►Introduction

Keypads are a part of HMI or Human Machine Interface and play really important role in a small embedded system where human interaction or human input is needed. Martix keypads are well known for their simple architecture and ease of interfacing with any microcontroller. In this part of tutorial we will learn how to interface a 4x4 matrix keypad with AVR and 8051 microcontroller. Also we will see how to program then in Assembly and C.


►Constructing a Matrix Keypad

Constuction of a keypad is really simple. As per the outline shown in the figure below we have four rows and four columns. In between each overlapping row and column line there is a key.


4x4 matrix Keypad outline

So keeping this outline we can constuct a keypad using simple SPST Switches as shown below:


4x4 matrix Keypad schematic

Now our keypad is ready, all we have to do is connect the rows and columns to a port of microcontroller and program the controller to read the input.


►Scanning a Matrix Keypad

There are many methods depending on how you connect your keypad with your controller, but the basic logic is same. We make the coloums as i/p and we drive the rows making them o/p, this whole procedure of reading the keyboard is called scanning.


In order to detect which key is pressed from the matrix, we make row lines low one by one and read the coloums. Lets say we first make Row1 low, then read the columns. If any of the key in row1 is pressed will make the corrosponding column as low i.e if second key is pressed in Row1, then column2 will give low. So we come to know that key 2 of Row1 is pressed. This is how scanning is done.


So to scan the keypad completely, we need to make rows low one by one and read the columns. If any of the button is pressed in a row, it will take the corrosponding column to a low state which tells us that a key is pressed in that row. If button 1 of a row is pressed then Column 1 will become low, if button 2 then column2 and so on...


Now lets move on to the programming part of keypad in our next section.

◄ Back to Index  |  Connecting a Keypad ►

Conversation

Fri Sep 29 2017, 02:45 AM
Maaz
i am doing the same project on verilog please contact me [email protected]
Wed Sep 20 2017, 12:36 AM
Ted
In a missing pulse detector using a 555 timer connected as a monostable vibrator with a PNP transistor,how does the positve input pulse turn on the PNP transistor?
Sun Sep 03 2017, 02:29 PM
martymarty
How do I connect an <NOKIA 1100 LCD > to an atmega328P ?
poojab51296
Sun Aug 20 2017, 10:23 AM
i am intending to interface sd card with STM32F4 and want to write a file in sd card using SPI protocol but using HAL only. Can anyone help me PLEASE!!!!
poojab51296
Sun Aug 20 2017, 10:22 AM
hello
rawat742
Fri Aug 18 2017, 11:37 AM
hi @ angel patel i will attach a file i hope it will be helpfull for you
ExperimenterUK
Mon Aug 14 2017, 09:57 PM
@ angel patel... just log in and post your problem
Mon Aug 14 2017, 01:45 PM
angel patel
hey any one help to make the led scrolling display
desuza6
Sat Jul 29 2017, 07:09 AM
I see the code for step motor h l 298 to rotate 45 degree, but all delay time, if I want to input sensor to h the pulses to stepmotor
rammichael
Thu Jul 27 2017, 12:05 PM
okay fine

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