►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.

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Mon Jun 12 2017, 02:36 PM
madhusoodanan
how to receive string using 8051
ajay_bhargav
Thu Jun 08 2017, 12:48 PM
@Vinoth post in forum.
Wed Jun 07 2017, 01:40 AM
vinothkannan
how interface eprom in this code
Thu May 25 2017, 12:25 AM
Monir Hossain
Can i change the 7-Segment are common pin ? And how to?
Mon May 08 2017, 07:45 AM
ivan muvunyi
please can you send me wiring diagram for automatic control of 3 phase induction motor for production of maize flour
Wed May 03 2017, 03:39 PM
imran qureshi
hello friend
Sun Apr 30 2017, 12:49 AM
Lijin G Varghese
Can u send me the circuit diagram for Program to interface GSM Module with 8051 microcontroller (AT89C51) using PC and LCD
Fri Apr 28 2017, 10:47 AM
SANDEEP T S
I need pcb wizard 3.5 version kindly send valid link of yours
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Thu Apr 13 2017, 02:29 PM
Piyush Aughad
I want circuit & program for radar detection using Microcontroller 8051

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richard1976
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Posted By ExperimenterUK
Mon Jun 26 2017, 08:42 PM
I have attached a demonstration file.It will echo ...
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Posted By richard1976
Sat Jun 24 2017, 08:47 PM
Hi can you tell me how to send and recieve usart d...
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Posted By ExperimenterUK
Sat Jun 24 2017, 08:24 PM
HiUnfortunately there is too much code here to wor...
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Posted By richard1976
Sat Jun 24 2017, 06:01 PM
hi i have written this programme and can send data...
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Fri Jun 23 2017, 08:19 PM
>Should I need to check PWR_VLD bits every time on...
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Fri Jun 23 2017, 07:42 PM
I would say yes, but data transfer will be slower ...
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Hello ExperimenterUK, Thanks for your support. Fro...
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Wed Jun 21 2017, 11:51 AM
Is it possible to Use 8051 bit-banging method to p...
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Posted By ExperimenterUK
Tue Jun 20 2017, 06:27 PM
You could start by looking at this tutorial on ke...
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Posted By firdaus0hsem
Sat Jun 17 2017, 04:58 PM
I have an issue regarding how to use 4x3 keypad to...