Keypad is the combination of buttons which is used for more options using less number of pins (wires). Such keypads are used in mobiles for typing SMS or dialing number.

In all of above keypads you have seen there, number of buttons are greater than the number of pins.

In keypad the knowledge of detecting pressed key is important. In example suppose mobile phone keypad the first row is connected to pin A and every button is connected with different pin 1,2&3 .

Suppose we are detecting the button from row1. For this we have to make pin A LOW and pin 1,2&3 HIGH then continuously monitor the pins 1,2&3 that which pin show LOW, if pin 1 show low it means digit 1 is pressed, if pin 2 shows LOW it means digit 2 is pressed and if pin 3 shows LOW it means digit 3 is pressed. Same procedure for all rows in keypad. There also possibility that may be LOW is due to noise. So when button pressed is detected then with small interval confirm that button again.

Interfacing with microcontroller:

Let’s interface keypad with microcontroller and shows its button pressed on 7-segment.

Have a look on circuit.

In this circuit common anode 7-segment is used to display the digit which will pressed on keypad. By using this technique, we can interface any keypad with microcontrollers.

Check the commented c language code of this circuit.

Thanks.

This article was prepared for you by Hafiz Abdul Haseeb Tariq from FAST-National University of Computer and Emerging Sciences-Pakistan. He’s an Electronics & Embedded system engineer and has practical experience in circuit designing, networking, assembling, PCB making, 8051 & Arduino programming.

You can check out his previous article in the below link:

https://www.electronicsrepairfaq.com/door-security-lock-with-keypad