#define trigPin 12 // define trig pin
#define echoPin 11 // define echo pin
#define MAX_DISTANCE 500 // define max distance
// define the timeOut according to the maximum range. timeOut= 2*MAX_DISTANCE /100 /340*1000000 = MAX_DISTANCE*58.8
float timeOut = MAX_DISTANCE * 58.8;
int soundVelocity = 340; // speed of sound = 340m/s

void setup() {
  // put your setup code here, to run once:
  pinMode(trigPin, OUTPUT); // trig pin set to output mode
  pinMode(echoPin, INPUT); // echo pin set to input mode
  Serial.begin(9600); // baud rate 9600
}

void loop() {
  // put your main code here, to run repeatedly:
  delay(100); // 20 pings per second (29ms is shortest delay)
  Serial.print("Ping: ");
  Serial.print(getSonar()); // Send ping, get distance in cm, print result (0 if out of range)
  Serial.println("cm");
}

float getSonar(){
  unsigned long pingTime;
  float distance;
  digitalWrite(trigPin, HIGH); // make trigPin output high level to help triger HC_SR04
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
  pingTime = pulseIn(echoPin, HIGH, timeOut);
  // calculate distance
  distance = (float)pingTime * soundVelocity / 2 / 10000;
  // return distance value
  return distance;
}