Replacing an Apple 2e Clone's keyboard controller with an Arduino

This is about my vintage Apple 2e clone. It’s a bit of a turd but I love it. I picked it up in a junk store in the mid 90s for something like $20.

When you boot it up, instead of saying APPLE ][, it says, simply, COMPUTER.

Upon firing it up for the first time in 20 years I discovered the keyboard was not working, and quickly deduced the keyboard decoder chip was burned out. This is an article about how I reverse engineered the keyboard decoder circuit enough to replace it with an Arduino. I would have just replaced the actual chip but it is ridiculously obscure and there was not one shred of information on it on the internet on it, arguably till now!

The old, dead chip was labelled C35224E, and had 40 pins.

The keyboard decoder chip scans an 8 by 10 matrix keyboard, and serially outputs the keypresses as ASCII. This is different to a genuine apple where the decoder chip outputs the keypresses as parallel data. This is a good time to have a quick look at Mike Willegal’s write ups about Apple keyboards. Short version is that genuine Apple 2 keyboards have the decoder chip as part of the keyboard assembly, while this had it on the main board.”