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www.siliconchip.com.au January 2003  1 Contents Vol.16, No.1; January 2003 www.siliconchip.com.au FEATURES 7 Receiving TV From International Satellites; Pt.2 How to install your own C-band (free-to-air) system and aim the dish – by Garry Cratt 82 Chips Monitor Tyre Pressure Two-chip remote sensing module from Motorola fits inside the tyre to monitor inflation pressure – by Peter Holtham PROJECTS TO BUILD Reader/Programmer For Smart Cards – Page 16. 16 Reader/Programmer For Smart Cards Low-cost Phoenix-type reader/programmer lets you program your own Smart Cards for all kinds of applications – by David Freeman 26 The SC480 50W RMS Amplifier Module At last! – an amplifier module to replace the venerable ETI-480. It has less distortion, is much quieter, has inbuilt protection and sounds a lot better – by Peter Smith & Leo Simpson 34 A “Tiptronic-Style” Gear Indicator It’s easy to build and indicates the selected gear in both manual and automatic cars on a digital readout – by John Clarke 58 Active 3-Way Crossover For Loudspeaker Systems Get the very best from your 3-way loudspeaker system with this easy-to-build high-performance design – by Mick Gergos SPECIAL COLUMNS 53 Serviceman’s Log SC480 50W RMS Power Amplifier Module – Page 26. When the going gets tough – by the TV Serviceman 71 Circuit Notebook (1) DC Motor Speed Control With Protection; (2) Magic Wand For 3-Way Control; (3) Automatic Tape Control For Display Stand; (4) Filter Reduces Supply Ripple By 40dB. 84 Vintage Radio Intermediate Frequency (IF) Amplifiers; Pt.2 – by Rodney Champness COMPUTERS 74 Using Linux To Share An Optus Cable Modem; Pt.3 Masquerading modules and a firewall – by John Bagster DEPARTMENTS 2 4 81 89 Publisher’s Letter Mailbag Silicon Chip Weblink Ask Silicon Chip 92 Notes & Errata 93 Market Centre 95 Advertising Index Apology: unfortunately, due to problems debugging the Windows software for the EPROM Programmer, we have had to hold this project over this month. www.siliconchip.com.au “Tiptronic-Style” Gear Indicator For Cars – Page 34. Active 3-Way Crossover For Loudspeaker Systems – Page 58. January 2003  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 Jim Rowe, B.A., B.Sc, VK2ZLO Rick Walters Reader Services Ann Jenkinson Advertising Enquiries Leo Simpson Phone (02) 9979 5644 Fax (02) 9979 6503 Regular Contributors Brendan Akhurst Rodney Champness, VK3UG 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, Noble Park, Victoria. 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 Queensland TV repairs now need an electrical licence Yep, the Queensland Government, via its union-dominated Electrical Safety Office, has been at it again. With its new Electrical Safety Act, commencing on October 1st, 2002, any business doing repairs on electronic or electrical appliances now needs an electrical contractor’s licence. Previously, this re­quirement only applied to those doing electrical installation work but now, after the farcical electrical safety review at the beginning of 2002, the vise is tightening. So if you are in a business in Queensland doing any sort of electronic or electrical appliance repairs, you now need an electrical contractor’s licence. The fact that you are more highly skilled than any electrician cuts no ice – you now need an electrical contractor’s licence; end of story. This is supposedly all in the interest of reducing death from contact with electric­ity but as anyone who knows the true situation can attest, most people who die in Queensland from electrocution are either elec­tricians or trades people working on construction sites. No doubt there will be plenty of people who will bleat about this new licence requirement but we gave heaps of warning about this nonsense when we had our long and ultimately futile campaign about do-it-yourself electrical wiring. I cannot believe that the affected various trade organisations, engineers and businesses have allowed this legislation to be enacted. They have been utterly supine. Well, the reward for apathy is more government regulation and since there are Labor governments in every Austra­lian state, this nonsense will probably spread throughout the country. The requirement for businesses to have an electrical contra­ctor’s licence takes effect from 1st February 2003. Furthermore, “If an applicant cannot complete the necessary competency for the business component (public service speak for shutting you out), an application will be accepted so long as the applicant provides a certificate of attainment within six months of obtaining their licence and before 1st August 2003”. If you want to read more of this mindless bureaucratic drivel, go to the website www.eso.qld.gov.au The net result of this stupidity will not be an improvement in the death rate from electrocution in Queensland. But as always happens when government becomes intrusive, there will be lots of unintended consequences and ordinary people will be worse off. Many small electrical and electronic repair businesses in Queens­land will close. There is not a shadow of doubt about this. These small businesses already have enough burdens without having to try and satisfy this unnecessary regulation. Many who have been soldiering on for years will now close up and take retirement. Can you blame them? Even larger repair businesses that do warranty work on new appliances will look askance at this new requirement. I would not be surprised if some of these decide to give up as well. So not only will Queenslanders not be able to get their TV, PC, fax machine or other electronic gear fixed, they won’t get their washing machine, dryer, stove, vacuum cleaner or other appliances fixed either. Good result, eh? Far more repairable appliances will end up on the tip. And how much hardship will be caused to those who can ill-afford to buy replacement applianc­es. Of course, those few Queenslanders who do manage to find a repairer in the future will sleep much more soundly because their appliance was fixed by a “licenced electrical contractor”. Won’t that be nice? Is there any hope? Well, we do still live in a democracy (sort of). If the affected business organisations get off their behinds and really lobby the government, this nonsense could be overturned. But I’m not hopeful. Happy New Year. Leo Simpson www.siliconchip.com.au Multi-PC Controllers MicroGram’s 2003 KeyBoard Kolumn More than one computer? Control them with one keyboard/monitor/mouse. Save space & big dollars in both redundant hardware cost, & wasted power. Cat 11654 Cat 11654-7 Manages 2 computers ideal for small office/home $199 Cat 11655-7 Manages 4 computers $399 Cat 11655 Cat 11656-7 Manages 8 computers $949 Cat 11657-7 Manages 16 computers $1299 Cat 11657 Cat 11658-7 USB KVM switch - 2 computers - needs only USB and a VGA cable $219 Cat 11659-7 USB KVM switch Cat 11658 4 comps $449 Keyboard Accessories. 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T.O.L. offers a comprehensive range of quality courses at prices that students will appreciate. www.tol.com.au Easy Transfer Bay Cat 2857 Cat 2857-7 Use your spare floppy drive bay to provide front access for FireWire, USB (1.1) and Serial, plus an Audio in and Audio out (RCA) $89 Low Voltage PCI Expansion Cards (Ideal for new P4 motherboards) Cat 2870-7 2 Port RS232 16550 PnP 3.3V $179 Cat 2871-7 Single port printer card 3.3V PnP $169 Cat 11902-7 BlueTooth Compact Flash Card for Pocket PC’s with CF slot $199 Cat 11907-7 BlueTooth Head Cat 11902 Set, no more wires or Cat 11907 “radiation” issues, try this incredibly small mobile solution with a 10-metre range $199 Cat 11901-7 BlueTooth USB Adapter Class 2 The ideal solution for providing Cat your notebook computer with the 11901 Cat 11906 power of $149 Cat 11906-7 BlueTooth LAN Access Point; Provides a gateway for Palm or Pocket PC’s to access your Network or Internet resources 100 metre range $349 Cat 11904-7 BlueTooth USB DualDongle 100 metre range $299 Cat 11903-7 Bluetooth USB SingleDongle 100 metre range $169 All “range” capabilities are for “free-air” situations. Cat 11904 We stock the latest in Barcode Scanner Technology, both CCD & Laser, Cash Drawers & Magnetic Card Readers! So let us fill your Point-Of-Sale needs Overnight delivery Our couriers typically deliver overnight to all capital cities & major regional centres in Australia providing orders are received by phone, fax or email before 4.30pm EST - only $15 (3kg max) We have a range of terminals to suit most emulations - Serial, Windows based & Linux MicroGram Computers Ph: (02) 4389 8444 FreeFax: 1800 625 777 sales<at>mgram.com.au info<at>mgram.com.au Vamtest Pty Ltd trading as MicroGram Computers ABN 60 003 062 100, 1/14 Bon Mace Close, Berkeley Vale NSW 2261 All prices subject to change without notice. Pictures are for illustrative purposes only. SHOREAD/MGRM0103 MAILBAG Internet Sharing with Linux and WiFi security After all these years, you guys still are the best! Seriously though, I loved the article about WiFi in the November 2002 issue and intend to try setting up a test link P2P between my house and my brother’s sometime soon. However, I am concerned that the writer is understating the risks involved in running wireless with standard security. It is widely accepted within the IT industry now that 802.11b and WEP offer little practical security for the modern business. So serious is the issue that companies like Cisco systems are now selling their wireless products with “temporary” addi­tional security measures to enhance the defaults until a suitable new standard is finally settled upon. I feel that security issues need a better airing, perhaps in a future issue of SILICON CHIP. I also loved the article in November 2002 about using a Linux box for sharing a cable modem. This is something I haven’t tried yet. I thought, however, that you may want to have a look at a ready built Linux based firewall/ sharing software kit. I have been playing with and actively promoting (to anyone who will listen) the IPcop firewall project for the last six months or so. IPcop is a spinoff of the early GPL code used in the now commer­cial Smoothwall firewall. The IPcop team have made significant changes to the origi­nal code over recent months and are now close to releasing their second revision (0.1.2). What makes these firewalls stand out is that the system installs via a self-booting CD (supplied as an ISO image), formatting and setting up any suitably fitted old PC as the gateway machine. The build asks a few simple ques­tions to establish its interfaces for the trusted network, DMZ and Internet, etc, and then after the first reboot is fully managed via a Web browser on the internal network. No more edit­ing lots of config files! IPcop is free software as for most Linux distributions and the development team are friendly and engaging to 4  Silicon Chip all the folk who use the system. I have had one running for six months or so now and have set up a few for friends who use ADSL. The firewall is easy to manage, reliable and even lends itself to modifications and tweaks via the SSH remote access for adding extra features. Have a look at www.ipcop.org for more information. Ray Ellison, Adelaide, SA. Comment: We agree that wireless security (or lack of it) is a big issue. Thanks for the Linux articles A big thank you for the articles on Linux. I would like to see more, especially for those of us who use ADSL. I have tried to use Linux for some time now but get so frustrated because no one has easy to read help (in plain Eng­ lish) until you started to print some. I have been an avid reader of SILICON CHIP for years and sweat on the copy to arrive each month in the post. Keep up the good and informative work. Robert Carnes, via email. Subwoofer saga with an ETI-480 amplifier I have been meaning to write for some time and congratulate you on an excellent magazine. I have an extensive library of every EA since 1965, every ETI and almost every SC (just missed a few of the early ones). I find that SC projects are of the highest standard and this was brought home recently when I decided to build a self-powered subwoofer for a recently purchased DVD player. I obtained a suitable speaker and made a substantial box based on its Thiele & Small parameters and various designs published on the Internet. I just happened to have a half-finished ETI480 amp and power supply lying around so thought this would be suitable. I finished off the amp and installed it along with a kit sub-bass processor purchased from Dick Smith Electronics, based on the design in EA September 1999. When finished, I ini- tially connected the new subwoofer to my existing stereo and was amazed at how bad it sounded on some program material. To cut a long story short, I made literally dozens of changes to the internal bracing of the box, the power supply, the sub-bass processor and finally, the ETI-480 itself and although I improved the sound somewhat there was still distortion and in­stability on certain low-level tracks. I had almost given up and decided to buy a commercial unit when I read your article on the problems school students were having with the ETI480. I knew as soon as I read it that the power amplifier was the problem so I raced down to my local Dick Smith store again and bought the last SC 50W amplifier module (based on the LM3876 and published in February 1994) and a power supply they had in stock. The subwoofer now sounds first class. Tony Lohrey, via email. Cat.5 tester is a beaut My thanks to Craig Stephen. His simple Cat.5 network tester on page 72 of the November 2002 Circuit Notebook is a beaut. I have wanted to build something like that for ages since I got a crimper and started making Cat.5 cables. It’s a pain testing them with a multimeter. I found that the stop/step was really start/step, but whatever! It cost about $15 for the parts; mostly $10 for a bag of 50 LEDs. I got a couple of microswitches out of a dead mouse and used an old token ring network cable converter for the remote assembly. I know you can buy the whole thing brand new from DSE ($90 on www.siliconchip.com.au special for November) but half the fun is building it out of old bits. Ray Haverfield, via email. CD deterioration due to foam packing I wonder if other readers have experienced the same problem of major deterioration of music CDs that I have had? I am aware of the literature on CD “bronze” corrosion, after being guided to the appropriate website http:// personal.riverusers.com/~manderso/ uhjdisc/bronzing.htm However, my problem does not appear to be a bronzing of the disc. Rather it is “decay” of the silver (aluminium) reflective surface. It happened on Disc 1 of a 2-CD set of the opera “La Bo­heme”, from EMI. The last two tracks on the disc would not read and when I examined the disc, I found two holes in the reflective layer, about 2-3mm in diameter on the outer edge of the disc. I also noticed that the label surface of the disc felt sticky and gritty, and realised that the foam plastic sheet often put in CD sets to hold the disc in place had rotted and bits of it had stuck to the label surface. When I took Disc 2 out of its case, I found the foam plas­tic sheet stuck hard to the label side. I managed to remove it but the surface is still sticky and gritty, and when I hold this Disc up to the light, it appears to be peppered with thousands of tiny pin holes, which seem to correspond to the places where the foam plastic had stuck to the surface. Disc 2 plays but with jumps. I now relate this to similar reflective layer breakdowns in two other single CDs which I also found with the foam plastic liner stuck to their label surface. I am dreading going through my entire collection of a couple of thousand CDs, wondering how many more might have been affected. My CDs are stored in special shelves in a cool, dry room, with no direct sunlight and I believe my storage arrangements meet the general recommendation. Since the literature on CD corrosion, dealing largely with discs pressed in Europe by Philips and Du Pont from www.siliconchip.com.au 1998 to 1993, says the corrosion was caused by inappropriate inks and gels which attacked the disc itself, I am wondering if the rotting of the foam plastic could have released chemicals or corrosives which attached themselves to the disc surface and damaged it? Incidentally, the La Boheme was a remaster from 1986 (out­ side the generally accepted time frame of faulty pressings) and was mastered by Nimbus. It does not have the “PDO” legend, around the centre-hole, which identifies the Philips-Du Pont press­ ings. Not being a chemist, I don’t know what reactions might occur between the foam and the surface of the disc but I imagine a breakdown of the foam is probably a chemical action and could well cause some kind of reaction. I am told the damage is irre­parable. In any event, I feel some exposure should be given to the fact that not all CDs are born equal and that, especially in the case of particular press­ ings from a specific time and place, deterioration is likely. People who have large collections might be wise to check discs which still have foam packed with them, and also to inform themselves of the bronze corrosion phenomenon. We have been led to believe that CDs last for anything up to 100 or 200 years and are virtually indestructible. It appears, to the contrary, that they might be very mortal. Knowing your propensity for taking up thorny issues, I can think of no better vehicle than your excellent magazine for informing people about this danger. John Tingle MLC, Parliament House, Sydney. Comment: most plastic foams will be corrosive when they perish and break down, so the label is at risk. Most plastic foams will not last beyond 1015 years in Australia – the heat does it. Even a slight scratch on the label can cause serious tracking prob­lems. Our recommendation is to go through all your discs and root out any plastic foam packing. Nothing should be in contact with the label surface or the underside. Apart from that, there could be a The Tiger comes to Australia The BASIC, Tiny and Economy Tigers are sold in Australia by JED, with W98/NT software and local single board systems. Tigers are modules running true compiled multitasking BASIC in a 16/32 bit core, with typically 512K bytes of FLASH (program and data) memory and 32/128/512 K bytes of RAM. The Tiny Tiger has four, 10 bit analog ins, lots of digital I/O, two UARTs, SPI, I2C, 1-wire, RTC and has low cost W98/NT compile, debug and download software. JED makes four Australian boards with up to 64 screw-terminal I/O, more UARTs & LCD/keyboard support. See JED's www site for data. Intelligent RS232 to RS485 Converter The JED 995X is an opto-isolated standards converter for 2/4 wire RS422/485 networks. It has a built-in microprocessor controlling TX-ON, fixing Windows timing problems of PCs using RTS line control. Several models available, inc. a new DIN rail mounting unit. JED995X: $160+gst. Www.jedmicro.com.au/RS485.htm $330 PC-PROM Programmer This programmer plugs into a PC printer port and reads, writes and edits any 28 or 32-pin PROM. Comes with plug-pack, cable and software. Also available is a multi-PROM UV eraser with timer, and a 32/32 PLCC converter. JED Microprocessors Pty Ltd 173 Boronia Rd, Boronia, Victoria, 3155 Ph. 03 9762 3588, Fax 03 9762 5499 www.jedmicro.com.au January 2003  5 Mailbag: continued wider consumer issue here, with record companies being obliged to replace faulty discs. Amateur radio articles still wanted I am just catching up with the last couple of issues of SILICON CHIP and would like to support G. J. Wilson of Tasmania, for his letter in Mailbag in the October 2002 issue. This is a wonderful opportunity you have at the moment to enrich your magazine with amateur radio articles. Indeed since the demise of “Electronics Australia” and other radio magazines, all “radio-interested” people, including me, are left in limbo. Your magazine will definitely increase its readership by a fair bit if you were to grab this chance and present a much richer magazine with a much better variety of articles. In the last few years, I stopped buying every issue of your magazine simply because it is getting more and more into comput­ers. In the recent AGM of the Australian Radio DX club, the general consensus was that everybody would buy your magazine if they found a few articles on amateur radio. And this club does have about 300 financial members. I do hope my mild criticism will be very constructive, Peter Theodorakis, via email. Comment: if you looked at SILICON CHIP over the last 10 years or more, you would not find any increased emphasis on computers – we’ve always covered them. Publisher’s letters endorsed I have subscribed to SILICON CHIP since a trip to Oz in 1992. I also subscribe to “Everyday Practical Electronics” here in the UK. I completely disagree with your Mailbag subscriber Doug Thwaites and many of his comments in December’s issue – particularly in reference to the Publisher’s Letter. I anxiously await the arrival of SILICON CHIP each month by airmail and it is read religiously in the following order: 6  Silicon Chip (1). Publisher’s letter. (2). Mailbag. (3). Ask Silicon Chip. (4). Serviceman’s Log. (5). Jaycar and Dick Smith’s adverts, mainly to compare them with things here in the UK. (6). The rest – word by word!! I am usually most disappointed if Leo Simpson writes solely on matters electronic! To me, his asides reflect the character of the man and I hope he does not change things. You will never please everyone but it’s a good magazine pleasing 95% of its readers, I am sure. G Wilsher, via email. Easy labelling method for cables I’ve just solved a problem that had been bugging me for some time. When faced with the problem of labelling 18 audio and video cables linking the various parts of my video editing suite, I came to the conclusion that the paper labels I had originally used were not durable enough. So I sought something better. Some time ago I had made a series of transparencies for an overhead projector and I still had left a few sheets of clear acetate film. So I composed the requisite labels on my computer and printed them on the acetate sheet. I then backed the clear labels with plain white adhesive tape, punched the necessary mounting holes and cut out each of the 36 labels, one for each end of the cables. They look quite professional and I expect that they will greatly outlast the previous labels. The labels are best if slipped onto the wires before the plugs are attached but where this was not feasible, I cut into the side of the holes, slipped the label over the wire and closed the gap with a piece of adhesive tape. By the way, this method is unsatisfactory if acetate sheet is used with an inkjet printer. The ink takes a long time (30mins) to dry on the acetate sheet and afterwards tends to crack and flake off. The alternative is to print the la- bels on paper with the inkjet printer. Then copy them onto acetate sheet in a photocopy­ing machine. After that, the procedure is exactly as described above. Jim Lawler, Hobart, Tas. Double fuses for extra safety May I revisit the issue of fuses in a circuit? Should it be on the positive supply or negative earth? The air force teaches its technicians to disconnect a battery’s earth before the power lead. Consider for a moment, that while disconnecting a power lead with earth still attached, your spanner touches the earthed chassis or frame. The little blue spark can have rather nasty consequences in certain circumstances. Power inverters or circuits dealing in larger currents are normally fused in the positive supply in contrast to the above principle. In my experience, failure of this sort of equipment often leaves the fuse intact, with power supply capacitors fuell­ing the fire, so to speak. My point is that a fuse rated to protect a power circuit provides no protection whatsoever for control circuitry that needs protection of a different order altogether. This leads me to believe that a good practice is to provide a fuse on the earth side of a logic or control circuit of a power supply to allow the circuit’s potential to float; ie, to reduce the potential difference between power and control circuits. Two fuses allows protection of circuitry used to control power supplies, inverters, voltage cut-outs and so on. The large fuse would relate to the maximum current in the power circuit, which offers no protection for the control circuit, while the small fuse would be rated at 1.5 times the design current for the control circuitry. A blown small fuse would allow the control circuit to pro­tect itself by letting its potential float; ie, to minimise the potential difference between power and control circuits. The resistance of the small fuse would result in negligible shift in voltage values. Stephen Butcher, SC Masterton, NZ. www.siliconchip.com.au International satellite TV part 2. . . by Garry Cratt* Last month we discussed the basic principles of satellite TV reception, equipment required and the type of free-to-air programming that is available. This month we explain, in detail, how to install your own C-band (free-to-air) system. T he most important aspect of installation is dish placement. Obviously the dish must be able to point in the right direction to receive a satellite signal. With satellite dishes, “near enough” is most definitely not “good enough.” An error or 1°– or even less – can make all the difference on Earth (or off it!). The “view” to the satellite must be clear of all obstructions. Generally this means locating the dish away from trees, fences and buildings that might obstruct the line of sight to the satellite. As we mentioned last month, a dry tree usually makes only a marginal difference to satellite reception. The smallest rain shower, though . . . In order to find the best location, a decision has to be made as to which satellite(s) are to be received. The pointing co-ordinates for the desired satellite can be determined mathematically. These days, computer software makes this task relatively simple. We’ll look at software shortly. Azimuth and elevation The dish pointing co-ordinates will comprise two parts: an azimuth bearing, or the direction the dish must face to point at the appropriate satellite (for Australia that’s somewhere between 270° and 90°) and a value of dish elevation, or the angle between the vertical and the axis of the parabolic dish. At the equator, the dish points straight up but the angle increases as you get further south. Typical values for the most popular satellites and capital cities are shown in Table 1. That’s all the information you need to point your dish for a single satellite. Many people, though, want to look at a range of satellites. As all geo-stationary satellites are located above the equator and as the earth is round, the satellites aren’t in a straight line across the sky; rather they follow what is known as a geostationary arc. To view more than one, a motor is attached to the dish, designed to follow the curve of the arc. It is important to locate the dish so that all wanted satellites are visible to the dish at its extremeties of travel. A motorised installation is a bit beyond the scope of this article – that’s when you really do need professional STEP-BY-STEP: Putting in your own C-band system Open up the box of accessories which is supplied along with your dish box. You should find a set of instructions (which will vary from gibberish to excellent, depending on the brand of your dish – and even then not always constant), a plastic bag of nuts and bolts and a mounting plates. Along with the four dish panels (petals), you should get four feedhorn struts (inside the long box) and an LNB cover. www.siliconchip.com.au January 2003  7 help. So we will concentrate on viewing the signals from just one satellite. Councils and neighbours Most local councils now require a development application to be submitted for the installation of any satellite dish over 1m in diameter (some councils even smaller) and it is wise to check your local council’s policy. It’s also good policy to install the dish where it will have the smallest impact on the neighbours. While it might be possible to install the dish in a location not visible to the neighbours (or council), it should be remembered that councils can issue demolition orders for illegally erected satellite dishes (especially big ones!). One other point about neighbours: it’s amazing how paranoid some can get about those nasty microwaves jumping off your dish and curdling the milk in their fridge, causing untold cancers and even rotting the wooden legs on their tables and chairs. Of course, none of your assurances that it is for receiving only, that it doesn’t emit any microwaves, will satisfy them. One bloke we know finally placated a whining, threatening neighbour by telling him he was actually doing the whole neighbourhood a favour, collecting all the stray microwaves from space in his dish and piping them away. The overall result was less harmful microwaves in the neighbourhood, not more. Yes, it is stupid. But most people are when it comes to things they don’t understand. (And yes, the neighbour swallowed it hook, line and sinker). Site survey Assuming a position can be found that is both unobtrusive and has a clear view of the sky, the next step should be a site survey. Professional satellite companies always perform a site survey to ensure that there is good access to the satellite signals and just as importantly, that there is no terrestrial interference to the desired satellite signals. Unfortunately, C band (3.4-4.2GHz) is shared with terrestrial microwave services. Such services can be the source of interference and in some cases, completely prevent the reception of satellite signals. The site survey is done using a small (1.2m) dish with LNBF and a spectrum analyser. By pointing this small dish using the correct azimuth and elevation values for the desired satellite, the satellite signal can be verified and any interference can easily be seen. Dig your post-mounting hole deep enough to accommodate half the post length. For a 2.4m dish, that means 1.2m concreted into the ground. Standard mounting pipe is galvanised 76mm (OD). When you concrete in the post, it is vital that it be exactly vertical AND it stays that way until the concrete has well and truly cured. We normally use standard concrete, not quick-set, because it gives a stronger job. 8  Silicon Chip The table at right Pointing data for major Australian and S-E Pacific capitals. The figure immediately after the city is its magnetic deviation, while the figures underneath are its exact location (usually the major airport). These are given for those who wish to use dish pointing software. To use this chart, select capital city, then satellite number from list below. First data line is magnetic azimuth, second line is elevation. The main satellites listed are prime signal sources. The other satellites (listed underneath) have marginal footprints and may also be received on an itinerant basis. N/A means that the particular satellite is below the horizon for that city and is therefore unviewable. Even though this size dish is too small to connect to a digital satellite receiver for decoding, it allows the satellite signals – and any interference – to be viewed on the spectrum analyser. Where a dish is not available, even using a standard LNB to detect interference is better than no check at all. Where interference is detected, it can sometimes be eliminated by using the building itself as a shield. Where a satellite dish is to be installed in a location where there is known interference (eg, near airport radar), the value of using quad shielded coaxial cable can be appreciated. This simple step (choosing quad shielded over the cheaper dual shield) can mean the difference between perfect reception and no reception. In extreme cases, the coaxial cable can be run inside steel water pipe for even greater immunity to an interfering RF field. Now we are not expecting you to own a spectrum analyser but you may be able to find a local satellite TV company who will do this for you, albeit at a price. Digging the hole The most common installation and perhaps the most manageable is the backyard pole mount. There is one logical rule that applies here: whatever length of pipe that is above the ground should also be below the ground. This means that if you plan to install a 2.4m (diameter) dish, you’ll need to leave a length of pipe at least half the diameter of the dish (1.2m) protruding out of the ground and another 1.2m buried in the ground. So it’s pretty easy to remember – mounting pipe length equals dish diameter. Butt up two dish panels and finger-tighten just the outermost and innermost bolts with a flat washer under every bolt-head and nut. www.siliconchip.com.au www.siliconchip.com.au JANUARY anuary 2003  9 276 29.2 266.1 5.2 267.3 5.8 275.3 27.1 N/A N/A 266.0 4.1 273 18.8 N/A N/A N/A N/A 269.1 7.2 280.1 15.8 267.8 5.6 278.8 14.2 N/A N/A Azimuth Elevation Azimuth Elevation Azimuth Elevation Azimuth 273.6 Elevation 7.7 Sydney (12.6E) Canberra (11.9E) Adelaide (8.0E) 273.3 9.9 306.8 35.3 270.1 6.8 272.0 8.4 304.9 33.8 268.6 5.4 N/A N/A Azimuth 298.0 Elevation 27.4 N/A N/A Azimuth Elevation Perth (2.5W) 1. 2. 3. 4. 