token:
Thanks for your compliments. It really isn't that complicated; I learned everything I needed to know, designed it, & built it in under 1-week. I only took one circuits course in college & most of that material I couldn't remember without review. I also have no professional experience in electronics.
Brad:
It handles 4A. The details including costs are on my updated site:
PWM Homepage
webmedic:
It adjusts the speed of fan(s) according to the temperature of a probe, displays the speed of the fan in 10% increments, has an RPM monitoring passthrough, & has a switch that switches the fan from the thermal speed control to 12V (manual full speed override switch). The switching for the override can also be done by a Digidoc. The speed control is accomplished using PWM (Pulse Width Modulation). A power MOSFET fan output makes the speed controller very efficient & capable of driving up to 4A of fans (or a single 4A fan, which I have not been able to locate yet :P).