►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

Sat May 30 2015, 06:11 AM
lakshmikanth
can you plz guide me how can i open web home page through gprs
Sat May 30 2015, 06:09 AM
lakshmikanth
Hi,
ExperimenterUK
Mon May 25 2015, 06:21 PM
@Subrat Sahu not a simple answer.Create a thread in "General help Guidance and Discussion" forum
Sun May 24 2015, 06:51 AM
Subrat Sahu
I have a confusion about 10 bit adc formula as describe bellow that resolution = Vref/1023 or Vref / 1024
ExperimenterUK
Sat May 23 2015, 08:54 PM
@utpal.. Create a thread in the Pic forum
Thu May 21 2015, 01:04 AM
utpal
i am a hobbist. i work on 8051. just i have started with pic 16f877. but a bitter experiance is going on. as i am programming any code to my pic877 and putting it in my board and it is working, but the 2nd time it is not taking any program,I have experimented just 7 new one pic mcus. result is the same. please tell me the reason. my programmer is TOP3000(universal programmer).
ajay_bhargav
Wed May 20 2015, 04:48 AM
@lak you can use the same code provided you are not using any s52 specific ports and registers.
Mon May 18 2015, 05:58 AM
lak
i used to develop a code for at89s52 shall i use the same code for at89c4051
Sun May 17 2015, 07:57 AM
Ayoosh
what if i have to rotate motor continuously at a step angle of 1.8 degree
ExperimenterUK
Fri May 15 2015, 06:02 PM
@oracle1946.. Post your question in the PIC forum

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vipinpathakg
Wed May 27 2015, 05:57 AM
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oracle1946
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Tue May 12 2015, 04:29 PM
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Sat May 09 2015, 02:46 AM
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Fri May 08 2015, 06:40 PM
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Fri May 08 2015, 11:53 AM

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