This calculator uses a full 16 button matrix keypad. The Arduino deciphers button pushes with the help of the Keypad library, at which time the appropriate character is displayed on the 2×8 LCD ...

But not so if you’ve got this beautiful custom RPN calculator in a wooden case ... Next up, a custom PCB to connect the keypad to an Arduino and a 20×4 LCD display was milled up, while a ...