5. Azimuth Elevation N/A N/A 263.1 4.1 268.1 17.2 N/A N/A 273.4 10.0 311.4 38.7 276.5 13.4 283.3 19.4 271.9 10.8 270.0 9.5 268.3 9.2 277.5 33.9 83.0   4 261.4 3.0 266.4 21.8 272.4 35.6 260.2 4.0 287.9 22.0 334.6 49.2 290.3 26.6 298.0 32.9 284.6 24.7 282.0 23.8 278.3 24.8 286.7 52.2 100.5   5 287.6 35.8 292.8 33.5 296.0 34.0 312.0 41.1 302.8 35.0 354.7 52.7 300.2 29.7 268.5 13.8 277.2 49.0 269.6 34.9 281.7 29.2 286.0 27.7 288.8 28.6 303.2 36.4 295.0 30.1 343.0 51.1 292.6 25.2 263.4 7.9 274.0 40.9 267.6 27.0 265.7 14.9 300.3 64.8 291.0 57.4 263.1 7.7 113.0   7 105.5   6 Satellite Number Index – with type and launch date 6. Asiasat 3, HS 601HP 1999 11. Optus B1 HS 601 1992 Panamsat 10, HS 601HP 2001 7. Palapa C2, HS 601 1996 12. Optus A3, HS 376 1987 Apstar 2R, FS 1300 1997 13. Panamsat 8, FS 1300 1998 Thaicom 3, Spacebus 3000A 1997 8. JCSat 3, HP 601 1995 9. Measat 2, HS 376HP 1996 14. Panamsat 2, HS 601 1994 Insat 2e, ISRO 1999 10. Optus B3, HS 601 1994 15. Intelsat 701, FS 1300 1993 Asiasat 2, GE 7000 1995 (18°S, 178°E) Suva (12.7E) N/A N/A N/A N/A (9°S, 156°E) Honiara (9.2E) (9.5°S, 147°E) N/A N/A N/A N/A N/A N/A Azimuth 265.4 Elevation 2.8 Pt Moresby (6.6E) (37°S, 175°E) N/A N/A 267.2 12.7 266.8 10.6 Azimuth Elevation Auckland (19.4E) Azimuth Elevation N/A N/A N/A N/A N/A N/A Azimuth Elevation (43°S, 147°E) Hobart (14.7E) (32°S, 116°E) (38°S, 145°E) Melbourne (11.5E) (35°S, 138.5°E) (35°S, 149°E) (34°S, 151°E) (27.5°S, 153°E) Brisbane (10E) Azimuth Elevation Darwin (3.5E) (12°S, 130.5°E) 78.5   3 76.5   2 68.5   1 Orbital Location (°E) Satellite No. 272.0 29.7 275.6 51.1 289.0 65.1 280.1 25.4 318.1 36.8 024.2 50.5 321.9 42.8 333.8 47.9 313.8 43.3 309.9 43.4 303.5 47.7 344.0 75.1 128.0   8 294.6 56.7 327.0 77.8 036.9 74.7 311.1 42.8 358.0 39.7 059.9 33.1 006.1 44.7 020.6 45.4 359.4 48.4 356.0 50.2 355.3 57.7 62.1 57.4 156.0    10 300.7 60.0 349.7 78.8 047.7 71.3 316.9 44.4 003.6 38.8 063.4 29.9 012.1 43.5 026.3 43.5 006.0 47.4 003.0 49.4 003.7 57.0 65.6 53.2 160.0   11 308.0 63.1 012.8 77.9 055.0 67.4 323.1 45.7 009.1 37.7 066.7 26.7 017.8 41.9 031.6 41.3 012.3 46.0 009.6 48.2 011.6 55.6 068.4 49.1 164.0   12 312.3 64.4 022.4 76.9 057.7 65.3 326.2 46.2 011.7 37.0 068.2 25.0 020.5 41.0 034.1 40.1 015.3 45.2 012.8 47.5 015.4 54.8 69.6 47.0 166.0   13 319.5 66.1 034.0 74.8 061.2 62.2 331.1 46.7 015.6 35.8 070.4 22.5 024.5 39.5 037.6 38.2 019.2 43.9 017.4 46.2 020.6 53.3 71.3 43.8 169.0   14 LM-1, A2100AX 1999, 75 E Gorizont 28, NPO 1993 96.5E Apstar 1A, HS 376 1994 138E Apstar 1, HS 376 1996 138E Agila 2, FS 1300 1997 146 352.7 68.6 056.2 64.4 069.2 50.4 349.3 46.8 028.6 30.6 077.6 13.3 037.3 33.1 048.9 30.5 033.6 37.6 032 40.0 036.6 46.2 76.0 32.2 180.0   15 Gorizont 33, NPO 2000 145E ntelsat 802, GE 7000 1997 174E Intelsat 702, FS 1300 1994 176E Other itinerant satellite source (craft, launch date & position) 285.5 49.4 298.3 71.9 358.8 78.8 300.6 38.8 346.3 40.5 051.9 39.2 353.3 46.1 008.0 16.1 345.6 49.0 341.7 50.4 338.1 57.4 051.9 65.2 148.0   9 Table 1: Dish Pointing Guide for Capital Cities In practice its best to add 100mm or so out of the ground, so that even if the dish is tilted down for maintenance (rarely required), the lower rim of the dish cannot quite touch the ground, avoiding any possibility of damage. For mounting most 2.4m dishes, 76mm OD (outside diameter) This magnetic mount Anglemeter pipe, available from has 0.1° accuracy and a large dial larger hardware and face, allowing dish elevation to be plumbing stores, is read directly. used. For a few dollars more the store will even cut the pipe. In fact, it’s quite likely that you will be buying an offcut length anyway, as pipe tends to come in 6m lengths. Dig a hole at least 300 x 300mm, 1.2m deep and stand the pipe vertically in the centre. To keep the pipe vertical, wedge bricks, rocks, etc between the pipe and the wall of the hole, and check that the pipe is perfectly vertical by using a spirit level. Check the alignment at two positions 90° apart around the circumference of the pipe. In some circumstances it will be necessary to brace the pipe with two “starposts” or similar. A 300 x 300 x 1200mm hole is a little over 0.1m3. You can either use ready-mixed concrete or mix it yourself. For the latter, you will need four bags of standard concrete mix. (If you wanted a really strong mount, a 440 x 450 x 1200mm hole will take about 0.25m3 of concrete; 10 bags). Pour the concrete into the hole until it reaches a level 50mm below the ground level. This allows enough room for topsoil to allow grass to grow under the dish. Leave the concrete to set for two days, ensuring that the pipe remains untouched for that period (that includes making sure the kids don’t come out and give the pole a jiggle to see if it has set!). You might be tempted to use rapid set concrete but for maximum strength, ordinary concrete mix is used and allowed to dry normally. If you are digging the hole in an area comprised mainly of backfill (ie, low density soil) it may be necessary to weld a piece of flat bar across one side of the bottom end of the pipe, to ensure the pipe remains bonded to the concrete. A larger hole would also be more prudent. Repeat for the second pair of panels. They will happily stand up like this if there is no wind. But don’t risk it in ANY breeze! Sit both halves on a milk crate or small garbage bin and bolt them together. Now insert the missing bolts and tighten them all up. 10  Silicon Chip Dish assembly Once the pipe has been set in the ground, the dish can be assembled. Most mesh dishes are supplied as four pre-assembled panels which must be bolted together to form the parabolic reflector surface. Also supplied are four steel or aluminium tubes called “feed struts”. These hold the feed horn assembly at the focal point of the dish. In addition, there is a dish mount. This is the mechanical assembly that connects the reflector to the pipe. It is very cleverly designed so that elevation, azimuth and declination can all be separately adjusted. This is necessary for a motorised dish system, where a single motor makes the dish track in an arc, not a straight line!! All dishes come with some instructions. Depending on the brand, they may be very comprehensive or almost non-existent. Here are some “generic” instructions based on our experience. Much of the assembly can be performed by one person but several steps require at least two, if not three people. The main thing to remember is that the performance of the dish is dependent on the accuracy of the surface. So dents and rips in the mesh, apart from not looking at all aesthetically pleasing, will cause a reduction in dish performance and should be avoided at all costs. Even small dents can cause significant degradation and sometimes mean the difference between a good picture and a noisy (or no) picture. Take two of the dish panels (also known as quadrants) and stand them on their edge. Provided there is no wind (!), and the surface is flat (a concrete driveway is often useful) the panels will stand on their edge, the curve of the panel preventing it from falling over. Butt up the two panels and insert just the outermost and innermost bolts. Use a flat washer under every bolt-head and nut to prevent crushing the aluminium ribs of the dish panels. Do the nuts up “finger tight”. Place this “half dish” assembly to one side and make another half dish from the two remaining mesh quadrants. Once both halves of the reflector have been assembled, lie them face down on a horizontal surface (perfectly flat if available) with an inverted plastic garbage bin (or something similar) supporting the centre of the dish while you assemble it. www.siliconchip.com.au Then butt the two halves together and insert the outermost and innermost nuts and bolts. Do these up finger tight. You should now have a reflector lying face down on the ground. Insert all bolts and nuts (don’t forget the flat washers), working from the perimeter of the dish to the centre in a clockwise direction, tightening them with two spanners as you go. There are four mounting holes for the dish mount, so leave them vacant. Don’t forget to tighten the nuts you originally had only finger-tight. Find an assistant, then carefully pick up the reflector and turn it over so it is lying face up. Be very careful if there is any wind: even a mesh dish can get away from you. The feed struts The next step is to bolt the feed struts onto the feedhorn. Do this a short distance away from the reflector to eliminate the possibility of accidentally piercing the reflector mesh. The feed struts should be spaced 90° apart and are secured to the feed ring using four bolts and nuts. Using that same friendly assistant (or two of them if available), pick up the feed assembly complete with struts, and carefully position it over the reflector, making sure that none of the struts damage the mesh. Two people can hold up the feed assembly (each holds the assembly by two struts), while the third person inserts a bolt, washers and nut, at the location point on the reflector. You should now have a reflector lying face up, with four feed struts bolted to the rim, holding the feed ring at the focal point of the dish. As soon as the feed assembly is secured, there is a noticeable improvement in the rigidity of the entire assembly, as it is secured in both axes. The dish mount The next step is to place the dish mount on the pipe protruding from the ground. As long as the pipe does not protrude more than about 1.5m, one person can generally lift the mount onto the pipe. But it’s always better with two. That mount is heavy! First a few precautions: Ensure that the securing bolts on the outside of the mount sleeve (designed to clamp onto the pipe) are loosened off so that the mount can slide onto the pipe. Fix an azimuth bar (supplied with the dish) to lock the east /west movement of the mount. This prevents the mount rolling around the horizontal axis as you lift it onto the pipe. Once the mount has been lifted onto the pipe, rotate it Hopefully your completed dish looks something like this! Be even more careful now you’ve got this far; from now on it’s a 2-man job! www.siliconchip.com.au such that it is in a position where the dish can be lifted (by two people) onto the mount, then tighten up the mount securing screws to hold it solid. This is not the final position of the dish, merely a convenient position to finish the assembly. Adjust the mount elevation to about 30°. This will enable you to lift the reflector up against the mount, rather than lifting it above the mount. Up she goes! We now need to lift the reflector (dish) onto the mount, orienting it so that the four lugs on the mounting ring correspond with the four double ribs formed by bolting the quadrants together. We also need to consider the LNB securing bolt on the feed horn. This needs to be facing downwards (towards the ground), so it is easier to adjust once the dish is mounted. With the mount clamped to the pipe, the azimuth bar in place, and using two or three people, carefully lift the upturned reflector and feed assembly onto the mount, positioning the four lugs on the mount and corresponding double ribs. While one person holds the reflector in place against the mount, another person must insert the four securing bolts. It’s necessary to operate from behind the dish to do this, inserting the uppermost bolts first. Don’t forget the flat washers under the bolt heads and nuts. Once the two uppermost bolts have been inserted, the reflector will sit on the mount without support, while the remaining two bolts are inserted. Now tighten all bolts, making sure the mesh is not damaged by the action of the spanner against the securing nuts. The dish is now ready to have the LNB added and to be pointed towards the satellite. Pointing the dish There are four critical parameters that must be determined for every dish installation. They are dish azimuth, dish elevation, LNB orientation and dish focal point. Fortunately, the focal point is almost always determined by the length of the feedarms. When the feedhorn/LNB is set in correct position, no further adjustment should be needed. The azimuth and elevation of the dish need to be mathematically calculated. All satellites are given an orbital location, which in the case of Asiasat 2 is 100.5° east longitude. This means that the satellite is located 37,000km Connect the feed struts to the LNB hardware – do this away from the dish so you don’t risk damaging the dish mesh. January 2003  11 This satellite signal indicator comprises a broadband amplifier and diode detector, intended to be used at the dish to assist in signal peaking. up, at the intersection of the equator and 100.5° east line of longitude. From a map you’ll see that this location is over Indonesia. For Sydney, even the most rudimentary geography indicates that the dish will be facing somewhere in the western sky. Ummmm – west – that’s away from the coastline in Sydney. Fortunately, there are plenty of computer programs available that simply require the latitude and longitude of the dish, together with the longitude of the satellite.You can find a variety of software on the net, some of it freebies. One such program, GEOSAT.EXE, is one we use at Avcomm Pty Ltd – in fact, we wrote it! Alternatively, a quick “Google” will find any amount of similar programs, such as SMW Link, from Swedish Microwave AB (www.smw.se/smwlink/smwlink.htm). Make sure you get the latest version (3.05) because earlier versions had a southern hemisphere calculation bug! But it’s often even easier than that, because most modern receivers have a dish pointing menu, where these parameters can be entered to calculate the desired azimuth and elevation of the dish. has at least one (and usually more) latitude and longitude reference on the side. Alternatively, if you have ’net access you can Google something like “latitude longitude Gulargambone” – especially handy if you happen to live in Gulargambone. You should find several websites which will give you the exact (to the minute and sometimes even second) location of your town/city, especially if it has an airport. Beware, though, in big cities, the figures are likely to be that of the main airport – and if you happen to live on the opposite side of the city, you could be out by as much as a degree or so. One further alternative is a very useful book called “The Dick Smith GPS Guide”. Available from DSE stores or Australian Geographic, this lists over 16,000 locations in Australia and the corresponding latitude and longitude. If using this book, its important to remember that most dish pointing programs require latitude and longitude in degrees and tenths of degrees (eg, 34.5) not in the format provide by the book: degrees, minutes, seconds (or 34°30’0”). Fortunately the book does have a conversion chart – and even mental calculations aren’t rocket science. (Rocket science? Satellites? Get it . . . ? Oh, don’t bother . . .) Azimuth You probably don’t know the exact latitude and longitude of the dish site. To work out the exact (to the minute) location, we normally use either a good map or GPS. Detailed topographic maps of your area will enable you to extrapolate your exact location because the grid always One further parameter is required to calculate the dish azimuth – remember, that’s the direction it points. But there is a little wrinkle here called magnetic variation. That’s the difference between what you read on a compass as north, and true north (ie, lines of longitude from pole to pole). Magnetic variation varies all over the place depending on the specific place you are at, while computer software invariably works on true north – and you have to add or subtract the local magnetic variation to achieve the desired result. Magnetic variation can usually be found for any particular location on a specific map called a “WAC” (World Aeronautical Chart), often used by pilots. These charts are available at all good map shops and pilot supply centres. Magnetic variation is also listed on topo maps. A point to note: as well as varying by location, magnetic variation changes over time. The map may give a misleading figure if it is more than a few years old. Once again, Google is a great way to find out magnetic variation (which is, by the way, also known as magnetic declination). Google ‘“magnetic variation” Sydney’ and you’ll find several sites giving the result: 12.6° E. Very carefully bolt the struts onto the dish using the mounting holes provided. Place the dish assembly somewhere safe. Here’s what the dish mounting hardware looks like straight out of the box (albeit photographed here almost upside down). The cylindrical section with the four bolts at right actually points vertically down (it’s the bit which slips over the top of the in-ground 76mm pipe “post”). Those bolts are tightened against the post to ensure the dish cannot “windmill” in strong winds. The ring (on the ground in this pic) is the part which bolts on to the assembled dish. Where am I? 12  Silicon Chip www.siliconchip.com.au Recalling the rhyme “east is least” reminds us to subtract lines of magnetic variation marked “E” from the calculated true azimuth. In the case of Sydney the magnetic variation is 12.6° E, so we need to subtract 12.6° from the calculated “true” azimuth. The magnetic variation for Perth is around 2.5° W, so we must add 2.5 to that “true” azimuth. Elevation The dish pointing software calculates elevation directly in degrees. Fortunately, this is much easier to measure and set. The simplest method is to use a protractor and a piece of cotton and a weight but if this is too much trouble a simple analog inclinometer can be purchased reasonably cheaply. This type of instrument has an oil filled chamber with a pivot and a counterweighted pointer. A far more sophisticated digital instrument is used by professional installers, as the dish geometry of a motorised system must be set to within one tenth of one degree, or six minutes. The reality is that most home installers will be able to set up a system to look at any single satellite but without sophisticated measuring equipment, the alignment of a motorised system will require professional help. Where’s the satellite? Now that we have been able to work out the dish azimuth and elevation, we can get to work. Let’s use the example of Sydney and the Asiasat 2 satellite. We know the latitude of Sydney is 34° south, and the longitude is 151° east. We also know that the longitude of Asiasat 2 is 100.5° east. Our software tells us that the dish elevation must be 23.87°, and the true azimuth is 294.75°. Subtracting 12.6° from the true azimuth gives 282° magnetic. This is the required compass heading. A cheap and nasty compass won’t cut the mustard here: it needs to be a decent, fluid-filled model graduated in individual degrees. Good orienteering compasses are usually a reasonable compromise between cost and usefulness. Also remember when aiming a dish that the compass itself is likely to be affected by close metal (usually steel) objects. Just keep that in mind if your compass readings keep changing as you move about. The elevation is somewhat easier to set. Assuming the mounting pipe has no elevation (just like a dish standing on the rim), calibrate the inclinometer for zero degrees. Up the right way: the threaded rod in the centre of the pic adjusts the dish elevation, while the rod at right adjusts declination. www.siliconchip.com.au When you get really serious (!) this digital inclinometer has one degree accuracy and resolution. It’s a must for setting up motorised dishes. Place the inclinometer on the centre plate of the dish (from behind), so that the counterweight is vertical. The elevation of the dish can be directly read. Adjust the threaded rod until the elevation reaches 24°. This should be close enough, once the dish is pointed in the right direction, to acquire a signal. One tip – before setting elevation, run the spirit level over your pipe one last time to make sure it hasn’t moved before the concrete had a chance to harden. It happens! Installing the LNB Now is the time to install the LNB into the feed rings. Do this by slipping the LNB through the ring assembly, so that the front edge of the waveguide protrudes 20mm past the level of the concentric rings. Rotate the LNB so that the flat part of the housing is vertical. This is a good starting point for further adjustments once the system is operational. This brings us to the next point: how do we measure the signal? Fortunately, there exists simple in-line signal strength meters for this task. One popular (and economic) type is called, logically enough, a “Satellite Finder”. The meter has an input port that requires DC voltage from the satellite receiver and an output port that feeds that DC voltage to the LNB and reads the amount of signal being sent from the LNB to the receiver. Basically, it is a simple broadband amplifier and a rectifier driving an analog meter movement and a tone generator. As the signal gets stronger (as we peak up the dish), the meter deflection becomes greater and the tone gets louder. The meter also has a sensitivity adjustment. Now, having set the dish elevation, set the LNB orientation and calculated the magnetic azimuth of the dish, rotate the entire reflector and mount assembly on the pole The completed mount. The solid bar (arrowed at left) locks the dish azimuth (set by rotating on the pole). This bar can be replaced by a suitable motor to enable the dish to track any number of (viewable) satellites. But for single-bird systems, this bar is bolted in place as shown here.  January 2003  13 until it points in the desired direction. At this point, connect the LNB to the signal meter and the signal meter to the receiver via short lengths of coaxial cable. Because you are not trying to display a picture right now, you don’t need any monitor so setup is most easily done close to the dish with the receiver on a suitably long power cord. Adjust the meter sensitivity to maximum and turn the receiver on. As the dish assembly is rotated on the pole, the signal strength meter will begin to respond. As the meter reaches full scale, back off the sensitivity while continuing to move the dish, until the signal is peaked. Carefully adjust the clamping screws on the dish mount so that they are all tightened evenly, clamping the mount to the pole without causing any skew in the vertical plane. It may be necessary to optimise this adjustment several times. Once this has been done, the elevation adjustment should be optimised for maximum signal, by slowly turning the elevation rod. When this is peaked, lock it in place. At this stage, select the desired channel on the satellite (most receivers come pre-programmed) and carefully rotate the LNB (with the meter still connected) until the signal is peaked. This adjustment will only be in the order of 10-15°. Making adjustments greater than this will mean the LNB is peaking on signals of the opposite polarity, as most satellites have signals of both horizontal and vertical polarisation (and sometimes on the same frequency). This adjustment is called cross polarisation optimisation. Connecting up your system. Like most pieces of audio visual equipment, a digital satellite receiver has several different outputs for connection to a TV set, VCR or hifi system. For best results, especially where a recording facility is desired, it is normal practice to connect the direct line audio and composite video outputs from the satellite receiver to the VCR and then use either the RF or (again preferably) the A/V output of the VCR to connect to the TV set. Most satellite receivers have two or more A/V outputs, allowing separate connections to a hifi system for enhanced audio. However, many overseas stations broadcast in dual mono and often in different languages. In some cases the redundant audio channel is used to carry a separate radio service. Place the dish on the mount. This is definitely a two-man job (the missing man in this picture was the photographer!) The double edges (joins between the dish panels) slot into the U-shaped brackets on the mount. Place the upper-most bolts and nuts first. Some to-ing and fro-ing of the dish panels might be necessary to get the bolts to go right through the holes in the double-thickness joins. Make sure all dish panel and mounting bolts are tight. 14  Silicon Chip For this reason, satellite receivers allow the user to determine which output will be routed to the sockets on the rear panel. Assuming there is coaxial cable supplying TV wall outlets in several rooms in the house, the RF output of the satellite receiver can be combined with the existing internal TV cabling to provide a “satellite” channel. While the limitation of this system is that only one channel is fed into the system, it does mean that satellite TV can be enjoyed in many rooms. Anyway, you can only watch one channel at a time, no matter which room you are in! Channel surfers (or those with the remote control permanently super-glued to their hands) need not apply! If the ability to record is not required, best results are obtained by running the line audio and composite video outputs of the satellite receiver, directly in to a spare A/V input on the TV set. This is an easy way to switch from normal terrestrial TV to satellite TV. Most modern TV sets are multi-system, meaning they have the ability to convert an NTSC video signal into a PAL signal. If you don’t have one of these, and the station you want to watch broadcasts in the American (NTSC) video format, you may need a video systems converter. Countries using the NTSC format include USA, Canada, Mexico, Japan, Taiwan and Korea – in fact pretty well anywhere where there has been a US influence in the development of the country, use NTSC. All other countries use PAL these days (even digital signals from Russia use PAL!). PAL or Phase Alternating Line, is of course the system used for analog TV transmission in Australia. Analog converters start at $99, while fully fledged digital converters (that allow recording on a PAL VCR) range from $750 to $2000 for a top-of-the-line model (near broadcast quality). As a digital satellite system is capable of delivering very high quality video, the appropriate quality cables should be used. This means going to a reputable electronics outlet to obtain them. In the old analog days it might have been possible to put up with the video performance of audio cables, such as the inexpensive twin RCA-RCA types we have all seen. However, to preserve the quality of the video performance from the satellite receiver, it is important to use well-screened, moulded, three-conductor low capacitance cables, which can normally be identified by the larger There are four possible adjustments for maximum signal: azimuth, elevation, declination and LNB polarity/focal point. These must be set as explained in the text. In this shot, Erin is setting the elevation – the angle in the sky to which the dish points. Turning the elevation rod raises and lowers the top of the dish with respect to the vertical mounting pole. Azimuth is adjusted even more easily – by rotating the dish on the mounting pole. The focal point is almost always fixed. Don’t worry about declination unless setting up a motorised system. www.siliconchip.com.au A typical digital satellite receiver – in fact, this or one very similar is the one in the special offer at right. diameter of the video cable. The effect of using inferior cables will be colour smearing, ringing along the leading edge of the video and generally poor definition. Do I leave the receiver on? Most satellite receivers have a standby function, putting the receiver to sleep but allowing voltage up to the LNB. This has the effect of keeping the LNB stable and at a constant temperature. For this reason, it is wise to leave the receiver in the standby mode when it is not being used. This also eliminates the possible ingress of moisture into the receiver itself. Like all electronic equipment, keep the receiver well ventilated. This is particularly so when several pieces are stacked together in a typical hi fi cabinet. Spacing equipment apart with small blocks of wood can help in this aspect. Avoid the practise of some people (let’s not be sexist here) of putting doilies on top of the receiver (or VCR or CD or DVD or anything else for that matter) and putting a pot plant or vase of flowers on top, “to make it look more attractive”. Apart from the fact that this may well cover the ventilation slots and cause overheating, there is always the danger of the vase being knocked over and the internals taking an unwanted and probably highly damaging shower. For the same reason, empty video sleeves, CD/DVD/ cassette cases, etc, should never be placed on top of electronic equipment. SC EXCLUSIVE SPECIAL OFFER FOR S ILICON CHIP READERS Av-Comm Satellite Equipment has a very special offer, exclusively for SILICON CHIP readers: a complete, brand new, state-of-theart DIGITAL satellite receiving system ready to put together, connect up and turn on! Here’s what you get:  A 2.4m 4-panel mesh dish complete with all mounting hardware (except the post!)  A dual polarity, low noise, block downconverter (LNB)  A high efficiency feedhorn  A Digital Satellite TV Receiver with remote control, MPEG-2 and digital DVB compliant.  25m RG-6 (satellite grade) coaxial cable and two “F” connectors  An analog inclinometer  A “SatFinder” in-line signal strength meter Current Av-Comm catalog price for all this is $1450.00 – but until February 28 2003, if you tell Av-Comm you’re a SILICON CHIP reader, you can have the complete package for just $1295.00 – that’s better than 10% off. And remember, all this equipment is brand new, with full warranty. Order direct from Av-Comm (do not call SILICON CHIP!) Phone Av-Comm on (02) 9939 4377, fax 9939 4378, email cgarry<at>avcomm.com.au or use the special SILICON CHIP SYSTEM order form on Av-Comm’s website (www.avcomm.com.au). * Director, Av-Comm Pty Ltd The LNB is a friction-fit into the feed horn (at the junction of the struts). After fitting and connecting the coaxial cable, you need to adjust the LNB polarity for maximum signal by rotating it in the feed horn. You will probably need to re-adjust elevation and azimuth. To complete the job, run the coax down one of the struts and secure it with black cable ties (white ones will break down over time due to UV). Make a loop around the back of the dish and cable-tie the coax to the mounting post. www.siliconchip.com.au And now it’s finished. We’ve left the LNB cover off for clarity (quite often they are left off anyway!). The coax is connected to the LNB and secured to the strut and post – now it is just a matter of connecting it to your satellite receiver, tuning in the required channel and watching your satellite programs. After the dish has settled in, it might pay you to re-peak the azimuth, elevation and LNB output as previously detailed. But if you have wall-to-wall signal, it’s probably not worth the bother. Enjoy! January 2003  15 READER/ PROGRAMMER FOR SMART CARDS Since blank smart cards are now available at attractive prices, it’s quite feasible to program them with your own software and data for all kinds of applications. Here’s a low cost and easy to build ‘Phoenix type’ reader/programmer, which can be used with most of the programming software available on the Web to suit this type of serial-port device. W ith their embedded microcontroller and serial EEPROM combination, today’s ‘smart cards’ have many more uses than dumb cards which merely have a magnetic stripe. Smart cards are already used for pay TV set-top box and mobile phone authorisation but these applications really only scratch the surface of their potential. You could use them to build your own personalised security access system, for example, or to provide a ‘plugin brain and memory’ for small robots and digitally controlled machines. Or to provide plug-in schedules for 16  Silicon Chip automatic control of a model railway, or pointing data for a computer-positioned telescope, or whatever... Using smart cards for your own applications is now quite feasible because blank smart cards and matching ‘sockets’ are now available at quite reasonable cost. For example, Jaycar stores are offering blank cards with an embedded PIC16F84A micro and 24LC16B EEPROM for $19.95 (Cat ZZ-8800). Jaycar can also supply suitable ‘sockets’ in both through-hole (PS-0012) By David Freeman and SMD (PS-0010) versions for only $8.75 each. By the way, the PIC16F84A micro-controller chip (made by Microchip Technology) is used in many of the commonly used smart cards. Although only an 8-bit processor it’s quite powerful, with 1024 words of program memory, 68 bytes of data RAM and 64 bytes of data EEPROM. It is even smarter when it’s teamed up with the 24LC16B serial EEPROM (which has a capacity of 16K bytes); the combo is capable of a surprising range of applications. Other smart cards team up the PIC16F84A micro with a 24C64 EEPROM www.siliconchip.com.au which offers 64K bytes of memory. They can, of course, because the for reading and programming. (Note The Atmel AT90S8515 micro is also cards are available over the coun- that the card’s EEPROM is read and used in some smart cards. Usually it’s ter as well as being used in pay TV programmed ‘through’ the micro, with teamed up with either the 24C64 or set-top boxes and mobile phones. its ‘cooperation’.) 