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Notes & Errata Motorbike Alarm, January 2002: the Veroboard layout shown on page 56 contains a number of errors. The correct layout for both the copper pattern and the parts overlay is shown at right. ticed that the circuit specified a 1µF capacitor just after D1 but in the PC board layout diagram it specified a 100µF (which was supplied). I put in a 1µF unit and that fixed it for about 10 minutes, then it stopped altogether. All that happens now is that the neon goes on, permanently. I did some testing and I think the neon is staying on because the 0.1µF 250VAC in series with T2 is only discharging to about 68V. Beyond that, I have no idea what’s wrong. Can you help please? (T. D., via email) • The capacitor at the cathode of D1 should be 1µF. Trigger transformer T2 is probably at fault. Replace this and the circuit should work. Check the voltages across the 0.1µF capacitor and the 6.5µF capacitors before working on the circuit. A high voltage across them could give a nasty electric shock. Video colour inverter wanted I am a student at Swinburne University, Melbourne. I am currently doing a project involving video editing and production. I am looking for a video colour inverter to add in those effects I have sometimes seen on TV. I was wondering if you had a kit or project that takes a standard composite video signal and inverts the colours. (G. W., via email). • While we have not described a video inverter project, you could adapt the circuit of the Video Fader we published in August 1993. You need to strip the sync off the video signal, invert the video and then add the sync back again. The August 1993 circuit will show you how. We can supply this issue for $7.70 including postage. Stepper motor control needed I am after a circuit that controls a 12V motor. It would control the number of turns in either direction the motor can make; ie, I want the motor to complete 50 revolutions in a clock­wise or anti-clockwise direction. It would also allow the number of revolutions to be stored for later retrieval (multiple storag­es would be nice). Basically, I want to be able to open and close curtains using a motor and be able to open them a preset amount. Do you know of a circuit that would suit my needs and where I could get it? (B. S., via email). • We published a number of articles on Stepper Motor control from a PC during 1997 but one entitled “Manual Control Circuit For A Stepper Motor” in the June 1997 issue is probably the most appropriate for your application. It will drive a stepper motor in one direction or the other for a fixed time. We can supply the issue for $7.70 including postage. Extra inputs for AV distribution amplifier I would like to add additional (switchable) inputs for the AV Distribution Amplifier project (Nov­ember 2001) to cope with the situation of, say, using a Cable TV box, two VCRs and a DVD feeding a TV and also feeding the output back to the VCR’s line-input for recording/dubbing, plus (sound) to a hifi system. This situation must be quite a usual setup in the home and would cope with recording the ‘input’ device at any time, whether the TV was on or off. Is it just a case of buying a video switch box to use before the distribution amplifier or is there a more elegant solution? Or indeed has a project been designed for this purpose? (B. F., Brighton, Vic). • The best way is to use an AV switch box ahead of the distri­bution amplifier, as you suggest. Trying to build input source switching into the amplifier would be messy. A switch box should SC be fine. 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 February 2002  93