www.audiomulch.com/midipic/, From the page:
By combining a PIC microcontroller or Basic Stamp II with a few passive components it is not difficult to construct your own knob box, trigger box, or other MIDI input device. A knowledge of electronics may be required for interfacing to some sensors. Both the Stamp and PIC provide an economical (under US$100) entry point into the world of alternative MIDI controllers.
This page was created to provide a starting point for people interested in building their own MIDI control devices using Microchip PIC microcontrollers or Parallax Basic Stamps. If you have any comments or suggestions please feel free to email me.