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Building a Simple Unipolar Stepper
Motor Controller
By
Amber Grey Mathes
November 9, 2007
Executive Summary
Motors are used in all types of applications from the electrical to the mechanical and beyond. Stepper motors are used everywhere in a wide range of applications, for instance, the common floppy drive uses a stepper motor and PC hard drives used to use them for head positioning. So designing a mechanism for controlling the movements of such motors is very important in today’s society. These controllers can range from simple to complex and can include electrical devices such as buck and boost converters. Our project only requires a simple motor controller for a unipolar stepper motor that enables a step when a signal is passed indicating the necessary information has been received.
Keywords
Unipolar Stepper Motor PIC RS Serial Connector/Port Zener Power FET H-bridge
Introduction
Designing a simple controller for a unipolar stepper motor is relatively simple as long as the application does not require a vast array of different functions to be run by the controller. A simple controller such as team 8’s can be run from any microport; however, this application note will utilize the serial port found on any standard PC. Stepper controllers can be relatively expensive and some can be quite cheap, the trick is to know what your controller needs to do and how to implement those functions if deciding to design and build your own.
Objective
To demonstrate how to build a simple unipolar stepper motor controller using nFET’s a PIC and Zener diodes.
side to pin 2, (2) negative side into pin 3 and positive into pin 1, (3) negative side into pin 5 and the positive side into pin 4, finally (4) negative side into pin 6 and the positive side should go directly to ground. The RS232 must be connected to a PIC in this case we will use the PIC18F4520 (Fig. 4), pin 11 of the RS232 should be connected to pin 25 (transmit) of our PIC, and pin 12 of the RS232 should be connected to pin 26 (receive) of the PIC. Finally the PIC needs to be powered, connect power to pins 11 and 32 and connect pins 12 and 31 to ground. The gate of your transistors should be connected to pins 19-22 of the PIC, in any order, but be sure to wire this in a way you will be able to remember quickly. For convenience Fig. 5 depicts gate, drain, and source on the IRF530N a common power FET. The source of the transistors should be connected to the motor leads and the drain of S1 and S3 (from Fig. 1) should be connected to your battery and S2 and S4 should be connected to ground. Your stepper motor should come with designations for the different leads; COM A and COM B of the stepper motor should be connected to ground. For our stepper motor the source S1 should be connected to lead A of the motor, S2 to lead A, S3 to B and S4 to the B\ lead. Finally to prevent burning your circuit out a Zener diode should be wired between gate and source of each power FET. For our project a 6V source is used and 12-15 volt Zener diodes should be more than sufficient. The only thing left is connecting and programming your PIC and a program for controls, but that is another day another demon.
Conclusion
A unipolar stepper motor controller is relatively easy to build for simple applications. After wiring your Zener diodes between gate and source of all four transistors, this circuit is very durable and it is very unlikely, if done correctly, that you would burn out your motor Regardless, stepper motors are pretty hard to burn out. If you wired your circuit correctly you should have a durable, reliable, and inexpensive stepper motor controller.
Figures
Fig. 1 H-bridge using simple switches
Fig. 2 Power FET Schematic (gate to left, drain top lead, source bottom lead)
