I built a motor controller for a stepper motor using a 'full step' configuration and an HC11 microcontroller to control the motor speed. The idea of a stepper motor is the potential for accuracy. The HC11 can be interfaced to accept l/P (inputs) from any electronic device and be programmed to react in the way that you need to controller the motor speed. The microcontroller is very expensive when compared to a potentiometer though, but gives much flexability in the interfacing. The program for the HC11 is written in assembly language. The stepper motor I used used 12 VCD. Also I used 4 NPN transistors, 4 diodes, 8 resistors, and TTL IC to interface the HC11 to the motor control curuit. I have a schematic that worked in controlling the motor.