Using a HC-SR501 PIR to detect movement.

This PIR sketch detects movement in a room and prints a message to the Serial Monitor as well as sounding a buzzer. The Arduino pin used to drive the buzzer could just as easily drive a LED or a relay.

The layout is shown below, a small speaker is connected between Gnd and pin 10. The PIR unit has three connections, connect Vcc to the Arduino 5volts , Gnd to Arduino Gnd and the signal output to Arduino pin 2.


The sketch is shown here.


Uses a PIR sensor to detect movement, sounds a buzzer


int ledPin = 13; // choose the pin for the LED
int inputPin = 2; // choose the input pin (for PIR sensor)
int pirState = LOW; // we start, assuming no motion detected
int val = 0; // variable for reading the pin status
int pinSpeaker = 10; //Set up a speaker on a PWM pin (digital 9, 10, or 11)

void setup() {
pinMode(ledPin, OUTPUT); // declare LED as output
pinMode(inputPin, INPUT); // declare sensor as input
pinMode(pinSpeaker, OUTPUT);

Serial.println ("Calibrating sensor");
delay (2000); // it takes the sensor 2 seconds to scan the area
Serial.println ("Done!");

void loop(){
val = digitalRead(inputPin); // read input value
if (val == HIGH) { // check if the input is HIGH
blinky(); // blink LED when motion haas been detected
//digitalWrite(ledPin, HIGH); // turn LED ON
playTone(300, 160);
if (pirState == LOW) {
// we have just turned on
Serial.println("Motion detected!");
// We only want to print on the output change, not state
pirState = HIGH;
else {
digitalWrite(ledPin, LOW); // turn LED OFF
playTone(0, 0);
if (pirState == HIGH){
// we have just turned off
Serial.println("Motion ended!");
// We only want to print on the output change, not state
pirState = LOW;

void playTone(long duration, int freq) {
// duration in mSecs, frequency in hertz
duration *= 1000;
int period = (1.0 / freq) * 1000000;
long elapsed_time = 0;
while (elapsed_time < duration) {
delayMicroseconds(period / 2);
digitalWrite(pinSpeaker, LOW);
delayMicroseconds(period / 2);
elapsed_time += (period);

void blinky() {
for(int i=0; i<3; i++) {
digitalWrite(13, HIGH);
digitalWrite(13, LOW);


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