24C128 (128K bytes) EEPROM. So because the matching sockets In this article, I’m describing a Fig.1 shows what’s acsimple reading/programtually inside a common ming interface which is smart card, of the type quite low in cost and using the PIC18F84 with easy to build. I can’t a 24LC16. Because both claim it involves any chips use serial commugreat design innovation. nication, all of the conIn fact, it’s very simnections to the ‘outside ilar to quite a few deworld’ are made via only signs that have been five of the tiny array of available on the Internet eight gold-flashed conand like them, based on tacts. what seems to be called Contact C1 is used to the ‘Phoenix’ configusupply the chips with +5V, ration. C2 to reset the micro, C3 (I haven’t been able to provide the micro with to find out where that clock signals (3.75MHz name came from – perFig.1: here’s what is inside that innocuous-looking piece or 6.0MHz), the large ‘L haps the person who of plastic. There’s a lot more to it than meets the eye! shaped’ C5 for ground and came up with the first C7 for serial data input design lived in Phoenix, amd output. Arizona!) This kind of card makes a compact are readily available as well, it has The main advantage of using this (86 x 54 x 0.8mm) and cost effective become quite feasible to use them in kind of design is that it’s compatible package containing such a useful your own projects. with a lot of the smartcard reading micro and EEPROM. How they can All you really need for this is a small and programming software available fit those chips, bonding wires and hardware interface to connect the card for free downloading from many sites contacts inside a card with a total up to your PC, and suitable software to on the internet. thickness of only 0.8mm is beyond me! allow you to ‘talk’ to the card’s micro By the way, SILICON CHIP will NOT The smart card reader/programmer is assembled on a single PC board. Basically, it is just an interface between the card, which slides into the slot at right, and the PC. www.siliconchip.com.au January 2003  17 Fig.2: the complete circuit. There’s not much to it – just a couple of crystal oscillators, an RS-232 chip and power supply. be able to provide you with any software to go with the hardware, because according to Australian federal law this combination of hardware and software is capable of being ‘used for the purpose of defeating encryption systems’, and is accordingly deemed illegal. Needless to say, we are certainly not describing this project with the idea that you would use it to defeat any encryption systems. In fact we must warn you that it should NOT be used for this purpose, because doing so would be illegal and make you liable to be prosecuted. All we can do with regard to helping you find suitable software is list the URLs for some of the web sites where you may be able find some, and leave the rest to you. These are shown in the accomp-anying panel. Be warned again, though: some of the software on these and other sites MAY be designed specifically for illegal smart card applications. So let the user beware! Incidentally, we understand that kits for this hardware interface will be available from Jaycar Electronics. So you shouldn’t have any problems building up the interface itself or get18  Silicon Chip ting blank smart cards for use with it. Free-standing board As you can see from the photo, there’s very little in the project and all of its components fit on a small freestanding single-sided PC board. The board measures only 89 x 76mm, and is coded 07201031. It’s supported on four small rubber feet and has the smart card socket on the front, flanked by two LEDs: one (green) to indicate when the unit is powered up, the other (red) to show when the PC is reading from or writing to the card. Here’s a selection of “blank” smart cards showing different types of contacts available. This reader/ programmer suits only the 8-contact version, as shown on the left. Along the back of the board are a DB9F socket for a standard RS-232C serial link cable to the PC serial port, plus a 2.5mm concentric DC power connector to accept the cable from a 9-12V plugpack power supply. Everything else is on the board itself. Circuit description The hardware of this project is designed to perform just three main functions: (a) to provide +5V DC to the smart card plugged into its socket; (b) to provide the card with a clock signal of either 3.75MHz or 6.0MHz, selectable via a jumper shunt; and (c) to provide a serial communications interface between it and the PC’s software, to allow reading and writing. Referring to the circuit diagram, power for the interface is derived from a 9-12V DC plugpack, connected to the unit via CON3. Series diode D1 prevents damage due to an accidental reverse polarity connection, while low power regulator REG1 provides smoothed and regulated 5V DC for both the smart card and the rest of the interface circuitry. LED1 is the green power indicator, which runs directly from the unregulated input. Clock signals for the smart card are provided by the circuitry around IC2, a www.siliconchip.com.au Full-size view of the completed PC board. . . low-cost 74HC00 quad gate. Two of its gates (IC2c/d) are connected as crystal oscillators, one for 3.75MHz using crystal X1 and the other for 6.0MHz using X2. Which oscillator runs at any particular time is determined by the position of the jumper shunt in the 3-pin header LK1, because this applies +5V to the second input of either IC2c or IC2d. Each oscillator only operates when its second gate input is taken to +5V, so the oscillator whose second input is held low via the 10kΩ resistor is disabled. The outputs of the two oscillators are fed into IC2a, used here as an OR . . . along with the matching component overlay. gate. Then the clock signals are passed through IC2b, used as a buffer, before being fed to the CLK pin of the smart card socket (C3). The rest of the circuitry forms the interface between the smart card and the serial port of the PC (via CON2). The heart of the interface is IC1, a standard MAX232 dual RS-232C serial bus transceiver. This chip is very handy because it contains internal ‘charge pump’ circuitry which generates the correct RS-232C voltage levels from a standard +5V supply rail, using the four 1µF capacitors connected to pins 1-6. One of the two receivers of IC1 has its input (pin 8) connected to the transmit data line from the PC (TxD, pin 3). The output of this receiver (pin 9) is used to operate LED2, the Read/ Write indicator. The same output is also used to pull down the Data I/O pin on the smart card socket (C7) via Schottky diode D2, to send data to the card during write operations. The smart card pin (Data I/O) is normally pulled high by a 10kΩ resistor to +5V but can easily be pulled low by pin 9 of IC1 because of the very low voltage drop in D2. When the smart card micro itself pulls the Data I/O pin low during a read operation, this is fed back to Fore and aft close-up views of the business ends of the smart card reader/programmer, showing the RS232 and power supply connections (left photo) and the smart card slot (right photo) www.siliconchip.com.au January 2003  19 Parts List – Smart Card Reader/Programmer 1 1 1 1 1 1 1 4 2 6 4 PC board, code 07201031, 89 x 76mm 3.57MHz crystal (X1) 6.00MHz crystal (X2) 3-pin SIL header strip with 2-way jumper shunt (J1) ICA-700 DIP smart card socket (CON1) DB9F connector, 90° PCB mount (CON2) 2.5mm DC power connector, PCB mount (PS-0520) (CON3) M3 x 6mm cheesehead machine screws M3 x 9mm cheesehead machine screws M3 hex nuts small rubber feet, screw attachment type PC via the ‘carrier detect’ line (CD, pin 1) of the serial comms port, this allows the software to monitor when a card is present in the socket. Putting it together You shouldn’t have any trouble putting the interface together if you follow the board assembly diagram carefully, as a guide to positioning the various components and their orientation. I suggest that you fit the card socket, the DB9 connector and the DC power socket to the board first, as all three Semiconductors of these may need a small amount of 1 78L05 low current regulator(REG1) board hole ‘tweaking’ before their pins 1 MAX232 or ST232CM interface (IC1) all mate with the board correctly. It’s 1 74HC00 quad NAND gate (IC2) easier to do this before you add all of 1 3mm green LED (LED1 — power) the other components. 1 3mm red LED (LED2 — read/write) Note that the card socket mounts 1 1N4004 power diode (D1) with its card entry slit towards the 1 1N5819 Schottky signal diode (D2) front(!), and that as well as the various contact connection pins it also Capacitors has a couple of 3mm diameter plastic 1 10µF 16V RB electrolytic locating spigots which sit in matching 4 1µF tantalum holes in the board. 3 100nF metallised multilayer ceramic (code 100n or 104) Once the three connectors are fitted 4 22pF NPO disc ceramic and soldered in place, you can then Resistors (0.25W 1%) add the remaining components in the 2 1MΩ (brown black green brown or brown black black yellow brown) usual order. That is, wire links first 4 10kΩ (brown black orange brown or brown black black red brown) (there are only two), then the 3-pin 1 1.5kΩ (brown green red brown or brown green black brown brown) SIL header, then resistors, capacitors 3 1kΩ (brown black red brown or brown black black brown brown) and crystals. Finally come the diodes, regulator, LEDs and ICs. As always, make sure you fit all pothe serial port (CON2) via one of the in card sensing switch. The other larised parts with the correct polarity IC1 transmitters, as pin 10 is also side of the switch is connected to as shown in the diagram. connected to this point. The output +5V, so when a card is inserted into Both LEDs have their cathode ‘flat’ from pin 7 of IC1 is connected to pin the socket and pushed right in, the side towards the front of the board, 2 of CON2 which is while both ICs the RS-232C receive have their notch data (RxD) line. end towards the The second reback. Take special Here are some website links where software compatible with this smart ceiver of IC1 has its care with the pocard reader/programmer is available for free download: input (pin 13) conlarity of the four www.adteknik.se/english/ nected to the Ready 1µF tantalum cawww.angelfire.com/space/aussiemulate/ to Send (RTS) line pacitors on the outfrom the PC (CON2 er side of IC1. www.maxking.co.uk pin 7), and its output When the board www.maxkingtunisia.com (pin 12) to the Reset is fully assembled, www.skyvisiontech.com/card_reader.htm pin of the smart card the four small rubNote that neither SILICON CHIP nor the author of this article can accept socket. This allows ber feet can be responsibility for the operation of any of this software or its potential to the software in the attached to it usbe used for unlawful purposes. PC to issue a reset ing M3 x 6mm command to the mach-ine screws micro in the smart and nuts. card whenever this The feet are important with this kind switch operates and pin 11 of IC1 is of ‘naked board’ assembly because is required. The input of the second transmitter pulled high. they give the board proper support The output of this transmitter (pin while lifting the solder joints away section of IC1, pin 11, is connected 14) thus swings to RS-232 ‘mark’ level, via a 10kΩ resistor to ground but also from whatever surface the interface to one side of the card socket’s built and as this output is passed back to the may be placed on. Where to look for software 20  Silicon Chip www.siliconchip.com.au That’s about it. Your smart card interface should now be ready to use, but before hooking it up to one of the serial comms ports of your PC you might want to give it a quick check-out. 1-minute checkout To do this, connect the output cable of the 9V plug pack to CON3, and apply power to the plugpack. Power indicator LED1 should immediately light — if not, remove the power and check that you’ve fitted it the right way around. The only other reason for ‘no glow’ is that you may have wired in diode D1 in wrong way around, or the plug is fitted to the plug pack output cable with the connections reversed. Assuming the LED is happily glowing, check the DC voltage at pin 14 of IC2 and pin 16 of IC1 with your DMM. In both cases you should get a reading within a few millivolts of 5.0V, and you should also be able to measure the same voltage at the ‘+5V’ pin of the card socket and/or the end of the 1kΩ resistor right next to it (and alongside D2). If these voltages measure OK, you must have connected the regulator in the correct way around. At this stage your interface is probably working as it should. However, if you have access to a scope (CRO) you might also want to check the crystal oscillators. This too is very straightforward. With the unit powered up, try fitting the jumper shunt joining the centre and lefthand pins of the SIL strip (looking from the front). With the scope probe on pin 6 of IC2, you should find a 5V peak-peak square wave of 3.75MHz. If you shift the jumper shunt to join the centre and righthand pin instead, the waveform at pin 6 should simply change in frequency to 6.0MHz. Assuming this is what you find, you can conclude that your smart card reader/programmer is all present and correct. All you need now is a cable to con- nect it to a spare comms port of your PC and of course some software so that your PC knows how to talk to a card plugged into the front socket. Plus a card or two, of course... Incidentally there’s a lot of specialised knowledge and jargon associated with some areas of smart card technology. You’ll find a lot of this explained in some of the documentation files available on the Angelfire website. If you’d also like more information on the PIC 16F84A micro and the 24LC16 EEPROM, this can easily be downloaded from the Microchip website (www.microchip.com). There are applications notes available as well as device data sheets — most of them in PDF file format. So once you have the interface, your future with smart card technology will SC await. Over to you! Where from, how much. . . This project was designed for Jaycar Electronics and is only available through Jaycar Electronics stores, dealers and mail order service. Expected retail price is around $29.95. Jaycar also have blank smart cards available for $19.95 each. Contact your nearest Jaycar Electronics store. ELECTRONICS Do You Eat, Breathe and Sleep Technology? Jaycar is a leading electronics retailer with over 6,000 products from electronic components to computer accessories. Management Opportunities plus Full and Part Time Sales Positions Available Nationwide We are growing rapidly with 30 stores and we have an expansion programme to open many more. Backed by mail order and a fully interactive website, we need dedicated individuals to help achieve our goals. You need to be customer focused, with an eye for detail and empathy for the products we sell. Ideally you will have some experience in retailing, coupled with management experience for the senior positions. You will also need to be energetic, enthusiastic and have excellent interpersonal skills. Career opportunity with full training is available if you have the drive and ambition to make your future at Jaycar. We offer a competitive salary, sales commission and many other benefits. To apply for any of the above positions please ask in-store for details or alternatively send a full C.V. indicating the roll you are interested in, location and details of current salary to; Retail Operations Manager Jaycar Electronics Pty Ltd P.O. Box 6424 Silverwater NSW 1811 Fax: (02) 9741-8500 Email: jobs<at>jaycar.com.au www.siliconchip.com.au January 2003  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: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au E R U FEATJECT PRO Build the –– aa new, new, high high perform perform By LEO SIMPSON & PETER SMITH The transmogrification of an amplifier. Many readers will recognise the venerable (26-year-old!) ETI-480 top left. But the SC480 (bottom right) is as modern as tomorrow – with performance to match. Performance into 4Ω 50 watts into 8Ω; 70 watts Output Power tts into 4Ω 77 watts into 8Ω; 105 wa Music Power 1W – see Fig.1) B at 14Hz and 70kHz (at Frequency response -1d 0.875V for 50W into 8Ω Input sensitivity typically <.003% 5% from 20Hz to 20kHz; d, Harmonic distortion <.0 22kHz); -119dB A-weighte 4dB unweighted (22Hz to -11 io Rat ise -No -to nal Sig into 8Ω both with respect to 50W t PTC thermistor h respect to 8Ω and withou wit z, 1kH & Hz 100 at >140dB Damping factor thermistor es plus “Polyswitch” PTC Protection fus 26  S ilicon Chip onditional Stability unc www.siliconchip.com.au SC ETI-480 mance mance amplifier amplifier module module Have you built one – or more – of the popular ETI-480 power amplifier modules over the years? Here is the module to replace that old design. The SC480 produces a great deal less distortion, is much quieter and has inbuilt protection. It also sounds much better. B ack in the October 2002 issue we noted that we intended to produce a replacement module for the very popular ETI-480 amplifier module which was published back in December 1976 – 26 years ago. In the same note we stated, somewhat controversially, that the ETI-480 was a dog of an amplifier and that it was not a good performer, even by 1976 standards. Having made that outrageous statement (to some readers, at least), we had to come up with the goods. Fortunately, we were pretty confident that we could, and we are pleased to state that this new module is even better than we had hoped. It uses the same power output transistors as in the ETI-480 and just one more low-cost transistor has been added to the overall component count. Kit cost should be about the same as for the ETI-480. When this project was first mooted, we decided to base it on TIP3055 and TIP2955 plastic power transistors. These are 60V 15A 90W transistors in the TO-218 (SOT-93) encapsulation. We i n t e n d e d to produce a new version of a 100W module which was published in the December 1987 issue of SILICON CHIP. That design was based on a Hitachi amplifier circuit and used 2N3055/MJ2955 power www.siliconchip.com.au transistors in TO-3 metal encapsulation. Accordingly, we produced a PC board pattern for the new module and while we waited for it to be produced by RCS Radio Pty Ltd (thanks Bob), we realised that a substantial number of readers who had built countless ETI-480 modules would probably like to “graduate” to our new design but would wish to at least reuse the TO-3 power transistors from their ETI-480s on the new board. Hence, the idea of a TO-3 version of the new module also came to pass, as is featured here. The plastic version of the module has the power transistors lined up along the back edge, making it easy to mount them to the vertical surface of a finned heatsink. The TO-3 version is larger and has the four power transistors mounted on the horizontal shelf of a cast heatsink or on a rightangle bracket which can then be mounted on a vertical heatsink. Why publish both modules? The simple answer is that we had produced them both, so why not? However, each module has its own advantages. Version 2, using the TO-3 transistors, is rugged but takes up more space and is likely to be less convenient to mount in a typical chassis. There is also more work in assembling Version 2 with the TO-3 transistors. Version 1, with the plastic power transistors is quite a bit more compact and less trouble to mount in a typical chassis but the module assembled onto a heatsink is not quite as rugged to handle. By the way, if you decide to build Version 1, don’t be tempted to substitute the (usually) cheaper MJ“E”... versions of the transistors. These TO-220 transistors are rated lower (only 75W) and will inevitably cause you great pain and suffering. January 2003  27 Which version to build? Our preference is for Version 1 but we have a sneaking suspicion that Version 2, with the TO-3 power transistors, will be the more popular module (especially amongst those looking for a somewhat look-alike ETI-480 substitute). Depending on the particular brand of power and driver transistors used, both modules will give virtually identical performance. Regardless of which version you decide to build, the performance will be vastly better than the old ETI-480 design. And that is as it should be. After all, we should have learnt quite a bit about amplifier design in 26 years or so, shouldn’t we? Performance Power output is 50 watts RMS into a 8Ω load and 70 watts into 4Ω load, before the onset of clipping. Music power is around 77 watts into 8Ω and 105 watts into 4Ω. Hang on a minute! Wasn’t the ETI-480 claimed to be 100W into 4Ω? Well, it was but the distortion graph published by ETI back in December 1976 shows the amplifier heading well into clipping at around 70W RMS. This is to be expected since both the ETI-480 and the new SC480 use the same voltage rails and the same output transistors. A particular feature of the SC480 is low distortion. Distortion for all power conditions, up to clipping, into an 8-ohm load, is less than .05% for the full range of frequencies from 20Hz to 20kHz. Similarly, with a 4-ohm load, total harmonic distortion is less than .07% for the full audio frequency range. In reality, this is a very conservative rating as the distortion will typically be .003% or less for both load conditions. And for very lower power levels, less than 100mW, where noise becomes a significant part of the measurement, the distortion is really low, down to as low as .0005%. This is two orders of magnitude better than the ETI-480! Signal to noise ratio is better than -114dB (unweighted, 22Hz to 22kHz) with respect to full power into an 8Ω load. Frequency response is just 1dB down at 14Hz and 70kHz (see Fig.1). Fig.1: this is the frequency response of both versions of the new amplifier, taken at a power level of 1W into an 8Ω load. Transistor quality As in most things, you get what you pay for and it is no different with these modules. The plastic version (Version 1) of the amplifier was built with the output and driver transistors in what we would call the premium brands: Philips, Motorola (On Semi) and ST Micro. Version 2 was built with second rank power and driver transistors (Mospec). We did this to compare performance and we are pleased to report that although the premium branded transistors do give slightly better performance, there is a not a lot in it. Refer to the distortion graphs of Figs.2-9 to make the comparisons. Either way, the performance of these modules is very good, especially considering that we are not using expensive transistors such as Motorola MJL21193/4 or the even more expensive MJL1302A & MJL3281A. In fact, in some respects the measured performance challenges that of our popular and more powerful Plastic Power module published in the April 1996 issue. Interestingly, a These two oscilloscope screen grabs show just how clean this new amplifier is. The first screen (left) shows a 1kHz output waveform at a level of 40W into 8Ω at top. The lower trace is the distortion waveform which has been “averaged” by the scope to remove noise. Note that it is mostly second harmonic distortion. The same process has been applied to the screen shot at right except that it is a 10kHz signal. Again, the distortion is mainly second harmonic. 28  Silicon Chip www.siliconchip.com.au key part of that performance standard comes about because of improved PC board and wiring layout. We’ll discuss these vitally important aspects in more detail later in this article. Oh, and we should state that the SC480 Version 1 and Version 2 modules are a drop-in replacement for the ETI480 modules but will sound a great deal better. While nominally of the same rating, they will deliver more power, they’re quieter and as already detailed, much lower in distortion. By the way, these modules are not suitable for driving 2Ω loudspeakers as used in car sound systems. We do not have space to publish the load/line curves in this article but suffice to say that attempting to drive 2Ω loads will blow the fuses and may blow the output transistors as well. Protection The trouble with all high-power amplifiers is that, if a transistor fails, there is a big chance that the loudspeaker system could be damaged, despite having fuses in the power supply. The problem is that the fault condition may place a large DC voltage across the speaker’s voice coil and the resulting current may not blow the fuses. The speaker’s voice coil then gets red hot and may actually set the speaker cone on fire! Once that happens and if you’re not there to kill the power to the amplifier, you can have a raging fire in your home and enormous amounts of smoke being generated by the burning of the filling material in the cabinet. Our normal approach to this problem is to incorporate relay protection which will disconnect the loudspeaker in the event of a large DC fault condition occurring in the amplifier. Relay protection works as far as the speaker is concerned but it doesn’t protect the amplifier itself if the loudspeaker leads are shorted. Here again the fuses may not blow before the output transistors are damaged. Neither do fuses protect the speakers if you seriously over-drive the amplifier. This is a particular risk for tweeters but even woofers can have voice coil damage by serious over-drive. Complete protection The method we have used to provide protection to both the loudspeaker and amplifier is to connect a high current positive temperature coefficient (PTC) thermistor (known commercially as a “Polyswitch”) in series with the output circuit. This is the same method of protection as we used in the original module published in December 1987. The PTC thermistor normally has a very low resistance but when the current through it rises to high value, it immediately switches to a high resistance state and stays in that condition until the fault is fixed or power is removed. The resistance of the PTC thermistor is so low (typically 0.1Ω or less), it has a negligible effect on amplifier performance, apart from the fact that it does cause a reduction in damping factor. In practice, it works extremely well. It allows you to drive the amplifier to full power on program signals but the moment a short circuit is applied or the amplifier is seriously over-driven, the PTC thermistor goes high in resistance to cut off the fault current. After the protection thermistor has switched to its high state, it takes some time to revert to its low resistance condition, after the fault current has ceased. This depends on how much current is passing through it. If the drive level is maintained after a fault has occurred, the protection thermistor will stay high in resistance. Circuit description Now let’s have a look at the circuit of Fig.10. 13 transistors and three diodes make up the semiconductor complement. The input signal is coupled via a 1µF bipolar electrolytic capacitor and 2.2kΩ resistor to the base of Q2. Q2 & Q3 make up a differential pair. Q1 is a constant current source which sets the current through Q2 & Q3 and renders the amplifier largely insensitive to variations in its supply rails Just to confuse you, Version 2 of the SC480 amplifier (with TO-3 transistors) is on the left, while Version 1 (with TO-218 transistors) is on the right. There is only a small difference in performance between the two versions. www.siliconchip.com.au January 2003  29 Fig.2: THD versus power at 1kHz into an 8Ω load for Version 1 (TO-218). Fig.3: THD versus power at 1kHz into a 4Ω load for Version 1 (TO-218). (power supply rejection). Signals from the collectors of Q2 & Q3 drive another differential pair, Q4 & Q5 which have a “current mirror” as their collector loads. The current mirror, comprising D3 and Q6, ensure that this second differential stage has high linearity (ie, low distortion). The output of Q5 is then used to drive class-AB output stage consisting of drivers Q8 & Q9 and power transistors Q10, Q11, Q12 & Q13. Q7 is a Vbe multiplier, so-called because it multiplies the voltage between its base and emitter to provide a fixed voltage between its collector and emitter, regardless of the drive current delivered to the output stage by Q5. The voltage is adjusted by trimpot VR1. The function of Q7 is to set the DC voltage applied between the bases of Q8 & Q9. By doing this it sets the “quiescent current” in the output stage (ie, the current when no signal is present). This is to minimise crossover distortion. In fact, our tests did not reveal any signs of crossover distortion. The complementary output transistors are connected in parallel to give high output current capability. Each transistor has its own 0.22Ω emitter resistor. These are included to ensure that the output current is shared reasonably well between the output transistors. Negative feedback is applied from the output stage back to the base of Q3 via a 22kΩ resistor. The level of feedback, and therefore the voltage gain, is set by the ratio of the 22kΩ resistor to the 1kΩ at the base of Q2. The 47µF bipolar capacitor in series with the 1kΩ sets the DC gain to unity and sets the -3dB point of the frequency response to about 3Hz. The other determinant of the amplifier’s low frequency response is the 1µF input capacitor and the 22kΩ base bias resistor feeding Q1 and these set a -3dB point at about 7Hz. The 330pF capacitor together with the 2.2kΩ resistor feeding Q2 form a low pass filter to roll off frequencies above 200kHz. The 68pF capacitor between the base and collector of Q5 and the 10pF capacitor between base and collector of Q2 roll off the open-loop gain of the amplifier to ensure stability with feedback applied. Note that the 68pF capacitor can be a ceramic or polystyrene type and must a have a voltage rating of 100V or more. Other capacitor types are not recommended. Another important factor in the amplifier’s excellent Fig.4: THD versus power at 1kHz into an 8Ω load for Version 2 (TO-3). Fig.5: THD versus power at 1kHz into a 4Ω load for Version 2 (TO-3). 30  Silicon Chip www.siliconchip.com.au Fig.6: THD versus frequency at 40W into an 8Ω load (Version 1). Fig.7: THD versus frequency at 60W into an 4Ω load (Version 1). stability is the output RLC network consisting of the 6.8µH choke, a 6.8Ω resistor and a 150nF capacitor. Not only does this network ensure stability but the capacitor is an effective killer of any RF and mains-interference signals which can be picked up by long loudspeaker leads. As noted earlier, the design of the PC board is a very critical part of the overall circuit. The placement of the components and the way that heavy currents flow in the tracks is all arranged to minimise the radiation of harmonics into the input stage involving Q1 & Q2. This board is yet a further refinement of the topology we first introduced in the Ultra-LD amplifier featured in March, May & August 2000 and then again in November & December 2001. The PC board for version 2 and the component placement is shown in Fig.12. It incorporates “star earthing” whereby all earth currents come back to a central point on the board, thereby avoiding any flow of output, supply and bypass currents flowing in the signal earths. Furthermore, placement of the copper tracks to the output stages is arranged, as far as possible, to cancel the magnetic fields produced by the asymmetric currents drawn by each half of the output stage. By way of explanation, when the positive half of the output stage (Q10 & Q12) conducts, the DC current drawn is effectively a positive half wave (ie, rectification takes place) of the signal waveform. And when the negative half conducts (Q11 & Q13), the DC current is the negative half wave. A major cause of harmonic distortion in class-B amplifiers is the magnetic fields produced by these asymmetric Fig.8: THD versus frequency at 40W into an 8Ω load (Version 2). Fig.9: THD versus frequency at 60W into an 4Ω load (Version 2) Power supply The power supply circuit is shown in Fig.11. This uses a centre-tapped 56V transformer driving a bridge rectifier comprising four 1N5404 diodes and two 4700µF 50V filter capacitors. This produces unregulated supply rails of about ±40V. Depending on the mains AC voltage, the rails will drop to around ±32V or less when the amplifier module is delivering full power into a 4Ω load. We have also provided a ±15V DC supply for a preamplifier. This is derived with 2.2kΩ resistors and two 15V 1W zener diodes. PC board topology www.siliconchip.com.au January 2003  31 Fig.10: this direct-coupled amplifier module uses a differential input stage (Q2,Q3) with a constant current tail (Q1). This drives another differential amplifier (Q4,Q5) with current mirror load (D3,Q6). Quiescent current in the output stage is set by VR1 and Q7. The output stage is a complementary class-AB configuration using Q8 & Q9 as drivers and Q10 to Q13 as the output devices. Voltage readings are taken with no signal applied. currents inducing unwanted signals into the input stages, in this case involving Q1 & Q2. So we have tried to cancel these fields as much as possible (in a single sided PC board). For example, notice how the positive fuseholder (F1) is placed close and parallel to the emitter resistors for Q10 & Q12. So what happens is that the magnetic field produced by the asymmetric current in fuse F1 is more or less cancelled as the same current flows back in the emitter resistors. This is the main reason why the layouts for these two modules is much tighter than our designs of recent years. You will see the same method employed in the Version 1 of the board, with the heavy collector and emitter tracks 32  Silicon Chip placed close together but we think this has been more fortuitous on Version 2 than on Version 1. It is then most important to arrange the DC supply cables to the amplifier to further this cancellation process. We’ll detail this in the construction description. To make the input stage less vulnerable to spurious magnetic fields from the output stage, we have concentrated it into as small an area of the PC board as possible. Another trick is the location of the takeoff point for the 22kΩ resistor and its orientation at rightangles to the output stage emitter resistors. Finally, the signal earth for the input stage is separated from the main amplifier earth by a 10Ω resistor. www.siliconchip.com.au Fig.11: the power supply is very simple but adequate. The ±15V preamplifier supply is optional. This is not so important when a single module is in use but it is most important when two modules are used in a stereo system. In that situation, the joining of the two signal earths back via the input cables to a single program source such as a CD player will cause an earth loop and a resulting major degradation in the separation between channels and lesser degradation in the distortion performance. Well, that’s probably enough discussion of the PC board but suffice to say that the overall design has been carefully arranged to minimise distortion and leave as little to chance in the wiring layout so that constructors are certain to get excellent results. Next month, we’ll give the full details of assembly, wiring and setup of both versions, the parts list and the PC SC board patterns. Fig.12: version 2 of the SC480 amplifier with the TO-3 (steel) transistors. We’ll be presenting this again next month as part of the constructional details but it is reproduced here to demonstrate the attention we have paid to the PC board design to achieve the exceptional performance figures depicted on earlier pages. www.siliconchip.com.au January 2003  33 • • • • • • Indicates up to 9 gears • Display dimming Neutral indication Reverse indication Easy gear calibration Adjustable parameters Adjustable reverse gear switch level A “Tiptronic-style” Gear Indicator Do you know what gear your car is in at any given time? “Just look at the gear stick”, you say. Actually, it’s not that easy, especially if you have a 4-speed automatic or a 5 or 6-speed manual gearbox. And what if you ride a motorbike? So you need the Gear Indicator – it will give you the answer on a digi­tal readout. By JOHN CLARKE I F YOU’RE DRIVING in traffic, it is quite easy to be in the wrong gear, especially as the noise of the traffic can drown out the engine. And if you have your stereo system blaring as well, then what chance have you got? Yes, you can deliberately look at the gearstick but you’re not likely to do that unless you suspect you might be in the wrong gear. 34  Silicon Chip Why would you be in the “wrong gear” in the first place? If your car is stuck in heavy traffic you might easily continue on for some time in 2nd or 3rd after the traffic clears, particu­larly if your engine is not noisy. Much the same can happen with an automatic, if you are in the habit of “flicking” back to 3rd or 2nd (eg, when going up a hill or for engine braking downhill). It’s all too easy to forget to flick it back into Drive later on. As a result, you could finish up driving quite some distance in a low gear and that’s not good for fuel consumption. The same problem can happen if you ride a motorbike. Wouldn’t it be nice to have a digital display to show the gear you’re in? In fact, when driving an automatic it can still be useful to know which gear you are in, even if Drive is correctly selected. Modern automatics are so smooth that it can be difficult to “pick” the changes. Now you can “see” what the transmission is doing. This idea is not new, of course. All cars with Tiptronic transmissions and the latest Honda Jazz with its 7-speed gearbox have a digital gear indicator on the dashboard. Main features Basically, the Gear Indicator consiliconchip.com.au sists a small box which incorporates a single-digit LED display. This can show gear selections from 1-9, Neutral (which is shown on the display as a dash; ie, “-”) and Reverse (which is shown as an “r”). Inside the case are several switches which allow the unit to be calibrated and set up for best gear detection results. Once it’s all set up, that’s it – there are no user controls on the front panel to fiddle with. As presented, the unit is designed to be mounted on the dashboard. Alternatively, you could hide the unit under the dashboard and mount the LED display separately, if space is a problem. A 9-strand cable (eg, rainbow cable) would then be re­quired to connect the display back to the main circuit. The right gear The Gear Indicator works by monitoring both the speed of the vehicle and the engine RPM. It then decides which gear has been selected by feeding the results into a lookup table that’s programmed