🔥 Project: Motion-Activated Light System Using Arduino + PIR Sensor

1. Introduction

In this project, we’ll build a motion-activated light system using an Arduino and a PIR (Passive Infrared) sensor. When motion is detected in the sensor’s range, an LED light (or relay-controlled bulb) will turn on automatically and stay on for a set time before turning off. This concept is commonly applied in security lighting, automatic hallway lights, and energy-saving systems.

2. Learning Objectives

• Understand how a PIR sensor detects motion using infrared radiation.
• Learn to handle digital inputs from sensors.
• Control an LED or a relay module to operate lights.
• Implement timing functions in code for delay-based control.
• Understand practical applications in home automation and energy efficiency.

3. Components and Tools Needed

You will need:

• Arduino Uno or Nano
• PIR Sensor (e.g., HC-SR501)
• LED (or a 5V relay module for real bulbs)
• Resistor (220Ω for LED)
• Jumper wires and breadboard
• Optional: External power supply if using relay and high-power light

4. Key Definitions and Concepts

PIR Sensor:

• Stands for Passive Infrared Sensor.
• Detects infrared radiation emitted by moving objects (like humans or animals).
• Outputs a digital HIGH signal when motion is detected.

Digital Input:

• Arduino reads a HIGH (1) or LOW (0) from digital pins.
• Used to respond to real-world events (motion, switches, etc.).

Delay Function:

• The delay(milliseconds) function pauses program execution, used to keep the light on for a set time.

5. Wiring Instructions (Circuit Description)

• PIR Sensor VCC connects to Arduino 5V.
• PIR Sensor GND connects to Arduino GND.
• PIR Sensor OUT connects to Arduino Digital Pin 2.
• LED long leg (anode) connects to Arduino Digital Pin 13 through a 220Ω resistor.
• LED short leg connects to GND.
• If using a relay module, connect its IN pin to Pin 13, VCC to 5V, and GND to GND.

6. Complete Arduino Code with Explanations

// Define pins
int pirPin = 2;       // PIR sensor output
int lightPin = 13;    // LED or relay control

void setup() {
  pinMode(pirPin, INPUT);       // Set PIR sensor as input
  pinMode(lightPin, OUTPUT);    // Set light as output
  Serial.begin(9600);           // For debugging
}

void loop() {
  int motionDetected = digitalRead(pirPin);  // Read PIR sensor

  if (motionDetected == HIGH) {
    Serial.println("Motion detected! Turning light ON.");
    digitalWrite(lightPin, HIGH);  // Turn on light
    delay(5000);                   // Keep light on for 5 seconds
    digitalWrite(lightPin, LOW);   // Turn off light
    Serial.println("Light OFF.");
  } else {
    // No motion detected, keep light off
    digitalWrite(lightPin, LOW);
  }

  delay(100);  // Small delay to reduce sensor polling noise
}

7. Testing and Debugging Tips

• If the LED doesn’t light up:
  • Check PIR sensor orientation and connections.
  • Use Serial Monitor to verify PIR output status.
• Adjust the PIR sensor’s onboard potentiometers:
  • Sensitivity (distance detection).
  • Time delay (how long output stays HIGH).
• If using a relay, ensure the light bulb’s voltage and current are within the relay’s specs.

8. Project Extensions and Enhancements

• Replace LED with a relay module to control real 220V AC lights.
• Add a light-dependent resistor (LDR) to activate lights only at night.
• Log motion events to an SD card or send via Wi-Fi (ESP8266) for IoT-based home security.
• Add a buzzer for an audible alarm when motion is detected.
• Install in real-world environments like doorways, gardens, or staircases.