const int TRIG_PIN_1 = 6; // Arduino pin connected to Ultrasonic Sensor's TRIG pin
const int ECHO_PIN_1 = 7; // Arduino pin connected to Ultrasonic Sensor's ECHO pin
const int TRIG_PIN_2 = 5; // Arduino pin connected to Ultrasonic Sensor's TRIG pin
const int ECHO_PIN_2 = 8; // Arduino pin connected to Ultrasonic Sensor's ECHO pin

// variables will change:
float duration_us_1 , distance_cm_1 ;
float duration_us_2 , distance_cm_2 ;

void setup() 
{
  Serial.begin (9600);       // initialize serial port

  pinMode(TRIG_PIN_1, OUTPUT); // set arduino pin to output mode
  pinMode(ECHO_PIN_1, INPUT);  // set arduino pin to input mode

  pinMode(TRIG_PIN_2, OUTPUT); // set arduino pin to output mode
  pinMode(ECHO_PIN_2, INPUT);  // set arduino pin to input mode

}

void loop() 
{
  // generate 10-microsecond pulse to TRIG pin
  digitalWrite(TRIG_PIN_1, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN_1, LOW);

  // measure duration of pulse from ECHO pin
  duration_us_1 = pulseIn(ECHO_PIN_1, HIGH);
  // calculate the distance
  distance_cm_1 = 0.017 * duration_us_1;
  
  // print the value to Serial Monitor
  Serial.print("distance_1: ");
  Serial.print(distance_cm_1);
  Serial.println(" cm");
  delay(500);



  // generate 10-microsecond pulse to TRIG pin
  digitalWrite(TRIG_PIN_2, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN_2, LOW);

  // measure duration of pulse from ECHO pin
  duration_us_2 = pulseIn(ECHO_PIN_2, HIGH);
  // calculate the distance
  distance_cm_2 = 0.017 * duration_us_2;
  
  // print the value to Serial Monitor
  Serial.print("distance_2: ");
  Serial.print(distance_cm_2);
  Serial.println(" cm");
  delay(500);
}