Hi,

I have just built a prototype of the simple USB MIDI expression pedal,
which uses very simple self-made capacitance sensor to measure 
the position of the pedal.
The device is based on the AVR (ATmega8) microcontroller, but
can be easily ported to PIC.
The capacitance between two copper plates creates the low-pass
RC circuit. This circuit is connected to the PWM output, and its output
is connected to the ICP (Input capture) system working with the same
timer as PWM. It allows to measure the delay between slopes of signal on the
input and on the output of the RC circuit.

More details of the design may be found at my website:
http://www.ise.pw.edu.pl/~wzab/MIDI/pedal/index.html

Firmware is significantly based on the V-USB MIDI design, available
at http://cryptomys.de/horo/V-USB-MIDI/

I hope that the above may be useful for someone.
-- 
Regards,
Wojtek
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