int t_p=5;
int e_p=18;
float ss=0.034;
long durn ;
float dist_cm;

void setup(){

  Serial.begin(115200);
  pinMode(t_p, OUTPUT);
  pinMode(e_p, INPUT);

}

void loop()
{
  digitalWrite(t_p, LOW);
  delayMicroseconds(2);
  digitalWrite(t_p, HIGH);
  delayMicroseconds(10);
  digitalWrite(t_p, LOW);
  durn=pulseIn(e_p,HIGH);
  dist_cm=durn*ss/2;
  Serial.print("distance= ");
  Serial.print(dist_cm);
  delay(1000);
}