const int trigPins[4] = {5, 7, 9, 11};  // Trig 
const int echoPins[4] = {6, 8, 10, 12}; // Echo 

void setup() {
  Serial.begin(115200);
  for (int i = 0; i < 4; i++) {
    pinMode(trigPins[i], OUTPUT);
    pinMode(echoPins[i], INPUT);
  }
  Serial.println("Starting RCWL-1655 test...");
}

void loop() {
  for (int i = 0; i < 4; i++) {
    digitalWrite(trigPins[i], LOW);
    delayMicroseconds(2);
    digitalWrite(trigPins[i], HIGH);
    delayMicroseconds(10);
    digitalWrite(trigPins[i], LOW);

    long duration = pulseIn(echoPins[i], HIGH, 30000);
    float distance_cm = duration * 0.0343 / 2.0; 

    Serial.print("Sensor ");
    Serial.print(i + 1);
    Serial.print(": ");

    if (duration == 0) {
      Serial.println("No Echo");
    } else {
      Serial.print(distance_cm);
      Serial.println(" cm");
    
    delay(200);
  }

  Serial.println("----");
  delay(300);
}