Remember those old-school sci-fi movies with squeaky and eerie background music? Those unique sounds were made using a theremin, an electronic instrument that can be played without physical contact. When playing a theremin, the operator can control volume and pitch with his or her hand position relative to two antennas.
This project is going to demonstrate how to build a simple theremin on a breadboard using a soda can as the antenna! With simplicity in mind, the theremin in this project will only demonstrate pitch modulation. The design that is implemented is shown in the block diagram above. However, it doesn't take too much extra work to add volume control, so I encourage you to try it if you're looking for an extra challenge.
To keep it short and sweet, we won't get too deep into the theory of how a theremin works. Briefly though, the antenna (our soda can) acts as one plate of a capacitor. Your hand will act as the other plate of the capacitor. Thus, by moving your hand nearer and further from the can, you are changing the capacitance. This takes place within the variable-frequency oscillator portion of our circuit. As the capacitance in the oscillator changes, the oscillator's output frequency changes as well. This change in frequency can be heard at the speaker at the end of our circuit.
Step 1: Gathering the Materials
The specific parts used in this design are shown in the picture above.
- OP27 Operational Amplifier (x2)
- OP37 Operational Amplifier
- Small speaker
- 100pF Ceramic Capacitor
- 0.047uF Ceramic Capacitor
- Small-signal Diode (1N3064)
- 10kΩ resistor (x2)
- 20kΩ resistor (x2)
- 47kΩ resistor (x2)
- 100kΩ resistor (x3)
- a few breadboard pins and jumper wires
- Breadboard (not pictured)
- Soda can (not pictured)
- Digilent WaveForms Software (Free Download)
All of these parts are right out of the Analog Parts Kit.