How to Use PIR Motion Sensor with Arduino: Simple Guide

To use a PIR motion sensor with Arduino, connect its power and output pins to the Arduino, then read the sensor's digital output in your code using digitalRead(). When motion is detected, the sensor outputs HIGH, which you can use to trigger actions like turning on an LED.

Syntax

Here is the basic syntax to read a PIR sensor connected to an Arduino digital pin:

• pinMode(pin, INPUT); sets the sensor pin as input.
• digitalRead(pin) reads the sensor state: HIGH means motion detected, LOW means no motion.

arduino

const int pirPin = 2;  // PIR sensor output pin

void setup() {
  pinMode(pirPin, INPUT);  // Set PIR pin as input
  Serial.begin(9600);     // Start serial communication
}

void loop() {
  int motionState = digitalRead(pirPin);  // Read PIR sensor
  if (motionState == HIGH) {
    Serial.println("Motion detected!");
  } else {
    Serial.println("No motion.");
  }
  delay(1000);  // Wait 1 second before next read
}

Example

This example shows how to connect a PIR sensor to Arduino pin 2 and turn on the built-in LED on pin 13 when motion is detected.

arduino

const int pirPin = 2;      // PIR sensor output pin
const int ledPin = 13;     // Built-in LED pin

void setup() {
  pinMode(pirPin, INPUT);  // PIR sensor as input
  pinMode(ledPin, OUTPUT); // LED as output
  Serial.begin(9600);      // Start serial communication
}

void loop() {
  int motionState = digitalRead(pirPin);  // Read PIR sensor
  if (motionState == HIGH) {
    digitalWrite(ledPin, HIGH);            // Turn LED on
    Serial.println("Motion detected!");
  } else {
    digitalWrite(ledPin, LOW);             // Turn LED off
    Serial.println("No motion.");
  }
  delay(500);  // Check twice per second
}

Output

Motion detected!
No motion.
Motion detected!
No motion.
...

Common Pitfalls

Common mistakes when using a PIR sensor with Arduino include:

• Not giving the sensor enough warm-up time (usually 30-60 seconds) before reading values.
• Connecting the sensor output to an analog pin and using analogRead() instead of digitalRead().
• Not using the correct power supply voltage (usually 5V) or wiring the sensor incorrectly.
• Ignoring sensor noise by reading too fast without delay.

arduino

/* Wrong way: reading PIR sensor on analog pin with analogRead() */
const int pirPin = A0;

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

void loop() {
  int val = analogRead(pirPin);  // Incorrect for PIR sensor
  Serial.println(val);
  delay(500);
}

/* Right way: use digital pin and digitalRead() */
const int pirPinCorrect = 2;

void setup() {
  pinMode(pirPinCorrect, INPUT);
  Serial.begin(9600);
}

void loop() {
  int val = digitalRead(pirPinCorrect);  // Correct
  Serial.println(val);
  delay(500);
}

Quick Reference

Summary tips for using PIR motion sensor with Arduino:

Step	Description
Connect VCC to 5V	Power the PIR sensor with 5 volts from Arduino.
Connect GND to GND	Connect sensor ground to Arduino ground.
Connect OUT to digital pin	Use a digital pin (e.g., pin 2) to read sensor output.
Use pinMode(pin, INPUT)	Set the sensor pin as input in setup().
Use digitalRead(pin)	Read sensor state: HIGH means motion detected.
Add delay	Add delay to avoid noisy readings and allow sensor warm-up.

Key Takeaways

Connect PIR sensor output to an Arduino digital input pin and power it with 5V and GND.

Use digitalRead() to detect motion: HIGH means motion detected, LOW means no motion.

Allow the PIR sensor 30-60 seconds to warm up before reading values.

Add delays between readings to reduce noise and false triggers.

Use the built-in LED or serial output to verify sensor detection in your code.