Punch in your secret key into this numeric matrix keypad. This keypad has 16 buttons, arranged in a telephone-line 4x4 grid. 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.
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