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FEBRUARY 2001  1 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings.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.circuitmaker.com Contents Vol.14, No.2; February 2001 FEATURES 6 How To Observe Meteors Using Junked Gear The Earth gets hit by countless small meteors every day. Here’s how to observe and count them using readily available “junk” – by Bruce Mitchell 56 Review: Sony’s Big Rear-Projection TV Set Big, bright and impressive, this 121cm set makes you want to start watching TV again – by Leo Simpson 72 An Easy Way To Make PC Boards At Home Learn how to transfer etching patterns to blank PC boards using nothing more complicated than a laser printout and a hot iron – by Heath Young Observing Meteors Using Junked Gear– Page 6. PROJECTS TO BUILD 14 L’il Pulser Train Controller Here’s a pulse-power train controller that’s cheap and easy to build. It works from any standard 12V model train supply – by John Clarke & Leo Simpson 26 MIDI-Mate: A MIDI Interface For PCs Easy-to-build project connects to your PC’s sound card to provide full MIDI input and output ports – by Jim Rowe 32 Build The Bass Blazer It gives a visual readout of the bass signals from your home theatre or car stereo system on four bargraph displays – by Rick Walters L’il Pulser Train Controller – Page 14. 62 A 2-Metre Elevated Groundplane Antenna Novel design includes a matching section to match the impedance of the feed cable. It’s easy to build too – by Philip Watson 76 The LP Doctor: Cleaning Up Clicks & Pops; Pt.2 Second article has all the construction details – by John Clarke SPECIAL COLUMNS 40 Serviceman’s Log The spirit of Christmas past – by the TV Serviceman MIDI-Mate: A MIDI Interface For PCs – Page 26. 84 Vintage Radio The Healing 412E: a PC-board valve radio – by Rodney Champness DEPARTMENTS 2 4 53 55 71 Publisher’s Letter Mailbag Product Showcase Electronics Showcase Subscriptions Form 89 91 94 96 Ask Silicon Chip Notes & Errata Market Centre Advertising Index 2-Metre Elevated Groundplane Antenna – Page 62. FEBRUARY 2001  1 PUBLISHER’S LETTER www.siliconchip.com.au Publisher & Editor-in-Chief Leo Simpson, B.Bus., FAICD Production Manager Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Peter Smith Ross Tester Rick Walters Reader Services Ann Jenkinson Advertising Enquiries Rick Winkler Phone (02) 9979 5644 Fax (02) 9979 6503 Mobile: 0408 34 6669 Regular Contributors Brendan Akhurst Louis Challis Rodney Champness Garry Cratt, VK2YBX Julian Edgar, Dip.T.(Sec.), B.Ed Mike Sheriff, B.Sc, VK2YFK Philip Watson, MIREE, VK2ZPW Bob Young SILICON CHIP is published 12 times a year by Silicon Chip Publications Pty Ltd. ACN 003 205 490. ABN 49 003 205 490 All material copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Hannanprint, Dubbo, NSW. Distribution: Network Distribution Company. Subscription rates: $69.50 per year in Australia. For overseas rates, see the subscription page in this issue. Editorial & advertising offices: Unit 8, 101 Darley St, Mona Vale, NSW 2103. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 9979 5644. Fax (02) 9979 6503. E-mail: silchip<at>siliconchip.com.au ISSN 1030-2662 * Recommended and maximum price only. 2  Silicon Chip Time is ripe for a renaissance of electronics clubs Years ago, there were a lot of electronics clubs, particu­ larly in schools and many students “cut their teeth” on crystal sets, simple valve radios, guitar amplifiers and so on. It was a great breeding ground for a vast number of technically qualified or otherwise “switched-on” people. Now, it seems as though we could see a resurgence in elec­tronics clubs and not necessarily just in schools. Why do I say this? First, we recently have had an increase in the number of people asking to be put into contact with an electronics club, largely so that they could have someone help them with a current electronics project that they were having difficulty with. Sadly, apart from referring people to amateur radio clubs, we have not been able to give such contacts. Second, we have been contacted by a number of teachers in schools who are interested in starting an electronics club. Some schools do have quite a thriving club and they do use SILICON CHIP articles as a major source of material. It also seems that a major cause of this resurgence is a requirement in the curriculum for teaching a certain amount of electronics. I find this a very gratifying development. More importantly, many young people have become disenchanted with just playing games on their computers and want to have some real “electronics” fun. A school club could be just what they are looking for. But the concept could go a lot further. It occurs to me that there a large number of electronically knowledgeable people in Australia who would enjoy the process of “mentoring” those who are just starting out in the wonderful world of electronics. As part of a club structure, they could provide a sterling service to those who are floundering with projects but are otherwise extremely enthusiastic about electronics as a hobby. I am think­ing mainly of retired people as the “mentors” but often it is retired people who are the novices, taking up this hobby now that they have the time. So are there people out there who are willing to start up such clubs? We would do whatever we can to help the process, including publishing an annual list of clubs in the magazine and on our website. Electronics retailers would also happily refer people to electronics clubs and would probably provide some special pricing for clubs. It also occurs to me that amateur radio clubs could do a lot to grow their stagnating memberships if they actively promot­ed themselves as “electronics” clubs. In fact, they might give thought to that as their major activity and not have the inten­tion of just promoting the amateur radio side of things. Such a change in emphasis might really boost things along. Anyway, I feel that the time is ripe for a renaissance of electronics clubs. Let’s see if we can’t give the idea a big push. Finally, if you know of or are a member of an electronics club, please send us your particulars so we can compile a data­base. Leo Simpson                                                                                                                                                                                                                                        The missing link                                                                                                                                                                                                                                                                                                                                            We welcome Bankcard,                                                                                                                                                                                     Mastercard and VISA NO SURCHARGE! Website, online catalogue & shop: www.mgram.com.au  Phone: (02) 4389 8444 sales<at>mgram.com.au   info<at>mgram.com.au    Fax: (02) 4389 8388    FreeFax: 1 800 625 777 MicroGram Computers        Unit 1, 14 Bon Mace Close, Berkeley Vale NSW 2261 Vamtest Pty Ltd trading as MicroGram Computers ABN 60 003 062 100. FEBRUARY 2001  3 MGRM0201 All prices subject to change without notice. MAILBAG NZ homeowners cannot work on live electrical wiring The situation in New Zealand is not quite as you describe it in the Publisher’s Letter in the November 2000 issue. Homeown­ers are certainly not allowed to do work on a switchboard, for example. Homeowners can do the physical work but cannot go any­where near a live conductor and the work must be inspected by an inspector (not just an electrician) before connection. There are similar provisions with regard to repair of appliances. The person undertaking the repair must own the ap­pliance, it must be used by the owner or a near-relative, only be used for private use and must be disconnected from the supply while the repair is undertaken. Certainly the situation in Australia seems to mirror what we had until 10 years or so ago. I have no knowledge of the statistics about accidents but the Energy Safety Service of the Ministry of Economic Development in NZ is currently holding discussions about whether the licensing system is working and whether it should be extended to the gas industry. See http://www. energysafe.med.govt.nz Incidentally, all NZ Acts of Parliament are available for free from http://www.knowledge-basket.co.nz/ gpprint/ Malcolm Moore, Wellington, NZ. Don’t mess with 240V So we should be able to do our own electrical work? I think not. I grew up in New Zealand and did my apprenticeship in the electrical trade there. That was over 40 years ago and if I ever learned anything, it was don’t mess with 240 volts. I live in Australia these days, and sometimes (often) I have been known to connect this wire to that connector, replace a fuse, or replace a GPO (General Power Outlet). OK, I no longer work in the trade, I do other technical work but I do know what I’m doing, mostly. Now think of the average house- 4  Silicon Chip keeper – who knows absolutely nothing about electricity. Should he or she wire up their own home? And would you let your son or daughter do it? Would you turn them loose next Christmas in a high-powered car, with no training, and no licence? Get real; even putting a 3-pin plug on a toaster cord is hi-tech to the untrained house­holder. So, please leave electrical work to the (hopefully) trained tradespeople who hold a licence for such work. Euan Miller, via email. Homeowners could not understand AS/NZS 3000 I read with alarm your editorial in the November 2000 issue. Whilst I can appreciate some of the senti­ ments expressed therein, and they are perfectly understandable for someone with no experience in the industry, I am compelled to draw a number of serious matters to your attention. Firstly, “no-one, in fact, has died in New Zealand due to hazardous wiring created by a householder.” I regard those sta­tistics with a healthy degree of scepticism. Did Mr Hoolhorst mention how many had been seriously injured by DIY wiring? Or how many had been killed by wiring faults of any type. What about fires caused by faulty wiring? Selective presentation of statis­tical information, deliberately or otherwise, has enormous poten­tial to obscure the truth of the situation. Secondly, in regard to AS/NZ 3000: yes, we do have the same standard. But let me ask you this: how many ‘you-beaut’ DIY electricians even know this standard exists, let alone are pre­pared to shell out for a copy of it. And even supposing they did, could they really comprehend what a particular clause actually means when they may not even know the correct terminology for the items involved in the task they are attempting? Thirdly, in more than 20 years of working in the electrical industry, I have all too often encountered wiring in houses that was very dangerous indeed; real fatalities waiting to happen. Fourthly, some years ago, an ac- quaintance of mine who, before going into business as an electrical contractor, had worked for many years as an electrical installation inspector for what was then Sydney County Council, was killed by faulty wiring under a house he was working on. If someone who has been a pro­fessional identifier of defects in wiring can be killed by a wiring fault, despite their clearly knowing all the dangers involved, can anyone seriously suggest that anybody should be able to cut loose on their home wiring? Sure, if you want to build or work on a plug-in project or appliance, fine – just be very careful. But no-one should touch fixed wiring unless they are qualified – and authorised to do so. I would be as comfortable with the unqualified doing wiring in my house as they would be for me to do their dental work with my pliers and screwdriver. The road to hell, as they say, is paved with good intentions. Geoff Hahn, via email. Vintage radio is part of our history So your correspondent, Alfred Fischer, (SILICON CHIP, Janu­ary, 2001) does not like reading about the revival of corpses. Perhaps he would like to see all the restored veteran and vintage cars interred and perhaps the Sydney Town Hall reduced to rubble. Then the restored and operating steam locomotives should also be cut up and destroyed, as were hundreds of their brothers. The preservation of past technical equipment is a vital part of our living history. The more than 1000 members of the Historical Radio Society of Australia will become heroes in the future when the examples of their restoration work may be the only reminder we have of a bygone age of electronic technology. The Vintage Radio pages in SILICON CHIP each month are an impetus to others to take up the art of restoration of old technical equipment. To those of us who look forward each issue to what is displayed in these pages, it becomes an incentive to continue buying the magazine. I correspond with people all over the world who restore old electronic equipment. There are societies in the United States which specialise in many varied aspects of early electronics. Some are only concerned, for example, with the restoration of 1920s radio receivers; now that is a Lazarus revival! To those of us who appreciate the restoration of electronic technology of a past age, there is little more rewarding pastime than to acquire a filthy, non-operative domestic radio receiver and with loving care bring it back to life. The end result, in almost showroom condition, becomes a vital part of almost forgot­ten technology. And what a joy it is to hear it receive all the still operating AM radio stations within range as it did when first manufactured. Restorers are not just weird people. We also appreciate modern technology and many of us keep up to date with as many current electronic developments as we are able. However, valve technology (like steam locomotives) is a fascinating aspect of a remnant of a technology that is expanding probably faster than any other aspect of science. Keep on with Vintage Radio and I can only say I feel sorry for your correspondent. Jim Lowe, Heatherbrae, NSW. More support for vintage radio I thought that Mr Fischer’s letter was extremely arrogant on the part of all the people who still take an active interest in Vintage Radio. I would say that I am probably one of the youngest Vintage Radio enthusiasts (15 years old) who enjoys reading your columns by Mr Champness, which are very interesting and in­ -form­ a­ tive. I would be annoyed, angry and sad to see such columns go. Cris Koch, via email. Strong opinions on vintage radio Alfred Fischer gave some pretty strong opinions against Vintage Radio (“reviving corpses”) and also stated his opposition to the Vintage Radio column in the magazine. While I don’t agree with his comments, he is certainly entitled to his views. What does concern me is the response from Silicon Chip . . . “we like your attitude”. I don’t like SILICON CHIP’s attitude at all – I was sur­prised to see your statement which denigrates the interest in vintage radio that is held by thousands of people world wide and a great many people in Australia. The statement also doesn’t seem to defend Mr Champness’ (and his predecessor’s) ongoing contribu­ tion to the success of SILICON CHIP. Vintage radio enthusiasts are of all ages (I’m 45) and come from all walks of life. For example, I am a professional telecom­munications engineer, who deals with cutting edge technology on a daily basis and yet, the revival of radio “corpses” gives me more pleasure than the modern stuff. To each their own – that is what the multi-faceted hobby of electronics is all about. I buy SILICON CHIP, sometimes for the modern day content, but more frequently for the interesting vintage radio articles. That 5% of total content is enough to justify the outlay of $6.60; any other content is a bonus. I am happy to skip over some simple, beginner construction projects, which don’t interest me, because there are other readers who want those articles. Similarly, I like to read one article per month on vintage radio. By all means, make your judgement of required content based on reader surveys but may I suggest that you don’t first alienate a segment of your readership by thoughtless remarks. Finally, I endorse your position on not presenting new construction articles on valve equipment – the line has to be drawn somewhere – but that is only my view. P. K., Sydney, NSW. Vintage radio should be retained With regard to Vintage Radio, Mr Fischer is quite entitled to his viewpoint, however I suspect he is treading on more than just a few toes when he chooses to denigrate valve technology and the history that accompanies pre-solid state electronics. I was fortunate enough to have been formally trained in both valve and solid state electronics in the early seventies and can therefore accept and appreciate both technologies. At most, there are only three or four pages out of a hundred or so pages in SILICON CHIP that are dedicated to the restoration and repair of valve radios and they can be easily skipped if they don’t happen to appeal to the reader. The most disturbing aspect, however, is your response to Mr Fischer. It would appear that your magazine supports Mr Fischer’s comments to a large degree when you state, “we like your atti­tude,” in your response to his observations. You then go on to repeat your statement that SILICON CHIP “would never publish a new design for a valve amplifier (regard­ less of how they might be revered by some audio­ philes).” Just for the record, I am not an “audiophile”. I find your attitude towards anything with valves rather puzzling when you consider that there are some hundreds of col­lectors and restorers of valve radios and equipment in Australia alone (they number in the thousands worldwide), many of whom regularly access your publication for the Vintage Radio section. In closing, I feel that I speak for the majority of valve enthusiasts who enjoy their monthly “dose” of Vintage Radio, when I say that SILICON CHIP would be much the poorer if this important part of the magazine was discontinued to appease the readers who don’t happen to enjoy or understand what essentially was the forerunner of everything else in your magazine. Ron Pond, Bunbury, WA. Comment: we did not intend to denigrate vintage radio, nor do we intend ditching the Vintage Radio column. There are lots of practical reasons for not publishing a valve amplifier. FEBRUARY 2001  5 By Bruce Mitchell Everyone knows that a large asteroid or comet probably killed off the dinosaurs. But did you know that the Earth gets hit by countless small meteors every day? This article tells you how to observe and count them using readily available “junk” and a little ingenuity. Y ou’ve probably noticed by now that the Earth wasn’t destroyed by the Leonid meteor shower last November. But all this could change. Out there in space there are enough big lumps of rock (aka asteroids) to keep at least a few researchers on the lookout for the sort of encounter that would make nuclear war seem a pleasant alternative. These scientists sift through all kinds of astronomical observations, trying to predict and identify asteroids that could make an unwanted entry into the Earth’s comfort zone. In this article we’ll first look at how meteors, asteroids and comets are related and then look at ways of automatically counting meteors using a passive radar technique. It’s not 6  Silicon Chip a cut-and-dried list of instructions on how to make a fully-featured meteor detector. It provides some background information, describes one (of many) approaches to the task and mentions a few practicalities on the way. It assumes a moderate degree of competence in electronics and construction and an honours degree in the fine art of scrounging. Be prepared for disappointments, frustration, lots of reading and hopefully, a sense of accomplishment. You’ll certainly learn more about astronomy, electronics and computing on the way. Did you feel that? We’re seldom aware of it, but as the Earth orbits the Sun it keeps hitting things. There are some boulders, quite a few lumps the size of pebbles and lots of dust that nobody’s got around to cleaning up yet. The pebbles and dust are nothing to worry about unless you earn your living in a space shuttle but as anyone who’s worked in a mine knows, a stray boulder can really ruin your day. Way out in space they’re hard to see even with a large telescope, because on the astronomical scale of things they’re not all that big, maybe no more than a kilometre across. Asteroids and comets leave wispy trails of debris in their wake, so one sign of their passing is higher-than-usual numbers of meteors entering the atmosphere at certain times. These trails persist for a long time. For example, the Leonid meteor shower results from debris associated with comet 55P/Tempel-Tuttle. This insignificant little comet orbits the Sun every 33 years and each November the Earth passes through a small cloud of its debris. Unexpected increases in meteor numbers can indicate the Earth is passing through the trail of debris left by an unknown object. NASA coordinates a project that collects meteor counts from volunteer observers around the world. Each month these observers email an hour-by-hour summary of their observations to NASA’s Ames Research Center for inclusion in the various models used to study meteor and asteroid distribution in and around the orbit of the Earth. Analysis of this sort of data can help identify the orbits of previously unknown asteroids and comets. Just what to do if someone does find an asteroid heading straight towards your place is probably more of a political than scientific decision, given the size of the issues and budgets involved in trying to avoid it. Counting meteors is easy! Try it tonight: lie down in your back yard and make a mark on your notepad every time a “shooting star” appears. (Making a wish is optional.) You’ll soon find, however, that long-term activities of this kind have a few drawbacks. Relationships suffer (“Where were you last night?”); careers can be affected (yawning while the boss tells a joke is risky); it’s cold out there in winter and even the most enthusiastic observer can get discouraged after three weeks of non-stop rain. Oh, and it’s desperately hard to spot them during the day, but that doesn’t matter because you’ll be in bed catching up on lost sleep. Video and photographic methods also have severe limitations (daylight and clouds being the most obvious), so can electronics offer an alternative? Well, at this stage you can’t walk into your local hobby shop and buy a $99 meteor counter because the demand just isn’t there. But anyone with an interest in electronics and computing definitely can make one for that sort of money if they’re prepared to tinker and fiddle, scrounge and improvise. Fortunately, for those of us who prefer bed to backyard during the dark hours, a meteor leaves a telltale trail that can be detected using radio waves. How does this happen and how can we detect it? Frying high Meteors that get into the Earth’s path appear to be moving pretty fast compared to the speeds at which humans operate. The Earth wobbles along around the Sun at something like 100,000km/h, so anything it happens to bump into is going to suffer in a way that can’t be ignored. An innocent grain of space dust suddenly finds itself rubbing against an increasingly dense collection of molecules around 100km above the ground. This friction quickly gets converted to heat so intense that electrons get stripped off some of the molecules in the vicinity, ionising a small patch of sky. The ionised matter may disperse in only a fraction of a second if the dust particle is small but larger ones generate more energy and it may take a few seconds before things are back to normal up there. The same process produces light, which is why we see the familiar streak when a meteor hits. Bigger ones (and we’re talking about ball-sized stones here) can even reach the ground before they vaporise completely, emitting lots of light and even sonic bangs on the way. Every few hundred years a really big one impacts spectacularly, becoming a useful source of hyperbole for bad TV docos (and even worse movies) about the Impending End of Civil- isation As We Know It. And every few million years... well, just don’t mention the dinosaurs! How can we detect that brief signature high in the atmosphere? At light wavelengths we could use our eyes or a camera, techniques which are fine as long as it’s dark and not cloudy and as long as the observer is looking at the right part of the sky and hasn’t fallen asleep, frozen to death or been divorced. Infrared detectors might also work but are subject to the same limitations as visible light detectors in cloud or sunlight. Further down the electromagnetic spectrum, things look more promising. Radio wavelengths aren’t swamped by solar interference during the daytime and can penetrate cloud. It’s Fig. 1: meteor trail reflecting FM signal to a receiver beyond the horizon. FEBRUARY 2001  7 even possible to use radar to pick up the ionised trails. A few observers still do but the ionised trails don’t reflect microwaves or UHF signals all that well. It turns out that some of the most strongly reflected frequencies are in the low VHF band, between 40 and 150MHz; the lower the frequency, the longer and stronger are the reflections. For decades, radio amateurs have bounced short messages off meteor trails but not everyone has the financial or technical resources to use specialised transmitters and receivers to detect meteor trails. Free radar, anyone? What we need is a reliable and powerful source of VHF signals and a simple receiving setup that can look after itself. No problem! All around the world there are thousands of 50100kW VHF transmitters pumping out FM radio signals 24 hours a day at between 88MHz and 108MHz. Despite the best efforts of antenna designers, not all of the signals transmitted by these stations travel near the ground. Some get radiated straight up and unless something gets in the way, they continue off into space to become interstellar electronic pollution (see Fig.1). At SILICON CHIP we’ve long maintained that old computer cases are too good for the tip . . . here’s proof – two receivers, using the XT’s power supply! Occasionally an aircraft reflects FM signals back to the ground, causing that familiar ghosting on TV screens and flutter in FM receivers’ sound (socalled multi-path reception). Aircraft are seldom more than 12km above the ground, so those signals aren’t reflected very far. The line-ofsight range of an FM station is a couple of hundred kilometres at best and an aircraft reflection may double this. But a meteor trail is anywhere from 60 to 120km above the ground, so they can reflect signals up to 2000km. There’s little chance of direct reception by a VHF receiver of a transmitter more than 500km away or even reflections from aircraft. Any signals received would have to come either from a meteor trail reflection or from sporadic ionisation of the ionosphere’s “E” layer. And it’s easy to tell the difference: sporadic E reception lasts for minutes or even hours, whereas meteor reflections seldom last longer than a couple of seconds. What about interference? TV video signals are (amplitude modulated) AM, so they are subject to interference from electrical noise. This can be bad in the lower VHF bands, especially if there’s a busy road or industrial complex nearby. FM receivers don’t have this problem because just about all AM interference is removed by their limiter stage. In practical terms, perhaps the most difficult source of interference to eradicate is cross-modulation in the receiver’s front end from nearby stations. In cities, this can be a serious challenge to overcome. Some observers use preamps with bandpass filters, while others opt for more subtle approaches. Mine was to set up the observation site at the bottom of a valley about 80km from the nearest powerful transmitter. Although not necessarily a cheap or convenient solution, it sure works. Choosing a transmitter A three-element Yagi cut for 89MHz, mounted seven metres above the ground. The preamplifier is protected from rain and sun by a piece of PVC drainpipe. The boom has been left a bit longer than necessary to make room for experiments with spacing, or maybe another element. 