1 1N4001 diode; 10 1N4148 diodes; ... The input circuit is a simple keypad matrix. ... the Arduino brings one keypad input line high and checks the voltage of the four output lines in order.

He used an Arduino, and multiplexed RGB LEDs with some digital potentiometers to create a color mixing keypad. Since we couldn’t fit the complete 4×4 keypad into a standard 2 gang wall box, we ...