Function Generator/Oscillator VCO

Here is a simple circuit based around the 8038 chip that will create Triangle, Sine, and Square waves along with others. http://www.mitedu.freeserve.co.uk/Circuits/Testgear/funcgen.htm Simply add a few photo resistors and you got a 3 wave opto Theremin! A little note in the extra circuitry in the schematic, this person also includes the power supply and the output stage. I would just ignore those.