4×4 Matrix Keypad Membrane

This keypad has 16 buttons, arranged in a telephone-line 3×4 grid + 4 extra keys – A, B, C and D. It’s made of a thin, flexible membrane material with an adhesive backing (just remove the paper) so you can attach it to nearly anything. The keys are connected into a matrix, so you only need 8 microcontroller pins (4-columns and 4-rows) to scan through the pad.