►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
Thu Nov 20 2014, 06:00 PM
@Mehboob.. I don't think you can do that.
Sat Nov 15 2014, 06:41 AM
Mehboob
Pls can you send me code in c of PWM generation using UART/serial port in 8051.
Fri Nov 14 2014, 02:51 PM
mohammad aqil
NEED A BOOK ON MICROPROCESSOR AND INTERFACING BY D.V.HALL. RIGHT NOW, I SHALL BE VERY THANK FULL TO U....
Thu Nov 13 2014, 02:15 PM
m
please code hex project avr blood pressure monitor
Thu Nov 13 2014, 05:56 AM
Lambo
hi mate, whats the ajay-bhargav? tell us more pls
ExperimenterUK
Wed Nov 12 2014, 12:56 AM
@tmtm000.. have you been able to join ?
ExperimenterUK
Wed Nov 12 2014, 12:54 AM
@Alice..become a member,then send a PM to ajay_bhargav the site owner.
Tue Nov 11 2014, 03:58 AM
Abhishek Bansal
Thanks a lot for your informative tutorials!
Mon Nov 10 2014, 09:03 AM
Alice
Hello, This is Alice from a PCB rototype manufacturer. Our company is interested in your website contents, and wonder if we can advertise our company with payment on your website. There are two ways to advertise: first, if we an get a instant quote section on your main site columns; second, whether we can get a advertising section if you have any avaliable one. If any of above ways avaliable, please contact me with your detailed scheme and advertising charge. Thanks. Alice
Sat Nov 08 2014, 11:58 AM
Mohamed_123sd
Signals and Systems, 2nd Edition by Alan V. Oppenheim Alan S.willsky with S.Hamid Nawab?

Downloads

Comments

VikiPeter
Tue Nov 18 2014, 09:13 AM
gentlboy
Sun Nov 16 2014, 11:13 PM
philipeastbourne
Wed Nov 12 2014, 05:32 AM
astra91
Mon Nov 10 2014, 08:11 AM
francise
Thu Nov 06 2014, 02:55 AM
ashbir
Tue Nov 04 2014, 11:13 PM
shruthig
Tue Nov 04 2014, 10:50 AM
sk8boardboy
Mon Nov 03 2014, 11:20 AM

Online

Guests: 70, Members: 0 ...

most ever online: 182184
(Members: , Guests: 182184) on 06 Aug 2010: 05:37 AM

Members: 37547
Newest member: VikiPeter
Forum Activity
ExperimenterUK Avatar
Posted By ExperimenterUK
Sat Nov 22 2014, 06:15 AM
@ExperimenterUKI make small table to observe Outpu...
Max.otto Avatar
Posted By Max.otto
Fri Nov 21 2014, 02:31 PM
@ExperimeterUKForgot my last question.As i told be...
Max.otto Avatar
Posted By Max.otto
Fri Nov 21 2014, 02:05 PM
@ExperimenterUKI make small table to observe Outpu...
Max.otto Avatar
Posted By Max.otto
Fri Nov 21 2014, 01:12 PM
@ExperimenterUKThank u. I do it. Ohne Period it's ...
ExperimenterUK Avatar
Posted By ExperimenterUK
Thu Nov 20 2014, 05:56 PM
You set the on/off times here as 47%float PWMcom...
vijay.parmar1992 Avatar
Posted By vijay.parmar1992
Thu Nov 20 2014, 04:06 AM
Right now i am studying Bootloader.I want to writ...
Max.otto Avatar
Posted By Max.otto
Wed Nov 19 2014, 03:11 PM
How can i get PWM on-off time..?pls check the atta...
Max.otto Avatar
Posted By Max.otto
Wed Nov 19 2014, 03:05 PM
I am using PSoC 5LP.pls check the attached design ...
ankitbajaj01 Avatar
Posted By ankitbajaj01
Wed Nov 19 2014, 01:49 PM
Thanks for the prompt response, I will try it out ...
engr1931 Avatar
Posted By engr1931
Wed Nov 19 2014, 11:45 AM
this one sir! i attached the whole project! ...