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@siliconchip.com.au

Motor speed controller for 120VAC

I have purchased a Universal Motor Speed Controller from Jaycar Electronics, as published in the October 2002 issue of SILICON CHIP. I live in the USA and of course will be using it with 120VAC line voltage.

Will it work OK using 120VAC? If not, what modifications do I need to make to the circuit?

(R. W., Torrance, CA, USA).

Operation at 120V and 60Hz will require one resistor change. Substitute a 56k&Omega 1W resistor for the 100kΩ 1W resistor. That is all there is to it.

12V LED light wanted

You have had two torch projects based on LEDs (December 2000 and May 2001) and the last one was terrific. I would like to see a lamp made out of three LEDs that runs off 12V. I think that there would be a huge amount of interest in such a lamp because there are a lot of situations where this could be used.

Every boat, motor home and caravan owner would love the low consumption with the lovely crisp white light that these devices put out.

I would like to know whether you would do such a project. If not, could you please give me some pointers as to how to go about it? Would a simple current limiting circuit be the best way?

(N. Z., via email).

Running three white LEDs from 12V is easy - just connect them in series via a 56Ω 0.25W resistor.