Here are some instructions on how to make your own photocell theremin inside a Altoids box:
(2) 555 timers
(2) Photocells or phototransistors
(2) .01 mF capacitors (play with different sizes for different sounds)
(1) 1K resistor
(1) 1/8" audio female input or speaker
(1) Hookup wire
(1) Toggle Switch
(1) LED indicator light
(1) 9V battery and battery connector
(1) Altoid Box
The circuit diagram is above (taken from popular science) along with the PCB design (designed using Fritzing use the fzz file for labels and part positioning, note second battery labeled ToggleSwitch is not a battery but a toggle switch).
Here is a project that I created using this circuit as a starting point just as an example to show how you can get creative with it!