YourITronics

This motor speed controller powered by the PIC16F873 detects and controls the rotational speed of the motor. When lower than the specification speed, it increases a control electric current. When higher than the specification speed, it reduces a control electric current. It is possible to use when wanting to keep constant speed even if the load to the motor changes.

DC motor speed controller: [Link] - [Via]

Stepper motors are a very powerful, yet accurate type of motor. The ability to ’step’ through motion instead of to run uncontrollably like dc motors do is a great advantage. This write-up shows you how to use an L298 to control a stepper motor.

L298 stepper motor controller: [Link]