I recently completed a long-standing goal: I shelled out for an Arduino Duemilanove, got my hands on some components, and built some stuff. Toy Project #1 was the Photoflexophone, perhaps the least practical musical instrument ever invented. Have a look:
The button on the breadboard selects between the photoflexophone’s three modes: light, flex, and off. The off mode is the most important, since the thing makes infuriating noises if you leave it on. The other two modes allow you to produce different pitches either by shining varying amounts of light on the photocell or by bending the flex sensor. If you change the flex sensor out for a thermistor, you can also play it by altering the ambient temperature in the room. If there’s ever been an instrument controlled by anything less practical than ambient temperature, I’d desperately love to hear about it.
At the moment it plays notes in the A minor harmonic scale, but it can play in any mode or just a continuous range of pitches. The sound all comes from a piezo, though, so it’s pretty terrible.
Ingredients: Arduino, breadboard, flex sensor, light-sensitive resistor, push button, piezo element, a few ordinary resistors, and a whole bunch of jumper cables.