red brown yellow violet brown brown orange white brown brown red red gold brown 5-Band Code (1%) brown black black yellow brown brown black black orange brown blue grey black red brown brown grey black red brown brown black black red brown green blue black brown brown yellow violet black brown brown red violet black brown brown brown black black brown brown yellow violet black black brown orange white black black brown red red black silver brown High Purchase Costs Taking a “Bite” Out of Your Budget? NOT AT MACSERVICE. WE HELP YOU STRIKE BACK BY OFFERING THE LOWEST PRICES AND GOOD OLD FASHIONED SERVICE - Just look at these SPECIALS BALL EFRATOM M100 Rubidium Frequency • Factory cal. certs. • Perfect for ISO    accreditation • GPS applications • Ruggedised military    design TEKTRONIX 5440 Oscilloscope • DC to 60MHz • 1mV - 100V/div (x 10) • Dual Trace • Dual Timebase • Large Screen TEKTRONIX 7603 Oscilloscope • Mil spec AN/USM 281-C • Triggers to 100MHz • Dual Trace • Dual Timebase • Large Screen SUPER SALE $850 GREAT VALUE $2950 (new) Video Dist Amp & Cable Equaliser   $100 ADVANCE PP7 30V3A DC Power Supply   $150 AVO MK.IV Avometer With Cal.   $275 BPL CB154/4 Electrolytic Cap Bridge   $450 B&K 1466A 10MHz Oscilloscope   $275 EH 129 Pulse Generator   $90 ELGENCO 603A White Noise Gen 5MHz   $200 ENI 503L RF Power Amp 40dB 510MHz $1025 FLUKE 102 VAW Cal Meter    $75 FLUKE 9010A Logic System Troubleshooter $1000 GR 1608 LCR Meter – Lab Standard $1500 HP 211B 10MHz Square Wave Generator   $275 HP 302A Audio Selective Level Meter   $145 HP 400L True RMS Voltmeter   $170 HP 410B Vacuum Tube Voltmeter   $130 HP 432A 10GHz Power Meter (c/w sensor)   $875 SUPER DEAL $950 HP HP HP HP HP HP HP HP I/S Elect. 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Maximum sweep rate 5ns/div. Built-in component tester With delay sweep, single sweep Two high quality probes $1050 + Tax PS303D Dual Output Supply • 0 to 30V and 0 to 3 amps • Four output meters • Independent or Tracking modes • Low ripple output $385 + Tax PS303 Single Output Supply PS305D Dual Output Supply PS305 Single Output Supply • 0 to 30V and 0 to 5 amps $430 + Tax • 0 to 30V and 0 to 3 amps • Two output meters • Constant current/voltage • Low ripple output $225 + Tax • 0 to 30V and 0 to 5 amps $260 + Tax IF IT’S NOT HERE WE CAN GET IT... CALL US FIRST OR CALL US LAST... BUT DON’T FORGET TO CALL US! MACSERVICE Australia’s Largest Remarketer of Test & Measurement Equipment 26 Fulton Street, Oakleigh Sth, Vic., 3167   Tel: (03) 562 9500 Fax: (03) 562 9615 **Illustrations are representative only The completed PC board is mounted on the base of the case using machine screws & nuts, while a dab of epoxy resin can be used to secure the inductor (L1) in position on the board. Note that although a small heatsink was fitted to Q4 in the prototype, this is not really necessary & may be safely deleted. supply decoupling. The current consumption is about 120mA while the output capacitors are charging, reducing to about 15mA once they are fully charged and the ready LED is lit. Construction All of the components for the Nicad Zapper, except for the switch and LED, are installed on a PC board coded 11106941 and measuring 102 x 57mm. Fig.3 shows the wiring details. Before you begin the construction, check the board careful­ ly for any shorts or breaks in the copper tracks by comparing it with Fig.4. Fix any faults that you do find (such faults will be rare), then begin the assembly by installing PC stakes at the external wiring points, followed by the resistors and capacitors. Table 1 shows the resistor colour codes but it’s also a good idea to check each unit with your multimeter to be doubly sure of its value. The zener diode (ZD1), diodes (D1- D3) and transistors (Q1-Q8) can now be installed, taking care to ensure that each part is mounted in the correct location and with the correct polarity. Note particularly that diode D3 is an FR104 fast recovery type, so don’t confuse it with D1 or D2. Note also that some of the transistors are NPN types while others are PNP types, so refer to the circuit (or to the parts list) for their type numbers when mounting them on the board. The MOSFET (Q7) must be in­stalled with its metal tab towards the adjacent 1kΩ resistor – see Fig.1 for the pinout details. Inductor L1 is made by winding two layers of 0.4mm enam­ elled copper wire on a toroidal core. The simplest way to wind it is to first take a 2-metre length of wire and feed it half-way through the core so that you have two equal lengths. Now take one end and wind on one complete layer, keeping the turns tight and close together. The other half of the wire is then used to wind the second layer over the top of the first. When the windings have been completed, strip and tin the wire ends and solder the inductor into place on the board. The board assembly can now be completed by connecting LED 1 and switch S1 via flying leads. Make sure that the LED polarity is correct, otherwise it won’t light when the circuit is ready. Testing Before applying power, it’s a good idea to carefully check the board against the wiring diagram (Fig.3) for possible errors. You will need a power supply capable of delivering between 9V and 20V DC (a 12V DC plugpack supply is ideal). This should be connected to the board via your multimeter 12VDC which should be set to the + 400mA (or 1A) range. Check that the supply polarWhen LED is on, + ity is correct before switching press button to on. After an initial surge current zap battery of about 100-150mA, (depending on the supply voltage), ZAP READY the current should drop back to around 15-20mA and, after about four seconds, the LED should light. If the current doesn’t drop and Fig.3: this full-size artwork can be used as a drilling template for the front panel, or the LED doesn’t light, check the you can vary the front panel layout to suit your own requirements since the layout circuitry around zener diode is not critical. NICAD ZAPPER 72  Silicon Chip PARTS LIST Fig.4: check your board carefully against this full-size etching pattern before mounting any of the parts. ZD1 and transistors Q5 and Q6. In particular, make sure that these parts have been installed correctly and that there are no solder splashes on the underside of the board. If the current does drop but the LED refuses to light, check the voltage across the 100µF capacitor. If this voltage is 1.2V less than the supply voltage, check the pulse generator circuit (Q1 & Q2) and the step-up converter circuit (Q3 & Q4). If the voltage is correct (ie, about 33V), check Q6 and Q8 in the LED indicator circuit and check the LED polarity. Finally, connect a 0.22Ω 1W resistor across the output terminals to the nicad cell and use your multimeter to monitor the voltage across the 1000µF capacitors. This should normally be about 33V but should drop to almost 0V when S1 is pressed. If it doesn’t, check the Q7 has been installed correctly. Assuming that the board works correctly, it can now be installed in its plastic case. First, attach the label to the lid of the case and drill out the mounting holes for the switch and the indicator LED. It’s best to drill a small pilot hole for the switch to begin with and then enlarge this to the correct size using a tapered reamer. The hole for the LED should be made just large enough to ensure a tight fit. If you make the hole too big, then you will either have to use a LED bezel or epoxy resin to secure the LED. The DC socket is mounted on one end of the case and an additional hole is drilled adjacent to this to provide access for the leads to the nicad cell. In addition, you will have to drill four mounting holes in the base of the case to mount the PC board. You can use the board itself as a template when marking out these holes. The various items of hardware can now be mounted in posi­tion and the PC board secured using 3mm screws and nuts, with an additional nut under each corner to serve as a spacer. This done, the wiring can be completed as shown in Fig.3. The output leads can be fitted with crocodile clips (red for positive and black for negative), or fitted with some other connector to suit your nicads. Battery packs While this circuit was really designed to work with single nicad cells, it is quite possible that it will also work with some nicad battery packs, such as camcorder and racing packs. However, it will generally be less effective with these because of the higher impedance of a battery pack and because of the lower voltage that would appear across each cell. In addition, because of the experimental nature of this project, we can’t guarantee that it will work with every dud nicad cell you have lying around. Nicad cells do fail eventually and no amount of zapping will bring them back to life. However, it should work with at least some cells and if you use lots of nicads, it will save you money in the long run. Upgrading the MOSFET Finally, be warned that the output circuitry of the Nicad Zapper is not short-circuit proof. MOSFET Q7 can 1 PC board, code 11106941, 102 x 57mm. 1 2.1mm DC panel mount socket 1 momentary pushbutton switch (S1) 1 plastic zippy case, 130 x 68 x 41mm 1 front panel label, 126 x 62mm 1 14.8mm OD toroidal core (Altronics Cat. L-5110, Jaycar Cat. LF-1240, or equivalent) 2 metres of 0.4mm dia. enamelled copper wire 1 black medium alligator clip 1 red medium alligator clip 4 self-adhesive rubber feet Semiconductors 3 BC548 NPN transistors (Q1,Q2,Q8) 1 BC558 PNP transistor (Q3) 1 BD139 NPN transistor (Q4) 2 BC557 PNP transistors (Q5,Q6) 1 MTP3055A/E MOSFET (Q7) 2 1N4004 power diodes (D1,D2) 1 FR104 1A fast-recovery diode (D3) 1 33V 400mW zener diode (ZD1) 1 red 5mm LED (LED1) Capacitors 2 1000µF 35VW electrolytics 2 100µF 35VW electrolytics 1 0.1µF 63VW MKT polyester 1 .01µF 63VW MKT polyester 1 .001µF 63VW MKT polyester Resistors (0.25W, 1%) 1 1MΩ 2 4.7kΩ 1 100kΩ 1 2.7kΩ 2 68kΩ 4 1kΩ 1 18kΩ 1 470Ω 2 10kΩ 1 390Ω 1 5.6kΩ 1 2.2Ω 1W Miscellaneous Machine screws, nuts & washers; light duty hook-up wire. fail if S1 is pressed repeatedly while the output leads are shorted together, but it should be adequate for normal cell “zapping”. If you do want to make the output short-circuit proof, then a higher rated MOSFET, such as an IRF540, should be used but note that this device costs about $5 more than SC an MTP3055. August 1994  73 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. Rod Irving Electronics Pty Ltd 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. Rod Irving Electronics Pty Ltd 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. Rod Irving Electronics Pty Ltd 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. Rod Irving Electronics Pty Ltd 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. Rod Irving Electronics Pty Ltd ORDER FORM BACK ISSUES MONTH YEAR MONTH YEAR PR ICE EACH (includes p&p) TOTAL Australi a $A7.00; NZ $A8.00 (airmail ); Elsewhere $A10 (airmail ). Buy 10 or more and get a 10% discount. Note: Nov 87-Aug 88; Oct 88-Mar 89; June 89; Aug 89; Dec 89; May 90; Aug 91; Feb 92; July 92; Sept 92; NovDec 92; & March 98 are sol d out. 