A Theremin is a musical instrument that is controlled without contact from the player. In this simple project, the pitch (frequency) of a Wein Bridge sine wave oscillator is controlled by moving your hand close to an antenna (to raise the frequency) or away (to lower the frequency). To play a tune is quite intuitive with a little bit of practice.
To keep things simple, this project does not include a way to change the volume level using a second antenna. I think it is very important to be able to control the volume as well, so I'll think about an "add-on" project that will allow just that.
This project is based on the ideas posted on Art's Theremin Page - the Wein Bridge Theremin. Refer to that website for schematics as they are protected by copyright.
Here is a view of the inside of the enclosure. The 2N5484 JFET transistors required by the Wein oscillators were only available in an SMD package but the SOT23 format is surprisingly easy to work with. An internal power supply is used primarily due to the fact that the unit must be grounded to work - an external wall transformer power supply would not provide the necessary ground. I found that the antenna lead had to be kept as short as possible and away from the enclosure, so I brought it out to the side of the enclosure and as close to the PCB connection as possible.
The front panel control is the "Pitch Null". The "Null Calibration" trimmer capacitor can be adjusted through a small hole in the bottom of the enclosure.