Basic DC Fan Controller
PWM is used because it wastes much less heat than "linear" methods like that shown in your schematic. A TO-92 voltage regulator and a DIL8 microcontroller is all you need to read the voltage from a 10kohm pot and then generate a PWM signal to put through a power MOSFET on the low side of the fans. You could even substitute a 555 and associated passives, but the MCU will give you better control.







simulate this circuit &ndash; Schematic created using CircuitLab