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No._______________   ❏ Gift subscription ☞ RATES (please tick one) Australia Australia with binder(s)* NZ & PNG (airmail) Overseas surface mail 2 years (24 issues) 1 year (12 issues) ❏ $A90 ❏ $A49 ❏ $A114 ❏ $A61 ❏ $A135 ❏ $A72 ❏ $A135 ❏ $A72 ❏ $A240 Overseas airmail ❏ $A120 *1 binder with 1-year subscription; 2 binders with 2-year subscription GIFT SUBSCRIPTION DETAILS Month to start__________________ Message_____________________ _____________________________ _____________________________ Gift for: Name_________________________ (PLEASE PRINT) YOUR DETAILS Your Name_________________________________________________ (PLEASE PRINT) Address___________________________________________________ Address______________________ _____________________________ State__________Postcode_______ ______________________________________Postcode___________ Daytime Phone No.____________________Total Price $A __________ ❏ Cheque/Money Order ❏ Bankcard ❏ Visa Card ❏ Master Card 9am-5pm Mon-Fri. Please have your credit card details ready ______________________________ Card expiry date________/________ Card No. Phone (02) 9979 5644 Signature OR Fax (02) 9979 6503 Fax the coupon with your credit card details 24 hours 7 days a week Mail coupon to: OR Reply Paid 25 Silicon Chip Publications PO Box 139, Collaroy 2097 No postage stamp required in Australia August 1994  79 PRODUCT SHOWCASE Review: Philips P65 UHF CB radio Radios of all kinds continue to get smaller & CB radios are too, as is shown by this latest offering from Philips. Small enough to fit in your pocket, it has plenty of power & more features than most people will ever use. The first thing that strikes you about the new Philips P65 UHF CB transceiver is its size. At only 300 grams, it is tiny and very comfortable to hold but has features you would expect from larger radios. Styled in black with a stubby "rubber ducky" antenna, it has two scanning modes, a facility for repeater operation and a back-lit LCD. It has two knobs on the top, on/off volume and channel selection. The squelch control is also on the top but does not protrude, to avoid accidental adjustment. The digital display shows the current channel number and function settings, while a 14-segment bar­graph serves as both a transmit and receive signal strength indicator. The push-to-talk switch is on the lefthand side of the case, making it easy for right or left-handed opera­tion. The FUNC switch immediately above the push-to-talk switch accesses the control settings. The triangular buttons to the left of the display are pressed in conjunction with FUNC to adjust the output power, the scanning options and the backlight for the LCD. The radio covers all 40 channels of the UHF CB band from 476.425MHz to 477.400MHz in 25kHz steps. There are a further eight channels (41-48) that operate with offsets for repeater use. Scanning modes can either tog­gle between all 48 channels or a group of user programmed channels. While scanning, the unit can also be instructed to stop at busy channels until the carrier disappears or to pause for five seconds before resuming. Scan­ ning modes are indicated on the LCD by a 80  Silicon Chip flashing hyphen between the CH and the channel number. Four different battery packs are available for the P65. The battery packs slide into the bottom of the case and lock into place. A 7.2V 700mAh nicad pack is standard while a 12V 600mAh nicad pack, for higher power, is optional. There are also two other op­tional packs that accept indi­ vidual cells; a dry cell pack (six AA cells) and a pack that takes six AA nicad cells. The last pack has a charging socket to charge the individual cells in situ. The radio comes with a trickle charger plug pack for the 7.2V pack. This will fully recharge the battery in 14 hours, with the battery still connected to the radio or sepa­rately, via a small socket in the bottom of the pack. The optional 12V nicad pack has a separate match­ing trickle charger that will also re­charge it in 14 hours. A desktop fast charger is also available that will recharge nicad battery packs in one hour and shut off automatically. It has dual slots to allow charging of two batteries simultaneously. Another worthwhile accessory is a speaker-microphone that plugs into a socket adjacent to the antenna. This allows you to leave the radio in your pocket or clipped onto your belt while it is in use. Nominal output power with a 12V pack is 5 watts for the high power setting and 1 watt for the low. This reduces to 2.5 watts (high) and 1 watt (low) using the 7.2V pack. When you power up, the output power is always initially set to low, to conserve the battery. The P65's size (60 x 32 x 142mm) and smoothly sculpted edges make it very comfortable to hold and operate. The LCD is large enough to read at a glance and in low light conditions, the greenish backlight is very effec­tive. To save power, the backlight turns off after five seconds, giving you just enough time to find out what channel you're on and the power setting you're using. If you want to use the various scanning modes and functions, you must read the manual first, as they certainly are not self-evident. The need to press the FUNC button to access each feature is a double-edged sword. It does mean that you can't accidentally change any of the set­tings whilst handling but means you have to go through a complicated set of steps to modify any function. This aside, the P65 performs well and from signal reports, has good audio quality. It a comes with a vinyl case that has a clear window for the display. With its neat styling, transmitter capable of 5 watts output, a receiver that is surprisingly sensitive and a price tag of $599, it is an attractive package. (M.C.) PC-mount toroidal transformers now available PC-mount transformers have been widely used in industry for many years but up till now, toroidal transformers have not been available in PC-mounting form. Now they are. This new range of toroidal transformers is fully encapsulated and each has a threaded 4mm insert for securing it to the PC board. They are available in seven power ratings – 1.6, 3.2, 5, 7, 10, 15 and 25VA – and all have class A insulation (105°C). There is a choice of secondary voltages – 2 x 7V, 2 x 9V, 2 x 12V, 2 x 15V, 2 x 18V and 2 x 22V – and the two secondary windings may be con­nected in series or parallel. For further information, contact the Australian distributors, Tortech Pty Ltd, 24/31 Wentworth Street, Greenacre, NSW 2190. Phone (OZ) 642 6003 or Fax (OZ) 642 6127. Universal drill has collet chuck Pictured is one of two drills available for a range of hobby work. The Model O400 has coilets to take drills ranging from 0.3 to 3.2mm. The unit can be powered from a model train controller or battery charger with an output of 12-18V DC and a current capacity of at least one amp. Depending on the input voltage, the no-load chuck speed ranges from 12,000 to 20,000 RPM. It is priced at $56.00. Also available is the larger model 0600 which has a quick change chuck and thrust ball bearing for long life. PC COMPUTERS (08) 364 0902 (08) 332 6513 36 Regent St, Kensington, South Australia High Power 2.5 Watt Transmitter Kit FMTX1 $69 This kit uses a single transistor to provide up to 2.5 watts into a 50-ohm load. It can be set on the FM band from 88-108MHz. Audio is 500mV P-P with Australian pre-emphasis. Power supply from 12-24 volts DC. Range up to 100 miles. Leaky coax distribution can be used with any of our transmitters, terminate up to 2km of coax with a 50-ohm resistor and no radiation occurs. Use a 150-ohm WW pot and you can set the level of radiation up to 300 metres from the coax. You can use this method to comply with DOTC schedule 3. XTAL Locked 30mW Transmitter (The best quality kit transmitter in Australia) FMTX2B $49 This transmitter is XTAL-locked on 100MHz (XTAL supplied) and is the most stable kit transmitter on the market. It features a 3-stage design with only two tuned circuits and a clean output. This design can be used as the basis of a station exciter. Digital Stereo Coder (All Digital Design With Australian Pre-emphasis) FMTX2A $49 This is a universal stereo coder able to be used with all of our transmitter designs and many others. Its performance is superior to domestic encoder single chip designs. Dozens have been sold to FM stations as a standby stereo coder or with the FMTX2B as an exciter. Both FMTX2A and FMTX2B on 1 PCB as a complete stereo transmit­ter FMTX5 $99 MAX I/O Board for PCs (Talk To The Outside World) $169 This kit features 7 relays, ADC, DAC, stepper motor driver with sample software in Basic and connects to a PC’s parallel port. Now also available I/O bits software for MS Windows so you can program functions without being a programmer. Call relays by a name like stop relay, assign its own icon - uses a simple VISUAL interface to make your own PLC. Full developer’s version has DOS runtime so you do not require Windows and optional sup­port for LCD displays. Data logging ADC and DAC boards and more. MAX version $169. FM Band Linear Amplifier Kits (All Imported Kits) New 30mW to 1 watt linear coming in September 1994 (advance orders taken) 500mW to 5 or 10 watts $199 250mW to 25 watts 15 watts to 110 watts $599 40 watts to 300 watts Power supplies and heatsinks not included in short form kit price. $99 $249 $999 Other kits available. Call for a list or see Silicon Chip April-June 1994 or the Silicon Chip Model Railway Book. August 1994  81 SATELLITE SUPPLIES Aussat systems from under $850 SATELLITE RECEIVERS FROM .$280 LNB’s Ku FROM ..............................$229 LNB’s C FROM .................................$330 FEEDHORNS Ku BAND FROM ......$45 FEEDHORNS C.BAND FROM .........$95 DISHES 60m to 3.7m FROM ...........