#define TRIG_PIN 2
#define ECHO_PIN 3
#define LED_PIN 4

long duration;
int distance;
bool timerPaused = false;
unsigned long previousMillis = 0;
const unsigned long interval = 5000; // 5 seconds

void setup() {
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
  pinMode(LED_PIN, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  unsigned long currentMillis = millis();

  // Start timer for the first 5 seconds
  if (currentMillis < interval) {
    digitalWrite(LED_PIN, LOW); // Turn off the LED
    timerPaused = false;
    delay(100);
  }

  // Wait for the sensor to detect something within 30cm
  else if (currentMillis >= interval && !timerPaused) {
    digitalWrite(LED_PIN, HIGH); // Turn on the LED
    digitalWrite(TRIG_PIN, LOW);
    delayMicroseconds(2);
    digitalWrite(TRIG_PIN, HIGH);
    delayMicroseconds(10);
    digitalWrite(TRIG_PIN, LOW);
    duration = pulseIn(ECHO_PIN, HIGH);
    distance = duration / 58;
    Serial.println(distance);
    
    if (distance > 0 && distance < 30) {
      // Start timer for the second 5 seconds
      previousMillis = currentMillis;
      timerPaused = false;
    }
    else {
      // Pause the timer and turn on the LED
      timerPaused = true;
      digitalWrite(LED_PIN, HIGH);
    }
    delay(100);
  }

  // Wait for the sensor to detect nothing within 30cm
  else if (currentMillis - previousMillis >= interval && timerPaused) {
    digitalWrite(LED_PIN, HIGH); // Turn on the LED
    digitalWrite(TRIG_PIN, LOW);
    delayMicroseconds(2);
    digitalWrite(TRIG_PIN, HIGH);
    delayMicroseconds(10);
    digitalWrite(TRIG_PIN, LOW);
    duration = pulseIn(ECHO_PIN, HIGH);
    distance = duration / 58;
    Serial.println(distance);

    if (distance == 0 || distance >= 30) {
      // Start the next cycle
      previousMillis = currentMillis;
      timerPaused = false;
    }
    delay(100);
  }

  // Turn off the LED when the timer is over
  else {
    digitalWrite(LED_PIN, LOW); // Turn off the LED
    timerPaused = false;
    delay(100);
  }
}