Homemade Theremin: how to assemble this peculiar instrument

Sheldon Cooper playing Theremin

Now that the famous and successful series The Big Bang Theory is over, if you’re a fan of it you’ve surely seen the episode where Sheldon Cooper plays one of these strange musical instruments with his hands. A strange instrument that emits a rather peculiar sound just by moving our hands over it. Well, if it caught your eye, in this guide we will teach you how to build your own homemade Theremin and show you how it works.

First we will see what a Theremin is and what principles this strange musical instrument is based on. And after that, we will detail the steps to build a simple Theremin and another one a little more complex, depending on your needs, as it may be simple curiosity and the simplest tutorial is enough or maybe you want to do a more pro one and you want to spend a few hours practicing with these strange tunes.

What is a Theremin?

Theremin wooden instrument

A theremin is a device also known in its time as a thereminophone, thereminophone, termenvox or thereminvox. It is one of the first electronic musical instruments and was created in Russia in 1920, although it was not patented until 1928. The inventor was Léon Theremin, hence its name.

It consists of two metal antennas that detect the relative position of the theremist’s hands, that is, the musician who is playing it. Depending on the proximity, the acoustic signals that we listen to are altered thanks to some oscillators to control the frequency (with one hand) and the amplitude or volume with the other. This way the melody is generated through the speaker. Therefore, it is a simple mechanism.

Little by little it has become popular and has been included in some movie soundtracks like Remember, Days Without a Footprint, Ultimatum to Earth, series like The Midsomer Murders, etc., as well as in some bands or musical bands from classical music to other rocks or more indie. And as I said at the beginning, it has also appeared in fiction as in the series Big Bang Theory.

And now, there could be one in your home…

How does it work?
Diagram of the operation of a Theremin

The principles on which it is based are quite simple. We have a circuit created with our source or stack powered oscillators, resistors and capacitors. We won’t need to touch it, since the control is based on the interference of any body, in this case our hand, with the radio frequencies produced by the instrument. In one of the schemes we propose, the first one, is not based on RF, but on light thanks to a photoresistor, but the principle is the same. In the second example we have based it on RF.

Well, summarizing, we have that circuit producing the oscillation or vibration of the electronic wave, something that would be interesting to study if you have an oscilloscope connected to the output of this circuit and see what happens with the alterations of the hand. If you have the opportunity to check it, you will see that when you move your hand the speed of the wave varies, producing noise through the speaker we have placed at the output.

This allows us to hear these variations that we could see on the screen of an instrument like the oscilloscope. In the previous image it is shown how the hand forms a capacitor with the antenna when we are approaching it, and depending on the proximity or distance, the signal will vary as if our arm was connected to a ground (GND).

As I say, some theremin have a double antenna, one controls the volume and the other the oscillations. But in the case of the optical based one there is only one form of control with the photoresistor that modulates the sound. In the second project there is also a single antenna to control the sound, but it includes two potentiometers with which we can manually adjust the volume with the other hand and the pitch, that is, to make it more or less sharp.

Build your own Theremin step by step

Single Theremin:

simple theremin

Our simplest prototype will be based on a project from the digital magazine Make. What you will need is the following material:

  • Protoboard, although you can also make it permanent by soldering it on a PCB.
  • 9v battery or power supply with this voltage.
  • 8 Ohms speaker.
  • CI 555
  • 5pK photoresistor
  • 2 capacitors of 0.22μF (connected in series) or one of 0.47
  • Electrolytic capacitor from 100μF (be careful when placing it as it has polarity)

To mount it, you can use the following circuit diagram, connecting the elements in this way on the breadboard you can get your home theremin, that simple:

Now you just have to connect it to the poles of the battery so that it starts to work, then put your hand on the theremin and you can start your tunes…

Advanced Theremin:

theremin

Although from the blog Instructables they describe it as ‘a simple theremin design’ and so it is, we have designated it advanced to distinguish it from the first model that was somewhat simpler. For this project you will need the following components:

  • CI NAND CD4093
  • Microchip Operational Amplifier MCP602
  • 1nF capacitor, another one of 4.7µF, and 2 capacitors of 100 pF
  • Resistances: 6 of 10KOhm, 1 of 5.1K, 1 of 6.8K
  • 2 of 10K potentiometers
  • Radio Athens
  • Power Jack
  • Audio Jack
  • PCB for soldering or protoboard
  • Plastic or wooden box to integrate everything (optional). You can build it with the necessary measures if you want or print it in 3D.

We now assemble all our elements according to the following circuit diagram:

By the way, I recommend you to mount it first on a protoboard so you can test its operation, because if you decide to solder all the elements and then it does not work, it will be more complicated to remove the soldering and reset the circuit.

Finally you can see and enjoy the result:

Sources:

If you want to see the original projects in English, you can go to these sources:

Instructional – Theremin (advanced)

Make Magazine – Theremin (single)

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