Hardware Hacking 51You can put the cell at one end of an opaque tube (such as a drinking straw
painted black) to make it very directional in its light sensitivity: it will only
respond to light aimed directly down the tube. This is the core technology of
certain carnival shooting galleries.
You can place the photocell in your mouth and make a very expressive controller
that responds to both the change in light level as you open and close your mouth
and the conductivity of your saliva-laden tongue (a naughty extension of the
licked-finger-on-circuit-board effect.) Once again: DON’T EVER THINK OF
TRYING THIS WITH ANY CIRCUIT THAT IS EVEN BATTING ITS
EYELASHES AT A WALL OUTLET!!!
Try placing a fan between a light source (such as flashlight/torch) and the
photocell, or reflecting light off a record turntable – you may hear a vibrato effect
or other wobbly modulation. If the toy has blinking lights or LEDs you can tape
the photocell to one of the lights and the toy will “self-modulate” itself to
produce interesting patterns.
A photocell can be a good compromise between the fluid, if somewhat
unpredictable (and occasionally dangerous,) effect of the finger on the circuit
board and the more controllable but less expressive potentiometer. You can use
it as a very responsive performance interface, to interpret hand shadows or
flashlight movement, or as an installation sensor, reacting to ambient light and
the shadows cast by visitors. We’ll look at more photocell applications in
Chapters 18 and 22.
Electrodes
If you want to use your fingers to connect points on the board that are widely
separated, or you just want a more formal playing surface, dimes or other silver-
plated coins make excellent electrodes. Strip 1/4” of insulation off both ends of
a few 5” pieces of wire. Solder one end of each wire to one of the “sensitive
points” you’ve found on the circuit board, and solder the other end to a dime.
Arrange the dimes in a pattern that lets you bridge them easily with your fingers
(but avoid direct shorts.)