8  Silicon Chip There are hundreds of FM stations in Australia and New Zealand, many of which are very powerful. You may be lucky enough to have access to a comprehensive list of frequencies such as those published for scanner enthusiasts. Another approach is to look up the list of transmitters on the ABA’s website (www.aba.gov. au/what/bro-plan/broadcasting_stations/ind-ex.htm). There are lists sorted according to both frequency Fitting the receiver(s) into the computer case leaves lots of room for future expansion. and exact location. Your browser will need the Acrobat Reader plugin to read this info. When you’ve done that, take out your Jacaranda Atlas and try to find a transmitter somewhere between 750 and 1500km from your location, ensuring it uses a frequency well clear of local stations. This is not a trivial task but in places like the USA and Europe it’s almost impossible to find clear channels so consider yourself lucky. You then need to step through every channel on your digital FM receiver (all 200 of them) and make a note of those that seem to be free of interference. With luck, there will be at least one distant transmitter available on a clear channel. In my case, I eventually opted for ABC FM on 88.3MHz, transmitting from near Cootamundra with a power of 50kW ERP (Effective Radiated Power). Its transmitter at Mt Ulandra is about 980km from my observing location just north of Brisbane. Using The interface board, data and coax connectors inside the XT case. (NOT a pretty board.) a nationally networked station is a big advantage. In the early stages of setting up, its signal can be compared with the same content coming from a local transmitter. Otherwise it’s pretty hard to identify a station when the bursts last less than a second and are spaced minutes apart! By the way, there’s nothing wrong with observing two or three stations on the same frequency, as long as they’re all a long way from the receiver. In fact, this a very desirable setup because it increases the amount of data available for collection. The dish? Relax – you don’t need one. A suitable antenna is a three to 5-element Yagi cut to a frequency within a megahertz or so of the station(s) you’ve chosen as your “radar transmitter”. It only needs to be a few metres above the ground and pointing accuracy isn’t all that important either. Some observers elevate the front of the boom ten or twenty degrees if they’re observing transmissions from less than 600km or so but it didn’t make any difference in my case. There’s no shortage of software to help design a Yagi. A DOS-based package called Quickyagi (http:// www.raibeam.com/wa7rai.html) is well worth looking at. Or even easier: SILICON CHIP March 1998 issue had a design for a 5-element build-it-yourself Yagi antenna for the FM band. A larger antenna will bring in more signal but that may not be a blessing if your receiver’s front end gets swamped by other transmitters. More useful is a preamp at the antenna to boost the signal-to-noise ratio. For cheapness, reliability, ease of construction and performance it’s hard to beat the venerable VK5 2-metre preamp. Contact the VK5 branch of the WIA (see references for further details). The coils will need an extra turn or two so that they resonate in the FM band. (Don’t buy the relays for it Fig.2: a starting point for your data interface. Depending on your logging software’s requirements, you may need to reverse the op amp’s inputs. FEBRUARY 2001  9 Fig. 3: a typical day’s plot. More meteors are detected near dawn than dusk. – you’re not going to be transmitting!) See the references at the end of this article for an alternative design. Our photograph shows a homemade three-element Yagi cut for 89MHz, mounted seven metres above ground level. The preamplifier is protected from rain and sun by a piece of PVC pipe. The boom has been left a bit longer than necessary to make room for experiments with spacing, or maybe another element. Yagi construction needs only basic metalworking skills and the only design challenge I had was keeping water out of the preamp box since the rainfall at my location can be over two metres per year and usually arrives by the bucketful. Eventually, I used a small diecast aluminium box mounted inside a 30cm length of 90mm PVC drainpipe, capped by an overhanging “roof” of UV-resistant plastic sheet. The bottom has been left open to help with cooling and to drain any leaks. The entire assembly hangs from the antenna boom. All connections are coated in self-amalgamating tape and neutral cure silicone sealant. Use decent quality coax for the run to your receiver and don’t waste money on cheap connectors. Avoid the clunky old PL239 and SO239 types: BNC or F styles work well and are much neater. The expense of type N connectors is not warranted at these frequencies. Choosing a receiver If you have a high performance digital communications receiver you can spare for 24 hours a day, 365 days a year, then by all means tune it to the 10  Silicon Chip transmitter of your choice and leave it. The rest of us need something a little less capital-intensive, which is where a talent for sniffing out recycled treasure is vital. Most car radios have excellent sensitivity and if you’re using a preamp at the antenna, their signal-to-noise ratio isn’t a big issue. Garage sales, school fairs and car wreckers offer a selection of junked car radios. But choose a digital one: nothing else will do. (If you need convincing, try tuning an analog receiver to a station that’s irregularly audible for 200 milliseconds once every five minutes or so.) Make sure the FM section is working and don’t pay too much for it. Old hifi FM receivers may be OK but they must be digital and sensitive. I was lucky enough to buy two matching Pioneer units for $10. Experience has shown that nearby lightning strokes can make a real mess of the meteor data, so a future enhancement will use the spare (and desensitised) receiver to monitor an unused frequency in the AM band and log local thunderstorm activity. If you have a frequency counter or digital VHF communications receiver, it’s worth checking the frequency accuracy of the car radio before doing anything else. The local oscillator frequency should be 10.7MHz away from what ever frequency the radio shows on its display, usually higher. (For example, if the display shows 100.0MHz, the local oscillator should be running at 110.700000MHz.) If the frequency is more than a couple of kHz off, try a ceramic capacitor in the 2.2 - 47pF range across the crystal, to pull it back into line. I fitted a receiver into an old desktop XT computer case rescued from our suburb’s annual roadside junk collection. It has a good power supply, the case provides plenty of ventilation and there’s heaps of room to mount everything. It also looks slightly less ugly than a nest of cables and boxes side by side and makes the whole setup easy to transport. The antenna lead attaches to a BNC socket in one of the card slots in the back panel and the two-wire data cable to the computer leaves from the slot containing the interface card. All 5V and 12V power wires connect to a chunky great terminal block mounted down the middle of the computer case. That way it’s easy to fiddle with various sections without resorting to a soldering iron and it’s all very accessible. Power for the masthead preamp also comes from the XT supply via some RF filtering and is fed up the coax in the usual way. Connect the computer’s internal speaker to one of the receiver’s audio channels so you can monitor the channel when necessary. Most of the time you’ll want the audio turned right down. Set the mode switch to “mono” and if there’s a “Local/DX” control, set it to “DX”. If the receiver defaults to a particular frequency on power-up, make sure you configure this to be the one you’re observing so that it will be able to keep observing after power failures. Getting a signal out of the receiver You’ll need some kind of data logger to record the time when the system picks up a signal. That requires a digital output, a feature I’ve yet to see on any car radio, so it’s time to open the case and start poking around with a multimeter or scope. You’ll be looking for a mute signal or failing that, an AGC line. This may be easy to find if you have a circuit diagram but it’s unlikely you’ll be that lucky. Take some time to look at the circuit board layout. First, try to identify the RF section (the antenna lead is a giveaway), then the frequency synthesiser (probably near a crystal) and audio sections. The signal you want will probably not be in these sections, so now you know where not to start. It’s more likely to be near a large IC containing the IF and demodulation components. Just measure the voltage on each pin methodically. Tune in a local signal and try to find a pin where the voltage level changes when you switch to an unused frequency. It’s easy to be fooled by voltages that change gradually as you shift frequency: these control the local oscillator. My Pioneer receiver didn’t appear to have a mute line but the AGC wasn’t hard to find. It varied from 1.4V with no signal down to 50mV on a very strong station. Data logging Although there are alternatives, the obvious way to go here is to use a computer. Any old computer will do, as long as you can keep its RF interference out of the receiver. Even the slowest XT or early Mac would be fine. The early Macs featured excellent RFI shielding, which makes them quite attractive for this application. (If you intend using a Mac or Linux system, bear in mind that supplies of readyto-go shareware for observing meteors seem to be pretty sparse, if they exist at all, so you’ll be writing your own.) All your computer needs is a reliable clock, a few megabytes of disk space or even just a floppy and an operating system that doesn’t fall flat on its face twice a day. Avoid operating systems like Win 95/98, which are much too unstable for this kind of application. Use DOS as early as version 3.3 or if you must use Windows, opt for Windows for Workgroups. Systems 6 or 7 should be fine on older Macs. Another advantage of an older OS is that, in the event of a power failure, you can configure your machine to reboot itself in seconds. Display quality is irrelevant, because 99% of the time the monitor won’t even be switched on. Low power consumption is important because this device is going to be on all the time. An old laptop running from a float-charged battery would be ideal. Data interface There’s no need to rush out and buy an A/D conversion board. All we’re dealing with here is an on/off signal that needs to be sampled 100 Fig. 4: Leonid shower 15-17th November 2000 (freq = 88.3MHz). Area observed: NE NSW. The red vertical lines show the number of meteors detected per 10 minute period. The green vertical lines show midnight local time. FEBRUARY 2001  11 times per second at the most. This is not leading-edge stuff, so you can interface to the computer through just about any port. I chose the games port as it’s electrically pretty basic, has multiple data lines and happened to be available on my machine, but most observers’ setups use a COM port. If you’re using a Mac, its serial port would be the obvious choice. To tell the computer there’s a signal present we need some kind of threshold detector. Its trigger point has to be set to an arbitrary level, ideally just above the receiver’s background noise. Too low a threshold leaves you with megabytes of false data, while a higher threshold ignores data from weak reflections. As with any piece of real-world equipment, judging where to set it is an art based on experience. A suitable comparator circuit can be based on the design on page 75 of the December 2000 issue of SILICON CHIP. Whether you use an inverting or non-inverting comparator depends on the logic level required by your data logging software. An alternative comparator circuit suggestion is shown in Fig.2. The three diodes in series act as a 2.1V zener, preventing minor offset voltage variations in the op amp from affecting the optocoupler. The comparator circuit was built on a piece of scrap Veroboard and uses power from the XT supply. It’s well worth including an optocoupler on the data output to isolate the receiver from your computer. Keeping computer noise out of the receiver I could say I was lucky to find a cheap DEC 486 that was screened by a high-quality metal case but actually it took several weeks of searching classifieds and making phone calls to find one of that quality at a sensible price. Was it worth it? Unquestionably! Any computer with a unscreened plastic case will need lots of work to keep its RF emissions inside the box. As it was, even the superbly engineered DEC required a ferrite toroid on the data lead (scrap figure-8 speaker cable) as it left the case, along with a choke and filter capacitors at the receiver end. It also helped a lot to put the receiver on the opposite side of the room, as far away from the computer as possible and to keep the data lead well away from other leads. Yes, it would have been a lot smarter to use shielded data cable but I’m a slow learner. Software Data logging software is not all that difficult to write, though a medium level of programming ability is helpful. It needs to record when each event occurs and its duration. This means sampling the digital output of the receiver at regular intervals. Most observers sample every 10 to 40ms which is within the capabilities of even the slowest machines. It’s important to save to disk at regular intervals so that a minimum of data is lost when (not “if”) there’s a power failure or system crash. Save your data in a format that doesn’t leave you with hundreds of megs of data to wade through each month. It may be fun the first time but most people soon tire of unnecessary drudgery. Aim to keep your monthly files under 500Kb; that way they can be saved on a floppy with room to spare and then on newer systems you could set your BIOS to turn off the hard disk once the program is running. My software uses 16 bytes to record the time (expressed as the number of seconds after midnight on 1 January 2000) and the length of the burst in milliseconds. This is probably more detail than is needed but it only comes to a couple of hundred kilobytes a month and leaves open the opportunity to analyse the data in great detail should this be necessary. A conversion program summarises this data in a simple comma-separated variable (CSV) text file. Part of a typical summary looks like this: 355530, 355540, 355550, 355560, 355570, 355580, 355590, 355600, 355610, 355620, 0.012, 0.002, 0.003, 0.001, 0.005, 0, 0, 0.005, 0.001, 0.006, 11, 4, 5, 3, 5, 0, 1, 5, 2, 2, 0.2 0.025 0.075 0.025 0.2 0 0.025 0.175 0.025 0.35 The first column shows the start of the observation period in minutes since midnight UT on 1 January 2000. The second column shows the total duration of reflections during that period in seconds. The third column shows the number of hits detected during the period. The fourth column shows the duration of the longest reflection during the period, in seconds. Other observers directly record their data in this format, which is all that NASA’s survey requires. Re- Useful sources of inspiration and information Global MS-Net (details of observers’ setups): http://www-space.arc.nasa.gov/~leonid/Global-MS-Net/GlobalMSNet.html Monthly summaries: rec.radio. amateur.space newsgroup SILICON CHIP March 1998 issue: Building a 5-Element Yagi Antenna for FM Radio ARRL Handbook (any recent edition) for meteor scatter background info and tips on building Yagi antennas International Meteor Organisation (IMO): http://www.imo.net/radio/ Ilkka Yrjola’s meteor site (includes a preamp design and interfacing info): http://www.sci.fi/~oh5iy/ Society of Amateur Radio Astronomers (SARA): http://www.bambi.net/sara.html Meteor scatter communication and background: http://www.borg.com/~warrend/metburdu.html ABC FM station frequencies (sorted lists): www.geocities.com/meteorcount/abcfm.htm Wireless Iinstitute of Australia, VK5 Branch (2-metre preamp kit): WIA Equipment Supplies Committee, PO Box 789,   Salisbury SA 5108. http://www.sant.wia.org.au/esc.htm 12  Silicon Chip member that Universal Time is always used, so you must set the logging computer’s clock accordingly. Data analysis More talent is needed for writing data analysis software. Mere mortals can write something to produce simple monthly summaries such as the one in Table 1, while those with time and talent can create applications that show fancy graphs and hourly distributions. When you have a few days of observations on file, look for a variation in counts showing a peak at dawn and a trough around sunset. Fig.4 shows a typical day’s plot. As the Earth rotates on its axis, it encounters more cosmic debris around sunrise. By sunset you’re looking into the Earth’s wake, so there will be much less material to bump into. This daily cycle is a good way of confirming you really are observing meteors and not a neighbour’s arc welder in action. If all the fun of writing your own data analysis software seems like something you could do without, just use a spreadsheet to analyse your data. Versions of Lotus 123 are available as freeware these days and have powerful graphing and date manipulation functions. Another excellent freeware package is StarOffice, which is available for Linux as well as Windows. On my setup, Lotus is quicker to load and remarkably stable, so that’s what I use. All spreadsheet programs readily import CSV files. The graph in Fig. 4 was created from a CSV file using Lotus 123. Reliable data logging software for DOS is available from the website of Finnish meteor guru Ilkka Yrjola (www.sci.fi/~oh5iy/), along with masses of far more useful information than I could possibly provide here. Another good package with useful self-adjustment features is Meteor (radio.meteor.free.fr/us/accueil. html), though it helps if you can read documentation in French. Its companion analysis package Colorgramme (pierre.terrier.free.fr/ meteor/us/art.htm) is also available and this pair may well meet all your needs. R_Meteor (sapp.telepac.pt/coaa/r_ meteor.htm) is designed to be used with WinRadio cards or sound cards connected to a communications Table 1: Part of a typical observer's monthly summary 2000 Sep UT 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 —————————————————————————————————— 00 23 18 14 12 38 48 21 30 30 4 12 4 8 6 22 01 76 61 6 127 13 17 16 14 7 36 9 11 14 22 40 02 13 17 128 24 118 3 22 24 9 7 20 15 17 8 36 03 13 6 25 2 80 14 33 41 22 7 31 54 67 9 25 04 13 15 20 31 21 20 10 10 17 3 47 20 36 9 25 05 5 31 33 33 9 14 15 5 3 8 3 4 18 6 11 06 7 18 31 13 15 11 28 13 10 5 9 21 10 26 5 07 13 10 29 11 7 53 17 7 10 4 13 33 55 4 9 08 17 24 25 13 12 62 28 4 7 7 10 35 7 6 10 09 20 11 19 66 30 20 28 43 24 15 34 12 13 14 14 10 23 15 21 20 14 37 37 8 27 22 19 32 12 51 9 11 52 56 77 42 37 52 41 98 8 27 20 25 16 23 44 12 65 60 17 47 58 26 851? 24 27 19 5 12 20 31 23 13 27 46 26 18 22 36 839? 10 8 16 258 13 13 6 16 14 42 40 87 18 21 31 67 19 57 30 15 13 9 5 7 15 63 19 77 15 182 55 35 38 18 17 60 20 17 24 97 16 24 102 64 62 75 64 48 31 44 45 12 57 28 180 37 17 48 80 62 96 57 58 56 29 56 21 34 102 93 24 36 18 170 75 147 33 40 47 43 45 76 47 20 22 53 165 31 19 106 56 *E* 49 32 61 30 47 54 41 145 74 33 59 99 20 78 118 62 49 45 35 28 45 111 70 36 54 133 118 106 21 36 90 100 65 73 54 431? 41 78 60 42 128 23 57 119 22 105 50 84 80 61 36 29 16 38 41 87 107 29 34 10 23 41 16 19 91 28 33 14 19 20 9 22 22 13 17 17 ——————————————————————————————————— *E*denotes probable sporadic E ? denotes possible sporadic E (As published in the rec.radio.amateur.space newsgroup.) receiver tuned to a shortwave AM station. It displays the Doppler shifts of ionisation trails and other moving objects that cause reflections. (You can also use it to detect aircraft thousands of kilometres away but that’s another subject altogether.) If you can’t find a suitable VHF transmitter to monitor, shortwave techniques could be a good alternative. World Distance, by Eric J. van Drop, is a handy little shareware utility for Windows that calculates the distance between any two points on the Earth’s surface. Visit www.zdnet. com/ downloads/ and search for “distance”. Is it worth the effort? It certainly has been for me. I get huge satisfaction from making something unique from old bits and pieces. At times I had to brush up on theory I should never have forgotten and that can’t be a bad thing. From a geek’s viewpoint it sure is satisfying to hear the hum of a good computer in the background as it logs fiery events happening hundreds of kilometres away in the outer reaches of the atmosphere. Data pours in each day and at the end of the month there’s the challenge of matching up the summaries and graphs with various meteor showers, turfing out the bits affected by sporadic E and thunderstorms and then comparing it with those of other observers around the world. For software addicts, there’s that added attraction of knowing your analysis package will always have room for one more feature. But do remember that observing meteors is not a short-term proposition. Long runs of data spanning over several years, rather than weeks or months, are vital. While it’s exciting to hear those first bursts from the edge of space, you must be seriously committed to a sustained effort if your data is to be of any real use. By all means give it a try. Scour the Web and read widely before you begin and take it one step at a time. There is precious little specific help available but that makes it all the more satisfying when your system finally comes together. SC FEBRUARY 2001  13 An Easy-To-Build, Compact and Cheap Model Train Controller Li’l Pulser is a little power-house of a train controller that you can build for around $45. It is designed to work with any standard 12V model train supply or even a 12V battery charger. It is rated up to 2A and features full pulse power control for very smooth operation at all speeds. By JOHN CLARKE & LEO SIMPSON 14  S 14  Silicon ilicon C Chip hip then it takes off like a rocket. Then you wind back the control to get the speed back to something reasonable and then it stops or jerks because the track is not real smooth or because it is a little dirty. After half an hour of this, they (or you) are likely to pack the whole train set and not think about it for another few months. Smooth running pulse power T In model railway jargon, “pulse power” is what makes this little train controller such a good performer. This is essentially the same thing as the “pulse width modulation” (PWM) or “switchmode” that is used in the highly efficient switching power supplies used in all computers and TV sets. However, the Li’l Pulser train controller doesn’t use switchmode operation just to get high efficiency, although that is a side benefit. No, the real reason for using switchmode is so that we can apply relatively high voltage pulses, up 17V or more, to the track, even at low throttle settings. These voltage pulses are much more effective at starting and running a loco, particularly at low settings, because they are better at overcoming track resistance and motor & gearbox stiction (ie, static friction). his little train controller incor- you!) got a new train set from Santa. porates most of the best fea- You’ve already discovered the limitatures of our popular train con- tions of typical (ie most commercial!) trollers of the past but does it all in train controllers and would like to ima compact case and at low cost. The prove it – without breaking the bank? basic speed control uses a readily Typical low cost rheostat or series available power Mosfet and the for- transistor train controllers really ward/reverse switching is done with cannot deliver realistic control of Features a relay. your trains. The loco often starts off Apart from pulse power and backSimple? You bet. like a startled kangaroo and slows EMF monitoring for very good speed Should you build it? Well unless down whenever there is the slightest regulation, the Li’l Pulser has overyou already have a previous SILICON incline. load protection, an over-current alarm CHIP train controller design, then this This is really frustrating if you are and three LEDs to indicate Power On, is a good place to start, especially if trying to operate the train smoothly. Reverse Direction and Track Voltage. you have a small layout and don’t First, you have to wind up the conLi’l Pulser is mounted in a compact want anything too elaborate. trol just to get the loco to start and plastic case measuring just 140mm This is especially true wide, 35mm high and if you just have a basic 110m deep. L’il Pulser Features train set with a locoOn the front panel it has * Pulse power for smooth low speed operation motive, a few carriages two rocker switches, one or wagons and a circle for power and one for For* Speed control pot of track. The first thing ward/Reverse switching, * Power on indication to do is ditch the basic a small Throttle knob and * Track voltage LED indication controller it came with the three LEDs mentioned and build this SILICON above. The Track Voltage * Reverse indicator CHIP design. It will allow LED is a bi-colour unit * Overcurrent alarm your train to start and which shows green for the * Excellent low speed control run much more smoothly forward direction and red and you will have less for reverse. The reverse * Speed regulation problems of unreliable LED is orange, to give you * Compact size operation due to dirty an extra indication when track. the train is going back* Maximum current limited to 2A. Perhaps the kids (or wards. FEBRUARY 2001  15 There are four binding post terminals on the rear panel, two for the input power and two for the leads to the track. You can use a train power supply, a 12V battery charger or a 12V DC plugpack with rating of at least 1A, to power the Li’l Pulser. Circuit description In contrast with some of our previous train controllers, the circuit for the Li’l Pulser is relatively simple. It uses two low-cost ICs, an economy Mosfet to do the current switching to the loco’s motor and a relay for the Forward/Reverse switching. The circuit is shown in Fig.1. As already noted, the power for the circuit can come from the power supply you already have with your train set or layout. It will comprise a 12V (nominal) transformer and a full wave bridge rectifier (4 diodes). Alternatively, you can use a low-cost battery charger which will also comprise a transformer and bridge rectifier or you can use a 12V DC plugpack with a rating of at least 1A. The DC voltage from your chosen power supply is applied to the circuit via diode D1 to two 2200µF electrolytic capacitors. The resulting filtered DC supply is likely to be at least 17V and may be higher, depending on the transformer characteristics. Switch S1 and diode D2 pass the DC voltage through to the 3-terminal regulator, REG1, which produces a 12V regulated supply for the circuit. LED1 indicates that power is on. The 17V is used to power the train motor and is switched via the relay contacts and Mosfet Q1. Q1 is switched on and off at about 180Hz to control the average track voltage. The 2-pole 2-position relay is connected as a change-over switch so that the track voltage can be reversed. In the normal condition, with the relay off, +17V is applied to the anode of the green LED within LED3 to indicate forward operation. Switch S2 is the reversing switch and it energises the relay coil. When this happens, the +17V is now applied to the anode of the red LED and LED2 Fig.1: the circuit uses a dual op amp (IC1) and a dual comparator (IC2) to provide gate drive to the Mosfet Q1. It has pulsed output and feedback from the motor to provide good speed regulation. 16  Silicon Chip Fig.2: demonstrating the action of IC2a. The top trace is the sawtooth waveform at pin 6 while the horizontal trace intersecting the sawtooth represents the voltage from VR1. The pulse waveform on the bottom trace is the output at pin 7. There is a positive pulse every time the constant DC voltage (horizontal trace) from the throttle pot is above some part of the sawtooth waveform. This throttle setting gives fairly narrow pulses and this would correspond to a low speed setting. Fig.3: this demonstrates a higher throttle setting. As you can see, the pulses from pin 7 (bottom trace) are much wider than shown in Fig.2, corresponding to a higher speed setting. is powered to indicate the reverse direction. Diode D6 is connected across switch S2 to quench the reverse voltage spike produced when the relay is switched off. The rest of the circuit is used to generate the gate drive signals for Q1, the MTP3055 Mosfet. Op amp IC1b is connected as a triangle wave generator. It charges and discharges the .022µF capacitor at pin 2 via the 220kΩ resistor at pin Fig.4: these waveforms show Q1 driving a resistive load. The top trace is the gate signal from pin 7 of IC2a while the bottom trace is the signal at the drain of Q1. Each time the gate signal goes high, the Mosfet turns on and so its drain voltage drops to virtually zero. Fig.5: the output waveform changes drastically when a 12V locomotive motor is connected instead of the resistive load in Fig.4. While the top trace showing the gate pulses is much the same, the lower trace shows that the drain voltage is now “messed up” by the motor back-EMF. The drain voltage still drops to zero at each positive gate pulse but now in the “off” times we see the motor voltage and its commutator hash (ie, the noise from its brushes). 1 to produce a sawtooth waveform at around 180Hz. The top trace of the scope waveform of Fig.2 shows the result. It is fed to the inverting input, pin 6, of comparator IC2a. IC2a also monitors the speed pot (VR1) wiper at pin 5, its non-inverting input. When the speed pot wiper voltage at pin 5 is above the sawtooth voltage at pin 6, then the output at pin 7 will go high. Fig.2 demonstrates this action. The horizontal trace intersecting the sawtooth represents the voltage from VR1. The pulse waveform on the bottom trace is the output at pin 7. As you can see, there is a positive pulse every time the constant DC voltage (horizontal trace) from the throttle pot is above some part of the sawtooth waveform. Note that this result gives fairly narrow pulses and this would correspond to a low throttle setting. What happens when we wind the FEBRUARY 2001  17 Notice too that while the gate voltage amplitude is about 12V peakpeak, the pulse voltage at the drain of Q1 has an amplitude of above 17V. This is what we expect because the voltage applied to one side of the motor is the nominal DC input of 17V. Fig.5 shows a very different picture when a 12V locomotive motor is connected instead of the resistive load. While the top trace showing the gate pulses is much the same, the lower trace shows that the drain voltage is now “messed up” by the motor backEMF. The drain voltage still drops to zero at each positive gate pulse but now in the “off” times we see the motor voltage and its commutator hash (ie, the noise from its brushes). We’ll talk more about back-EMF later in this article. Overload protection Fig.6: there is not much wiring inside the case. You will need to bend over the LEDs so that they poke through holes in the front panel. Fig.7 (below) is the same-size artwork for the front panel, lined up with the controls in the drawing above. This artwork can be also be used as a drilling template. throttle up? This is demonstrated in Fig.3 and as you can see, the pulses from pin 7 (bottom trace) are now much wider, corresponding to a higher throttle setting. By the way, if you are attempting to duplicate these measurements on a scope, you will find that when you vary the setting of VR1 the sawtooth waveform will move up and down on the scope screen, reflecting that its DC level is changing. This is normal and is a function of 18  Silicon Chip another part of the circuit, to do with the back-EMF monitoring. We’ll get to that in a moment. So the output pulses from IC2a drive the gate of Mosfet Q1 and this drives the motor. Fig.4 shows Q1 driving a resistive load. This time the top trace is the gate signal from pin 7 of IC2a while the bottom trace is the signal at the drain of Q1. Each time the gate signal goes high, the Mosfet turns on and so its drain voltage drops to virtually zero. Comparator IC2b provides the overload current protection. The motor current passes through Q1 and the 1Ω resistor in series with its source (S) electrode. The voltage drop across this 1Ω resistor is therefore directly proportional to the motor current. However the voltage is quite “spikey” and needs to be filtered via a 47kΩ resistor and 0.1µF capacitor before being applied to pin 2 of IC2b. -The non-inverting input at pin 3 is connected to a reference voltage derived from trimpot VR3, the “current set” control. If the voltage at pin 2 exceeds pin 3, the output at pin 1 goes low to shunt pin 7 of IC2a to ground via diode D3. When this happens, it kills the gate drive to Q1. What actually happens in an overload condition is that IC2b tries to shut down the gate drive to Q1 and this has the effect of cutting the overload current. However, if the output current is reduced, the voltage across the 1Ω resistor is reduced and so IC2b can no longer cut off the gate drive pulses. Eventually we have a “fight” condition between IC2a and IC2b and the current is limited to 2A, as set by VR3. IC2b also drives a piezo alarm to indicate when current limiting is occurring. Motor feedback Why do we need feedback from the motor? Answer: because the motor motor speeds up, it will generate more voltage and so the voltage we measure will be lower. So while the back-EMF may appear to fall with rising speed, it is in fact increasing. The back-EMF voltage is monitored by error amp IC1a. It amplifies the voltage by a factor of close to 2.1 and its variable DC output is used to control the pin 3 threshold voltage of the IC1b triangle generator via a 100kΩ resistor. So as the motor voltage drops, the back-EMF decreases, and the DC level from pin 7 of IC1a drops. This causes the DC level of the sawtooth generated by IC1b to drop. This will mean that more of this waveform is below the speed setting pot. This will increase the pulse width and drive the motor harder to regain the original speed. This provides a control loop to maintain motor speed when under load. VR2 is there to give some degree of adjustment for different motor characteristics. It is set so that pin 7 of Inside the case as viewed from the front (above) and the rear (right). The piezo buzzer is stuck to the case lid with super glue. generates a back-EMF which is directly proportional to its speed. We can use the back-EMF as a feedback signal to make sure that the circuit more or less maintains a constant motor speed for a given throttle setting, regardless of variations in load. Let’s explain that a little more. The vast majority of model locomotive motors are permanent magnet types which means that they work as a generator when they are spun. More to the point, if they are spinning, they generate a back-EMF all the time, whether an external voltage is applied to their terminals or not. We have already seen this effect in the scope waveforms of Fig.5. When Mosfet Q1 is off, we see the motor back-EMF and the commutator hash. This voltage (at the drain of Q1) is monitored via diode D5; when Q1 is on, D5 is reverse-biased and when Q1 is off, D5 conducts and the back-EMF from the motor is fed to a 1µF capacitor via a voltage divider consisting of two 4.7kΩ resistors. Note that we are monitoring the back-EMF generated by the motor from its negative terminal, ie, at the drain of Q1 which will be negative with respect to the +17V rail. Hence, at low speeds, the back-EMF will be close to the 17V supply. As the IC1a is at about mid supply voltage at around 6V when a motor is connected. Construction The Li’l Pulser Train Controller is assembled onto a PC board codFEBRUARY 2001  19 Parts List: L’il Pulser Train Controller 1 PC board, code 09102011, 117 x 102mm 1 front panel artwork, 134 x 27mm 1 instrument case, 140 x 110 x 35mm (Jaycar HB-5970 or equivalent) 1 mini PC board relay 12V 5A DPDT (RLY1) (Jaycar SY-4062 or equiv.) 1 piezo siren (DSE L-7024 or equivalent) 2 mini rocker switches (S1,S2) (Jaycar SK-0975 or equivalent) 2 white banana sockets 1 red banana socket 1 black banana socket 1 mini TO-220 heatsink, 19 x 19 x 10mm 1 knob 16mm diameter 6 M3 x 6mm screws and nuts 10 PC stakes 1 200mm length of 0.8mm tinned copper wire 1 50mm length of twin light gauge hookup wire 1 50mm length of medium duty black hookup wire 1 25mm length of medium duty blue hookup wire 1 25mm length of medium duty red hookup wire Semiconductors 1 LM358 dual op amp (IC1) 1 LM393 dual comparator (IC2) 1 7812 12V regulator (REG1) 1 MTP3055A or MTP3055E power Mosfet (Q1) 1 1N5404 3A diode (D1) 4 1N4004 1A diodes (D2,D4-D6) 1 1N914, 1N4148 switching diode (D3) 2 5mm red LEDs (LED1,LED2) 1 5mm red/green bicolour LED (LED3) Capacitors 2 2200µF 25VW PC electrolytic 1 10µF 25VW PC electrolytic 3 10µF 16VW PC electrolytic 1 1µF 16VW PC electrolytic 2 0.1µF MKT polyester (code 100n or 104 ) 1 .022µF MKT polyester (code 22n or 223 ) 1 .01µF MKT polyester (code 10n or 103 ) Resistors (0.25W 1%) 1 1MΩ 1 220kΩ 5 100kΩ 3 47kΩ 1 12kΩ 1 10kΩ 1 6.8kΩ 4 4.7kΩ 3 2.2kΩ 1 1kΩ 1 10Ω 1 1Ω 5W 1 10kΩ linear 16mm PC mounting pot (VR1) (code 10k or 103) 1 10kΩ horizontal trimpot (VR2) (code 103) 1 2kΩ horizontal trimpot) (VR3) (code 202) ed 09102011 and measuring 117 x 102mm. The PC board is housed in a small instrument case measuring 140mm wide, 35mm high and 110m deep. The front panel artwork panel measures 134 x 27 mm. You can begin construction by checking the PC board for shorts between tracks and breaks in the copper pattern. Check your PC board against the published pattern. Check for hole sizes on the PC board. You will need 1.5mm holes for diode D1, for the speed pot and relay. 