matrix keypad pic microcontroller

  
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Matrix Keypad is a very useful and userfriendly when we want to design certain applications like Calculator, Telephone etc. MatrixKeypad is made by arranging push button switches in rows and columns. Just imagine, if you want to interface a 4*4 (16 keys) matrix keypad with a microcontroller. In the straight forward way, you will need 16 pins of a microcontroller for that,
matrix keypad pic microcontroller - schematic

but by using a simple technique we can reduce it to 8 pins. In the matrix keypad switches are connected in a special manner a shown in the figure below. Pressed keys can be detected by Scanning. For the sake of explanation, lets assume all column connections (Col1 Col4) are input pins and all row connections (Row1 Row4) are output pins. In the normal case (not scanning) all column inputs where in LOW (GND) state. For scanning keypad, Then each Row output (row1 row4) is scanned one by one. If any of the key belongs to first column is pressed, the Logic high signal from the Col1 will pass to that row. Through we can detect the key. In this post I am explaining only about detecting one key at a time. For explaining the working I am using a 4*4 matrix keypad and the result is displayed in a Seven Segment Display. Matrix Keypad scanning is stopped as soon as any key press is detected and the Scanning is restarted if we need more inputs. Matrix Keypad is connected to the PORTB of the PIC Microcontroller. Each column of the Matrix Keypad is connected to RB0 RB3 of the PIC Microcontroller, which are configured as output pins. While each row of the Matrix Keypad is connected to RB4 RB7 of the PIC Microcontroller, which are configured as input pins. Here I am using 4*4 matrix keypad, having characters 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, -, C, U, E, F. B` is replaced by -` and D` is replaced by U` because Seven Segment Display is used...



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