►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

plinniocom2n
Fri Feb 12 2016, 12:17 AM
thank you
Tue Feb 09 2016, 05:17 PM
Ankush SS
Can i get the source code of this project? Please n thnk u for ur kindness
Fri Feb 05 2016, 08:33 AM
SANJYOT JADHAV
sir did we have to use Gsm modem for testing the circuit on proteus
Tue Feb 02 2016, 11:17 AM
upendra kumar
i want information about 3-phase motor control using gsm technology
Sat Jan 16 2016, 05:33 PM
Kenneth Etuk
Hi everyone, I need help with a project involving MCU,rttc, and DC motor. I will pay for it. please reply to my mail [email protected] if you are interested. thanks
ExperimenterUK
Sat Jan 16 2016, 02:08 AM
@Kabona Log in and create a thread. Tell us what you want to do
Tue Jan 12 2016, 08:24 PM
Kabona
how can I make my pc be input and output device for the microcontroller
Sat Jan 09 2016, 07:04 AM
Ravz
Thank u..... one more doubt Will ultrasonic sensor HC-SR04 works with aurdino board in operating system linux
Tommy.Kofisterix
Fri Jan 08 2016, 08:50 PM
I know it detects also the mud on rear bumper, this means other obstacles will
Tommy.Kofisterix
Fri Jan 08 2016, 08:48 PM
Hey hi, hello

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plinniocom2n
Fri Feb 12 2016, 12:12 AM
designAAA
Sat Jan 30 2016, 08:49 AM
syavash_kasraeee
Sat Jan 16 2016, 05:54 AM
hamudi
Thu Jan 07 2016, 04:40 AM
Spandan89
Tue Jan 05 2016, 04:06 PM
siimao
Thu Dec 24 2015, 04:00 PM
moinabbasqureshi
Thu Dec 17 2015, 03:35 PM
dodo
Tue Dec 15 2015, 11:36 AM

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plinniocom2n Avatar
Posted By plinniocom2n
Fri Feb 12 2016, 12:18 AM
How do I get the link to the file? Newbie here.
sankalp_s Avatar
Posted By sankalp_s
Thu Feb 11 2016, 06:28 PM
Hello phil sir finaly i'm dumping my code, now i'm...
ExperimenterUK Avatar
Posted By ExperimenterUK
Thu Feb 04 2016, 04:10 AM
Sir I didn't understand that. Could you explain ab...
sankalp_s Avatar
Posted By sankalp_s
Tue Feb 02 2016, 07:26 PM
but good use of sub routines will save a lot of ...
ExperimenterUK Avatar
Posted By ExperimenterUK
Tue Feb 02 2016, 12:25 AM
after removing ALLON instruction it's working fine...
ExperimenterUK Avatar
Posted By ExperimenterUK
Tue Feb 02 2016, 12:14 AM
Which micro controller are you using ?.Does it hav...
sankalp_s Avatar
Posted By sankalp_s
Sat Jan 30 2016, 07:40 PM
You need to explain exactly what you want the code...
ExperimenterUK Avatar
Posted By ExperimenterUK
Sat Jan 30 2016, 06:57 PM
>sir can you code this in any other method?You nee...
sankalp_s Avatar
Posted By sankalp_s
Sat Jan 30 2016, 06:47 PM
CALL ALLONCLR L1CLR L2CLR L3CLR L4CALL DELAY ;del...
designAAA Avatar
Posted By designAAA
Sat Jan 30 2016, 10:03 AM
I have used to timer 2 external pin for other purp...