But not so if you’ve got this beautiful custom RPN calculator in a wooden case ... figure out how the matrix was wired. Next up, a custom PCB to connect the keypad to an Arduino and a 20×4 ...

The keypad uses an onboard ATMega328P to scan the matrix for button presses, decode them, and send them via UART or I²C to an Arduino. [ELECTRONOOBS] has the PCB files available via Patreon for ...