I have a small card that does this: card is about 3.1" x 1.3" and is designed to fit snugly in one of the Hammond plastic boxes (don't recall exactly which one right now). It's suitable for supply voltages ranging from 5Vdc through 28Vdc, depending on how you stuff the power supply section. The power supply section also contains a FET clamp that ensures reliable power-up reset. It uses a IRF3708 FET (30V, 62A, 12mOhms) and MBR745 or MBR1045 7A (10A) @ 45V Schottky clamp diode driven from an 8 pin PIC. There is room for a standard-size pot to mount right smack in the middle of the PCB (on the back side of the card). I've got code written for both the 12c508 (976Hz PWM rate) or any of the 8-pin 14-bit core parts (4KHz PWM rate). Both of those offer full-OFF and full-ON modes at the extremes of the pot rotation. However, you can also write your own code, if you wish. We use these in a wide range of places: motor speed control, LED panel dimming (the map boards used in air-traffic control towers), heater controls. Contact me OFF-LIST if this sounds useful. dwayne At 03:17 PM 12/17/2007, alan smith wrote: > > Second....is adjusting the speed. Cheap and dirty is to just > trim the voltage but then you have all that power being disipated > by the resistor. Better is PWM? Anyone have some links to example > designs? I can generate the PWM just fine, looking at the hardware side only. -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist