Check out:

DIY MIDI Controllers using PIC Microcontrollers and Basic Stamps
http://www.audiomulch.com/midipic/

There's lots of info and links there including midi transmit source code for
the 16F84.

Although most of the info there relates to using various RC circuits to read
pots, I've actually opted for a tlc542 8 bit AD with 11 way input
multiplexing - i've used it to build a 11 knob midi knob box. I'm planning
to make a web page about it but havn't had time yet.

The problem with RC based pot circuits is that they are too slow (imho) to
use for scanning a lot of knobs, especially if you want to oversample to
reduce noise etc. Unless you already have the capacitors lying around the
tlc542 isn't much more expensive. Using an AD also allows you to interface
non resistive devices.

Hope that helps

Ross
<rossb@audiomulch.com>