/* Sensor Ultrasonik HC-SR04 — ukur jarak */ const int trigPin = 9;const int echoPin = 10;const int ledPin  = 13; long duration;int  distance; void setup() {  pinMode(trigPin, OUTPUT);  pinMode(echoPin, INPUT);  pinMode(ledPin, OUTPUT);  Serial.begin(9600);} void loop() {  digitalWrite(trigPin, LOW);  delayMicroseconds(2);  digitalWrite(trigPin, HIGH);  delayMicroseconds(10);  digitalWrite(trigPin, LOW);   duration = pulseIn(echoPin, HIGH);  distance = duration * 0.034 / 2;   Serial.print("Jarak: ");  Serial.print(distance);  Serial.println(" cm");   if (distance < 20) {    digitalWrite(ledPin, HIGH);  } else {    digitalWrite(ledPin, LOW);  }   delay(100);}