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
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.
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.
motor is a unipolar
using the wiring
SERVO 11.2016 57
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Figure 3. Full demo.
Figure 2. Wiring the L293D on the BOE.