►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

ExperimenterUK
Wed May 25 2016, 05:05 AM
@ Ramanjaneyulu, post in forum,explain your problem
Mon May 23 2016, 11:34 PM
Ramanjaneyulu
Hi, I Am using at89c4051 for my application, I want 5u sec dely.. Up to 1milli sec iam able to producing delay. Beyond the 1milli second, I am unable to produce the acceurate dely. Plz any one help me
Sat May 21 2016, 09:51 PM
A K
i want to mak an auto dialer using gsm and atmega 16. please helpe me how to write a code to auto dial a number saved in sim
Sat May 21 2016, 10:42 AM
Alec
Hi im trying to program my 89s51 with a usbasp so any ideas on the circuit?
Wed May 18 2016, 10:08 AM
Tashu joshi
anyone know how to develop
Wed May 18 2016, 10:07 AM
Tashu joshi
i'm working for resporatry system using 8051,
Wed May 18 2016, 10:06 AM
Tashu joshi
i'm developing a respiratory system using Arduino
Fri May 13 2016, 11:03 AM
MEGHANA
i need c code for counting frequency of two sensors and compare these frequencies and it has to give high/ low signal after comparision
ExperimenterUK
Tue May 10 2016, 05:02 PM
@Suren ..create a thread in the 8051 Discussion Forum to discuss your problem
Tue May 10 2016, 04:04 PM
Suren Avushyan
how can I increment address not the content of it, like 0x70 and get 0x71

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Comments

zaft93
Sun May 15 2016, 01:52 AM
CELEBI
Thu May 12 2016, 08:28 AM
Suro1996
Wed May 11 2016, 06:07 PM
yigithan
Sat May 07 2016, 09:09 PM
jaque
Fri May 06 2016, 07:51 PM
afzal42
Wed May 04 2016, 11:16 AM
pd
Sun May 01 2016, 01:35 AM
uk2308
Fri Apr 29 2016, 12:27 PM

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ExperimenterUK Avatar
Posted By ExperimenterUK
Sun May 15 2016, 10:58 PM
zaft93 Avatar
Posted By zaft93
Sun May 15 2016, 01:55 AM
ExperimenterUK Avatar
Posted By ExperimenterUK
Fri May 13 2016, 07:59 PM
If you want only one relay to be on at a time the ...
CELEBI Avatar
Posted By CELEBI
Fri May 13 2016, 06:16 AM
Yes. It must be as you said. It must be 1.5 second...
ExperimenterUK Avatar
Posted By ExperimenterUK
Thu May 12 2016, 08:35 PM
Here is one way.If you have the Keil compiler you ...
ExperimenterUK Avatar
Posted By ExperimenterUK
Thu May 12 2016, 05:20 PM
Sorry I don't understand what you want.Is that 1.5...
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Posted By CELEBI
Thu May 12 2016, 08:53 AM
Hello Guys, I want to make a Project with 89s51 bu...
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Posted By ExperimenterUK
Wed May 11 2016, 09:28 PM
No this is all I've got, the algorithm I think is ...
Suro1996 Avatar
Posted By Suro1996
Wed May 11 2016, 09:27 PM
Is this all the code you have ?As it is, it will n...
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Posted By Suro1996
Wed May 11 2016, 07:31 PM
Hello, I am new to assembly programming and I am h...