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Commodore Keyboard Tester
Some weeks ago, a friends showed me, what he had built on a perfboard to test his C64 keyboards. I immideately knew, what it was good for and how it is working and I thought: "Wow, such a good idea!".

The Commodore computers, prior to the Amigas, have matrix keyboards. That means, every key is connected to one ROW and one COL(umn) signal.

Excerpt of the
C64 keyboard schematics

The Keyboards can be scanned by the kernal this way.

If you now connect all rows and all columns, you can measure the single key press by connecting an ohmmeter (multimeter) between the rows and the columns without disassembling the keyboards.

Schematics of the Keyboard Tester

The keyboard tester is planned to test C64, VIC-20, PET&CBM keyboards and also C16, C128, C128D and SX-64 keyboards.

Layout of the Keyboard tester

It will be possible to make adapter boards for other retro computer (matrix) keyboards.

This project is a work in progress and will be published on
my github after testing it successfully and finishing the documentation.