Servo - November 2016

of the positive characteristics to using a stepper motor. Four I/O pins are used to control the stepper motor; each pin is an output controlling the specific phase.

For door control, we’re not as concerned with precision in the steps per se — at least in this demo. However, if your system involves a gear driven model and you want position control, these would be important properties.

Figure 2 shows the wiring of the L293D on the breadboard area of the Parallax Board of Education (BOE) for use in this demo. See the full schematic for more details.

Stepper Motor Demo

In the previous articles, I showed you the demos I built for the servo controlled door and DC motor controlled door. In this article, I have built an entirely new demo (Figure 3) with a unipolar stepper motor in place of the servo/DC motor, and with magnetic sensors in place of the optical sensors and custom contact switches on the previous demos. Other than those changes, the demo units are virtually the same. Remember, the limit switches are interchangeable. I could have just as easily used optical limit switches here or even mechanical. However, this article demonstrates magnetic limit switches.

You may have noticed the BOE is upside down on the demo. That’s because I needed the breadboard area to be close to where the stepper motor wires came through the back due to their short length. Figure 4 shows how the wires come through behind the BOE.

The stepper motor is mounted in the same position and manner as the servo and DC motor in the previous demos. Like the previous demos, I chose a mobile power pack. Figure 5 shows the back side where the power supply sits opposite the BOE. The stepper motor wires run in between through the hole shown in Figure 4.

This stepper motor is a unipolar motor. However, using the wiring

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