Small computer interface to a stepper motor

A Commodore VIC-20 computer has been interfaced with a stepper motor to provide an inexpensive stepper motor controller. Only eight transistors and two integrated circuits compose the interface. The software controls the parallel interface of the computer and provides the four phase drive signals for the motor. Optical sensors control the zeroing of the 12-inch turntable positioned by the controller. The computer calculates the position information and movement of the table and may be programmed in BASIC to execute automatic sequences.