HC-SR04: Echo Time to Distance

Why it’s here

Connect a distance reading to a simple decision.

How it works

For this simplified ultrasonic example, echo duration in microseconds divided by 58 estimates centimeters. The model uses the distance control directly; it does not simulate sound propagation, reflection or timing noise.

Try it

1. Open this experiment
2. Run and move the obstacle between 10 cm and 50 cm. Compare the displayed distance with the changing echo duration.

Connections

• D9 — Ultrasonic trigger
• D10 — Ultrasonic echo
• 5V / GND — Module supply

Example sketch

void setup() {
  pinMode(9, OUTPUT);
  pinMode(10, INPUT);
  Serial.begin(9600);
}

void loop() {
  digitalWrite(9, LOW);
  delayMicroseconds(2);
  digitalWrite(9, HIGH);
  delayMicroseconds(10);
  digitalWrite(9, LOW);
  long cm = pulseIn(10, HIGH) / 58;
  Serial.println(cm);
}

Check your understanding

Why does a farther obstacle produce a longer echo time?