I have a very old keyboard, a CASIO MA-100 that I want to convert to a MIDI keyboard:
Being a programmer and a digital electronics enthusiast, I know how to do it, but I could use some help to save time.
I guess the biggest issue is choosing a µC. Something with a USB interface* would be great, something that can also be powered by USB, even better. Then there's the issue of talking MIDI or MIDI-over-USB. I don't know how hard they would be, but I could probably do with some already written code there, too. (Unless they're very simple and don't need much testing.)
I looked around some electronics project sites this morning, trying to find some open source MIDI or MIDI-over-USB controller firmware, but couldn't.
I did find some Arduino projects, but a prototyping board seems a bit overkill for such a simple project.
The key matrix is 10x8 (10 select in * 8 data out), simple boolean logic, no velocity data. (Though two select lines are easily expendable.)
So I guess my simplest option would be a ~1 MHz µC with 8 input, 8 output pins and a serial buffer (+I/O pins) for MIDI. My best would be a project called "USB MIDI device firmware for Make SeriesXX microcontrollers."
*: An easy USB interface, i.e. not PIC18. (Edit: This was a simple prejudice arising from the state of the organisation and documentation of the PIC USB framework a few years back. I guess it's time to break it.)