Digital Theremin, University of Glasgow () - from the Archives

Digital Theremin, University of Glasgow

Lindsay Reid and Brendan

The digital theremin uses CMOS oscillators and logic gates to produce two DC Levels. One DC Level varies with the proximity of the player's hands from the pitch antenna, and the other DC Level varies when the volume antenna is approached. This design of circuit is advantageous because it pretty much depends on the imagination of the constructer, what he/she wants to do with these DC Levels. Obviously, a basic instrument would have the DC Levels controlling a voltage-controlled oscillator (VCO) and voltage-controlled amplifier (VCA). However, such a DC Level could also control a voltage-controlled filter (VCF). There are numerous designs of such voltage-controlled circuit elements. In this circuit which you can download, it shows a VCO and VCA block based on commonly available commerical integrated circuits. Each block is controlled by a CMOS oscillator/logic gate stage, of which there are two (one for each antenna). The design has proven very successful in recording, where the signal-to-noise is of HI-FI quality, and also in playability, since the tuning and volume offset is easily trimmed by adjustable knobs on the front panel. The pitch control circuit has been revised and can easily replace the original circuit. (Designed and built by Lindsay Reid and Brendan Dougan for a final year project )

Please Do look carefully at the updated digital theremin schematic. It corrects a few mistakes and omissions in the original circuit. Zener Diode is drawn incorrectly - Be aware that the "2V7" diode should be symbolized as a Zener, with the cathode up, not down, as shown. (It is a 2.7 volt Zener diode.) Thanks to Art Harrison for this tip!

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We have constructed two Theremins, one based on an analog circuit and the other employing digital techniques. Photographs of our completed instruments are shown above. The visual appearance of the analog and digital versions contrast sharply, which was deliberate, in order to reflect the different design approaches used in the digital device and the more 'traditional' analog instrument.