Monday, March 05, 2012

4x4 Matrix Keypad

This is as simple routine how to read 4x4 keypad keys using AVR-GCC language. The keypad is connected to AVR microcontroller 8 bit port. In this example it is B port. You can change ports depending on your needs – this is only an example ant it is not the only way to this.

How it works. Well very simply. PORTB is divided into two nibbles PINB0 – PINB3 as inputs (as rows) and PINB4-PINB7 as outputs (columns). The keys are checked in a loop in series. Lets say if we set first row output (PORTB bit 7) to 0 then when checking rows we are looking which bit is set to 0, because of key pressed with function bit_is_set(PINB, bitNo). This function gives non-zero if bit is clear.

10k resistors protect AVR from shortcuts.


int main()


//high nibble for output(columns) low for input(rows);


//enable internal pullups for PB0-PB3


//Port D for indication only


while (1) //loop key check forever


//first column

PORTB =0b01111111;

//check for rows and send key number to portD

//instead sending key number to PORTD you can use

// any function that serves pressed button

if (bit_is_set(PINB, 3)) PORTD=1;

if (bit_is_set(PINB, 2)) PORTD=2;

if (bit_is_set(PINB, 1)) PORTD=3;

if (bit_is_set(PINB, 0)) PORTD=4;

//second column

PORTB =0b10111111;

if (bit_is_set(PINB, 3)) PORTD=5;

if (bit_is_set(PINB, 2)) PORTD=6;

if (bit_is_set(PINB, 1)) PORTD=7;

if (bit_is_set(PINB, 0)) PORTD=8;

//third column

PORTB =0b11011111;

if (bit_is_set(PINB, 3)) PORTD=9;

if (bit_is_set(PINB, 2)) PORTD=10;

if (bit_is_set(PINB, 1)) PORTD=11;

if (bit_is_set(PINB, 0)) PORTD=12;

//fourth column

PORTB =0b11101111;

if (bit_is_set(PINB, 3)) PORTD=13;

if (bit_is_set(PINB, 2)) PORTD=14;

if (bit_is_set(PINB, 1)) PORTD=15;

if (bit_is_set(PINB, 0)) PORTD=16;



No comments: