This is part 3 in a series of posts in which I will document my journey (and mistakes) of building a 6502 based computer.

A Keypad

We have output via the seven segment screen from part 2, now we need some kind of input. To stick with the KIM-1 style as per part 1 I will go for a hex keypad with a few extra control keys.

After asking around about options for keys I landed on Kailh Choc switches. The Kailh Choc switch is a low profile mechanical switch, another option would be the classic Cherry MX but it’s not low profile.

This is a simple row/column arrangement. Each keyswitch crosses a row and column. Using the I/O of the 6522 we set each column high one at a time, then check if any row is high.

NOTE: Each row is held low via a 1K resistor tied to ground.

Mistakes?

The spacing of the key switches is wrong between rows, its too small by about 1mm. I should have read the documentation.

What’s next?

In part 4 we will look at some software.