Obligatory Warning/Disclaimer

I first poked around the web looking for light sensitive theremins. I found this very simple light theremin and built it on an experimenters board. It's not bad for so few parts (a total of 7), but the sound was kind of weak (sounded like a mosquito).

So I managed to slap together a circuit that uses a 555 to generate a square wave (now it's more like a beetle). Much nicer. It has pitch and volume control, and two push buttons: one momentarily turns off the sound (a "cutout" button), and the other is an octave drop button.

I didn't draw the power switch or battery in the circuit. The 50k pot is the manual pitch adjustment. All I had was a 5k audio pot for the volume control and it's crappy. Really need a 1k. Also, I used a closed circuit jack so the speaker cuts out when you plug in a patch cable. The 100 ohm resistor is just to limit the pitch from going ear piercingly high. The octave drop is achieved by placing another 0.1 cap in parallel. Each time you add one in parallel you drop the pitch by an octave.

For a case I used a kiddie walkie-talkie (which came with a speaker and 9 volt battery connector). The photocell is in where the antenna used to be. Don't be fooled by the speaker holes: the speaker is not that big. I also put a red LED in what was the morse code button, which could not be reused as a button.

Ideas: Use another 555 as an LFO the modulate the pitch/volume.
Other waveforms, square->triangle

I am not an electrical engineer, so any corrections/additions would be appreciated.

Parts List - All available from Radio Shack

Resistors:
1	100 ohm
1	10k ohm
1	50k ohm pot
1	1k ohm pot
Capacitors:
1	10 mfd electrolytic
2	0.1 mfd
Misc:
1	555 Timer IC
1	Photocell
1	Momentary switch (normally closed)
1	Momentary switch (normally open)
1	On/off switch
1	8 Ohm Speaker
1	1/8" or 1/4" output jack
2	Knob
1	9V battery connector
1	8 pin IC socket
1	Case