Four main types of motion sensors: ①PIR Sensor②ultrasonic sensor③microwave sensor④Capacitive Sensor

				
					#include <Wire.h>
#include <BH1750.h>

BH1750 lightMeter;

// Pin definitions
const int pirPin = 2;    // PIR sensor connection pin
const int ledPin = 3;    // LED connection pin

// Variable definitions
int lightThreshold = 50; // Light threshold (lux)
bool isDark = false;     // Flag for dark environment
unsigned long ledOnTime = 0; // LED on timestamp
const unsigned long ledDuration = 5000; // LED keep-on duration (5 seconds)
bool ledActive = false;  // Flag for LED active state

void setup() {
  Serial.begin(9600);
  Wire.begin();
  
  // Initialize BH1750
  if (lightMeter.begin(BH1750::CONTINUOUS_HIGH_RES_MODE)) {
    Serial.println(F("BH1750 initialization successful"));
  } else {
    Serial.println(F("BH1750 initialization failed"));
  }
  
  // Set pin modes
  pinMode(pirPin, INPUT);
  pinMode(ledPin, OUTPUT);
  
  // Initial state
  digitalWrite(ledPin, LOW);
}

void loop() {
  // Read light intensity
  float lux = lightMeter.readLightLevel();
  
  Serial.print("Light intensity: ");
  Serial.print(lux);
  Serial.println(" lx");
  
  // Check if ambient light is insufficient
  isDark = (lux < lightThreshold);
  
  if (isDark) {
    Serial.println("Insufficient ambient light, activating motion detection");
    
    // Read PIR sensor (with debounce)
    bool currentMotion = checkMotion();
    
    if (currentMotion && !ledActive) {
      Serial.println("Human motion detected - turning on LED");
      digitalWrite(ledPin, HIGH);
      ledOnTime = millis();
      ledActive = true;
    }
    
    // Check if LED needs to be turned off
    if (ledActive && (millis() - ledOnTime >= ledDuration)) {
      digitalWrite(ledPin, LOW);
      ledActive = false;
      Serial.println("LED has been on for 5 seconds, turning off automatically");
    }
    
  } else {
    // Ensure LED is off when ambient light is sufficient
    if (ledActive) {
      digitalWrite(ledPin, LOW);
      ledActive = false;
      Serial.println("Sufficient ambient light, turning off LED");
    }
  }
  
  delay(200); // Shorten detection interval
}

// Improved motion detection function (with debounce)
bool checkMotion() {
  // Read 3 consecutive times for confirmation
  int positiveCount = 0;
  for (int i = 0; i < 3; i++) {
    if (digitalRead(pirPin) == HIGH) {
      positiveCount++;
      delay(50); // Small delay
    } else {
      break; // Interrupt if there's a low level in between
    }
  }
  return (positiveCount == 3); // Confirm only if 3 consecutive high levels
}