►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

Thu Jun 11 2020, 06:27 AM
anudee
sir could please send the code for I2C and wifi interfacing with 8051
scena
Tue May 19 2020, 10:29 PM
Does anyone have microcontroller programming software for STC15F104W (core 8051, 4 k, 128 byte, 6 I/O pin, UART ... DIL8), that works?
Sat May 02 2020, 07:38 PM
Tamu Gurung
Hi I am looking for a assembly language program for a digital decimal counter. Time counts max limit of 2 mins starting from 2.00 mins and ending at 0.00. time is to be displayed on 4 7-segment LED displays. Edsim51 simulator to be used. Thanks
Wed Mar 25 2020, 01:39 PM
Tajammul
Sir kindly send the code file i2c for 8051
ExperimenterUK
Fri Mar 13 2020, 10:36 PM
@ Rohitnani,ABEBE..which project ?
Fri Mar 13 2020, 12:55 PM
ABEBE
how can get hadwere of this project
Rohitnani
Sat Mar 07 2020, 05:11 PM
Sir, Could you please send me the zip file input password....
Wed Feb 26 2020, 04:58 PM
Peter Parker
Is it possible to send multiple messages using only 1 GSM module?
Sat Feb 01 2020, 10:12 AM
Pearl Olin
Hello,
Wed Jan 22 2020, 06:16 PM
MINU CHAUDHARY
I m getting errors while simulation process during interfacing socket output and lcd... Can i get the report of ur project which is same as us.

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Mirza123
Thu Jun 25 2020, 03:46 PM
eunicelove124
Mon Jun 22 2020, 03:03 PM
cerouno
Tue Jun 16 2020, 05:10 PM
Marce
Sat Jun 13 2020, 09:43 PM
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Thu May 21 2020, 12:44 PM
Jakeror
Thu May 21 2020, 01:28 AM
motorCar
Wed May 20 2020, 07:05 PM
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Wed May 20 2020, 11:52 AM

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Posted By ExperimenterUK
Wed Jul 01 2020, 11:07 PM
PS: I am a new learner thats why my question may s...
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Posted By Mirza123
Wed Jul 01 2020, 02:05 PM
Thanks for the assistance. I have read the data sh...
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Posted By ExperimenterUK
Wed Jul 01 2020, 10:12 AM
See section 15 (Ports) of the data sheet. ...
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Tue Jun 30 2020, 10:05 AM
How did you know that it is not 8051. Mirza123It i...
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Posted By Mirza123
Tue Jun 30 2020, 08:39 AM
It seems ports on the AT89LP2052 is not like on th...
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Posted By ExperimenterUK
Tue Jun 30 2020, 08:34 AM
It seems ports on the AT89LP2052 are not like on t...
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Hello!i am trying to use AT89LP2052 ( AT89LP2052 h...
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Wed Jun 17 2020, 09:42 PM
It is about capacitor? i should put it between Vcc...
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Posted By cerouno
Wed Jun 17 2020, 10:37 AM
Take another look at the power supply to the LCD.A...
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Posted By ExperimenterUK
Wed Jun 17 2020, 02:01 AM
Take another look at the power supply to the LCD.A...