Dan's Tesla Info Website Non Linear Pitch Thanks Christopher. I'm actually building your theremin circuit  for my Uncle who has the desire to own one of these things. Ironically, I've been working on my own optical theremin version which will be used to control one of my solid state Tesla coils I'm building. There will be two optical sensors, with one controlling PRF (pitch) of the system, and the other controlling pulse width (or rather arc length / volume) Obviously, because of the RF put out by the tesla coil, I needed to go the optical route. Could be possibly the first high voltage theremin!!! Attached is a photo of this mini coil hitting 48" arcs. By adjusting the PRF of the system, you can create very cool audio effects from about 20Hz to about 1kHz. Dan