used a Parallax Propeller prototype
board; for the audio, I hacked an
old MP3 player. When I retrieved
the box for the upcoming
Halloween, the MP3 player was
not working. I either had to hack
another MP3 player (which was
really quite hard) or find another
Luckily for me, Parallax had
just released their Propeller activity
board which had all the audio stuff
I needed right there. The activity
board is the brains of the current
In order to turn the cam, I
decided to use a stepper motor
and a Step Stick driver board.
Initially, I wanted the monster to
be in different “phases,” and I was
going to slowly turn the wheel
back and forth in a slightly curved
area of it to simulate a relaxed and
“breathing” state where the lid
would just slowly raise and lower.
I later scrapped that idea, but still
have that ability if I ever want to
For detecting “victims,” I used
a PIR sensor. They are very simple
and very reliable. Basically, it’s
wired directly to pins on the
To control the strobe light and
fog machine, I needed to use a
relay board. The strobe light didn’t
even have an on/off button; it was
basically just plugged in. So, I
spliced the wires and ran them
through the relay board. The fog
machine was a little more
complicated as it had a remote
that released the fog once the unit was heated up.
I hacked the remote section and ran that through the
relay so the unit would have power to heat up and the
relay would simulate pressing the remote button. Your
strobe light and fog machine might be different, so it make
take some trial and error to figure it out. However, with
the activity board and a relay board, you should be able
to control just about anything.
The last bit of electronics which has not been
mentioned so far is the audio amplifier. The audio from
the activity board is not nearly loud enough to make the
kids jump out of their shoes, so I took apart an old guitar
amp and put those parts in the box. (If there were room, I
As you can see in the photos, everything was glued
and screwed to the sides of the box. I drilled a hole in the
back bottom area of the box to run the power cord for
the power strip.
Constructing the Box
The first thing I needed was the box — simple enough.
I used some leftover wood from building a fence, but you
obviously can choose any kind of wood that you can get
September 2014 63
Here, you can see the teeth on the cam.
The entire contents of the box.