$130 Baby stereo mixer from Jaycar This little mixer is designed to mix up to four stereo sources and a microphone input. The stereo in­puts all accept line levels with two switchable to accept phono signals from turntables. A crossfader permits fading between these two channels. A talkover switch adjacent to the microphone input drops the music level to allow announce­ments to be made. With the aid of a set of headphones, individual channels may be cued, prior to being added to the output mix. Headphone LOTS OF OTHER ITEMS FROM COAXIAL CABLE, DECODERS, ANGLE METERS, IN-LINE COAX AMPS, PAY-TV DECODER FOR JAPANESE, NTSC TO PAL TRANSCODERS, E-PAL DECODERS, PLUS MANY MORE For a free catalogue, fill in & mail or fax this coupon. ✍     Please send me a free catalog on your satellite systems. Name:____________________________ Street:____________________________ Suburb:_________________________ P/code________Phone_____________ L&M Satellite Supplies 33-35 Wickham Rd, Moorabin 3189 Ph (03) 553 1763; Fax (03) 532 2957 82  Silicon Chip levels are adjustable too. Two 5-segment LED VU meters above the input sliders display the output levels of the mixer. RCA sockets are used for all inputs and outputs except for the microphone input and record output which use 6.5mm jack sockets. The case is steel finished in black crinkle enamel and with moulded plastic side panels. Power to the unit is via a 3.5mm jack socket on the rear panel and a 12V AC plugpack is supplied. Priced at $159, themixer is available from all Jaycar Electronics stores and dealers. (Cat AM-4212). The chuck will take drills from 0.4 to 3.5mm and has a no-load speed the same as above. It is priced at $77.00. Both drills are available in carrying cases with 11 tool bits. For further information, contact Anton's Trains, Cnr Prince & Mary Sts, North Parramatta, NSW 2151. Phone (02) 683 3858. Micron soldering station from Altronics This temperature controlled soldering station has a 40 watt ceramic heater element and a stainless steel barrel. The iron-clad tip is chrome plated and has a large thermal inertia to improve temperature stability. The tem­perature dial on the front panel selects tip temperatures from 250430°C while a LED indicates when the heat­ing element is on. Instead of the usual step-down transformer, this soldering station uses zero voltage switching circuitry to cy­cle the element on and off. At the same time, the insulation between the heating element and the grounded tip is quoted at greater than 100MW, so tip voltages are very low. The soldering station is priced at $129 and is available from Altronics, 174 Roe St, Perth, WA 6000. Phone 1800 999 007 (toll free). Tiny B/W CCD camera on a PC board Now available: the complete index to all SILICON CHIP articles since the first issue in November 1987. The Floppy Index comes with a handy file viewer that lets you look at the index line by line or page by page for quick browsing, or you can use the search function. All commands are listed on the screen, so you’ll always know what to do next. Notes & Errata also now available: this file lets you quickly check out the Notes & Errata (if any) for all articles published in SILICON CHIP. Not an index but a complete copy of all Notes & Errata text (diagrams not included). The file viewer is included in the price, so that you can quickly locate the item of interest. The Floppy Index and Notes & Errata files are supplied in ASCII format on a 3.5-inch or 5.25-inch floppy disc to suit PC-compatible computers. Note: the File Viewer requires MSDOS 3.3 or above. ORDER FORM PRICE ❏ Floppy Index (incl. file viewer): $A7 ❏ Notes & Errata (incl. file viewer): $A7 ❏ Alphanumeric LCD Demo Board Software (May 1993): $A7 ❏ Stepper Motor Controller Software (January 1994): $A7 ❏ Gamesbvm.bas /obj /exe (Nicad Battery Monitor, June 1994): $A7 ❏ Diskinfo.exe (Identifies IDE Hard Disc Parameters, August 1995): $A7 ❏ Computer Controlled Power Supply Software (Jan/Feb. 1997): $A7 ❏ Spacewri.exe & Spacewri.bas (for Spacewriter, May 1997): $A7 ❏ I/O Card (July 1997) + Stepper Motor Software (1997 series): $A7 POSTAGE & PACKING: Aust. & NZ add $A3 per order; elsewhere $A5 Disc size required:    ❏ 3.5-inch disc   ❏ 5.25-inch disc TOTAL $A Enclosed is my cheque/money order for $­A__________ or please debit my ❏ Bankcard   ❏ Visa Card   ❏ MasterCard Card No. Signature­­­­­­­­­­­­_______________________________ Card expiry date______/______ Name ___________________________________________________________ PLEASE PRINT Street ___________________________________________________________ Suburb/town ________________________________ Postcode______________ Send your order to: SILICON CHIP, PO Box 139, Collaroy, NSW 2097; or fax your order to (02) 9979 6503; or ring (02) 9979 5644 and quote your credit card number (Bankcard, Visa Card or MasterCard). ✂ It's amazing what you can find on a PC board these days. This tiny PC board, which measures just 70 x 46mm, is actually a complete black and white (B&W) CCIR video camera. It has only three connections: +12VDC, video out and ground. The video output is CCIR 50Hz standard, which means that it's compatible with any PAL VCR. All you do is hook up the power supply and connect the video output from the camera to the video input of th,e VCR, and you are ready to record. The charge-coupled device (CCD) image sensor has 320,000 pixels (picture elements) and 400 TV lines and the picture is excellent for something so small. It also has auto-iris control so that you don't need to set the light level. The automatic shutter can vary between 1/50th to 1/32,000th second speed. The wide-angle lens has a lens cover and a grub screw to lock the current focus into place. This can be loosened and the lens focused either on infinity or as close as 4mm! Minimum re­quired luminance is quoted as 0.1 Lux. Six infrared LEDs provide extra light for low-light applications. The output signal is composite video with 1V p-p amplitude and 750 impedance. Power requirements are 11V to 15VDC but it will run down to around 9VDC. The supply current requirement is quoted at less than 200mA (the supply current for the sample pictured above measured 130mA). The price of this camera is just $239 and it is available from Oatley Elec­tronics, PO Box 89, Oatley, NSW 2223. Phone (02) 579 4985 or fax (02) 570 7910. (D.Y.) SILICON CHIP SOFTWARE August 1994  83 VINTAGE RADIO By JOHN HILL Watch out for incorrect valve substitutions in old receivers There are many traps to watch out for when repairing old valve radios. Often, valve radios are obtained with an incorrect valve fitted or with the valves in the wrong sockets. I was repairing a radio recently and ran into a distortion problem that took quite a while to solve. As is often the case, once the fault had been found and rectified, it was all fairly obvious and I should have solved it much sooner than I did. Sometimes, what should be obvious isn’t very obvious at all. The receiver in question was a mid-1950s 5-valve Philips mantel, a relatively small, budget-priced radio which is quite straightforward in design and normally a simple one to repair. This particular receiver had been well worked over long before it found itself on my workbench. Someone had already replaced the paper capacitors with polyester types and several of the mica capacitors had been replaced with an assortment of styros and ceramic disc types. Someone had also installed a few resistors and these stood out like neon signs because they were the old, large, one watt types and not the smaller units that were originally used in the receiver. The electrolytics, however, had not been replaced and looked in very poor condition. These were removed and new 450-volt capacitors installed in their place. All things considered, the underside of the chassis looked far from original, as there had been many replacements and alter­ations, some of which were not very neat. The valve complement consisted of: 6AN7, 6N8, 8BD7, 6M5 and a 6V4 rectifier. The valves were checked in a valve tester and all tested good. The reason for the receiver not working was soon found to be an open primary winding in the output transformer, which is a fairly common fault. A new transformer was installed and the set worked once again. Distortion problems Although the receiver in the text was referred to as a 5-valve Philips, it is in fact the Fleetwood version of that radio. The set had been worked on extensively in the past & came fitted with a substitute valve that was not working correctly. 84  Silicon Chip However, it did not work very well, the most obvious symptom being noticeable distortion in the sound. What’s more, after the set had warmed up and was starting to work, there was a background squeal accompanying the sound for about a 10-second period before it faded away. Squeals and distortion can sometimes be due to a faulty valve and, although all of the valves tested OK, valve testers cannot diagnose a valve with a built-in squeal. After replacing the valves, one at a time, the same faults remained. Both the squeal and the distortion were still there, which quickly disproved the theory that it might be a crook valve that was causing the problem. It was a very hot day and my patience was wearing thin. It was time to put the job aside and do something else. That night, I lay awake thinking about my distortion prob­lem and went through all the likely possibilities. It was well after midnight when it suddenly dawned on me. The 6N8 was the wrong valve for that particular line up. Almost never does one find two valves with twin diodes in the one receiver. Why use a 6N8 with diodes and a 6BD7 also with diodes in the same set? Surely the 6N8 had been used as a substitute for a 6BH5. The next morning, I withdrew the 6N8 from its socket and slipped in a 6BH5 to take its place. The result was as expected – no squeal and no distortion. Someone at some time had installed an incorrect valve and I wasn’t observant enough to pick it up. In fact, all I had to do was check off the valves in the receiver against those listed on the sticker attached to the rear dust cover. There it was in full view for anyone who cared to look – a 6BH5 was used as the IF amplifier, not a 6N8. These are the two valves mentioned in the text: the 6BH5 & the 6N8. While both valves can be used as intermediate fre­quency (IF) amplifiers, they require slightly different socket connections. In the case of the Philips set, someone’s failure to make the necessary modifications resulted in a distort­ed output. Pin connections If one checks the base pin connections of these two valves, everything works out reasonably well until pins 7, 8 and 9. Pin 9 on a 6N8 connects to the suppressor grid and, in this case, it wasn’t earthed. There is no connection at pin 9 on a 6BH5. In a 6BH5 valve, the suppressor grid is earthed internally via the cathode, whereas in the 6N8, the suppressor connects to pin 9 and must be earthed externally from the socket connection if the valve is to function properly. Therefore, using a 6N8 as a substitute for a 6BH5 was simply asking for trouble because it was operating without the suppressor grid. In a pentode valve, the electrons from the cathode strike the plate with such velocity that some bounce back and would be attracted to the positively charged screen grid except that the suppressor repels them back to the plate. Without the suppressor grid, noticeable distortion results. If pin 9 had been earthed, then the 6N8 would probably have worked quite satisfactorily and the two valves could then be interchanged. Table 1 shows the base pin details of the 6N8 and 