Adafruit silicone elastomer 4x4 button keypad adafruit 1616 the adafruit trellis monochrome driver pcb is the perfect partner for adafruits 4 x 4 elastomer keypad to save you the time needed to design a suitable pcb each trellis pcb has a 4 x 4 matrix of switch contacts that exactly match the elastomer keypad and each contact has pads for a 3mm led the board uses an i2c controlled keypad and led matrix chip to handle the details you will need to supply a microcontroller such as the arduin