#define TRIG_PIN 5   // HC-SR04 Trigger pin
#define ECHO_PIN 18  // HC-SR04 Echo pin

#define RED_LED  21  // Red LED pin
#define GREEN_LED  19 // Green LED pin
#define YELLOW_LED  23 // Yellow LED pin
#define BUZZER_PIN  22 // Buzzer pin

// Thresholds for distance control
#define DANGER_DISTANCE 10   // Critical zone for red LED & buzzer
#define WARNING_DISTANCE 20  // Warning zone for yellow LED
#define SAFE_DISTANCE 30     // Safe zone for green LED

// Function to calculate distance in cm
long getDistance() {
    digitalWrite(TRIG_PIN, LOW);
    delayMicroseconds(2);
    
    digitalWrite(TRIG_PIN, HIGH);
    delayMicroseconds(10);
    digitalWrite(TRIG_PIN, LOW);

    long duration = pulseIn(ECHO_PIN, HIGH);
    long distance = duration * 0.034 / 2;  // Convert time to distance
    return distance;
}

void setup() {
    Serial.begin(115200);

    // Pin modes
    pinMode(TRIG_PIN, OUTPUT);
    pinMode(ECHO_PIN, INPUT);

    pinMode(RED_LED, OUTPUT);
    pinMode(GREEN_LED, OUTPUT);
    pinMode(YELLOW_LED, OUTPUT);
    pinMode(BUZZER_PIN, OUTPUT);

    // Start with all LEDs and buzzer off
    digitalWrite(RED_LED, LOW);
    digitalWrite(GREEN_LED, LOW);
    digitalWrite(YELLOW_LED, LOW);
    digitalWrite(BUZZER_PIN, LOW);
}

void loop() {
    long distance = getDistance();
    Serial.print("Distance: ");
    Serial.print(distance);
    Serial.println(" cm");

    // Logic for LEDs and buzzer
    if (distance < DANGER_DISTANCE) {
        digitalWrite(RED_LED, HIGH);
        digitalWrite(GREEN_LED, LOW);
        digitalWrite(YELLOW_LED, LOW);
        digitalWrite(BUZZER_PIN, HIGH); // Buzzer ON for danger
    } 
    else if (distance < WARNING_DISTANCE) {
        digitalWrite(RED_LED, LOW);
        digitalWrite(GREEN_LED, LOW);
        digitalWrite(YELLOW_LED, HIGH);
        digitalWrite(BUZZER_PIN, LOW); // Buzzer OFF
    } 
    else if (distance < SAFE_DISTANCE) {
        digitalWrite(RED_LED, LOW);
        digitalWrite(GREEN_LED, HIGH);
        digitalWrite(YELLOW_LED, LOW);
        digitalWrite(BUZZER_PIN, LOW); // Buzzer OFF
    } 
    else {
        // All off if distance is safe
        digitalWrite(RED_LED, LOW);
        digitalWrite(GREEN_LED, LOW);
        digitalWrite(YELLOW_LED, LOW);
        digitalWrite(BUZZER_PIN, LOW);
    }

    delay(500); // Delay for stable readings
}