■ PHOTO 3. Motor control dialog.
‘Use Commands’ checkbox is for
future capability to queue up
multiple commands so a motor
control profile can be built and stored,
for example, an acceleration or
The temperature indicator
samples the heatsink temperature on
a periodic basis. Smarter software can
use this to set limits and to prevent
self-destruction of an overtaxed
controller. The temperature can also
control the fan operation to lower the
power drain when the system is idle.
For some information on the RoHs
For information on the CodeVision
As I mentioned in Part I, dealing
with large currents on small PC boards
can be dangerous ... I reminded myself
of that fact when I first powered up
the board, so I brought the controller
to life in stages.
First, I populated the DC/DC and
power supply components and tested
for correct operation. When I first
powered it up, a capacitor blew, just
missing my nose peering into the
works!! This was due to my rushing
the assembly and putting it into the
board with reversed polarity. Luckily,
there was no shrapnel.
Next, I added the opto-isolators
and related logic to be sure the
correct signals were produced. I
powered it up again and measured
signals with an oscilloscope.
This was followed by the driver
section and protection components
buildup, everything except the FETs. I
scoped the driver outputs again to be
sure nothing was disturbed.
Lastly, the FETs were added on
the heatsink before being soldered
into the board. Particular care must be
taken in this step. Each mounting tab
is electrically connected to the center
pin of the FET. They are NOT electrically connected in the design. This
means that each FET must be isolated
from the heatsink. This is done with an
insulated phenolic washer and a
thermally-conductive pad instead of
heatsink grease. This is a lot less messy
and provides the needed isolation.
Each FET was tested with an ohmmeter to be sure there were no shorts.
The board passed all of the above
tests, so it was now time to try some
motors. I connected two 12-volt batteries in series for 24 volts and connected
those to the power inputs of the motor
controller. I connected the Silver
Bomber motor to the power outputs of
the controller, and finally connected
the CPU test board to the motor
controller. Photo 4 shows the finished
setup and you can see the serial
connection going to my PC on the left.
DID IT RUN?
You bet it ran. I had great control
over what we estimated to be a 30-35
amp motor, from stop to moving
slowly, all the way up to full speed. In
Photo 4, you can see the propeller I
had on the motor shaft whizzing
■ PHOTO 4. Test setup configuration.