Interfacing Arduino with PIR Sensor

Ever wished your Arduino could act like a tiny security guard who never blinks? Meet the PIR sensor—a clever little gadget that detects motion faster than your cat spots a snack. In this DIY electronics experiment, you’ll learn how to interface an Arduino with a PIR (Passive Infrared) sensor to create your very own motion detection system. Whether you’re a curious kid or a seasoned tinkerer, this project will show you how a humble sensor can transform ordinary circuits into smart guardians. From spotting sneaky intruders to automating lights, this tutorial makes motion sensing both fun and surprisingly easy. Ready to give your Arduino a sixth sense? Let’s get moving!

Objective

To detect motion using a PIR sensor connected to an Arduino.

Theory

What is PIR Sensor: A Passive Infrared (PIR) sensor detects motion by measuring changes in infrared radiation emitted by warm objects (like humans).
How Does It Work: The sensor has two slots that detect infrared levels. When motion occurs, the levels change, triggering an output signal.
Why Use It: Motion detection is used in security systems, automatic lights, and smart home devices.
Learning Outcome: Understand how to connect, configure, and program an Arduino to detect motion events using a PIR sensor.

Components Required

Arduino Uno
Breadboard
Resistor 220Ω (for LED)
PIR Motion Sensor Module (HC-SR501)
Jumper Wires (Male-to-Male) 5-6
USB Power Cable
LED (Optional for indication)

Pin Diagram

Circuit Diagram

Assembly Steps

Connect PIR VCC pin to Arduino 5V
Connect PIR GND to Arduino GND
Connect PIR OUT to Arduino digital pin 2
Insert LED anode in pin 13 via 220Ω resistor (optional)
Connect LED cathode to GND
Plug in the USB cable

Tip: If the sensor has sensitivity and delay knobs, set them to mid-range for testing.

Arduino Code

1int pirPin = 2;    // PIR sensor output pin
2int ledPin = 13;   // Onboard LED
3
4void setup() {
5  pinMode(pirPin, INPUT);
6  pinMode(ledPin, OUTPUT);
7  Serial.begin(9600);
8  Serial.println("PIR Motion Sensor Test");
9}
10
11void loop() {
12  int motionState = digitalRead(pirPin);
13  if (motionState == HIGH) {
14    Serial.println("Motion Detected!");
15    digitalWrite(ledPin, HIGH);
16  } else {
17    Serial.println("No Motion.");
18    digitalWrite(ledPin, LOW);
19  }
20  delay(500);
21}

Code Explanation

1. Variable Declaration

int pirPin = 2;

pirPin tells the Arduino where the PIR sensor’s output is connected to digital pin 2.

int ledPin = 13;

ledPin sets pin 13 to control the onboard LED.

2. setup() Function

1void setup() {
2  pinMode(pirPin, INPUT);
3  pinMode(ledPin, OUTPUT);
4  Serial.begin(9600);
5  Serial.println("PIR Motion Sensor Test");
6}

pinMode(pirPin, INPUT): Sets pin 2 as input for the PIR sensor.
pinMode(ledPin, OUTPUT): Sets pin 13 as output for the LED.
Serial.begin(9600): Starts serial communication at 9600 baud.
Serial.println(...): Prints a test message on startup.

3. loop() Function

1void loop() {
2  int motionState = digitalRead(pirPin);
3  if (motionState == HIGH) {
4    Serial.println("Motion Detected!");
5    digitalWrite(ledPin, HIGH);
6  } else {
7    Serial.println("No Motion.");
8    digitalWrite(ledPin, LOW);
9  }
10  delay(500);
11}

digitalRead(pirPin): Reads the state of the PIR sensor.
if (motionState == HIGH): Checks if motion is detected.
digitalWrite(ledPin, HIGH): Turns ON the LED.
digitalWrite(ledPin, LOW): Turns OFF the LED.
delay(500): Waits for 500ms before checking again.

Line-by-Line Code Breakdown

Line	Code	Description
1	int pirPin = 2;	Define PIR sensor pin (digital pin 2).
2	int ledPin = 13;	Define LED pin (digital pin 13).
3	void setup() {	Start setup function (runs once at start).
4	pinMode(pirPin, INPUT);	Set PIR pin as INPUT.
5	pinMode(ledPin, OUTPUT);	Set LED pin as OUTPUT.
6	Serial.begin(9600);	Start serial communication at 9600 baud.
7	Serial.println("PIR Motion Sensor Test");	Print test message.
8	}	End of setup function.
9	void loop() {	Start loop function (repeats forever).
10	int motionState = digitalRead(pirPin);	Read PIR sensor state.
11	if (motionState == HIGH) {	Check if motion detected.
12	Serial.println("Motion Detected!");	Print motion message.
13	digitalWrite(ledPin, HIGH);	Turn LED ON.
14	} else {	If no motion detected...
15	Serial.println("No Motion.");	Print no motion message.
16	digitalWrite(ledPin, LOW);	Turn LED OFF.
17	}	End if-else block.
18	delay(500);	Wait 500 milliseconds.
19	}	End loop function.

Expected Outcome

Once your code is uploaded and the setup powered on:

Startup: Serial Monitor displays: PIR Motion Sensor Test
Motion Detected: LED lights up and Serial prints Motion Detected!
No Motion: LED stays off and Serial prints No Motion.
Loop: The detection checks run every 500ms continuously.

Troubleshooting

PIR sensor always HIGH: Adjust sensitivity knob; check connections
No Serial output: Verify Serial Monitor baud rate (9600)
LED not lighting: Check resistor and LED orientation
Random triggers: Reduce sensitivity or shield sensor

Related Experiments

Use multiple PIR sensors for room coverage
Connect to a buzzer instead of LED
Log motion data to an SD card
Trigger camera capture with motion

Fun Facts about PIR Sensor

PIR stands for Passive Infrared
They detect changes in infrared levels, not static heat
Used in automatic doors and wildlife cameras

Glossary of Terms

PIR Sensor: Device detecting infrared radiation changes
VCC: Positive voltage supply
GND: Ground connection
Digital Pin: Pin reading HIGH/LOW signal
Serial Monitor: Tool for viewing text output from Arduino