20  Silicon Chip 3mm holes are needed to secure the tabs for REG1 and Q1 and for the four corner mounting holes on the PC board. The complete wiring diagram is shown in Fig.6. Install the resistors (except the 1Ω 5W type) and wire links first, using the accompanying resistor table as a guide to the colour codes. It is a good idea to use a digital multimeter to check each value as well. Then install the ICs, the diodes and trimpots, taking care to put the correct component in each place with the orientation as shown. Then you can install the 1Ω 5W resistor, the relay and potentiometer. Leave about 1mm clearance between the PC board and 5W resistor body for cooling purposes; if mounted down on the PC board it could also burn or char it. REG1 and Q1 are mounted horizontally and secured with M3 screws and nuts. Q1 is also mounted onto a mini heatsink. Now install the capacitors, using the codes listed in the parts list as a guide to their values and be sure to orient the electrolytic capacitors correctly. Note that the 10µF capacitor at the input terminals of REG1 should have a rating of 25VW, not 16VW. Fit PC stakes at the external wiring points and then the LEDs. The LEDs should be mounted with sufficient lead length to bend them over and be inserted through the front panel holes. Next, the PC board can be installed in the case. Remove all the internal pillars on the base of the case, using side-cutters, except for those at the four corners. The PC board is secured with M3 screws into the corner pillars. Drill holes in the rear panel for the four binding post terminals and secure them in position. Mark out the front panel, using the panel artwork as a guide to positioning the holes. Drill the holes for the LEDs and the 10kΩ potentiometer and drill small holes around the perimeter of the switch mounting holes and file them out to make suitable rectangular cutouts. Now install the front panel components. Clip in the two switches, secure the pot with its nut and bend the LEDs to insert into their respective holes in the front panel. The pot shaft will need to be cut to length to suit the knob. A 6mm hole should be drilled the case lid for the piezo siren’s sound outlet. Make sure it is positioned 28mm back from the front edge and 61mm to the left of the right hand edge of the lid. This will allow it to be glued to the lid and not foul the pot or other components on the PC board. We glued ours in position with super glue. Wire up the switches, rear panel sockets and piezo siren as shown in the wiring diagram. Resistor Colour Codes     No.  1  1  5  3  1  1  1  4  3  1  1 Value 1MΩ 220kΩ 100kΩ 47kΩ 12kΩ 10kΩ 6.8kΩ 4.7kΩ 2.2kΩ 1kΩ 10Ω 4-Band Code (1%) brown black green brown red red yellow brown brown black yellow brown yellow violet orange brown brown red orange brown brown black orange brown blue grey red brown yellow violet red brown red red red brown brown black red brown brown black black brown 5-Band Code (1%) brown black black yellow brown red red black orange brown brown black black orange brown yellow violet black red brown brown red black red brown brown black black red brown blue grey black brown brown yellow violet black brown brown red red black brown brown brown black black brown brown brown black black gold brown Testing Now is testing time. As mentioned, the train controller is powered from a train supply or a battery charger. Or you can use a DC power supply set to deliver around 17V DC. It should be rated to deliver 3A or more. The DC is applied to the red and black binding post terminals on the rear panel of the Li’l Pulser. Switch on and check that there is 12V between pin 8 and pin 4 on both IC1 and IC2. Now wind up the throttle pot and check that the track LED lights up green; it should get brighter as you wind up the throttle. Switch to reverse and the reverse LED should light and the track LED should change colour to red. Connect your digital multimeter between pin 3 of IC2b and ground (pin 4 of IC2b), with the throttle pot wound up so that the track LED is lit. Adjust VR3 for a reading of 2V DC. Set VR2 to mid setting. Now short the output terminals and wind up the speed pot. Check that the piezo alarm sounds to indicate a short. Now wind down the speed pot. Do not leave the controller short circuited for very long or Q1 and the 5W resistor will become very hot. Connect the train controller to length of track and test that your loco runs smoothly with the control. VR2 should be adjusted while you measure the DC voltage between pin 7 of IC1a and ground (pin 4). Adjust VR2 for a reading of 6V. Note that this adjustment must be done with a loco connected across the track. And that’s it: your controller is now SC complete. Have fun! The rear of the case has four terminals. The red & black terminals are for the unfiltered DC input while the two white terminals connect to the track. Fig.8: actual size artwork for the PC board. FEBRUARY 2001  21 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.dse.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.dse.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.dse.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.dse.com.au MIDI-Mate An easy-to-build MIDI interface for PCs OU’VE PROBABLY HEARD of Want to use your PC to control Y the MIDI system because it’s been around for quite a few years now. That acronym stands for “Musi­cal InMIDI synthesisers, key­boards strument Digital Interface” and it was originally designed to allow electronic & instruments? With the right musical instruments, keyboards and other “controllers” to communicate with each other. Then when computsoftware, most PCs make good ers and dedicated music sequencers came along, it was logical to use MIDI sequencers for electronic music to hook them up as well. Essentially, MIDI is a fairly low-tech based on serial data commumaking. You’ll also probably need system, nications at 31,250 bits per second, current loop circuit. It’s a this little MIDI interface, because inbit alike5mAa faster version of the system used to connect teleprinter machines, most sound cards don’t provide a about 40 years ago. You can find out more about MIDI and how it works in the accompanying panel – “MIDI In full MIDI port. A Nutshell”. By JIM ROWE 26  Silicon Chip PCs & sound cards Modern PCs make good sequencers Fig.1: the circuit uses two low-cost ICs – a 6N138 optoisolator and a 74HC04 hex inverter. The optoisolator provides the correct isolation for the MIDI IN socket, while the inverter stages buffer the signal outputs from the sound card. Please note: It has been found that the MIDI-in port does not work with all PC sound cards. The simplest solution is to increase the value of the resistor in series with LED1 to 680Ω (from 330Ω) and then fit a 470Ω resistor on the underside of the PCB in parallel with the series combination of LED1 and the 680Ω resistor, ie, from the +5V rail directly to pin 13 of IC1. for electronic music. That’s because they have plenty of memory and “crunch power” for editing and manipulating music files, plus lots of hard disk space to store them. All you need for a PC to control a bunch of instruments is a MIDI port – and once you have this, you can also use it to hook up music keyboards, drum machines and other “controllers” to feed music into the PC as well. Ironically, most PC sound cards already provide what’s usually called a MIDI port (also known as an MPU401 port) but it’s really only “half” of such a port. It includes an addressable UART designed to send and receive data at the correct 31.25kb/s, for example. However, the UART’s serial input and output operate at logic voltage levels and the connections are simply made available at two pins on the card’s game port. There’s no attempt to provide the correct current-loop interface or the standard MIDI connectors needed to communicate with normal synthesisers, instruments or keyboards. So that’s what this little “MIDI-Mate” project provides: the extra circuitry needed to provide a PC sound card with a full MIDI port. It gives your PC and its sound card a properly isolated MIDI input, two standard MIDI outputs and also a MIDI THRU output which provides a buffered replica of the MIDI IN signal (for driving other instruments). There’s also a couple of LED indica­tors on the front panel, to let you easily monitor the activity on the MIDI IN/THRU and MIDI OUT sides of the interface. The complete circuit uses only two low-cost chips, plus a handful of resistors and other parts. Everything fits on a small PC board, including the MIDI connectors, and it’s all housed in a compact low-profile plastic instrument case. The interface circuitry needs only a few tens of milliamps at 5V DC and this is sourced “free” from the PC itself – via the ribbon cable which connects the MIDI-Mate to the sound card’s 15-pin game port socket. Incidentally, a duplicate 15-pin socket is provided on the end of the ribbon cable, which extends back out from the MIDI-Mate case. This allows you to still use the game port to connect a joystick or similar for playing games, even when the MIDI-Mate is connected. Circuit details Fig.1 shows the circuit details for the MIDI-Mate. As you can see, there are only two chips involved: a 6N138 high-speed optocoupler (OPTO1) and a 74HC04 hex inverter (IC1). As stated above, both chips are run from a +5V supply rail which is obtained from the PC sound card – via pins 1, 8 and 9 of the game port connector (via the ribbon cable and CON1). The 10µF capacitor is used to provide a local peak current reservoir. Optocoupler OPTO1 is used to provide the correct isolation for the MIDI IN socket (CON2), which is wired in the standard way with pins 4 and 5 connected to the optocoupler’s LED via a 220Ω series resistor. Diode D1 protects the LED against accidental polarity reversal (from a wrongly wired cable, for example). By the way don’t be tempted to try substituting another optocoupler for OPTO1. Most other optocouplers don’t have the switching speed of the 6N138 and won’t reliably transfer MIDI signals. FEBRUARY 2001  27 Parts List 1 PC board, code 01201011, 117 x 112mm 1 low-profile plastic instrument case, 141 x 111 x 35mm 4 5-pin DIN sockets, 90° PC board mounting 1 16-way DIL pin strip 1 DB15 male IDC connector 1 DB15 female IDC connector 1 16-way DIL socket, IDC type 1 2m length of 15-way IDC ribbon cable 4 small self-tapping screws, 6mm long Semiconductors 1 6N138 fast optocoupler (OPTO1) 1 74HC04 hex inverter (IC1) 2 3mm red LED 1 1N4148 or 1N914 diode Capacitors 1 10µF 10VW tag tantalum Resistors (0.25W, 1%) 7 220Ω 2 330Ω Fig.2: install the parts on the PC board as shown here. Make sure that all polarised parts are correctly orientated and note that the two 330Ω resistors go in the centre of the board (ie, they connect to the cathodes of the two LEDs). The PC board is very simple and should only take a few minutes to assemble. It is secured to the base of the case using self-tapping screws which go into integral plastic standoffs. 28  Silicon Chip OPTO1’s output transistor is connected as a simple switch, with its emitter grounded and its collector connected to the +5V rail via LED1 and a 330Ω series resistor. When MIDI information arrives via CON2, the transistor in OPTO1 switches on and off and its collector current causes LED1 to blink in sympathy. At the same time, the collector voltage at pin 6 swings up and down between 0V and +5V and it’s this logic voltage signal that’s fed to the UART in the PC’s sound card via pin 15 of CON1. This same signal is also used to produce the circuit’s MIDI THRU signal, by passing it through inverters IC1f and IC1a in series. Pin 2 of IC1a therefore provides a buffered version of the incoming MIDI signal. The two associated 220Ω resistors are used to regulate the 5mA current in any MIDI load circuit connected to CON3. The two MIDI OUT signals are produced in a similar way to the MIDI THRU signal. However, in this case they use the voltage signal from the sound card’s MIDI output instead of the signal from OPTO1. This signal comes from pin 12 of the sound card’s game port connector, via CON1. It’s passed first through inverter IC1e and The 15-way connecting cable passes through a slot that’s filed in the top of the rear panel. Also show here is the 15-way female IDC connector at one end of the cable. This allows devices such as joysticks to be connected to the game port, without disconnecting the MIDIMate. Fig.3: here’s how to assemble the connecting cable. Note that the red conductor goes to pin 1 of each connector and that pin 16 of the 16way header socket is unused. then through inverters IC1c and IC1d. These then drive the MIDI OUT sockets (CON4 and CON5), again via their own pairs of 220Ω series resistors. The remaining inverter (IC1b) is used to drive the MIDI OUT indicator LED2, using the logic signal from the output of IC2e. Construction All the components used in the MI- The 16-way IDC header socket plugs into a matching 16-way DIL pin strip on the PC board. Power for the unit is supplied via the PC’s game port, so no external supply is needed. FEBRUARY 2001  29 Fig.4: this is the full-size etching pattern for the PC board. DI-Mate are mounted on a PC board coded 01201011 and measuring 117 x 112mm. A 16-way section of DIL connector strip on the PC board is used as input connector CON1. This mates with a 16-way DIL socket on the 15-way ribbon cable, which links the MIDI-Mate to the PC sound card’s game port. The 16-way DIL socket is mounted about 100mm from one end of the cable, while the DB15 female IDC connector is mounted at the adjacent end. The DB15 male IDC connector is fitted at the sound card end of the cable (ie, at the far end). Note that all three connectors are IDC types for easy fit­ting. The 16-way DIL socket is simply fitted with the cable located over the connector teeth for pins 1-15. This is easy to do if you use the coloured side (red stripe) of the ribbon cable to indicate the “pin 1” conductor. Be sure also to connect the conductor with the red stripe to pin 1 on all the connectors – see Fig.3. There’s virtually no physical wiring inside the MIDI-Mate box, Fig.5: be sure to set up the options in either Multimedia Player or your sequencer program so that they’re talking and listening to the sound card’s MPU-401 MIDI port. because even the four DIN sockets and the indicator LEDs are mounted directly on the board. Fig.2 shows the layout on the PC board. The parts can be fitted in any order – the only things to watch are that you fit the polarity sensitive parts the correct way around. These in­clude OPTO1 and IC1, the 1N4148 diode, the two LEDs and the 10µF capacitor. Both LEDs are fitted with their cathode lead closest to CON3. It’s easy to identify the cathode lead – it’s always adja­cent to a flat section on the plastic collar of the LED body. It’s also shorter than the anode lead (see Fig.1). Initially, the LEDs can be fitted in the upright position, with their leads straight. Later on, the leads can be bent for­ward at a right angle about 11mm above the board, so that they protrude through matching holes in the front panel. Note that the board must be fitted with two short wire links. One is just above the 10µF capacitor and IC1, while the other is just behind CON4. Final assembly The assembled PC board is secured inside the case using four 6mm-long self-tapping screws. These mate with four of the moulded mounting pillars. The case rear panel has a 20 x 4mm rectangular notch cut into the top centre. This allows the ribbon cable from the PC to loop in and connect to the MIDI-Mate and then loop back out again. The front panel has six round holes – two 3mm holes for the LEDs and four 16mm holes for the DIN sockets. These holes can be marked out by using a photocopy of the front panel artwork as a template. The best way to make the holes for the DIN sockets is to first drill small pilot holes. These holes can then be carefully enlarged to the correct size using a tapered reamer. Trying it out No adjustments are required for the MIDI-Mate; if you’ve assembled it correctly, it should be ready for use Fig.6: you can use this fullsize artwork as a drilling template for the front panel. Drill small pilot holes for the MIDI sockets first, then carefully enlarge them using a tapered reamer. 30  Silicon Chip MIDI In A Nutshell: What It Is & How It Works MIDI is an acronym standing for “Musical Instrument Digital Interface”. It’s a standardised system for communicating between electronic musical instruments, keyboards, controllers and se­quencers (including PC-based sequencers). The MIDI standard was agreed on by a group of musical instrument makers in 1983 and has been used and extended since then. MIDI uses serial data communication at 31.25kb/s (kilobits per second). This involves using asynchronous 5mA current loop signalling, with the current provided by the “transmitting” end. Each byte of a MIDI message takes only 320µs to be transmitted (counting start and stop bits). Since most MIDI messages are 2-byte control codes, this means that over 1500 such codes can be sent each second via a single MIDI cable. Each MIDI cable carries only one signal, so for bi-direc­tional communication, two cables must be used. The cables them­selves use shielded two-conductor wire. All MIDI cables are fitted with standard 180° 5-pin DIN plugs at both ends. However, only pins 4 and 5 are used for the actual current loop signalling (wired 4-4 and 5-5). Pins 1 and 3 are left unconnected, while the shield braid is connected to pin 2 at each plug. Inside MIDI equipment, pin 2 is connected to earth only on MIDI immediately. You need only connect it to the sound card of your PC via the ribbon cable and game port connector, and fire up the computer. To try it out you will need to have some sort of synthesis­er or other MIDI instrument to hook up to one of the MIDI OUT sockets and also a way of playing MIDI files. This could be just the Windows 95/98 “Multimedia Player” accessory program, playing almost any handy “.MID” music file. Of course if you have a more elaborate sequencer program like Windjammer, Cakewalk or MidiSoft Recording Session, these would be even better. The main thing you need to watch OUT sockets. This allows correct earthing of the cable shield braids, without creating earth loop problems. Unlike most other current-loop signalling, current only flows in a MIDI link when data is actually being transmitted. This allows MIDI cables to be plugged and unplugged without any problems, as long as data is not actually being transmitted at the time. To prevent equipment damage due to wiring errors or compon­ent faults, all MIDI inputs are provided with 3kV of galvanic and electrostatic isolation via an optocoupler. For correct MIDI communication between equipment, a MIDI OUT or MIDI THRU socket at one end must be connected to a MIDI IN socket at the other. In most MIDI systems there is a single main controller or sequencer (often the computer), from which most of the MIDI messages originate. When these messages must be sent to more than one instrument, they can be distributed in either “star” or “daisy-chain” fashion, as desired. There’s no need to worry much about the actual code messag­ es sent over the MIDI links, because nowadays this is all handled by sequencer or other software running on the PC, and by firmware running in the other instruments and keyboards. It’s probably enough to know that most MIDI messages are short commands to allocate a is that you set up the options in either Multimedia Player or your sequencer program so that they’re talking and listening to the sound card’s MPU401 MIDI port, instead of its inbuilt FM or wavetable synthesiser. Otherwise, the fact that you’ve connected up MIDI-Mate will be ignored and your external synthesiser will remain silent. Assuming that you have a synth­ esiser or other MIDI instru­ment connected to the MIDI-Mate, getting it to “play” should now simply be a matter of loading a MIDI file and clicking on the “Play” button. And while the file is playing, MIDI-Mate’s MIDI OUT particular instrument to a particular channel, to tell it to start or stop playing a particular note, to change the instrument’s attack/decay or other performance parameters, and so on. As mentioned earlier, these commands are generally in the form of 2-byte codes. Using a PC-based music editing and sequencer program (and perhaps a MIDI music keyboard to feed in the actual notes), you can assemble a complete sequence of MIDI commands to play a piece of music – on say the “instruments” in a synthesiser. The synthe­ siser can then be made to “perform” that piece of music simply by sending the sequence to it, via the MIDI link. When you’re happy with the result, you can save the se­ quence on disk as a MIDI music file. These have a standardised format and are identified with the “.MID” extension. Disks with collections of pre-composed MIDI music files are also available and you can download them from the Internet as well. Finally, it’s important to realise that although a MIDI music file may look superficially similar to a .WAV file of a digital sound recording, it’s really quite different. It’s more like an electronic equivalent of sheet music – simply a sequence of instructions describing how to play the music. In this case, the instructions are for electronic instruments rather than for human players. LED should blink away merrily as the MIDI commands stream out to the synthesiser. Similarly if you have a MIDIequipped music keyboard or other controller, you’ll now be able to hook its MIDI OUT to the MIDI IN socket on MIDI-Mate and record your own music on the computer’s hard disk – after clicking on the sequencer program’s “Record” button, of course. And that’s really all there is to it. With MIDI-Mate and a sound card, your computer will have all the hardware it needs to become a powerful MIDI sequencer. The rest is up to you SC and your musical creativity! FEBRUARY 2001  31 BASS BLAZER 2-1/2 Octave Bass Frequency and Level Display By RICK WALTERS Do you have a subwoofer in your home theatre setup or in your car? Want to know the level of the bass signals you are hearing? This miniature 2-1/2 octave bass frequency display gives you the info. It has four vertical LED bar-graph displays to show the bass amplitude in four separate frequency bands. 32  Silicon Chip I f you're a bass fiend, you'll love this little display. It tells you the amplitude of those thumping bass signals you are listening to. Because it is powered from 12V DC it is just as happy in a car as it is in home theatre systems. It you are going to add a subwoofer to your home theatre system, you may find that one of the hardest tasks is to set the balance between the existing speakers and the sub. It's even harder if you have a variable frequency active crossover, as the combination of adjustments between this and the level control becomes huge. You can listen to some music but when you hear a low note, such as a bass drum, how do you know whether it is too soft, too loud or just spot-on? This little display gives you an indication of the relative level of the bottom octave from 32Hz to 64Hz, the next octave which is split in halves, from 64 to 96Hz and 96 to 128Hz, and lastly the range from 128 to 160Hz. The level is displayed on four vertical LED bargraphs, each covering 15dB in five 3dB steps. It is housed in a compact plastic case with the four bargraphs mounted at one end. There is quite a lot of circuit for such a small box but we've sandwiched it all onto three PC boards with rainbow cables linking them together. Theory of operation If you are going to monitor bass frequency signals in a circuit, it stands to reason that Fig.2: two of these "Multiple Feedback you need some filters so that Bandpass Filters" (MFBF) are used in each you can "hone in" on the freof the four bandpass filter stages. quencies of interest and ignore all the others. The response of the filters which drive the displays is shown in Fig.1. What we have done is to combine two Fig.1: the theoretical responses of the four filters. Fig.3: two multiple feedback bandpass filters are cascaded together and their responses combined to give and overall bandpass with an almost flat top and much steeper skirts. If you're a bass fiend you'll love this little bass frequency display with its four bargraph displays. Build it and install it in your car sound or home theatre system. It is shown here close to life-size. FEBRUARY 2001  33 filters for each band, "stagger-tuned" so that the resulting "bandpass" response has a reasonably flat top and steep "skirts". The filters we have used are known as "Multiple Feedback Band-pass Filters" (MFBF) each of which consist of an opamp with two capacitors and three resistors between input and output. The basic filter circuit is shown in Fig.2 and the values are selected to generate the response you require. R1 and R2 act as a voltage divider to control the overall gain. At high frequencies the reactance (impedance) of C1 becomes less thus rolling off the high frequency response. At low frequencies the reactance Fig.4: the circuit consists of four bandpass filter stages to monitor the bass frequency signals. The filter output signals are rectified and the DC level is fed to comparator stages to drive the bargraph LEDs. 34  Silicon Chip of C2 increases, thus rolling off the low frequency response. This is an over-simplified explanation but enough for you to get the idea. Fig.3 shows how cascading two multiple feedback bandpass filters gives an almost flat top and much steeper skirts as the response of the higher frequency filter is helping to at- tenuate the lower frequencies and vice versa. By having a small (1dB) dip at the centre frequency we get a steeper roll-off than if we had a flat top. We regard this as a good compromise. Circuit description Well, that's enough theory, let's get down to the nitty-gritty of the full cir- cuit which is shown in Fig.4. It looks pretty large but it essentially consists of the same circuit duplicated four times to give the four bands. The input circuit monitors both channels in a stereo system and mixes them together to form a mono signal which is fed through to the filter stages. Op amps IC6a and IC6b are connected as unity gain buffers to monitor the left and right channels, respectively. The buffer stages are used to avoid loading effects on the program source (CD, DVD, tape deck etc) and the outputs of the buffers are added together in op amp IC6d. FEBRUARY 2001  35 M N O Q T S GND IC4 LM339 IC5 LM339 1.6k 10F R 1 1 P Fig.5: this combined wiring diagram shows all three PC boards and most of the wires linking them together. The wiring from the comparator board to the display board (right) must be linked from point A to point A, point B to point B and so on, for “A” to “T” and ground. 1.2k F E D G H I J IC2 LM339 IC1 LM339 L K IC3 LM339 1 1 C 100F 25V 1 B 1N 4148 4.7k 68 68 68 A D5 D6 Q3 Q4 Q2 1N 4148 Q1 X 820 68 X 600 390 1k 10F 220k 10F 10F 10F .022F .047F .033F .033F .047F 4.7k 82k 91k IC8 LM324 1 820k 620k 820k .033F .033F 100k 100k .01F D8 *16V 0.1F 1N 4148 D7 47k 100k * F 100 50k 10k IC6 LM324 1 REG1 7808 10k VR1 4.7k 1M 0.1F 91k 110k 13k 6.2k 3k 4.7k 1k 0.47F D9 0.47F 1M + LEFT IN 10k 10k 10k .033F .047F .047F * F 100 110k 82k 680k .033F 1N 4148 .022F _ DC SOCKET 9.1k 1 IC7 LM324 .022F 1N 4148 .033F 2.4k 3.6k 62k .033F 56k .022F 430k 620k 680k 470k Trimpot VR1 is a preset level adjustment, to enable you to calibrate the indicators to display the correct maximum level. The summed left and right channels from VR1 are fed to the four op amp filters IC8b & IC8c, IC8a & IC8d, IC7b & IC7c and IC7a & IC7d. The bass frequencies from the output of each filter are rectified by a diode (D1, D2, D3 & D4) to a 10µF capacitor. The resistor across each capacitor discharges it and ensures that all the displays will turn off in the absence of a signal in that particular band. The resulting DC level across the respective 10uF capacitors is proportional to the bass signal level from the four filters and this DC signal is used to drive the bargraph displays. Bargraph displays 220k D4 1N 4148 D3 1N 4148 1N 4148 D1 D2 220k 220k Level set RIGHT IN RCA SOCKETS Each bargraph display uses a stack of five comparators, one for each 3dB step in signal level. The inverting inputs of all 20 comparators are individually biased to particular DC reference levels with a resistive divider fed from REG1, a 7808 8V fixed regulator. The reference voltages are set so that each successive comparator in the stack switches its output from low to high as the input level increases by 3dB. Let's now have a closer look at how each stack of five comparators works. Note that the DC signal level from each diode (D1, D2, D3 etc) is connected to the non-inverting input of all five comparators in each stack. Looking first at comparator IC1a, with no (or low) DC input level from diode D1, the non-inverting input (pin 5) will be lower than its inverting input, pin 4, which is set to +1.426V. Thus the open collector output transistor at pin 2 will be turned on and the constant current supplied by Q1 will all be diverted to ground (0V); hence no LED will be lit. Once the input voltage on pin 5 exceeds that on pin 4 the output transistor will be turned off and LED1 will light. This happens because current will pass from Q1, through LED1 and then through IC2a's output transistor which will still be turned on (as will the outputs of IC3a, IC4a & IC5a). Next, consider the situation as the DC level from D1 rises. Pin 5 of IC2a will now rise above pin 4 at +1.98V and its pin 2 transistor will now turn off allowing LED1 and LED2 to light. The output current now passes from Q1 through LED1 & LED2 and through IC3a's output transistor. So you can see how the sequence goes as the DC input voltage rises; each comparator turns off allowing the current to pass through its associated LED to the comparator which is the next in the stack. Ultimately all comparators in the stack will be turned off and so all five LEDs will be lit. The same system of operation applies to all four comparator stacks. Constant current source A constant current source is needed for each bargraph display as we can have from none to five LEDs turned on. Using a voltage feed, the LEDs would get dimmer and dimmer as more were turned on. By feeding them from a constant current source the LED intensity remains constant regardless of the number lit. 36  Silicon Chip PNP transistors Q1, Q2, Q3 & Q4 are the current sources for their respective LED bargraph. Their bases are all held at a reference voltage below the nominal 12V supply voltage by series diodes D5 and D6. Taking into account the base-emitter voltage of 0.7V there must be a voltage of 0.7V across each 68Ω emitter resistor for the four transistors and this sets the constant current to 10.2mA. This applies whether the first comparator in the stack is turned on or all five LEDs are turned on. Negative supply generator The only part of the circuit remaining to be described is the negative supply generator formed by op amp IC6c. While the quad op amp IC6 and all the LM339 quad comparators (IC1IC5) run from the nominal 12V DC supply, the filter stages involving quad op amps IC7 and IC8 need to run from plus and minus supply rails in order to get enough signal output swing for the rectifier diodes (D1-D4). This is where IC6c comes into the picture. IC6c is configured as a Schmitt trigger oscillator. Its output is used to supply a 2kHz square wave to the voltage doubler (or diode pump) formed by the two 100µF capacitors and diodes D7 & D8. The voltage doubler's output is around -8V which is used as the negative supply for IC7 and IC8. Putting it together There are three PC boards to assemble: the filter board (01102011), the comparator board (011020120) and the LED board (01102013). The diagram showing the component layouts for all three PC boards is shown in Fig.5. The first step, as always, is to inspect the PC boards for any undrilled holes, broken or shorted copper tracks. You can do this by comparing your boards to the PC patterns shown in Fig.6. It is much easier to fix any defects now, before you begin installing components on the boards. It is probably easier to assemble the comparator PC board first as it only has a few resistors and ICs. Start by inserting and soldering the four main links, followed by the six diodes and 15 resistors. If you use IC sockets fit them next, otherwise insert and solder the five LM339 comparators making sure that pin 1 on each device points towards the wider edge of the PC These photographs of all three PC boards are shown close to same size to help in construction. The boards must be connected to each other with short lengths of ribbon cable as shown opposite and then assembled in the case. The two larger boards fit one on top of the other (the board at the top of the page goes in the bottom of the case) while the small display board at left fits in vertically at the end of the case. When assembling, ensure nothing shorts out! board. I always identify pin 1 of every IC by using a rectangular pad (instead of a rounded rectangle) so use this feature to check, if you are unsure. Next, fit the four transistors and the six electrolytic capacitors. Now comes the time-consuming part: installing the on-board wiring links. These could have been avoided by designing a double-sided PC board but we like to keep the board cost as low as possible. First, pin 5 of each IC has to be connected together and linked to D1's cathode. These connections are shown as cyan (blue) on Fig.5. Similarly, FEBRUARY 2001  37 The opposite end to the bargraph display reveals the RCA stereo input sockets and (almost hidden) the 12V DC input jack. Parts List: Bass Blazer 1 plastic case, Jaycar HB-6013 or equivalent 1 filter PC board, code 01102011 1 comparator PC board, code 01102012 1 display PC board, code 01102013 2 RCA chassis-mounting sockets 1 chassis-mounting DC socket to suit your plugpack Semiconductors 3 LM324 quad op amps (IC1-3) 5 LM339 quad comparators (IC4-8) 1 LM7808 8V positive regulator (REG1) 4 BC557 transistors (Q1-Q4) 8 1N914 small signal diodes (D1-D8) 1 1N4004 silicon power diode (D9) 4 5-segment LED bargraph displays (Altronics Cat Z-0972) Capacitors 1 100µF 25VW PC electrolytic 1 100µF 16VW PC electrolytic 5 10µF 16VW PC electrolytic 2 0.47µF MKT polyester 2 0.1µF MKT polyester 4 .047µF MKT polyester 8 .033µF MKT polyester 4 .022µF MKT polyester 1 .01µF MKT polyester Resistors (0.25W, 1%) 2 1MΩ 2 820kΩ 2 680kΩ 2 620kΩ 1 470kΩ 1 430kΩ 4 220kΩ 2 110kΩ 3 100kΩ 2 91kΩ 2 82kΩ 1 62kΩ 1 56kΩ 1 47kΩ 1 13kΩ 5 10kΩ 1 9.1kΩ 1 6.2kΩ 3 4.7kΩ 1 3.6kΩ 1 3kΩ 1 2.4kΩ 1 1.6kΩ 1 1.2kΩ 2 1kΩ 1 820Ω 1 600Ω 1 390Ω 4 68Ω 1 50kΩ trimpot (VR1) Fig.6: use these actual size artworks to check or make your PC boards. 