6BH5 valves. Many valves use only some of their base connections. For exam­ple, the 5Y3 (left) has just 5 pins, while the 6V6 (right) has 6 or 7 pins. Receiver manufacturers often used vacant socket termi­nals as convenient mounting points for other components & so a substitute valve may require considerable socket rewiring. Table 1: Pin Connections For The 6BH5 & 6N8 Valves Pin No. 1 2 3 4 5 6 7 8 9 6BH5 G2 G1 K,G3,IS H H A IC IC NC 6N8 G2 G1 K,IS H H A D1 D2 G3 Obscure faults What I have just described is one of the seemingly endless problems that regularly confront the vintage radio repair man. Due to many obscure reasons, quite a number of old valve radios have “built in” faults that can be difficult to locate. The new chum to valve radio repairs can encounter many a headache. Wheth­ er he can solve them or not depends on his ability and perseverance. Those magnificent old radio servicemen from yesteryear, who have August 1994  85 Like all radiOs, the HMV Little Nipper will only work with the right valves in the right sockets. None of its valves are interchangeable. It is always an advantage to know what valve types go where because sometimes old radios are obtained with incorrect valves or with the valves installed in the wrong sockets. spent all or most of their working life in the trade, have a sixth sense when it comes to troubleshooting. They have encoun­tered every conceivable problem so many times that they almost instinc­tively know what it is going to be. On the other hand, vintage radio repairers are often hobby­ ists, like myself, and each repair is a new and baffling experi­ence. When this is the case, it takes a long time to become rea­sonably proficient and even then there are plenty of faults that can really fatigue the grey matter. A wrong valve, as in the previously mentioned Philips receiver, was something that I should have picked up immediately but my brain was out of gear and free-wheeling at the time. I will try to save face by blaming my lapse on the extremely hot weather at the time. Radios having an incorrect valve or two are a common occurrence when buying non-working receivers from secondhand deal­ers. Some dealers even have a big box of miscellaneous valves which they use to fill up the empty valve sockets CALLING ALL HOBBYISTS We provide the challenge and money for you to design and build as many simple, useful, economical and original kit sets as possible. We will only consider kits using lots of ICs and transistors. If you need assistance in getting samples and technical specifications while building your kits, let us know. YUGA ENTERPRISE 705 SIMS DRIVE #03-09 SHUN LI INDUSTRIAL COMPLEX SINGAPORE 1438 TEL: 65 741 0300    Fax: 65 749 1048 86  Silicon Chip of any receiv­ers that may need them. I have encountered this on many occasions – radios with two or three rectifiers, a radio frequency valve in the output sock­et, and so on. In fact, the variations are almost unlimited – just fit a couple of TV valves here and a frequency converter there; anything to fill the empty sockets and make a receiver look complete. Then again, a receiver may have all the right valves but some may not be in their correct sockets. It is therefore import­ant to learn the functions of various valve types and know how they work in relation to a superhet receiver. Of course, there is a decided advantage in buying a radio that actually works but then one always pays more for goers than non-goers. What’s more, as the radio described earlier clearly demonstrates, just because a set is working, it doesn’t necessar­ily mean that it has the right valves in it – working and working properly are two different things. The difference in the case of the little Philips receiver was just one valve with a slightly incompatible base pin configu­ration. Substitute valves There are not many substitute valves in the true sense of the term. If another type of valve is used as Valve data manuals are invaluable when it comes to substituting valves. These manuals contain details of various valve types & show their socket connections. rate components may be conveniently joined at a blank valve socket pin. This situation can cause problems when substituting another valve if what was once a non-connection becomes a valve pin connection. Naturally, any components soldered to that particular socket terminal must be removed and mounted somewhere else. Obviously, any radio repair involving valve substitutions is quite difficult if one does not have a comprehensive valve characteristics manual. A valve manual provides all the necessary base pin information and is a much needed guide when it comes to substituting valve types. Now for a quick change of subject. I recently came home from a fortnight’s holiday with a gramophone and four radios, including a 1936 console. Amazingly, there was still room for my wife and all our holiday luggage in our little Ford Laser. I might add that packing the car was a fairly delicate operation. And, with spare wheel located underneath all the junk, I was thankful that no roadside wheel changes were necessary on the SC way home. TRANSFORMERS • TOROIDAL • CONVENTIONAL • POWER • OUTPUT • CURRENT • INVERTER • PLUGPACKS • CHOKES Equivalent manuals are also handy guides when looking for sub­stitute valves. An equivalent valve is one that will fit into the socket & work without modifications to the circuit. A substitute valve, on the other hand, may require extensive socket rewiring or even the fitting of another type of socket. a replacement, it may need socket alterations (as was the case with the 6N8), and/or other changes such as different plate, screen and cathode resistors, so that the replacement valve can work as intended. There is nothing quite like using the right valve for the job. Regrettably, the right valve is not always available or afford­able and a compromise is the only way out. While we’re on this subject, there is another aspect to be wary of regarding the use of substitute valves. Many valves do not use all of their base pins and, in the case of some octal based valves, not all of the pins are fitted. For example, 6V6 valves often have 6 or 7 pins while 5Y3s have only 5 pins. The missing pins are not fitted for the simple reason there are no connections to them anyway and it makes economical sense not to have them. However, it is frequently the case that the socket connec­ tions corresponding to the missing pins have components soldered to them. Radio manufacturers often used these socket terminals as connection points to join other components and, in some instanc­es, three or four sepa- STOCK RANGE TOROIDALS BEST PRICES APPROVED TO AS 3108-1990 SPECIALS DESIGNED & MADE 15VA to 7.5kVA Tortech Pty Ltd 24/31 Wentworth St, Greenacre 2190 Phone (02) 642 6003 Fax (02) 642 6127 August 1994  87 Silicon Chip Mixing Desk, Pt.2; Using The UC3906 SLA Battery Charger IC. April 1990: Dual Tracking ±50V Power Supply; VOX With Delayed Audio; Relative Field Strength Meter; 16-Channel Mixing Desk, Pt.3; Active CW Filter For Weak Signal Reception; How To Find Vintage Radio Receivers From The 1920s. BACK ISSUES September 1988: Hands-Free Speakerphone; Electronic Fish Bite Detector; High Performance AC Millivoltmeter, Pt.2; Build The Vader Voice; Motorola MC34018 Speakerphone IC Data; What Is Negative Feedback, Pt.4. November 1988: 120W PA Amplifier Module (Uses Mosfets); Poor Man’s Plasma Display; Automotive Night Safety Light; Adding A Headset To The Speakerphone. Fluid Level Detector; Simple DTMF Encoder; Studio Series 20-Band Stereo Equaliser, Pt.2; Auto-Zero Module for Audio Amplifiers (Uses LMC669). October 1989: FM Radio Intercom For Motorbikes Pt.1; GaAsFet Preamplifier For Amateur TV; 1Mb Printer Buffer; 2-Chip Portable AM Stereo Radio, Pt.2; Installing A Hard Disc In The PC. April 1989: Auxiliary Brake Light Flasher; What You Need to Know About Capacitors; Telephone Bell Monitor/ Transmitter; 32-Band Graphic Equaliser, Pt.2; LED Message Board, Pt.2. 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 Disc Drive Formats & Options; The Pilbara Iron Ore Railways. May 1989: Electronic Pools/Lotto Selector; Build A Synthesised Tom-Tom; Biofeedback Monitor For Your PC; Simple Stub Filter For Suppressing TV Interference; LED Message Board, Pt.3; All About Electrolytic Cap­acitors. December 1989: Digital Voice Board (Records Up To Four Separate Messages); UHF Remote Switch; Balanced Input & Output Stages; Data For The LM831 Low Voltage Amplifier IC; Installing A Clock Card In Your Computer; Index to Volume 2. June 1989: Touch-Lamp Dimmer (uses Siemens SLB0586); Passive Loop Antenna For AM Rad­ios; Universal Temperature Controller; Understanding CRO Probes; LED Message Board, Pt.4. January 1990: High Quality Sine/Square Oscillator; Service Tips For Your VCR; Speed­ing Up Your PC; Phone Patch For Radio Amateurs; Active Antenna Kit; Speed Controller For Ceiling Fans; Designing UHF Transmitter Stages. July 1989: Exhaust Gas Monitor (Uses TGS812 Gas Sensor); Extension For The Touch-Lamp Dimmer; Experimental Mains Hum Sniffers; Compact Ultrasonic Car Alarm; NSW 86 Class Electric Locomotives. September 1989: 2-Chip Portable AM Stereo Radio (Uses MC13024 and TX7376P) Pt.1; Alarm-Triggered Telephone Dialler; High Or Low February 1990: 16-Channel Mixing Desk; 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 1990: 6/12V Charger For Sealed Lead-Acid Batteries; Delay Unit For Automatic Antennas; Workout Timer For Aerobics Classes; 16-Channel June 1990: Multi-Sector Home Burglar Alarm; Low-Noise Universal Stereo Preamplifier; Load Protection Switch For Power Supplies; A Speed Alarm For Your Car; Design Factors For Model Aircraft; Fitting A Fax Card To A Computer. July 1990: Digital Sine/Square Generator, Pt.1 (Covers 0-500kHz); Burglar Alarm Keypad & Combination Lock; Simple Electronic Die; Low-Cost Dual Power Supply; Inside A Coal Burning Power Station; Weather Fax Frequencies. August 1990: High Stability UHF Remote Transmitter; Universal Safety Timer For Mains Appliances (9 Minutes); Horace The Electronic Cricket; Digital Sine/Square Wave Generator, Pt.2. September 1990: Music On Hold For Your Tele­ phone; Remote Control Extender For VCRs; Power Supply For Burglar Alarms; Low-Cost 3-Digit Counter Module; Simple Shortwave Converter For The 2-Metre Band. October 1990: Low-Cost Siren For Burglar Alarms; Dimming Controls For The Discolight; Surfsound Simulator; DC Offset For DMMs; The Dangers of Polychlorinated Biphenyls; Using The NE602 In Home-Brew Converter Circuits. November 1990: How To Connect Two TV Sets To One VCR; A Really Snazzy Egg Timer; Low-Cost Model Train Controller; Battery Powered Laser Pointer; 1.5V To 9V DC Converter; Introduction To Digital Electronics; Simple 6-Metre Amateur Transmitter. December 1990: DC-DC Converter For Car Amplifiers; The Big Escape – A Game Of Skill; Wiper Pulser For Rear Windows; Versatile 4-Digit Combination Lock; 5W Power Amplifier For The 6-Metre Amateur Transmitter; Index To Volume 3. 