#define TRIG_PIN D2
#define ECHO_PIN D3
#define LED_PIN  D4
#define BUZZER_PIN D7

unsigned long duration;
float distance;

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

  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
  pinMode(LED_PIN, OUTPUT);
  pinMode(BUZZER_PIN, OUTPUT);

  digitalWrite(TRIG_PIN, LOW);
  digitalWrite(LED_PIN, LOW);
  digitalWrite(BUZZER_PIN, LOW);

  Serial.println("Distance-Based Warning System Started");
}

void loop() {
  // Send ultrasonic trigger pulse
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);

  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);

  // Read echo pulse
  duration = pulseIn(ECHO_PIN, HIGH, 30000UL);

  if (duration == 0) {
    digitalWrite(LED_PIN, LOW);
    noTone(BUZZER_PIN);

    Serial.println("No echo detected - Check wiring");
    delay(300);
    return;
  }

  // Calculate distance in centimeters
  distance = duration * 0.0343f / 2.0f;

  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm");

  // Warning when obstacle is within 20 cm
  if (distance <= 20.0f) {
    digitalWrite(LED_PIN, HIGH);
    tone(BUZZER_PIN, 1000);
    Serial.println("WARNING! Object too close!");
  } else {
    digitalWrite(LED_PIN, LOW);
    noTone(BUZZER_PIN);
  }

  delay(200);
}