The Minimin Aims To Be The Simplest Theremin

Hackaday.io user [eagleisinsight] is a high-school hacker whose dreams of becoming a Theremin virtuoso were thwarted by the high cost of a commercial instrument. His response is the Minimin, an affordable Theremin design using a 555 and an ATMega328.

The 555 is configured as an astable oscillator running at about 5MHz and with a loop antenna attached to its timing capacitor. The parasitic capacitance of the musician’s hand against the antenna varies the frequency of the oscillation, as you would expect. In a classic Theremin the signal from the 555 would be mixed with the output from a fixed 5MHz oscillator and the sound would be generated from the difference between the two oscillators, but in [eagleisinsight]’s design the 555 clocks the ATMega328’s timer. The processor can thus read the oscillator frequency and use that value to control a waveform generator.

There is something missing from this Theremin: a second antenna for volume. For now a potentiometer does that job, but [eagleisinsight] is working on a MkII device to correct this omission, along with plans to replace the ATMega with an XMega processor whose DAC can produce a sine wave output and whose USB port can be used to enable the Minimin as a MIDI controller.

As you might expect, we’ve covered numerous Theremins over the years here on Hackaday. You can browse them all, but we’d like to draw your attention to a typical breadboard instrument using a soda can antenna, people using Theremins as Guitar Hero controllers, and Léon Theremin’s terpistone, a full-body instrument.

5 thoughts on “The Minimin Aims To Be The Simplest Theremin

  1. Yes, I can imagine a commercial Theremin being expensive, especially since demand can’t be high.

    But a Theremin is simple. An oscillator that can be varied, beating against a fixed oscillator. A third oscillator used to control volume. Popular Electronics in the sixties showed how to make one from a common ac/dc radio. The effect can be done endless ways, though maybe not giving the same action. Eliminating the volume element certainly simplifies, but then no way to put an envelope on the resulting output sound thing.

    This becomes an interesting way to do it, but I’m not sure it really simplifies it. That 555 with a photoresistor controlling frequency is simpler still, no envelope control either, though the action will be different.

    I wouldn’t use a 555 at radio frequency, but it or some other variable oscillator could be beat against one of those ttl oscillators for simple.

    Michael

  2. The real problem with this device is the 50/60 Hz noise coupled from the musician’s hand into the high-impedance inputs of the 555. In the traditional theremin, the antenna is connected to a tank circuit with a grounded coil, which looks like a short for such low frequencies.

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