Use a PIR sensor to detect human movement and automatically switch ON an LED. This demonstrates the technology used in security systems, automatic lights, smart homes, and occupancy detection.
Every step includes a visual reference and a plain-language explanation, so you always know what to do next.
This sketch triggers a pulse, times the echo, converts it to centimetres using the speed of sound, and prints the result every 500ms.
const int pirPin = 2;
const int ledPin = 8;
void setup() {
pinMode(pirPin, INPUT);
pinMode(ledPin, OUTPUT);
Serial.begin(9600);
}
void loop() {
int motion = digitalRead(pirPin);
if (motion == HIGH) {
digitalWrite(ledPin, HIGH);
Serial.println("Motion Detected!");
} else {
digitalWrite(ledPin, LOW);
Serial.println("No Motion");
}
delay(100);
}Confirm the baud rate in the Serial Monitor is set to 9600, matching Serial.begin(9600) in the code.
Make sure nothing is placed right in front of the sensor (under ~2cm) and that the sensor is on a stable, flat mount.
Re-check TRIG is on pin 9 and ECHO is on pin 10, and that VCC/GND are wired correctly — a reversed connection can prevent it from powering on.
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