into an internal microcontroller. And that means that the unit must first be calibrated, so that it knows what the results are for each gear. Note, however, that neutral (-) is always shown when the unit is first powered up and also if the vehicle is stationary (or almost stationary) while the engine is running. By contrast, reverse (r) is shown when ever the vehicle’s reversing lights are activated. One thing you should note is that the Gear Indicator does not work by detecting gear changes – eg, by fitting switch actua­tors to the gearstick. This method would not only be unreliable but would also be a mechanical nightmare to set up. What’s more, the position of the gear selector in an automatic car doesn’t tell you which gear the transmission is in (unless 1st gear is manually selected). That’s because the transmission can still select any one of the lower gears in the remaining positions. For example, if the gear selector is set to 3rd, 2nd and 1st can also be selected. Of course, it is conceivable that the signals from an elec­ tronically controlled automatic transmission could be used to drive a gear display. However, we have not provided for this in the Gear Indicator because these signals would be different on each siliconchip.com.au Fig.1: block diagram of the Gear Indicator. It works by counting the number of ignition pulses that occur during a fixed number of pulses from a speed sensor and comparing the result with a “lookup” table that’s stored in memory. type of vehicle and may be difficult to utilise effectively. Block diagram Fig.1 shows the basic operation of the Gear Indicator. There are three external inputs: speed sensor pulses, ignition coil pulses and the reversing switch input. The speed sensor pulses can be obtained from a rotating magnet and coil assembly mounted on the tailshaft. Alternatively, you can use the digital speed signal that comes from the vehi­cle’s engine computer, if this can be identified (and accessed). The ignition pulses can either be obtained from the ignition coil or you can use the low-voltage tachometer signal from the engine management computer if this is available. The reversing input is obtained, naturally enough, from the reversing switch. When this switch is closed (ie, when reverse gear is selected), the display will show an “r” for reverse as indicated previously. Conversely, when the switch is open, the display will show either neutral (when the unit is first powered up or if there are no pulses) or a gear number. If the vehicle is moving, the circuit counts the number of ignition coil pulses that occur during a fixed number of speed pulses. If a low gear is selected (eg, 1st gear), it follows that there will be more ignition pulses counted for a given speed compared to those counted at the same speed in a higher gear. The gear selection number is shown on the 7-segment LED display. This number is obtained by comparing the number of ignition pulses counted with the stored values (in a microcon­ troller). These stored values are obtained during calibration of the Gear Indicator. Fig.2 shows how the Gear Indicator compares the ignition pulse counts with the calibration values. These calibration values are different for each gear and are obtained by driving the vehicle in each gear during the initial setup. This means that comparing the counted pulses with the cali­bration values should give the correct gear number. However, in practice, the calibration number may differ from the value ob­ tained during driving. That’s because the number of ignition pulses counted may vary by up to several counts for the same number of speed pulses, depending on the phase difference between the two. To counter this effect, a set amount of hysteresis is added to each gear range – see Fig.2. This can be varied to suit the vehicle during calibration and also corrects for any slippage in the transmission – either in the clutch or in the torque converter. As a further refinement, a slight January 2003  35 IC2a’s output is fed to pin 6 of IC1 via a 3.3kΩ resistor. The signal on pin 6 is then clamped by pin 6 (via internal diodes) to 0.6V above IC1’s supply rail (5V), as before. In operation, IC1’s pin 6 input is set as an interrupt – ie, the microcontroller’s embedded software increments the count each time pin 6 goes low. Display brightness Fig.2: a small amount of hysteresis is added at the end of each gear range to correct for phase errors and transmission slippage. This is set to suit the vehicle and is one of several parameters that are adjusted during the setup procedure. delay is added between each display update. This delay prevents the display from behav­ing erratically during gear changes, when clutch slippage and changes in engine RPM could otherwise produce an incorrect gear indication. Circuit details Refer now to Fig.3 for the circuit details. As indicated above, it’s based on a PIC microcontroller (IC1). This device accepts inputs from the various sensors and switches and drives the 7-segment LED display. OK, let’s start with the speed sensor circuit. This con­sists of a sensing coil which mounts on the chassis, plus four magnets which mount on a drive shaft (or tail shaft). As the magnets spin past, they induce a voltage into the coil and this is detected by comparator stage IC3. One side of the speed sensing coil connects to a 2.5V sup­ ply, derived from a voltage divider consisting of two 2.2kΩ resistors between the +5V rail and ground. This 2.5V rail is decoupled using a 47µF capacitor and biases pin 3 (the non-in­verting input) of IC3 via a 22kΩ resistor. It also biases pin 2 of IC3 via the coil and a series 1kΩ resistor. Diodes D1 & D2 clamp the input signal from the coil to 0.6V, while the asso­ciated 10nF capacitor filters the pickup signal. IC3 is wired as an inverting Schmitt trigger comparator. Its hysteresis is set by a 1MΩ positive feedback resistor, which prevents false triggering due to noise. The output signal from the speed sensor is a 250mV peak-to-peak pulse waveform and this is fed to pin 2 of IC3. Each time the input swings nega36  Silicon Chip tive, IC3’s output (pin 1) goes high (ie, to about 10V). This output is fed to pin 12 (RB6) of IC1 via a 3.3kΩ cur­rent limiting resistor. The internal diodes at RB6 then clamp the signal voltage to about 5.6V. Note that the feedback signal for IC3 is derived from this point to ensure a consistent hysteresis level, regardless of the 12V supply level. Ignition coil pulses As shown, signals from the ignition coil are first fed to a voltage divider consisting of 22kΩ and 10kΩ resistors. The asso­ciated 68nF capacitor then shunts any signals above 700Hz to ground to eliminate noise. From there, the signal is AC-coupled via a 1µF capacitor to diode D3 and thence to pin 2 of op amp IC2a. Zener diode ZD2 limits the signal amplitude at D3’s anode to 20V, while D3 prev­ ents negative signals from being fed into IC2a. The associated 10kΩ resistor pulls pin 2 low in the absence of a signal input via D3. A low input (LOW IN) has also been provided at the junction of D3 and ZD2. This input allows the tacho­meter signal from an engine management computer to be applied instead of using the ignition coil input. The signal level at this input can be any­ where from 2.3V up to a maximum of 20V. IC2a is wired as an inverting comparator with hysteresis. Its pin 3 input is nominally biased to about 1.6V via a voltage divider connected to the 5V rail, while the 47kΩ feedback resis­tor provides the hysteresis to set the high and low trigger points (1.7V and 1.5V respectively). The resulting square-wave signal at Trimpot VR1, light dependent resistor LDR1 and op amp IC2b are used to control the display brightness. As shown, IC2b is connected as a voltage follower and this drives buffer transistor Q1 (which is inside the negative feedback loop) to control the voltage applied to the anode of the 7-segment LED display. When the ambient light level is high, LDR1 has low resist­ance and so the voltage on pin 5 is close to the +5V supply rail. As a result, the voltage on Q1’s emitter will also be close to +5V and so the display will operate at full brilliance. As the light level falls, the resistance of the LDR in­creases and the voltage on pin 5 of IC2b decreases. As a result, Q1’s emitter voltage also falls and so the display operates with reduced brightness. When it’s completely dark, the LDR’s resistance is very high and the voltage on pin 5 of IC2b is determined solely by VR1. This trimpot is adjusted to give a comfortable display brightness at night. The 7-segment LED display is driven via the RA1, RB1-RB5 and RB7 outputs of IC1 via 470Ω resistors. A low output on any one of these output lines lights the corresponding display seg­ment, with the output at RA4 controlling the decimal point. Switch inputs Pushbutton switches S1, S2 and S3 are monitored using the RA2 and RA3 inputs. These two inputs are normally tied high via 10kΩ resistors and are only pulled low when the switches are pressed. When S1 (Mode) is closed, RA2 is pulled low and this is recognised as a closed switch by the software. Similarly, when S2 (Number) is closed, RA3 is pulled low, while pressing S3 (Store) pulls both RA2 & RA3 low to ground (via diodes D4 & D5). As a result, the software can recognise which siliconchip.com.au Fig.3: the complete circuit of the Gear Indicator. The PIC microcontroller (IC1) processes the signals from the various inputs and drives a single 7-segment LED display (DISPLAY1) to show the result. IC2b, Q1 & LDR1 automatically dim the display at night, so it is not too bright. switch has been pressed and respond accordingly. Clock signals Clock signals for IC1 are provided by an internal oscilla­tor and a 4MHz siliconchip.com.au crystal (X1) connected between pins 15 & 16. The two associated 22pF capacitors are there to provide the correct loading and to ensure that the oscillator starts reliably. The crystal frequency is divided internally to produce clock signals for the internal circuitry and the various parame­ters used in the software. It is also used to give a precise time period to count the speed pulses. Power Power for the circuit is derived from the vehicle’s battery via a fuse and the ignition switch. This supply line January 2003  37 Table 2: Capacitor Codes Value 100nF (0.1µF) 68nF (.068µF) 10nF (.01µF) 22pF (22p) IEC Code EIA Code 100n 104   68n 683   10n 103   22p   22 to power IC1. IC2 and IC3 derive their power directly from the de­ coupled +12V rail. Construction Fig.4 shows the assembly details. Most of the work involves building two PC boards: a microcontroller board coded 05101031 and a display board coded 05101032. These two boards are then stacked together piggyback fashion using pin headers and cut down IC sockets, so that there is very little external wiring. Begin by carefully checking the PC boards for defects, by comparing them with the published patterns. It’s rare to find problems these days but it doesn’t hurt to make sure. The microcontroller board can be assembled first. Install the three wire links first, then follow with the resistors and diodes. Table 1 shows the resistor colour codes but we also recommend that you check each value using a digital multimeter as some colours can be hard to decipher. Note that the six 470Ω resistors are mounted end-on to save space. Take care when installing D1 & D2 as they face in opposite directions. Similarly, watch the orientation of ZD1. REG1 can go in next. It is mounted with its metal tab flat against the PC board. As shown, its leads are bent Fig.4: install the parts on the two PC boards as shown here. Note that all the electrolytic capacitors must be mounted so that their bodies lie parallel to the board surfaces (see photos), so that the boards can later be stacked together. is decoupled using a 10Ω 1W resistor and filtered using a 47µF electrolytic capacitor. ZD1 provides transient protection by limiting any spike voltages to 16V. It also provides reverse polarity protection – if the supply leads are reversed, ZD1 conducts heavily and “blows” the 10Ω resistor. The decoupled supply is fed to 3-terminal regulator REG1 to derive a +5V rail. This rail is then filtered using 10µF and 100nF capacitors and used Table 1: Resistor Colour Codes o No. o  1 o  2 o  2 o  5 o  2 o  2 o  3 o  2 o  7 o  1 38  Silicon Chip Value 1MΩ 47kΩ 22kΩ 10kΩ 4.7kΩ 3.3kΩ 2.2kΩ 1kΩ 470Ω 10Ω 4-Band Code (1%) brown black green brown yellow violet orange brown red red orange brown brown black orange brown yellow violet red brown orange orange red brown red red red brown brown black red brown yellow violet brown brown brown black black brown 5-Band Code (1%) brown black black yellow brown yellow violet black red brown red red black red brown brown black black red brown yellow violet black brown brown orange orange black brown brown red red black brown brown brown black black brown brown yellow violet black black brown N/A siliconchip.com.au down at right angles so that they pass through their respective mounting holes. This is best done by slipping an M3 screw through the hole in the device tab, positioning it on the PC board and then gripping one of the leads with a pair of needle-nose pliers, just before it reaches the mounting hole. The device is then lifted clear of the PC board and the lead bent down at right angles, after which the procedure is repeated for the next lead. Next, install a socket for IC1, taking care to ensure that it is the right way around. Don’t plug the microcontroller in yet – that step comes later, after you’ve checked out the power supply. IC3 can then be installed, followed by the capacitors. Note that the 47µF capacitor near the speed sensor input must be installed so that it lies parallel with the PC board – see photo. Similarly, the adjacent 47µF & 10µF capacitors below REG1 lie over the regulator’s leads. In each case, it’s simply a matter of bending the capacitor’s leads at right angles before installing it on the PC board. Crystal X1 mounts horizontally on the PC board and can go in either way around. It is secured by soldering a short length of wire between one end of its case and an adjacent PC pad. Finally, you can complete the assembly of this board by fitting PC stakes to the external wiring points and fitting the 7-way single in-line (SIL) sockets. The latter are made by cut­ting down two 14-pin IC sockets into in-line strips using a sharp knife or fine-toothed hacksaw. Clean up any rough edges with a file before installing them on the PC board. Checking the supply rails Before plugging in IC1, it’s a good idea to check the supply rails (note: you don’t need to have the display board connected to do this). All you have to do is connect a 12V supply to the board and check that there is +5V on pins 4 & 14 of the socket (use the metal tab of REG1 for the ground connection). If this is correct, plug IC1 in as shown in Fig.4 – ie, pin 1 to­wards bottom right. Display board Now for the display board. Install the wire link first, followed by the resistors, diodes D3-D5, ZD2 and transistor Q1. The three capacitors can siliconchip.com.au This is the fully-assembled microcontroller board. Note particularly how the three electrolytic capacitors are mounted – ie, so that they lie horizontally across other components. The pin headers on the underside of the display board plug into the in-line sockets on the microcontroller board. Take care to ensure that the 7-segment LED display is correctly oriented. then be installed, along with trimpot VR1 and the 7-segment LED display. Note that the 1µF bipolar capacitor is installed so that it lies across ZD2 – see photo. Watch the orientation of the LED display – its decimal point goes towards bottom right. LDR1 can go in next. It’s mounted so that its top face is about 3mm above the face of the 7-segment display. Once it’s in, you can install switches S1-S3 and PC stakes at the external wiring points. The three 7-way SIL pin headers are installed on the copper side of the PC board with their leads just protruding above the top surface. You will need a fine-tipped soldering iron to in­stall them. Note that you will have to slide the plastic spacers along the pins to allow room for soldering, after which the spacers are pushed back down again. Final assembly Work can now begin on the plastic case. First, remove the integral side pillars with a sharp chisel, then slide the micro­controller board into place. That done, mark out the two mounting holes on the base – one aligned with the hole in REG1’s metal tab and the other diagonally opposite on the lefthand side. Now remove the board and drill January 2003  39 Parts List 1 microcontroller PC board, code 05101031, 78 x 50mm 1 display PC board, code 05101032, 78 x 50mm 1 plastic utility case, 83 x 54 x 30mm 1 dark red transparent Perspex or Acrylic sheet, 14 x 16 x 2.5mm 1 4MHz parallel resonant crystal (X1) 1 LDR (Jaycar RD-3480 or equivalent) 4 or 6 button magnets 1 coil former, 15mm OD, 8mm ID x 7mm 1 20m length of 0.18mm enamelled copper wire 1 6mm x 25mm steel bolt, 2 washers and nut 6 PC stakes 3 7-way pin head launcher 2 DIP-14 low-cost IC socket with wiper contacts (cut for 3 x 7-way single in-line sockets) 3 PC-mount tactile membrane switches (S1-S3) (Altronics S 1120 or equivalent) 2 6mm long M3 tapped spacers 1 10mm Nylon spacer or 2 x 6mm spacers with one cut to 4mm 1 9mm long untapped metal spacer 2 M3 x 6mm countersunk screws 2 M3 x 15mm brass screws 1 100mm length of 0.8mm tinned copper wire 1 2m length of single core shielded cable 1 2m length of 7.5A mains rated wire 1 2m length of red automotive wire 1 2m length of black or green automotive wire (ground wire) 1 2m length of white automotive wire these two holes to 3mm. Once drilled, they can be slightly countersunk on the outside of the case to suit the mounting screws. In addition, you will have to drill two holes in the back of the case to accept the power leads, the shielded cable from the speed sensor, the ignition coil and the reversing switch. These 40  Silicon Chip 1 200kΩ horizontal trimpot (VR1) Semiconductors 1 PIC16F84P microprocessor programmed with gear.hex (IC1) 2 LM358 dual op amps (IC2,IC3) 1 7805 or LM340T5 5V 1A 3-terminal regulator (REG1) 1 BC337 NPN transistor (Q1) 1 HDSP5301, LTS542A common anode 7-segment LED display (DISP1) 5 1N914, 1N4148 signal diodes (D1-D5) 1 16V 1W zener diode (ZD1) 1 20V 1W zener diode (ZD2) Capacitors 2 47µF 25VW PC electrolytic 1 10µF 16VW PC electrolytic 1 1µF bipolar electrolytic 3 100nF MKT polyester 1 68nF MKT polyester 1 10nF MKT polyester 2 22pF ceramic Resistors (0.25W 1%) 1 1MΩ 2 3.3kΩ 2 47kΩ 3 2.2kΩ 1 22kΩ 2 1kΩ 1 22kΩ 1W 7 470Ω 5 10kΩ 1 10Ω 1W 2 4.7kΩ Alternative speed sensor 1 PC board, code 05101033, 14 x 30mm. 1 UGN3503 Hall senosr 1 100nF MKT polyester capacitor 1 2m length of twin-core shielded cable 3 PC stakes Miscellaneous Automotive connectors, heatshrink tubing, aluminium brack­et, self-tapping screws holes should be located so that they line up with the relevant PC stakes. The display PC board can now be plugged into the microcon­troller board and the assembly fastened together and installed in the case, as shown in Fig.5. Once it’s all together, check that none of the leads on the display board short against any of the parts on the microcontroller board. It may be necessary to trim some of the pigtails on the display board to prevent this. The panel artwork can now be used as a template for marking out and drilling the front panel. You will need to drill a hole for the LDR plus a series of small holes around the inside peri­ meter of the display cutout. Once the holes for the display cutout have been drilled, knock out the centre-piece and clean up the rough edges using a small file. Make the cutout just big enough so that the red Perspex is a tight fit. A few spots of superglue along the inside edges can be used to ensure that the window stays put. That done, you can affix the front panel label and cut out the holes with a utility knife. Testing Now for the smoke test! First, apply power and check that the display shows “-”. If it doesn’t, switch off immediately and check for wiring errors and solder faults. Assuming that everything is OK, you can test the dimming feature by holding your finger over the LDR. Adjust VR1 until the display dims to the level you want at night. Next, connect the leads from the ignition coil (or low level input), the reversing switch and the speed sensor. These leads all connect to the underside of the PC board and the igni­tion and reversing switch wires pass through to the base of the case via notches cut in the side of the microcontroller PC board. These notches are located on either side of the adjacent 7-way socket and their positions are marked on the PC board using a fine track outline. Speed sensor Two different speed sensors can be made up, one based on a coil pickup and the other using a Hall sensor pickup. However, both rely on the use of an adjacent rotating magnet assembly . The coil pickup is likely to be more rugged and less prone to water damage but the Hall sensor will allow for very low speed operation. That’s because its output voltage doesn’t depend on the speed at which the magnets rotate past the sensor. It’s just a matter of waterproofing it correctly, using heatshrink tubing and silicone sealant. The coil sensor version is shown in Fig.6. It is made by winding about 400 siliconchip.com.au Fig.5: this diagram shows how the two PC boards are stacked together and secured to the bottom of the case using screws, nuts and spacers. Be sure to use nylon spacers where specified. Fig.6: the pickup coil used in the speed sensor is mounted on a L-shaped bracket that’s secured to the vehicle’s chassis. Position the coil so that it is no more than 10mm away from the magnets as they pass, to ensure sufficient signal pickup. Note that the magnets must all be installed with the same pole facing outwards – either North as shown here or South. turns of 0.18mm enamelled copper wire onto a plastic bobbin measuring 15mm OD x 8mm ID x 5mm. Use electrical tape to secure the turns and leave about 10-20mm of lead length at each end. Once the coil has been wound, solder its leads to a suit­able length of shielded cable – ie, one lead goes to the shield wire and the other goes to the core. Secure this lead to the side of the coil with some tape, then cover the coil with silicone sealant (preferably the non-acid type such as roof and gutter sealant). Finally, cover the coil with a short siliconchip.com.au Fig.7: the alternative speed sensor uses a Hall effect device mounted on a small PC board. This is the completed PC board assembly, ready for mounting in the plastic case. Note that the various external leads are all soldered to PC stakes on the copper side of each board, with the leads from the display board resting in small grooves cut into the microcontroller board. January 2003  41 Adjustable Parameters For The Gear Indicator Because each vehicle is different, the Gear Indicator must be correctly set up in order to obtain the best results. Consequently, the unit has been designed to cater for up to nine gears and there are various parameters that can be adjusted to control its operation. Table 3 shows the details of the various parameters. These are as follows: (1) The first parameter that can be set is the number of speed pulses used to gate the ignition pulses. This is adjustable from 4-36 pulses in increments of 4, using numbers from 1-9. The initial setting is for 12 pulses but this may have to be varied to cater for various speed sensor characteristics. (2) Next is the amount of hysteresis for each gear compari­son. In practice, this value is made just large enough so that the display does not sometimes briefly show the next highest gear number. The default value is 6% of the ignition pulse count and this should be suitable in most cases. This value will have to be increased if the display shows a tendency to occasionally jump to the next highest gear. Converse­ly, it should be made length of heatsh­rink tubing and shrink it into place using a hot-air gun The sealant should now be left to dry for about eight hours. A 100mm-long cable tie can be placed around the coil to secure the lead in place. The alternative Hall sensor is assembled on a small PC board coded 05101033. Fig.7 shows the assembly details. Apart from the Hall sensor itself, there’s just a single 100nF capacitor to be installed. Note that the UGN3503 Hall sensor is mounted flat against the PC board with the label side up. The connecting lead to the main unit is run using twin-core shielded cable. Installation Be sure to use proper automotive cable and connectors when in­stalling the unit into a vehicle. The +12V supply is derived via the ignition switch and the fusebox will provide a suitable 42  Silicon Chip Table 3: Adjustable Parameters Display Value Speed Puls- Hysteresis es (S) Delay (d) Timeout (-) Reverse (r) Clear (C) 1 4 2% 0.1s 0.5s 12V = r* - 2 8 4% 0.2s* 1s 0V = r - 3 12* 6% 0.3s 1.5s 12V = r* - 4 16 8% 0.4s 2s 0V = r - 5 20 10% 0.5s 2.5s* 12V = r* - 6 24 12% 0.6s 3s 0V = r - 7 28 14% 0.7s 3.5s 12V = r* - 8 32 17% 0.8s 4s 0V = r - 9 36 20% 0.9s 4.5s 12V = r* - Note: an asterisk (*) denotes the default value. lower if this tendency is not apparent and then adjusted back the other way until the effect disappears. In practice, you can adjust the hysteresis over a range from 2-20%. The lower the value the better, since this gives the greatest range of ignition pulses that are counted for each gear. The third parameter is the delay between gear changes. Without this delay, the display could show the incorrect number since the engine RPM can vary widely when changing gears. The initial setting for this is 0.2s which should be suit­able for most cars. However, depending on the driver, the 0.1s setting may be better for cars with manual gearboxes. Conversely, a longer delay may be needed for cars with automatic transmis­sions. You can set the delay to any value between 0.1s and 0.9s. The fourth parameter is the timeout connection point. Be sure to choose the fused side of the supply rail, so that the existing fuse is in series. You should also be able to access the reversing switch connection at the fusebox. The ground connection can be made by connecting the lead to the chassis using a solder eyelet and self-tapping screw. Fig.6 shows the mounting details for the speed sensor. Note that the four magnets must all be installed with the same pole facing outwards – ie, they must all have either their north pole facing outwards or their south pole facing outwards (it doesn’t matter which). This is done by attaching the magnets together in a stack. This will either give an N-S-N-S, etc stack or an S-N-S-N, etc stack. You then mark the outside face of the top magnet and remove it from the stack, then mark the next magnet and remove it and so on until all the magnets are separate. The magnets can then be attached to the driveshaft with the marked faces on the outside. The magnets should be equally spaced around the driveshaft and can be affixed using builder’s adhesive (eg, Liquid Nails, Max Bond, etc). Covering the magnets with some neutral cure silicone sealant will protect them from damage due to stones and other debris thrown up by the wheels. Mounting the pickup coil The pickup coil can be secured by bolting it to an L-shaped bracket which is then fastened to the chassis. Position it so that there is about a 10mm maximum gap between it and the magnets as they pass. Alternatively, you can use a Hall sensor instead of the pickup coil, as shown in Fig.7. The ignition coil input is connected siliconchip.com.au period. Normally, the ignition pulses are counted during a set number of speed pulses. However, if the vehicle is moving very slowly or is stopped, the speed pulses may not reach the count setting. Instead, the time­out stops the count and places a neutral (-) reading on the display. The timeout parameter is initially set at 2.5s but can be set anywhere in the range from 0.5-4.5s, using numbers from 1-9. Its setting is a compromise between showing neutral only when stopped or at a very low speed (long timeout) and getting a fast neutral indication after coming to a stop (short timeout). The next parameter is the reversing switch sense. Setting an odd number between 1 and 9 (1, 3, 5, 7 or 9) will cause the display to show reverse when the reverse input goes to +12V. Conversely, setting an even number (2, 4, 6 or 8) will cause reverse to show when the reverse input goes to 0V. This selection is simply made so that the unit shows re­verse (“r”) when the reversing lights come on. The final parameter is “clear”, which clears all the gear calibration values. The gear ranges will then need to be recalibrated. This “clear” operation should be carried out if the unit is fitted into another vehicle. directly to the switched (negative) side of the ignition coil using a 250VAC rated cable. Using computer signals As mentioned earlier, instead of making you own speed sen­sor, you may be able to obtain the speed signal from the engine management computer. This signal is simply fed to the 1kΩ resis­tor at the speed input. If the car’s speedometer stops operating after connecting the Gear Indicator, increase the 1kΩ resistor on the speed input to 10kΩ and remove the 10nF capacitor. Similarly, you can use the low-voltage tachometer signal from the computer instead of ignition coil pulses if this is available. In fact, it will be necessary to do this if your car uses several double-ended coils to fire the spark plugs, rather than a single coil. The low-voltage tachometer signal siliconchip.com.au Setting The Parameters The various parameters are set by first pressing (and hold­ing down) the Mode switch while the Gear Indicator is powered up. The display decimal point then lights to indicate that the unit is in the “setting mode”. The first parameter shown is an “S” which refers to the speed pulses. If the Mode switch is then released, the display will show the value stored (from 1-9) after 1s. Conversely, if the Mode switch is held down, the other parameter indicators will appear in succession, at a 1s rate. The parameter values are altered by pressing the Number switch. Each press increments the number by one, while holding the Number button down causes the value to automatically increase at a 1s rate – ie, the numbers cycle from 1-9 and then back to 1 again. When the required value is selected, you simply release the Number switch and press the Store switch to store the value in memory. Once the “S” (speed) parameter has been set, the other parameters are selected and set in turn. These are “H” (hystere­ sis; “d” (delay); “-” (timeout) and “r” (reverse). These are all modified and stored exactly as before. Note that no changes are stored until the Store switch is pressed. This enables you to cycle through the parameters to check their values without making any changes. The last parameter to be selected simply shows a “C” on the display, without any value. Pressing Store will clear all the gear settings. Finally, you exit from the Param­ eter Mode, by switching off and then reapplying power. The display will then show a “-” (ie, the neutral gear indication) and the decimal point will be off. Gear Calibration Pressing the Mode switch after the unit has powered up places the unit into the “Calibrate Mode”. The decimal point will light to indicate this mode and the number shown initially will be a “1” (ie, 1st gear). To calibrate the unit, just follow these step-by-step instructions: (1) Drive the vehicle at light throttle with 1st gear selected (for automatics, you have to select 1st gear rather than Drive). After a few seconds, press the Store button and the calibration for 1st gear is saved. Note that it may be necessary to drive relatively fast in 1st gear to ensure that the speed pulses are counted within the timeout period. Also, with an automatic, be sure to drive along a flat section of road without accelerating to eliminate torque converter slip. (2) Next, press the Number button so that the unit shows a “2” (ie, 2nd gear). Now drive at light throttle in 2nd gear for a few seconds and press the Store switch to calibrate the 2nd gear. Note that it is not necessary to drive at a fast speed in this gear to achieve calibration. If the car is an automatic, be sure to select 2nd gear and drive fast enough to ensure that the car is in this gear (ie, not 1st). The remaining gears are calibrated in exactly the same manner. (3) Once you have calibrated all the gears, press the Mode switch again and the decimal point will extinguish. The unit will now revert to the “Gear Indicator” mode. If you make a mistake during cal-ibration, or if the unit is to be used in a different vehicle, the data should be cleared using the “C” parameter before re-calibrating the unit. Note too that if you subsequently change the speed pulses parameter after calibration, the gears will need to be recal­ibrated. Also, if you don’t obtain a successful 1st gear calibra­ tion, this gear can be recalibrated after extending the timeout delay. In that case, the Store button should be pressed after about 10 seconds to ensure a suitable count for the ignition pulses. Note that some automatics start in 2nd gear rather than 1st when light throttle settings are used. January 2003  43 Fig.8: this full-size artwork can be used as a drilling template for the front panel. You will need to make cutouts for the LDR and the 2-segment LED display. Fig.9 (right): check your etched PC boards against these full-size patterns before any of installing the parts. The smallest board (ie, 05101033) is for the optional Hall speed sensor. The corners of the two PC boards must be cut away to clear the mounting pillars inside the case. This should be done before any parts are installed. should be applied to the low input terminal on the Gear Indicator (not to the ignition coil terminal). On-road testing Once fitted to the vehicle, the various parameters can be set and the unit calibrated as described in the 44  Silicon Chip accompanying panels. The speed pulses setting for the parameters can be made a larger value as described earlier. This will give more ignition pulses to be counted and give a better resolution for the differ­ences in counts for each gear ratio. The larger value will also pro­vide less tendency to show a lower gear due to clutch or torque converter slippage. The compromise is that the time required to count the pulses will be longer and the display will have a tendency to show the neutral (-) indication at a higher speed compared to using a smaller speed pulses number. This is because the timeout period will occur before the pulses are count­ed at slower speeds. Gear change response will also be slower with a higher speed pulse count number. In general, use 16 or more speed pulses if you use four magnets on the tailshaft and use 12 or less if you use magnets on the wheel shaft. Use of the speedometer sensor signal should require 28 or more speed pulses but this may need to be smaller if the response at slow speeds is too long, causing neutral indica­tion at not so slow speeds. Note also that using magnets and a coil pickup will not provide gear indication at very slow speeds since the output from the sensor will be too low to register. The Hall effect pickup will be much better at slow speeds and will provide gear indication down to where the speed pulse count takes SC longer than the timeout. siliconchip.