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Can the segment currents be elevated a little via the 150Ω resistors or would a green display be more appropriate? (F. D., via email). • The speed alarm LED displays specified are not suitable for reading in direct sunlight. Suitable high brightness sunlight viewable displays are available (in red only) and can be used as a drop-in replacement for the standard displays. Agilent common anode HDSP-H151 are the ones to use. Their output is 16mcd (milli-candela) at 20mA compared to 1.3mcd at 20mA for standard displays. The HDSP-H151 displays are available from Farnell, Cat No 264-313. Phone 1300 361 005. Rev limiter and gear shift indicator I recently bought the Rev Limiter and Gear Shift Indicator (SILICON CHIP, April 1999) from Jaycar at Penrith. However, I just found out that I already have a Rev Limiter in my car and I was wondering if I could bypass the Rev Limiter and use it as a gear shift indicator only. (B. D., via email). • If you already have a rev limiter then don’t connect the Ignition Switch­ er board. Connect the input of the rev limit controller board to your distributor (points, reluctor etc), connect the +12V supply and that’s all that’s needed. Multi-Spark CDI on a VW In the information pack enclosed with a Dick Smith Elec­tronics kit for the High Energy Ignition project (June 1998), there is a section titled “High Energy Ignition or CDI?” Here is a line from the text: ‘of course, we recommend the Multi-Spark CDI design for 2-stroke and 4-stroke engines in motorbikes, outboards and Go-karts, in racing applications and older cars (pre-1975) which do not have lean mixtures’. I have a 1968 1500 VW Beetle which comes standard with the most basic of fuel and ignition systems. In the opinion of your designers should I return the HEI and try to source a MS-CDI kit? If so where do I find a MS-CDI kit? (R. D., Auckland, NZ. • We would definitely not use the CDI with a VW. The long parallel runs of spark plug leads give rise to severe crossfire (we speak from experience here). Build the HEI. Weird fault in touch dimmer After a long wait, I was finally able to purchase the Touch/Remote Controlled Light Dimmer kit described in January & February 2002. It worked straight away, even the IR part with the remote control from my LG TV. Then it started to do something strange. If I tapped the panel twice, it would go to full bright­ ness and cut out straight away. If I held my hand on the panel, it would increase the light slowly, but when it reached full power it would turn off; the same thing happened with the remote. If I did not get it to full brightness, it was fine. I went out for a few hours and when I got back the unit would not turn on at all. What now? (P. E., via email). • We think you need to connect the dimmer up using the low voltage transformer connection shown in Fig.10 of the article. This way you can check operation safely. Check the supply voltage to IC1 for 5V. Note that your problem seems to lie with the phase control extending into the next half waveform so that the lamp goes out when it should be at full brightness. Is the .01µF near ZD1 the correct value and are the 680kΩ resistors correctly in place. Bleed resistors in power amplifier Just a question about the 100W Ultra-LD Stereo Amplifier featured in the May 2000 edition: On the filter capacitors, there are two 8.2kΩ 1W resistors across the supply rails. Could you please tell me what they do? (C. D., via email). • They are bleed resistors. They discharge the capacitors in case the supply rails have been disconnected (or the fuses have blown). Without them, the capacitors stay charged for long periods even after the power is turned off and this could be hazardous if you are working on the amplifier. The same resistors are present in the power supply of the rack case version presented in the Novem­ber & December 2001 issues. Notes & Errata Battery Guardian, May 2002: instead of being listed as 05106021, the SC PC board should be 05105021. 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 July 2002  89