In this paper an electronic interface circuit for controlling the speed of a small permanent magnet DC motor with the aid of a personal computer (PC) has been designed and implemented. The basic operation of the proposed circuit is based on the pulse width modulation (PWM) using a pulse generator with variable pulse width to drive the motor circuit. The ON and OFF time periods of the PWM signal are changed by means of mechanical relays connected to the pulse generator circuit. These relays are connected at the same time to the parallel port of the PC via a buffer and a driver. A computer program written in C++ programming language was used to generate the proper digital sequence needed to drive the control circuit in three different speed levels. This circuit was thereafter implemented and tested successfully.