From the MAKE Flickr photo pool
Wow – Holotone grafted a toy phone circuit to an old PC gaming joystick and added onboard speaker, touch contacts, photocell/LED control, pitch control and more! – thus the Tiny Optotouch is born.
The joystick itself is just two potentiometers, so I use them as switchable pitch adjustment on the X axis in the opposite direction of the envelope-modulated optical pitch. The Y axis is switchable subtle volume / fuzz.