In “Circuit provides bidirectional, variable-speed motor control,” Jean-Bernard Guiot, DCS AG, Allschwil, Switzerland describes the design of a simple, bidirectional motor controller with a speed adjustment capability. It uses everyday components with tolerances and ratings that are unimportant as long as they sustain the required voltage, current, and power.

He used a transistor-based H-bridge that allows two directions of rotation and a chopper to control the upper arms of the H-bridge, thereby enabling the speed adjustment. The circuit was a help in determining speeds or gear ratios to use during test and adjustment of prototypes on small machine tools.