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Or call (02) 979 5644 & quote your credit card details or fax the details to (02) 979 6503. ✂ Card No. January 1991: Fast Charger For Nicad Batteries, Pt.1; Have Fun With The Fruit Machine; Two-Tone Alarm Module; LCD Readout For The Capacitance Meter; How Quartz Crystals Work; The Dangers When Servicing Microwave Ovens. February 1991: Synthesised Stereo AM Tuner, Pt.1; Three Inverters For Fluorescent Lights; LowCost Sinewave Oscillator; Fast Charger For Nicad Batteries, Pt.2; How To Design Amplifier Output Stages; Tasmania's Hydroelectric Power System. March 1991: Remote Controller For Garage Doors, Pt.1; Transistor Beta Tester Mk.2; Synthesised AM Stereo Tuner, Pt.2; Multi-Purpose I/O Board For PC-Compatibles; Universal Wideband RF Preamplifier For Amateurs & TV. April 1991: Steam Sound Simulator For Model Railroads; Remote Controller For Garage Doors, Pt.2; Simple 12/24V Light Chaser; Synthesised AM Stereo Tuner, Pt.3; A Practical Approach To Amplifier Design, Pt.2. 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. June 1991: A Corner Reflector Antenna For UHF TV; 4-Channel Lighting Desk, Pt.1; 13.5V 25A Power Supply For Transceivers; Active Filter For CW Reception; Electric Vehicle Transmission Options; Tuning In To Satellite TV, Pt.1. July 1991: Battery Discharge Pacer For Electric Vehicles; 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. August 1991: Build A Digital Tachometer; Masthead Amplifier For TV & FM; PC Voice Recorder; Tuning In To Satellite TV, Pt.3; Step-By-Step Vintage Radio Repairs. Railroads; Differential Input Buffer For CROs; Studio Twin Fifty Stereo Amplifier, Pt.2; Understanding Computer Memory; Aligning Vintage Radio Receivers, Pt.1. May 1992: Build A Telephone Intercom; LowCost Electronic Doorbell; Battery Eliminator For Personal Players; Infrared Remote Control For Model Railroads, Pt.2; Aligning Vintage Radio Receivers, Pt.2. June 1992: Multi-Station Headset Intercom, Pt.1; Video Switcher For Camcorders & VCRs; Infrared Remote Control For Model Railroads, Pt.3; 15-Watt 12-240V Inverter; What’s New In Oscilloscopes?; A Look At Hard Disc Drives. July 1992: Build A Nicad Battery Discharger; 8-Station Automatic Sprinkler Timer; Portable 12V SLA Battery Charger; Off-Hook Timer For Tele­phones; Multi-Station Headset Intercom, Pt.2. August 1992: Build An Automatic SLA Battery Charger; Miniature 1.5V To 9V DC Converter; Dummy Load Box For Large Audio Amplifiers; Internal Combustion Engines For Model Aircraft; Troubleshooting Vintage Radio Receivers. September 1992: Multi-Sector Home Burglar Alarm; Heavy-Duty 5A Drill speed Controller (see errata Nov. 1992); General-Purpose 3½-Digit LCD Panel Meter; Track Tester For Model Railroads; Build A Relative Field Strength Meter. October 1992: 2kW 24VDC To 240VAC Sine­wave Inverter; Multi-Sector Home Burglar Alarm, Pt.2; Mini Amplifier For Personal Stereos; Electronically Regulated Lead-Acid Battery Charger. January 1993: Peerless PSK60/2 2-Way Hifi Loudspeakers; Flea-Power AM Radio Transmitter; High Intensity LED Flasher For Bicycles; 2kW 24VDC To 240VAC Sine­wave Inverter, Pt.4; Speed Controller For Electric Models, Pt.3. September 1991: Studio 3-55L 3-Way Loudspeaker System; Digital Altimeter For Gliders & Ultralights, Pt.1; Build A Fax/Modem For Your Computer; The Basics Of A/D & D/A Conversion; Windows 3 Swapfiles, Program Groups & Icons. February 1993: Three Simple Projects For Model Railroads; A Low Fuel Indicator For Cars; Audio Level/VU Meter With LED Readout; Build An Electronic Cockroach; MAL-4 Microcontroller Board, Pt.3; 2kW 24VDC To 240VAC Sine­wave Inverter, Pt.5; Making File Backups With LHA & PKZIP. October 1991: Build A Talking Voltmeter For Your PC, Pt.1; SteamSound Simulator Mk.II; Magnetic Field Strength Meter; Digital Altimeter For Gliders & Ultralights, Pt.2; Getting To Know The Windows PIF Editor. March 1993: Build A Solar Charger For 12V Batteries; An Alarm-Triggered Security Camera; Low-Cost Audio Mixer for Camcorders; Test Yourself On The Reaction Trainer; A 24-Hour Sidereal Clock For Astronomers. November 1991: Colour TV Pattern Generator, Pt.1; Battery Charger For Solar Panels; Flashing Alarm Light For Cars; Digital Altimeter For Gliders & Ultralights, Pt.3; Build A Talking Voltmeter For Your PC, Pt.2; Modifying The Windows INI Files. April 1993: Solar-Powered Electric Fence; Build An Audio Power Meter; Three-Function Home Weather Station; 12VDC To 70VDC Step-Up Voltage Converter; Digital Clock With Battery Back-Up; A Look At The Digital Compact Cassette. December 1991: TV Transmitter For VCRs With UHF Modulators; Infrared Light Beam Relay; Solid-State Laser Pointer; Colour TV Pattern Generator, Pt.2; Windows 3 & The Dreaded Un­ recov­erable Application Error; Index To Volume 4. May 1993: Nicad Cell Discharger; Build The Woofer Stopper; Remote Volume Control For Hifi Systems, Pt.1; Alphanumeric LCD Demonstration Board; Low-Cost Mini Gas Laser; The Micro­soft Windows Sound System. January 1992: 4-Channel Guitar Mixer; Adjustable 0-45V 8A Power Supply, Pt.1; Baby Room Monitor/FM Transmitter; Automatic Controller For Car Headlights; Experiments For Your Games Card; Restoring An AWA Radiolette Receiver. June 1993: Windows-Based Digital Logic Analyser, Pt.1; Build An AM Radio Trainer, Pt.1; Remote Control For The Woofer Stopper; A Digital Voltmeter For Your Car; Remote Volume Control For Hifi Systems, Pt.2 February 1992: Compact Digital Voice Recorder; 50-Watt/Channel Stereo Power Amplifier; 12VDC/240VAC 40-Watt Inverter; Adjustable 0-45V 8A Power Supply, Pt.2; Designing A Speed Controller For Electric Models. July 1993: Build a Single Chip Message Recorder; Light Beam Relay Extender; AM Radio Trainer, Pt.2; Windows Based Digital Logic Analyser; Pt.2; Quiz Game Adjudicator; Programming The Motorola 68HC705C8 Micro­controller – Lesson 1; Antenna Tuners – Why They Are Useful. March 1992: TV Transmitter For VHF VCRs; Studio Twin Fifty Stereo Amplifier, Pt.1; Thermostatic Switch For Car Radiator Fans; Telephone Call Timer; Coping With Damaged Computer Direct­ ories; Valve Substitution In Vintage Radios. April 1992: Infrared Remote Control For Model August 1993: Low-Cost Colour Video Fader; 60LED Brake Light Array; A Microprocessor-Based Sidereal Clock; The Southern Cross Z80-based Computer; A Look At Satellites & Their Orbits; Unmanned Aircraft – Israel Leads The Way; Ghost Busting For TV Sets. September 1993: Automatic Nicad Battery Charger/Discharger; Stereo Preamplifier With IR Remote Control, Pt.1; In-Circuit Transistor Tester; A +5V to ±15V DC Converter; Remote-Controlled Electronic Cockroach; Restoring An Old Valve Tester; Servicing An R/C Transmitter, Pt.1. October 1993: Courtesy Light Switch-Off Timer For Cars; FM Wireless Microphone For Musicians; Stereo Preamplifier With IR Remote Control, Pt.2; Electronic Engine Management, Pt.1; Mini Disc Is Here; Programming The Motorola 68HC705C8 Micro­ controller – Lesson 2; Servicing An R/C Transmitter, Pt.2. November 1993: Jumbo Digital Clock; High Efficiency Inverter For Fluorescent Tubes; Stereo Preamplifier, Pt.3; Build A Siren Sound Generator; Electronic Engine Management, Pt.2; More Experiments For Your Games Card; Preventing Damage To R/C Transmitters & Receivers. December 1993: Remote Controller For Garage Doors; Low-Voltage LED Stroboscope; Low-Cost 25W Amplifier Module; Peripherals For The Southern Cross Computer; Build A 1-Chip Melody Generator; Electronic Engine Management, Pt.3; Index To Volume 6. January 1994: 3A 40V Adjustable Power Supply; Switching Regulator For Solar Panels; Printer Status Indicator; Mini Drill Speed Controller; Stepper Motor Controller; Active Filter Design For Beginners; Electronic Engine Management, Pt.4; Even More Experiments For Your Games Card. February 1994: 90-Second Message Recorder; Compact & Efficient 12-240VAC 200W Inverter; Single Chip 0.5W Audio Amplifier; 3A 40V Adjustable Power Supply; Electronic Engine Management, Pt.5; Airbags: More Than Just Bags Of Wind; Building A Simple 1-Valve Radio Receiver. March 1994: Intelligent IR Remote Controller; Build A 50W Audio Amplifier Module; Level Crossing Detector For Model Railways; Voice Activated Switch For FM Microphones; Simple LED Chaser; Electronic Engine Management, Pt.6; Switching Regulators Made Simple (Software Offer). April 1994: Remote Control Extender For VCRs; Sound & Lights For Model Railway Level Crossings; Discrete Dual Supply Voltage Regulator; Low-Noise Universal Stereo Preamplifier; Build A Digital Water Tank Gauge; Electronic Engine Management, Pt.7. May 1994: Fast Charger For Nicad Batteries; Induction Balance Metal Locator; Muilti-Channel Infrared Remote Control; Dual Electronic Dice; Two Simple Servo Driver Circuits; Electrronic Engine Management, Pt.8; Passive Rebroadcasting For TV Signals. June 1994: 200W/350W Mosfet Amplifier Module; A Coolant Level Alarm For Your Car; An 80-Metre AM/CW Transmitter For Amateurs; Converting Phono Inputs To Line Inputs; A PC-Based Nicad Battery Monitor; Electrronic Engine Management, Pt.9 July 1994: SmallTalk – a Tiny Voice Digitiser For The PC; Build A 4-Bay Bow-Tie UHF Antenna; PreChamp 2-Transistor Preamplifier; Steam Train Whistle & Diesel Horn Simulator; Portable 6V SLA Battery Charger; Electronic Engine Management, Pt.10. PLEASE NOTE: all issues from November 1987 to August 1988, plus October 1988, December 1988, January, February, March & August 1989, May 1990, and November and December 1992 are now sold out. All other issues are presently in stock. For readers wanting articles from soldout issues, we can supply photostat copies (or tear­sheets) at $7.00 per article (incl. p&p). When supplying photostat articles or back copies, we automatically supply any relevant notes & errata at no extra charge. August 1994  89 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. Drum kit amplification I have a drum kit at home and would like to amplify it. I realise I need microphones, a mixer, a preamp, an amplifier and, of course, speakers. When it comes to building electronic kits there is no problem at all. However, I don’t understand all the technical jargon that comes with these kits. I’m not sure on the type of mic I should use so maybe you could tell me the type (unidirectional vs. omnidirectional) and what impedance I need if I want to use two mics overhanging my cymbal clusters and a mic on each drum. I was very keen on the Digitor series with the XLR plugs on page 24 of the Dick Smith Electronics catalog (93/94). These mics are quite affordable and I would like to use them if they are suitable. If not, could you recommend something similar? I have read about the 4-Input Guitar Mixer