I have a bit of a problem that in hoping someone can shed some light on.
I have a 4 wire fan (from a power mac g5) and I found that the pinout is positive, negative, PWM and rpm output. It's a bit strange in that the 12v must be connected constantly and the fan speed is actually controlled with either a variable voltage to the PWM pin or I'm guessing an actual PWM of 12v would be more likely. I have tested this with 12, 5 and 3v to the PWM input and it works.
I'm not trying to PWM the main 12v rail, most examples I've seen show this.
So what I am trying to do is control 4 of these fans with an arduino uno.
If I take a 12v wall wart and power the 12v rail on the fan, then use a mosfet to produce the 12v PWM signal using the arduino to drive the PWM input on the fan, is this the way to go? Can anyone show me an example of how to do this using 1 12v PSU?
My knowledge of transistors/mosfets is nil!