ESP32: HC-SR04 Ultrasonic Distance
ESP32: HC-SR04 Ultrasonic Distance is a runnable microcontroller simulation example on SensBench — open the wired circuit, inspect the code, and compile real firmware in your browser, no install needed. Last updated Aug 14, 2026.
FREE SIMULATOR EXAMPLE · BEGINNER
ESP32: HC-SR04 Ultrasonic Distance
This example measures distance with an HC-SR04 ultrasonic sensor: TRIG on GPIO18, ECHO on GPIO19, and the result in centimetres printed to the Serial Monitor twice a second. No libraries at all — the timing protocol is done by hand, so you can see exactly what the sensor expects.
| Board | ESP32 DevKit (Xtensa LX6, 240 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 — HC-SR04 Ultrasonic Distance Sensor
// Wiring: TRIG → D18 | ECHO → D19 | VCC → 3V3 | GND → GND
#define TRIG_PIN 18
#define ECHO_PIN 19
void setup() {
Serial.begin(115200);
pinMode(TRIG_PIN, OUTPUT);
pinMode(ECHO_PIN, INPUT);
Serial.println("ESP32 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
measureCm() bit-bangs the whole protocol: TRIG low for 2 µs, high for exactly 10 µs via delayMicroseconds(10), then low again. That 10 µs pulse is the contract — it tells the HC-SR04 to fire eight 40 kHz ultrasonic bursts and raise ECHO for as long as the sound takes to come back.
The measurement is pulseIn(ECHO_PIN, HIGH, 30000UL): it times the ECHO pulse in microseconds with a 30 ms timeout, returning 0 if nothing echoes. Then d * 0.0343 / 2.0 converts time to centimetres — 0.0343 cm/µs is the speed of sound, halved because the pulse flew there and back. A −1 sentinel on timeout is what prints “Out of range”.
Before you build it for real
The simulator wires VCC to 3V3 and it works — on a real bench the HC-SR04 is a 5 V part. At 3.3 V the transducers are underdriven and range collapses, and at 5 V the ECHO pin pushes 5 V back into GPIO19, which is not 5 V tolerant: use a voltage divider (1 kΩ + 2 kΩ) on ECHO. Second, pulseIn() is blocking — with the 30 ms timeout your loop stalls up to 30 ms per reading. Fine for a demo, fatal for a robot that also needs to steer.
Get the parts
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FAQ
Why does it print "Out of range"?
pulseIn() returned 0, meaning no echo arrived within the 30 ms timeout — roughly five metres of round trip. On real hardware it usually means the sensor is aimed at a soft or angled surface, the target is beyond range, or TRIG and ECHO are swapped.
How accurate is the 0.0343 conversion?
0.0343 cm/µs is the speed of sound at about 20 °C; it drifts roughly 0.6 m/s per degree of air temperature. For a demo expect ±1 cm — plenty for a parking sensor. If you need better, scale the constant by a measured temperature from a second sensor.