in the January 1992 issue of SILICON CHIP. That is similar to what I need but I would like a mixer with more channels, preferably 8-12, reverb, and some kind of echo or effects that could be used in each or some of the channels. Is there a kit or kits that can do most of this and still accept microphone outputs and possibly contain a 9-band equaliser or similar? Could you match a preamp to this and specify a power supply for this preamp. Where does the Effects Loop go in relation to the amplifier or preamp? Also, where does the mixer go exactly; after the mics but before the preamp, I thought? In the amplifier, I would like 100W or preferably more. This allows me to expand in other areas and not be restricted by my gear. I noticed a 100W module in the Dick Smith Electronics catalog, page 145. This was good as Tape equalisation for preamp Thanks for the universal preamp project in the April 1994 issue. It is a most useful project and I will be building a few for applications that I have. However, I would like to ask for feedback network details to allow the module to be used with open reel tape decks. I want to provide NAB equalisation at 1.875ips (possibly the same as cassette), 3.75ips, 7.5ips and 15ips. (R. C, Pakenham, Vic). • While it is possible to modify the circuit to provide equalisation for the different tape speeds, we must emphasise that the results may be far from optimum. This is because the preamplifier really needs to be designed to suit the impedance 90  Silicon Chip and the record/playback response of the particular heads. The accompanying sketch shows suggested equalisation but we should also point out that this is a starting point only and we have not tried it out. there was a power supply designed for it. There was also a 200W module in an advertisement for Al­tronics. It says that it comes with no power supply. Perhaps you could suggest one and the transformer that corresponds with it. Also, what type of heatsink would be suitable for each amplifier? Would these amplifiers go with your suggestions about the mixer and preamp? Finally, the speakers: if I were to use the above combo or similar, what power rating would the speakers need (as I don’t understand the relationship between RMS and maximum power). Also, what line/brand would you recommend if I would like a woofer and a horn and I don’t want to spend over $250 for one enclosure. What design for enclosure would be suitable to your recommenda­tion of speakers. Also would I need a cross­ over or anything? Could I build all of the above, except mics and speakers, into a cabinet (so it becomes a power mixer) without any inter­ ference, humming, or extra distortion, etc? (S. R., Cronulla, NSW). • We are not able to give detailed answers to your questions since your application is so specialised. For a start, since the sound pressures associated with drum amplification are so high, you need microphones which have a very high dynamic range, other­wise they will distort. As we understand it, the best microphones for drum work are condenser types and these are generally “phan­tom powered” at 48V DC via the balanced microphone lines. They need to be matched to the following preamplifier or mixer. We have published a 16-channel mixer with equalisation and an effects loop (in the Feb-May 1990 issues) but it did not have phantom power for condenser microphones. In any case, since it was such a large and complex device, it was quite expensive to build (around $2000) and it is no longer available in kit form. You could still build it though, as all parts except the front panel are readily available. A mixer normally has a preamplifier for each channel and the preamplifier signals are then mixed in an “adder” stage. The effects loop in a mixer can be thought of as the tape monitor loop in a normal stereo system. It allows devices such as rever­beration systems to be readily inserted in the signal path. If you build a power amplifier you will also need to build a power supply to suit and normally a suitable circuit would be included in the design, even if it is not included in the kit. Suitable heatsinks are also suggested in the article. You should also be prepared to pay a lot more for the power supply than for the amplifier module and then a suitable case will also be re­quired. We cannot suggest any designs for the loudspeakers which will need to be large and very rugged for your application. Jaycar Electronics can provide cabinet designs for some of their PA loudspeakers which might be suitable. Really, if you are going to do the job properly you will need to spend quite a few thousand dollars. We suggest you con­sult someone who has been in the music business for a number of years before you start spending. Keep those projects coming I have been buying your magazine since it began in 1987 and I congratulate you for keeping the quality so high. I would like to suggest some ideas you may like to use for articles and/or projects. First, how do voice scramblers work? Are they simple to build? I have seen on some of the more expensive micro recording cassette players that they have variable speed and variable pitch, so that you can play at a higher speed but be able to hear the voice playing faster but without the “Chipmunk” sounds (Tandy sells such a device). The variable speed is easy to make but what about the gadget that varies the pitch? During summer, it gets quite hot here at nights (yes, Armi­dale can get hot). We have a 3-speed desk fan. However, it’s not much help at night as it is too strong (even on the lowest Substitute for magnetic detectors I have just purchased your excellent production “14 Model Railway Projects” as I am still a novice in the world of elec­tronics and I am trying to learn more about the possibilities of adapting electronics to my own model railway. Of particular interest to me is the article titled “Level Crossing Detection for Model Railways”. However, I have a small problem in that my stock is fitted with delayed action un­couplers for which I have placed permanent magnets between the rails at strategic locations. Having previously tested the principle used in the article of placing magnets under the rolling stock, albeit with a locomo­ tive fitted with magnets for magnetic track adhesion (no longer used), I have found that the magnets tend to retard the loco movement when passing over the track mounted magnetic uncouplers. While this particular loco would work fine on the system in your article, I am reluctant to use this method of detection on other items of stock as I have a considerable number of uncou­plers already in place around the layout. While reading through the book I noticed that the “Diesel Sound Gen­ erator” (on page 30) uses a photo-interrupter to detect the train. Would it be possible to adapt the photo-interrupter to the Level set­tings) and it makes too much noise to allow you to sleep. Would it be OK to install a dimmer switch to the fan? It has a rating of 50W. I was very interested in the Security Camera project which was in the March 1993 edition. However, it seemed to me to be a bit inefficient firing the shutter. I would have thought that the shutter on many of these cameras was electrically controlled. If so, then some of the trickiest parts of the circuit could be bypassed (the electric motor and gears). Perhaps you could pub­lish the modifications. I was interested to read a letter published in the January 1994 edition by Crossing Detector circuit? If so would you please supply me with the revised circuitry. (G. K., Valley Heights, NSW). • Magnetic uncouplers may pre­ sent a problem with retarding the train. However, your tests were carried out with magnets for track adhesion and these would probably be considerably more powerful than the magnets specified for the Level Crossing Detector. We recom­ mend testing the train by using the magnets specified in the article. If the train is not slowed down significantly, use the magnets and Hall effect detector circuitry as described. The optical method used for the Diesel Sound Generator can be used but this does have the problem of multiple triggering as the carriage wheels pass between the optical sensor pickup and the light source. The LED from the optical sensor can be powered from the +12V supply via a 470Ω resistor and the emitter load for the detector can be a 180kΩ resistor as per the diesel sound genera­tor circuit. Simply connect the emitter output to the input of the Level Crossing Detector at position 3. Note that you will need to have a common earth connection between the position 2 input and the ground supply for the opti­cal sensor. The sensitivity from the optical pickup is far great­er than that from the Hall Effect sensor and so the 1MΩ feedback resistors on IC1a & IC1b should be reduced to 100kΩ. C. P. regarding the muting of wireless micro­phones. I agree with what he says about the problems with noise when the mike is switched off. I see in the March 1994 issue a “voice activated audio switch for FM wireless microphones” pro­ ject. This would obviously be good in many situations. It would be more use to me if the FM receiver had a squelch. Is it a simple matter to add one to the “Simple FM Receiver”? Many projects become costly when they require a meter or an LCD display and as I am only an experimenter I rarely build any that are expensive. I am always pleased when projects are August 1994  91 Long distance communication via CB In 1991, my wife and I purchased two Midland 70-530D UHF CB sets. Since 1991 we have not been able to use these sets between our farm and our house in Brisbane. There is 125km in a straight line between our farm and our house. So-called Australian radio experts (university doctor, professor, specialised firm) have all told me it was impossible to communicate beyond a mountain with UHF (300-3000MHz). In October 1993, a very comprehensive article on long distance UHF propagation appeared in “The Australian National Geographic”. Mention was made of UHF CB bouncing from planes, large struc­ tures, Moon bouncing, etc. I wrote seven letters to each one of the people mentioned in the article. Every letter came back saying that what was described in the article was only theory and imagination. That is why I really welcome your very positive article in the May 1994 issue on passive TV re-broadcasting. Last year, ARRL (USA) told me very positively we should be able to communicate over 125km on UHF CB, even with a mountain between; especially if we use Yagis and some power. This obviously conflicts with infor­mation from the Australian experts. This is a serious matter. We have been quoted $10,000 to put in 2km de­scribed that connect to the multi­ meter. There are a couple of things that I would like to make that may be able to use the multimeter (perhaps using the frequency