Code 06 Measure distance

// Measure distance

/*
 * HC-SR04 ultrasonic
 * 
*/
// librairies declaration
#include <MKRWAN_v2.h> // to control the LoRaWAN Modem (execute first the MKRWANFWUpdate_standalone)

// variables declaration
String codeversion="1.06";
double ustime; //variable used to measure the US time [µs]
float usdist; // variable used to measure the distance [m]

// Pins wiring (hardware)
const int TrigPin = 3; // pin to trigger a measure from the ultrasonic sensor
const int EchoPin = 4; // pin to measure the duration of the sound wave

///////////////////////////////////////////////////
void setup() //SETUP - EXECUTE ONLY ONCE AT THE START
{   
  Serial.begin(9600); // initial serial connection
  pinMode(TrigPin, OUTPUT); // Set up the pin to start a new ultrasonic measure
  pinMode(EchoPin, INPUT);  // Set up pin to input mode to detect the ultrasonic wave 
  delay(2000); // sometimes it's good to wait a little
  Serial.println("version: "+codeversion); // write the version in the serial
} 

//////////////////////////////////////////
void loop() // MAIN PROGRAM LOOP - FOREVER
{ 
  // Measurements
  ustime = single_measure_US(); //ultrasonic measure - duration of signal in µs
  usdist = ustime/2*343/1E6; // convert duration into distance (speed of sound = 343 m/s)

  // Display values
  Serial.print("Ultrasonic time = ");
  Serial.print(ustime,0); // duration without decimals
  Serial.print(" µs and distance = ");
  Serial.print(usdist,3); // distance in m with 3 decimals (up to the millimeter)
  Serial.println("m.");

  delay(10000); // wait 10 seconds for the next measurement
}

///////////////////////////////////////////////////////////////////////////
double single_measure_US() { // SUBROUTINE TO DO ONE ULTRASONIC MEASUREMENT
  double dtime; // variable use to store the duration of the pulse (for the measure of the distance)
  digitalWrite(TrigPin, LOW); 
  delayMicroseconds(10); // To be sure that the pin is low (0 V)
  digitalWrite(TrigPin, HIGH); 
  delayMicroseconds(10); // Generate a 10us high wave to trigger TrigPin (3.3 V)
  digitalWrite(TrigPin, LOW); 
  dtime = pulseIn(EchoPin, HIGH); // measure the duration in microseconds, https://www.arduino.cc/reference/en/language/functions/advanced-io/pulsein/
  delay(50); //pause (50ms) to make sure there is no interferences with the next measure
  return dtime; // send back the value from the subroutine to the main program (loop), time is in µs
}