Monthly Archives: October 2015




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Raspberry Pi theremin

This was the supposed to be just a quick project to fill some time while waiting on an eBay purchase from China. I had been building up parts ready to build a simple Raspberry Pi-powered robot (inspired by articles in both Linux Format and The MagPi magazines).

The distance sensor is an HC-SR04, only a couple of quid on eBay, and I then found a simple guide on ModMyPi showing how to wire the sensor into a Raspberry Pi and read the distance in Python.

It being half-term, I had ordered the required resistors and was delighted at how easily the code work. “Fabulous!” I said to myself, “Now I just need to make it round the distance to, say, the nearest 5cm and then play a tone from there.”

How wrong can one statement be?!

After a good two days of intermittent playing, I have managed to get *something* working, basing my theremin on Zulko’s Pianoputer as I simply couldn’t find an easy way to just get Python to play a pitched tone. His code was set to use a keyboard, mine now reads the distance from the HC-SR04 and plays the relevant sound from there. In place of his “bowl.wav” I’ve grabbed (and trimmmed, and down-sampled) a clarinet sample from and use that as my base sound, which Zulko’s code then down/up-samples to make the various pitches required, at startup.

So yes, it’s a little clunky. And yes, it can take a while to start up and transpose the various samples.

But I’m a happy geek – I built my own personal theremin!