How to Build a Homemade Theremin using Basic Electronic Components

Introduction

A theremin is an early electronic musical instrument controlled without physical contact by the performer. It consists of two metal antennas, one that controls pitch and one that controls volume, allowing the musician to move their hands in the space around the instrument to create eerie, wavering notes. Theremins are fascinating devices that seem almost magical, and are fun to build at home as an electronics project. In this article, I'll walk you through step-by-step how to build your own basic homemade theremin using common electronic components and tools.

Required Materials

To build a homemade theremin, you will need the following materials:

• Soldering iron and solder: To assemble the electronic components on a circuit board.
• Circuit board: A blank printed circuit board works best. You'll solder the components to this.
• Electronic components: At a minimum you'll need two variable capacitors, two fixed capacitors, two inductors, two transistors, two resistors, a diode, potentiometer, audio transformer, speaker, and 9V battery connector.
• Enclosure: A box or enclosure to mount the circuit board and components inside. Plastic or metal both work.
• Antennas: Metal rods or extendable antennas to use as the theremin's pitch and volume controls.
• Wires and connectors: For connecting components and antennas.
• Tools: Wire strippers, screwdriver, glue, etc for assembly.

Component Selection

Choosing the right electronic components is important so your theremin produces clear audio tones. Here are some guidelines on selecting components:

• Variable capacitors: These control pitch and volume. Larger capacitance values like 500pF work well. Sturdy construction is good.
• Inductors: Should be good quality in the range of 10mH. Film type is recommended.
• Transistors: Low noise NPN transistors like 2N3904 or 2N2222 are ideal. Match their spec sheets.
• Resistors: Standard 1/4 watt resistors in mid-range values like 10K ohms and 220K ohms are fine.
• Diode: A general purpose 1N4148 silicon switching diode is perfect.
• Potentiometer: 10K ohms to adjust volume. Linear taper.
• Transformer: An audio transformer matches the transistor to an 8 ohm speaker.

Shop around for deals, but get quality components rated for the proper voltages and frequencies.

Theremin Circuit Design

The theremin uses a simple oscillator circuit with two variable capacitors to control pitch and volume. Here is the circuit diagram:

This shows the key components and how they are connected. The LC tank circuits with the variable capacitors determine the frequency and amplitude. The transistors amplify the signal to drive the speaker and produce audible tones.

Follow this diagram when soldering your circuit together. Use good wire management and orderliness.

Constructing the Oscillator Circuit

Here are the step-by-step instructions to build the theremin oscillator circuit:

1. Mount the Components

First, place and solder all the components onto the circuit board according to the diagram. Make sure diodes, transistors, and capacitors are oriented properly. Leave space to run wires later.

2. Connect the Components

Next, use hookup wire to interconnect the components. Follow the circuit diagram closely. Double check connections before soldering.

3. Install Potentiometer and Transformer

Solder longer wires to the potentiometer and transformer. Mount them separately in the enclosure with hot glue. Later you will connect them to the board.

4. Test for Issues

Power the board temporarily and check for shorts or backwards components using a multimeter. Troubleshoot any issues before continuing.

5. Connect Power and Antennas

With the board working, solder longer wires for the power, ground, antennas, and speaker. Install an on/off switch.

Your theremin oscillator circuit is now ready to use!

Creating the Theremin Enclosure

The theremin circuitry will be housed in a custom enclosure for a clean look. Here is how to make the enclosure:

• Select a sturdy plastic or metal box big enough for the circuit board and components.

• Mark and drill holes for the power switch, volume knob, antennas, and any connectors needed.

• Paint or finish the enclosure for aesthetics and durability. Consider metal mesh over the speaker hole.

• Mount the circuit board securely inside. Hot glue works to avoid vibrating parts.

• Attach rubber feet on the bottom so the theremin sits nicely on a table.

Take your time making a durable, well-designed enclosure that looks great and shows off your homemade theremin inside!

Connecting and Testing the Theremin

With the enclosure complete, the final steps are connecting and testing:

• Plug in the power, antennas, potentiometer, and speaker wires. Use shielded cable for the antennas to reduce interference.

• Turn on power and adjust the volume knob and transistor bias for clear tones.

• Move your hands near the antennas. One controls pitch and the other volume. Adjust so hands are far apart for range.

• Troubleshoot any issues with oscillation or noise. Check your wiring and solder joints.

Once tuned up, your homemade theremin will produce its characteristic eerie wavering tones ready for you to start playing some spacey sci-fi music! Enjoy exploring this fun electronic musical instrument you built yourself.

Conclusion

Building a homemade theremin is an achievable and educational electronics project using basic components. This guide covered sourcing quality parts, constructing the oscillator circuit, troubleshooting, and finishing the enclosure. With careful construction and testing, you can successfully create your own theremin to explore the magical world of gesture-controlled electronic music.