Hi friends, today in this instructables I am going to tell you, how to use a PIR Motion sensor with Arduino. You can use this as a security system at night. So, lets makethis project !!!

Step 1: Components Needed

1.) Arduino UNO

2.) PIR Motion sensor

3.) USB B Type cable

4.) Laptop with Arduino IDE installed

5.) Some wires

6.) Breadboard

7.) LED

Step 2: The Schematic

Step 3: The Code

Copy the following code and upload it in your Arduino.

//VARS
//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 = 2;    //the digital pin connected to the PIR sensor's output
int ledPin = 8;
/////////////////////////////
//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);
           }
       }
  }

Step 4: Implementation

You can install this system at your home so that you can know that something or somebody is moving. You can also use it during Halloween to scare people. This system can also be used to power the lights. This can help you in walking downstairs during night.