int trig_pin = 2;
int echo_pin = 3;
long echotime;
float distance;

void setup() {
Serial.begin(9600);
pinMode(trig_pin, OUTPUT);
pinMode(echo_pin, INPUT);
digitalWrite(trig_pin, LOW);
}

void loop() {
digitalWrite(trig_pin, HIGH);
delayMicroseconds(10);
digitalWrite(trig_pin, LOW);
echotime= pulseIn(echo_pin, HIGH);
distance= 0.0001 * ((float)echotime * 340.0) / 2.0;
Serial.print(distance);
Serial.println("cm");
delay(2000);
}