To regulate the speed of a motor trough a simple potentiometer. With a small microcontroller this job can be done quite easily.

We needed of a speed regulator to control the motor of our cnc machine (a small machine, for pcb); to achieve the result we've used a 8 pins microcontroller, a 12f675, using the analog to digital internal converter and using the pwm to drive 3 power mosfets.

The circuitry is classical, a 12F675 microcontroller and a small 7805 to get from the same power of the motor the voltage necessary to the pic itself. The circuit has been tested the circuit with three IRF540 and IRF730 mosfet and with a 540 class motor (Mabuchi) the mosfets remain almost cold. The use of logic gate mosfets is preferred (IRL series).

Here follows schematics and board, remember to put a power diode and a couple of capacitors over the terminals of the motor as suppressors: