Theremin

I have been wanting to build a Theremin for ages, so I have started.

There is a YouTube video HERE so you get the idea of what is going on.

To start I need some oscillators.  I have chosen this for an oscillator for no other reason than I like it and have been wanting to design it into something for a while.

Its a 'lambda diode' oscillator, which is basically using the 'lambda diode' in its negative resistance region.  I need two of these, one reference oscillator and the other that will be detuned by your hand.

The output of these oscillators go to a mixer.  To prevent the two oscillators 'pulling' each other, the mixer is this....

With the two oscillators built and connected to the mixer, thats the basic Theremin done.  One oscillator requires a small tuning capacitor across its main tank capacitor to get both oscillators running at the same frequuency.  The other oscillator has an aerial connected to the top end of its L-C tank, this is where your hand waves about.

Next I need to build the volume control bit and something to drive a speaker...

This is the pitch oscillators and mixer with a speaker amplifier.  The volume oscillator and associated bits aren't shown in this schematic.

I'll put up pictures of the prototype shortly and a full nice schematic.