Hall Effect sensors...

[Eric Barbour]

>I'm thinking about a pseudo Teremin controll with a magnet, why should
>I bother with coils and other rf stuff, if I can get some nice Hall
>sensor, three leg device, just power on and there you go.

Try a vacuum tube! Inherent magnetic field sensitivity!
In fact, I have heard of people using small CRTs as
amplifiers, and deflecting the beam magnetically, thus
providing waveform/volume control.
Eric Barbour
Svetlana Electron Devices
Portola Valley CA USA