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Compact fluoro inverter for horse float I would like to modify the Compact Fluorescent Lamp Driver kit (SILICON CHIP, July 2000) to operate off a 24VDC supply. We have a horse truck that has on-board 24VDC only, with ample cur­ rent. We use this truck to transport horses to venues. We also sleep in the truck. Some venues we attend don’t have 240V avail­able and we are forced to use torches and Tilly lamps at night. My electrician friend and I have thought about wiring up the truck using CFLs as a primary lighting source in the horse area and sleep- the buzz? Could I connect a capacitor or retrim the circuit RC network to reduce or increase the timing and thereby eliminate the buzz sound? (M. O., via email). • A buzzing sound can be produced by the Mosfet and is due to its rapid switching. The same effect can be heard with SCRs, Triacs and the power transistors in high power audio amplifiers when handling the higher frequencies. Having said that, it should only buzz while starting and then any buzzing would be louder from the ballast as the starter is then out of circuit. If you are concerned with the buzzing during starting then the only way to stop it would be to fully encapsulate the unit in epoxy resin. CD input for 50W module Will your 50W amplifier module (March 1994) accept a CD input without pre-amplification and still ing quarters. These are thoughts on modifying the above kit. All the ICs would have to run from a 12V regulator and the centre tap of the primary of T1 would be taken to +24V via L1. The voltage rating of the 2 x 4700µF electros would be upgraded to say 35V. I also wonder if the primary windings of T1 have to be increased by a few turns? (B. B., Mittagong, NSW). • As you state, it will be necessary to run the ICs from a 12V regulator. The inverter transformer will need to be rewound with more turns on the primary; ie, 2 x 12 turns instead of 2 x 6. The 16V zeners should also be increased to 39V. produce full power? If not, can I increase the gain so that it will? If so, how? (C. C., via email). • Input sensitivity for full power is 1V so a CD player could overdrive with its 2V (max.) signal. Fit a 50kΩ log pot and 22µF bipolar capacitor from the wiper to the amplifier input to solve the problem. Cheap headlight dimmer wanted I am looking for a way to dim my headlights to act as park­ing lamps. Just wondering if there is a cheaper way than the $50 Jaycar kit for the Daytime Running Lights project featured in the August 1999 issue, to run them at about 50% brightness? (A. L., via email). • Have a look at the 10A Speed Controller kit we published in June 1997. It is available from Jaycar (Cat. KC-5225) for $21.05. You will need the dimmer modification featured in the October 1997 issue. Jumbo LED clock has faulty displays I am having problems with the Jumbo LED Clock in the March 1997 issue. I purchased the displays and most of the ICs from Jaycar. The hour display blinks at one-second intervals, the third display does not light at all and some segments in the fourth display do not light up. I have replaced most of the ICs. (D. B., Port Macquarie, NSW). • The fact that the hour display blinks at one second inter­vals suggests that there is a short on the display board (or between the inter-board connections) associated with the flashing colon; ie, the DP connections to DISP2 & DISP3. The display that does not light is likely to have an open circuit in the connections to the common cathode line, pins 3 & 8. The missing segments for the fourth display will be associated with open circuit connections to the relevant 390Ω resistors, the display pins or the interboard connections. We do not think it should be necessary to replace any ICs as most of the problems are likely to be due to missed or bridged solder connections. You may need a magnifying glass to carefully inspect the PCboard for these faults. Notes & Errata Structured Cabling Systems (August 2000): in the Cat5 cable diagram on page 74, pair 1 (blue/blue-white) are shown reversed - blue should connect to pin 4 and blue-white to pin 5 of the RJ45 jack. Fortunately, this diagram would rarely be translated into practice because the vast majority of RJ45 jacks are colour-coded to show which SC wires go to which pins. 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. 90  Silicon Chip