Simple. Two oscillators feeding into a ring modulator. One oscillator acts as the main signal, the other as the carrier. The knob on the bottom left hand side is a voltage control knob that effects each oscillator. The bottom, right hand knob is a rate control for the ring mod. Runs on any 9 v, ground tipped power adapter.
Here's a video, shot on a super shitty hi8 handycam!