Reference

Principle

The general working principle of this key pad is a 4*4 matrix. We use four digital ports as HIGH voltage scanning the row of button pad and four analog ports to read the column of button pad connected with four pull-down resistors. If button is pressed,the voltage will be HIGH when it is scanned by HIGH voltage concurrently. Otherwise, the voltage is pulled down and will be LOW. Using eight ports totally, we can read 16 buttons.