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.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 SERVICEMAN'S LOG When the going gets tough When the going gets tough, the tough get going or so the old saying goes. But in my case, when the going gets tough, I compromise, by taking on unusual service jobs – like a couple of 20-year old reel-to-reel tape recorders and a Sony set intended for South Africa. There are times when I swear blind that I will never touch any equipment that’s over 10 years old again. That’s because of all the warranty implications when something else inevitably fails and because you often cannot get a critical part or it is prohibitively expensive. www.siliconchip.com.au But then I reach a quiet business patch and in a panic I accept not one but two 20-year old units for repair. Yes, I regret to say that muggins was guilty of this when two unrelated people brought in Sony TC-366 reel-to-reel tape recorders. These Sony TC-366s are nicely built 3-speed machines. They have one motor, their fastest speed being 7.5ips (inches per second), and all the tape action is controlled via a large single knob. In both instances, the symptoms were no or little play torque but each fault was different. Removing the covers involved unscrewing five Philips screws, undoing two special poles which also hold the head cover, and removing the Pause/ Instant Stop switch knob. This round knob is about 1mm larger that the slot it is meant to go through when removing the tape deck escutcheon. It is screwed onto its shaft and one has to manually unscrew it in order to release the escutcheon from the machine. Unfortunately, some 20 years later, this knob refused to unscrew, so I had to gingerly widen the slot with a round file. I really don’t know why they couldn’t have made it pass through when it was manufactured! When I could finally see inside the mechanism, it was obvi­ous that the large play idler wasn’t moving to engage the motor and capstan shafts. Lubricating the bearings of the associated levers solved this problem on one of the machines. The second was more complicated. The motor wasn’t rotating at all until I gave it a little nudge. But although I could get it going, it didn’t have much get up and go about it. In fact, it kept slipping, especially in fast forward, and was also getting very hot. As a matter of interest, this particular machine had been imported from the USA and was connected to our 240V mains by a stepdown transformer. The machine was rated at 117V 60Hz and the AC motor at 100V 50/60Hz. The 1.5µF starter capacitor (PN 117034) looked to be the main culprit. As luck would have it, when I rummaged through an old box of capacitors I found not one but two original re­ placements still sealed in plastic bags. The only difference was that they had an additional 0.5µF terminal on them as well (PN 117-036). This fixed the problem immediately but not being a rocket scientist when it comes to AC motors, I wasn’t really sure wheth­er to simply connect the 1.5µF section of the replacement capaci­tor or connect the 1.5µF and 0.5µF sections together to make 2µF January 2003  53 for 50Hz (as opposed to 1.5µF for 60Hz). Well, I initially left it at 1.5µF and put the machine on soak test. Three hours later, I revisited it and was horrified to find that the motor was nearly too hot to touch and had stopped. The replacement capacitor had failed and I had only one left. This time I connected the two sections in parallel, lubri­cated the motor and soak tested it again. Fortunately, this one held and, hopefully, will continue to do so. If not, it means ordering in a very expensive industrial one. Anyway, I finished up with two satisfied customers, so my gamble with these 20-year old machines paid off. An interesting Sony An interesting TV set came in the other day. It was a 1990 Sony KV-2184SA (GP-1A). So what is interesting about that? Well, the “SA” designation in the model number (rather than AS) indi­cated that it was from South Africa. In addition, it had a built-in FM radio on the lefthand side of the cabinet for simulcast transmissions. This surprised me because I thought the whole purpose of simulcast transmissions was to receive stereo and yet this was fed into the monaural TV sound system and only one small ellipti­cal loudspeaker. So I really can’t quite see the point; perhaps some expat can enlighten me, as there is no instruction book or service manual 54  Silicon Chip available for this model in Australia. The set was dead, with an IC link fuse (PS801) open cir­cuit. This led me on a merry dance as I was using my old service manual for a KV-2184AS and there was an extra transistor circuit (Q622) that wasn’t marked. This supposedly monitors the current through R621 and turns off the horizontal drive from pin 27 of the jungle IC (IC301, CXA-12135) by biasing pin 22. First, I found the D608 R2M safety zener to be short cir­cuit, which implied the 115V rail had risen high enough to de­stroy it. So I replaced this, along with IC601 (STR50115, B ver­sion). I then found that R621 (1Ω) had gone high, as well as R622 (470kΩ). I was getting closer but the set gave a high-pitched squeal when I switched it on and the 115V rail was at 87V. Yet when connected via a 100W globe, with a clip lead between base and emitter of the horizontal output tran- Items Covered This Month • • • • • Sony TC-366 reel-to-reel tape recorders. Sony KV-2184SA (GP-1A) TV set. AWA 65850 S/T TV set. Grundig ST70-755 TOP/LOG TV set (CUC 6360 chassis). AWA C5105 TV set. sistor, the voltage was spot on at 115V and there was no squealing. When I re-enabled the horizontal output stage, I could get sound and a white raster. And when I subsequently replaced R851 1.2Ω (200V supply to the CRT), I could get a coloured picture, albeit small and distorted due to the low HT. From this, I deduced that the horizontal output stage might possibly be drawing too much current. But it wasn’t and it took a very long time to work out that R609, a 33Ω 3W resistor, was open circuit in the power supply and that this was part of a feedback circuit to pin 2 of IC601. By now, I had a good picture and sound when I connected a video recorder to the AV inputs. However, that wasn’t the case off air. The reason for that wasn’t hard to figure out. South Africa uses the CCIR system with a 6MHz sound IF and with no Band I VHF (V-L). This meant removing the IF module IF201 (IFB-389SA) and replacing the three 6MHz ceramic filters with 5.5MHz units (CF01 for D5.5E, CF02 5FE5.5MB and CF03 T5.5B). The set now gave good sound and colour for all stations except for the ABC (Ch2, Band I). Now all that was left to be done was to fit the extra band switching transistor (Q151, DTA114ES) – along with 6.8V zener D152 and C150 (1µF 25V) – and link it to pin 7 of microprocessor IC002 via a 2.2kΩ resistor (R098). I did all this but it still didn’t work. The tranwww.siliconchip.com.au sistor would still only scan high-band VHF (ie, no Band I) and UHF. Initially, I thought this was due to the microprocessor being a PCA84­ C 640P/037 instead of PCA84C640P/016 as in the cir­ cuit diagram. However, this was just a red herring as I discov­ered that the Australian module also used the same “037” suffix and worked OK. What I did discover was an extra diode (D005) fitted in the South African model that connected pin 22 to the vertical pulse going to Q005 from the vertical output stage. Removing this diode breaks the TV scan mode into VL, VH and U and the set could now be tuned like an Australian TV receiver. Obviously, the easiest way to solve the above problem would have been to fit an Australian tuner and an the IF module as well (as they would be better matched). However, I hadn’t scrapped any of these sets lately, so I couldn’t scrounge the necessary parts and fitting new units would not have been cost-effective. Finally, to select the simulcast FM radio, it is necessary to rotate the system switch inside the front control panel and then tune the knob on the side. The tuner is connected via CN302 and CN201 to the de-emphasis pin (pin 10) on the IF module and pin 7 of analog switch IC702. AWA TV set AWA is now used as a brand name on a series of TV sets imported from China. These sets are very similar to those of Teac, Akai and Masuda, and are probably produced by the same ONWA factory. www.siliconchip.com.au In fact, the 1993 66cm AWA 6850ST on my bench could easily have been mistaken for a Teac CT-M711 or a Masuda 28AV. And it was completely dead. After removing what seemed like an unnecessary quantity of screws, the set was seen to consist of a motherboard, a Teletext board, a stereo decoder and a power supply. And a quick examina­ tion soon revealed that two capacitors in the power supply had spilled their guts. I replaced the two culprits – namely C910 47µF 25V and C908 10µF 50V – before replacing the parts they had destroyed: Q909 (2SD1403), R944 (2.2Ω, 5W), C925 (1000µF, 25V), R916 (0.68Ω, 1W) and C925 (22µF, 160V). Judging by the soldering, I wasn’t alone in going down this path. I also checked the HT voltage and set it to 143V at TP B+. Intermittent flicker The next problem was the picture which was intermittently flickering horizontally with colour problems. Sometimes the picture would tear and sometimes it would shift horizontally. It’s not only a horrible fault to describe but was equally hard to diagnose and fix. And it was somehow temperature related, the set getting better when hot. By trial and error, I discovered that the fault seemed to be located around IC102 (TDA8305A). This is predominantly an IF detector processor but also a jungle IC and is located underneath the stereo decoder board in a soldered-in metal cage. There was a lot of black silicone rubber all over this set which, like the brown PCB POWER TRANSFORMERS 1VA to 25VA Manufactured in Australia Harbuch Electronics Pty Ltd 9/40 Leighton Pl. HORNSBY 2077 Ph (02) 9476-5854 Fx (02) 9476-3231 glue before it, tends to conduct after many years. Well, I had to start somewhere so I scraped off the black silicone rubber and replaced the IC. This didn’t work, so I started replacing the capacitors. Fortunately, I struck gold with C127 (3.3µF), which is a decoupling capacitor for the AGC detec­tor and sync demodulator. At this time, I didn’t have a remote control but fortunate­ly I had a Remote Master RM0900 Universal remote control and tuned that into this set’s command set. This was a good idea, as I found then that the remote control power on/standby function wasn’t switching off. This set used a relay for switching the 143V on and off to the rest of the set, so it was just a matter of tracing it back to the microprocessor. How- January 2003  55 Serviceman’s Log – continued ever, the fault turned out to be a lazy momentary contact on the main on/ off switch (S512) that was sticking in the on position. A little lubrication soon fixed that and the set was back in operation. Grundig day I don’t see many Grundig TV sets these days, probably due to the dealer network set up by Grundig in recent years. I nor­mally try to avoid house calls but when Fred Schmidt called and gave me his address as being only a block away, I bent the rules and arranged to “have a look” at his 10-year old Grundig ST70-755 TOP/ LOG (CUC 6360 chassis). The fault complained of was intermit­ tent no picture and it was the “intermittent” bit that worried me. When I arrived, the set gave no picture but a green raster with retrace lines. After it had been on for sometime, the pic­ture flashed on. 56  Silicon Chip I removed the back – there were only four screws to undo (other manufacturers please note) – and checked for faulty joints or anything obvious. The only thing I learnt was that by varying the CRT screen control SG/VG2 clockwise to give a very bright green raster and then slowly reversing it anticlockwise, the picture would return. However, it was too bright and too green and turning the brightness control down on the remote control still couldn’t make the blacks black. Basically, if the screen control is turned too far anti­ clockwise, the picture loses definition and gives poor colour contrast. This looked to me like the RGB video output stage was pro­ducing signals that were outside the optimal characteristic curve sections of the CRT guns. I told Fred that it had to go to the workshop and though it was a fine TV set, perhaps he ought to think about updating it considering its age. However, being rather short of cash, he decided to have the set fixed rather than dumped. Back on the workshop bench, I first replaced the RGB video output IC (IC790, TEA5101A/D), which is a very complex FET ampli­fier. Initially, I fitted a generic IC from my local supplier but later, when I became more desperate, and at Grundig’s sugges­ tion, I ordered and fitted a genuine replacement but it made no difference either way. This type of circuit is used in a lot of European-designed sets like Philips and the fault can quite often be caused by a low-emission tube. To prove this one way or another, I decided to test the Philips A66 EAK71X01 picture tube thoroughly. First, I connected my CRT analyser directly to the tube and, at 6.3V RMS, I measured an even 0.62mA emission from each gun, which is rea­sonably good. Next, I measured the voltage across the CRT filaments with my RMS voltmeter and that too was spot on at 6.3V. Finally, I connected an external power supply to the heaters and wound it up to 8V to see if it made any difference but it didn’t. I now concentrated on the diodes and electrolytic capaci­tors on the CRT module (29305-022.48). Note that this differs from the one in the service manual (29305-022.44) – it has four more diodes fitted, as well as other modifications. I tried replacing all the 1N4148 diodes with higher-rated BAV21 (used mostly as clamps) but that didn’t help. I also meas­ured all the voltages around the CRT socket but of course, the voltage for each colour was not consistent and besides, the service manual does not give voltages. The thing I did notice was that the voltage drive for each colour from the colour decoder module was 4V for red and blue and 5V for green. I also measured the beam limiting SB voltage from the horizontal output transformer (A) on pin 1 of the module to be 16V and the SW voltage on the CRT RGB pin 1 plug to be 0.63V in the fault condition. I should also add that it was not possi­ble to set up the screen control according to the alignment instructions, as the picture would be far too bright (in AV mode, there should be 172.5V on each cathode). The EHT was spot on. Colour module All this was very time consuming and all I had really achieved was to confirm that the CRT and socket were probably OK. So now I shifted my attention to the colour module – 29504-105.67 – which also differs from the 29504-105.56 module in the service manual. The other drama with this double-sided module concerned the access to its surface-mount components. About all I could measure were the voltage supplies (12V, 8V) and the inputs and outputs. Fortunately, the service manual gave a pretty good explanation of the circuit. The circuits I was interested in were mostly in IC5040 (TDA8376) and the 10 surface-mount transistors after it. I pulled the module out and using an ohmmeter, checked all the transistors to be OK. I then replaced all the electros and measured all the diodes. An exchange module (if available) would cost $227.25 trade and the TDA8376 $119.70 plus freight charges of $11. www.siliconchip.com.au I gambled on the latter and ordered it. A few days later, after replacing this 52-pin high-density IC, I discovered I had lost and blown all my money! So far I wasn’t doing very well. If only I had had another set to compare it with. As I had the necessary ICs in stock, I replaced all the other ICs on the Chroma Module but even that was a waste of time. Finally, I decided to replace the surface mounted transis­tors, starting with CT5127 (Red), CT5128 (Blue) and CT5129 (Green) – all BC858s. Naturally, with my luck, these are no longer available, so I fitted BC858Cs. This fixed one problem – the green caste was gone and the grey scale was correct even if it was too bright. I surfed the net and found one German site for TV and Video Service Repair Tips that had to be translated, suggesting I replace CT5066, another BC858. This I did and I noticed a small improvement. Thus encouraged, I moved along and replaced CT5060 as well. This finally produced an acceptable picture after rea­lignment. These transistors are part of the beam limiting current circuit to pin 22 of IC5040 (3-4V). I couldn’t fault any of the PNP transistors I replaced but because of their size and position, it was almost impossible to hook up complicated test gear to test them. I have even had cases where the glue used to cement these components onto the board affected their characteristics. Anyway, the picture was now quite acceptable but will Fred go ahead with my quote? How could I possibly guess at the likely cost beforehand? And to finish off, here is another reader contribution. It is from A. B. of Glen Waverley, Victoria. He has titled it: The perils of modern test gear Mr Smith staggered up the path clutching an AWA C5105 TV set, moaning “I couldn’t find the place”. I resisted the tempta­tion to ask if he had seen the sign out the front but in this game you soon learn that the customer has a good reason for whatever they say. “Its dead, just stopped – is it the picture tube?” he puffed on. After reassuring him it was unlikely, I booked it in and shoved it onto the “look at” pile. www.siliconchip.com.au I got to it a few days later. It was a 51cm AWA set of Chinese manufacture and only about 18 months old. The first thing you do in these sets is go straight for the power supply, in this case the electrolytic capacitors in the primary circuit (C614 and C615). Both measured faulty on the ESR meter and were promptly replaced. As well, the EHT circuit was checked for shorts and a DC resistance measurement to chassis showed no obvious faults. The set was then powered up and I fully expected it to burst into life. Alas, it was not to be – the red standby LED was on but no amount of prodding at the usual user controls made any difference. At this point, you start to wonder if the remote control is needed to start the set – most modern TV sets are switched on by firing a start-up pulse from the remote using the on/off button or a channel button. I worked on this assumption and turned the chassis upside down on the workbench to access the underside of the board. It was soon established that the HT rail was at 110V – a figure I assumed to be OK on a set this size. After diligently studying the circuit, a 5V regulator and an 8V regulator were also found to be functioning. As well, there was HT on the col­lector of the horizontal output transistor and about 85V on the collector of the driver transistor. However, a quick check with the CRO revealed that there was no drive waveform to the base of the driver transistor. Unfor­tunately, the relevant track soon disappeared into a mess of similar tracks wandering all over the board. At this point, it was decided to obtain a circuit diagram. Unfortunately, when this turned up, it proved to be a 15th gener­ation copy (or thereabouts), plus a booklet full of useless (in a practical sense) information on how to do alignments, etc. The circuit was of limited help as all the figures were unreadable. However, I did manage to locate the jungle IC and I checked that this had supply volts. I also discovered that there was no horizontal drive waveform on the relevant output pin. So what was going on? All the routine tests had been done to no avail. After staring at the board, I decided to measure all the high-wattage low-value resistors. All checked OK (or as near as could be judged given the useless circuit diagram) with the exception of R320, the dropping resistor to the horizontal driver circuit - it was reading about 6MΩ! However, the HT on the tran­sistor measured OK at 85V! Suddenly the penny dropped, and I mentally kicked myself around the workshop. I pulled the resistor out and replaced it with a 2.7kΩ 5W unit, switched on the power and the set came to life. What happened? So what had happened – easy, and if I had remembered basic theory I would have found it a lot quicker. What happened was this – at switch on, the start-up pulse gives enough energy to kick the set into life and all is well. In this case, because the set wasn’t running, my high impedance digital multimeter was indeed reading a nearly correct voltage across the driver tran­sistor because the thing was still stuck in standby mode, the transistor not drawing any current. By contrast, an old, cheap analog meter with its higher loading would have shown a lower voltage at this point and the true fault would have been revealed at once! Ah well, that’s the problem with getting older – what was once routine is now new if you haven’t seen it for SC awhile. January 2003  57 This stereo 3-way active crossover is for those enthusiasts who want the very best from their 3-way loudspeaker systems. It avoids the disadvantages of passive crossover networks and allows the power levels to the speakers to be optimised. W hat is an active crossover and why would you want one? Most hifi enthusiasts are aware that 2-way and 3-way loudspeaker systems contain passive networks to split up the audio spectrum into two frequency bands in the case of 2-way systems and three bands in the case of 3-way systems. Passive crossover networks use inductors, capacitors and resistors to split the audio into the various bands and set the signal levels to the various speaker drivers. For example, the woofer is often less sensitive than the midrange driver and tweeter and so the signals 58  Silicon Chip to the latter drivers have to be reduced so that the overall output from the three drivers is equal. In the higher performance speakers, the crossover networks are often very complex and they can be very difficult to design and optimise. And because they usually do attenuate the midrange and high signals, that means they do waste ames ur at Fe      plifier power.  1-unit rack case They also interpose a com Single PC board plex network between the r transforme speakers and the amplifier  15V+15V 20VA toroidal which means a loss of damping  Stereo module stages t tpu ou d factor, particularly for the lowan ut inp  Buffered impots) (tr ts er frequencies where it is most tpu ou ble ria va  Individually needed, if you are to achieve ly pp su r  On-board powe tight, clean bass and midrange tors  On-board RCA connec onents reproduction. mp OK, so that’s the passive ap Made from standard co proach. It involves just one stewww.siliconchip.com.au An active 3-way crossover for loudspeaker systems Design by Mick Gergos reo amplifier to drive the two speaker boxes in a stereo system. In an “active” system, we eliminate the passive crossover networks and electronically split each of left and right channel signals into three frequency bands: low, midrange and high. This is the job of the “active crossover”. Its output signals are fed to six (yep, six) separate amplifiers to drive the woofer, midrange and tweeter units in each loudspeaker enclosure. The overall system layout is shown in the block diagram of Fig.1. So you end up with a lot more amplifiers than in a conventional system but it gives you a lot more flexibility. And ultimately, you can end up with a system with higher performance, including much higher power levels. This shot inside the box reveals the simplicity of construction. Everything except the transformer is on one PC board! www.siliconchip.com.au January 2003  59 Fig.1: the block diagram shows the overall system layout. It replaces the crossover currently in the speaker enclosure. The active crossover approach also means you can mix 4Ω and 8Ω drivers in the same system and match the levels easily, without power wastage. Active crossover The Active Crossover presented here is housed in a 1-unit high rack case with just the power switch on the front panel. There are no user controls for the crossover; no switches to alter the crossover frequencies nor external level controls for the output signals. To alter the drive to the loudspeakers, you will need to adjust the volume controls of the driver amplifiers. On the rear panel there are four pairs of RCA sockets, one pair for the stereo input signals while the other three are for the stereo low (woofer), midrange and high (tweeter) signals. Also on the rear panel is the IEC mains power socket and a fuseholder for the primary circuit of the power transformer. Inside the case, all the circuitry is on a PC board measuring 219 x 99mm and this includes the dual RCA input and output sockets. The only external wiring to the board are the secondary connections to the toroidal power transformer. Circuit description Now let’s have a look at the circuit of Fig.2. Since both channels are identical, this shows only the left channel. While the power supply is also on the PC board, it is shown in Fig.3. In total, the left channel uses 12 op amps, in three TL074 quad FET-input op amp packages. Four op amps, IC1a, IC1b, IC5a & IC5b, act as input or output buffers while the remaining eight op amps are Linkwitz-Riley active filter stages with 12dB/octave filter slopes. In each case, two 12dB/octave filters are cascaded to give an overall filter slope of 24dB/octave. This is far steeper than is normally used in passive crossover networks. The voltage gain of all these filter stages in the passband is unity. Low pass, high pass Before we go any further we should explain some terms which often confuse beginners: low pass, high pass and bandpass. A low pass filter is one that allows low frequencies to pass through and it blocks the higher frequencies. Hence, a circuit to drive a subwoofer would be called a low pass filter since it only delivers frequencies below 200Hz or thereabouts. Similarly, a high pass filter is one that allows high frequencies to pass through and it blocks low frequencies. Hence, the part of a crossover network which feeds a tweeter is said to be a high pass filter, even though it may consist of only one capacitor. If we cascade (ie, connect in series) a high pass filter with a low pass filter, the combination will pass a band of Specifications Voltage gain: Unity Frequency response Within ±1dB from 10Hz to 20kHz (see Fig.5) Filter attenuation slope 24dB/octave Total harmonic distortion Typically .003% at 1V RMS Signal to noise ratio -94dB unweighted (22Hz to 22kHz) with respect to 1V RMS Separation between channels Typically better than -100dB from 10Hz to 20kHz Input impedance 47kΩ Output impedance 60  Silicon Chip less than 200Ω www.siliconchip.com.au www.siliconchip.com.au January 2003  61 Fig.2: just 12 op amps and a few other components make up each channel of the active crossover. The six outputs (three only shown here; three more in the right channel) each drive separate power amplifiers for the tweeter, midrange and bass drivers in your loudspeakers. Fig.3: the power supply is entirely conventional, using positive and negative 15V regulators to give ±15V rails. Everything from the bridge on is mounted on the PC board. The seven 100nF capacitors are bypasses distributed around the PC board. frequencies and we then refer to it as a bandpass filter. We use a band-pass filter for the midrange output in this active crossover circuit. The other points you need to know about high and low pass filters are the so-called cut-off frequency and the filter slope. The filters used in this circuit have an attenuation of 12dB/octave; this is the filter slope and it applies for frequencies after the cut-off frequency. The cut-off frequency is where the signal output is -3dB down on the normal level. For example, in a low pass filter we might have a cut-off frequency of 1kHz (ie, -3dB point) and from there on the filter slope could be 12dB/octave. In theory, this means that the response at 2kHz (ie, one octave above 1kHz) will be -15dB although in practice it might not be quite that good. The filters used in our circuit are of the Linkwitz-Riley configuration and we use eight of these filters, four high pass and four low pass, in each channel. Each filter consists of an op amp connected as a voltage follower, preceded by two RC networks. As already noted, for each high pass and low pass filter we are using two 12dB/octave filters cascaded, to make the total roll off 24dB/octave (4th order) per filter stage. The basic filter configurations are shown in Fig.4, together with the formula for calculating the crossover frequency. In this particular case, the crossover frequency is at the -6dB point and the reason for this is that we are cascading two filters for each section (2 x 3dB = 6dB). Note that the capacitors in the low pass filter are shown with values of C and 2C while in the high filter we have resistors with values of R and 2R. In the main circuit of Fig.2 you will note two capacitors of equal values have been used for the 2C component, as it is difficult to obtain capacitor values exactly double that of another. On the other hand, resistors are much easier and so we have values of 10kΩ for R and 20kΩ for 2R. Now after that little diversion, let’s refer back to the circuit of Fig.2. The input to the left channel is fed via an RC filter, to roll off frequencies above 100kHz, and then to op amp IC1a which is connected as a unity gain buffer (or voltage follower). It drives two high pass filter stages associated with IC1d & IC1c, and two low pass filters associated with IC3a & IC3d. Both these low pass and high pass filters have cutoff frequencies set to 5.1kHz. The output of the second high pass filter, IC1c, is fed to the level setting trimpot VR1 and then to op amp IC1b which is connected as a non-inverting amplifier with a gain of two. It drives the left treble output (tweeter). Hence the tweeter only gets frequencies above 5kHz. Midrange band-pass Fig.4: the basic arrangements for the low pass and high pass filters. 