press button in top left to start. Bottom right pot controls pwm high range. The one above it controls the mid range. It's hard to get low range duty cycle with this circuit but this shouldn't be needed for the purpose its intended for as I've read most cheap 4 wire fans like the ones I want to drive won't respond well to <25% duty cycle anyway. The other horizontal pot sets the circuit frequency. The top pot is used to tune the pulse train dead time. The left pot was used to squeeze in as much of the duty cycles top end as I could. Its a work in progress and I'm about to ask the breadboard what it thinks. It's not nominal, but I need a solution without shipping time or a loan. if it works, ill try to tune it so that it works on the most unknown fans I have, replace as many pots with fixed resistors as possible, and repost the circuit with info on the fans it will control. Surely eventually someone else will need a one day solution to drive a ton of salvaged fans and think "good thing this guy was poor" lol I also can't shake the feeling that if I stared at this a little longer I could probably just use a single quad op am chip.
