Parallel Port Stepper Motor Driver With Discrete Components

Using PC`s parallel port is a convenient way to control a stepper motor. For unipolar stepper motors, up to two motors can be controlled with the 8bit data line. The standard way of connecting a unipolar stepper motor to the parallel port is to use a Darlington driver such as ULN2003 and there are already many examples out there on how to do this.
Parallel Port Stepper Motor Driver With Discrete Components - schematic

In this post, I will show you how to build a simple stepper motor driver using discrete MOSFET s. In the circuit diagram below, you will find that the four power MOSFETs are used as switches for each coil in the stepper motor (the stepper motor I used in this example is a MITSUMI M35SP-9. In theory, any uni-polar stepper motors should work with this circuit). A pull-down resistor is attached to the gate of each MOSFET. This is important as otherwise the interference from the port would prevent the MOSFET from switching reliably. The following C code sets the data port (pin 2, 3, 4, 5) to high in order so that the stepper motor would rotate clockwise. If you want the motor to rotate counter-clockwise, simply change the output order to 8, 4, 2, 1.

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