PIR Motion Indicator

Steps

1. Identify the module pins

   Read the markings on your HC-SR501 PCB: pin order can vary. With USB disconnected, connect VCC to UNO 5V, GND to GND and OUT to D2.

2. Add an indicator

   Connect D8 through a 220 ohm resistor to the red LED anode and connect its cathode to GND.

3. Upload and allow warm-up

   Upload the sketch and open Serial Monitor at 9600 baud. Keep the area still for at least 60 seconds while the PIR settles.

4. Test the detection

   Move across the sensor field of view. The LED lights while OUT is HIGH. Adjust the module sensitivity and hold-time controls gently. The sensor detects changes in infrared energy; it cannot prove someone is still present.

Code

const byte PIR = 2, LED = 8;
void setup() {
  pinMode(PIR, INPUT); pinMode(LED, OUTPUT); digitalWrite(LED, LOW);
  Serial.begin(9600); Serial.println("PIR warming up: keep still for 60 seconds");
  delay(60000);
}
void loop() {
  bool detected = digitalRead(PIR) == HIGH;
  digitalWrite(LED, detected ? HIGH : LOW);
  Serial.println(detected ? "Motion output HIGH" : "Motion output LOW");
  delay(250);
}