I've been wanting to try hand wiring and writing firmware for a keyboard, and after trying out mepler's TI-99 keyboard conversion tutorial
(
http://www.instructables.com/id/RaspTI-Convert-a-Vintage-Computer-TI-994A-into), I set about attempting
to hand wire a Televideo 925 keyboard and then modify/write the Arduino firmware code for it. The Futuba switches on this board looked good for this kind of
project and I saw that others have done it before with success . I used the Teensy++2.0 since it has plenty of pins and I just found its size a little
easier to work with for this project than the Teensy2.0.
First desoldered the PCB, then wired the rows and columns:
Next decided which pins to use and then using mepler's code as a template, made the code modifications and additions for my keyboard matrix. A bit tedious coding for each key
but I really just wanted the experience of doing it. One code modification I made was to use an Active Low configuration using the Teensy internal pull-up resistors,
rather than the Active High with external pull-down resistors configuration mepler used in his TI-99 code.
Next the very messy looking initial breadboard, uploaded my hex file to the Teensy, did a little debugging, and it worked! Once I was sure everything was working I soldered
directly to the Teensy and tucked everything back in the case. I'm sure my code is not the most elegant solution but I do feel like I learned quite a
bit by doing it (again much thanks and credit to mepler for his TI-99 matrix template and tutorial).