62  Silicon Chip The output of low pass filter IC3d www.siliconchip.com.au feeds high pass filters based on IC3c & IC3b, both with cut-off frequencies of 239Hz. The output of high pass filter, IC3b, is fed to trimpot VR2 and then to op amp IC5a which has a gain of two. This drives the left midrange output which gets the band of frequencies between 239Hz and 5.1kHz. As well as driving high pass filters IC3c & IC3b, op amp IC3d also drives the cascaded low pass filters based on IC5d & IC5c, again with a cut-off frequency of 239Hz. IC5c drives trimpot VR3 and then op amp IC5b which has a gain of two. It drives the left bass output which only gets signals below 239Hz. All the outputs from each stage are in phase at the crossover points. Voltage gain at the crossover frequency for each section is -6dB (ie, half the reference level). Thus when the response curves of all three sections are added together, the result is an extremely flat frequency response with an overall gain of unity. Just how well this works is shown in the response curves of Fig.5. We’ve plotted the three filter responses and then the resultant curve is plotted along the top. The adder circuit we used to do this is shown (for interest only) at the end of this article in Fig.8. Power supply The power supply circuit is shown in Fig.3. It uses a 20VA toroidal power Parts List – 3-Way Active Crossover 1 1RU rack-mounting case, Altronics H-5011 or equivalent 1 PC board, code 01101031, 219 x 99mm 1 IEC power socket 1 chassis-mount safety fuseholder (3AG or M205 type) 1 0.5A fuse (3AG or M205 type to suit fuseholder) 1 DPST rocker switch with inbuilt neon (S1) 1 20VA toroidal transformer with 2 15V secondaries 1 3-way insulated terminal block 4 dual gold-plated RCA PC-mounting sockets, Altronics P-0212 or equivalent 6 multi-turn 100kΩ trimpots (VR1-VR6), Altronics R-2382A or equivalent Semiconductors 6 TL074 quad FET-input op amps (IC-IC6) 1 7815 positive 3-terminal regulator 1 7915 negative 3-terminal regulator 4 1N4004 silicon diodes (D1-D4) Capacitors 2 1000µF 25V PC electrolytic 2 100µF 25V PC electrolytic 2 1µF 50V bipolar electrolytic 14 100nF (0.1µF) multi-layer ceramic (code 100n or 104) 20 47nF (.047µF) metallised polyester (code 47n or 473) 20 2.2nF (.0022µF) metallised polyester (code 2n2 or 222) 2 220pF ceramic Resistors (1% metal film) 2 47kΩ (yellow violet orange brown or yellow violet black red brown) 8 20kΩ (red black orange brown or red black black red brown) 38 10kΩ (brown black orange brown or brown black black red brown) 4 100Ω (brown black brown brown or brown black black black brown) transformer with two 15V secondaries driving a bridge rectifier (diodes D1 D4) and two 1000µF 25V capacitors to derive unregulated DC supplies of around ±22V DC. These are fed to 3-terminal regulators REG1 and REG2 to produce supplies of ±15V DC. These are each bypassed by a 100µF 25V capacitor and seven 100nF multi-layer ceramic capacitors distributed around the PC board. Construction Fig.5: this graph shows the three filter response curves which were plotted separately. The overall response curve at top (red) was plotted using the mixer circuit in Fig.8. The overall response curve is extremely smooth. www.siliconchip.com.au As already noted, all the circuitry is on a single PC board measuring 219 x 99mm, so construction is very straightforward. The only complication will occur if you you wish to set your own crossover frequencies. If so, you will need to select values from Table 1. For example, if you decide you want a tweeter crossover frequency of around 3kHz, go to Table 1, run your finger down the righthand column until you get to 3100 and the R and C values are in columns 1 & 2. In practice, the 2.2nF capacitors in the high- pass and lowpass filters associated with IC1 and IC3 now have to be changed to 3.3nF, while the 10kΩ January 2003  63 Fig.6: the component overlay, as viewed from above the PC board. Note the polarity of electrolytic capacitors and ICs when soldering them in! 64  Silicon Chip resistors increase to 11kΩ and the 20kΩ values go to 22kΩ. Note that it is essential that both the high pass filters (ICd & IC1c) for the tweeter and the low pass filters (IC3a & IC3d) for the midrange must have exactly the same cut-off frequencies otherwise you will not get an overall flat frequency response. Similarly, if you want to change the bass cut-off frequency to around 350Hz (say), run down the righthand column of Table 1 to 347Hz. The R values then become 11kΩ and 22kΩ while the C values become 27nF. Alternatively, if you want to do the calculations yourself, visit www. sherlab.com/filter/filter.htm for a filter calculator. Lots more information regarding Linkwitz-Riley crossovers can be found at www.rane.com/note160.html Here they discuss lobing errors, driver alignment & phase correction, phase shift vs frequency etc. Having decided on your crossover frequencies, you can start assembly of the PC board by closely checking it for shorts between tracks, open circuits etc, against the pattern opposite. Then install all the resistors, followed by the capacitors and multi-turn trimpots. Make sure that the electrolytic capacitors are installed the right way around. The bipolar electro-lytics are not polarised and can go in either way. Ideally, 1% capacitors should be used in all of the filter circuitry. As an alternative, purchase a bag of 100 capacitors of the value you require and pick the 20 that are the closest in value to each other, using a capacitance meter or DMM with capacitance ranges. Next, install the two regulators which are laid flat on the PC board. Be careful not to swap them over otherwise the circuit definitely won’t work and you may have to replace quite a few damaged semiconductors. Finally, you can install the op amps and the RCA sockets. You will then need to wire up the power transformer, using the diagram of Fig.7. Temporarily install the PC board into the chassis and you are ready for some voltage checks. Voltage check Apply power and check the regulated supply rails with your digital www.siliconchip.com.au This photo of an early prototype PC board shows the general layout of components. It should be noted that there have been substantial changes since this photo was taken, particularly along the bottom (rear) of the board. The component overlay (Fig.6) shows the final version. multimeter. They should be close to ±15V DC. Then check that +15V is present at pin 4 of each TL074 and that -15V is present at pin 11 of each IC. Lightly touch each IC to ensure that none of them are getting hot – they should all be cool. The next step is to align the whole circuit using the trimpots. This is a simple matter of setting up each output for unity gain in its passband. This can be done at three frequencies, say 100Hz for the bass, 1kHz for the midrange and 12kHz for the treble. You will need an audio oscillator and a digital multimeter with an AC frequency response to 20kHz or better. Connect your audio oscillator to the input RCA connector in one channel. Set the frequency to 100Hz, 1kHz or 12kHz, depending on which section you wish to align. Set the level of the oscillator to 1V RMS. Then measure the signal level at the output of the stage that you are adjusting. For the treble output, use 10kHz and adjust trimpot VR1 (left channel) or VR4 (right channel) to obtain 1V RMS at the output socket. Similarly, for the midrange, use 1kHz and adjust VR2 (left channel) or VR5 (right channel) to obtain 1V RMS at the output sockets. Finally, for the bass, use 100Hz and adjust VR3 (left channel) or VR6 (right channel) to obtain 1V RMS at the output. That done, it is now a matter of finally completing the wiring inside the case and checking it before connecting the unit to your amplifiers. Your amplifiers We mentioned before that six amplifiers are required; one for each of the bass, midrange and treble speakers, times two (for stereo). But what amplifiers should you use? The completed project showing the rear panel arrangement, power supply wiring and PC board placement. Use this in conjunction with Fig.7 (opposite) during final assembly. www.siliconchip.com.au January 2003  65 Fig.7: follow this wiring diagram and you should have no problems with final assembly. Be especially careful with the mains wiring – note the heatshrink covering all the “bitey” bits! 66  Silicon Chip www.siliconchip.com.au amplifier module featured in this issue for the midrange and treble. The Ultra LD (Nov, Dec 2001, Jan 2002) or even the Plastic Power module (April 1996) would make a superb bass amplifier. Connection It is simply a matter of connecting the stereo outputs from the 3-Way Active Cross-over to the appropriate bass, Fig.8: here is the adder circuit we used to produce the mid-range and trediagram shown in Fig.5. You don’t have to make one of ble stereo amplithese unless you are interested in measuring your own fier inputs, then circuit. connecting the amplifiers’ outTypically, the woofer amplifier puts direct to the appropriate drivers needs to be about double the power of in each of the speaker enclosures. the midrange and tweeter amplifiers, Needless to say, the existing crossoto take into account the lower sensi- ver network in the speaker enclosures tivity of the woofers. is disconnected completely – and you So if you have been running a 100W will need to put an extra two sets of per channel stereo amplifier into your terminals on the back of your enclo3-way speaker system, you will still sures with each of the three connected need two 100W amplifiers for the directly to a driver (and appropriately woofers (eg, your exisiting amplifier!) labelled). but you can get away with two 50W The tone controls should ideally be amplifiers for each of the midrange flat on all amplifiers (although that can and tweeters (ie, four total). be a matter of individual taste – but the You may be able to put back into ser- treble control won’t do much on the vice an amplifier that you pensioned bass amplifier nor the bass control on off as “underpowered”. the treble amplifier!). Or, if you want to go the whole hog Volume controls can be individuand build new amplifiers to go with ally adjusted to get the best balance your new active crossover, you could between the bass, midrange and treble SC do a lot worse than the new SC480 speakers. There are no screws holding the PC board in place. Instead it sits on selfadhesive holders (as used in many computers) and the RCA sockets on the back panel are themselves held in by screws. www.siliconchip.com.au Table 1: Values for R & C R C 2R Crossover Frequency (kΩ) (nF) (kΩ) (Hz) 15 47 30 160 15 39 30 192 12 47 24 200 11 47 22 218 15 33 30 227 10 47 20 239 12 39 24 240 11 39 22 262 15 27 30 278 12 33 24 284 10 39 20 289 11 33 22 310 7.5 47 15 319 15 22 30 341 10 33 20 341 12 27 24 347 11 27 22 379 7.5 39 15 385 10 27 20 417 12 22 24 426 7.5 33 15 455 11 22 22 465 10 22 20 512 7.5 27 15 556 7.5 22 15 682 15 4.7 30 1596 15 3.9 30 1924 12 4.7 24 1995 11 4.7 22 2177 15 3.3 30 2274 10 4.7 20 2394 12 3.9 24 2405 11 3.9 22 2623 15 2.7 30 2779 12 3.3 24 2842 10 3.9 20 2886 11 3.3 22 3100 7.5 4.7 15 3193 15 2.2 30 3410 10 3.3 20 3410 12 2.7 24 3473 11 2.7 22 3789 7.5 3.9 15 3848 10 2.7 20 4168 12 2.2 24 4263 7.5 3.3 15 4547 11 2.2 22 4650 10 2.2 20 5115 7.5 2.7 15 5558 7.5 2.2 15 6821 January 2003  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. Please feel free to visit the advertiser’s website: www.altronics.com.au CIRCUIT NOTEBOOK Interesting circuit ideas which we have checked but not built and tested. Contributions from readers are welcome and will be paid for at standard rates. Motor speed control with protection This DC motor speed controller provides compensation for the voltage drop in the armature circuit. Voltage drop in the armature circuit is mostly responsible for the poor low speed running characteristic of small motors. This characteristic is most noticeable at start up and when running at low speed driving a varying load. Small motors can have an armature resistance of less than one 1Ω to several tens of Ohms. From DC electric motor theory: Vm = Vb + IaRa where Vm is the applied voltage; Vb is the back-EMF generated by the armature, proportional to the speed; Ia is the current in the armature circuit; and Ra is the armature resistance. When a motor is running without a load, it will draw only a small current and so IaRa will be small. Conversely, its speed will be high and so Vb will be high as well. When the motor is loaded, it draws more current and so IaRa will be increased. The speed will therefore reduce and so will Vb. For a given motor speed, the applied motor voltage must be increased to compensate for the increase in IaRa. This circuit can perform this task. It works as follows. The speed setting control VR1 adjusts the base voltage of Q1 to set the current flow in resistors R2 & R3. The voltage across R3 is applied to the base of the compound transistor comprising Q5 & Q6 and this drives the motor. Q2, Q3 and VR2 provide compensation for the armature vol­tage IaRa. The motor current flows through Q6 and its emitter resistor R8 and the resulting voltage is applied to the emitter of Q3 to be reflected at the emitter of Q2 and applied to trimpot VR2. Varying the resistance of VR2 thus changes the voltage across R8. This means that the voltage across R3 has two components, the speed setting from VR1 and the speed compensation from VR2. www.siliconchip.com.au VR2 must be adjusted to provide the correct amount of com­pensation otherwise the motor will surge or stall whenever a load is applied. VR3 sets the maximum current, to protect the speed control circuit or the motor itself from excessive load. Before adjusting VR2, make sure the wiper of VR3 is at 0V. Then adjust VR1 to run the motor slowly, say about 200 RPM. Load the motor by pinching the motor shaft with your fingers. Now adjust VR2 so that the motor runs smoothly without stalling or surging. Depending on the motor, speeds of 60 RPM under varying load should be easily achievable. C1 gives the circuit stability. How- ever, if your motor and cable capacitance is large, surging (instability) may occur. C1 can be inDunc creased to compensate. is this man Graham onth’s Q6 must have a heatsink. ner of the Wavetwinek Meterman 85XT For motors with less tru e RMS digital than 6Ω armature resistmultimeter. ance, change R8 to 1Ω. If the armature resistance is greater than 20Ω, change R8 to 4.7Ω. A value of 2.2Ω suits motors in between. VR3 is adjusted to limit the current as desired. Duncan Graham, Hamilton, NZ. NEW! HC-5 hi-res Vid eo Distribution Amplifier DVS5 Video & Audio Distribution Amplifier Five identical Video and Stereo outputs plus h/phone & monitor out. S-Video & Composite versions available. Professional quality. 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 348, Woy Woy NSW 2256 Ph (02) 4343 1970 Fax (02) 4341 2795 Visitors by appointment only January 2003  71 Circuit Notebook – continued The circuit uses an IR sensor to pick up the reflected light from two IR LEDs, plus two CMOS 7555 ICs (IC2 & IC3) to debounce the incoming signal and provide timing. Switch S2 is used to select between toggle on/off operation, timed operation & “press switch” operation (see text). Magic wand for 3-way control This was devised to enable handicapped children who lack manual dexterity to operate electrical toys. 72  Silicon Chip No doubt it could have many other applications. A wave of the hand or a “magic wand” over the box can oper­ate the relay in three ways: (1) as a toggler – one wave on, next wave off; (2) as a timer – one wave turns it on for a set time; (3) as a press switch – hold the wave over the sensor and the relay stays closed. The circuit depends on infrared sensor IC1 which sends a coded signal through two IR LEDs 1 and 2. IR light from these LEDs is reflected by a wand or hand back on to the sensor and this causes its output at pin 2 to go low. This “low” is connected to two 7555 timers (IC2, IC3) and to PNP transistor Q1 which is used as an inverter. Selector switch S2 determines which of these three devices is connected to transistor Q2 which drives relay RLY1. IC2 is a short time monostable to debounce the incoming signal and toggle IC4, a 4013 flipflop. Its output at pin 1 goes high and low on alternate input pulses. This is option 1. IC3 is another monostable to give a relay closed time of about 16 sec­ onds. This time can be varied by changing the associated resistor and capacitor. This is option 2. In the third switch position, the inverted low from Q1 becomes a high and operates the relay for as long as the hand is held over the sensor. A wave can be quite fast and about 10cm above the sensor, on each side of which is one IRLED – about 13mm away. The sensor is from RS Components (Cat 564-396) and the relay is from Jaycar – a 500Ω reed relay (Cat SY-4030). The wand must be white and about 15mm in diameter. A rolled up sheet of A4 paper works well. The LED in series with the relay indicates when the relay is operating. If your selector switch does not short circuit the contacts when between positions – ie, it is a “breakbefore-make” type – then you can omit diodes D4-D6. The IRLEDs should be mounted in bezels to prevent leakage of IR light to the sensor. The 330nF capacitor is a supply bypass for IC1 and should be as close to the sensor as possible. Because the signal is coded, the circuit is immune to ambient light. A. J. Lowe, Bardon, Qld. ($45) www.siliconchip.com.au Automatic tape control for display stand This circuit controls an autoreverse Walkman cassette player, via the relay in a standard security light unit (about $20 from Kmart). These units are unsuitable for connection to inductive loads, so to overcome this and still maintain isolation from the AC supply, it is arranged so that the sensor’s relay activates a pair of NE2 neons with integral resistors. These are encased with an LDR in heatshrink tubing. The LDR switches on transistor Q1 which activates the relay. This in turn switches the supply to the cassette player which is left with the Play button permanently activated. A second set of relay con­tacts pro- vides a 12V supply to an audio amplifier, fed with the signal from the Walkman. The duration of operation is set by the adjustment provided on the movement sensor which is also set for daylight operation. Two LM317 adjustable regulators provide the +12V and +3V supply rails. Max Walker, Blackburn, Vic. ($30) Filter reduces supply ripple by 40dB This circuit reduces noise and ripple voltage by 40dB over the 100Hz to 20kHz audio range. It provides a clean source of 5V power for driving audio circuits in portable applications such as cellular phones and multimedia notebook computers. Most linear regulators reject noise only up to 1kHz or so, which can be inade­quate in many applications. When operating, the circuit acts as a wide bandwidth buf­ fered voltage follower (not a regulator) whose DC output level is 7% below the input. R1 and R3 form a voltage divider that provides the 7% attenuation while C4 provides filtering. The op amp’s small input bias current (25nA typical) allows large resis­tor values for R1 and R3, yet limits the maximum DC error to only 20mV. The result is a low-pass filter with a 2Hz corner frequency and 20dB of attenuation at 20Hz. www.siliconchip.com.au The physical layout can be very small: one SOT23 transis­ t or, one µMAX (shrink SO-8) op amp and a few passive components. The largest capacitor is 10µF and the resistors can be 0.1W or surface mount 0805 size. Because the op amp’s common mode input range extends from rail to rail, its non-inverting input can sample the output voltage directly. The op amp’s supply voltage is filtered by R2 and C5, providing lower output impedance and better power supply rejection for the op amp at high frequencies. This filter’s 300Hz rolloff augments the op amp’s PSRR (already impressive at 110dB). A similar article appeared in the January 18, 1996 issue of EDN magazine. January 2003  73 COMPUTERS: masquerading modules & a firewall Using Linux to Share an Optus Cable Modem Internet Con­nection Pt.3: masquerading modules & a fire­wall In this article, we show you how to load various modules that are required for effective Internet access, along with a simple yet effective firewall. We also tell you what you need to do to connect a cable modem to Telstra Bigpond Advance instead of to Optus CableNet. By JOHN BAGSTER In order to effectively use your Linux box as a gateway, you need to set the machine up so that it loads some “masquerad­ing modules” on start-up. In addition, you need to set up a firewall so everything is secure. After all, you don’t want someone break­ing in and taking over! We’ll get to our firewall shortly. Let’s deal with the masquerading modules first. The various masquerading modules are required so that the gateway correctly forwards IP packets for various Internet utili­ties on the client machines. Basically, these modules work with IP masquerading (or IP forwarding) so that it looks as though everything that’s forwarded to the Internet is coming from a single machine – ie, the Linux box. This is done by translating IP addresses from the local network into a valid Internet IP number before relaying the packets out onto the Internet. At the same time, IP masquerading translates any incoming packets into local addresses before forwarding them to the client machines. It’s all really something of a masquerade because the real IP addresses of the clients are hidden – hence the name “IP masquerading”. IP masquerading (forwarding) is carried out using a program called “ipchains” and this is also used to create the firewall rules. Recent versions of Linux also include an updated replace­ment for ipchains called iptables (although 74  Silicon Chip ipchains is still included). The firewall described here is based on ipchains (since this is used by default with RedHat 7.0) but both are supported in system startup, so you could use iptables if you want. Note, however, that the commands for iptables are differ­ ent. The differences are well documented in manual pages if you wish to convert the firewall to iptables. Loading modules In most cases, the firewall rules and the rules to load the various module are all in one script – ie, the firewall script. However, in this case, they have been separated into two scripts so that the firewall can be enabled before networking is enabled. Note that this not only applies to a cable modem connection – it is equally applicable to a dial-up modem. There are quite a few masquerading modules for Linux, most of which are optional for audio, instant messaging, and various games, etc. Basically, you only need to load the modules that you require. This is roughly similar to selecting which options you want when you install Windows. OK, so how do we ensure that these modules are loaded at start-up? The answer is that we use a file called rc.local which RedHat Linux stores in the /etc/rc.d folder. This file is the last thing executed at start-up and you can add your own commands to it. You could put all the module loading commands diwww.siliconchip.com.au Masquerading script: /etc/rc.d/rc.modules #!/bin/bash # # rc.modules # rc.modules should be called via rc.local # Load powerswitch so Linux will shutdown neatly when switched off. # Only works with ATX power supplies. Uncomment the following line and modify to suit # #/sbin/insmod /lib/modules/3rdparty/powerswitch.o # Load all required IP masquerading modules # Uncomment the modules you need. /sbin/depmod -a # Supports the proper masquerading of FTP file transfers /sbin/modprobe ip_masq_ftp # Supports the masquerading of RealAudio over UDP. # Without this module, RealAudio WILL function but in # TCP mode. This can cause a reduction in sound quality #/sbin/modprobe ip_masq_raudio # Supports the masquerading of IRC DCC file transfers #/sbin/modprobe ip_masq_irc # Supports the masquerading of Quake and QuakeWorld. # This module is for multiple users behind a Linux gateway. # If you are going to play Quake I, II, and III, use the second one. # Quake I / QuakeWorld (ports 26000 and 27000) : #/sbin/modprobe ip_masq_quake # Quake I/II/III / QuakeWorld (ports 26000, 27000, 27910, 27960) : #/sbin/modprobe ip_masq_quake 26000,27000,27910,27960 # Supports the masquerading of the CuSeeme video conferencing software #/sbin/modprobe ip_masq_cuseeme # Supports the masquerading of the VDO-live video conferencing software #/sbin/modprobe ip_masq_vdolive rectly into the rc.local file and that would work without problems. However, it’s far neater to have the commands in a separate file and then call this from /etc/rc.d/rc.local (we’ll show you how shortly). We’ve called this separate file rc.modules and placed it in the /etc/rc.d folder. The rc.modules file OK, let’s take a look at the /etc/rc.d/rc.modules file that you need to create. You can either download this file from the SILICON CHIP website or type it in on your Linux box using a text editor. The file is shown in the accompanying www.siliconchip.com.au panel and contains the common masquerading modules that you might need. However, most of these have been commented out by placing a “#” at the beginning of their command lines. All you have to do is “uncomment” the mod­ ules that you need by removing the relevant “#” symbols. The various lines in the rc.modules file are all self-explanatory except for the “powerswitch” line. To explain, Pow­erswitch is a nifty little utility that shuts down Linux properly (and switches the PC off) when you press the power switch on the system case – provided you have an January 2003  75 COMPUTERS: masquerading modules & a firewall Firewall rules: the cablefirewall.simple script #!/bin/bash # # cablefirewall.simple # run this to set up the rules, then run # /etc/rc.d/init.d/ipchains save # to save the rules to be used every time the machine is started # modem interface (change to suit) MODIF="eth1" # local network (change to suit) LOCNET="192.168.0.0/24" # ============================================================================= # blocking rules for the input, output, forward chains respec­tively Iblock="DENY" ; Oblock="REJECT" ; Fblock="DENY" # Flush all existing rules and remove any user defined chains /sbin/ipchains -F ; /sbin/ipchains -X # loopback and local interfaces are OK on input and output /sbin/ipchains -A input ! -i $MODIF -j ACCEPT /sbin/ipchains -A output ! -i $MODIF -j ACCEPT # set policies to block everything /sbin/ipchains -P input $Iblock /sbin/ipchains -P forward $Fblock /sbin/ipchains -P output $Oblock # masquerading timeouts /sbin/ipchains -M -S 7200 10 160 # ============================================================================= # input chain: # block and log modem interface claiming to be local network (IP spoofing) /sbin/ipchains -A input -i $MODIF -s $LOCNET -l -j $Iblock # allow return tcp packets (those not requesting a connection) /sbin/ipchains -A input -p tcp -i $MODIF ! -y -j ACCEPT # allow incoming tcp ftp-data connections (for outgoing active ftp) /sbin/ipchains -A input -p tcp —sport ftp-data —dport 1024:65535 -i $MODIF -y -j ACCEPT # allow all udp and icmp in /sbin/ipchains -A input -p udp -i $MODIF -j ACCEPT /sbin/ipchains -A input -p icmp -i $MODIF -j ACCEPT # uncomment to reject and log anything else (required since policies can’t log) # the policy is the same so leave this line commented out if you’re not logging #/sbin/ipchains -A input -l -j $Iblock # ============================================================================= # output chain: continued next page . . . 76  Silicon Chip www.siliconchip.com.au Cablefirewall.simple – continued # allow everything except local network traffic out to the modem /sbin/ipchains -A output -i $MODIF ! -s $LOCNET ! -d $LOCNET -j ACCEPT # set delay and throughput times if using a dial-up modem (ppp interface) # these are not to be used if using a network card (cable modem) if [[ $MODIF == “ppp”* ]] then # set minimum delays for p in www ssh telnet ftp pop3 smtp ; do /sbin/ipchains -A output -p tcp —dport $p -t 0x01 0x10 ; done # set ftp-data for maximum throughput /sbin/ipchains -A output -p tcp —dport ftp-data -t 0x01 0x08 fi # reject and log anything else (required since policies can’t log) # the policy is the same so comment this line out if you’re not logging /sbin/ipchains -A output -l -j $Oblock # ============================================================================= # forward chain: # Masquerade from local network to anywhere on the modem inter­face /sbin/ipchains -A forward -i $MODIF -s $LOCNET -j MASQ # all other forwarding is blocked and logged # the policy is the same so comment this line out if you’re not logging /sbin/ipchains -A forward -l -j $Fblock ATX power supply, that is. It’s just the shot if you intend operating your Linux gate­ way without a mouse, monitor or keyboard. The powerswitch module does not come with the Linux distri­bution. If you intend to use it, you can download it from http://deadlock.et.tudelft.nl/~joris/powerswitch/ and install it as described in the instructions (more on this next month). In this case, the powerswitch.o file was placed in the /lib/modules/3rdparty folder (you will have to create this). #!/bin/sh # # This script will be executed *after* all the # other init scripts. # You can put your own initialization stuff in here if # you don’t want to do the full Sys V style init stuff. Modifying rc.local Once rc.modules is set up, your Linux gateway is complete except for a firewall. The one described here offers good security while not compromising access to the Internet. It is about as simple as you can get and is easy to set up. We’ll look at how the various firewall rules operate first, then give the firewall script and describe how it works. RedHat has a start-up script called /etc/rc.d/init.d/ ipchains (not to be confused with the /sbin/ipchains program). This is run before networking starts and loads a saved set of firewall rules. Furthermore, to save a new set of rules, you simply run the firewall script and then type: You now have to modify /etc/rc.d/rc.local so that it calls the rc.modules file during start-up. The start of the rc.local file initially looks like this: #!/bin/sh # # This script will be executed *after* all the # other init scripts. # You can put your own initialisation stuff in here if # you don’t want to do the full Sys V style init stuff. if [ -f /etc/redhat-release ]; then All you have to do is edit it to add a call to the /etc/rc.d/rc.modules file, so that it looks like this: www.siliconchip.com.au /etc/rc.d/rc.modules if [ -f /etc/redhat-release ]; then Setting up a firewall /etc/rc.d/init.d/ipchains save January 2003  77 COMPUTERS: masquerading modules & a firewall Once you’ve done that, the firewall is automatically set up before any networking each time you start the Linux PC. This not only gives you full security but also saves you from having to manually modify or add any start-up scripts yourself! To reload your saved rules you can type: /etc/rc.d/init.d/ipchains start and the previously saved rules are restored! Conversely, to remove all rules, you type: /etc/rc.d/init.d/ipchains stop This flushes all rules and removes all user-defined chains, thereby disabling the firewall. However, this will leave your PC wide open to attack, so it is not recommended. On the other hand, typing /etc/rc.d/init.d/ipchains panic does the opposite – ie, it denies everything (including local network traffic). Don’t do this from a local telnet or ssh connection – if you do, you will be stuck and will have to recov­er from the console! Firewall rules The firewall consists of three basic sections, called “chains”: an input chain, an output chain and a forward chain. They can be applied to each network card in the Linux PC but all we are really concerned about here is the network card connected to the cable modem (no restrictions are usually applied to the local network card, although they could be if required). The input chain covers anything coming in from the Inter­net. This is the one that the restrictions usually apply to, as you do not have any control over who or what is trying to gain access to your PC. The output chain covers anything being sent out to the Internet. The forward chain is used to transfer packets from the input chain of your local network card to the output chain of your modem network card (ie, to send stuff from your Linux PC or one of your Windows PCs to the Internet). Anything coming back from the Internet (ie, reply packets) is simply transferred directly from the input of the modem card to the output of the internal LAN card. A fourth type of chain is one you create yourself. This is effectively a subroutine, for want of an analogy, and would normally be used if you want to apply the same set of rules in more than one place. Note that in ipchains, the forward chain comes from the input chain and goes to the output chain. This means that the forward chain does not usually require any specific blocking rules. Conversely, in iptables the forward chain does not tra­verse the input or output chains at all. As a result, it requires similar security to the output chain. All chains can be told to DENY (DROP in iptables) or 78  Silicon Chip REJECT something. The difference between the two is that REJECT returns an error message (so the hacker knows what has happened) while DENY does not return any messages. This means that DENY is ideal for use with the input chain as hopefully potential crackers will give up if they get no response at all. Another option is called ACCEPT, which means to allow something through. This is not normally used in the forward chain. Instead MASQ is used, which instructs the chain to change the internal network addresses to the external (eth1) address. The input, output, and forward chains also have a thing called a “policy”, which is simply what to do when all else fails. By contrast, user defined chains do not have a policy – they simply return to the point they were called from. For a detailed description on ipchains (with lots of exam­ p les), go to the following Internet site: http://www.tldp.org/HOWTO/IPCHAINS-HOWTO.html To find out how iptables works, you can go to: http://www.linuxguruz.org/iptables/howto/iptables-HOWTO.html How the firewall works OK, let’s now take a look at the firewall rules listed here in cablefirewall.simple. We’ll start from the top and describe what each rule does: First, MODIF="eth1" is a variable that defines the network card your cable modem is connected to. Change the eth1 to eth0 if required, or to ppp0 if you are using a dial-up modem. The reason for using a variable is that you can change it here and then all later references to $MODIF will refer to the correct network card. This saves you from having to change it throughout the whole script. Similarly, LOCNET="192.168.0.0/24" refers to your internal network. The /24 means the same thing as /255.255.255.0 Iblock="DENY" ; Oblock="REJECT" ; Fblock="DENY" are three statements on one line (hence the semicolons). You can change the DENYs to REJECTs and visa versa if you want. I have used DENY for the input (so crackers get no indication) and REJECT for the output so users on the internal network are warned of any prob­lems with outgoing traffic. Next any existing firewall rules are removed by flushing all existing rules and any user-defined chains. The local and loopback networks are allowed for both input and output, so the loopback (required for internal Linux use) is enabled as quickly as possible. The local network is allowed to do anything, the theory being that users on your internal network are friends, not enemies! This is done by allowing everything except the cable modem interface (the “!” means “anything but”). Next, the policies for all three chains are defined to deny or reject everything. The following masquerading timeouts are standard values which are used everywhere. The input chain is where we stop crackers getting in. Here, crackers who are devious enough to supwww.siliconchip.com.au Connecting To Telstra Bigpond Advance Unlike OptusNet cable, Telstra Bigpond Advance requires a login script for full Internet access. Under Linux, this login script is called bpalogin and several readers have asked for further information on how this is installed. Although we haven’t tested it, the following procedure should work: (1) Go to http://bpalogin.sourceforge.net/, then click the “Download BPAlogin” link and select the download you require - eg, “RedHat Linux RPMs v2.0”. The bpalogin-2.0-1.i386.rpm file that’s download is about 170Kb in length. (2) Copy this file to the Linux PC and install it by typing: rpm -i bpalogin-2.0-1.i386.rpm This creates the following files and directories (as shown by rpm -q -p -l bpalogin-2.0-1.i386.rpm): /etc/bpalogin.conf /etc/rc.d/init.d/bpalogin /usr/doc/bpalogin-2.0 /usr/doc/bpalogin-2.0/COPYING /usr/doc/bpalogin-2.0/CREDITS /usr/doc/bpalogin-2.0/INSTALL /usr/doc/bpalogin-2.0/README /usr/sbin/bpalogin (3) Open /etc/bpalogin.conf in a text editor and change the following two lines (near the top of the file): username yourname password yourpass ply an internal IP address to try to get through are stopped. Now the important one. Anybody trying to break in must be stopped but you have to be able to get stuff back from the Inter­net yourself. The next line achieves this by allowing TCP traffic that is not a connection (ie, it allows return packets). One problem with this is that when you download data using FTP, it requires a connection! So the next line defines a rule that allows FTP data connections only. Next we allow UDP and ICMP packets in. UDP is used by DHCP and DNS, while ICMP is used for error messages, pings, etc. This does mean that crackers can ping the PC but it is possible to prevent this by setting up several ICMP rules, to be selective. The last input chain rule blocks and logs anything else, so you can check who or what is trying to break in. This is only required if you want to log any blockages. Since the only thing being blocked is TCP connections, www.siliconchip.com.au You obviously set “yourname” and “yourpass” to whatever your Bigpond Advance user name and password are. I notice that the file is set to -rwx------ and is owned by root, so it already is protected against unwanted peaking. The start of the file looks like this: # Default debug level is 1. Values range from 0-2 # with 0 being silent # All information goes to the syslog. debuglevel 1 # The user name you have for your BPA account username yourname # Your BPA password password yourpass Note that there is also a /etc/rc.d/init.d/bpalogin startstop script. Now type: chkconfig --list bpalogin This shows that the rpm installation sets the startup and shutdown as follows: bpalogin 0:off 1:off 2:off 3:on 4:on 5:on 6:off This means that after editing /etc/bpalogin.conf, you can start bpalogin either by restarting Linux or by typing: /etc/rc.d/init.d/bpalogin start which you should never allow anyway, this line is commented out. If you do want to log TCP blockages then remove the “#” from the start of the line. The output chain is a lot simpler. Everything is allowed out to the cable modem, except internal IP addresses. This is a simple safeguard in case you make a mistake configuring any of the services on your local network. Next are some delay rules which only apply to a dial-up modem (delays are optimised for a network card by default). A test is done for the external interface being ppp* (ie, a modem). The last thing is to block and log everything else. Since the output chain policy is to block, you can remove this if you do not want to log anything but that would not be a good idea. Anything logged here will be something you will need to fix. The forward chain is also quite simple and has just two January 2003  79 COMPUTERS: masquerading modules & a firewall rules. First, internal IP addresses are changed (masqueraded) to the cable modem’s IP address. Everything else is then logged and blocked. Again, if anything is logged here, it will be a problem you need to fix. Making the firewall work To get the firewall rules up and running, you must have IP forwarding enabled as described in Pt.1. The local and cable modem networks will also be up and running at this stage. Note, however, that this means that the PC is wide open to attack, so have the firewall ready to roll if you are starting with the cable modem plugged in. Actually, only the local network needs to be up for IP for­warding to be enabled, so a better scheme would be to unplug your cable modem before starting the PC. In fact, this is the recommended method as it will keep you safe while you install the firewall. You can either type cablefirewall.simple in yourself or, better still, save yourself the hassle by downloading the script from the SILICON CHIP website at: www.siliconchip. com.au It doesn’t really matter where you save it since it is only run once to initially set the rules up before they are saved (see below). However, /usr/local/bin is probably as good a place as any to store the firewall script. It’s then just a matter of running the script to activate the rules. You do that by typing: /usr/local/bin/cablefirewall.simple Note that if you have the cable modem unplugged, this script will take a while to run but it will get there. Follow this by typing: /etc/rc.d/init.d/ipchains save This command saves the firewall rules so that they are now automatically invoked on system startup, before networking is enabled. This gives you full security. By contrast, if /etc.rc.d/cablefirewall.simple was called from /etc/rc.d/rc.local, then the networking would be up long before the firewall was. And that could create security problems. The interesting thing here is that the saved rules will be restored before IP forwarding is enabled without a problem. However, trying to set the rules via cablefirewall.simple without IP forwarding enabled won’t work! Note that this isn’t a problem with cablefirewall.simple – it’s simply the way ipchains works. Assuming that you unplugged your cable modem for security, you can now plug it back in and type: ifup eth1 This will start the cable modem network. Don’t forget to use eth0 instead of eth1 if this is the cable modem interface. And that’s it. If you’ve followed all the instructions so far, you will now have a working Internet gateway, firewall, DHCP server and DNS server. In Pt.4, we will describe a script to enable easy viewing of any firewall logs and show you how to run your Linux box without a screen or keyboard, including shutting it down via the power switch (if it has an ATX power supply). We’ll also briefly discuss a few security SC safeguards. Subscribe & Get This FREE!