This simple circuit and program listing allows the Maximite microcomputer (SILICON CHIP, March-May 2011) to control a stepper motor. It could be expanded to allow for the control of multiple motors, with four of the Maximite’s external I/O pins used to control each motor with identical driver circuits. A ULN2003 Darlington transistor array (IC1) switches current through the stepper motor’s two windings in either direction. When one of the four Maximite output pins (8, 12, 16 & 20, corresponding to I/Os 19, 17, 15 & 13) goes high, the corresponding output pin on IC1 goes low, sinking current through a motor winding. Conversely, when these pins are high, the corresponding Darlington transistor is off and so no current flows through that portion of the winding. Maximite Stepper Motor Interface Circuit Diagram The centre tap of each motor winding is connected to a current source comprising PNP Darlington transistor Q1 and some resistors. The maximum current is determined by the res...