Experiment 33: Moving in Steps
286 Chapter 5
The coil inside the motor is holding the shaft in position, and the power that
the motor draws will be dissipated as heat. It’s quite normal for the motor to get
warm while you’re using it. The trouble is, if you use a battery to power it, and you
forget that you have it connected, the battery will not hold its charge for long.Quick Demo
Now that you’ve proved that your motor is functional, how can you actually
run it? You need to send a pulse to each of the four wires in turn, in a rapidly
repeating sequence. If you can also adjust the speed of the pulses, so much
the better. I’m thinking that for a quick and simple demo, you can handle the
challenge simply by using four 555 timers, all of them in monostable mode,
with each one triggering the next.
The schematic in Figure 5-108 shows what I have in mind. It looks more com-
plex than it really is. Each timer has the same pattern of components around it,
so after you create the first module, you just make three copies of it.55510K10K8K222uF1K1K1K1K22uF22uF22uF0.01uF0.01uF0.01uF0.01uF10K10K10K10K10K555555555Stepper
Motor Figure 5-108. A very quick and simple
circuit to control a stepper motor uses
four 555 timers, each in monostable
mode, triggering each other in a
repeating sequence.1
2
3
4
Figure 5-107. This greatly simplified
diagram helps in visualizing the way in
which a stepper motor works. In reality,
almost all motors rotate by less than 90° in
response to each pulse.