Echo sensor

#define triggerPin D4
#define echoPin D0

void setup() {
Serial.begin (9600);
pinMode(triggerPin, OUTPUT);
pinMode(echoPin, INPUT);
}

void loop() {
long duration, jarak;
digitalWrite(triggerPin, LOW);
delayMicroseconds(2);
digitalWrite(triggerPin, HIGH);
delayMicroseconds(10);
digitalWrite(triggerPin, LOW);
duration = pulseIn(echoPin, HIGH);
jarak = (duration/2) / 29.1; // rumus ultrasonic
Serial.println("jarak :");
Serial.print(jarak);
Serial.println(" cm");
delay(1000);
}