const int TrigPin = 13; // define TrigPin
const int EchoPin = 14; // define EchoPin.
int duration = 0; // Define the initial value of the duration to be 0
int distance = 0;//Define the initial value of the distance to be 0
void setup() 
{
  pinMode(TrigPin , OUTPUT); // set trigPin to output mode
  pinMode(EchoPin , INPUT); // set echoPin to input mode
  Serial.begin(9600);  // Open serial monitor at 9600 baud to see ping results.
}
void loop()
{
 // make trigPin output high level lasting for 10μs to triger HC_SR04 
  digitalWrite(TrigPin , HIGH);
  delayMicroseconds(10);
  digitalWrite(TrigPin , LOW);
  // Wait HC-SR04 returning to the high level and measure out this waitting time
  duration = pulseIn(EchoPin , HIGH);
  // calculate the distance according to the time
  distance = (duration/2) * 0.0343;  //velocidad app 343m/s = 0.043 cm/us
  Serial.print("Distance: ");
  Serial.print(distance); //Serial port print distance value
  Serial.println("cm");
  delay(300); // Wait 100ms between pings (about 20 pings/sec).
}