The circuit is very simple and inexpensive. This is good thing because most commercial stepper motor controller ICs are quite expensive. This circuit is built from standard components and can easily be adapted to be controlled by a computer. If you use cheap surplus transistors and stepper motor, the price of the circuit can be kept to under $10.
Note:
You should be able to substitute any standard (2N3055, etc.) power transistor for Q1-Q4.
Every time the STEP line is pulsed, the motor moves one step.
S1 changes the motors direction.
