I made a combination Theremin/Synthesizer for my sister, who's a musician, and I'm pretty happy with the way it came out. It has the following features:
- Four octaves of continuous pitch variation by moving your hand nearer or farther from an ultrasound sensor
- Digital volume control
- Continuous waveform variation–can generate a pure sine tone like a classic theremin, or one with overtones, which sounds like an 80's synth organ.
- Spectral glide–similar to a Wah pedal or the instrument used in Peter Frampton's 'Do You Feel Like I Do'
- Decay/Sustain–envelope shaping to play notes
- Distortion–sounds like the guitar effect.
- Blue case lighting with 'heartbeat' effect
It's powered by a 5V/16Mhz Arduino Pro 328. Pitch control is done with ultrasound, the other effects by controls which move an LED nearer or farther to a photoresistor.
I've done a pretty extensive write-up of the hardware and software on my blog, might be helpful for someone who's working on a similar project.http://blog.wingedvictorydesign.com/2009/06/20/arduino-thereminsynth-final-walkthrough/