18 SERVO 12.2016
revealed the problem and the hunt for an inexpensive
solution began. After several ideas were designed and built,
a final method was chosen. It consisted of a two-transistor
driver circuit which could be easily built and added into the
enclosures with the Propeller boards (see Figure 2 and
Figure 3). This circuit has performed flawlessly through all
of our tests to date, and I no longer consider this an issue.
Well done, Brian!
Now that the nod actuator was working as planned, a
larger board needed to be constructed to provide the same
signal levels to the actuators for the skeleton body. My first
plan was to use six actuators for the body movements.
Once the skeleton was constructed, we decided to
substitute pneumatic cylinders for the arms which meant
we only needed
four of the six
transistor circuits. The board was already constructed, so
we now have two extras for future expansion.
Commanding Pneumatics and
The pneumatics and the electronic eyes are not
proportionally controlled. The eyes simply need to be turned
on and off, and the pneumatics energized and de-energized. We use the same switch to accomplish both of
these actions. Brian achieved this by fabbing up a small
circuit with a PICAXE08M2 microcontroller at its core (see
Figure 4). After being covered in shrink tube, the board
was installed in line between the Propeller boards and the
skeleton’s eyes and pneumatic solenoids. We did not need
one for the witch; her eyes would stay on all the time so
they only needed to be connected to power.
Some basic code was programmed into the PICAXE
and it was ready to go. Its purpose was to measure the
PWM and convert it, allowing it to turn the port on and
off. If the pulse is greater than 1.5 ms, it turns the ports
on; if 1.5 ms or less, it turns it off (see the sidebar).
Although similar circuits are available commercially, we
decided to build our own so we have complete control of
Trigger and Light Control Using
With so many devices to control, we decided to
incorporate this scene into my master DMX control system.
Figure 2. The
makes it work.
Figure 4. Just turn it on, and then turn it off.
Figure 5. DMX box links
to the main show
Figure 3. The two boards working