Home theremin: how to assemble this peculiar instrument

Sheldon Cooper playing Theremin

Now that the famous and successful series The Big Bang Theory has ended, if you are a fan of it, you have surely seen the chapter in which Sheldon Cooper plays one of these strange musical instruments with his hands. A rare instrument that emits a rather peculiar sound just by moving our hands over it. Well, if it caught your attention, in this guide we will teach you how to build your own Home theremin and we show you how it works.

First we will see what a Theremin is and on what principles it is based. strange musical instrument. And after that, we are going to detail the steps to build a simple and a more complex Theremin, depending on your needs, since it may be a simple curiosity and the simplest tutorial will suffice or you may want to make a more pro and you want to spend a few hours practicing with these strange melodies.

What is a Theremin?

Theremin wooden instrument

A theremin is a device also known in its time as etheróphone, 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 hands of the theremist, that is, of the musician who is playing it. Depending on the proximity, the acoustic signals that we hear are altered thanks to oscillators to control the frequency (with one hand) and the amplitude or volume with the other. In this way the melody is generated through the speaker. Therefore, it is a simple mechanism.

Poco a poco it has become popular and has been included in some film soundtracks such as Remember, Days without a Footprint, Ultimatum to Earth, series such as The Midsomer murders, etc., as well as in some groups 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 Big Bang Theory series.

And now, there could be one in your home ...

How It Works

Diagram of the operation of a Theremin

Each filtering bag principles on which it is based they are quite simple. We have a circuit created with our oscillators, resistors and capacitors powered by the source or battery. We will not 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 that we propose, the first of them, it is not based on RF, but on light thanks to a photoresist, but the principle is the same. In the second example we have based it on RF.

Well, in summary, 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 hand alterations. 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 that we have placed at the output.

That allows us grasp these variations by our ear that we could see on the screen of an instrument like the oscilloscope. The previous image shows 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 were connected to a ground connection (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 optics-based one, there is only one form of control with the photoresist that modulates the sound. In the second project, there is also a single antenna with which to control the sound, but it is true that 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:

Simple theremin:

simple theremin

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

  • Protoboard or prototyping board, although you can also make it permanent by soldering it on a PCB board.
  • 9v battery or power supply with this voltage.
  • Speaker 8 Ohms.
  • CI 555
  • Photoresistance by 5pK
  • 2 capacitors 0.22μF (connected in series) or 0.47
  • Electrolytic condenser 100μF (be careful when placing it since it has polarity)

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

Now you just have to connect it to the poles of the battery so that start working, then put your hand on the theremin and you can start with your melodies ...

Advanced theremin:

theremin

Although from the Instructables blog 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
  • Operational Amplifier Microchip MCP602
  • Condenser 1nF, another 4.7µF, and 2 capacitors of 100pF
  • Resistors: 6 of 10KOhm, 1 of 5.1K, 1 of 6.8K
  • 2 potentiometers of 10K
  • Radio athena
  • Power jack
  • Audio Jack
  • License plate PCB for soldering or breadboard
  • Plastic or wooden box to integrate everything (optional). You can build it yourself with the necessary measurements if you want or print it in 3D.

Now we assemble all our elements following the following circuit diagram:

By the way, I recommend that you ride it first on a breadboard so that you can test its operation, since if you decide to solder all the elements and then it doesn't work, it will be more difficult to remove the solders and re-establish 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:

Instructables - Theremin (advanced)

Make Magazine - Theremin (easy)


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