* *Australia only. Offer valid only while stocks last. THAT’S RIGHT! Buy a 1- or 2-year subscription to SILICON CHIP magazine and we’ll mail you a free copy of “Electronics TestBench”, just to say thanks. “Electronics TestBench” is a valuable 128-page collection of the best test equipment projects from the pages of Australia’s only consumer electronics magazine. By subscribing to SILICON CHIP you’ll save money on the news-stand price. And we’ll give you a 10% discount on any other SILICON CHIP merchandise (books, etc). Contact: Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097 Phone Orders: (02) 9979 5644   Fax Orders: (02) 9979 6503   Email Orders: office<at>silchip.com.au 80  Silicon Chip www.siliconchip.com.au SILICON CHIP WebLINK How many times have you wanted to access a company’s website but cannot remember their site name? Here's an exciting new concept from SILICON CHIP: you can access any of these organisations instantly by going to the SILICON CHIP website (www.siliconchip.com.au), clicking on WebLINK and then on the website graphic of the company you’re looking for. It’s that simple. No longer do you have to wade through search engines or look through pages of indexes – just point’n’click and the site you want will open! Your company or business can be a part of SILICON CHIP’s WebLINK . For one low rate you receive a printed entry each month on the SILICON CHIP WebLINK page with your home page graphic, company name, phone, fax and site details plus up to 50 words of description– and this is repeated on the WebLINK page on the SILICON CHIP website with the link of your choice active. Get those extra hits on your site from the right people in the electronics industry – the people who make decisions to buy your products. Call SILICON CHIP today on (02) 9979 5644 We’re one of Australia’s most innovative electronic equipment suppliers. For over 10 years we’ve served Australian industry with an extensive range of electronic components and equipment from the world’s leading suppliers. We ensure our customers have the best selection and service. We stock the full range of fischertechnik robotic kits and models plus spare parts, computer interfaces and control software. Learn about industrial automation and robotics with fisch-ertechnik. See our website for the latest news and FREE software downloads. Don’t forget to mention this ad for a 5% discount! · Hifi upgrades & modification products - jitter Tel:(07) 4934 0413 Fax: (07) 4934 0311 Tel: (02) 9482 1944 Fax: (02) 9482 1309 WebLINK: clarke.com.au Tel: (03) 9830 6288 Fax: (03) 9830 6481 WebLINK: procontechnology.com.au Syd: (02) 9660-1228 Melb: (03) 9859-0388 SPECIALISTS in AUDIO, VIDEO, CD, DATA Media and Multimedia manufacturing & wholesale. We also specialise in DVD Production & editing. We can produce Short Run or Bulk CD Audio, CD Rom & DVD projects. Distributor of Emtec (by Basf) TDK, HHB and Quantegy Professional Products. JED designs and manufactures a range of single board computers (based on Wilke Tiger and Atmel AVR), as well as LCD displays and analog and digital I/O for PCs and controllers. JED also makes a PC PROM programmer and RS232/RS485 converters. A 100% Australian owned company supplying frequency control products to the highest international standards: filters, DIL’s, voltage, temperature compensated and oven controlled oscillators, monolithic and discrete filters and ceramic filters and resonators. PIC chip specialists – microEngineering Labs and others. Easy to learn, easy to use, sophisticated CPU based controllers & peripherals. We specialise in providing a range of Low Power Radio solutions for OEM’s to incorporate in their wireless technology based products. The innovative range includes products from Radiometrix, the World’s leading manufacturer. TeleLink Communications WebLINK: telelink.com.au PRO-COPY Clarke & Severn Electronics Jed Microprocessors Pty Ltd Tel: (08) 9375 3902 Fax: (08) 9375 3903 Tel: (03) 9762 3588 Fax: (03) 9762 5499 WebLINK: procopy.com.au WebLINK: jedmicro.com.au For everything in radio control for aircraft, model boats and planes, etc. We also carry an extensive range of model flight control modules including GPS, altitude and speed, interfaces, autopilot and groundstation controllers. More info on our website! RCS Radio has available EVERY PC Board ever published in SILICON CHIP, EA, ETI and AEM (copyrighted boards excepted). Many late boards are available ex stock, others can be made to order within a few days.Custom & production boards too! Silvertone Electronics Tel/Fax: (02) 9533 3517 WebLINK: silvertone.com.au www.siliconchip.com.au RCS Radio Tel: (02) 9738 0330 Fax: (02) 9738 0334 WebLINK: cia.com.au/rcsradio Procon Technology Hy-Q International Pty Ltd Tel:(03) 9562-8222 Fax: (03) 9562 9009 WebLINK: www.hy-q.com.au International satellite TV reception in your home is now affordable. Send for your free info pack containing equipment catalog, satellite lists, etc or call for appointment to view. We can display all satellites from 76.5° to 180°. Av-COMM Pty Ltd Tel:(02) 9939 4377 Fax: (02) 9939 4376 WebLINK: avcomm.com.au reduction and output stage improvement. · Danish high-end hifi kits - including preamps, phono, power amps & accessories. · Speaker drivers including Danish Flex Units plus a range of accessories. · GPS, GSM, AM/FM indiv. & comb. aerials. Soundlabs Group WebLINK: soundlabsgroup.com.au See our website for new range of ATOM products! MicroZed Computers Tel: (02) 6772 2777 Fax: (02) 6772 8987 WebLINK: microzed.com.au When it comes to purchasing quality products over the Web, you can count on the Wiltronics team to provide you with the best value for money. For over 25 years, Wiltronics has supplied the needs of the Electronics Industry, and look forward to continuing this service. Wiltronics Pty Ltd Tel: (03) 9762 3588 Fax: (03) 9762 5499 WebLINK: wiltronics.com.au JJanuary anuary 2003  81 Chips monitor tyre pressure US electronics giant Motorola is set to introduce computers into the last electronics-free zone in a car – its tyres. The company has developed a two-chip remote sensing module (RSM) small enough and light enough to fit inside a tyre without unbalancing the wheel. A sensor chip, code-named Daytona, measures pressure to within 7.5kPa (typical car tyre pressure is 220kPa), and temperature to within 4° Celsius. Temperature measurement is necessary to compensate for pressure changes due to tyre heating during driving. The Daytona chip is fabricated using low power CMOS technology and draws just 0.55µA on standby. The second chip in the RSM is a combination of Motorola’s HC08 microcon-troller and a UHF radio transmitter in a 32-pin package. It processes the raw measurements into a tyre pressure reading and transmits the data to the in-car receiver. 82  Silicon Chip The transmitter operates in the 315, 434 or 868MHz bands, sending the pressure data at up to 9600 baud by either on/off or phase shift keying. The HC08 has 2Kb of on-board FLASH memory and enough I/O and computing power to handle the pressure and temperature reading task. It also has built-in power management capabilities to get the most out of the lithium battery powering the module. When the car is parked, an inertial switch can be used to turn off the transmitter and leave the HC08 in low power sleep mode. By PETER HOLTHAM These power-saving features of the RSM will ensure a battery life of at least ten years. A simple PC board antenna completes the RSM hardware. It provides a signal strong enough to be picked up by the receiver inside the car. Making the module is one thing, keeping it alive in the harsh environment inside a tyre is another. Temperatures can range from a freezing -40°C to a scorching 150°C . The RSM is also subjected to accelerations as high as 2000G as the wheels rotate. The computer and transmitter can be protected but the pressure sensor must be in contact with the air in the tyre. Motorola engineers have develwww.siliconchip.com.au oped a special Teflon filter to protect it against attack by liquids, dust, and corrosive gases. The tyre pressure signal is picked up inside the car with the same receiver already installed for remote keyless entry. The information presented to the driver will depend on the software programmed into the HC08 and the receiver by car component suppliers. It could be as simple as a dashboard warning light showing that one of the five tyres (including the spare) needs pumping up. More complex systems will automatically identify each tyre and provide the exact pressure. Motorola plans to begin volume production of RSMs in September this year. The price will depend on end-user requirements and will vary based on volumes and specifications. But with around 50 million cars produced every year, demand for remote tyre pressure monitoring is expected to soar, driving prices down. All of which means monitors are likely to become standard equipment within the next few years. KALEX PCB Makers! • High Speed PCB Drills • 3M Scotchmark Laser Labels • PCB Material – Negative or Positive Acting • Light Boxes – Single or Double Sided; Large or Small • Etching Tanks – Bubble • Electronic Components and Equipment for TAFEs, Colleges and Schools • Prompt Delivery We now stock Hawera Carbide Tool Bits Other Manufacturers Join The Fray Given the huge global market for new cars, Motorola was not going to be left as the sole supplier of tyre pressure monitors for long. Now European electronics company Philips has launched a rival chip to assist in the measurement of individual tyre pressures. The P2SC signal-conditioner works together with pressure sensors built into the tyre. It mounts directly on the tyre rim, providing a wireless link to transmit the pressure to the keyless entry receiver in the car. The monitor inside the car sends a low frequency ‘wake-up’ signal to www.siliconchip.com.au each P2SC chip every time the ignition is switched on. The chip returns pressure information at frequencies in the 315 and 434MHz bands. While the car is being driven, the P2SC chips send regular status reports on each tyre back to the driver. The low frequency wake-up also allows the monitor to automatically identify which tyre is where; even after tyre position is changed during maintenance. Industry analysts expect pressure monitors to become the fastest growing segment of car electronics over SC the next few years. 718 High Street Rd, Glen Waverley 3150 Ph (03) 9802 0788 FAX (03) 9802 0700 ALL MAJOR CREDIT CARDS ACCEPTED January 2003  83 VINTAGE RADIO By RODNEY CHAMPNESS, VK3UG Intermediate Frequency (IF) Amplifiers; Pt.2 Last month, we looked at how the IF stage evolved in early broadcast-band AM radios. This month, we look at high-fidelity IF amplifier stages and describe how to get rid of the 9/10kHz whistle. P RIOR TO THE introduction of FM into Australia, some radio manufacturers produced receivers that were capable of reproducing the full transmitted audio bandwidth. Typically, this involved designing 20kHz IF (intermediate frequency) stages to give a maximum audio frequency response of 10kHz. However, the use of a wide-bandwidth IF laid the receiver open to annoying “monkey-chatter” – ie, distorted modulated audio signals from stations close to the tuned frequency. It also gave rise to annoying 10kHz Fig.1: the circuit for a 9/10kHz audio notch filter. It is designed to filter out 9kHz or 10kHz whistles (depending on the station spacing) in a wideband AM receiver. 84  Silicon Chip heterodyne whistles from stations on adjoining channels. The monkey chatter couldn’t be eliminated but the 10kHz whistle could be and often was. Basically, the 10kHz whistle was “eliminated” by installing a simple 10kHz audio notch filter. This filter effectively re­duced the whistle to an insignificant level. The 10kHz filter often took the form of a narrow-band rejection filter, as shown in Fig.1. In this case, the filter is physically tuned to 10kHz by varying L1 or C1 and C2, while the depth of the notch was adjusted by VR1. Note that, with the advent of 9kHz channel spacing, these filters had to be retuned from 10kHz to 9kHz. Variable selectivity IF stages In most cases, broadband amplifiers did a good job on local stations and gave an audio output which was considered high-fidelity at the time (10kHz compared to FM which has frequencies as high as 15kHz). However, listening to more distant stations was often quite unpleasant at night, due to fading, noise and interference, monkey chatter and 10kHz heterodynes. To counter these extremely annoying problems, most high-fidelity receivers included a switch that reduced the IF amplifi­er bandwidth to around 10kHz. This meant that the receiver could produce audio signals up to only about 5kHz when the switch was in the “narrow” position. Fig.2: a variable bandwidth IF stage. Switching the resistors across the IF transformer windings increased the bandwidth, while reducing the gain of the amplifier. www.siliconchip.com.au This photo shows an assortment of 455kHz IF transformers. They came in a wide range of sizes. Of course, this meant that the full frequency range was no longer reproduced, so listeners had to be content with less than “hifi” reproduction. However, on the positive side, the 10kHz whistles, monkey chatter, noise and interference were all signif­i cantly reduced. This was important because before the advent of TV, the evening’s entertainment often involved listening to the radio. Variable bandwidth Taking this a step further, some manufacturers designed variable bandwidth IF stages that could be switched to suit the listeners’ requirements. This was done in a variety of ways. One method involved switching resistors across the IF transformer windings. This lowered the Q of the windings and the gain of the amplifier, while at the same time increasing the bandwidth of the amplifier – see Fig.2. Another method involved removing one IF transformer completely, replacing it with an untuned inductance-capacitance network. Still another method involved switching a tertiary winding in and out of circuit in a special IF transformer. There were even circuits which automatically adjusted the bandwidth accord­ing to the strength of the received signal – ie, the bandwidth was www.siliconchip.com.au controlled by the AGC. However, although such circuits were around, very few showed up in the average domestic receiver. It’s also interesting to note that specialised high-fidelity tuners/receivers often used an IF of 1900kHz (or some other frequency above the broad­cast band) to achieve good bandpass shape and 20kHz bandwidth. Unfortunately, fading – and selective fading in particular – remained as a severe impediment to good quality reception on distant stations. For those unfamiliar with selective fading, it manifests itself as severe distortion and fading of the received signal. It is usually due to multi-path reception, which causes the relative levels and phase of the carrier and its two side­ bands to vary. Keeping IF amplifiers stable It is rare to have instability and oscillation problems in well-designed amplifier stages. By using an IF of 455kHz and normal high-gain IF transformers, a valve with a mutual conduc­tance of around 2000 was all that was necessary to obtain the necessary performance. Valves such as the 6U7G and the 6N8 fall into this category. To ensure stability under all circumstances, it is neces­sary to make sure that the layout of the amplifier is such that inputs and outputs are kept well apart. This particularly applies if using high-gain valves. In some cases, such as when using high-gain valves like the 6BA6 (and more so with the 6AU6), a shield may need to be soldered across the valve socket, isolating the input from the output. As a matter of interest, I’ve found a number of Healing sets using the 6AU6 to be marginally stable. Neutralisation Fig.3: this diagram shows the correct pos­itions for the slugs in an IF trans­former. Note that the coils are tuned with the slugs towards the outside ends of the former (not in the centre). Neutralisation was used in circuit design back in the 1920s when triodes were used as RF amplifiers. It was necessary if reasonable gain was to be obtained without the amplifier oscil­lating. However, with the advent of RF tetrode and pentode valves, January 2003  85 Fig.4: typical IF, detector and audio stages for an AM broadcast band receiver. The components marked with an “A” suffix are often missing but their inclusion improves performance (see text). neutralisation became unnecessary in most circuits, particularly in IF amplifiers with their relatively lower fre­quency of operation compared to RF amplifiers. However, I’ve found that EMI/HMV have been sticklers for doing things right. Fig.4 shows a circuit in which the IF stage is approximately neutralised. The 5pF (C2) capacitor from the plate of the 6BA6 to the bottom of the secondary of the IF trans­former acts with the AGC bypass (C1) to form a bridge neutralis­ing circuit. I had a Little Nipper receiver to restore some time back which had an unstable IF amplifier – it tended to oscillate if I wasn’t careful with the alignment. It turned out that someone had been at the set before it came to me and had replaced the .01µF AGC bypass capacitor (C1) with a value of 0.1µF. Replacing this capacitor with the correct value restored the neutralisation and the IF stage was again quite stable. Detector & AGC leads The leads from the detector and the AGC diode tend to be treated as having no RF energy on them. In reality, however, they carry quite a bit of RF (IF) energy and this needs to be prevent­ed from radiating and causing instability within the receiver. For example, resistors R3 and R4 should have minimal lead length on the ends connecting to pin 5 of the 6AV6. Similarly, the 47pF capacitor 86  Silicon Chip (C7) lead from pin 5 of the 6BA6 should be as short as possible, as should C5’s lead on the IF trans­former terminal. By observing these precautions, minimal IF energy will be radiated from the IF amplifier circuits. The detector lead to the volume control can also radiate energy if it isn’t shielded. However, few receivers in the later valve radios have this lead shielded so it isn’t always neces­sary. Note too that some receivers have the volume control di­ rectly connected to the bottom of the IF coil as shown in Fig.4 (assuming that R2A is a wire link). In that case, only the 100pF bypass capacitor (C5) provides RF filtering. By contrast, the better receivers include another section of filtering based on resistor R2A and capacitor C6A. This fur­ther reduces the level of RF (IF) energy getting through to the audio amplifier. Although the audio amplifier favours audio frequencies, it also amplifies any IF signals that find their way into this stage. This signal can then be radiated from the audio amplifier and picked up by the front-end of the receiver, or by other receivers nearby, where it can cause some strange effects. In some cases, this radiation causes the receiver to per­form poorly at the low-frequency end of the broadcast band. It’s difficult to describe the exact symptoms. However, the set does­n’t have the sensitivity it should and also seems to be a little strange in its alignment, with a certain amount of “swish” heard as the set is tuned across a station. So what can be done to overcome this problem. The amount of IF signal getting into the audio amplifier has already been reduced by the filter consisting of R2A and C6A. In addition, capacitor C8 from the plate of the 6AV6 to earth also reduces the amount of IF energy in the circuit. However, if the lead lengths from the plate of the 6AV6 to the grid of the 6M5 are short, it would be better to connect a small-value capacitor (such as C11A) between the grid of the 6M5 and earth. The combination of R8 and C11A would then be more effective at reducing the IF energy applied to the grid of the 6M5 than using just C8. Most output stages have a capacitor from the plate to chas­sis or to the high voltage supply. This reduces the amount of IF energy at the output of the audio amplifier, as well as acting as a mild top-cut audio filter. The suggested added components that reduce this problem are shown with an “A” after them in Fig.4 (R2A is normally a short circuit in most sets). By carrying out these modifications, I’ve found that many receivers offer im­proved performance. Another set I looked at some time ago had an extremely unstable IF amplifier. It didn’t take long to establish that RF signals were being amplified in the audio stage and were being fed www.siliconchip.com.au back through the set. In fact, it was so unstable that even bringing the plastic handle of a screwdriver near some of the normal supply wiring caused the set to either go into oscillation or to stop oscillating, depending on the state it was in at the time. In this case, the problem was found to be lack of proper filtering of the high-tension (HT) supply line. In this particu­lar receiver (from a well-known manufacturer), R9 was not includ­ ed in the circuit design – there was just a length of wire where a resistor could (should) have been. I decided to decouple the HT line by installing a resistor in this location and the set imme­ diately became stable and proved to be a really hot performer. Problems can also occur when IF cans are not earthed prop­ erly or a shield can is missing from a valve. These are problems that are easily fixed. Despite a few problems, I have generally found IF amplifi­ ers to be quite reliable. In most cases, all that is necessary to restore the performance is to replace leaky paper capacitors and perhaps the odd valve. The AGC bypass capacitor(s) are particu­ larly important and these should have no discernible leakage. If they do, the normal AGC control voltage will not be applied and this usually results in overloading of the IF amplifier. An IF amplifier with low gain It’s important that IF transformers be wired the correct way, as reversing the connections on one winding can cause the gain to be quite low. Many replacement IF transformers, such as those produced by Aegis, have the connections marked on the can, so they are easy to identify. For unmarked transformers (eg, those salvaged from derelict receivers), the windings can usually be identified by taking the transformer out of its shield can. The grid winding is the one furthest from the base. If the performance is poor and you know the transformer is good, try reversing the connections. Also, if an IF transformer is being taken out of a wreck, observe what each lead is attached to and label the leads accordingly. The following information from the 4th edition of the Radiotron Designer’s Handbook (by Langford-Smith) will help in identifying IF transformer windings: “For the ca­pacitance and mutual inductance coupling to be aiding, the prim­ ary and secondary wind­ings are arranged so that if the plate connects to the start of the primary, then the grid (or diode plate) of the next stage connects to the finish of the secondary winding; both coils being wound in the same direction . . . the grid and plate connections should be as far from one another as possible”. Aligning the IF amplifier The standard IF transformer usually has critical coupling between the two tuned circuits. Critical coupling provides maxi­ mum gain with the transformer adjusted by simply tuning for a peak. IF transformers employ a variety of methods when it comes to adjusting the slug-tuned types. Older types have an earthed metal screw thread which can be adjusted with a normal metal screwdriver. Conversely, if the tuning tool has to be inserted into the Looking for an old valve? or a new valve? BUYING - SELLING - TRADING Australasia's biggest selection Also valve audio & guitar amp. books SSAE DL size for CATALOGUE ELECTRONIC VALVE & TUBE COMPANY PO Box 487 Drysdale, Victoria 3222. Tel: (03) 5257 2297; Fax: (03) 5257 1773 Mob: 0417 143 167; Email: evatco<at>mira.net Premises at: 76 Bluff Road, St Leonards, Vic 3223 www.evatco.com.au Subscribe & Get This FREE!* *Australia only. Offer valid only while stocks last. THAT’S RIGHT! Buy a 1- or 2-year subscription to SILICON CHIP magazine and we’ll mail you a free copy of “Electronics TestBench”, just to say thanks. A selection of plastic alignment tools will be necessary if you intend restoring vintage receivers. www.siliconchip.com.au Contact: Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097 Phone Orders: (02) 9979 5644 Fax Orders: (02) 9979 6503 Email Orders: office<at>silchip.com.au January 2003  87 Photo Gallery: Eclipse Monarch DKL Manufactured by Eclipse Radio (Melbourne), the 1947 Monarch DKL is a good example of the 4-valve reflex superhet designs that were popular during that period. The set was available in a number of different cabinet colours, including white as shown here. The following valves were used: 6A8-G frequency changer; 6B8-G IF amplifier/reflexed 1st audio/detector/ AVC amplifier; 6V6-GT output; and 5Y3-GT rectifier. (Photo and information courtesy Historical Radio Society Of Australia). IF transformer, you use a non-metallic alignment tool. It is also important to use the right tool here for two reasons: (1) so that the slugs are not damaged; and (2) so that the transformer is not detuned by the presence of a metallic ad­justment tool. Plastic alignment tool kits are available from various electronics stores or you can use knitting needles which have their ends filed to a screwdriver blade shape. The older type IF transformers that use trimmer capacitors across the tuned winding are also best adjusted with a plastic alignment tool. That’s because the plate voltage (ie, the HT) is usually present on at least one trimmer – use a metal tool and you could get a nasty shock. The alignment procedure is as follows: first, with the set turned off, connect a digital multimeter (DMM) across C1 on the AGC line and switch to the 0-20V range. That done, connect a signal generator to the antenna terminals of your set and tune the set to the low-frequency end of the broadcast band. The next step is to apply a high-level signal modulated at 1kHz at around the expected IF frequency and tune 88  Silicon Chip the generator across the band. If the set hasn’t had its IF tuning adjustments fiddled with, a response should be heard at or near 455kHz (or what ever the nominal IF of the set is). If the signal through the set is quite strong, the DMM will register an extra -2V along the AGC line. Adjust the output of the generator so that only -1V or so of extra voltage is shown on the meter. If the frequency is some way away from the expected IF (eg, 20-30kHz), it is possible to “walk” the IF adjustments onto the required frequency. To do this, first tune the signal generator just to the side of the spot where the maximum response is (ie, towards the wanted frequency). That done, adjust each of the IF slugs for a peak, then go through the whole procedure again until the maximum response is at 455kHz (if this is the target frequency). Now it is necessary to accurately tune the IF amplifier. Once again, adjust the signal generator so that the DMM reads a volt or so above the standing bias on the AGC line. Adjust each of the internal slugs or external screws for a maximum reading on the DMM, except for the tuned winding going to the detector diode. This one, at the top of the transformer, is adjusted for maximum audio, not maximum meter reading. If the DMM is connected across the volume control (VR1), peak all adjustments for a maximum reading. Reduce the generator signal level if the DMM reading is above about -4V, as the IF amplifier tunes (peaks) slightly differently with a strong signal compared to a weak signal. Note that for best performance on weak signals, it is necessary to align the set on weak sign­als. Note particularly that the slugs or screws should adjust to the correct frequency with the slugs and screws away from the centre of the former, as shown in Fig.3. If they are close to­gether (ie, towards the centre of the former), the coupling between the two tuned circuits will be upset and the performance will be compromised. If you don’t have a signal generator it’s still possible to align the set, although not quite as accurately. Once again the DMM is connected to either the AGC line or to the detector output. All you have to do then is tune to a relatively weak sta­ tion and peak the signals as described in the previous paragraph. Of course, you won’t know if the IF stage is tuned to exactly 455kHz but that doesn’t really matter. Note that this job should be done in the middle of the day, to avoid signal fading which would make it difficult to accurately align the IF amplifier. So there you have it – a straightforward method of tuning the IF amplifier stages in most sets. In times gone by, when high impedance voltmeters were scarce, the audio output was measured and the IF adjustments peaked for maximum audio. However, I believe that the method I’ve described is more appropriate today as it also gives an idea as to whether the AGC system is working as it should. Occasionally, one slug in an IF transformer will be stuck. If you strike this, don’t force it as broken slugs are hard to get out. Instead, just adjust all the other slugs so that all tuned circuits are on the same frequency as the circuit that’s tuned by the stuck slug. Being precisely on 455kHz isn’t at all necessary. Finally, for anyone who wants to know more about IF ampli­fiers, take a look at the relevant chapters in the “Radiotron De­signer’s Handbook” by SC Langford-Smith. www.siliconchip.com.au ASK SILICON CHIP Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line and we’ll answer your question. Write to: Ask Silicon Chip, PO Box 139, Collaroy Beach, NSW 2097; or send an email to silchip<at>siliconchip.com.au Cheap 12V power supply wanted I want a power supply to convert 240VAC from the power point to 12V DC at 3A. I am currently using a car battery but that is inconvenient. (D. F., via email). • The cheapest way to get a high current 12V power supply is to obtain a computer power supply and tie all the +12V output leads together and all the 0V leads together (ie, connect the 12V outputs in parallel). We have not done a project along these lines. Problems with LP Doctor kit I recently completed construction of the LP Doctor (SILICON CHIP, January 2001) kit but now I find several problems that defy repair. In the “bypass” switch position, the straight through phono preamp and output level control work perfectly, however in any of the “processed” switch positions, there is no audio output. I also notice that the left/right LEDs appear to function normally, although they flash regardless of the selector Adjusting mixture on a VR Commodore I have just purchased a Fuel Mixture Display kit. If the vehicle is running rich, is it possible to adjust the vehicle’s computer to make it run in the correct mixture range? For a VR Commodore, is there room for adjustment to make it run lean? (D. G., via email). • Although it’s possible to change the “chip” in the engine management computer (eg, to alter the timing curve and/or to change mixture settings), this really is a job for the spe­cialist. And generally speaking, it’s difficult to do better than the manufacturer’s original chip. www.siliconchip.com.au switch position. Is this normal? I have thoroughly checked my work and can see no apparent error. I have also successfully completed the voltage adjustment as outlined in the construction manual. Can you offer any advice? (F. S., Ingham, Qld). • It is normal for the click detection LEDs to operate inde­pendently to the selector switch. The signal is somehow being lost through IC3, IC7 IC4, IC8, etc. Check the supply to each of the IC3 and IC7 delays and op amps IC5a and IC7a. Also check that there is -7.5V at pin 2 of IC4 and IC8. Alternatively, the wiring to switch S2 is incorrect. Check that there is audio signal directly at the outputs of IC5a and IC7a. 10-channel remote receiver queries The following queries relate to the 10-Channel IR Remote Receiver published in the February 2002 issue. Firstly, in forc­ing IC1 to display its remote control status by connecting pin 1 to the 5V supply (TP2) via a 220Ω test resistor at power up, can the same be achieved by connecting the two If the fuel mixture display indicates that the engine in your VR Commodore is running rich, then there are two possibili­ties: (1) either the fuel mixture display is incorrectly cal­ibrated; or (2) there is a fault in your vehicle’s fuel system which should be corrected by a specialist service outlet. Note that there are times when the engine should run rich – eg, under acceleration. If your vehicle is performing normally, then it’s likely that the fuel system is operating correctly. Note also that the VR Commodore also runs quite lean when at speed under light throttle settings. It can return very good fuel economy on a trip. stakes (TP1 & TP2) on the completed board? Or should another resistor be employed, so that LED11 does not blow (ie, does the 100kΩ resistor take enough of the current)? Is this resistor best connected from TP2 straight into the terminal contacts of pin 1 with IC1 in place. Secondly, is the decoded signal at TP2 for all signals received or only those matching Sat1/Sat2 codes? Thirdly, if the use for some outputs is currently unknown, is it OK to just leave out the 1.8kΩ resistor, which selects toggle or momentary, or do some other parts need to be left out too? (eg, respective tran­sistor). Fourthly, is there a part that comprises a variable resis­tor on a reversible motor for volume control? What would happen if power is supplied to both directions at once; ie, both buttons are pressed down by the remote user or would only signal for one button be sent from the remote? (D. K., via email). • TP1 cannot be directly connected to TP2 or the LED (LED1) will have 5V across it with no current limiting and consequently it will be destroyed. This is why we use a 220Ω resistor at pin 1 to TP2 instead. Connecting a 220Ω resistor between TP1 and TP2 will not bring pin 1 of IC1 high enough as it will be at about 1.8-2V as set by the LED voltage. The decoded signal at TP1 will reflect the incoming code sent by the IR transmitter. The code does not have to be SAT1 or SAT2 but the 10 outputs will not respond unless the code is correct. The 1.8kΩ resistors on the outputs need to be connected to set the momentary or toggle option. If these are left out of circuit, the output could be either option, depending on what level the pins float at when powered up. Generally, the RA out­puts will be set at momentary and the RB outputs for Toggle if no resistor is connected. The decoder can only respond to one code at a time and so driving the January 2003  89 SuperCharger vs Multi-Purpose Fast Charger I have read the SuperCharger articles with interest and I am keen to build one, if you can first answer a couple of ques­tions. I have been using your Multi-Purpose Fast Charger II for quite some time now. It has charged quite a few of the new high capacity batteries (AA 1800mAh) and seems to do it well. What is the difference between the two chargers in their ability to charge the new high capacity batteries and am I doing my batteries harm by using the Fast Charger? I always refresh before charge. The standard number of AA cells I charge is four; ie, 4.8V. I always use the thermistor when charging and have never had any problems with overcharged or overheated batteries. One advantage of the new charger is it could be used away from a 240VAC power source which is attractive when using a digital camera on motoring or camping holidays. (C. N., via email). • There are a few potential probmotorised potentiometer using the two outputs will not cause any problems. And no problems occur if outputs are in any state as the motor will only have power (with either polari­ty) or have no power with the motor terminals both at positive or both at ground. Delayed audio on parliament broadcast I am interested in politics and enjoy watching the daily broadcast, when parliament is sitting, of Question Time on ABC-TV between 2:00pm & 3:00pm. Normally, when ABC-TV is broadcasting the House of Representatives, ABC NewsRadio broadcasts the entire day’s proceeding from the Senate and vice versa. However, on some occasions, both the TV and radio broadcasts were from the same House (in this case, the House of Representatives). On such occasions, when I have the TV on and also try to listen to the proceedings of the same House on the radio, I notice that there is a delay of a few seconds in the audio between the TV & radio broadcast. 