Infrared Theremin

You know about Theremin, the amazing electronic instrument? This one is very simple, made with infrared LEDs and photodiodes. And it works!

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You can play music just like on the original theremin, just waiving your hands, but sensors are not made of the antennas, but the modulated infrared light. Diodes LED13 and LED14 are IR emitters, and photodiodes (marked as FREQ and VOL on the schematics diagram) are receivers. The signal is amplified, filtered with bandpass filters, demodulated and amplified again as the DC signal. One channel is used to determine the period of the divided frequency, and the other one for PWM modulated volume of the output signal. Simple as can be.

The instrument is built on two PCBs, the upper one contains the analogue circuitry, and the lower one is with the microcontroller PIC16F18426 and USB interface. However, USB is not used in this project, so it is for power supply only. But the FTDI chip is still in its place - who knows, maybe I'll upgrade the firmware once.

Two groups of 6 white LEDs each, driven by T3 and T4, are just for visual effect, and they do not affect the audio operation.

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mpbarrett wrote 04/05/2021 at 18:54 point

I heard a real Theremin played in a lunch time free concert in Cambridge UK. Amazing but he did have to recalibrate 3 times as the conference hall warmed up. Still such interesting visual music! Always wanted to build one might have to use this design. Thanks Mike

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Ken Yap wrote 04/05/2021 at 05:02 point

Very nice. 👍 Something I might actually want to build. I'll never be as good as illényi Katica (a fantastic musician) though, even if I live to be 1000. 👍 again.

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Voja Antonic wrote 04/05/2021 at 05:09 point

It's the same with me. All I need now is somebody who can play this thing :))

You are right, there are really great players!

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