FREE SIMULATOR EXAMPLE · BEGINNER

ESP32-C3: HC-SR04 Ultrasonic Distance

This example measures distance with an HC-SR04 ultrasonic sensor — TRIG on GPIO5, ECHO on GPIO6 — and prints a centimeter reading to the Serial Monitor twice a second. There are no libraries at all: the whole protocol is a ten-microsecond trigger pulse and a timer, written out by hand so you can see exactly what the sensor does.

Board	ESP32-C3 (RISC-V single-core, 160 MHz)
Difficulty	beginner
Category	sensors
Libraries	None — just the Arduino core
Runs in	Sensbench browser simulator — free, no account

The exact circuit you get when you open this example — already wired, ready to run.

The sketch

// ESP32-C3 — HC-SR04 Ultrasonic Distance Sensor
// Wiring: TRIG → GPIO5  |  ECHO → GPIO6  |  VCC → 3V3  |  GND → GND

#define TRIG_PIN 5
#define ECHO_PIN 6

void setup() {
  Serial.begin(115200);
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
  Serial.println("ESP32-C3 HC-SR04 ready");
}

long measureCm() {
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);
  long d = pulseIn(ECHO_PIN, HIGH, 30000UL);
  return (d == 0) ? -1 : (long)(d * 0.0343 / 2.0);
}

void loop() {
  long cm = measureCm();
  if (cm < 0) Serial.println("Out of range");
  else        Serial.printf("Distance: %ld cm\n", cm);
  delay(500);
}

How it works

An HC-SR04 transaction has two halves: you ask, it answers. measureCm() pulls TRIG low, then high for exactly ten microseconds — delayMicroseconds(10) — which tells the sensor to fire its burst of 40 kHz pulses. ECHO then goes high for as long as the sound takes to reach the target and come back.

pulseIn(ECHO_PIN, HIGH, 30000UL) measures that high time in microseconds, with a 30 ms timeout — about five meters of round trip, comfortably past the sensor’s rated 400 cm. If it times out, pulseIn returns 0, measureCm() returns -1, and the sketch prints “Out of range” instead of a bogus zero-centimeter reading.

The conversion, d * 0.0343 / 2.0, is the speed of sound in cm/µs at 20 °C, divided by two because the pulse travels out and back. No library, no floating-point mystery — the entire protocol is visible in about twelve lines, which is exactly why this example is worth reading before you reach for a library.

Before you build it for real

Get the parts

Related examples

FAQ

Why does it print "Out of range"?

pulseIn() timed out — 30 ms passed with no ECHO pulse, which means either nothing is within roughly five meters, the target is closer than the sensor’s 2 cm blind spot, or a wire is loose. In the simulator, first check ECHO actually landed on GPIO6.

How accurate is the 0.0343 factor?

That is the speed of sound at 20 °C expressed in cm/µs. It drifts roughly 0.17 % per degree, so expect centimeter-scale error outdoors on a hot day. For a parking sensor it is fine; for anything tighter, add a temperature sensor and scale the constant.