MIKROE 4x4 Key Click carries a 16 button keypad. The design of the board — inputs are read by a pair of connected 8-bit parallel-in serial-out shift registers — allows for multiple key presses at the same time. For ease of use, each button has silkscreen markings. The right-most column is marked with letters A-D, the other 12 buttons are marked like a telephone keypad. The board is designed to use either a 3.3V or 5V power supply.