Until now, it has been relatively difficult for the experimenter
to properly control stepper motors using a computer. That’s because most stepper
motor kits sold today interface the step and direction inputs to a parallel port
and then require you to write the software to switch these inputs.
If you need to incorporate limit switches and acceleration and
deceleration of the stepper motor, what started out as a simple job turns out to
be complicated and time consuming. What’s more, parallel port designs can
generally control only one or two motors and some designs don’t allow multiple
boards to be cascaded together.
Fig.1: up to four Serial Stepper Motor Controller (SSMC) boards can be cascaded together, so that you can separately control up to 16 stepper motors from the PC. Note that each stepper is driven via a separate driver board (see text).
The Serial Stepper Motor Controller (SSMC) described here
overcomes these problems. It’s a relatively compact microcontroller-based design
that attaches to a PC’s serial port and provides control for up to four stepper
motors (via a suitable driver board). What’s more, it does away with the need
for special software to control the acceleration and deceleration of the motors.
Instead, you just issue the basic commands and the software inside the
microcontroller does all the hard work for you.
It’s really very easy to program. There are just nine commands
(see Table 2) and these are all entered via a standard serial terminal program
(eg, HyperTerminal). We’ll have more on this later.
Want to control more than four steppers? No problem – up to
four Serial Stepper Motor Controller boards can be cascaded (or "ganged")
together and individually addressed. This allows you to control up to 16 stepper
motors, all from the one serial port.
You can’t do that with most parallel port designs and, in any
case, the parallel port is rapidly disappearing (many laptops no longer include
a parallel port, for example). And with the availability of cheap USB-to-serial
converters, this controller could easily be adapted for use on any USB port.
Fig.1 shows how the SSMC boards are connected. Note that the
SSMC board does not directly drive the motors, since it has no on-board driver
circuitry. Instead, each stepper motor is driven via a separate driver
There are several stepper motor driver kits available that can
be used with the SSMC board. These include kits K179 (unipolar) and K142B
(bipolar) from Oatley Electronics. The unipolar driver board was originally
published as the Mini-Stepper Motor Driver in the May 2002 issue of
SILICON CHIP. It can control both 5-wire
and 6-wire unipolar stepper motors, while the bipolar board controls 4-wire and
Each of these kits has step and direction signal inputs
which allow the user to control the movement of the motor. The Serial Stepper
Motor Controller simply connects to these step and direction inputs on the