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Motion-Activated Light (PIR + Arduino)

Turn an LED on when a PIR sensor detects movement. Learn digital input from a real-world sensor.

Beginner15 min

What you need

Wiring

Arduino Uno
PIR sensor
LED

Hover a pin or a wire to trace the connection.

Code

pir_light.ino
// Light an LED whenever the PIR sensor detects motion.
const int pirPin = 2;
const int ledPin = 13;

void setup() {
  pinMode(pirPin, INPUT);
  pinMode(ledPin, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  if (digitalRead(pirPin) == HIGH) {   // motion detected
    digitalWrite(ledPin, HIGH);
    Serial.println("Motion!");
  } else {
    digitalWrite(ledPin, LOW);
  }
  delay(100);
}

Steps

  1. Wire the PIR: VCC to 5V, GND to GND, OUT to D2.
  2. Wire the LED on D13 through a 220Ω resistor, cathode to GND.
  3. Upload, then let the sensor settle ~30–60s.
  4. Wave your hand — the LED lights. Tune the sensor's two pots for range and hold time.