38  Silicon Chip all the pin 7s have to be joined and connected to D2's cathode (shown in purple); don't forget the link between pin 7 of IC2 to pin 7 of IC5, shown as "X". All pin 9s are joined and linked to D3's cathode (shown in magenta) and finally, all pin 11s joined and linked to D4's cathode (shown in green). Keep all the linking wires as short as possible and lay them flat on the PC board to keep them neat. Now its time to tackle the filter PC board. Fit the one link, then the resistors, diodes and trimpot, followed by the IC sockets (or ICs), the MKT capacitors and lastly the electrolytics and the regulator. Fold the regulator (REG1) over the top of the capacitor to keep its height down as the compar- ator PC board has to fit in the plastic case above the filter board. Finally, the display board can be assembled. The LED displays must be inserted with the short lead (cathode) at the end with the earth strip running the width of the PC board (marked E). They should then be pushed hard in until the wider part of the pin hits the PC board. Just tack solder the cathode pin and the anode pin at the other end of each display keeping the displays at rightangles to the PC board. Now, using the panel artwork of Fig.7 as a template, mark and cut out the four 35mm long slots for the displays. If you keep the cutouts tight you may be able to push the display assembly into position and have it stay there. Otherwise, drill a hole through the plastic case and the display PC board and use a small countersunk bolt and nut to hold it in place (or use some Blu-Tak or other adhesive to hold it in place). If the displays do not align properly, unsolder the tacked leads and adjust them until they do. Once you are satisfied, solder all the LED leads. Then cut three lengths of brown to green (brown, red, orange, yellow, green) rainbow cable 120mm long, one black to green 120mm. From the rear of the display board, with the earth track at the top, the cable with the black lead terminates the lefthand display (the highest frequency band). The wire sequence is black to (E) earth, then green, yellow, orange, red and finally brown to the next pad. The other three cables are terminat- ed in a similar manner (without the black lead). All these leads terminate on the comparator PC board. We did not use PC stakes but inserted the wires directly in the holes and soldered them. You may use PC stakes if you prefer. The high frequency display connects to pin 13 on all comparators. The brown wires all go to IC1, the red to IC2, the orange to IC3 the Fig.7: use this panel artwork as a yellow to IC4 and the green to IC5. template when cutting the slots in the All these wire links are indicated case for the bargraph displays. with the letter A to T on both the Mount these components and link comparator board and display board the two solder lugs of the RCA conon Fig.5. You will also need to connect the nectors with a piece of resistor lead offcut. Connect them to earth and the filter outputs to the diodes (D1 to D4) centre lugs to the left and right input on the comparator PC board. These on the filter PC board. wires are also shown on Fig.5. Finally, connect the DC power If you have not already done so, you connector. The positive lead from will need to drill the two holes for the RCA connectors and a hole to suit the the connector goes to the anode of diode (D9) on the filter board while power connector you plan to use in the negative lead goes to E (adjacent the plastic case. to REG1). This diode has been included othResistor Colour Codes: Bass Blazer erwise you could do damage to the circuit if you connect a DC plugpack No. Value 4-Band Code (1%) 5-Band Code (1%) with a different polarity to the DC  2 1MΩ brown black green brown brown black black yellow brown connector.  2 820kΩ grey red yellow brown grey red black orange brown Apply power and check the current consumption with a multimeter.  2 680kΩ blue grey yellow brown blue grey black orange brown It should be around 60mA. If it is a  2 620kΩ blue red yellow brown blue red black orange brown lot higher than that, turn the power  1 470kΩ yellow purple yellow brown yellow purple black orange brown off and check for bridged tracks etc.  1 430kΩ yellow orange yellow brown yellow orange black orange brown The voltage at pin 11 of IC7 and IC8  4 220kΩ red red yellow brown red red black orange brown should be around -8V. If this voltage  2 110kΩ brown brown yellow brown brown brown black orange brown is zero, it means the oscillator is not  3 100kΩ brown black yellow brown brown black black orange brown oscillating, so check your soldering  2 91kΩ white brown orange brown white brown black red brown and components around IC6c.  2 82kΩ grey red orange brown grey red black red brown If you have an audio oscillator, you can sweep through the frequency  1 62kΩ blue red orange brown blue red black red brown ranges of the filters and check that  1 56kΩ green blue orange brown green blue black red brown they operate over the correct band  1 47kΩ yellow purple orange brown yellow purple black red brown and thus all your capacitors are in the  1 13kΩ brown orange orange brown brown orange black red brown correct position.  5 10kΩ brown black orange brown brown black black red brown Once you set VR1 to let the LEDs  1 9.1kΩ white brown red brown white brownblack brown brown hit 0dB on the peaks, you may be  1 6.2kΩ blue red red brown blue red black brown brown amazed just how high the frequen 3 4.7kΩ yellow purple red brown yellow purple black brown brown cies are that sound like really low  1 3.6kΩ orange blue red brown orange blue black brown brown SC bass.  1 3kΩ orange black red brown orange black black brown brown CapacitorCODES Codes  1 2.4kΩ red yellow red brown red yellow black brown brown CAPACITOR  1 1.6kΩ brown blue red brown brown blue black brown brown Value IEC Code EIA Code  1 1.2kΩ brown red red brown brown red black brown brown  0.47µF   470n   474  2 1kΩ brown black red brown brown black black brown brown  0.1µF  100n  104  1 820Ω grey red brown brown grey red black black brown  .047µF   47n   473  1 600Ω blue black brown brown blue black black black brown  .033µF   33n   333  1 390Ω orange white brown brown orange white black black brown  .022µF   22n   223  4 68Ω blue grey black brown blue grey black gold brown  .01µF   10n   103 FEBRUARY 2001  39 SERVICEMAN'S LOG The spirit of Christmas past On the first day of Christmas, there were brought to me three weird repairs, lots of crook TVs and a compressor that carked it and which I had to fix. OK, so I had better stick to my day job – just as well really, because lots of work came in over the Christmas break. The Christmas holiday season can bring on some weird re­ pairs, especially when combined with hot summer weather and high humidity. In my case, there was the added complication of pur­chasing and moving to a new location. The exquisite bad timing of this move during the busy period was bad enough. However, you would have thought that not many people would be watching TV during the non-ratings period and hence there would be less repairs. Not so! – there is something very fishy about the logic in­volved with TV programming over Christmas! As I said last month, I’ve just returned from a fabulous holiday around the world. This coupled with the onset of the festive season and my move has disrupted my normal routines and I’ve found it difficult to get back into the swing of things. To make matters worse, several unusual repairs came in but at least they break the monotony. The first unusual repair I had came about when the painters wanted to use my compressor to blow away the dust inside the new premises. Now my compressor is getting on a bit – it’s about 13 years old and all it’s ever used for is blowing dust out of VCRs and TV sets. In greater detail, the compressor is an Ingersoll Rand SCD25E8, which is a portable 50-litre electric motor belt-driven model. Unfortunately, the extra work load imposed on it by the two painters turned out to 40  Silicon Chip be too much for it. They had used it non-stop all that first day to blow out the sawdust from what used to be a cabinet maker’s workshop and, according to one of the perpetrators, the motor “just stopped and smoke poured out of it”. Of course, they had switched it off immediately – or even sooner! The job, of course, was uncompleted and this was a major blow with so much sawdust to get rid off. By the time I got there to check it out, the compressor had cooled and so I plugged it in once more to confirm the symptoms. Now let me tell you that I am the first to admit that I know nothing useful about motors and so I reluctantly carted it off to the nearest authorised service centre for a repair quote. Two days later, I phoned them to find that it would cost in excess of $350 to fix as the motor was burnt out. I was aghast at this dreadful news and – just like some of my own clients – blurted out stuff along the lines of “I can get a new one for that!” I was politely informed that oils ain’t oils Items Covered This Month • Ingersoll Rand SCD25EA compressor. • Weconic VX-4270 4-channel car amplifier. • Akura CAN1 3-1 stereo system. • Clarion RT-4042B car stereo receiver. and I wouldn’t get one this good for that sort of money. The problem was I was already short of cash due to the cost of opening and decorating the new premises – not to mention actually paying for it! However, I needed a compressor right now – today – and so I went down to Repco and bought a small 25-litre unit for $200. Well, of course, the repair centre was quite right; this poor little beast had to pump almost continuously to keep up the same airflow as my old one and it got very hot. This was only going to be a stopgap answer and I really needed to get the big unit back into service. I called around to pick up the old Ingersoll Rand and ar­ rived to find that the AC motor was in pieces. I was shown the armature coils which had become so hot they had melted the string that had kept them in neat bundles. The reason it had failed was that a safety cutout switch had been activated and the switch wafer had hit the metal casing of the motor and spot welded to it – probably because the thick sawdust had jammed it open. The AC motor is an Australian-built 300W single-phase Betts Motor EP1987 15 HO13-21 (James N. Kirby) and looks well made. I don’t quite know how the safety switch works but it is either bimetallic or, I suspect, centrifugally operated. I subsequently took the disassembled motor around to all the local electric motor repair shops to see if I could get it fixed more cheaply. However, in each case I found that it was quite difficult to get past the “expert” receptionist who to a man/ woman said that the motor was burnt out, shorted and beyond repair and I would have to get a new one. The cost would be around $500 plus fitting and the shaft or pulley might have to be modified to suit the compressor. This was all very depressing but it forced me to examine my old motor more carefully. Perhaps I could repair it myself and so I blew out the remaining dust and cleaned it. Despite what every­one had been telling me, the coil windings didn’t look that bad and the insulating shellac still looked intact. OK, so the coil windings had become hot and melted the coil formers – but wouldn’t you if you were shorted to earth where you shouldn’t be? I decided to reassemble it to see what happened – after all, what else did I have to lose? The thing is so well made and has so many safety features that even if it did catch fire it would be confined to its metal case. Before starting the assembly, I checked the two capacitors and the coils for shorts and continuity. Although some shops had told me that the coils had shorted, I couldn’t find any resist­ance between the windings. Uunfortunately, I don’t have a shorted turns tester that works at 50Hz and so I could only assume that the coils were OK. My next problem was to reassemble the motor, which was entirely in pieces with 13 unidentified colour-coded wires to reconnect! I went back to the original repair centre and asked if they had drawn out the wiring for the motor. Although not 100% delighted to see me, they politely said they would ask their electrician – who was subcontracted – if he had drawn one and kept it! The problem was, he only came in when there was enough work and I was told to try again at the end of the week. In the meantime, I had to work out how the safety switch fitted back in around the bearings where it had arced and welded onto the back plate. I filed away the metal to give it better clearance and removed all the welded excess metal caused by the accident. The main problem here was how to get the safety mechanism into the correct position. It has two springs and a multiple axle system that causes it to move axially along the shaft (please excuse the layman’s terms here – if I was an expert in electric motors I would probably be a lot wealthier than I am now). Even­tually, after a lot of coarse language, I managed to get the whole thing back into its case and turning freely. All I had to do now was connect the 13 wires. There were three for the 240V input and earth, two for the reset switch, two for the starter capacitor, two for the running capacitor and two for each of the two windings. These were all connected to five studs – A1, A2, 71, 5 & 4 – on a mounting assembly connected to the cutout switch. This switch was between points A1 & 71 and A1 was permanently wired to point 5 which was all extremely confus­ing. Fortunately, when I returned to the service centre, I was given the hand-drawn wiring diagram by the electrician, which I duly followed. I was still somewhat nonplussed by one of the capacitors (Plessey P419 900V DC 15µF) as its orange wires go to A1 and 5 which are permanently wired together. I can only assume that this is superfluous to requirements or that the diagram is wrong. Not feeling very confident, I connected all the colours as shown on the drawing and with the motor on the bench and my hand on the main switch, I finally plucked up enough courage to switch it on. The motor leapt into life and settled down to a quiet 2835 rpm purr. It was working perfectly with no distress and no heat. Then I refitted it into the compressor, connected and tensioned the belt and tried again. The whole compressor was working like before. As I write now, some six weeks later, it is still going well and had blown out all the rest of that sawdust. I can’t help feeling that sooner or later the problem may re-occur and this time the motor will be really “cactus” but until then, every day is a bonus. As for the repair centre, they pointed out that they would have been unable to guarantee such a repair and I fully agree with them – you can’t. In fact, they had gone to a lot of trouble for me and had correctly diagnosed what had happened and quoted a lot lower than anyone else. As a result, I will certainly recom­ m end their services to others. Ron’s amplifier The next “weird” repair that came in was via a friend of my kids called Ron. Ron loves his car, or rather, his car stereo. The car is somewhat less than average but it is one of those vehicles that “throbs” from the subwoofer at the rear and you can hear – or rather feel it – from two blocks away. However, to Ron’s consternation one day, there was peace in his entire FEBRUARY 2001  41 Serviceman’s Log – continued area as his amplifier wasn’t working any more. Appar­ e ntly, I was the obvious choice to “have a go”. I did explain that my dubious expertise lay more in the field of TV and video but no, as it had wires and electricity, I was definitely the guy to fix it. The amplifier is an enormous Weconic VX-4270 which adver­tises its audio power output on its large heatsink as 800W. It didn’t explain what sort of watts these are and I would have dismissed them as being peak music power with a following wind but for the fact that this unit is made in Germany and is really quite heavy. I assume therefore that these are 800 genuine RMS watts (ie, 800W RMS). It is also a 4-channel amplifier, so I would say that it probably is 200W RMS per channel into a 4-ohm load. The symptoms were fairly straightforward, with the amplifi­er drawing virtually no current when connected to +13.6V. The only thing that happened was that the red “protect” LED came on. This probably meant that the power supply was being disconnected from the amplifier stages by an internal protection circuit. Unfortunately, I knew very little about this amplifier and so I thought that the best course of action would be to find out who the agents were and try to obtain a circuit diagram. After two weeks of searching, it became apparent that there was no local agent 42  Silicon Chip and even searching the Internet failed to reveal any trace of Weconic. I was on my own. Ron’s a nice guy and my kids like him, so I persevered. After removing something like 100 screws, I removed the PC board and transistors from the heatsink. The amplifier looked reason­ ably well made and I could distinguish four separate 12-transis­ tor audio amplifiers and a large 8-FET power supply with a couple of ICs for protection and regulation control. With the amplifier laid out on the workshop bench, I found that I could momentarily measure +24V and -24V rails before they decayed as the protection circuit cut in. My guess was that the power supply was probably OK but one or more of the amplifier stages wasn’t. There were no signs of any distress on the board due to overheating, nor could I see anything else that was obviously wrong. I therefore decided that the best course of action was to disconnect each amplifier in turn from the power supply until the protection was released – assuming that the protection circuit itself was OK. I was fairly lucky and soon discovered that it was the left rear amplifier that was causing the problem and that it was probably due to the offset sensor circuit which is activated via R363. A quick check with a multimeter in circuit failed to reveal any faulty active devices but this wasn’t a good way of checking them. Rather than remove each transistor and measure it out of circuit, I decided that it would be far quicker to replace them all one at a time. I started at the beginning of the amplifier and after re­placing seven of the small signal transistors, I finally found that Q308 (2SD600) was the culprit. This transistor is a flatpack device and its base-emitter junction was open circuit. Replacing it cured the problem and the amplifier burst into life. Ron is now back to terrorising his neighbourhood and there is no longer any peace. The Coca Cola can The next unusual repair was the Coca Cola can! I kid you not. It is 900mm high, 510mm in dia­ meter and weighs 26kg. It is bright red with Coca Cola all over it, has two concealed doors and contains a stereo system! The reason I reluctantly became involved was through anoth­er friend of a friend routine because no sound was coming out of the can any more. I helpfully suggested that Coke and electricity didn’t mix, but this wasn’t appreciated and the missus insisted that it wouldn’t be any trouble at all for me to look at it. Wonderful, I thought, there goes the better part of my summer holidays. When I got it onto the bench, I discovered that it was a 1994 Akura (model CAN 1) 3-1 stereo consisting of Fig.1: this circuit section shows the tone control and audio output stages of the Clarion RT-3042B car amplifier. an AM/FM stereo tuner, dual cassette deck and CD player, with a bass reflex speaker system built into each of the doors. Surprisingly, con­sidering its age, they still make them and you can see them on the web at http:// www.akura.com Removing it from the can wasn’t too difficult except for the mains lead – the plug has to be removed in order to get it out. I then tested the unit on the bench and found that a low-level noise could be heard through the loudspeakers which indi­ cated that the main amplifiers were OK. However, none of the three sources could be heard. I ran my fingers over the main amplifier IC connec­tions and found that this produced loud noises in each channel. Similarly, loud noises were produced when I touched the PC board tracks around the volume control but the unit was quiet as soon as I moved closer to the source switching. The main volume rotary control (VR305) is of an unusual construction, with six in-line solder connections. Noise could be induced by touching its third and sixth connections but not on any of the others. I felt sure this was where the problem was and so I removed it and checked the connections out of circuit. I could find no continuity between these two pins and any of the rest of the control in any position. By prising off the metal clamps that hold the shell onto the wiper board, the construction of the control could easily be seen. It is a double-gang 100kΩ potentiometer with the outer and inner tracks being the wipers and the two inner tracks being the carbon resistors. The plastic wiper former had cut through the inner and carbon tracks on the righthand side due to constant wear. The diagnosis had been easy but where was I to get the part for a 7-year old stereo that was so unusual? Eventually, I purchased a spherical 16mm 100kΩ conventional PC-mount ganged pot (R7612) from Dick Smith Electronics. I drilled a hole through the PC board and mounted it. The next part was to extend the splined shaft to a “D” shaped one. Fortunately, I found an old plastic extension shaft from an ancient black and white TV set and cut it to size. The whole thing fitted together excellently and worked perfectly. The boss was exceedingly pleased with my efforts so I’m in the good books. A tricky car stereo I’ve mentioned before that I really don’t like servicing car stereo systems. Like video cameras they are now becoming so specialised, small and hi-tech, that it is best to stick to what one knows. Jim’s stereo system was a Clarion model and was housed in an old Mazda bus which he used to carry children to and from school. Jim needed this fixed as it helped keep the rowdy kids quiet at the back. This outfit was more of my vintage; like the bus – old, crotchety, and large. I mean, I could actually see the components with the naked eye – and not a microprocessor in sight. The complete system consisted of two Clarion units – an RT-4042B receiver and PT-8039F cassette deck – and separate front and rear amplifiers. He complained that it was dead. Happily, he had taken the vital section out of the bus for me. What landed on my bench was simply the two Clarion units. As such, it was almost a self-contained system. FEBRUARY 2001  43 Serviceman’s Log – continued All it needed was a 12V power supply and a pair of speakers to become functional. The front and rear amplifiers, and their associated speakers – still in the bus – were extras. My first problem was to work out which of the many sockets and plugs was used for what. Normally, there is an in-line fuse which indicates 12V in but this fuse was internal. The 12V supply is applied via a 3-pin plug/ socket connection and the pres­ence of the third pin – and its wiring – added to the confusion. Tracing out the wiring and working out which lead was which was rather tricky. As I eventually traced it, a volume control/double-pole switch (S3) combination controlled both the positive (active) and negative (chassis) lines, which seemed reasonable enough. One of the three pins was the positive 12V ACC line, going to a 3A fuse, then to a choke (CH1) and finally to the on/ off switch, on the main PC board. The second pin connected, via the other pole, to chassis. But what was the third pin’s function? Apparently, this is an output connection to operate a separate device; eg, an exter­nal power antenna. Having sorted out this much, I encountered the first real problem. The on/off switch was obviously faulty and needed re­ placing. It therefore seemed logical to bypass this switch and check the rest of the system first, before changing it. With the switch bypassed, only one globe lit – the AM indi­cator – and I still had to guess which socket was the speaker output. There are in fact no less that six unmarked sockets – in­cluding three DIN sockets – on the back of the radio and two on the cassette deck, involving 32 possible connections in all! In the end, I conceded defeat and ordered a set of service manuals, a volume-on/off control assembly and seven replacement lamps. Not being familiar with this system, it wasn’t easy replac­ing these items but the service manual at least made it possible. As it turned out, the three DIN sockets feed the front and rear external power amplifiers and the cassette deck. Another two 3-pin sockets are used to feed a stereo speaker pair from an inter­nal audio amplifier IC (IC7) and to provide illumination and power to the power antenna. Replacing the volume control-on/ off assembly meant removing or at least loosening the top PC board and flexing it to let the old unit out and the new one in. Everything was put back and reconnected. It glowed like a Christmas tree and I connected the workshop speaker to one channel via a pin in the 3-pin sock­et and there was sound. Then I checked the other channel in the same way, only to find it was low and distorted. The circuit itself consists of two tuners – one AM and one FM – either one switched in as required. Their outputs are fed to a stereo pream­ plifier stage consisting of three ICs (IC4, IC5 & IC6), several transistors, the treble and bass controls, and the gain and balance controls – see Fig.1. From here the signals go to an audio output IC (IC7, TA7264), the output of which feeds one of the 3-pin sockets. And, at that point, the system is essentially self-contained. But this is not the end of the story. As well as going to IC7, the signals are also fed – via transistors Q8 & Q10 in one channel and Q9 & Q11 in the other – to the front and rear output DIN sockets and their associated amplifiers and speakers. The whole system could, in theory, supply no less than six speakers if everything was connected. But it was IC7 that was the prime suspect now. Signals into it from both channels were normal and I could not measure any­thing abnormal around it. This was a blow because I hadn’t really budgeted for the cost of an output IC – let alone the time and effort involved. It would also involve some effort, since IC7 was on another PC board underneath the controls and the top board. Once again I loosened the top board, removed the screws, stressed the metal supports and pulled out the wiring harness. Then I inserted a screwdriver and loosened the amplifier board and released the IC heatsink. Finally, after lots of wiggling, I managed to remove the board for a close examination. What a relief – there were faulty joints on almost every other pin of the IC. I resoldered and reassembled everything and switched it on. Both channels came up in stereo. Checking further along the line, to the rear and front amplifier DIN sockets, cleared that section and the system worked like a bought one. Jim was pleased, the kids were SC quiet and I was worn out! MORE FROM YOUR EFI CAR! Own an EFI car? Want to get the best from it? You’ll find all you need to know in this publication  Making Your EFI Car Go Harder  Building A Mixture Meter  D-I-Y Head Jobs  Fault Finding EFI Systems  $70 Boost Control For 23% More Grunt  All About Engine Management  Modifying Engine Management Systems  Water/Air Intercooling  How To Use A Multimeter  Wiring An Engine Transplant  And Much More Including Some Awesome Engines! AVAILABLE DIRECT FROM SILICON CHIP PUBLICATIONS PO BOX 139, COLLAROY NSW 2097 - $8.95 Inc P&P (Aust). Call (02) 9979 5644 9-5 Mon-Fri with your credit card details or fax the order form on p71 to (02) 9979 6503. 