I will use a PWM controller (MC33060A) that will drive a MOSFET, then the motor.
3 potentiometers will allow to fine pitch the 3 speeds coming out of the selector.
Two major issues are :
- There are only 4 wires coming out of the selector : 3 carrying the battery voltage (one at 12V depending on the speed selected, and the 2 others floating) and the 4th goes directly to the motor's (+) pole. No ground, no other way to get the main Vbat.
- And the PWM controller input has its own 5V reference, so I can't put one potentiometer per selector output to set each PWM ratio. I could do that, but the battery voltage is never exactly 12V, it can vary from 11v to 14v resulting in a changing of the fan speed.
I have several ideas in mind to get rid of these. They wil be detailed and tested in the logs.