INTERFACING PIR SENSOR WITH AVR MICROCONTROLLERS

Sometimes we have to interface a variety of sensors with microcontroller for monitoring different environmental conditions such as temperature, humidity, light intensity , motion, color etc. most of the sensors are making its output pin HIGH or LOW when the desired value is met or detected. For example a motion sensor makes its output pin HIGH when a motion is detected in its covering area and otherwise its pin is pulled LOW.  So this kind of sensors is very easy to interface with microcontroller because only we have to check the sensors output pin status. Following examples shows how to interface different sensors with AVR microcontroller. 

1)      Interfacing PIR sensor with AVR

A PIR sensor is used to detect the motion of living things around its covering area.   Normaly it has three pins namely Vcc, GND and OUT. When the sensor detects a motion, it makes its OUT pin HIGH. So we can simply check the OUT pin status to know whether the motion is detected or not. The following points and program illustrates how to interface a PIR sensor with AVR microcontroller

·         At first point we have to decide what  we have to when a motion is detected by the motion sensor

·         Here we are going to detect the motion sensor output and when it detects we glow a LED

·         I am decided to interface the motion sensor OUT pin with PA0 of the PORTA of AVR. So make PA0 as input pin. We use DDRA register to set the direction of PA0 as input. For that any of the following code can be used

DDRA=0x00; //makes all the PORTA pins as input

DDRA=0xFE; //makes PA0 input and all other pins are output

DDRA |=(0<<PA0); // this code helps us to make PA0 of PORTA as input without altering the   

                                    value of other bits in DDRA register

·         Next we have to choose a pin in PORTB to connect the LED which will glow when the senor makes a HIGH output at its OUT pin. I decided PB0 of PORTB to connect with LED. So we have to make this pin as out pin in PORTB. The following are methods to do so

DDRB=0xFF; //makes all the PORTB pins as output

DDRB=0x01; //makes PB0 output and all other pins are input

DDRB |=(1<<PB0); // this code helps us to make PB0 of PORTB as output without altering the   

                                    Values of other bits in DDRB register

·         Next we have to monitor the PA0 pin of PORTA whether it is set or not. For that we have to check the PINA register. For this case we don’t want to check all value of PINA register because we need only PA0 of the PINA register is set on not. For doing that we can use the following code.

If (PIN_is_set (PINA, PA0))

{

}

                          This code checks the PA0 of the PINA register is set (HIGH) or not. When it is high the code in the brackets will run. So we are using IF condition to monitor the PA0 pin of PORTA.

·          Next step we have to glow the LED when the PA0 detects a HIGH in its pin. So LED is connected to the PB0 pin of the PORTB.

If (PIN_is_set (PINA, PA0))

{

PORTB=0x01; // makes PB0 high which glows LED and all other pins LOW

Or

PORTB|=(PB0<<1); // this makes PB0 high without effecting the other pins of PORTB

                }

The complete code and diagram of PIR sensor interfacing  is as given below.

The complete Code

#include <avr/io.h>

int main(void)
{
   
    DDRA|=(0<<PA0); //making PA0 as input pin
    DDRB|=(1<<PB0); //making PB0 as output to connect LED
 
  PORTB|=(0<<PB0); // LED is off by sending zero to PB0
 
 
 
    while(1) //infinite loop
    {
        if(bit_is_set(PINA,PA0)) //checking  whether PA0 is set
        {
            PORTB|=(1<<PB0); //switch ON LED
        }           
    }
}