44  Silicon Chip 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 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 PRODUCT SHOWCASE Advanced Jaycar digital and analog multimeter Despite today's digital multimeters having many advantages over analog models, there are times when a digital can’t cut the mustard and you really need that old analog pointer. Does that mean you need two multimeters? Not any more, now that Jaycar have released their QM-1050 Multimeter – a digital & analog model in one case. A 3-1/2 digit digital display is inset into the middle of the moving coil meter and both meters respond at the same time. But there’s more to it than that. As well as the “usual” measurement capabilities – DCV (to 1kV), ACV (to 700V), resistance (6 ranges 200Ω to 20MΩ) and current (AC/DC, 2mA to 20A in 4 ranges), you can also measure capacitance (.002µF to 20µF in 5 ranges), frequency (20kHz and 200kHz), temperature (-30° to 400° and 400° to 1000°), diode test, continuity test and battery test (button cells, 1.5V cells and 9V batteries). Now that’s a very comprehensive range of testing in one unit! As well, you get data hold facilities on the DMM and the voltage and current ranges are auto AC/DC (with a push button to select AC/DC if you want it.) The meter measures 190 x 85 x 40mm and is supplied in a protective holster. Weight, including holster, is about 600g. Red and black probes are supplied, as would be expected, along with a “K” type probe thermocouple for temperature measurement. With a retail price of $87, this meter has a lot to recommend it – especially when you consider that it not only replaces two metres but has a raft of functions normally only found on the most expensive digitals. Contact: Jaycar Electronics PO Box 185 Concord NSW 2137 Phone: (02) 9743 5222 Fax: (02) 9743 2066 Email: techstore<at>jaycar.com.au Website: www.jaycar.com.au Ex-Olympic Comms Gear from Oatley Electronics Oatley Electronics have available some little-used telecommunications equipment used for the Sydney Olympic Games at bargain prices. First item is a genuine Netcomm 56K V90 Mega-modem. The ones we saw looked so good you’d swear they were brand new, not used. Some might need just a little spit and polish to bring them up to mint condition. They're supplied with a 240V power adaptor and RS232 lead but don’t have instructions or driver software but these can be down-loaded from the Net-comm website. Oatley are selling these modems for just $75.00 The other bargain is a PANASONIC model KXTS85ALW Data Port phone. These are really advanced models featuring include Data Port, Programmable Call Restriction, 16 digit LCD Readout, One touch speed dialler, Hands Free Handset compatibility, Built in Hands Free Speakerphone, 9 Step Electronic Volume Control for Speakerphone, 5 step Electronic Volume Control for headset and handset, Call Waiting, Ringer Indicator, Call Forward immediate, Dial lock, Redial, Recall. Oatley have spotted them in a retail catalog for $161 but their price is just $50 or two for $90. Contact: Oatley Electronics PO Box 89, Oatley NSW 2223 Phone: (02) 9584 3563 Fax: (02) 9584 3561 Website: www.oatleyelectronics.com Dick Smith Electronics PowerHouse Powers Young Lifesavers In recognition of the opening of the latest Dick Smith Electronics PowerHouse store at Warringah Mall on Sydney's northern beaches, the company has recently undertaken the sponsorship of Rookie Surf Life Savers in the 21 northern beaches Surf Lifesaving Clubs. During their last year as a junior, or “nipper” at 13 years, children undertake the training and examination for the first life saving qualification, the Surf Rescue Certificate, which is the minimum qualification they require to join a patrol on the beach. For some time Surf Lifesaving has been concerned about the drop-off rate in the years immediately after the SRC. Dick Smith Electronics PowerHouse sponsorship has enabled the introduction of a program specifically designed to arrest this drop-off and to help children in this transition period. All will receive a unique patrolling uniform which identifies them as a Dick Smith Electronics PowerHouse Rookie Lifesaver and all will have the opportunity to participate in a variety of special events, training and activities (including non-surf activities) under the Rookie Program. For more information on the Rookie Program, contact Surf Life Saving Sydney Northern Beaches (02) 9971 4996. Contact: Dick Smith Electronics Phone: (02) 9937 3200 Fax: (02) 9805 1159 Website: www.dse.com.au FEBRUARY 2001  53 D-I-Y Alternative Energy Books Tasman Energy have available two books which could be of interest to anyone who is (a) sick of paying too much for fuel or (b) sick of paying too much for electricity (or who is off the beaten track and cannot get mains power). The first book is called “Make your own diesel fuel” and yes, that is exactly what you can do after reading this book. It tells you how to make perfectly usable, 20c/litre bio-diesel fuel (for automotive/stationary engine/etc etc use) using old cooking oil (which it also tells you how to scrounge from local restaurants, etc). The author claims to not only power his diesel vehicle from the fuel but also his power generation plant. And that brings us to the second tome: “Build your own battery charging plant”. This is a blow-by-blow account of the author's own installation which was forced on him when the electricity authority wanted $$$$ and months of delay to run mains power to his bush hideaway. Both books contain a wealth of information and, thankfully, warnings about the dangers involved (the common chemicals you mix for the fuel-making process make a pretty nasty brew!) The books are web-published; that is you pay for either or both the via the web and it or they are downloaded to you in Microsoft Word format. You can then print them out yourself on any graphics-enabled printer (eg laser). Both are just over 20 pages and cost $25 each. We must state that SILICON CHIP has not tried or tested any of the information in these books and makes no claims for the accuracy or veracity of the contents. For more information, visit the company's website or call. Contact: Tasman Energy PO Box 266, Deloraine Tas 7304 Phone: (03) 6362 3050 Fax: (03) 6362 Website: www.tasmanenergy.com.au 54  Silicon Chip Hitachi Super Bright LCD Projector There’s nothing worse than trying to present information using an LCD projector which has insufficient brightness to overcome room brightness. That’s why Hitachi's new CP-X325 Super Bright multimedia projector will be of interest to those involved in the presentation, display and PR industries. With a 1400 ANSI lumens display and true XGA resolution (1024 x 768) the Hitachi is claimed to offer unmatched quality, sharpness and colour contrast. All this is in a unit measuring just 300 x 76 x 225mm and weighing in at only 3.2kg. It also offers digital keystone correction, off-axis viewing without distortion, manual zoom and focus as well as auto configuration for easy setup. It has two RGB/video inputs, RGB output, stereo sound and a mouse-based remote control. The projector is now available through Hitachi dealers for $12495 including GST. Contact Hitachi Australia 13-15 Lyonpark Rd, North Ryde 2113 Phone: (02) 9888 4100 Fax: (02) 9888 4188 Website: www.hitachi.com.au TOROIDAL POWER TRANSFORMERS Manufactured in Australia Comprehensive data available Harbuch Electronics Pty Ltd 9/40 Leighton Pl. HORNSBY 2077 Ph (02) 9476-5854 Fx (02) 9476-3231 ADI’s one-chip decoder Analog Devices have released the only 32-bit single-chip decoder/ post-processor which can handle THX Surround EX, DTS-ES Extended Surround and Dolby Digital. The new Melody decoder post-processes THX Surround EX on the same chip as it decodes either DTS or Dolby Ditigal. The new decoder will enable future A/V receivers, PC audio cards and set-top boxes to process, in the same product, all of the leading audio algorithms: THX and THX Surround EX, DTS, Dolby Digital, Dolby Headphone and Dolby Pro Logic, HDCD, MPEG1 Audio Layers 1, 2 and 3 (MP3), MPEG2, Surround Sound and Stereo. Contact: Analog Devices PO Box 2098, Rosebud Plaza Vic 3939 Phone: (03) 5986 7755 Fax: (03) 5986 4688 Website: www.analog.com Central Coast Hobby & Communications Expo 2001 One last reminder: the NSW Central Coast Field Day will \\be held on the last Sunday in February (25th). It promises to be the biggest and best ever with more than 2000 people from clubs and organisations all over Australia converging on Wyong Racecourse to display and trade equipment, new and “pre loved”. Just about every aspect of amateur and CB radio is represented, along with electronics as a hobby, vintage and historical radio collections, volunteer emergency communications, satellite reception, computers and more. Wyong Racecourse is about an hour north of Sydney with plenty of parking within the grounds. Gates to the public open at 8.30am. Admission is $10 for adults; $5.00 for students, seniors and pensioners; with children under 12 free. Food and drinks are available on site. More information is available via the Central Coast Amateur Radio Club website, www.ccarg.org.au, or by phone: (02) 4340 2500. E ELECTRONICSHOWCASELE MicroZed Computers GENUINE STAMP PRODUCTS FROM EMC Technologies' internationally recognised Electromagnetic Compatibility (EMC) test facilities are fully accredited for emissions, immunity and safety standards. EMC Technologies Melbourne: (03) 9335 3333 Sydney: (02) 9899 4599 Scott Edwards Electronics microEngineering Labs & others Easy to learn, easy to use, sophisticated CPU based controllers & peripherals. PO Box 634, ARMIDALE 2350 (296 Cook’s Rd) Ph (02) 6772 2777 – may time out to Mobile 0409 036 775 Fax (02) 6772 8987 http://www.microzed.com.au Most Credit Cards OK NEW! HC-5 hi-res Vi deo Distribution Amplifier DVS5 Video & Audio Distribution Amplifier Five identical Video and Stereo outputs plus h/phone & monitor out. S-Video & Composite versions available. Professional quality. For broadcast, audiovisual and film industries. Wide bandwidth, high output and unconditional stability with hum-cancelling circuitry, front-panel video gain and cable eq adjustments. 240V AC, 120V AC or 24V DC VGS2 Graphics Splitter High resolution 1in/2out VGA splitter. Comes with 1.5m HQ cable and 12V supply. Custom-length HQ VGA cables also available. Check our NEW website for latest prices and MONTHLY SPECIALS www.questronix.com.au Email: questav<at>questronix.com.au Video Processors, Colour Correctors, Stabilisers, TBC’s, Converters, etc. QUESTRONIX All mail: PO Box 548, Wahroonga NSW 2076 Ph (02) 9477 3596 Fax (02) 9477 3681 Visitors by appointment only Do you want YOUR product or service showcased to Australasia's most important electronics marketplace? CALL ME: RICK WINKLER on (02) 9979 5644 and let me explain how cost effective the SILICON CHIP ELECTRONICS SHOWCASE can be for YOU! FEBRUARY 2001  55 Sony's BIG TV Review by LEO SIMPSON Most people are amazed at how big this new Sony TV set is. And how bright. They immediately want to sit down and start watching. Hours later, they are visibly reluctant to leave. When a TV has that effect on people, you know it must be impressive. 56  Silicon Chip “...a screen area three times larger than a 68cm set. That mightn’t sound like a big increase: in truth, it’s not. It’s a HUGE increase!” W e’ve said this before and it’s worth saying again: “If you want a really satisfying home theatre experience, you must have a big screen”. After all, what is the point of spending lots of money on a surround sound system but still sticking with a standard 68cm TV set? If you are going to simulate a cinema experience, you need a screen with the same impact as at the movies There are several ways to obtain a big screen and they all have their pros and cons. Plasma screens are big and bright and take up very little space but few people can afford to spend the best part of $20,000; that’s more than the price of many small cars. Full projection systems certainly give a huge picture but they need to be viewed in very subdued lighting and are hardly practical if you just watch the evening news bulletin. And they, too, are very expensive. That leaves rear projection TVs. They give a big picture and can be viewed in normal room lighting (more about this aspect later) and they are not outrageously expensive – although they would be too costly for many readers. Read on though, because many of the features found on this big set will tend to become standard on smaller sets in the years to come. It doesn’t take up much more floor space than a standard 68cm TV set – but the picture is dramatically larger. Don’t let the height worry you – it’s just about spot on when you are sitting down. And sit down you must, otherwise you’ll miss the full impact of the huge picture. In this extra-close-up shot of the screen, you can start to see the horizontal lines in the DRC100 mode. The vertical fresnel lens lines seen by the camera are not obvious to the eye. Actually, this 121cm Sony set, the KP-ES48SN1 (just how do they come up with these numbers?), is not the biggest in the range; it is the second smallest. The biggest is a 154cm model. Having previewed the four models in the range, we decided that the 121cm model probably represented the best value for the money and would fit most easily into most homes with a reasonably large viewing room. That might seem like a fairly obvious statement but it is not until the set arrives in its carton that you realise how big it is. In fact, in many homes and apartments, it would not be possible to unpack the set indoors or even carry the carton up internal stairs. Let’s back up a bit and describe the basic features of this set. The 121cm (48-inch) dimension refers to the diagonal measurement of the screen. This gives it a screen area three times larger than a 68cm set. That mightn’t sound like a big increase: in truth, it’s not. It’s a HUGE increase! Overall dimensions are 1091mm wide, 1336mm high and 580mm deep. But it doesn’t take up significantly more floor space than the average 68cm set. At 68kg, it is not unduly heavy either and it is fitted with castors so it can be moved around quite The same shot in DRC 1250 mode. The horizontal lines have all but disappeared but the image does not seem to be quite so sharp or bright. It’s all a matter or preference and program. FEBRUARY 2001  57 You don't have to fossick around the back to connect a camera or TV game: these sockets are (nicely hidden) on the front. On the opposite side are the switches used for convergence and channel setup. patches of colour (green, red and blue, in succession) at the top, bottom and in the middle of the sides, coinciding with the abovementioned sensors. Once it has gone through the procedure, lasting about a minute, it produces a white cross-hatch in the middle of the screen and the job is done. You can then watch a great picture which is bright and sharp all over the screen. Viewing angle We couldn’t resist a peek inside the Sony: there’s a lot packed into the quite thin “base”. The circular image on the screen is the fresnel lens, not seen from the front. easily. However, it comes in a carton which measures 1190mm wide, 1430mm high and 650mm deep; dimensions which would make it difficult to unpack in many homes. Instead of being finished all over in drab black or charcoal, the plastic cabinet has a brushed silver frame around the screen and a “metal look” control panel below the screen, both of which lighten up the styling. In reality though, once a program is on the screen, you cease to look at the set and see only the big picture. As with most modern sets, you can have quite a few video sources although most people will just connect a DVD player, a VCR and the antenna lead. You can use normal (composite) video inputs or so called “component video” inputs and you can connect a video game or camcorder to RCA 58  Silicon Chip sockets at the front of the set. Interestingly, in addition to the normal stereo speakers inside the set, there is another speaker which can be used as the centre speaker in a Dolby surround sound system; maximum input is 30W. Provided you largely ignore the instruction manual, basic setting up of the Sony set is reasonably easy. It can be arranged to automatically tune in all the local stations and it has automatic (static) convergence, an important feature in any large TV set. The auto convergence relies on optical sensors in the middle of each side of the screen and at the top and bottom. To put the set into auto-convergence mode, you push a button on the popout panel underneath the screen. It then produces a small cross-hatch in the centre of the screen and square The overwhelming feature (and that Fig. 1: the principle behind projection TV systems. The three tubes (at bottom) project onto the mirror (top right) which in turn reflects onto the screen (at left). A closer look from the rear of the set with the mirror removed. At the top are the three powerful red, green and blue projection tubes. Notice how each is set at a specific angle. If all is OK (not the least being the convergence of the tubes), the result is a very clean, bright TV “picture”, reflected onto the screen by the large mirror behind it. word is no exaggeration) of the Sony 121cm set is the size and brightness of its picture. If you’ve only seen rear projection sets in retailers’ showrooms or clubs it is doubtful whether you have ever seen them to best advantage and the same point applies to this Sony set. All rear projection TV sets have a limited vertical viewing angle – you must sit down to watch them. Otherwise, if your head is above the top of the screen and the room is brightly lit, you will think that the screen brightness is woeful. But sit down (or lower your head to achieve the same result) and you will see a dramatic increase in brightness. So you really can enjoy a bright, full contrast picture in a brightly-lit room – but only if you sit down! The reason all rear projection sets have a more limited viewing angle is because of the large Fresnel lens used for the screen. Fig.1 shows the general arrangement of the three projection tubes (red, green and blue) used. They fire up against a large mirror at the back of the cabinet and this throws the light at the Fresnel lens screen which has been optically ground to project the image out in a horizontal beam, more or less. The Fresnel lens has fine vertical grooves and the surfaces between the grooves have a parabolic convex cross-section to spread the light out in a horizontal axis. You can see the overall lens structure in one of the photos in this article. It is this lens and the higher power from the 7-inch CRTs (cathode ray tubes) that is responsible for the overall high brightness – Sony claim that brightness is 20% improved over previous models. Actually, the Sony’s vertical viewing angle is better than some other rear projection sets at ±20° from the centre line of the screen. Its horizontal viewing angle is ±60° from the centre-line. This means that if you watch from far off to the side you will also see a dull and lifeless picture. But look at it from where you are supposed to and you’re really in the picture. You’ll be disappointed to find there is no girl selling popcorn or choc-top icecreams appearing during the ad breaks! I had this TV in my loungeroom for the Olympic Games and I have to tell you that having a near-life-size Cathy Freeman charging straight at you at a million miles an hour is a whole new experience! High definition picture Sony’s rear projection sets all have DRC (Digital Reality Creation) which is Sony’s fancy name – and their proprietary technology – for field doubling and pixel doubling. Notice that we said “field doubling” not “line dou-bling”. While most large screen sets do not have line doubling, they all need either it or a field frequency doubling technique to display 50Hz PAL pictures without troublesome flicker. Sony has two display modes: DRC 100 and DRC 1250. Briefly, DRC 100 shows fully interlaced 625-line pictures at 100Hz while DRC 1250 shows 1250-line pictures at 50Hz. DRC 100 stops picture flicker FEBRUARY 2001  59 The worst feature of the Sony is its remote control, seen here closed (left) and open (right). Can you see the labelling on the open section? Neither could we – even in a brightly lit room (and yes, I did have my glasses on!). while DRC 1250 eliminates any line structure from the picture. Line doubling vs field doubling Line doubling (commonly used in direct video projection systems) uses an interpolation system to add the extra lines. This works but can give odd trailing ghosts on moving images. Sony’s DRC system actually creates extra fields in a sequence running A, B’, A’ and B where A’ is interpolated from transmitted fields A & B and B’ is interpolated from B & A. The pixel doubling scheme feeds the video signal to an A-D converter, adds in extra data bits and then converts it back to analog again. As far as I can tell, it is the digital equivalent of “video peaking” such as is used in the HQ technique in VHS video recorders. But while video peaking can improve the sharpness of video images, it can also increase apparent noise in the picture. Both the DRC 100 and DRC 1250 modes provide pixel doubling and this begs the question: why are the two modes provided? The answer is that it all depends on the video material you are watching and how close you are to the screen. When you are watching in DRC 100 mode, the impression is that the picture is very sharp and bright but most viewers will be quite aware of the line structure in the picture. When you switch over to the DRC 1250 mode, the line structure in the picture disappears but it also appears to become not quite as sharp and as bright. This is quite a subtle effect. And if the video signal tends to be a little on the noisy side (ie, a little snowy in the darker scenes), then it is more noticeable in the 1250 mode. On the other hand, if you watching program material with a strong graphics content where there are bright horizontal elements to the picture which tend to make flicker noticeable, the DRC 100 mode is preferable. This is particularly the case if you are watching weather forecasts, pie-charts or graphs showing sporting statistics or video games. In these cases, switching over to the DRC 100 mode eliminates any flicker to give a rock steady picture. In summary, my preference for most video material was to use the DRC 1250 mode to eliminate the line structure which can otherwise be 60  Silicon Chip quite obvious and detracts from the big bright picture. We’ve taken some slides of video stills to try and demonstrate the differences between the two modes but I have to say that they don’t really show the effects fully. Oh, that remote control! I must confess that several times I have felt like throwing the remote control up against the wall – it is that frustrating. And the instruction manual is not much better! Both let down an otherwise superb product. To make any sense at all of the remote control, you must be less than 12 years old and willing to press buttons willy-nilly to get a result. To any person used to “logical” controls though, I think the Sony remote control for this set is one of the most irritating, badly conceived and downright diabolical controls I have ever come across. It is also badly labelled and you can hardly see the markings, especially those under the flip-up panel; light orange markings on a grey panel are not a good combination. Where it is particularly annoying is when you are trying to use the menu button and joystick control to change the various settings. Never let it be said that the Sony KP-ES48N1 doesn’t give you exceptional input/ output options. The biggest difficulty is the labelling – it’s not particularly intuitive and you need the instruction manual to work it out. The instruction manual? Now that’s another story . . . Say you want to change the picture settings; you find that unless you press the joystick in a particular way, it will fly off into another section of the menu where you don’t want to be. Reading the manual just confuses the issue so you have to persevere until you get the result you want. It does not have to be this way. By contrast, while we were doing this review, we used a Sony DAV-S300 system which is a combination DVD player, tuner and 6-channel surround amplifier and speakers. It comes with a remote control which is the same shape as that for the Sony rear projection set and with similar buttons and yet is a delight to use – the buttons are clearly labelled too. If they can get it right for one product, why not for the Sony rear projection set? OK, that’s enough whinging. Let’s look at just some of the other goodies this otherwise very nice receiver has to offer. Other features Sets in this price range can be expected to have plenty of extra features and these Sony sets are not lacking. They have picture-in-picture and Teletext. Picture in picture requires an extra tuner, IF strip and video/audio demodulation as well as the PIP chipset but it is a very worthwhile feature on a large screen set. It allows you to watch two video programs at the same time and you can choose which sound feed you want. It is particularly satisfying when you are watching sports programs and you want to check what’s happening on another channel. When the appointed moment comes and you want to watch the program in the inset picture, you can use the joystick button to swap between the programs. Naturally, you can use the remote control to change the position of the inset picture. This is often desirable if you need to move the inset picture from one corner to another, to avoid it obscuring something on the main picture. Other related features are TWIN and Program Index. Twin allows you to watch two programs with the same-size pictures side by side on the screen. You can then use the joystick to increase the size of the main program, (ie, the one you are listening to) while the other is reduced. Again, on a large screen such as this, Twin mode works well because both pictures are still pretty large. Program index is quite good too. It shows the main program in the centre of the screen while stills from another 12 channels or sources are “tiled” around the border and are continually updated so that you can see their progress. Teletext is a feature that some people might perhaps regard as having little use but it does give access to the “closed captions” on many programs, for the hard of hearing. Apart from that, it does have the limitation that Teletext pages are rather slow to update or access if you want news or sports scores. However, if you want to check share prices, Teletext can be quite a bit faster than using your computer to log on to your internet broker. And it has the advantage that you don’t have to pay for a phone call! Teletext is also widely used to distribute horse and dog racing information. Moreover, with the mixed picture facility, you can have Teletext super- imposed over a watched program (admittedly only from the Seven network in Australia). Having talked about and used these additional features, I have to say that they are really the icing on the cake. They’re good… but as I said before, the main attraction of the Sony 121cm set is its big bright picture. An enjoyable luxury For my money, even if you don’t have or aspire to a full home cinema setup, a big rear projection set is an enjoyable luxury, provided you have a large room in which to view it. (To be frank, I don’t think the average-size Aussie loungeroom is really big enough to do it justice). And while rear projection sets are quite a lot more expensive than even the largest CRT sets, in real dollar terms they are not as expensive as the quite modestly sized sets that people bought at the advent of colour TV broadcasting about 25 years ago. Recommended retail price of the Sony is $8199. For further information, see your local video retailer or contact SC Sony on 1300 137 669. Sony’s DAVS300 DVD Combo Player The so-called “DVD DreamSystem” – this can form the heart of a home theatre system. Inside this relatively tiny (355 x 70 x 365mm) case is a 5.1 channel digital amplifier, an FM/AM tuner with 30 preset memories and of course the DVD/CD player. The DVD can be programmed to repeat the disc, the title or the chapter. The amplifier has 6 x 30W channels with inbuilt Dolby Digital, Dolby Pro Logic and dts decoders. Recommended retail price is $1699. The remote control at front is pre-programmed to cover a number of brands of add-on equipment, as well as this Sony. FEBRUARY 2001  61 2m Elevated Groundplane Antenna An antenna designed to exactly match the impedance of the feed cable has much to recommend it. The transmitter will develop its maximum power, losses in the feed cable will be minimised and any risk of damage due to mismatch is avoided. By PHILIP WATSON, VK2ZPW 62  Silicon iliconCChip hip This view shows all the pieces of the antenna just before the final assembly. The copper tube forms part of the matching section. The materials used are all ready available and you should be able to scrounge most of the parts for little cost. T HIS VHF ANTENNA was originally constructed as part of the author’s research into the impedance of an elevated groundplane antenna, as set out in the June 1999 issue of SILICON CHIP. In particular, the author wanted to establish that an impedance matching section (or “Q” section) could be constructed, to match the 52Ω impedance of the feed cable to the 18Ω antenna impedance. In fact, the finished device has proved to be a completely practical antenna. It is simple to construct, easy to mount and because it provides the correct load, it allows the transmitter to generate maximum power. This is important because not every transmitting device is completely safe from mismatch damage. Typical commercial power amplifiers (“afterburners”) frequently carry a warning that an SWR above a specified figure will void the warranty, for example. A feature of the unit is that the “Q” section is of solid construction. It makes a substantial “handle” which can be lashed or clamped to a mast or, if the mast is in tubular form, the “Q” section can sit inside the mast, along with the coax cable. Another feature of the unit is the use of screw-on radials which can be easily detached for transport. In fact, this antenna has proved extremely useful as a temporary base antenna during WICEN exercises. Alternatively, as a permanent base station antenna, it would suit any situation requiring an omnidirectional VHF antenna for 2-metres (144-148MHz). Useful background In the June 1999 issue of SILICON CHIP, the author present­ed an article entitled “What Is A Groundplane Antenna?”. This article sought to clarify the difference between two different types of groundplane antenna – the earthed variety and the ele­vated type. Having established that the elevated version has a theoretical impedance of 18Ω, the article went on to discuss the problem of matching the antenna to the feed impedance (52Ω) and briefly described a practical antenna. However, the arrangement described in that article is not the only approach. In that case, the idea was to design the antenna itself to provide the required 52Ω feed impedance. In the current approach, the antenna is left in its simple basic form, compatibility between the two impedances being achieved by in­serting a matching device between the cable and the antenna. One of the simpler forms of matching device is what is commonly called a “Q” section; a quarter wavelength coax section having an impedance value intermediate between the two impedances (ie, between 18Ω and 52Ω). A simple formula (1) is used to cal­culate this value: (1). Zq = √(Za * Zb) where Zq = Required Q section impedance; Za = Cable Impedance; and Zb = Antenna Impedance In this case, the value for Zq comes out at 30.6Ω. And so it all appears to be delightfully simple; just insert a quarter wavelength of Zq impedance coax between the cable and the anten­ na. It’s all too easy. But of course, there’s a catch – just where do you find 30.6Ω coax? You certainly can’t get it from any of the regular electronic outlets. In fact no such material exists – all that is readily available are the (nominal) 52Ω and 75Ω varieties. Granted, there are some tricks available – eg, two lengths of coax connected in parallel will provide half the impedance. From this, the best choice would seem to be two 52Ω parallel lengths to produce an impedance of 26Ω. That’s much better than the gross mismatch of 2.88/1 using a straight connection but still short of the ideal. The error is similar using two parallel 75Ω lengths. A possible solution to this problem might be to use a parallel arrangement made up of one length of 52Ω cable and one length of 75Ω cable. This would produce an impedance of 30.7Ω (which is very close to the required value of 30.6Ω) – assuming that the simple resistances-in-parallel law holds true. The author hasn’t tried using this technique, however, and so is unable to vouch for its authenticity. Transmission line tricks Fortunately, some of the techniques FEBRUARY 2001  63 How it goes together – the 6.35mm (OD) brass tube is pushed down the 12.7mm copper tube to form the matching section. It is then soldered to the centre pin of a PL259 plug via a short length of tinned copper wire – see Fig.1. employed by users of open wire transmission lines can be used to solve our impedance matching problem. An open wire transmission line can be made with any impedance value (over a wide range) simply by selecting a suitable wire gauge and spacer dimensions. So, if a “Q” section is required, it is easily made to the required value. Coming back to the coax scene, could the same trick be pulled there? Could a length of “coax” be constructed to have any required impedance? The answer is yes and a formula is available to design it. Taken from the ARRL Antenna Handbook, it is as follows: (2). Zo = 138(log D/d) where Zo = Characteristic Impedance; D = Inside Diameter of Outer Conductor; and d = Outside Diameter of Inner Conductor This, of course, is for an air-spaced device. In theory, the use of any spacers would alter both the impedance and the velocity factor. In practice, this can be ignored – at least in the context of this article and the antenna described here. Practical considerations So much for the theory. Putting this idea into practice is another matter, since we are no longer thinking of a flexible cable. Instead, we are talking about a rigid device which must somehow be mounted. And, of course, suitable materials with the appropriate dimensions must be found to build the matching sec­tion. Strangely enough, finding the materials turned out to be the least of our problems. A hunt through my scrap­metal box soon yielded an odd length of 12.7mm OD copper water pipe plus a length of 6.35mm (0.25inch) OD brass tube. Well, that was as good a place as any from which to start. The water pipe would serve as the outer conductor, while the brass tube would become the inner conductor. As it turned out, I was lucky – when the appropriate meas­urements were The PL259 plug is connected to the “Yorkshire” fitting at the end of the copper tube using 1/8-inch Whitworth screws, as shown here and in the photo at right. 64  Silicon Chip fed into Eqn.(2), the result came out within a whisker. More exactly, it worked out as follows. The diameter (d) of the brass tube inner conductor (6.35mm) was already known but the inside dia­ meter of the outer conductor had to be measured. Since I didn’t have an inside micrometer or callipers, the best I could come up with was a finely calibrated steel rule and this gave a figure of 10.5mm (D). When these two figures were fed into Eqn.(2), the charac­ teristic impedance (Zo) came out as 30.14Ω – not quite the 30.6Ω being sought but probably “within acceptable tolerance” as an engineer might say, or “near enough” in layman’s terms. Mechanical design Now it was a matter of deciding on a suitable mechanical design and the physical construction. Originally, the idea was to build the matching section as a separate unit which could be coupled to the antenna base using an appropriate plug and socket combination. However, while assembling a rough mock-up of the inner and outer conductors, a much simpler approach suddenly suggested itself. If the inner conductor was extended beyond the antenna end of the “Q” (matching) section, it would form the beginning of the antenna. And by further extending this to an appropriate length, it would form the antenna itself. This changed the whole approach; the tail was starting to wag the dog. Instead of starting with an antenna and making a “Q” section to attach to it, we are now making a “Q” section which also becomes the antenna. So the logical approach is to combine the two items into one structure. Not only is it simpler and cheaper to build, obviating the need to supply and fit a plug and socket assembly, but also rather more elegant technically. In theory, the presence of conventional plug and socket assemblies – or any junction – in a coax cable creates a discontinuity which increases losses. Just how serious this is in practice may be debatable but, anyway, every little helps. So much for the theory. The first construction step is to ensure that the ends of the copper tube are cut square. Ideally, this should be done using a tube cutter, as used by plumbers, if one can be begged or borrowed. If a hacksaw is to be used, take care in marking and cut­ ting. Use the straight edge of a piece of paper wrapped around the tube to mark out a cutting guide, then cut a shallow groove right around the tube. Deepen this cut progressively by rotating the tube a little at a time until the operation is complete. Be sure to cut slightly to one side of the cutting guide, so that the end can later be cleaned up with a file. Don’t try to cut straight through the tube in one opera­tion. It will almost certainly come out crooked if you do. The antenna end of the tube is fitted with a small metal plate which supports the four radial elements. In the writer’s case, this was made from a piece of scrap brass, cut to about 110mm square (although this isn’t critical) and drilled with a central hole to match the OD of the brass tube. The plate is simply flush-mounted with the end of the tube and secured by soldering (eg, using flux, a solder Fig.1: this exploded diagram shows how the antenna is assembled. Note that the 6.35mm OD brass tube is used as both the radiator and as part of the matching (Q) section (ie, the brass tube is 1004mm long). An insulating grommet isolates the radiator from the copper tube at the brass plate end. FEBRUARY 2001  65 The radials are tapped at one end to 4BA x 10mm to match the spacers on the brass plate and fitted with a soldered “stopper” nut. This makes it easy to dismantle the antenna for transport. Alternatively, for a fixed installation, the radials can be soldered directly to the brass plate. stick and a gas flame to provide the heat). An alternative form of plate is a press-on lid as used on large coffee tins or similar containers, painted for protection from the weather. The radial elements can be made from any convenient size and type of material. The writer used 3.175mm (0.125in) brass rod but larger dia­meter tubing could also be used. The radials are each about 450mm long and can be directly soldered to the four corners of the metal plate. Alternatively, the radials can each be tapped at one end to 4BA x 10mm. A brass nut is then threaded onto each radial to act as an end stop (and soldered in position). The radials are then screwed into 4BA brass spacers soldered to the corners of the metal plate (see photo & Fig.2). The prototype used round brass spacers but hexagonal spacers would be much easier to position during soldering. You can buy a pack of six from any of the parts re­tailers for around $3.00. The advantage of this latter scheme is that it allows the antenna to be easily dismantled and transported, if necessary. plumber’s “Yorkshire” fitting. (Note: the metric dimen­sions are rounded to 12mm in hardware literature). The “Yorkshire” and “Yorkway” unions are designed to join (ie, buttjoin) two lengths of 12.7mm OD copper tube. In this case, the unit used should be specified as a “slip fitting” which has no stop in the centre (as normally used to simplify correct This close-up view shows how the end of the brass rod is plugged and drilled to accept the short length of 1.3mm tinned copper wire which connects to the PL259 plug. Termination The cable end of the tube is terminated with a PL259 plug. The plug body is the same diameter as the OD of the tube (ie, 12.7mm) and is buttjoined to the tube. It is secured using a brass sleeve consisting of a 12.7mm (0.5-inch) ID union – a standard 66  Silicon Chip The insulating grommet should be a tight fit over the inner brass tube. It is pushed down into the copper tube at the end of the matching Q section during the final assembly. positioning over a junction). Both fittings are designed to be soldered to the copper tube. The “Yorkshire” fitting is supplied with two internal rings of solder. The copper tubes should first be cleaned and fluxed, after which everything is fitted together and hit with a gas flame until solder flows right around the end of the union. A “Yorkway” fitting is treated similarly, except that the solder has to be applied externally to the ends of the union. In the writer’s case, a “Yorkshire” fitting was used simply because it was on hand but it would probably be the preferred device. The PL259 plug was secured into the sleeve using two 1/8-inch Whit­ worth screws. Matching holes are drilled through the sleeve and the plug body, initially to suit a 1/8-inch Whit­worth tap. The holes in the plug are then tapped, while the holes in the sleeve are enlarged to provide clearance. The same arrangement can be used to secure the sleeve to the tube or, as in this case, the sleeve can be secured by sol­dering. The distance from the end of the PL259 plug to the start of the pin is about 20mm (as measured inside the plug) and the internal diameter of its body is similar to, but not identical with, that of the tube. But although not exact, it really is close enough considering that only 20mm is involved. As a result, the plug can be treated as an extension of the tube. This means that the tube must be cut 20mm shorter than the calculated section length (ie, to 494mm instead of to 514mm, as quoted later on). The cable end of the inner conductor (ie, the 6.35mm tube) has to be joined to the pin of the PL259 plug. This was done by first plugging the end of the tube using a 3/16-inch brass ma­chine screw. This screw was soldered into place with its head cut off and filed square with the end of the tube. The screw was then drilled longitudinally to accept 16g (1.3mm) tinned copper wire (about 25mm long), using a No.55 or 5/64-inch drill, to a depth of about 6mm. The 16g wire was then sol­dered in place. When the antenna is later assembled, this 16g tinned copper wire slides into the plug pin and is soldered. Longitudinal drilling can be a tricky operation unless one has access to a lathe. However, provided care is taken, it can be done using a hand drill (eggbeater). Just be sure to accurately centre-punch the end before drilling. Small off-centre errors are easily corrected simply by bending the wire. Larger errors can be corrected by drilling an oversize hole and accurately positioning the wire prior to sol­dering. The inner conductor is secured where it emerges from the outer conductor (ie, at the ground­ plane) using a simple plastic grommet. This insulator should have a bore size of 6.35mm (0.25-inch) to accept the inner conductor and should be a tight fit into the 12.7mm outer brass tube. Scrounging the copper tube Obtaining a suitable length of 12.7mm copper water pipe for the outer conductor shouldn’t present any problems. Normally, plumbers buy it in standard 6-metre lengths but most hardware stores will sell it to you by the metre. There are also two other likely sources of scrap lengths: (1) a local plumber and (2) a scrap metal yard. A scrap metal yard will also usually have brass rod and tubing in a range of sizes and this can be cheaper than buying commercial lengths from a hardware store. Fig.2: the four tapped brass-rod radials screw into threaded brass spacers (or standoffs) which are soldered to the four corners of the mounting plate. Antenna dimensions The exact dimensions of the antenna assembly will depend on the particular frequency to be favoured. The antenna described here was designed for 146MHz which equates to a freespace quar­ter-wavelength dimension of 514mm. This means that the outer copper tube in the “Q” (matching) section had to be cut to 514 - 20 = 494mm, as mentioned previously. The calculated length of the radiator, after allowing for end effect or “K” factor, is 490mm (ie, 514/1.05) and so the 6.35mm brass rod is cut to 514 + 490 = 1004mm. And how did all this work out in practice? Extremely well, as indi- This photo shows the finished antenna with the four radials screwed into position. Also visible is the insulating grommet (red) at the end of the matching section. Use silicone sealant to seal around this grommet. cated by the following SWR figures, which speak for them­selves. 144MHz ..................... 1.02/1 145MHz ..................... 1.02/1 146MHz *.................... see note 147MHz *.................... see note 148MHz ..................... 1.02/1 * Too Low To Measure So that’s it; a near perfect antenna - well, impedance-wise anyway. SC FEBRUARY 2001  67 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. 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Ever wished that there was a way to transfer complicated PC board artwork from a magazine without having to resort to messy (and expensive) techniques such as photo-etching? Well, you can do it using nothing more complicated than a photocopy or a laser printout and an iron! By Heath Young I f you have ever used 3M’s “Dalo” pens for doing PC board artwork you will pretty soon realise that they have their limitations. The quality of the tracks you can produce is dependent on how steady your hand is and when the time comes to etch your board, you will discover that the pen is not quite impervious to all aqueous etchants. I have thrown out many a board due to severe pinholing in the tracks when I have used ammonium persul-phate etchant. The procedure that I have now come to use almost exclusively, even for small boards, is a method known as toner transfer. This uses the toner from a laser printed or photocopied page as the resist material. Toner is made from colourant (carbon black, etc) and a low melting point plastic. The plastic is impervious to aqueous etchants, so pin-holing should not be a problem. The question is, “How do you get the toner off the printed page and onto the copper laminate?”. It’s done by remelting the toner while it is in intimate contact with a very clean, slightly roughened PC board. You’ll need an iron To melt the toner, you need to beg, borrow, buy or steal an iron. No, not a soldering iron – the iron used to press clothes. Step 1: print a “reverse direction” PC board pattern with a laser printer or photocopier. You’re looking for dense blacks and no break-up in the pattern. 72  Silicon Chip A tip: don’t tell anyone what you are going to use it for otherwise they might not let you have it! Tell them you’re going to iron a shirt (on second thoughts, that’s not such a good idea – they’ll certainly not believe you!). While the iron is used to melt the toner onto the black PC board, done correctly this won’t harm the iron. Artwork preparation There are a lot of different printer papers and a lot of different toners around. So some experimentation may be necessary but the basic method remains the same for all. Firstly, you must get your artwork – this must be the mirror reverse of the track outlay. The PC board Step 2: clean the slightly oversize blank PC board thoroughly then slightly roughen it with 600 wet’n’dry. Avoid touching the copper surface once clean. artwork for projects printed in SILICON CHIP must be mirror reversed (inverted) before they are suitable for toner transfer. This is actually simpler to do than it sounds and can be done in a couple of ways. A good quality photocopy of the artwork can be made onto an overhead transparency sheet and this- sheet is then flipped and photocopied again onto paper. (Note that the photocopy of the transparency has to be done so that you can read the lettering when it is placed on the glass – otherwise you will get an inversion of an inversion - not what is wanted!) An even easier method, though, is to download the PC board file in either EPS or PDF format from the SILICON CHIP website (www.siliconchip. com. au) and simply tell your laser printer to print a negative (also sometimes called “inverse” or “reverse”) which can usually be selected as part of the printing process. If you are using programs like PCB Designer 1.0 or Easytrax (which may be downloaded from the ’net for free) then you will probably have designed a board in “mirror reverse” anyway, as it is much more intuitive. Mirror image boards (as if you are looking through them from the component side) are much easier to produce as there is no messing around reversing the pins when designing the board. The importance of a good quality laser print-out or photocopy cannot be over-emphasised. It must have good dark tracks, without any breaks or bridges which will obviously cause you grief later. Once satisfied with your printed image, you are ready to move on to the next step. Copper laminate preparation Cut the board slightly over-size, as the toner does not transfer well very close to the edges of the copper laminate. About a 3-5mm margin is safe (even more if practical) – the extra material may be trimmed off later. The copper laminate must be prepared before the toner can be applied. The toner requires a roughened surface otherwise it simply will not adhere or ‘key’ to the copper surface and will come off while etching. The board is cleaned up and roughened with 400 grit silicon carbide paper (“wet and dry”). Roughen the board by swirling the sandpaper (wet) in a light, circular motion taking care not to remove too much copper or the tracks will be too thin. Wash off all of the grit and dry the board with a lint-free cloth – a clean linen tea-towel is ideal for this. Do not touch the copper with your fingers from now on as the oil in your fingers may stop the bonding between the toner and the board surface. Toner transfer Cut the prepared artwork so that there is a border of about 10-15mm around the edges of the circuit board pattern. Now cut the corners off the artwork at a 45° angle – this will allow you to fold and tape the edges without creasing. Centre the artwork, toner-side down, onto the copper side of the circuit board and fold the artwork over the edges onto the non-copper side. Tape the longest side first, with Sellotape or similar adhesive tape. Don’t be tempted to use masking Step 3: cut the page out with a 10-15mm. border, then cut the corners off at a 45° angle (not too close to the artwork!). Fold the longest edge over 180° 10mm from the pattern. tape as its glue will melt from the heat and the artwork will shift and destroy your good work by smudging. The rest of the edges of the artwork are then taped onto the board, keeping the paper as tight as possible. It’s a bit like covering a book. Once you are satisfied that the artwork is well secured to the board, set the iron for the maximum temperature (ie, the “linen” setting) and turn the steam off. Put the board on a firm, flat surface (one which will not be damaged by heat!) and run the iron over the whole of the artwork. Apply a reasonable amount of pressure while you are doing this. The paper will scorch and go brown when the board is done properly and the sticky tape on the reverse side goes yellow from the heat. If you keep the heat on for too long, the copper may delaminate from the substrate – you can see this as a blistered copper surface and a discolouration on the other side of the board. Warning: the copper does get very hot! Once this happens, stop heating the board and allow it to cool naturally – do not quench in water! When the board is cool enough to touch, you will notice that the paper appears to be bubbling up from the board. This is normal with boards with wide track spacing and means that it is time to remove the paper. Removing the paper The paper is removed from the board by running it under a cold water tap and, when it is well and truly soaked, gently ‘rubbing off’ the paper fibres with your thumb and forefinger. Patience is the key here; do not be tempted to use anything harder than Step 4: wrap the folded edge over the PC board (toner to copper) and sticky tape it to the other side (not masking tape). Then tape the other three sides, stretching the paper as you go. FEBRUARY 2001  73 your fingers! You may not get all of the fibres out of the tracks but you do need to get rid of most of them. If at first you don’t succeed... You may discover at this stage that you have not used quite enough heat and the toner has not stuck well to the board. If this is the case, you can remove the toner with automotive paint thinners and start again with a fresh printout. Make sure you do a really thorough job with the iron. Etching Once the pattern is properly transferred and appears to have adhered properly, you are ready to etch the board. All of the normal aqueous etchants work well with this method but I prefer to use ammonium persulphate, at double normal concentration and very hot, to avoid undercutting thin tracks. Once you are finished etching, the toner can be removed with a cloth moistened in automotive paint thinners such as Prepsol. Then you can drill all the holes and cut the board to size. (Often it’s easier to do the reverse – drill the holes while the toner is still on the board, then strip it and cut it to size. We would also spray the board with a solder-through PCB lacquer to prevent oxidisation.) So there you have it, a cheap, easy way to make PC boards that are nearly as good as photo-etched boards but at a fraction of the cost. Boards produced by this method do have a few limitations though; very thick and very thin tracks sometimes don’t work that well but the results Designing your own PC boards is not too difficult, particularly when you use one of the many software packages around. They also allow you to print your pattern out reversed, ready to use in the process outlined here. This software is PCB Designer 1 – you can download a trial version from the ’net. with most of the boards published are quite good. As with all PC boards, commercial or otherwise, you should always give the pattern a thorough check before building a project. Use the published pattern as a guide or, if this is not available, print out another copy to check by. And one final tip: if you’re printing a pattern off the web, always ensure your board size agrees with the project board size before etching (SILICON CHIP always gives the size of the board in the parts list). We’ve seen whole production runs of double-size boards! The PCB Designer 1 program mentioned above is a 31-day evaluation version and is available from http://shareware.cnet.com/shareware/0-13628-500-2089325.html?tag=st.sa.16165_501_1.lst.titledetail Because it is such a long address we’ve also published it in the “Panels & PCBs – November 2000” page of the SILICON CHIP website (www. silicon-chip.com.au) – all you have to do is cut and paste the address into your browser. Easytrax is freeware and is also available via the ’net – try http:// www. protel.com.au/etech/freeware_ SC home.html Step 5: set the iron to its hottest (‘linen’) with steam turned Step 6: remove the paper fibres by wetting thoroughly then off. Iron firmly on a hard surface until the paper is scorched rubbing gently but firmly. This takes some time but when and the sticky tape starts to bubble. Allow to cool. successfully completed, your PC board is ready to etch. 74  Silicon Chip ATTENTION TEACHERS AND EDUCATION INSTITUTIONS A GREAT CHANCE TO BUY SCHOOL EQUIPMENT AT BARGAIN PRICES SCIENTIFIC CALCULATOR... CASIO FX-350D These will be on the education dept. list as of Feb.1 / 2001 8+2 digits, huge quantity: $15Ea., Buy 10 or more for $13.50 Ea. MORE CALCULATORS ON OUR WEB SITE BARGAINS OF THE MONTH (USED) NETCOMM 56K V.90 MEGA-i-MODEM: This modem was used during the Sydney 2000 Olympics. After one minute of cleaning they should appear new. They are in "as new" condition and are supplied with power adaptor and RS232 lead. The drivers can be downloaded from Netcomm: (GMOD56K) $75 (USED) BUSINESS SPEAKERPHONE: These PANASONIC model KX-TS85ALW telephones were used for a short period during the SYDNEY 2000 Olympics. Their features include Data Port, Programmable Call Restriction, 16 digit LCD Readout, One touch speed dial, NEW 6 CAN COOLER AS USED BY VOLUNTEERS DURING Hands Free Handset compatibility, Built in Hands Free Speakerphone, 9 Step Electronic Volume THE OLYMPICS. Soft, foldable $5 Control for Speakerphone, 5 step Electronic NEW HALOGEN LAMPS Osram brand Volume Control for headset and handset, Call 12V 5W $2.50 Waiting, Ring Indicator, Call Forward immediate, 12v 20W $2.50 Dial lock, Redial, Recall. See Pansonic website for more information. These may be a 8 O H M 7 5 m m M A G . - S H I E L D E D little dusty . The speed dial window has never been written on. You will find these as a newly introduced product in a Major Australian Electronics dealers' catalogue for SPEAKERS. $161. The manual is not supplied but can be downloaded. Our introductory price will Foam edged poly cone :2 for $9 be: (KXTS85) $50 each or 2 for $90 JUMBO SERVO KIT...Use it with our "German Motor" or a motor / gearbox of PENTIUM II MOTHERBOARD: Recent VIDEO CAMERAS your choice. This kit is designed to work motherboard made for the latest CPU's. The output of these cameras below is std just like a std R/C servo (with much greater Std ATX form factor. Has 3 x (16-bit) ISA video & can be plugged into the "VIDEO power) using 1-2mS pulse width. It has slot, 4 x (32-bit) PCI slots, 1 x AGP slot & 3 IN" socket of any Australian std VCR, proportional control ie. if you move the x DIMM (memory) slots, On-board 1 x video monitor or TV, or via an RF joystick a little, the servo moves a little. It PS/2 keyboard, 1 x PS/2 mouse socket, 2 x Modulator to an Ant. Input. The B/W can be used with a std. R/C receiver or with USB, 1 x parallel, 2 x serial ports. With cameras are Infra Red responsive & can our servo controller kit. Some applications setup manual & CD, IDE & FDD cables. be used in total darkness with IR inc... R/C models, Robotics, Gates & Brand new in original box. Accepts Intel Illumination. Doors, Fly by wire control (with our servo Pentium II & Intel Celeron CPU's (NOT MONOCHROME CCD VIDEO CAMERA controller) of things like Forward controls SUPPLIED) from 233 to 800MHz. The WITH AUDIO: B&W Camera built on a for outboards (steering, throttle etc), Pan & CPU socket is SLOT-1, S-370 CPU could PCB with auto iris. (0.1 lux). Can be tilt of Cameras, Antenna dishes etc. Could be use with a converter board (NOT focused sharply down to a SUPPLIED). Selectable 66 & 100MHz be used as a winch few mm(useful for people BUS speeds & a clock multiplier up to 8 for sails etc. with the with visual impairtimes. Should accept Pentium III CPU's, addition of a multi ment). Spec.: on a 100MHz bus: (SP6XS) $90 turn pot & a winch Power req.: 10V to drum. Kit includes 12V <at> approx. PCB, all onboard parts, feedback pot & KTX PENTIUM II HEATSINK & FAN: 50mA.CCD: 1/3", suitable mini case $35 (arm or winch Brand new in original 30grams: with 60° $89, with 92° lens: drum not included) Add $20 for geared pack with clips & power lead 60 SEC VOICE RECORDER MODULE German Motor. terminated with This is a small pre-built module and can be DUAL SERVO CONTROLLER KIT a 3 pin plug. set from 1 long up to 8 short messages. This is designed to control R/C (HHSP2) $4.50 Features include eight pushbuttons, one servos with 1-2mS pulse with. Others available. Check our web site for each message. Operates from Ideal for use with our 6Vdc:$28....Optional speaker $1 30 SEC VOICE RECORDER MODULE Jumbo Servo kit or with This is a pre-built module and is the size of BATTERIES std servos. Applications a postage stamp. Ideal as a personal Used in the opening and closing include testing of R/C reminder or could be integrated into other ceremony to illuminate the props etc. servos pan and tilt of kits like the shop minder to say "welcome Limited stock. 2V per cell, all have Y2K cameras etc. Std. people to a shop", "mind your step", date codes. Ideal for fishermen etc. kit includes PCB all onboard components, suitable case and "please close the door". pots. $14.... Std. Kit plus power supply Operates from 6Vdc : $16 suitable for powering 1 Jumbo Servo $24 Optional speaker $1 MICRO SWITCHES 3 mini micro switch assembly on a 600mm cable with a small plug. 3 assemblies for $5 (BRAND NEW) COMPRESSOR / VACUUM PUMP: Thomas brand, US made units, model # 500CAR75. 115V / 60Hz / 8.1A, 100V / 60Hz / 7.4A and 100V / 50Hz /6.8A. Maximum pressure 435PSI, maximum vacuum 27Hg. We ran these from a 24V DC supply, current drawn was 1.4A (No load) and they produced a pressure of 30000kPa. Two of these units could probably be connected in series to run from 240V, but their inputs or outputs (AS NEW) WEATHERPROOF MARINE HORN SPEAKERS: Military grade marine weatherproof horn speakers, made from stainless steel and extremely durable plastic (horn). The impedance of the speaker is 15ohm and its direct connections are accessible. An impedance matching transformer is also included (70V line?) and the power settings are switchable at 1/4, ½, 1, 2, and 4 watts. Overall dimensions are 290 x 260 x 215mm and the unit weighs 6.3Kg. These are unused and in "as new' condition: (ZA0119) $60 each or 2 for $110 (NEW) COMMUNICATIONS SPEAKER: Nokia brand high quality ABS slim line case measuring 110 x 60 x 50 with swivel would have to be bracket. Includes mounting screws and connected together so they double sided tape. share the load equally? Measures Approximately 1.5 approximately 264mm long and 205mm metre cable with high. Weighs 5.1Kg. A few only at a 3.5mm mono plug: bargain price: (ZA0118) $75 each (AS6) $5.50 12V 3.6 Aph gel cell on a waist belt $15 12V 8Aph $14 8 CHANNEL PC CONTROLLED RELAY INTERFACE KIT: Ref: Silicon Chip September 2000. This kit is designed to operate eight relays from a PC parallel port. The kit includes PCB and all onboard components including eight relays (2 are high current contact ratting) with "ON" indicating LED's and a PCB mounted DB25 connector. Also included is some simple software (on 3.5" floppy disk) written in Basic to operate the kit: (K164) $40 A suitable DB25 male to DB25 female data cable is also available for this kit: (K164C) $8 CCD CAMERA INTERFACE KIT: Ref: Electronics Australia October 2000. This kit is designed to interface between CCD Cameras and a Television. Features include regulated 11V to power the camera, an audio amp with an LM386 IC & a VHF video modulator for use with TV antenna inputs. Input to the kit is 14 - 17V AC or DC. The PCB also has provision for a UHF A/V Modulator Kit inc. PCB & all on-board components inc. VHF Modulator, electret mic, speaker & a plastic case: (K163) $18 Kit with CA41L92 CCD Camera: (K163C) $95 Suitable Plugpack: (PP13) $9 UHF A/V Modulator: (RM1) $18 NEW 30M 10A EXTENSION LEAD HEAVY DUTY TRADES QUALITY $30 (NEW) AUTO DOCUMENT FEEDER DF10II (FOR OVERHEAD PROJECTORS): Brand new in box with Infra-red remote control batteries inc & operation manual. Could be adapted to suit most photo copiers: (11) $ (70 only) FLIGHT FORCE PC JOYSTICK: This analogue joystick features 4 fire buttons - with disable function for 2 player compatibility, Contoured handgrip, auto centering, independent auto-fire & X & Y axis trim. Has a durable metal base with a large suction cup for stability. This item is new & in its original retail box: (ZA0098) $25 VHF-UHF TV ANTENNAS WITH ROTATOR New & complete in original box. Features include high gain RF amp. This antenna would be ideal for homes, units or caravans, weekenders and camper vans where it can be setup or stowed away quickly. These antennas come pre-wired with several meter of very flexible co-ax ready to plug into there base control unit. Features inc. Quick G-clamp style antenna mount and could be fitted to a balcony rail in seconds, rotary control from base control unit or its ultra-sonic remote control from the comfort of your armchair. The base control unit powered by 240Vac and comes with instructions for simple conversion to 12V operation as it doesn't have local approvals. We do not recommend connection to Australian mains supply!: $29 $29 CHECK OUT OUR BARGAIN CORNER FOR G R E AT B A R G A I N S L I K E THESE...AVO Multi-meters $30... Megger-meters $35...Great bargains at a fraction of the new cost. www.oatleyelectronics.com Orders: Ph ( 02 ) 9584 3563 or 64, Fax 9584 3561, sales<at>oatleyelectronics.com, PO Box 89 Oatley NSW 2223 major cards with ph. & fax orders, Post & Pack typically $7 Prices subject to change without notice ACN 068 740 081 ABN18068 740 081 SC_FEB_01 Clean up the clicks & pops on your vinyl records with the LP DOCTOR Building the LP Doctor sure is a lot easier than under­standing how it works. All the parts are mounted on a single PC board and this is installed in a rack case to produce an attractive unit. Pt.2: By JOHN CLARKE The PC board for the LP Doctor is coded 01101011 and meas­ures 311 x 160mm. Begin construction by checking your board for any shorts between tracks or breaks in the copper traces. Check also that the holes sizes are correct. You will need 3mm holes for the board mounting screws, 1mm holes for the 1N4004 diodes and 1.5mm holes for the terminals of the two potentiometers (VR1 & VR2). Finally, check that the PC stake 76  Silicon Chip holes are the correct size for the stakes that you are using. In most cases, everything will be correct but it’s always a good idea to check before installing any of the parts. Fig.9 shows the parts layout for the PC board. You can now start the assembly by installing the links and resistors. The resistor values can be checked against the colour code table (Table 2) or you can check their values using a digital multimet­er. The best approach is to install and solder 10 or 12 resis­tors at a time. The excess lead lengths are then trimmed close to the board using sidecutters before moving on to the next batch. The PC stakes can go in next – there are 25 stakes in all and these are installed at the external wiring points (for the LEDs, power supply, earth, signal inputs and outputs, and switch S2). Once these are in, install inductors L1 and L2. These con­sist simply of short lengths of tinned copper wire which are threaded through 5mm-long RF ferrite beads. Now for the semiconductors. Make Below: this view shows the general layout of all the hardware. The rotary switch terminals are connected to PC stakes on the PC board using lengths of tinned copper wire. The LP Doctor can be used every time you listen to your LPs or it can be used to clean up the sound from LPs before transferring them to CD-ROM. sure that each IC goes in its designated position and that it is correctly orientated. The ICs all face in the same direction and pin 1 is always adjacent to a small dot or notch in one end of the plastic body of the device. Similarly, watch the orientation of the diodes and transis­tors when installing them. Take care also not to get the transis­tors mixed up – Q1 & Q3 are PNP BC558s, while Q2 & Q4 are NPN BC338s. Use the 1N4004 power diodes for D1-D5 and the smaller-bodied 1N4148s for D6-D10. The three 3-terminal regulators (REG1-REG3) all face in the same direction but note that these devices are all different so don’t get them mixed up. In particular, REG1 is an LM317 type, while REG2 is an LM337. The third regulator, REG3, is an LM29405. Install them with their metal tabs positioned as shown on Fig.9 The board assembly can now be completed by installing the capacitors, trimpots, potentiometers (VR1 & VR4) and the two crystals (X1 & X2). You will find that the ceramic and MKT ca­pacitors have their values marked in code – see Table 1. The capacitors and crystals can go in either way around but make sure that the electrolytic capacitors are installed with the correct polarity. The exceptions here are the bipolar (BP) or non-polarised (NP) electrolytic capacitors, which can be installed either way. There are quite a lot of these, so check the parts layout diagram carefully for their locations. Preparing the case As supplied, the case comes in pieces and it’s a good idea to drill the front and rear panels before putting it together. Use the front panel artwork (Fig.10), the signal input wiring diagram (Fig.11) and the mains wiring diagram (Fig.12) as a guide to positioning these holes. Starting with the front panel, you have to drill holes for mains switch S1, potentiometers VR1 & VR4, the three indicator LEDs and rotary switch S2. The square hole for the mains switch (S1) can be made by first drilling a series of small holes around the inside perimeter, then knocking out the centre piece and carefully filing it to shape. Don’t make this hole too big – the mains switch must be a tight fit so that it is properly secured by its retaining tabs. The rear panel requires holes for the safety fuseholder, the mains lead cordgrip grommet, the 4-way RCA socket and an adjacent earth lug. Take care with the hole for the cordgrip grommet. This hole is not round - instead, it must be carefully profiled to match the shape of the grommet, so that the grommet can not later be pulled out when the mains cord is fitted. Once all the holes have been drilled, assemble the case without the lid, using the machine screws supplied. The next bit is important: be sure to scrape away the paint at the countersunk screw points, so that each section of the case makes good metal-to-metal contact. This ensures that each section is properly earthed to mains earth (important for safety reasons) and also stops hum problems. Next, position the PC board on the base of the case on 10mm standoffs with the shafts of the potentiometers protruding through the front panel. You can now fit the knobs to the pot shafts and mark out the locations for the six standoff mounting holes. You should also mark out the mounting holes for the power transformer and the mains earth lug (4mm hole). This done, remove the PC board and drill all the marked holes in the base. Once the holes have been drilled, scrape away the paint or anodising from the area around the two earth lug mounting holes (ie, adjacent to the power transformer and 4-way RCA terminal block). This is necessary to FEBRUARY 2001  77 10k 1F 0V 9V 25V AC IN 0V/9V D1 D2 25V D3 D4 REG1 470F 470F .0068F 10k 0.1F 470F 16V 0.1F 11k 22k 150pF 22k 560pF 10k TP4 150pF 10F + 100k 220 27k 1k 1k 150pF .068F BP 10k SOLDER TO POT BODY 1M 1M .0068F 270 10F 5.1k IC7 M65830P 1 IC14 TL072 VR7 250k 100pF 1 + SWITCH S2 (REAR VIEW) 9 C A R L BP 39k 1F 82k 10F BP 150pF 82k 39k 1F BP 10F BP 82k 100k 150 150 78  Silicon Chip 22k 11k 22k .068F 27 0.1F 0.1F 22k 150 100k 100k .0047F 100pF 16k 200k 10F BP 1k IC1 LM833 1 0.1F 100k 100k 100k 82k BP 1 LEFT IN BP SIG GND 10F RIGHT IN 1k L2 10F 47F 0.47F 10F LEFT OUT GND SIG SIG GND RIGHT OUT SIG TO CHASSIS EARTH L1 47F 150 9 BP 560pF 10F 47F + 8 L R IC9 LM833 560pF 100k 7 3 10F 16k 10 C 150pF 1 390pF 100k 560pF 6 IC5 LM833 BP 10F 10k .01F 10F 11 5 L 10k 100k 100k 2 PROCESS BYPASS 4 12 FILTER 1 BP 100k 47k H11F1 10F 10k BP 150pF + 2 A R 10F 11k 1 IC8 100k 1 IC4 BP 200k .01F 22k 10F + 3 8 L OUT 1 R 560pF 10F BP 100k 330pF 0.1F 10k 10k 10k 100k 10F BP 10k 100k 150pF .068F 10F + TO SWITCH S2 PIN NO. 7 470F 16V + VR1 10k 330pF H11F1 SOLDER TO POT BODY IC3 M65830P + 100k 100pF 1 + BP + LEVEL + BP 100pF 2MHz 1k 10k 2x 10F X1 .001F 10k 33F 2.2k IC2 LM833 + 56k A LED1 1M 10F 1 10F + K IC6 LM393 1 + 10F 1k 10k 33F .015F BP 56k 560pF 47k .015F .0047F 100pF 10k 10k 270 10F + 100k 47F 10F + 330pF Fig.10 (right): this is the front panel artwork, reproduced 50% actual size. 10k 10k .001F 22k 10k TP3 100pF 2MHz 11k 10pF 4.7k 27k 4.7k D9 D8 + + VR4 50k X2 BP 10F 1N 4148 VR6 250k 1M BP 10F 150pF 1N 4148 100k 10pF 10k 10k TP2 220 47k 47k .068F 27 100k 1 IC10 TL072 BP 10k 220 SENSITIVITY 1F 0.1F 10k 10F 5.1k VR3 250k 1 IC11 TL072 LED3 A Q4 10pF 10F + BP BC338 Q2 + VR2 250k 10F BC558 BC338 1N 4148 A K TP1 1N 4148 100k 10k + 220 LED2 Q3 10F BC558 D7 D6 + 10pF Q1 K 1 IC16 7555 Fig.9: install the parts on the PC board as shown here. Make sure that all parts are correctly oriented and are mounted in their correct locations. 