A keypad module is a set of buttons arranged in a block or “pad” which bear digits, symbols or alphabetical letters. Pads mostly containing numbers are called a numeric keypad. The 4 x 4 matrix keypad usually is used as input in a project. It has 16 keys in total, which means the same input values.The 4*4 matrix keypad usually is used as input in a project. ... The SunFouner 4*4 Matrix Keypad Module is a matrix non- encoded keypad consisting of 16 keys in parallel. The keys of each row and column are connected through the pins outside – pin Y1-Y4 as labeled beside control the rows, when X1-X4, the columns.