Arduino code to convert Atari CX85 keypad to a USB HID peripheral
The Atari CX85 keypad is a number pad w/ 4 additional function keys and - and +/[Enter] keys, which interfaced to the Atari 8-bit computers via the joystick port.
The CX85 can be modified internally by disconnecting the joystick cable, and connecting an Atmega 32u4-based Arduino (with 6 "analog" pins available) to the 8 connections on the PC board. This can be done non-destructively, as the joystick cable disconnects using quick-connect terminals.
An Arduino board with 6 "analog" pins (A0-A5) is required because this code reads the entire portF in a single read. Boards that have these pins include:
- Adafruit ItsyBitsy 32u4 (tested, working)
- Arduino Leonardo (technically works but is too large to install internally)
- Arduino Micro
- Pololu A-Star 32U4 Mini LV