ESP32 · HC-SR04

ESP32 HC-SR04 Simulator: Wiring, Code and a Live Circuit

This is an HC-SR04 ultrasonic distance sensor wired to an ESP32 DevKit, measuring live: the board pings ten times a second and prints the distance in centimeters. In the editor, drag the sensor’s distance slider and the reading follows.

The module runs from VIN (5 V from USB), TRIG is on GPIO 4 (D4) and ECHO on GPIO 5 (D5). Because the ESP32 is a 3.3 V board, the wiring notes show the two resistors a real ECHO line needs.

Run it in the editor Read the code

3.3 V logic
No library: pulseIn()
TRIG 4, ECHO 5
Range 2 to 400 cm

ESP32 · HC-SR04live0.000 s 0.00x

Click to open it in the editor

The circuit itself, running on the simulator with the sketch below. Press what can be pressed; click anything else to open it in the editor.

Wiring the HC-SR04 to the ESP32

Every connection in the circuit above, with the board’s own pin names.

HC-SR04 pin	ESP32 pin	Why
VCC	VIN (5 V from USB)	The HC-SR04 is a 5 V module; below about 4.5 V many units stop answering.
TRIG	GPIO 4 (D4)	Output from the board: a 10 microsecond pulse starts a ping.
ECHO	GPIO 5 (D5)	Input to the board. It swings to 5 V, so on a real board put a divider here (see below).
GND	GND	Common ground.

The HC-SR04 needs 5 V, so VCC goes to VIN (5 V from USB), and its ECHO output is then a 5 V signal. The ESP32 (Xtensa LX6)’s pins are not 5 V tolerant, so on the bench put a divider on ECHO: 1 k from ECHO to GPIO 5 (D5), and 2 k from GPIO 5 (D5) to GND, which brings 5 V down to 3.3 V. TRIG needs nothing; 3.3 V is enough to trigger it. The simulator draws the direct wire so the circuit stays readable, and does not model the damage.

Pins to leave alone on the ESP32

GPIO 34, 35, 36 (VP) and 39 (VN) are input only: they cannot drive a pin or take an internal pull-up. GPIO 0, 2, 5, 12 and 15 are strapping pins, read at power-on, and GPIO 6 to 11 are the flash chip.

On a real bench

The thirty-pin DevKit straddles a breadboard with one row of holes free on each side, which is where the HC-SR04’s jumpers go. Many ESP32 boards are wider and cover both rows; then use two breadboards side by side. Hold BOOT while uploading if the IDE cannot connect.

The code

The sketch the circuit above runs. Open it in the editor, change a line and press Run: it compiles in your browser.

HC-SR04 on ESP32

const int TRIG_PIN = 4;   // GPIO 4 (D4)
const int ECHO_PIN = 5;   // GPIO 5 (D5)

void setup() {
  Serial.begin(115200);
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
}

void loop() {
  // A pulse of at least 10 us on TRIG starts one measurement.
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);

  // ECHO stays high for the sound's round trip; 38 ms means nothing in range.
  unsigned long us = pulseIn(ECHO_PIN, HIGH, 38000UL);
  if (us == 0) {
    Serial.println("Out of range");
  } else {
    Serial.print("Distance: ");
    Serial.print(us / 58);
    Serial.println(" cm");
  }
  delay(100);
}

Holding TRIG high for 10 microseconds (the module needs at least 10) makes it send eight 40 kHz pulses. It then raises ECHO and lowers it again when the echo returns, so the width of the ECHO pulse is the round trip time of the sound.

pulseIn(ECHO_PIN, HIGH, 38000UL) measures that width in microseconds. Sound covers a centimeter and back in about 58 microseconds, so dividing by 58 gives centimeters. The 38 ms timeout is what the module does with nothing in range; without a timeout pulseIn() waits a full second.

The 100 ms delay keeps one ping’s echo from being heard by the next. Serial.begin(115200) opens the serial monitor. Serial is UART0 on the USB bridge. ESP32 sketches usually run it at 115200 baud, which this one does.

Common mistakes with the HC-SR04 on the ESP32

ECHO straight into a 3.3 V pin

It reads correctly, so it looks fine. But ECHO swings to 5 V and the ESP32 (Xtensa LX6) is rated to 3.6 V, so the pin is overstressed on every ping. Add the 1 k and 2 k divider, or use an HC-SR04P, the 3.3 V version.

pulseIn() without a timeout

With nothing in front of the sensor, pulseIn() with no third argument waits a whole second for a pulse that never comes, and the sketch looks frozen. Pass a timeout of about 38000 microseconds.

Pinging too fast

Fire the next ping before the last echo has died away and the module hears its own previous ping, so short random distances appear. Leave at least 60 ms between measurements.

Questions and answers

Can I simulate an HC-SR04 with an ESP32 DevKit?

Yes. The circuit at the top of this page is an ESP32 DevKit with a HC-SR04, running in your browser on a simulated ESP32 (Xtensa LX6). The sensor’s slider sets the distance to the object, from nothing in range up to 4 meters, and the ECHO pulse is as wide as a real one would be. Press Run it in the editor to change the wiring or the code; it is free and needs no account.

Does the HC-SR04 work with the ESP32?

Yes, powered from VIN (5 V from USB). TRIG works from a 3.3 V pin; ECHO needs a voltage divider down to 3.3 V on real hardware, or use the 3.3 V HC-SR04P.

Why do I get 0 or "Out of range"?

pulseIn() timed out. Either nothing is within 4 meters, TRIG and ECHO are swapped, or the module has no power. A soft or angled surface can also scatter the sound so no echo returns.

Should I use the NewPing library?

You can; NewPing.h compiles here too. This page uses pulseIn() because it shows what the module actually does, and it needs no library at all.

Build your own HC-SR04 project

Open this circuit in the editor, change the wiring or the code, and keep your version in a free account.

Start building free Open the editor