theremin as a capacitive sensing device

Posted on Feb 6, 2014

Here we show a little Theremin module which plugs onto a Arduino Board that gives out the tune to a speaker or puts out the tune as control signal like MIDI, Servo etc. We were using this device not only as a musical instrument, various kinds of proximity sensors, pointing devices or as interface in combination with Processing, Max or Pd have been

theremin as a capacitive sensing device
Click here to download the full size of the above Circuit.

build with this technique. The Theremin Module itself is as little LC type Radio frequency oscillator which generates a radio wave and gives out the frequency signal to the Arduino board. The Arduino itself acts in this case as a accurate frequency meter which transforms this frequency deviation into sound or control signals. Since you will find numerous articles in the Web describing the principle of a Theremin we leave here only that brief description. If you have a look at the Oscillator schematic you see the components L1 and C1 that are forming a resonator responsible for the oscillator frequency of about 4. 1 Mhz. The Gates IC1A and IC1B are building an analog amplifier block which is rising the oscillator signal to be fed back to the resonator. Capacitor C3 put an amount of energy back to the input as positive feedback so that an steady oscillation occurs. The Gates D and C are conditioning the wave into a digital logic level squarewave signal for the Arduino board Care must be taken in the choice of the parts L1 and C1. C1 must be a ceramic capacitor NP0 type (zero temperature coefficient) and L1 a high Q inductor suitable for high frequency such as a Neosid 00612299 but for the first test a standard 10uH Choke will do also the job. Because the oscillator frequency tends to drift by ambient temperature changes the circuit should be capsuled in a little plastic box. The antenna length should be not longer than about...

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