This sketch demonstrates the use of the PIR infrared motion sensor.

_0500_-_Infrared_Sensor_2.ino

/*  Infrred sensor demo sketch
 * 
 * This sketch demonstrates the use of the PIR infrared motion sensor.
 * 
 * The sketch adds to the bare minimum version by allowing extra time 
 * after the sensor goes LOW for the LED to remain HIGH. This could be 
 * useful in a scenario where you want a light to go on in a room when 
 * someone enters it, but to turn of a few minutes after they leave it.
 * 
 * This sketch was adapted from the original that comes with the 
 * Adafruit library for Arduino Step by Step by Peter Dalmaris.
 * The location of the original is at https://github.com/futureshocked/ArduinoSbS2017/blob/master/_0500_-_Infrared_Sensor_2/_0500_-_Infrared_Sensor_2.ino
 * 
* Components
 * ----------
 *  - Arduino Uno
 *  - Infrared motion sensor
 *  - An LED
 *  - A 220 Ohm resistor for the LEd
 *  
 *  Libraries
 *  ---------
 *  - None
 *
 * Connections
 * -----------
 *  Break out    |    Arduino Uno
 *  -----------------------------
 *      VCC      |      5V
 *      GND      |      GND
 *      OUT      |      4
 *      
 * Also connect an LED to simulate a controlled device. 
 *           220 Ohm
 *    3 ----/\/\/\/\----(LED |)----GND
 
 * 
 * Other information
 * -----------------
 * For information on PIR sensors: https://en.wikipedia.org/wiki/Passive_infrared_sensor
 * Datasheet: https://www.mpja.com/download/31227sc.pdf
 *  
 *  Created on October 14 2016 by Peter Dalmaris
 * 
 */
 
int ledPin   = 4;             // choose the pin for the LED
int inputPin = 3;             // choose the input pin (for PIR sensor)
int pirState = true;          // we start, assuming no motion detected
int val      = 0;             // variable for reading the pin status
int minSecAfterPIRLow = 5000; // If the sensor reports low 
                              // remain HIGH for this many milliseconds
long unsigned int timeTurnedLow;                  
boolean takeLowTime;  //This variable is used to record the event where the sensor turns off

//the time we give the sensor to calibrate (10-60 secs according to the datasheet)
int calibrationTime = 30;  
 
void setup() {
  pinMode(ledPin, OUTPUT);      // declare LED as output
  pinMode(inputPin, INPUT);     // declare sensor as input

  takeLowTime = LOW;  
 
  Serial.begin(9600);
  
  Serial.println("Waiting for the sensor to warm up.");
  delay(calibrationTime * 1000); // Convert the time from seconds to milliseconds.
  Serial.println("SENSOR ACTIVE");
}
 
void loop(){
  val = digitalRead(inputPin);  // read input value

  if (val == HIGH) {            // check if the input is HIGH
    digitalWrite(ledPin, HIGH);  // turn LED ON
    if (pirState == LOW) {
      // we have just turned on
      Serial.println("Motion detected!");
      // We only want to print on the output change, not state
      pirState = HIGH;
    }
  } else {
    
    if (pirState == HIGH){
      // we have just turned off
      Serial.println("Motion ended!");
      // We only want to print on the output change, not state
      pirState = LOW;
      timeTurnedLow = millis(); //take the millis at the moment the sensor went LOW
    }
  }
   
  //This block checks to see if enough time has passed after the PRI went LOW.
  //If yes, and assuming that the PIR sensor did not go HIGH again, turn off the LED
  if(!pirState && (millis() - timeTurnedLow) > minSecAfterPIRLow){
     Serial.println("Extended time HIGH ended!");   
     digitalWrite(ledPin, LOW); // turn LED OFF  
    }

  delay(1000);
}