range). The first is a pulse rate monitor and the second is an anemometer. If it isn’t a simple matter using a multimeter, what about using a computer? There haven’t been too many articles around lately about biofeedback. How about something about measuring brainwave activ­ity? Simple monitors costing about $100 were selling in the USA. How do they work? What about a project? I hope you don’t think I am demanding these projects or articles. That is 92  Silicon Chip of Telecom land line on our farm. All the ground below 600mm feet is granite and every pole has to be blasted by high explosive. Austel doesn’t allow people to use trees to hang telephone line. By arrangement with Mobile Net management, on the 2nd to 4th April 1994, I was able to use an extremely sensitive and well aligned portable telephone on 820MHz. I was able to receive signals 80 metres below the line of sight, 10km from the edge of the mountain, with the transceiver 50km from the Telecom repeat­ er. The so-called experts when confronted with my practical field results could not give any explanation. (G. C., Corinda, Qld). • UHF communication over the 125km path you refer to is certainly possible but it would not be consistent and would depend very much on the vagaries of the weather. Even if you are using high power plus Yagis, you would be depending on tro­ pospheric scatter for communication over the mountain and this would only be possible at certain times. Bounce communication via aeroplanes or the Moon is also possible but you could not depend on having the Moon or a plane handy to bounce the signals off every time you wanted to make a call. It seems that if you want consistent and reliable long distance communications 24 hours a day, the only way is to in­stall a telephone. not my intention. I am merely suggesting ideas that you may or may not want to use. Keep up the good work. I look forward to all your issues. (G. E., Armidale, NSW). • Thanks for your letter and enquiries about various circuits. We will answer them in order. First, scramblers work in a variety of ways which may involve analog or digital circuit techniques. Perhaps the simplest is a frequency shifting system whereby the signal is shifted by about 1kHz or so which is enough to make it unintelligible. We have not published any circuits along these lines. Speed and pitch normally have a direct relationship in a tape recorder – if you increase the tape speed, the pitch goes up in exact proportion. Those tape players which increase the speed of playback without changing the apparent pitch mainly do so by chopping out the pauses in speech. You cannot use a dimmer circuit to control a fan motor without modifications. The modification mainly involves an RC circuit called a “snubber” across the Triac. This enables the Triac to commutate (ie, switch off) properly at the end of each 50Hz half-cycle. We published suitable circuits for fan speed control in the December 1987 and January 1990 issues. While some low-cost cameras are available with motorised film winding, there are very few available with electronic or motorised shutters. Hence, the motorised firing scheme in the Security Camera was necessary. Most FM tuners used in home hifi systems have muting. Squelch is effectively the same thing except that the threshold is adjustable. Muting (or squelch) stops an FM receiver from producing spurious noise when the RF signal is insufficient to “quiet” the receiver (ie, to produce noise-free audio). The VOX circuit was published with the specific requirement that it mute the microphone while the transmitter circuit remained active. A squelch circuit would not achieve the same thing and it normally produces a “squelch” sound as it operates, which can be undesir­able in some cases. Thanks for your other circuit suggestions. We’ll put them on the list of things to do. Mixer has loss of bass I am using an op amp (circuit enclosed) as a mixer between several cassette decks and the main amplifier. When the signal (about 400mV) is run through the op amp circuit, there is a considerable loss of bass but with a direct connection between any tape deck and the amplifier there is no bass problem. Are you able to give me some information on overcoming the bass loss? (R. M., Cambridge Park, NSW). • The essential problem would appear to be that your input coupling capacitor is not big enough. Try using SC 1µF or larger. SILICON CHIP BOOK SHOP Newnes Guide to Satellite TV 336 pages, in paperback at $49.95. Installation, Recept­ion & Repair. By Derek J. Stephen­son. First published 1991, reprinted 1994 (3rd edition). This is a practical guide on the installation and servicing of satellite television equipment. The coverage of the subject is extensive, without excessive theory or mathematics. 371 pages, in hard cover at $55.95. Servicing Personal Computers By Michael Tooley. First pub­ lished 1985. 4th edition 1994. Computers are prone to failure from a number of common causes & some that are not so common. This book sets out the principles & practice of computer servicing (including disc drives, printers & monitors), describes some of the latest software diagnostic routines & includes program listings. 387 pages in hard cover at $59.95. The Art of Linear Electronics By John Linsley Hood. Pub­lished 1993. This is a practical handbook from one of the world’s most prolific audio designers, with many of his designs having been published in English technical magazines over the years. A great many practical circuits are featured – a must for anyone inter­ested in audio design. Optoelectronics: An Introduction By J. C. A. Chaimowicz. First published 1989, reprinted 1992. This particular field is about to explode and it is most important for engineers and technicians to bring themselves up to date. The subject is comprehensively covered, starting with optics and then moving into all aspects of fibre optic communications. 361 pages, in paperback at $55.95. Digital Audio & Compact Disc Technology Produced by the Sony Service Centre (Europe). 3rd edition, published 1995. Prepared by Sony’s technical staff, this is the best book on compact disc technology that we have ever come across. It covers digital audio in depth, including PCM adapters, the Video8 PCM format and R-DAT. If you want to understand digital audio, you need this reference book. 305 pages, in paperback at $55.95. Power Electronics Handbook Components, Circuits & Applica­ tions, by F. F. Mazda. Published 1990. Previously a neglected field, power electronics has come into its own, particularly in the areas of traction and electric vehicles. F. F. Mazda is an acknowledged authority on the subject and he writes mainly on the many uses of thyristors & Triacs in single and three phase circuits. 417 pages, in soft cover at $59.95. Surface Mount Technology By Rudolph Strauss. First pub­ lish-ed 1994. This book will provide informative reading for anyone considering the assembly of PC boards with surface mounted devices. Includes chapters on wave soldering, reflow­ soldering, component placement, cleaning & quality control. 361 pages, in hard cover at $99.00. Electronics Engineer’s Reference Book Edited by F. F. Mazda. First pub­ lished 1989. 6th edition 1994. This just has to be the best reference book available for electronics engineers. Provides expert coverage of all aspects of electronics in five parts: techniques, physical phenomena, material & components, electronic design, and applications. The sixth edition has been expanded to include chapters on surface mount technology, hardware & software design, Your Name__________________________________________________ PLEASE PRINT Address____________________________________________________ _____________________________________Postcode_____________ Daytime Phone No.______________________Total Price $A _________ ❏ Cheque/Money Order ❏ Bankcard ❏ Visa Card ❏ MasterCard Card No. Signature_________________________ Card expiry date_____/______ Return 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. semicustom electronics & data communications. 63 chapters, in paperback at $140.00. Radio Frequency Transistors Principles & Practical Appli­ cations. By Norm Dye & Helge Granberg. Published 1993. This timely book strips away the mysteries of RF circuit design. Written by two Motorola engineers, it looks at RF transistor fundamentals before moving on to specific design examples; eg, amplifiers, oscillators and pulsed power systems. Also included are chapters on filtering techniques, impedance matching & CAD. 235 pages, in hard cover at $85.00. Newnes Guide to TV & Video Technology By Eugene Trundle. First pub­ lish-ed 1988, reprinted 1990, 1992. Eugene Trundle has written for many years in Television magazine and his latest book is right up date on TV and video technology. 432 pages, in paperback, at $39.95.  Title Price  Newnes Guide to Satellite TV  Servicing Personal Computers  The Art Of Linear Electronics  Optoelectronics: An Introduction  Digital Audio & Compact Disc Technology  Power Electronics Handbook  Surface Mount Technology  Electronic Engineer’s Reference Book  Radio Frequency Transistors  Newnes Guide to TV & Video Technology $55.95 $59.95 $49.95 $55.95 $55.95 $59.95 $99.00 $140.00 $85.00 $39.95 Postage: add $5.00 per book. Orders over $100 are post free within Australia. NZ & PNG add $10.00 per book, elsewhere add $15 per book. TOTAL $A August 1994  93 MARKET CENTRE Cash in your surplus gear. Advertise it here in Silicon Chip. CLASSIFIED ADVERTISING RATES VINTAGE RADIO Advertising rates for this page: Classified ads: $10.00 for up to 12 words plus 50 cents for each additional word. Display ads (casual rate): $25 per column centimetre (Max. 10cm). Closing date: five weeks prior to month of sale. To run your classified ad, print it clearly in the space below or on a separate sheet of paper, fill out the form & send it with your cheque or credit card details to: Silicon Chip Classifieds, PO Box 139, Collaroy, NSW 2097. Or fax the details to (02) 979 6503. VINTAGE RADIO SWAP meet/fair. Inc. military, amateur radio and antique sound. Sunday 23rd October, 1994 10am to 5pm. Glenroy Technical School Hall, Melbourne. Bookings: R. Howarth, PO Box 9, Junortoun 3551. Phone (054) 49 3207. _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ FOR SALE THE HOMEBUILT DYNAMO: (plans) brushless, 1000 DC watt at 740 revs. $A85 postpaid airmail from Al Forbes, PO Box 3919 - SC, Auckland, NZ. Phone Auckland (09) 818 8967 any time. Rotor magnets (3700 gauss) kit now available. SATELLITE TV DX SUPER RX receiver. Threshold 2.5dB. Also digital picture, sound, synchron, resolution processors. Mobile DX re­ceivers, pay TV decoders. TV, radio, picture, sound mod­ulators. Digital, analog signal meters. Send $5 for info and catalog/refundable to John Papp, PO Box 472, Sanderson, NT 