I'm in the process of making a fan controller for a water cooled PC. The idea is to have an Arduino Nano control three 20-30W channels to which one can attach fans/pumps (three, because then you can control all intake fans, all exhaust fans and a pump separately) based on a number of temperature sensors. All values and controls will be displayed on a serial LCD housed in a 5.25" bay/
At the moment, I figured out how to read the RPM of a fan without using an interrupt (the Nano only has two interrupt pins, and I want three channels). However, I ran into a problem with the fan control: when I drive the fan with PWM, the RPM-signal isn't correct anymore. I guess this means the hall effect sensor that gives you the RPM-signal needs a constant power source. The problem is: I don't know how I can make an Arduino put out a constant power source with variating voltage.
Can anyone help?