An innovative product, the Vexter Wah Probe is a theremin-style antenna controlling a wah, getting brighter as your foot approaches. It has three extra features, however. There’s a Super Hard-On boost circuit in front of the wah, with a knob to set the exact level of boost for driving your wah sound. There is also a “Mix” knob for dialing in the desired wet/dry mix of the effect, and a “Range” knob for controlling/limiting the ultra-bright upper range of this circuit.
The probe circuit generates a small (one or two inches high) “bubble” of RF energy at about a million cycles per second above the antenna plate. As your foot or hand (or any wet or metallic object, for that matter) approaches the copper plate, the RF field is disturbed and the circuit reacts by increasing the brightness of an LED, which drives a photo-resistive cell and controls the Z. Vex wah circuit. The wah circuit is actually the Seek-Wah sound circuit without the sequencer control.