10k 10k 10F + VR5 250k 100k 10k 1 IC13 7555 + 10k 1 IC12 LM393 VR8 250k 100k 1F REG2 10F 100k + 1 IC15 LM393 2.2k LM337 1 IC20 74HC165 22k 47k D10 22k 6.8k 560pF 1N 4148 + 100k 1F 2.2k LM317 2200F 100k REG3 2940-5 + 1k 4.7k 10F 10F BP + 100F 100F 0.1F 1 + 10F 10F IC19 4022 + + IC18 4093 4.7k 10F + .001F + + IC17 4060 1 D5 1k + 10F + 1 2200F + 10F Table 1: Capacitor Codes               Value IEC Code EIA Code 0.47µF   474   470n 0.1µF   104   100n .068µF  683   68n .015µF  153   15n .01µF  103   10n .0068µF  682   6n8 .0047µF  472   4n7 .001µF  102   1n0 560pF   561   560p 330pF   331   330p 150pF   151   150p 100pF   101   100p 10pF   10   10p ensure that the earth lugs make good contact with the bare metal of the case. Final assembly The various hardware items – including the power transform­er, switch S2 and the earth lugs – can now be installed in the case. Use the mounting kit supplied to secure the toroidal trans­former – the large rubber washer goes directly on top of the transformer, then the metal washer is positioned over the top of this and the assembly secured using the mounting bolt. Make sure that the mains earth lug is properly secured – it must be attached using an M3 screw, nut and Fig.11: here’s how to wire up the RCA sockets on the rear panel. These connections must be run using shielded cable. star washer. We also recommend that you fit a second lock “nut” to this assembly, so that it cannot possibly come loose later on. Once it’s fitted, use your multimeter to confirm a good contact between the earth lug and the various panels of the case. The earth lug adjacent to the input sockets is secured using one of the mounting screws that’s used to secured the 4-way RCA terminal panel. Begin the wiring by running shield­ed cable connections between the RCA sockets and the PC board (Fig.11). The adjacent earth lug is connected to a PC stake on the board using insulated hookup wire. An additional length of insulated hookup wire is then run from this point and soldered to the bodies of potentiom­ eters VR1 and VR4. You will need to scrape away the Table 2: Resistor Colour Codes  No.    4    2  27    4    2    5    2    2    9    2    4  26    1    2    4    3    8    2    4    4    2 Value 1MΩ 200kΩ 100kΩ 82kΩ 56kΩ 47kΩ 39kΩ 27kΩ 22kΩ 16kΩ 11kΩ 10kΩ 6.8kΩ 5.1kΩ 4.7kΩ 2.2kΩ 1kΩ 270Ω 220Ω 150Ω 27Ω 4-Band Code (1%) brown black green brown red black yellow brown brown black yellow brown grey red orange brown green blue orange brown yellow violet orange brown orange white orange brown red violet orange brown red red orange brown brown blue orange brown brown brown orange brown brown black orange brown blue grey red brown green brown red brown yellow violet red brown red red red brown brown black red brown red violet brown brown red red brown brown brown green brown brown red violet black brown 5-Band Code (1%) brown black black yellow brown red black black orange brown brown black black orange brown grey red black red brown green blue black red brown yellow violet black red brown orange white black red brown red violet black red brown red red black red brown brown blue black red brown brown brown black red brown brown black black red brown blue grey black brown brown green brown black brown brown yellow violet black brown brown red red black brown brown brown black black brown brown red violet black black brown red red black black brown brown green black black brown red violet black gold brown FEBRUARY 2001  79 INSULATE ALL EXPOSED MAINS CONNECTIONS! 250VAC MAINS CABLE F1 CORD GRIP GROMMET LO W PANEL MOUNT FUSE HOLDER SECURE LUG TO METAL CHASSIS WITH M3 SCREW, NUT & STAR WASHER Fig.12: follow this wiring diagram exactly to install the mains wiring. Be sure to use mains-rated cable for all mains wiring and make sure that the earth lug makes good contact with the chassis. All exposed mains terminations should be sleeved with heatshrink tubing and the wires should be laced together using cable ties – see text and photos. N BLU BR OW L E E GREEN/ Y T1 MT-2082 0V .001F 250VAC D5 MAINS RATED S1 CLASS "X2" 250VAC CAPACITOR (REAR VIEW) passivating coating from the pot bodies so that the solder will “take”. If you don’t do this, you will get a “dry” joint for sure and the pot bodies will not be properly earthed to the signal input. And that could cause hum problems. The three LEDs are installed by pushing them through the holes in the front panel and then soldering their leads to the board-mounted PC stakes. Take care with the lead polarity – the anode lead is always the longer of the two and the cathode lead is adjacent to a flat on the plastic collar of the LED body. Switch S2 can be wired to the PC board using tinned copper wire. Make sure that the wires are positioned so that they don’t come in contact with one another. Mains wiring Fig.12 shows the mains wiring details. Exercise extreme caution when Table 3: Changing Delays For IC3 & IC7 With Linking On IC20 Delay 0.5ms 1.0ms 1.5ms 2.0ms 2.6ms 3.1ms 3.6ms 4.1ms 4.6ms 5.1ms Pin 12 GND GND GND GND GND GND GND GND GND GND 80  Silicon Chip Pin 13 GND GND GND GND GND GND GND GND GND GND Pin 14 GND GND GND GND GND GND GND GND + + Pin 3 GND GND GND GND + + + + GND GND Pin 4 GND GND + + GND GND + + GND GND Pin 5 GND + GND + GND + GND + GND + 9V 0V 9V D1 D2 D3 D4 470F + 25V 470F + 25V installing this wiring and be sure to follow Fig.12 exactly – your safety depends on it. First, strip back about 380mm from the outer sheath of the mains cord, so that the Active (brown) lead has sufficient length to reach both the fuse and the power switch (S1). This done, clamp the mains cord into position using the cordgrip grommet. Check that the grommet properly clamps the cord to the chassis; you must NOT be able to pull the cord back out. The Active (brown) lead goes to the centre terminal of the fuseholder and the excess lead then run between the outside terminal and the mains switch. Slip a 40mm length of heatshrink tubing over the two leads before soldering them to the fusehold­ er. Once the connections have been made, push the tubing over the body of the fuseholder (so that the terminals are covered) and shrink it down using a hot-air gun. The connections to the mains switch are made using fully-insulated female spade terminals. Make sure that the various leads are all securely crimped to these terminals before fitting them to the switch terminals (use the correct crimping tool for the job). The .001µF 250VAC capacitor is soldered (using minimum lead length) directly to the switch terminals, right at the switch body. It’s important to solder the leads right at the switch body, to leave sufficient room for the spade terminals to be pushed on. The earth (green/yellow) lead from the mains cord is sol­dered directly to the adjacent earth lug. This lead should be left long enough so that it will be the last connection to break if the mains cord is “reefed” out. Use four or five cable ties to lace the mains wiring to­gether, with one tie close to the mains switch and another close to the fuseholder. This will ensure that if a lead comes adrift, it will be secured to the other leads and the “live” end cannot make contact with the case. Finally, connect the transformer secondary leads to the relevant stakes on the PC board as shown in Fig.12. These leads should also be laced together using cable ties. Testing, testing At this stage, you should go over your work and carefully check the PC board assembly and chassis wiring. In particular check that all ICs and other semiconductors are correctly orien­tated and in their correct locations. You should also make cer­tain that the mains wiring is correct and that the chassis is properly earthed (use a multimeter to check for continuity bet­ween the chassis and the earth pin of the mains cord). Now install the fuse in the fuseholder, then set your multimeter to the DC volts range and connect its common lead to the metal tab of regulator REG3. Apply power and quickly check that there is +5V at pin 16 of IC17, +7.5V at pin 8 of IC1 and -7.5V at pin 4 of IC1. Note that the +7.5V supply rail will take a second or two to stabilise after power has been switched on. Also the voltage could be between 7.3V and 7.9V, depending on the particular regulator. If all is OK so far, you can check the supply rails to the other ICs. There should be +5V at pin 16 of IC17, IC19 Parts List 1 1U metal rack case (Altronics H 5035 or equivalent) 1 PC board, code 01101011, 311 x 160mm 1 9V 20VA toroidal transformer (Jaycar MT 2082 or equiv) (T1) 1 SPST mains rocker switch with neon (S1) 1 2P6W rotary switch (S2) 1 3AG panel-mount safety fuseholder (F1) 1 150mA 3AG slow blow fuse 1 cordgrip grommet for mains cable 1 7.5A mains cable and plug 4 rubber feet 1 dual 10kΩ linear 16mm pot (VR1) 1 dual 50kΩ linear 16mm pot (VR4) 6 250kΩ horizontal trimpots (VR2,VR3,VR5-VR8) 2 RF ferrite beads 5mm long (L1,L2) 2 16mm black anodised knobs 1 22mm black anodised knob 2 2MHz crystals (X1,X2) 1 7.5A mains power lead and plug 1 35mm length of 15mm diameter heatshrink tubing 1 4-way RCA socket strip 1 M4 x 10mm screw 1 M4 nut 1 M4 star washer 14 M3 x 6mm screws 2 M3 nuts 6 M3 shakeproof washers 6 M3 tapped spacers 10mm long 1 M4 crimp eyelet lug 1 M3 crimp eyelet lug 3 fully insulated 6.4mm female spade crimp lugs 1 4m length of 0.8mm tinned copper wire 1 400mm length of single shielded cable 1 300mm length of green hookup wire 6 100mm long cable ties 24 PC stakes Semiconductors 4 LM833 op amps (IC1,IC2,IC5,IC9) 2 M65830P or M65830BP (but NOT 65830AP (IC3,IC7) 2 H11F1 or H11F3 opto FETs (Quality Technologies QT or Isocom) (IC4,IC8) 3 LM393 comparators (IC6,IC12,IC15) 3 TL072, LF353 dual op amps (IC10,IC11,IC14) 2 7555 timers (IC13,IC16) 1 74HC165 8-bit shift register (IC20) 1 4022 divide by 8-counter (IC19) 1 4060 binary counter (IC17) 1 4093 quad dual NAND Schmitt trigger (IC18) 1 LM317T adjustable positive regulator (REG1) 1 LM337T adjustable negative regulator (REG2) 1 7805 5V regulator (REG3) 2 BC328 PNP transistor (Q1,Q3) 2 BC338 NPN transistor (Q2,Q4) 3 3mm red LEDs (LED1-LED3) 5 1N4004 1A diodes (D1-D5) 5 1N4148, 1N914 diodes (D6-D10) Capacitors 2 2200µF 16VW PC electrolytic 2 470µF 25VW PC electrolytic 2 470µF 16VW PC electrolytic 2 100µF 16VW PC electrolytic 2 47µF 25VW electrolytic 2 47µF bipolar electrolytic 2 33µF bipolar electrolytic 21 10µF 16VW electrolytic 15 10µF bipolar electrolytic 6 1µF bipolar electrolytic 1 0.47µF MKT polyester 9 0.1µF MKT polyester 4 .068µF MKT polyester 2 .015µF MKT polyester 2 .01µF MKT polyester 2 .0068µF MKT polyester 2 .0047µF MKT polyester 1 .001µF 250VAC X2 class polyester 3 .001µF MKT polyester 7 560pF ceramic 4 330pF ceramic 8 150pF ceramic 6 100pF ceramic 4 10pF ceramic Resistors (0.25W, 1%) 4 1MΩ 26 10kΩ 2 200kΩ 1 6.8kΩ 27 100kΩ 2 5.1kΩ 4 82kΩ 4 4.7kΩ 2 56kΩ 3 2.2kΩ 5 47kΩ 8 1kΩ 2 39kΩ 2 270Ω 2 27kΩ 4 220Ω 9 22kΩ 4 150Ω 2 16kΩ 2 27Ω 4 11kΩ FEBRUARY 2001  81 This is the view inside the completed unit. Keep the mains wiring tidy and make sure that the cord is properly secured. & IC20, pin 14 of IC18 and pins 1 & 24 of IC3 & IC7. Pin 8 of all the 8-pin ICs should be at +7.5V. Similarly, pin 4 of all the 8-pin ICs should be at -7.5V, except for IC13 & IC16. IC13 & IC16 should have +7.5V at pins 4 & 8 and -7.5V at pin 1. Assuming that all these voltages check out, you now have to adjust the voltage offsets using the onboard trimpots. The procedure is as follows: (1). Connect a multimeter to test point TP1 and adjust VR2 slowly until the voltage is below about ±60mV DC. This done, connect the meter to TP3 and adjust VR6 for a similar value. Note: this adjustment is a little tricky, as the voltage will jump suddenly from a positive value to a negative value, so proceed slowly here. (2) Monitor test point TP2 and adjust VR3 for 0mV, or as close to this as possible. (3) Monitor test point TP4 and adjust VR7 for a 0mV reading. (4) Set trimpot VR4 to mid-position and adjust trimpot VR5 so that the left blanking LED (LED2) is just past the threshold of turning off (ie, the LED should just remain off). Adjust VR8 so that LED3 also just remains off. 82  Silicon Chip You are now ready to give the LP Doctor a test run. To do this, connect a turntable to the inputs and connect the outputs to an auxiliary (line level) input on a stereo amplifier (use shielded leads fitted with RCA connectors for this job). Note that you must not connect to the LP Doctor’s outputs to the phono inputs on your amplifier. That’s because the LP Doctor has its own inbuilt RIAA phono preamplifier and you’ll really mess the sound up if you then feed the signal through another phono preamp stage. Now set the Sensitivity pot (VR4) fully anticlockwise, play an LP and adjust the Level pot (VR1) so that the clipping LED (LED1) just flashes on high level signals. You can then test the three positions for rotary switch S2 – ie, Bypass, Process and Process & Filter. In the Bypass mode, any clicks and pops on the LP will still be heard since no processing takes place. Switching to the Process mode should eliminate many of these clicks and pops, provided the sensitivity control is adjusted correctly. This control should be set so that the blanking LEDs light when there is a click or pop but not for normal program material. The third position (Process & Filter) should not only reduce clicks and pops but should reduce high frequency noise as well. Changing delay times Finally, some readers may want to experiment with different delay times for the delay chips (IC3 & IC7). This can be done by changing the connections to the D1-D6 inputs (ie, pins 12, 13, 14, 3, 4 & 5) of IC20. Table 3 shows the connections required for delays ranging from 0.5ms to 5.1ms in 0.5ms steps, which should be sufficient for experimenters. The PC board has been designed to make these changes easy. All you have to do is cut the thinned track sec­ t ions which connect each pin to the +5V or GND rail and solder a bridge to the alternative rail instead. Note that the pattern originally sets the delay to 1ms – ie, pin 5 high and the remaining pins low. Note also that the delay times for 7555 timers IC13 & IC16 must be greater than the set delay time for IC3 & IC7. This means that the .0068µF capacitor at pins 6 & 7 of IC13 & IC16 Silicon Chip Binders REAL VALUE AT $12.95 PLUS P&P These binders will protect your copies of S ILICON CHIP. They feature heavy-board covers & are made from a dis­ tinctive 2-tone green vinyl. They hold up to 14 issues & will look great on your bookshelf.  Hold up to 14 issues  80mm internal width  SILICON CHIP logo printed in gold-coloured lettering on spine & cover Price: $A12.95 plus $A5.50 p&p. Available only in Australia. Silicon Chip Publications PO Box 139 Collaroy Beach 2097 Or fax (02) 9979 6503; or ring (02) 9979 5644 & quote your credit card number. Use this handy form Enclosed is my cheque/money order for $________ or please debit my ❏ Bankcard ❏ Visa   ❏ Mastercard Card No:_________________________ Card Expiry Date ____/____ Signature ________________________ Fig.13: this is the etching pattern for the PC board, reproduced 70% of full size. Name ___________________________ Address__________________________ should be changed when longer delays are programmed. The delay time for IC13 & IC16 is equal to 1.1RC, where R is the resistor value (1MΩ) and C is the capacitor value on pins 6 & 7. Use the next available capacitor value up from the SC calcu­lated value required. __________________ P/code_______ FEBRUARY 2001  83 VINTAGE RADIO By RODNEY CHAMPNESS, VK3UG The Healing 412E: an Australianmade PC-board valve radio Valved radio receivers on PC boards were not all that common in Australia, mainly because few manufacturers took the plunge and adopted this technique. Among those that did were Healing, Pye and Admiral. There’s no doubt that PC board production methods simplify production line manufacture. However, with valve radios, there was the problem as to how to mount the heavy power transformer. Mounting it on the PC board wasn’t really a proposition, since the board could easily be cracked if a minor mishap occurred in handling the receiver. For this reason, the power transformer was usually mounted either on a small metal sub-chassis (eg, as in the Healing 412E mantle receiver) or on a substantial chassis which also accommo­dated other heavy items (eg, as used by Admiral). In the latter case, the PC board was mounted in a cutout on the chassis. Healing 412E The Healing 412E is a small mantle AM receiver which used three valves: a 6BE6 converter, 6N8 IF and detector stage, and a 6BM8 for the audio output stages. The power supply consists of a transformer and a half-wave solid state rectifier – see Fig.1. The dial system on this set is rather crude, being a di­ rect-drive system with the tuning knob mounted on the end of the tuning gang spindle. I had expected that it would be touchy to tune but the knob is big enough to make tuning easy. The dial leaves a bit to be desired, however – it consists of nothing more than a piece of gluedon cardboard with station markings (some radios apparently have the dial calibrated in frequency only). My radio has no cover over the dial although some units were fitted with a clear plastic cover. In this set, the power transformer was mounted on a small sub-chassis The PC board, mains transformer and the transformer sub-chassis are all removed from the cabinet as one piece. Note the earthing wire from the 6BE6 shield to the top of the adjacent IF transformer can – a necessary modification to improve sensitivity. 84  Silicon Chip at the righthand end of the cabinet (as viewed from the front). A PC board running across the remainder of the cabi­net width took care of most of the circuitry, while a multiple-turn loop antenna was wound on the back wooden board cover of the receiver. Interestingly, the more fashionable loopstick antenna was not used in this set. Restoring the Healing 412E So how did I come by the set? Well, a friend was cleaning out his garage and wanted to get rid of it. When I saw it, I could understand why – it was the grubbiest little mantle set I had seen in years. Despite this, I happily accepted the receiver although I had no idea at the time what I would do with it. Eventually, however, I decided to restore the set and I began by dismantling it so that it could be cleaned up. It was covered in oily, greasy dust-impregnated muck and had also had water through it if the rust was any indication. Initially, I decided to clean the PC board and chassis metalwork using a brush soaked in household kerosene. This did a reasonable job but some spots were difficult to get at, so the cleaning was not to perfection. It was then that I made my second mistake (the first being accepting the set) – I tried using methylated spirits to give the chassis and PC board a final clean but found that this removed the screen-printed track pattern on the top of the board. This was something I hadn’t expected. The screen-printed track pattern is handy because it mirrors the copper track pattern on the underside of the board, which makes it easy to trace the circuit. I dried the metho off as best I could and was relieved to find that most of the gunk was removed but not much of the print. The cabinet was an even worse disaster. It was scrubbed in the laundry tub using water and detergent to get the gunk off. This was a slow process because I had to be careful to avoid splashing water onto the paper dial scale. The front decorative grille is a real challenge to clean. It consists of many 5mm square holes which are around 5mm deep. It was extremely difficult to clean the sticky gunk out of these recesses, so I tried using methylated This view shows the Healing 412E before cleaning and restoration. The cabinet was covered in an oily dust-impregnated muck and was scrubbed clean in a laundry tub using water and detergent. spirits to help loosen the gunk. Unfortunately, the grille started to dissolve – or perhaps it was some paint (I’m not sure) – so I promptly stopped doing this. The grille returned almost to normal once the methylated spirits had evaporated but it left a dirty white-looking finish where the metho had been. Because I had nothing to lose, I decided to spray-paint the grille using several coats of white enamel. I had to hand-paint some bits around the dial and the end result was less than per­ fect but it was a definite improvement on the original. The rest of the cabinet needed a good cut and polish. I started by using a fine grade of wet-and-dry paper to get rid of the deep scratches but some were just too deep and I had to be content with getting rid of most of them. I then polished the cabinet with automobile cut and polish and it now looks quite reasonable, although not up to my normal standards. Water damage The thin composite wood panel used for the back of the set was also a problem. It had buckled due to water damage at some stage, although this The PC board was also covered with dirt and grease but responded quite well to a cleanup using a kerosene-soaked brush. FEBRUARY 2001  85 The composite wood panel used for the back cover had suffered water damage and was restored by spraying it with matt black paint. This panel also supports the antenna coil, which is mounted on the inside. hadn’t adversely affected the antenna loop that was glued to the back. This panel was sprayed with matt black paint to get rid of the water stains and this really improved its appearance, so that it now looks acceptable. When looking at a receiver, restorers should always ask themselves, whether the set is worth restoring in terms of time, effort and money. In this case, having restored the cabinet and cleaned the chassis, I was beginning to question the wisdom of tackling this particular project. Overhauling the circuit The next job was to get the set to operate. First, I checked that the power transformer had no shorts from any winding to earth using a high voltage tester. All was well, so I then had a good look at the power cord. It was a 3-core lead that someone had fitted with a bayonet connector, so that it could be plugged into a light socket! Naturally, the person who did this had cut the earth lead off which isn’t exactly the smartest thing to do. The bayonet connector was quickly removed, a new 3-pin plug fitted to the cord and the earth reconnected. Next, I checked the paper capacitors and found them all to be too leaky to leave in the set. These were all replaced, along with C7, a .01µF 25V redcap ceramic capacitor, even though it showed no sign of leakage. Redcaps have had a poor reputation for reliability and I believed it was cheap insurance to replace it. R7, the plate resistor for the 6BM8 triode, was also replaced as its value had increased from 220kΩ to 320kΩ. At this stage, all appeared to be in order and so the set was connected to power and switched on. The high tension (HT) voltage was around 140V which was close to normal. After a short time, the receiver showed signs of life and I was able to tune in a couple of the stronger local stations but the set’s performance was really quite poor. It was time to go through the alignment procedure and see if this would improve matters. Alignment To start the alignment, the tuning gang was closed and a 455kHz signal Fig.1: the circuit uses three valves: a 6BE6 converter, a 6N8 IF and detector stage, and a 6BM8 for the audio output stages. The power supply consists of a transformer and a half-wave solid state rectifier. 86  Silicon Chip This is the view inside the set after the restoration had been completed. An alignment, some valve changes and a couple of modifications turned it into a reasonable performer but it’s not as good as the Kriesler 11-99 mantle radio (July 1998). from a signal generator was applied to the grid of the 6BE6. I then attached a digital multimeter to the AGC line and increased the signal level so that some AGC could be meas­ured. This done, I was able to peak the alignment of the four IF windings, which were only slightly out of adjustment. An inter­esting feature of the IF windings is that they are all adjusted from the top. The slugs are hollow so it is possible to push an alignment tool through the first slug and adjust the second slug – nifty. Aligning the antenna and oscillator circuits is also fairly straightforward in this receiver. First, I closed the gang and applied a high-level 530kHz signal from the signal generator to the antenna terminal. I then adjusted the oscillator coil slug until the signal was audible. Next, I opened the gang, tuned the generator to 1630kHz and adjusted the oscillator trimmer capacitor until the signal was heard once more. I then repeated these adjustments at both ends of the dial, until the set would tune from 530kHz to 1630kHz. This set has no inductance trimming adjustment for the loop anten- na, so it can only be peaked for best performance at the high-frequency end of the dial. To do this, a relatively weak signal was coupled into the loop antenna and the tuned circuit adjusted at around 1400kHz for best performance. This was done by ear but a digital multimeter could again be attached to the AGC line to accurately indicate maximum sensitivity. Because there is no inductance adjustment for the loop antenna coil, the set’s sensitivity with a signal generator attached to the antenna terminal and earth varies across the band. A noisy signal could be heard at 10µV on 530kHz but only 3µV was required on 1600kHz to achieve the same result. And these results were obtained only after the problem described below had been solved. Improving the performance After the alignment had been completed, the set was still noisy and stations were weak at the low frequency end of the dial. The receiver certainly was not performing as well as I would have expected. Initially, I suspected that the 6BE6 was noisy. I’ve never liked 6BE6 Silicon Chip Binders  Each binder holds up to 14 issues  Heavy board covers with 2-tone green vinyl covering  SILICON CHIP logo printed in gold-coloured lettering on spine & cover REAL VALUE AT $12.95 PLUS P & P Price: $A12.95 plus $A5.50 p&p each (Australia only; not available elsewhere). Buy five and get them postage free. Just fill in & mail the handy order form in this issue; or fax (02) 9979 6503; or ring (02) 9979 5644 & quote your credit card number. FEBRUARY 2001  87 stalled and the back bias in­creased to -7.6V, indicating that the original valve lacked performance. I decided to replace it even though it probably had a reasonable amount of life left in it. Using a multimeter to monitor the AGC line and the back bias resistor is a relatively simple method of testing valves in a receiver to assess their performance. It’s worth remembering if you don’t have a valve tester. The bottom line The restored receiver looks quite presentable although it doesn’t exactly take pride of place in my collection. The tuning knob is direct-coupled to the gang. valves as they tend to be noisy due to their design. I tried another valve but no improvement was observed. I then placed my fingers around the valve and I noted a decrease in noise. It seemed that there were some strange radia­tion effects occurring, so I made a metal shield out of tinplate from a discarded fruit tin and placed it over the 6BE6. The shield was attached temporarily via a short length of wire to the gang and to the nearest IF transformer (both are earthed). By experiment, I found that the earthing point for the shield was critical. I ended up with around 50mm of wire running from the top of the shield to an earth point I made in one corner of an IF transformer. This can be seen on the photograph of the board. The radio now works very well on the low-frequency sta­tions. Why was it necessary to do this and what caused it? I have found that some radios are conditionally stable and it is neces­sary to do some remedial work on them to achieve good perfor­mance. In this case, I believe that the problem is caused by inadequate shielding due to the use of the PC board with its long, thin earth tracks. This causes the IF signal to radiate around the set and into sections where it shouldn’t, such as the aerial circuit which is resonant just above the IF frequency. The 6BE6 has no integral shield to stop radiation from its plate, so it will radiate signals on 455kHz. It’s likely that the set was regener88  Silicon Chip ative and on the verge of oscillation prior to the fitting of the earthed shield. It certainly sounds much better with the shield in place. Bypass capacitor Another small modification that also helped the general sensitivity of the receiver was to fit a 68pF ceramic capacitor on the underside of the PC board between pins 2 and 3 of the 6BM8. This bypasses any 455kHz signal that remains after the IF signal filter capacitors (C6 and C8). If this isn’t done, radiation from the 6BM8’s plate and screens finds its way back into the front end and tends to desensitise the receiver. Simple valve testing Despite my work so far, the radio was still somewhat lack­ing in performance. It was time to become a “valve jockey”. I left the digital multimeter attached to the AGC line and tuned the set to a strong station. The voltage reading on the AGC line was about -1.5V. I then tried a replacement 6BE6 which made no difference but when I changed the 6N8, the AGC increased to -3V. Obviously, the original 6N8 was rather sick and so it was con­ signed to the bin. The performance of the 6BM8 was checked by measuring the back bias across R11. This was around -7V but is supposed to be -7.5V. I removed the 6BM8 and the voltage decreased to -3.5V. A fresh 6BM8 was then in- This receiver appears to be similar in concept to American sets of the same vintage. The PC board, like many of that era, has the components going every which way. By contrast, modern PC boards invariably have the parts neatly placed and much more thought goes into making sure they are not overcrowded in any area. Mounting the PC board horizontally also created problems in this type of set. These receivers were destined to operate in the kitchen. The air flow due to the heat of the valves draws air through the set and cooking grease and dust settle on the board. If the boards had been mounted vertically, there would be much less grime on them, making it easier to identify components and printed tracks. However, I am not aware of any manufacturers that mounted PC boards vertically in their valve radios. The Healing’s performance doesn’t rival the Kriesler 11-99 that I described in July 1998. However, with the small modifica­ tions mentioned earlier, it is now quite a good performer. It’s a shame that the performance of many receivers suffered because manufacturers cut corners. Even the most prestigious manufactur­ers goofed from time to time. In summary, the Healing 412E is an interesting little re­ceiver designed for the lower end of the market and it does quite a creditable job. Cost cutting seems to have been one of the design objectives but despite this, it did all that was required of a kitchen set for that era. Personally, I prefer the Kriesler, which is a superior radio designed for the same market segment but I’m still happy to have this little unit in my collection. However, because of the less than pristine cabinet restoration, it won’t be sitting on the front row SC with my favourites. 