Matrix Keypad Interface Using I2C

[dkinzer]

I've created an example of how to connect a matrix keypad to a ZX using a PCF8574A I/O expander on the I2C bus. If you have other I2C devices already attached, the keypad can be added without using any additional I/O lines.

The circuit schematic for the connection and example source code are attached. The code implements auto-repeat but does not handle "multi-key rollover". It implements a polling technique but you could use the interrupt output of the PCF8574A to implement an interrupt-based interface. I haven't thought through how you would implement auto-repeat in this case but it could probably be done using WaitForInterval() to implement the check for the key-still-down condition.