0812. Fax/Ph:(089) 27 4985. SUBSTITUTE FOR A HANDFUL OF ICs: Parallax “BASIC STAMP”. A gen­er­al purpose small circuit module, it is really a 25 x 50mm board with a computer chip (4MHz PIC 16C56), EEPROM, 8 I/O pins, board space includes prototyping area. Program it on a PC (only 33 instructions) with development kit Enclosed is my cheque/money order for $­__________ or please debit my RCS RADIO PTY LTD Card No. ✂ ❏ Bankcard   ❏ Visa Card   ❏ Master Card Signature­­­­­­­­­­­­__________________________ Card expiry date______/______ Name ______________________________________________________ Street ______________________________________________________ Suburb/town ___________________________ Postcode______________ 94  Silicon Chip RCS Radio Pty Ltd is the only company that manufactures and sells every PC board and front panel published in SILICON CHIP, ETI and EA. RCS Radio Pty Ltd, 651 Forest Rd, Bexley 2207. Phone (02) 587 3491    Zelcon Technic Pty Ltd • • • • PCB Supplier Photoplotting Services SMT/Through-Hole Assembly CAD facilitites PO Box 149, Glenorchy, Tas 7010 Ph: (002) 71 8120, Fax: (002) 71 8182 BBS: (002) 73 0799 which includes one “BASIC STAMP” ($249 plus S/T & post), extra modules ($66 plus S/T & post). Send 45c stamp for more information. Parallax distributor and techni­cal support in Australia: MicroZed Computers, PO Box 634, Armi­dale, NSW 2350. Facsimile (067) 72 8987. MEMORY PRICES Building Your Speakers? Need Help? PRICES AT JUNE 8TH, 1994 SIMM 1Mb x 3 1Mb x 9 4Mb x 9 4Mb (72-pin) 8Mb (72-pin) 16Mb (72-pin) DRAM DIP 1 x 1Mb 256 x 4 IBM PS.2 55/65SXVP L40/N33 90/95 PS1 70ns 70ns 70ns 70ns 70ns 70ns 70ns 70ns $61 $63 $225 $238 $476 $952 $7.50 $8.00 4Mb 4Mb 4Mb $238 $238 $280 MAC 4Mb x 80 80ns 6Mb P’BOOK $210 $380 CO-PROCESSORS 387S/DX to 40 $90 LASER PRINTER HP 2Mb L’jet 4L $135 COMPAQ PROLINEA 8Mb $476 TOSHIBA 2000SX 46/1900 3.3 8Mb 4Mb $541 $300 SUN SPARC 10 16Mb $975 PCMCIA 1Mb V2 BAT SRAM 2Mb V2 BAT SRAM 2Mb FLASH RAM 20Mb SUN FLASH RAM 1st Floor, 100 Yarrara Rd, PO Box 382, Pennant Hills, 2120. PELHAM CAMCORDER BATTERIES: factory sealed rechargeable packs to suit SONY, SANYO, PANASONIC, JVC, SHARP, CANON. Best possible prices - eg, SONY 1800mAh - ONLY $54.90! Ring after 6pm (02) 818 4968. D. R. BATTERIES, 17 Bay Street, Birchgrove, 2041. SANYO NICADS - BEST PRICES: Sanyo nicads from 50mAh to 4400mAh. Separate cells or packs made to order. Best prices, eg N1300SC - $5.50; KR4400D - $14.00, N600AA - $3.50. Ring after 6pm (02) 818 4968. D. R. BATTERIES, 17 Bay Street, Birchgrove, 2041. EPROM & SRAM EMULATOR: 2K x 8 (or 16) to 64K x 8 (or 16). Down­load and verify via standard PC printer port. Supports Binary, Intel and Motorola hex formats. Including Binary Editor. For more information, contact Northern Eastern Digital, PO Box 1252, Collingwood, Vic 3066. Fax (03) 484 5133/432 1063; Phone (03) 432 1699. WEATHER FAX programs for IBM XT/ ATs *** “RADFAX2” $35 is a high resolution, shortwave weather fax, Morse & Rtty receiving program. Suitable for CGA, EGA, VGA and Hercules cards. Needs SSB HF radio & Radfax decoder. *** “SATFAX” $45 is a NOAA, Meteor & GMS weather satellite picture receiving program. Needs EGA or VGA plus “WEATHER FAX” PC card. *** “MAXISAT” $75 is similar to SATFAX but needs 2Mb expanded memory (EMS 3.6 or 4.0) and 1024 x 768 SVGA card. All programs are on 5.25-inch or 3.5-inch disks (state Australian Audio Consultants Box 1031, Aldinga Beach, SA 5173. Phone or fax on (085) 56 6370 CTOAN ELECTRONICS Got a great idea for a new device? Don’t leave it as just an idea. Call us; we can help make is work. You describe it – we’ll design it. PO Box 211, Jimboomba 4280. Phone (07) 297 5421. • TRANSFORMER REWINDS ALL TYPES OF TRANSFORMER REWINDS TRANSFORMER REWINDS Reply Paid No.7, PO Box 1058, St Marys, NSW 2760. Ph: (02) 833 1146. Fax: (02) 623 5559. which) & include documentation. Add $3 postage. Only from M. Delahunty, 42 Villiers St, New Farm, Qld 4005. Phone (07) 358 2785. VALVE AMPLIFIERS: Australian made. Mono, stereo, guitar using 2A3, 211, 6L6 or 807 valves. Williamson reproductions. Parts available for DIY constructors. Circuit diagrams and construction details for many types of valve amplifiers. Valve equipment repairs. Lancroft Pty Ltd, PO Box 439, Bexley 2207. Phone (02) 567 5390. BINARY CLOCK - OCTOBER 1993: complete documentation supplied, includes introduction to binary, how it works, PLD source list­ings, conversion tables. Kit with PCB and all components $75 + $5 p&p. Optional Z frame stand (includes spacers and chassis DC connector) $25 + $5 p&p. Prototype Electronics, 1/29 Stewart St, Parra­ matta, NSW 2124. Phone (02) 683 3510; Fax Speaker parameters measured Boxes designed & manufactured Crossovers designed Systems for lounge, car or PA For more details contact: $205 $330 $345 $1500 Sales tax 21%. Overnight delivery. Credit cards welcome. 5-Year warranty. Ring for latest prices. Tel: (02) 980 6988 Fax: (02) 980 6991 • • • • • • • 350 Watt Power MOSFET Amplifier Module As published in the June 1994 issue of Silicon Chip. Kit price $159.00. Postage and handling $8.00. Payment by M/C, B/C, Visa, Cheque or Money Order. 3kg O/N Air Bag $10.00 Computer & Electronic Services Pty Ltd 27 Osborne Avenue, Trevallyn Launceston, Tasmania 7250 Phone 003-34 4218; Fax 003-31 4328 (02) 630 3148. Pay by cheque, money order, credit card. THE 8051 MICRO-COMTROLLER book includes a simulator disk ($40). ROMLoader EPROM Emulator (EA Jan/ Feb 92, EA June 94) (PCB $30). 8051 Proto-Boards (EA Feb 93) (PCB $30). Tantau Australia, PO Box 1232, Lane Cove 2066. Phone AH (02) 878 4715. CONTROL RELAYS, Robots, Radios or Railways from LPT1: of your XT to 486 PC. 64 bits. Fully expandable. Demo programs, flow charts, circuits, drivers in M.L. & Basic. Bare PCB and software $38, or demo/promo disk $2. Don McKenzie, 29 Ellesmere Crescent, Tulla­marine, Vic 3043. Phone (03) 338 6286. PIC16Cxx PROTO-PCB for 18, 28-pin PICs. Includes Basic Stamp cct, XTL/ RC, up to 20MHz, MAX-232, MAD Bus, Relay Bus, 3 LEDs, and lots more. Don’s August 1994  95 ELECTROSTATIC LOUDSPEAKERS Microprocessor For Stereo Preamplifier 3-PANEL FULL RANGE DESIGN, AVAILABLE IN KIT FORM OR FULLY ASSEMBLED. LOCALLY DESIGNED & MANUFACTURED. FOR INFORMATION BROCHURE, PHONE/FAX (09) 397 6212 OR WRITE TO: E. R. AUDIO, 119 BROOKTON HWY, ROLEYSTONE, WESTERN AUSTRALIA 6111. Now back in stock: the 68HC705-C8P pre-programmed micro­p ro­c essor for the Infrared Remote Controlled Stereo Preamplifier (SILICON CHIP, Sept.-Oct. 1993). Also suits the Remote Volume Control (May & June, 1993). Price: $45 + $6 p+p Payment by cheque, money order or credit card to: Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097. Phone (02) 9795644; Fax (02) 979 6503. RS-232 driven O/S available soon for 18 I/O bits. PCB and data $20. Promo disk $2. Don McKenzie, 29 Ellesmere Crescent, Tullamarine 3043. Phone (03) 338 6286. INTELLIGENT INFRARED RECEIVER (ref SILICON CHIP, March 94). Now with 8 outputs. Use your TV or VCR infrared remote control trans­mitter to control your TV or hifi appliances with an intelligent infrared receiver kit. Also available infrared transmitters, preprogrammed and learning models. For details call BENETRON P/L (018) 20 0108. NEW CHINESE ANTENNA: made from recycled jam tins. Cost $79.50; sell $20 ono. Phone 971 9539. UNUSUAL BOOKS: Electronic Devices, Fireworks, Locksmithing, Radar Invisibility, Surveillance, Self-Protection, Unusual Chem­ istry and more. For a complete catalog, send 95 cents in stamps to Vector Press, Dept S, PO Box 434, Brighton, SA 5048. VALVES SPECIALIST: buy, sell, modify and service. Thousands valves in stock. Altronics ..........................IFC,20-22 Aust. Audio Consultants...............95 Av-Comm.......................................3 Computer & Elect. Services.........95 Ctoan Electronics........................95 David Reid Electronics ..............59 Dick Smith Electronics........... 10-13 E. R. Audio...................................96 Harbuch Electronics....................59 Instant PCBs................................95 EL34 $20, KT88 $38, 655OWA $34, 6922 $12, 12AX7WA $8, 300B $140, 845 $100. MIT, WONDER, SOLEN, OIL capaci­tors, etc. Wanted to buy valves and equipment. Mobile (0414) 22 3245. Fax (02) 816 4515. Jaycar ......................... 33-36,61-64 L & M Video.................................82 Macservice..................................71 McLean Automation.....................81 Oatley Electronics.................. 50-51 PRINTED CIRCUIT BOARDS for the hobbyist. For service & enquiries contact: T. A. Mowles (08) 326 5590. PC Computers.............................81 MICASOFT Electronics and Computing tutor program, written in UK, ideal for TAFE, schools, or individual use. Now available in Australia. Send $1.80 in stamps for demo disk (tell us what size). MicroZed Computers, PO Box 634, Armidale 2350. RCS Radio ..................................94 REAL TIME ICE!!! The only way to go. MOTOROLA 6805 EMULATOR and programmers. Prices and data from Graham Blowes, Mantis Micro Products, 38 Garnet Street, Niddrie 3042. Phone (03) 337 1917 (a/h), (03) 575 3349 (b/h). Fax (03) 575 3369. Silicon Chip Projects Book......OBC SILICON CHIP FLOPPY INDEX WITH FILE VIEWER Now available: the complete index to all SILICON CHIP articles since the first issue in November 1987. Now you can search through all the articles ever published for the one you want. The index comes as an ASCII file on a 3.5-inch or 5.25-inch floppy disc to suit PC-compatible computers and you can use any word processor or our special file viewer to search for keywords. Simply enter in the keyword(s) and the index will quickly find all the relevant entries. All commands are listed on the screen, so you’ll always know what to do next. Price $7.00 + $3 p&p. Send your order to: Silicon Chip Publications, PO Box 139, Collaroy 2097; or phone (02) 979 5644 & quote your credit card number; or fax the details to (02) 979 6503. Please specify 3.5-inch or 5.25-inch disc. 96  Silicon Chip Advertising Index Pelham........................................95 Philips.........................Centre Insert Rod Irving Electronics .......... 74-78 Silicon Chip Back Issues....... 88-89 Silicon Chip Binders..................IBC Silicon Chip Bookshop.................93 Silicon Chip Software..................83 Tortech.........................................87 Transformer Rewinds...................95 Yuga Enterprise...........................86 Zelcon Technic.............................95 _________________________________ PC Boards Printed circuit boards for SILICON CHIP projects are made by: • RCS Radio Pty Ltd, 651 Forest Rd, Bexley, NSW 2207. Phone (02) 587 3491. • Marday Services, PO Box 19-189, Avondale, Auckland, NZ. Phone (09) 828 5730. • H. T. Electronics, 35 Valley View Crescent, Hackham West, SA 5163. Phone (08) 326 5590.