Illustrates how a 4-phase stepper motor can be controlled bi-directionally using a conventional rotary switch

A high school student recently contacted the author for help in building a robotic arm for a school project. He had some stepper motors on hand, and was looking for a simple way to utilize them. Unfortunately there didn't seem to be any really simple way to do it - nor could the author find any published design to help - at least not any that fitted the description of "simplicity itself".

A typical stepper motor control system incorporates a microprocessor control unit, a drive card, and a dedicated power supply unit - as well as, of course, the motor itself. The author perceived in this a basic problem. The barrier between owning a stepper motor and actually using it is fairly great. Contrast this with the easy availability of stepper motors today, particularly from cast-off 5¼in. disk drives and fax machines, and you clearly have a problem waiting for a solution.

This project describes a simple way to rotate a four-phase unipolar stepper motor with the help of a single rotary switch, just eight inexpensive rectifier diodes, and some incidental components.