90  Silicon Chip lems charging small (AA/AAA) cells with the Multipurpose Fast Charger II. Of most concern is its high fixed charge rate. You may find that you can charge Nicads at this rate (using the thermistor for temperature sens­ ing) but it will depend greatly on the type of battery. Look specifically for “high discharge rate” types, intended for R/C applications and the like. For NiMH-chemistry types, we’re not aware of any small (AA/AAA) types that can be safely charged at 6A. You mention that you are currently doing this without problems. While it’s true that thermistor temperature sensing should prevent catastrophic cell failure, we doubt that the cells will be fully-charged before the charge terminates. You may like to verify this by doing a cell capacity test. We may publish a simple “addon” circuit for the Multipur­ pose Fast Charger that allows you to reduce the charge current at the flick of a switch. No promises though! Can you explain the reason or reasons for this delay? I can only assume that it may have something to do with the physics of the propagation of radio waves as, I suspect, both transmissions here in Canberra come from local transmitters. I suppose another question might be should there be a delay in the reception of the audio for a simulcast program received on both TV and radio? (P. M., Queanbeyan, NSW). • The delay has nothing to do with the propagation of radio waves and everything to do with the way the ABC routes signals between its various studios and transmitters. We would guess that the TV signals come direct from Canberra to the relevant station transmitter while the audio signal may go via the ABC radio studios in Adelaide (or wherever). There may even be a satellite link involved. Mic for measuring frequency response I would like to know if there is a cheap way of making a microphone and (preamp) with a known frequency response, to use in conjunction with the RTA spectrum analyser shown in the August 2002 issue. If not, I believe it would make a great project because being able to see the problem areas in the fre­quency response of a sound system setup would be very handy. I know you can buy calibrated microphones but these all seem to be quite expensive and for the small amount of use they might get places them out of reach of most people. Could SILICON CHIP do a project using an easy to get and cheap electret microphone and plot its response, etc, to use with RTA software? (B. B., Runaway Bay, Qld). • Producing a calibrated microphone is not a simple task – we have looked at it as a project but cannot see an easy way of doing it. Faulty speed control blows FETs I have built two 20A Speed Control kits from the June 1997 issue. One works OK while the other worked for one week and then the battery was put in reverse polarity. It blew one FET. I replaced the faulty parts and it worked for one week and then both FETs blew. I replaced both FETs but now I can’t vary the speed – always near flat out. (S. G., via email). • Strictly speaking, the circuit should not have been damaged by battery reversal. The fuse should have blown with diode D1 forward biased. However, since the FETs were destroyed, it may be that the transistors and IC were also damaged. This would explain the full-speed only operation. It may be wise to replace the FETs, transistors, IC1 and the regulator, plus the diodes at the bat­tery supply and across the motor. ETI pH meter wanted In the December 1980 issue of ETI a digital pH meter pro­ject was featured. This used an Intersil 7106 driver and a 3.5-digit LAD204 display. Do you know if this display is still avail­able? The driver and display were sold by Intersil as part of an evaluation kit. Perhaps an updated version of the pH meter could be considered as a SILICON CHIP project? (T. S., via email). www.siliconchip.com.au • The ETI pH meter is no longer available. SILICON CHIP de­scribed a pH meter based on an LM324 quad op amp and an analog meter, in the April 1988 issue. It would probably be much easier to source the parts for it but you would need to make sure you could get pH electrode before proceeding further. We can supply a photostat copy of the April 1988 article for $10, in­ cluding airmail postage. Splitting a line level signal Could you please advise me, if I split a line level stereo output signal (left & right channel) using two “RCA Y adaptors”, will it affect the level/ quality of the input signal at either of the destination components (power amplifiers in this case)? G. M., via email). • That’s not an easy question to answer. Superficially, it would seem that splitting line level signals would not cause a problem but there are a number of factors to consider. Factor one is the input impedance of the amplifiers, etc. Normally, this will be high and should not cause a problem but if it is low (say below 5kΩ), it could reduce the signal level, as well as degrade the frequency response and distortion perfor­mance. Two, if one of the amplifiers is driven into overload, the resulting distortion artefacts may be superimposed on the line signal to the other destination device. Three, if one of the destination devices and the signal source is earthed via the mains (rather than double-insulated) an earth loop will result which again could degrade the performance. From this, you will see that we are not keen on Y-connectors. Provided Hum in Plastic Power amplifier I have built the Plastic Power amplifier module described in the April 1996 issue of SILICON CHIP and it passed all the tests. However, I am getting hum. When I turn the power supply off, the hum stops and the amplifier continues to function for about 10 seconds or so. Do you have any suggestions to get rid of the hum or would bigger filter capacitors do the job? (S. G., via email). • The hum could be due to the filter capacitor value not being suffi­ ciently large but this is unlikely. Instead, hum at low levels is more likely due to a hum loop, due to the ground connections not being the input impedances of your two destina­tion devices are high, a better way is to make up a split­ter box with RCA connectors and feed the signal to the two devic­es via isolating resistors of, say, 4.7kΩ. That way, if something naughty happens in one destination device (say overload), it won’t degrade the rest of the signal chain. Generating different audio tones I am about to start a project that requires two different audio tones, one having a positive sound like a “ping”, the other having a negative sound like “baamp”. If you imagine, like a board game that has “yes” and “no” answers. I would like to know what I need for creating these two tones. I want to be able to trigger each tone with a microcontroller. (B. C., via email). • We suggest using Twin-T oscillators connected to the one point. To minimise hum, the ground connections for the capacitors should all connect to a single point with the 0V wiring from the transformer also connecting to this point. The amplifier output (speaker) ground then connects to this common ground. The input ground of the amplifier is not connected to the common ground as this is connected to the speaker ground on the PC board. In addition, the rectifier (+) and (-) outputs should con­nect to the capacitors first, with the amplifier supply rails connecting to the capacitor leads rather than the rectifier terminals. Use heavy gauge wiring for these power supply connec­tions. set to different fre­quencies and also set just below the point of oscillation; they can then be shocked into oscillation by a short pulse. SILICON CHIP has not published anything on this subject but there were two relevant articles in EA: “Electronic Bongos” in December 1979 and “Twin-T Oscillators” in May 1976. We can supply photostats of these articles for $8.80 each, including postage. How to suppress contact arcing I have a question about how to reduce the arcing across relay contacts. I’m switching a 240VAC 1A solenoid with a 24V DC relay. What is more reliable, using a Triac or relay? (Y. G., via email). • The normal way to suppress contact arcing when switching DC is to use a reverse-biased diode with a current 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. www.siliconchip.com.au January 2003  91 Notes & Errata 40W Fluorescent Inverter, September 2002: Mosfets Q1 & Q2 have been found to be prone to overheating when the PC board is placed within the confines of a slimline 36W fluorescent tube batten. To correct this, the inverter has been altered to improve efficiency without reducing the lamp brightness. Changes include reducing the 334V DC supply to 280V and winding transformer T1 differently. The voltage change requires replacing one of the 270kΩ resistors leading to pin 1 of IC1 with a 180kΩ resistor. The changes to T1 involve using 130 turns on the secondary. For the primary use figure-8 7.5A wire with a polarity stripe. Insert one end of the figure-8 wire in the S1 & F1 holes nearest to Q2 and wind on five turns, starting up through the centre of the core and anticlockwise towards S2 & F2. Insert the wire ends into S2 & F2 with continuity (same wire) between S1 and S2 and the second wire between F1 and F2. This means that if the polarity stripe on the figure-8 wire is at S1, it then terminates into S2. rating of more the than load current being switched. This should suppress any contact arcing across the relay contacts. When switching 240VAC with a solenoid, it is usual to con­nect a 250VAC-rated capacitor across the (solenoid) contacts. Try a 47nF (.047µF) 250VAC capacitor across the contacts. High input impedance amplifier wanted I would like a suggestion for a high input impedance ampli­ fier circuit. What I need is to be able to intercept a line level signal and basically split it in to two line level signals. I need it high impedance so that it doesn’t load the line too much. I want to build five of these amplifiers and then use them to provide line-level outputs from each channel of my Boston Acoustics BA7500G Speak­er system so I can feed external amps, without disturbing the internal 92  Silicon Chip Set the current drain from the battery at 3A (300mV across the 0.1W resistor used in the current measurement set-up in Fig.8). As noted in December 2002, it is recommended that the maximum current delivered to the fluorescent tube be adjusted using a trimpot. The 100kΩ resistor connecting between pin 2 of IC3 and the top of the dimming potentiometer (VR1) should be replaced with a 50kΩ trimpot and series 82kΩ resistor. The 1.2Ω resistor between the source of Q4 and ground should be changed to 2.2Ω to allow the full dimming range available from VR1. Using the current measuring setup of Fig.8, the trimpot should be adjusted for the 300mV, corresponding to 3A when the dimming pot (VR1) is turned fully clockwise. Note that this adjustment should be made after the inverter has been running for some time and is fully warmed up. Once adjusted, the trimpot and 82kΩ resistor can be swapped for a single resistor that is the same value as the total series combination. When testing the current (using amplifier. Any help would be greatly appreciated. (M. R., via email). • You really don’t need a high input impedance. What you need is a buffer amplifier that can drive a series of low impedance outputs. We have already published a suitable circuit – the audio portion of the Audio/Video Distribution Amplifier in November 2001. This circuit is based on an LM833 dual op amp. If you decide to use it, make sure you install 1kΩ resis­tors in the outputs instead of the 47kΩ resistors mistakenly specified in the original article. Speed control in cordless drills I recently bought a variable speed cordless drill/screw­ d river (Black & Decker) and would like to know what method is used to provide the variable speed feature. I guess I could open the drill and look inside but the setup of Fig.8), it is important not to have the 0.1Ω 5W resistor in series with the supply for any appreciable length of time as the current drain will begin to increase. To prevent this, short out the 0.1Ω resistor (with a clip lead) when not making the measurement. Remove the clip lead briefly to make the current measurement. In addition, use heavy gauge wire rated at 7.5A or more to connect the inverter to the 12V battery. It is recommended that the inverter not be used while the battery is being charged from a high current charger such as an automotive alternator or mains-powered unit. If the inverter Mosfets still run excessively hot, it is recommended to reduce the current drain to 2.5A (250mV across the 0.1Ω resistor) which will reduce the lamp brightness slightly. With slimline batten holders, ventilation can be improved by drilling some holes in the side of the batten adjacent to the Q1 and Q2 heatsinks and some extra holes at the other end of the batten to SC allow air flow. that will void my warranty. (H. P., via email). • Cordless drills are usually permanent magnet motors with a Mosfet switchmode power control, usually running at about 1kHz or so. In fact, you can usually hear the 1kHz tone at very low speed settings. Temperature controlled fan I want a circuit for a temperature-controlled fan for the heatsinks of an amplifier I’m working on. I am positive SILICON CHIP published one in the not-too-distant past but for the life of me I can’t find it in my back issues, nor can I locate it on your website. Can you recall where the circuit appeared please? (G. B., Scotland Island, NSW). • The circuit was associated with the Ultra-LD Amplifier in the August 2000 issue. There were two options: a SC thermistor or thermal cutout. www.siliconchip.com.au MARKET CENTRE Cash in your surplus gear. Advertise it here in Silicon Chip. CLASSIFIED ADVERTISING RATES Advertising rates for this page: Classified ads: $20.00 (incl. GST) for up to 20 words plus 66 cents for each additional word. Display ads: $33.00 (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______________ www.siliconchip.com.au FOR SALE 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. Eco Watch phone: (03) 9761 7040; fax: (03) 9761 7050; Unit 5, 17 Southfork Drive, Kilsyth, Vic. 3137. ABN 63 006 399 480. UNIVERSAL DEVICE PROGRAMMER: Low cost, high performance, 48-pin, works in DOS or Windows incl. NT/2000. $1364. Universal EPROM programmer $467.50. Also adaptors, (E)EPROM, PIC, 8051 programmers, EPROM simulator and eraser. Dunfield C Compilers: Everything you need to develop C and ASM software for 68HC08, 6809, 68HC11, 68HC12, 68HC16, 8051/52, 8080/85, 8086, 8096 or AVR: $198 each. Demo disk available. ImageCraft C Compilers: 32-bit Windows IDE and compiler. For AVR, 68HC­ 08, 68HC11, 68HC12, 68HC16. $385.00 Atmel Flash CPU Programmer: Handles the 89Cx051, 89C5x, 89Sxx in both DIP and PLCC44 and some AVR’s, most 8-pin EEPROMS. Includes socket for serial ISP cable. $220, $11 p&p. SOIC adaptors: 20 pin $132.00, 14 pin $126.50, 8 pin $121.00. Full details on web site. Credit cards accepted. GRANTRONICS PTY LTD, PO Box 275, Wentworthville 2145. (02) 9896 7150 or http://www.grantronics.com.au CENTRAL COAST FIELD DAY, SUNDAY 23rd FEB: Don’t miss Australia’s biggest Amateur Radio exhibition and sale of new and used radio and communication equipment at Wyong Race Course, just 1 hour north from Sydney. Gates open 8.30am. Special Field Day bargains from traders and tons of disposals gear in the flea January 2003  93 Silicon Chip Binders New New New Mark22-SM Slimline Mini FM R/C Receiver REAL VALUE AT $12.95 PLUS P&P These binders will protect your copies of SILICON CHIP. They feature heavy-board covers & are made from a dis­ tinctive 2-tone green vinyl. They hold up to 14 issues & will look great on your bookshelf.  80mm internal width • • • • • 6 Channels 10kHz frequency separation Size: 55 x 23 x 20mm Weight: 25gm Modular Construction Price: $A129.50 with crystal Electronics PO Box 580, Riverwood, NSW 2210. Ph/Fax (02) 9533 3517 Satellite TV Reception International satellite TV reception in your home is now affordable. Send for your free info pack containing equipment catalog, satellite lists, etc or call for appointment to view. We can display all satellites from 76.5° to 180°. AV-COMM P/L, 24/9 Powells Rd, Brookvale, NSW 2100. Tel: 02 9939 4377 or 9939 4378. Fax: 9939 4376; www.avcomm.com.au Need prototype PC boards? We have the solutions – we print electronics! Four-day turnaround, less if urgent; Artwork from your own positive or file; Through hole plating; Prompt postal service; 29 years technical experience; Inexpensive; Superb quality. 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DAS005 Parallel Port Data Acquisition Module features 8 12bit Analog inputs, 4 digital I/Ps & 4 digital O/Ps. Free windows software. FAB Programmable Logic Controllers. Low cost, high performance. Programming software and SCADA software free. Heaps of features. Full details and credit card ordering available at: www.oceancontrols.com.au PCBs MADE, ONE OR MANY. Any format, hobbyists welcome. Sesame Elec­tronics (02) 9586 4771. sesame777<at>optusnet.com.au; http:// members.tripod.com/~sesame_elec RCS HAS MOVED to 41 Arlewis St, Chester Hill 2162 and is now open, with full production. Tel (02) 9738 0330; Fax 9738 0334. rcsradio<at>cia.com.au; www.cia.com.au/rcsradio www.siliconchip.com.au Subscribe & Get This FREE!* *Australia only. Offer valid only while stocks last. Positions At Jaycar We are often looking for enthusiastic staff for positions in our retail stores and head office at Silverwater in Sydney. A genuine interest in electronics is a necessity. Phone 02 9741 8555 for current vacancies. Microzed.com.au PIC CHIP SPECIALIST PO Box 634 ARMIDALE 2350 (296 North Cooke’s Rd) (02) 6772 2777 – may time out to Mobile 0438 277 634 (02) 6772 8987 Advertising Index Acetronics....................................94 Altronics................................. 68-70 Av-Comm Pty Ltd.........................94 Clarke & Severn...........................81 Dick Smith Electronics........... 22-25 Elan Audio....................................83 Do you have a good circuit idea? We pay up to $60 for contributions to Circuit Notebook. Silicon Chip Publications, PO Box 139, Collaroy, 2097. THAT’S RIGHT! Buy a 1- or 2-year subscription to SILICON CHIP magazine and we’ll mail you a free copy of “Electronics TestBench”, just to say thanks. Contact: Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097 Phone Orders: (02) 9979 5644 Fax Orders: (02) 9979 6503 Email Orders: office<at>silchip.com.au FLUKE 123 SCOPEMETER: 60MHz, still in box, as new with battery charger + all accessories $1100, ONO. Ph: 0412 621822 or (02) 9831 1673. Audio, Video, S-Video and VGA cables distribution amps, switchers, adaptors, price lists at: www.questronix.com.au HALF RETAIL PRICE! Used Solar Panels, Inverters, Batteries, Surplus Components and more. See our specials pages at www.kcsolar.com.au USB KITS: Stepper Motor Controller, DTMF Transceiver, Thermometer, DDS HF Generator, Compass, 4 Channel Voltmeter, I/O Relay Card. Also available Digital Oscilloscope, Temperature Loggers, VHF Receivers and USB OCXs to control our kits from your application. www.ar.com.au/~softmark ADD SPEECH, SONAR OR DIRECTION SENSING to your next project. Fully contained modules. Full specs on website www.robotparts.com.au Ph 0412 350671 Evatco..........................................87 Grantronics..................................93 Harbuch Electronics.....................55 Instant PCBs................................94 Hy-Q International........................81 Jaycar ......................... 21,45-52,95 JED Microprocessors................5,81 Kalex............................................83 Microgram Computers...................3 MicroZed Computers..............81,95 Printed Electronics...................... 94 KIT ASSEMBLY Procon Technology.......................81 KIT ASSEMBLY & REPAIR. Small production or one off. Phone Robin Frost 08 8357 4441. Email: patrob<at>bigpond.com.au Procopy........................................81 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 RF Probes....................................83 Quest Electronics.........................71 RCS Radio...................................94 Silicon Chip Binders............55,OBC Silicon Chip Bookshop..........96,IBC Silicon Chip TestBench..............IFC Silvertone Electronics.............81,94 NOW AVAILABLE FROM Soundlabs Group.........................81 www.siliconchip.com.au Project Reprints Limited Back Issues Limited One-Shots If you’re looking for a project from ELECTRONICS AUSTRALIA, you’ll find it at SILICON CHIP! We can now offer reprints of all projects which have appeared in Electronics Australia, EAT, Electronics Today, ETI or Radio, TV & Hobbies. First search the EA website indexes for the project you want and then call, fax or email us with the details and your credit card details. Reprint cost is $8.80 per article (ie, 2-part projects cost $17.60). SILICON CHIP subscribers receive a 10% discount. We also have limited numbers of EA back issues and special publications. Call for details! visit www.siliconchip.com.au or www.electronicsaustralia.com.au www.siliconchip.com.au Telelink Communications.............81 Wiltronics.....................................81 _________________________________ PC Boards Printed circuit boards for SILICON CHIP projects are made by: RCS Radio Pty Ltd. Phone (02) 9738 0330. Fax (02) 9738 0334. January 2003  95 REFERENCE GREAT BOOKS FOR ALL PRICES INCLUDE GST AND ARE AUDIO POWER AMPLIFIER DESIGN HANDBOOK PIC Your Personal Introductory Course A handbook for professionals and students from one of the world’s most respected audio authorities. New edition is more comprehensive than ever with a new chapter on Class G amplifiers and further new material on output coils, thermal distortion, relay distortion, ground loops, triple EF output stages and convection cooling. 427 pages in paperback. Concise and practical guide to getting up and running with the PIC Microcontroller. Assumes no prior knowledge of microcontrollers, introduces the PIC’s capabilities through simple projects. Ideal introduction for students, teachers, technicians and electronics enthusiasts – perfect for use in schools and colleges. 270 pages in soft cover. by Douglas Self 3rd Edition 2002 89 $ by John Morton – 2nd edition 2001 NEW NEW NEW NEW 46 $$ VIDEO SCRAMBLING AND DESCRAMBLING AUDIO ELECTRONICS If you've ever wondered how they scramble video on cable and satellite TV, this book tells you! Encoding/decoding systems (analog and digital systems), encryption, even schematics and details of several encoder and decoder circuits for experimentation. Intended for both the hobbyist and the professional. 290 pages in paperback. For anyone involved in designing, adapting and using analog and digital audio equipment. It covers tape recording, tuners and radio receivers, preamplifiers, voltage amplifiers, audio power amplifiers, compact disc technology and digital audio, test and measurement, loudspeaker crossover systems, power supplies and noise reduction systems. 375 pages in soft cover. By John Linsley Hood. First published 1995. Second edition 1999. FOR SATELLITE AND CABLE TV by Graf & Sheets 2nd Edition 1998 4th EDITION $ 70 87 $ EMC FOR PRODUCT DESIGNERS 3rd EDITION UNDERSTANDING TELEPHONE ELECTRONICS By Stephen J. Bigelow. 4th edition 2001 Based mainly on the American telephone system, this book covers conventional telephone fundamentals, including analog and digital communication techniques. Provides basic information on the functions of each telephone component, how dial tones are generated and how digital transmission techniques work. 402 pages, soft cover. 103 $$ By Eugene Trundle. 3rd Edition 2001 3rd EDITION Eugene Trundle has written for many years in Television magazine and his latest book is right up to date on TV and video technology. includes both theory and practical servicing information and is ideal for both students and technicians. 382 pages, in paperback. Widely regarded as the standard text on EMC, provides all the key information needed to meet the requirements of the EMC Directive. Most importantly, it shows how to incorporate EMC principles into the product design process, avoiding cost and performance penalties, meeting the needs of specific standards and resulting in a better overall product. 360 pages in paperback. 63 $ By Ian Hickman. 2nd edition1999. Essential reading for electronics designers and students alike. It will answer nagging questions about core analog theory and design principles as well as offering practical design ideas. With concise design implementations, with many of the circuits taken from Ian Hickman’s magazine articles. 294 pages in soft cover. by Dogan Ibrahim. Published 2000. by Steve Roberts. 2nd edition 2001. Based mainly on British practice and first published in 1997, this book has much that is relevant to Australian systems as a guide to home and small business installations. A practical guide to installation of telephone wiring, ranging from single extension sockets to PABX, with the necessary tools, test equipment and materials needed by installers. 178 pages in soft cover. 89 $$ Microcontroller Projects in C for the 8051 TELEPHONE INSTALLATION HANDBOOK 69 By Tim Williams. First pub­­lished 1992. 3rd edition 2001. ANALOG ELECTRONICS GUIDE TO TV & VIDEO TECHNOLOGY $ 92 $ $ 73 Through graded projects the author introduces the fundamentals of microelectronics, the 8051 family, programming in C and the use of a C compiler. The AT89C2051 is an economical chip with re-writable memory. Provides an interesting, enjoyable and easily mastered alternative to more theoretical textbooks. 178 pages in paperback. BOOKSHOP ENQUIRING MINDS! LOWER THAN RECOMMENDED RETAIL PRICE WANT TO SAVE 10%? 10% OFF! SILICON CHIP SUBSCRIBERS AUTOMATICALLY QUALIFY FOR A 10% DISCOUNT ON ALL BOOK PURCHASES! Power Supply Cookbook Analog Cct Techniques With Digital Interfacing by T H Wilmshurst. Published 2001. by Marty Brown. 2nd edition 2001. An easy-to-follow, step-by-step design framework for a wide variety of power supplies. Anyone with a basic knowledge of electronics can create a very complicated power supply design . Magnetics, feedback loop, EMI/RFI control and compensation design are all described in simple language. 265 pages in paperback. 99 VIDEO & CAMCORDER SERVICING AND TECHNOLOGY by Steve Beeching (Published 2001) $ 69 $ $ Provides fully up-to-date coverage of the whole range of current home video equipment, analog and digital. Information for repair and troubleshooting, with explanations of the technology of video equipment. 318 pages in soft cover. 69 Antenna Toolkit by Joe Carr. 2nd edition 2001. Together with the CD software included, the reader will have a complete solution for constructing or using an antenna - bar the actual hardware. The software is based on the author’s Antler program, which provides a simple Windows-based aid to carrying out the design calculations at the heart of successful antenna design. 253 pages in paperback. NEW NEW NEW NEW PIC IN PRACTICE O R D E R H E R E by Howard Hutchings. Revised by Mike James. 2nd edition 2001. 63 $$63 $ Anyone interested in ports, transducer interfacing, analog to digital conversion, convolution, filters or digital/analog conversion will benefit from reading this book. The principals precede the applications to provide genuine understanding and encourage further development. 302 pages in paperback. PRACTICAL RF HANDBOOK by Ian Hickman 3rd Edition 2002 by D W Smith Published 2002 Based on popular short courses on the PIC, for professionals, students and teachers. Can be used at a variety of levels. An ideal introduction to the world of microcon-trollers for hobbyists, students and professionals. 255 pages in paperback. 87 $ Interfacing With C Electric Motors And Drives by Austin Hughes. 2nd edition 1993. Reprinted 2001. 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. Covers all the analog electronics needed in a wide range of higher education programs: first degrees in electronic engineering, experimental science course, MSc electronics and electronics units for HNDs. Text is supported by numerous worked examples and experimental exercises. 312 pages in paperback. 52 69 $$ $$ A guide to RF design for engineers, technicians, students and enthusiasts. Covers all of the key topics in RF: analog design principles, transmission lines, transformers, couplers, amplifiers, oscillators, modulation, transmitters and receivers, propagation and antennas. 279 pages in paperback. NEW NEW NEW NEW TAX INVOICE ANALOG CIRCUIT TECHNIQUES W/DIGITAL INT............$69.00 Your Name_________________________________________________ ANALOG ELECTRONICS..................................................$89.00 PLEASE PRINT ANTENNA TOOLKIT.........................................................$87.00 Address ___________________________________________________ AUDIO ELECTRONICS.....................................................$92.00 ___________________________________ Postcode_______________ AUDIO POWER AMPLIFIER DESIGN...............................$89.00 Daytime Phone No. (______) __________________________________ ELECTRIC MOTORS AND DRIVES..................................$63.00 STD EMC FOR PRODUCT DESIGNERS.................................$103.00 Email___________________<at>_________________________________ GUIDE TO TV & VIDEO TECHNOLOGY............................$63.00 INTERFACING WITH C.....................................................$63.00 ❏ Cheque/Money Order enclosed OR M'CONTROLLER PROJECTS IN C FOR 8051..................$73.00 ❏ Charge my credit card – ❏ Bankcard ❏ Visa Card ❏ MasterCard PIC IN PRACTICE............................................................$52.00 PIC - YOUR PERSONAL INTRODUCTORY COURSE........$46.00 No: POWER SUPPLY COOKBOOK..........................................$99.00 PRACTICAL RF HANDBOOK............................................$69.00 Signature______________________Card expiry date TELEPHONE INSTALLATION HANDBOOK.......................$69.00 UNDERSTANDING TELEPHONE ELECTRONICS.................$70.00 PLUS P&P (if applic): $........................... TOTAL$ AU.............................. VIDEO & CAMCORDER SERVICING/TECHNOLOGY........$69.00 VIDEO SCRAMBLING/DESCRAMBLING..........................$87.00                Orders over $100 P&P free in Australia. POST TO: SILICON CHIP Publications, PO Box 139, Collaroy NSW, Australia 2097. AUST: Add $A5.50 per book OR CALL (02) 9979 5644 & quote your credit card details; or FAX TO (02) 9979 6503 NZ: Add $A10 per book, $A15 elsewhere ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ P&P ALL TITLES SUBJECT TO AVAILABILITY. PRICES VALID FOR MONTH OF MAGAZINE ISSUE ONLY. ALL PRICES INCLUDE GST