Hi folks - I have done a lot of posting here, but not really contributed much.. Hope this makes up for it a bit! This is an incredibly simple theramin which has stunned me with its performance.. I got the idea about 36 hours ago, while looking at the TS555C data sheet, and noticing it could oscillate at 2.7Mhz, and could have extremely small timing capacitors.. I wondered if it could be used as a reliable capacitive sensor, which led to the theramin idea, which led to me staying up all night designing and building it, and all day playing with it! The concept is simple and based on the original theramin.. there are 2 555's operating in astable mode (using feedback from the output to charge / discharge the timing capacitor - this gives equal M/S ratio).. on one 555, the timing capacitance is the 'antenna' and controlled by proximity of earthed entity... I used a 6" strip of ribon cable, and had another strip next to it (but not too close) connected to -8V. The other 555 is set up to oscillate at a constant frequency, which can be tuned. With no 'entity' in the detection range, the 'constant' 555 output frequency should be adjusted to be the same as the frequency from the detection 555 (this process is easier said than done!) Outputs from the 555's are taken to crude low pass filters and attenuators, and drive the X and Y inputs of an AD633J analogue multiplier (the only slightly expensive part in this design).. This produces a signal which is the sum of the two incoming frequencies, modulated by the difference of the two incoming frequencies. Incoming frequencies should differ by (at maximum) about 15 kHz.. So the output from the multiplier is fed to a crude LPF which rolls off at about 10kHz.. This gets rid of the 'sum' component in the waveform (this component is arround 350 to 450 kHz).. Take the output (with care) to an audio amplifier, and have fun! When set up correctly, the audio output varies from 0 (no sound) at a distance (from antenna) of about 1 meter, to about 15kHz when touching the antenna.. But these figures will vary hugely depending on construction and environment. Down side to all this? .. Only one.. I always believed that all I needed to do was get an instrument like this, and it would be a doddle to play .. On this, and this alone, I was Deeply dissapointed!