Passive Infrared Sensors

Passive Infrared Sensor(PIR) is a device that can detect infrared radiation that is emitted by its surrounding objects. Also, this sensor is mostly used in home security system and as well to activate interior lighting when someone enters the room.

In Arduino, the hardware required are:

- Arduino Uno

- HC-SR501 Passive Infrared Sensor

- Jumper Wires

- LED


These PIR sensor consist of 3 pins(VCC, Ground pin, and Output pin in the middle).

Firstly, connect VCC of PIR to Arduino 5 volts. Then, connect ground to ground pin and output pin of PIR to digital pin number 3 of Arduino. Also, place the LED positive leg to pin 13 and negative leg to GND of  Arduino.

             





Code:

/the time we give the sensor to calibrate (10-60 secs according to the datasheet) int calibrationTime = 30; //the time when the sensor outputs a low impulse long unsigned int lowIn; //the amount of milliseconds the sensor has to be low //before we assume all motion has stopped long unsigned int pause = 5000; boolean lockLow = true; boolean takeLowTime; int pirPin = 3; //the digital pin connected to the PIR sensor's output int ledPin = 13; ///////////////////////////// //SETUP void setup(){ Serial.begin(9600); pinMode(pirPin, INPUT); pinMode(ledPin, OUTPUT); digitalWrite(pirPin, LOW); //give the sensor some time to calibrate Serial.print("calibrating sensor "); for(int i = 0; i < calibrationTime; i++){ Serial.print("."); delay(1000); } Serial.println(" done"); Serial.println("SENSOR ACTIVE"); delay(50); } //////////////////////////// //LOOP void loop(){ if(digitalRead(pirPin) == HIGH){ digitalWrite(ledPin, HIGH); //the led visualizes the sensors output pin state if(lockLow){ //makes sure we wait for a transition to LOW before any further output is made: lockLow = false; Serial.println("---"); Serial.print("motion detected at "); Serial.print(millis()/1000); Serial.println(" sec"); delay(50); } takeLowTime = true; } if(digitalRead(pirPin) == LOW){ digitalWrite(ledPin, LOW); //the led visualizes the sensors output pin state if(takeLowTime){ lowIn = millis(); //save the time of the transition from high to LOW takeLowTime = false; //make sure this is only done at the start of a LOW phase } //if the sensor is low for more than the given pause, //we assume that no more motion is going to happen if(!lockLow && millis() - lowIn > pause){ //makes sure this block of code is only executed again after //a new motion sequence has been detected lockLow = true; Serial.print("motion ended at "); //output Serial.print((millis() - pause)/1000); Serial.println(" sec"); delay(50); } } }

Outcome:

The outcome is that, the LED light lights up whenever anything passes near by the PIR Sensor.

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