Keypad is a widely used input device with lots of
application in our everyday life. From a simple telephone to keyboard of a
computer, ATM, electronic lock, etc., keypad is used to take input from the
user for further processing. In this article we are interfacing keypad with the
MCU AT89C51 and displaying the corresponding number on LCD. This module can be further used in a number
of systems to interfaced keypad with microcontroller and other processors to
get desired output. The program to interface keypad with controller is written
in C language which is very easy to understand.
Keypad is organized as a matrix of switches in rows and
column. The article uses a 4X3 matrix keypad and a 16x2 LCD for displaying the
output of keypad.
The circuit diagram shows the connection of keypad with the
controller. Port P2 of the microcontroller is used to send the data for
displaying on the LCD. P1^1, P1^2, P1^3 pins of microcontroller is connected to
RS, RW, EN pins of LCD respectively. Port P0 is used to scan input from the
keypad (refer circuit diagram for connection)
The concept of interfacing keypad with the MCU is simple.
Every number is assigned two unique parameters, i.e., row and column number
(n(R, C) for example 6 (2, 3)). Hence every time a key is pressed the number is
identified by detecting the row and column number of the key pressed.
Initially all the rows are set to zero by the controller and
the columns are scanned to check if any key is pressed. In case no key is
pressed the output of all the columns will be high.
Whenever a key is pressed the row and column corresponding
to the key will get short, resulting in the output of the corresponding column
goes to go low (since we have made all the rows zero). This gives the column
number of the pressed key.
Once the column number is detected, the controller set’s all
the rows to high. Now one by one each row is set to zero by controller and the
earlier detected column is checked if it becomes zero. The row corresponding to
which the column gets zero is the row number of the digit.
The above process is very fast and even if the
switch is pressed for a very small duration of time the controller can detect
the key which is pressed. The controller displays the number corresponding to
the row and column on the LCD.
If you want to C Code and more details about this circuit write your email id in comment box.we will send you details.