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. PIC rain gauge doesn’t like odd days I have just completed building the PIC-Powered Rain Gauge as featured in the June 2000 issue of SILICON CHIP. I have been planning such a project since seeing a similar concept in a long-forgotten magazine many years ago which used a mercury tilt switch as a sensor and a telephone exchange subscriber’s meter as a recording device. Your design is a tad more “state of the art” and immediately caught my eye. I thought that you may be interested in some observations and also be able to comment on one operational aspect of the design. On initial testing I found that even though the vane passed through the photo detector beam, it did not result in an increase in the count display. I fixed a piece of thin shim brass to the vane which resulted in a 100% accurate count. Could it be that the plastic is transparent to infrared light? It seems unlikely but the brass fixed the problem. After testing the unit with “real” rain I have concluded that the protective insect screen on the funnel is not such a good idea. I have mounted a conventional rain gauge next to the automatic version as a check on the calibration. The first rain event resulted in a reading in the automatic Electric wok control wanted I hope your staff at SILICON CHIP might be able to create a control for most, if not all, electric fry pans and woks. My electric wok is controlled by a mechanical thermostatic switch. Even though it still works fine (actually, it’s brand new), I find the control range is too sluggish. If I set it to halfway, it cools down to a quarter of the original setting before turning back on. I hope you may be able to design gauge half that of the conventional gauge. There may be three reasons for this error: (a) the surface tension of water tends to make drops sit on top of the insect screen and not enter the funnel; (b) drops striking the screen with sufficient velocity tend to break up and not all will enter the funnel and (c) the surface area of the funnel is reduced by the surface area of the screen. None of the above may be true but after removing the screen, the next rainfall event resulted in 17mm in the conven­tional gauge and 16mm on the display of the automatic gauge; close enough for me, so I will leave the screen off and regularly check for invasion by creepy crawlies. This next observation concerns the recording of the previous day’s rainfall. My understanding is that rainfall recorded today will, after the empty time which, in my case, is midnight, be transferred to the previous day’s log and be recorded in “day -1”. Any other previous readings will at the same time be pushed back one day and “day -60” will fall off the edge. In my case, today’s reading is recorded in “day -2” and the next day will be moved to “day -4” and so on, with all recordings in even days and no recordings in odd days. The movement of previous day’s rain seems OK but always stepping a device similar to, say, a light dimmer switch, which can control the range more accurately. It would need a capacity of 2400W. (W. S., Narangba, Qld). • We would not be keen on a phase-controlled Triac circuit (ie, a light dimmer) at such high power. However, we have pub­lished a zero voltage switching circuit which is ideal for the job. Have a look at the Heat Controller published in the July 1998 issue. We can supply the issue for $7.70 including postage. two days instead of one day means, in effect, that I can only record 30 days and not 60 days as designed. Could I have done something wrong or have I discovered a bug? (B. C. Ballina, NSW). • The plastic vane entering the light sensor will be detected correctly if the vane penetrates deep enough into the slot. Adding a brass shim probably added the necessary extra depth for correct counting. The flyscreen mesh should not affect readings. Surface tension of the water droplets will cause some storage in the screen but these droplets will fall through with further rain­fall. The screen does not decrease the area of catchment since all water caught within the inside diameter of the 90mm endcap will eventually fall through into the funnel. The only cause of water loss would be if the rain water droplets bounced off the flyscreen to outside the catchment area. If this is the case, you can form the flyscreen so it is a cone shape inside the funnel. Also raising the lip height around the end cap will help. The movement of the day’s reading into the second day previous rather than the first day previous suggests that there is a faulty storage register inside your PIC. The least signifi­cant digit is not changing but remaining at 0. We suggest that you obtain a replacement PIC (IC1) from your kit supplier. Also see the Notes & Errata on page 93. How to test the Theremin I have built the Theremin project as described in the August 2000 issue but I cannot get any output. I checked the voltage on pin 6 of IC3 and pin 8 of IC2 and they were both 5.7V as expected. No matter how I adjusted VR1, the maximum voltage I could get was 3V on pin 1 of IC2. No amount of FEBRUARY 2001  89 Fence controller changes zap rate I built the Electric Fence Controller in the April 1999 issue. It has worked fine till now. The first sign of any fault was when I noticed that the controller fired about five times instead of once every 1.5 seconds. This fault appears to have resolved itself but I now get only 150V on the high voltage check instead of 340V with the pulse timer disabled. I have checked every component on the board and all appear to be OK. I had spare ICs so I replaced them to prove the origi­nals, again all OK. The only part to check now is T1 for shorted turns which will mean a rewind. I find this doubtful (but not impossible) as the winding of small transformers used to be my job. The material used was nothing twiddling the IF coils would result in a measurable voltage at the cathode of D1. I used a signal generator to check the audio stages and injecting a signal at pin 5 of IC2 resulted in a signal through the speaker, indicating the circuit beyond this point is OK. It appears that none of the oscillator circuits are work­ i ng. Could this be due to Jaycar substituting a 2N5485 for the originally specified 2N5484 JFETs? I do not have access to an oscilloscope. What other troubleshooting methods are there for this kit? Do you have AC/DC voltage measurements or some other means of confirming the oscil­lators are working properly? (B. D., via email). • The Theremin will work with the 2N5485 FETs as supplied with the Jaycar kit. The adjustment of VR2 can be a little touchy though, so you might want to try a multi-turn trimpot. Testing the rest of the circuit without an oscilloscope could be difficult. You could disconnect the 1kΩ supply resistors (100Ω for the volume oscillator) leaving only one oscillator operating at a time. Bring an AM broadcast band radio close to the Theremin and check that you 90  Silicon Chip but the best and it was layer wound on an automatic winder. I have checked the ratio and pres­ sure tests indicate it is also OK. What should I look for? (D. T., via email). • The change in firing frequency from once every 1.5 seconds to five times a second would suggest a problem with the IC2b oscillator. Check that the 10µF capacitor at pin 6 and the resistors at pin 7 are correct and are soldered without dry joints. If you are only obtaining 150V instead of 340V, the fault could be a leaky 7µF 250V capacitor or a problem with the feed­back network which maintains the 340V. Check the two 1.5MΩ resis­tors, the 10kΩ resistor to ground at pin 2 of IC2a and the com­ponents between pins 1 & 2 of IC2a. Also Mosfet Q1 may have gone faulty so it cannot charge T1 correctly. obtain a whistle in the sound. This would indicate that the oscillator that is connected is working. Using a torch as an IR illuminator I recall that you published an article a few years back on converting a normal torch into one that provides an infrared (IR) light source. Can you help me with details of this project? (J. C., via email). • We published an IR illuminator in the March 1995 issue and it could have been put in a torch but we did not do it. On a similar line though, we published a LED stroboscope in the Decem­ber 1993 and the LED illuminator was built into a torch. However, if you specifically want an IR illuminator, the March 1995 cir­cuit is more relevant. We can supply both copies at $7.70 each, including postage. IR version of LED torch The LED torch featured in the December 2000 issue was interesting. Could the circuit be adapted to use an infrared LED, making an IR torch? The reason I ask this is that the IRLED “spo­tlight” for CCD cameras doesn’t reach too far. If an IR spotlight of sorts were available, it would make it possible to see things which would otherwise be out of range of the CCD camera in low light or total darkness. Your comments would be appreciated. (S. N., via email). • Infrared LEDs have a lower forward voltage than white LEDs. In practice, if you want an IR illuminator, just connect a string of four or five IR LEDs in series with a 100Ω resistor to a 12V supply. If you want more IR light, just use more series strings in parallel. Using the Zener tester on transistors I have built the Zener Diode Tester for DMMs (March 1996) and it works fine. I am curious if it could be modified to use as a breakdown tester for transistors? (N. P., via email). • The Zener Diode Tester can be used to test the breakdown voltage for any silicon device, including transistors, for vol­tages up to 112V. RF choke for the LED torch (1). If you want to build the LED Torch in the December 2000 issue, I have found a 220µH RF choke at Jaycar which is smaller than winding one on a trigger transformer. It is Cat LF 1538 on page 214 of the current Jaycar catalog. (D. H., via email). (2). I was fascinated by the LED Torch project using a white LED and the ingenious way in which you fitted the works into the space occupied by a single AA cell. Since a kit was not available I decided to build up a circuit on the breadboard and the only problem was the creation of the 220µH inductor. I didn’t have any spare pulse transformers and they appear to have been deleted from the electronics suppliers catalogs. I built a few inductors on some ferrite cores which I had and these worked after a while (remember, if you use a green LED for the test load, you will only generate 2.6V across it). Then came serendipity. I used a prewound ring cored ferr­ite suppression choke and got brilliant results. So I then cast around for some ferrite cores to try and wind a smaller coil which would fit into the AA cell version. The first version used a suppression bead which I found in my junk box. 20 turns of fine wire (about 0.2mm) and I had a choke which worked. The core was about 6mm OD, 6mm long with a centre hole about 3mm. I then purchased a pack of Jaycar LF-1250 ferrite suppression beads. These are 5mm long, 4mm in diameter and with a 1.5mm bore although some of the bores appear larger – nearly 2mm. I select­ed two with the larger bores, superglued them end to end and wound on about 20 turns. This also worked and I am now ready to tackle the miniature versions when I get some copies of the PC boards. This could help other readers complete this project. (B. L., via email). • Thanks to these readers for these tips. Dick Smith Electron­ics are about to release their kit for the torch as well. It will be supplied with a penlite torch for just $14.60 (Cat K-3018). VU meter needs auto level control I have constructed a LED VU level meter for my car stereo, which is purely for aesthetic purposes; ie, regardless of volume, the display should work over most of its displayable range. The only problem is that the stereo does not have a constant volume output and therefore the input sensitivity of the VU meter must be varied each time the volume of the stereo is varied. Is there a way to obtain a constant volume level from the stereo, so that I won’t have to turn two dials each time I change the volume? (J. P., via email). • Short of building our CD Compressor described in the July 2000 issue, the only way to avoid the need to change the LED VU setting is to take the signal from across the volume Using a different spring reverb module I have a large 3-spring reverb unit made by Belton Engi­neering, which I’d love to build into a home-brew valve guitar amp, using the circuitry from your Spring Reverb Module published in your January 2000 edition. The Belton unit has the following specifications (obtained from Belton’s website) and they differ considerably from the unit used in your design: input impedance 190Ω; output impedance 2.575MΩ. control; ie, you have to access the signal from inside the car stereo. Thorn Atlas B+W TV needs a good home I have an old valve TV set that I would like to go to an interested collector. It is an old large (59cm?) Thorn Atlas B+W valve TV set, part of a relative’s deceased estate. The cabinet, made of solid wood, is in Notes & Errata Audio/Video Transmitter, July 1999: the PC board overlay on page 38 shows the two regulators swapped. The circuit on page 37 is correct. Rain Gauge, June 2000: the software for this project has a prob­lem when used with the newer PIC16F84A version of the chip. The A suffix version has a faster EEPROM programming time and this interferes with the in- Could you please advise what modifications I would need to make to the circuit for this to work? (P. S., via email). • As far as the input side is concerned, you could use our circuit as is because Q1 & Q2 will quite happily drive a higher impedance. On the output side you need a higher input impedance for IC2a and this can simply be done by changing the 100kΩ resis­tor at pin 5 to say 1MΩ or higher. However, you haven’t quoted signal delay times or signal levels so the result may be a little hit or miss. excellent condition and I think that the internals are all there, although the circuit diagram is only half complete (pasted in the back of the set). It even has the original knobs intact and would make a fantastic restoration project (although most of the work would be internal as the externals are in such good nick). If anyone is interested, they can contact me at: p_sun<at>optusnet.com. au terrupt routine earlier than it does with the standard version of the PIC. It causes the daily rain read­ings to be randomly updated at 10 minute intervals into the next day rather than only once per day. A new version of the software solves the problem. RAINA.ASM and RAINA.HEX software must be used with the PIC16F84 A versions. This software will also run with the standard PIC16F84 and can be downloaded SC from our website. 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. FEBRUARY 2001  91 REFERENCE GREAT BOOKS FOR AUDIO POWER AMP DESIGN HANDBOOK INDUSTRIAL BRUSHLESS SERVOMOTORS By Douglas Self. 2nd Edition Published 2000 85 $ By Peter Moreton. Publ. 2000 From one of the world’s most respected audio authorities. The new 2nd edition is even more comprehensive, includes sections on load-invariant power amps, distortion residuals, diagnosis of amplifier problems, and much more. 368 pages in paperback. VIDEO SCRAMBLING AND DESCRAMBLING for Edition 1998 TCP/IP EXPLAINED 99 AUDIO ELECTRONICS Satellite & Cable TV by Graf & Sheets If you've ever wondered how they scramble video on cable and satellite TV, this book tells you! Encoding/decoding systems (analog and digital systems), encryption, even schematics and details of several encoder and decoder circuits for experimentation. Intended for both the hobbyist and the professional. 290 pages in paperback. NEW 2nd $ By John Linsley Hood. First published 1995. Second edition 1999. 65 $ This book is for anyone involved in designing, adapting and using analog and digital audio equipment. It covers tape recording, tuners and radio receivers, preamplifiers, voltage amplifiers, audio power amplifiers, compact disc technology and digital audio, test and measurement, loudspeaker crossover systems, power supplies and noise reduction systems. 375 pages in soft cover. By Philip Miller. Published 1997. $ 99 By Tim Williams. First published 1991 (reprinted 1997). $ LOCAL AREA NETWORKS: An Introduction to the Technology 65 Includes grounding, printed circuit design and layout, the characteristics of practical active and passive components, cables, linear ICs, logic circuits and their interfaces, power supplies, electromagnetic compatibility, safety and thermal management. 302 pages, in paperback. ELECTRIC MOTORS AND DRIVES By John E. McNamara. 2nd edition 1996. EMC FOR PRODUCT DESIGNERS By Austin Hughes. Second edition published 1993 (reprinted 1997). 69 $ For non-specialist users – explores most of the widely-used modern types of motor and drive, including conventional and brushless DC, induction, stepping, synchronous and reluctance motors. 339 pages, in paperback. ESSENTIAL LINUX By Tim Williams. First pub­­lished 1992. 2nd edition 1996. $ 99 Widely regarded as the standard text on EMC, this book provides all the information necessary to meet the requirements of the EMC Directive. It includes chapters on standards, measurement techniques and design principles, including layout and grounding, digital and analog circuit design, filtering and shielding and interference sources. The four appendices give a design checklist and include useful tables, data and formulae. 299 pages, in soft cover. 92  Silicon Chip 92  Silicon Chip 85 $ THE CIRCUIT DESIGNER’S COMPANION Assumes no prior knowledge of TCP/IP, only a basic understanding of LAN access protocols, explaining all the elements and alternatives. Combines study questions with reference material. Examples of network designs and implementations are given. 518 pages, in paperback. Want to become more familiar with local area networks (LANs) without facing the challenge of a 400-page text? . Gives familiarity with the concepts involved and provides a start for reading more detailed texts. 191 pages, in paperback. Designed as a guide for professionals and a module text for electrical and mechanical engineering students. A step-by-step approach covering construction, how they work, how the motor behaves and how it is rated and selected. It may only be a small book but it has outstanding content! 186 pages in hardback. 65 $ By Steve Heath. Published 1997. $ 85 Provides all the information and software that is necessary for a PC user to install and use the freeware Linux operating system. It details, setp-by-step, how to obtain and configure the operating system and utilities. It also explains all of the key commands. The text is generously illustrated with screen shots and examples that show how the commands work. Includes a CD-ROM containing Linux version 1.3 and including all the interim updates, basic utilities and compilers with their associated documentation. 257 pages, in paperback. BOOKSHOP WANT TO SAVE 10%? SILICON CHIP SUBSCRIBERS AUTOMATICALLY QUALIFY FOR A 10% DISCOUNT ON ALL BOOK PURCHASES! ENQUIRING MINDS! (To subscribe, see page 57) ALL PRICES INCLUDE GST UNDERSTANDING TELEPHONE ELECTRONICS SETTING UP A WEB SERVER By Stephen J. Bigelow. Third edition published 1997 by Butterworth-Heinemann. $ 59 A very useful text for anyone wanting to become familiar with the basics of telephone technology. The 10 chapters explore telephone fundamentals, speech signal processing, telephone line interfacing, tone and pulse generation, ringers, digital transmission techniques (modems & fax machines) and much more. Ideal for students. 367 pages, in soft cover. GUIDE TO TV & VIDEO TECHNOLOGY By Eugene Trundle. First pub­­lished 1988. Second edition 1996. Eugene Trundle has written for many years in Television magazine and his latest book is right up to date on TV and video technology. The book includes both theory and practical servicing information and is ideal for both students and technicians. 382 pages, in paperback. $ 59 SILICON CHIP'S ELECTRONICS TEST BENCH First published 2000 A collection of the “most asked for” Test Equipment projects and features from the pages of Australia’s “most asked for” electronics magazine. Exceptional value at $10.95 O R D E R H E R E P&P  AUDIO POWER AMPLIFIER DESIGN...............................$85.00  INDUSTRIAL BRUSHLESS SERVO MOTORS..................$99.00  VIDEO SCRAMBLING/DESCRAMBLING..........................$65.00  TCP/IP EXPLAINED.........................................................$99.00  LOCAL AREA NETWORKS...............................................$69.00  SETTING UP A WEB SERVER..........................................$69.00  THE CIRCUIT DESIGNER’S COMPANION........................$65.00  ELECTRIC MOTORS AND DRIVES...................................$65.00  UNDERSTANDING TELEPHONE ELECTRONICS.................$59.00  AUDIO ELECTRONICS.....................................................$85.00  GUIDE TO TV & VIDEO TECHNOLOGY............................$59.00  EMC FOR PRODUCT DESIGNERS...................................$99.00  DIGITAL ELECTRONICS ..................................................$65.00  ESSENTIAL LINUX..........................................................$85.00  SILICON CHIP TEST BENCH............................................$10.95  SILICON CHIP COMPUTER OMNIBUS............................$10.95               ORDER TOTAL: $...................... Orders over $100 P&P free in Australia. AUST: Add $A5.50 per book NZ: Add $A10 per book, $A15 elsewhere By Simon Collin. Published 1997. $ 69 Covers all major platforms, software, links and web techniques. It details each step required to choose, install and configure the hardware and software elements, create an effective site and promote it successfully. 273 pages, in paperback DIGITAL ELECTRONICS – A PRACTICAL APPROACH By Richard Monk. Published 1998. With this book you can learn the principles and practice of digital electronics without leaving your desk, through the popular simulation applications, EASY-PC Pro XM and Pulsar. Alternatively, if you want to discover the applications through a thoroughly practical exploration of digital electronics, this is the book for you. A free floppy disk is included, featuring limited function versions of EASY-PC Professional XM and Pulsar. 249 pages, in paperback. 65 $ SILICON CHIP'S COMPUTER OMNIBUS First published 1999 Hints, tips, Upgrades and Fixes for your computer from articles published in SILICON CHIP in recent years. Covers DOS, Windows 3.1, 95, 98 and NT. A must for the computer user. $10.95 INC GST TAX INVOICE Your Name_________________________________________________ PLEASE PRINT Address ___________________________________________________ ___________________________________ Postcode_______________ Daytime Phone No. (______) __________________________________ STD Email___________________<at>_________________________________  Cheque/Money Order enclosed OR  Charge my credit card –  Bankcard  Visa Card  MasterCard No: Signature______________________Card expiry date PLUS P&P (if applic): $........................... TOTAL$ AU.............................. POST TO: SILICON CHIP Publications, PO Box 139, Collaroy NSW, Australia 2097. OR CALL (02) 9979 5644 & quote your credit card details; or FAX TO (02) 9979 6503 FEBRUARY 2001  93 ALL TITLES SUBJECT TO AVAILABILITY. PRICES VALID FOR MONTH OF MAGAZINE ISSUE ONLY. ALL PRICES INCLUDE GST FEBRUARY 2001  93 MARKET CENTRE Cash in your surplus gear. Advertise it here in Silicon Chip. FRWEEBE YES! Place your classified advertisement in SILICON CHIP Market Centre and your advert will also appear FREE in the Classifieds-on-the-Web page of the SILICON CHIP website, www.siliconchip.com.au And if you include an email address or your website URL in you classified advert, the links will be LIVE in your classified-on-the-web! S! D E I F I S C LAS EXCLUSIVE TO SILICON CHIP! CLASSIFIED ADVERTISING RATES Advertising rates for this page: Classified ads: $11.00 (incl. GST) for up to 12 words plus 55 cents for each additional word. Display ads: $27.50 (incl. GST) 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) 9979 6503. Taxation Invoice ABN 49 003 205 490 _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ Enclosed is my cheque/money order for $­__________ or please debit my ❏ Bankcard   ❏ Visa Card   ❏ Master Card Card No. Signature­­­­­­­­­­­­ ________________________ Card expiry date______/______ Name _____________________________________________________ Street _____________________________________________________ Suburb/town _________________________ Postcode______________ 94  Silicon Chip FOR SALE VCR Controller use a standard home VCR for Surveillance Event Recording Wireless IR Control only $39 * DOME VIDEO CAMERAS COLOUR from $77 ! Mono from $53 ! BULLET from $97 TWO YEAR WARRANTY * DIY PLUG-IN 20 metre AV Cables from $20 * DOME 480 Line 0.05 Lux SONY CCD & ChipSet from $81 * COLOUR DSP DOME: 400 Line from $139 * 600 + Line from $164 * COLOUR DSP PIN in PIR CASE from $152 * MINI CAMS from $67 * DSP COLOUR from $133 * PC REMOTE VIEW, PAGING, WEB-CAM, DVR System High 768 x 576 Resolution from $219 * QUAD 1024 H-Pixels from $175 * COLOUR QUAD only ! $380 * MULTIPLEXER 4 Ch from $633 * 4 Ch Switchers only ! $79 * COLOUR Bullet Cameras from $122 * Digital PC 4 Ch Video Recorder System from $159 * BLEMISH FREE & LOW BLEMISH CCDs * UP TO 5 YEARS WARRANTY * OVERNIGHT DELIVERY * www. allthings.com.au TELEPHONE EXCHANGE SIMULATOR: test equipment without the cost of telephone lines. Melb 9806 0110. http://www.alphalink.com.au/~zenere COVERT VIDEO SURVEILLANCE Tiny Sub-Matchbox from ~ 6 grams Wireless Video & Audio TRANSMITTERS from $77 * Pinhole Cameras from $67. Easily concealed in: Mobile Phone Case, Clock, VCR Cassette, Toys, Teddy Bear (Nanny-Cam), Smoke Detector, Ornament, Cap, Cigarette Pack, etc. www. allthings.com.au WEATHER STATIONS: Windspeed & direction, inside temperature, outside temperature & windchill. Records highs & lows with time and date as they occur. Optional rainfall and PC interface. Used by Government Departments, farmers, pilots, and weather enthusiasts. Other models with barometric pressure, humidity, dew point, solar radiation, UV, leaf wetness, etc. Just phone, fax or write for our FREE catalogue and price list. Solar Flair/Ecowatch phone: (03) 5968 4863; fax: (03) 5968 5810, PO Box 18, Emerald, Vic., 3782. ACN 006 399 480. KITS KITS AND MORE KITS! Check ‘em out at www.ozitronics.com SEE-in-the-DARK Camera with in-built IR LEDs in Water Resistant Case for disturbance-free Baby - Bird - Animal observation from $147 * DIY Plug-In 20 metre Cable & Plug Pack from $33 * www.allthings.com.au C COMPILERS: everything you need to develop C and ASM software for 68­HC08, 6809, 68HC11, 68HC12, 68­ HC16, 8051/52, 8080/85, 8086, 8096 or AVR: $170.50 each. Macro Cross Assemblers and Disassemblers for above CPUs + 6800/01/03/05, 6502 and 68­HC12 for $88. Debug monitors: $88 for 6 CPUs. All compilers, XASMs and monitors: $5280. 8051/52 Simulator (fast, now incl. 80C320): $88. Try the C-FLEA Virtual Machine for small CPUs, build a “C-Stamp”. Demo desk: FREE. All prices + $5.50 p&p. Atmel Flash CPU Programmer: Handles the 89Cx051, 89C5x and 89Sxx series, and some AVRs in both DIP and PLCC44. Also does most 8-pin EEPROMs. Includes socket for serial ISP cable. $220 $11 p&p. SOIC adaptors: 20-pin $99, 14-pin $93.50, 8-pin $88. Credit cards accepted. GRAN­ TRONICS PTY LTD, PO Box 275, Wentworthville 2145. Ph (02) 9896 7150 or Internet: http://www.grantronics.com.au HOME CCTV Mono / Colour PAKS only ! $119 / $151 Full DIY Plug-In to TV / VCR 20 metre Cable, Plug Pack & Camera www.allthings.com.au RCS HAS MOVED to 41 Arlewis St, Chester Hill 2162 and is now open, with full production soon. Tel (02) 9738 0330; Fax 9738 0334. rcsradio<at>cia.com.au; www.cia.com.au/rcsradio SMD COMPONENTS, Resistor kit, 18 x 50 x 1206 popular values in case <at> $38.50 inc GST. Capacitor kit, 18 x 50 x 1206 popular values in case <at> $88.00 inc GST <at> www.lazer.com.au or call on 02 93 111 500. DON’T MISS AUSTRALIA’S biggest and best exhibition and sale of new and used radio and communication ROLA AUSTRALIA PH/FAX (08) 8270 3175 WEB SITE WWW.BETTANET.NET.AU/GTD CHECK OUR WEBSITE FOR DETAILS ON KITS AND COMPONENTS • • • • Silvertone’s RC Receiver Still the best little performer available! TRANSMITTER KITS AND MODULES AUDIO MODULES COMPUTER INTERFACE KITS RADIO STATION AUDIO SOFTWARE NEW: Our MP3-CD player in short form for $169 inc GST. Includes the following: processor board, front panel display and tactile keypad; just add a case, cables, 12V power supply and a CD-ROM drive. Play CDs and up to 2600 MP3’s from a CDR. Great for car or home. Satellite TV Reception International satellite TV reception in your home is now affordable. Send for your free info pack containing equipment catalog, satellite lists, etc or call for appointment to view. We can display all satellites from 76.5° to 180°. Still only $129.50 AM or $149.50 FM. May be used with most ppm transmitters. This and many other radio control products available from: Silvertone Electronics, PO Box 580, Riverwood 2210. Phone/Fax (02) 9533 3517. www.silvertone.com.au AV-COMM P/L, 24/9 Powells Rd, Brookvale, NSW 2100. Tel: 02 9939 4377 or 9939 4378. Fax: 9939 4376; www.avcomm.com.au Positions At Jaycar We are often looking for enthusiastic staff for positions in our retail stores and head office at Rhodes in Sydney. A genuine interest in electronics is a necessity. Phone 02 9743 5222 for current vacancies. equipment at the Central Coast Field Day, Sunday 25th February, Wyong Race Course, just 1 hour north from Sydney. Starts 8.30 a.m. Special Field Day bargains from traders and tons of dispos­als gear in the flea market. Exhibits by clubs and groups with interests ranging from vintage radio, packet radio, scanning, amateur TV and satellite communications. www.ccarc.org.au Ph (02) 4340 2500. DIY CCTV PAKS 4 Cameras & Switcher .................$354 as above COLOUR .....................$466 4 Cams, Switcher/Monitor ...........$495 as above 14" Monitor ................$528 4 Cams & QUAD .........................$478 4 COLOUR & QUAD ....................$752 Time-Lapse 24 hr VCR only $699 with CCTV Systems ! MORE at: www.allthings.com.au Fully Plug-In DIY Paks with Cables & Power Supplies ALSO PC Digital Motion / Sound detection & activated Video / Audio Recording systems 08 9349 9413. Need prototype PC boards? We have the solutions – we print electronics! Four-day turnaround, less if urgent; Artwork from your own positive or file; Through hole plating; Prompt postal service; 29 years technical experience; Inexpensive; Superb quality. Printed Electronics, 12A Aristoc Rd, Glen Waverley, Vic 3150. Phone: (03) 9545 3722; Fax: (03) 9545 3561 Call Mike Lynch and check us out! We are the best for low cost, small runs. QUAD 4 pixs 1 screen from $247 * Real Time * High better than SUPER-VHS 1024 Pixel Resolution * Time * Date * Camera Title * Alarm Input / Output * Remote Camera Selection * FREEZE * www.allthings.com.au USB DEVELOPMENT KIT CY3650, Temperature/Voltage measurement via phone line, PC-controlled VHF Receiver http://www.ar.com.au/~softmark KIT ASSEMBLY NEVILLE WALKER KIT ASSEMBLY & REPAIR: · Australia wide service · Small production runs · Specialist “one-off” applications Phone Neville Walker (07) 3857 2752 Email flashdog<at>optusnet.com.au continued next page FEBRUARY 2001  95 DON’T MISS THE ’BUS Advertising Index Altronics................................. 68-70 Av-Comm Pty Ltd.........................95 Dick Smith Electronics........... 22-25 Do you feel left behind by the latest advances in com­puter technology? Don’t miss the bus: get the ’bus! Includes articles on troubleshooting your PC, installing and setting up computer networks, hard disk drive upgrades, clean installing Windows 98, CPU upgrades, a basic introduction to Linux plus much more. EMC Technologies.......................55 Harbuch Electronics....................54 Instant PCBs................................95 Investment Technology..............IBC Price: $12.50 (incl. GST) Order now by using the handy order form in this issue or call (02) 9979 5644, 8.30-5.30 Mon-Fri with your credit card details. Special subscription offer available only while stocks last. Jaycar ................................... 45-52 Mass Electronics.........................55 Microgram Computers..........3,OBC Silicon Chip Binders  Each binder holds up to 14 issues  Heavy board covers with 2-tone green vinyl covering  SILICON CHIP logo printed in gold-coloured lettering on spine & cover REAL VALUE AT MicroZed Computers...................55 P Printed Electronics...................... 95 $12.95 PLUS P & Price: $A12.95 plus $A5.50 p&p each (Australia only; not available elsewhere). Buy five and get them postage free. Just fill in & mail the handy order form in this issue; or fax (02) 9979 6503; or ring (02) 9979 5644 & quote your credit card number. Protel Australia..........................IFC Questronix...................................55 RobotOz......................................55 RF Probes...................................55 Rola Australia..............................95 WANTED PERSON WITH EXPERIENCE / APTITUDE able to fault find & repair PCBs – without diagrams. GENEROUS PKG NEG. Tel John<at>AER (03) 9482 4958 0415 305 470. DO YOU HAVE A GOOD circuit idea? If so, sketch it out, write a brief description of its operation & send it to us. Provided your idea is workable, we’ll publish it in Circuit Notebook and you’ll make some money (up to $60). Silicon Chip Publications, PO Box 139, Collaroy 2097; email silchip<at>siliconchip.com.au R.T.N............................................42 Silicon Chip Binders....................96 Silicon Chip Bookshop........... 92-93 SC Electronics Testbench............31 Silicon Chip Subscriptions...........71 HELP SAVE THE NIGHT SKY! We are losing our heritage of starry night skies. Poor, inefficient outdoor lighting is causing glare and “light pollution”. This wastes energy and increases greenhouse gas emissions. You can help by joining SYDNEY OUTDOOR LIGHTING IMPROVEMENT SOCIETY (SOLIS). SOLIS aims to educate and inform about quality outdoor lighting and its benefits. We also lobby councils, government and other bodies to promote good lighting practice. SOLIS meetings are held third Monday night of each month at Sydney Observatory. Individual membership is $20 pa. Donations are also welcome. Cheques payable to “SOLIS c/- NSAS”, PO Box 214, West Ryde 2114. http://sites.netscape.net/solislp/ 96  Silicon Chip Silvertone Electronics..................95 Solar Flair/Ecowatch....................95 Tasman Energy............................55 _____________________________ PC Boards Printed circuit boards for SILICON CHIP projects are made by: • RCS Radio Pty Ltd. Phone (02) 9738 0330. Fax (02) 9738 0334. FEBRUARY 2001  97