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a way of making it capable of handling a 450W load? (R. B, via email). • The limit of 250W is set by the Triac’s dissipation limit. To increase it requires the addition of heatsink to the Triac. This is not easy to do because of the very confined space on the PC board and the limited amount of space within the wall cavity that the dimmer is installed in. Switched control for speed circuit I have built a motor speed control from a circuit published in your June 1997 magazine. I am a novice builder but managed to get the circuit to work as intended and control a 12V motor. I would like to know is if it is possible to replace the 5kΩ speed control pot (VR1) with a bank of resistors of different values that can be switched in and out of the circuit with a rotary switch. This would give a stepped range of speeds for the motor. I have tried this but can’t get the circuit to work properly. (D. C., via email). • Just get a single-pole 12 position rotary switch and wire eleven 470Ω resistors around it. The wiper of the switch then becomes the wiper of your “switched” pot. How to eliminate plugpacks I have been looking in to ways to try and eliminate my bulky power packs for my computer peripherals. I read the article on the PC Powerhouse (SILICON CHIP, December 1999) and found it won’t quite do what I need but it is a great concept. I have seven power supplies all up: 4 x 12V, 2 x 9V and one 7.5V, all of which are rated at 1A DC. I am not sure what they are actually drawing but I am sure they are Notes & Errata 4-channel UHF rolling code receiver, July 2002: the circuit on page 20 has the Set and Reset labelling on the four flipflops swapped over, ie, pin 6 on IC1a should be Set (S) and pin 4 should be Reset (R). In other respects the circuit is correct. Digital Reverberation unit, December 2000 & January 2001: the output resistor from pin 6 of IC3 is shown as 10kW on the PC board diagram on page 73 of the January 2001. It should be 150W, as shown on the circuit in the December 2000 issue. Also, the not all 1A each. I would like to be able to cater for additional power packs in the future. As I only have two power points in the room and power boards are useless to try and fit these things on to, I am hoping you might have a better suggestion. (R. A., via email). • Depending on current drains, you may be able to use one or two 12V DC plugpacks to run all your 12V accessories, then one 9V instead of two 9V plugpacks and so on. That way, you don’t build anything but you can eliminate most of the plugpacks. The only point do you have to watch is to make sure that all the peripherals are negative chassis, ie, the 0V line connects to the earthed metalwork of the peripheral device. Maximum cable length for water level gauge What would be the maximum length for the figure-8 cable between the sensor and the display unit in the water level gauge featured in the April 2002 issue of SILICON CHIP? (J. E., Silverwater, NSW). • This is not something we have wiring diagram one page 68 of the January 2001 issue has the earth and signal connections reversed on the output of the digital reverb board. Remote Control Extender, June 1996: this project was previously found to be incompatible with Mitsubishi VCRs. However a reader has discovered that it can be made to work if the Mitsubishi VCR’s remote is used to program an AR-1712 (4-in-1 model) learning remote (available from Jaycar). checked but it should be OK with cables up to at least 10 metres. Battery charger with UC3906 I am looking for an article describing a “Sealed Rechargeable Battery Charger”. In particular, it uses the UC3906N IC. Could you please advise me which article I am looking for and if I can purchase a reprint from you? (A. B., via email). • We first featured the UC3906 in July 1989 in an article entitled “Intelligent charger for 12V gel batteries as just a PC board. Later, it was featured in a full-blown charger for 6V/12V batteries, and the data sheets were in March 1990. Subsequently this charger was substantially revised in August 1992. However, if you want a comprehensive charger which includes SLA batteries we would recommend the Multi-purpose fast charger featured in the June & July 2001 issues. We can supply all these issues (except August 1992 available as a photostat) for $7.70 each, including postage. SC 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 www.siliconchip.com.au