Keypad Switch
Hossam Fattah · 2021
This chapter shows how to integrate a keyboard with the NB board so that the board can read the keys being pressed by a user. Keypads are used in all types of devices such as cell phones, fax machines, microwaves, ovens, door locks. Keypad is also called membrane switch. A matrix keypad is used. This is a keypad that follows an encoding scheme that allows it to have much less output pins than its keys. The hardware board detects which button is pressed by detecting the row and column pin that is connected to the button. This happens as follows. When no buttons are pressed, all the column pins are held HIGH, and all the row pins are held LOW. When a button is pressed, the column pin is pulled LOW since the current from the HIGH column flows to the LOW row pin.