Open the editorEditor
Arduino Uno R4 · HC-SR04

Arduino Uno R4 HC-SR04 Simulator: Wiring, Code and a Live Circuit

This is an HC-SR04 ultrasonic distance sensor wired to an Arduino Uno R4 Minima, 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.

Four wires: 5V, GND, TRIG to pin 2 and ECHO to pin 3, with no library at all, only pulseIn().

Run it in the editorRead the code
  • 5 V logic
  • No library: pulseIn()
  • TRIG 2, ECHO 3
  • Range 2 to 400 cm
Arduino Uno R4 · 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 Arduino Uno R4

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

HC-SR04 pinArduino Uno R4 pinWhy
VCC5VThe HC-SR04 is a 5 V module; below about 4.5 V many units stop answering.
TRIGpin 2Output from the board: a 10 microsecond pulse starts a ping.
ECHOpin 3Input to the board: high for as long as the sound takes to come back.
GNDGNDCommon ground.

Everything on this module is 5 V, the Arduino Uno R4’s own level, so TRIG and ECHO connect straight to the pins.

Pins to leave alone on the Arduino Uno R4

An Uno sketch’s source builds for the R4, but a compiled Uno program will not run on it: different chip. The R4’s pins source less current than an Uno’s, about 8 mA each, so do not drive a relay coil or a motor straight from one.

On a real bench

The Uno R4 Minima fits every Uno shield and every Uno breadboard layout, so wire the HC-SR04 exactly as you would on an Uno R3. It has a USB-C socket, and its VIN accepts up to 24 V where an Uno R3 stops at 12.

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 Arduino Uno R4
const int TRIG_PIN = 2;   // pin 2
const int ECHO_PIN = 3;   // pin 3

void setup() {
  Serial.begin(9600);
  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(9600) opens the serial monitor. Serial is the USB port; Serial1 is on pins 0 and 1, which on the R4 are free for other serial devices.

Common mistakes with the HC-SR04 on the Arduino Uno R4

Swapping TRIG and ECHO

TRIG is an input on the module and ECHO an output. Swapped, the board pulses the ECHO pin and listens on TRIG, and every reading is 0 or out of range. Check the labels on the module, not the order of the header.

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 Arduino Uno R4 Minima?

Yes. The circuit at the top of this page is an Arduino Uno R4 Minima with a HC-SR04, running in your browser on a simulated Renesas RA4M1 (Cortex-M4). 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 Arduino Uno R4?

Yes, directly: it is a 5 V module and the Arduino Uno R4 is a 5 V board.

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 freeOpen the editor