int Echo = D6;
int Trig = D5;
int Vcc = D4;
int duration=0, distance=0;

void setup() {
  Serial.begin(9600);
  pinMode(Vcc, OUTPUT);
  pinMode(Trig, OUTPUT);
  pinMode(Echo, INPUT);
  delay(1000);
  digitalWrite(Vcc,HIGH);
}

void loop() {
  digitalWrite(Trig,HIGH);
  delayMicroseconds(10);
  digitalWrite(Trig,LOW);
  duration=pulseIn(Echo,HIGH,4000); 
  //record the time duration between the trig and echo. 4000 is the number of microseconds to wait for the pulse to start
  Serial.print("The duration is ");
  Serial.print(duration);
  Serial.print("µs");
  distance=duration*0.0343/2;  
  //distance=duration time/2 * speed of sound(343 m/s = 0.0343 cm/µs), unit in cm
  Serial.print(". The distance is ");
  Serial.print(distance);
  Serial.print("cm");
  Serial.println(""); 
  delay(200);
}