place to leave the
box where it could
provide a nice
are simple to use and very affordable. However, they can be
extremely inaccurate. After reading the warnings regarding
the potentially wide variance in the precision of these
sensors, I bought extras to try to put a set together that
were similar in sensitivity. These sensors can certainly be
used to trigger your props, but let’s have a little more fun
and build something cool!
The design I chose would allow me to try these out
and at the same time construct a fun project. It is a head
that would follow our guests as they changed their position
in the room. It utilizes a number of CdS photoresistors to
sense your movements and turn towards you.
I used a stand-alone skull set on a shelf, but this could
easily be added to a complete character as well.
To bring my skull to life, the microcontroller I used was
an Arduino Uno from SparkFun (see Resources) which
would monitor the input pins and measure the changes in
the resistive value of the photoresistors. Upon sensing a
voltage drop, it sends a signal to the servo towards the
sensor measuring the greatest drop and moves the head to
face you (Figure 7).
It uses five sensors mounted on the bottom of the
shelf. One leg of the sensor was connected to 5V and the
other to a 10K pull-down resistor to ground. I then linked
the Arduino input pin to the point between the resistor and
the photocell (Figure 8).
This design is not mine, but was inspired by one done
by Jason Smith of DIY Hacks and How To’s. If you would
like to further your knowledge on the use of photocells,
Lady Ada has written a nice tutorial for Adafruit that can be
found at http://tinyurl.com/p7mxfnd.
The servo needs to be attached to the skull, but I
wanted a more secure connection than simply relying on
hot glue. I want to share with you a little tip on how I route
wire for attaching components when I do not have access
to both sides of a piece. I start by choosing a round object
— let’s say a dowel or coin — the proper size and mark the
holes. I then wrap the wire around a little more than half
the diameter of the coin. Finish the preparations by bending
the tail of the wire so that it is in line with your completed
It is now a quick and easy task to feed the wire
through one hole and with a little maneuvering, have it exit
the other hole (Figure 9 and Figure 10). It’s quick and easy
and works like a charm! The construction was completed by
securing the servo horn to a small wood mounting board
with a couple of small screws.
SERVO 12.2015 27
Step Mat — www.monsterguts.com/store/product.php?
Parallax BASIC Stamp Carrier Board —
Parallax Super Carrier Board —
BASIC Stamp Editor —
Ultrasonic Sensor Kit — www.parallax.com/product/
Servo Mounts —
Arduino Uno — www.sparkfun.com/products/11021