Build an Ultrasonic Distance Meter with Arduino

📋 What You'll Need

Arduino Uno or Nano
HC-SR04 Ultrasonic Sensor
16x2 LCD with I2C module
Piezo buzzer
Jumper wires
Arduino IDE

Understand how the HC-SR04 works

The sensor sends an ultrasonic pulse and measures how long it takes to bounce back. Speed of sound = 340 m/s.

// HC-SR04 Wiring:
// VCC  → 5V
// GND  → GND
// TRIG → Digital Pin 9
// ECHO → Digital Pin 10

const int TRIG = 9;
const int ECHO = 10;

void setup() {
  Serial.begin(9600);
  pinMode(TRIG, OUTPUT);
  pinMode(ECHO, INPUT);
}

long measureCm() {
  // Send a 10-microsecond trigger pulse
  digitalWrite(TRIG, LOW);  delayMicroseconds(2);
  digitalWrite(TRIG, HIGH); delayMicroseconds(10);
  digitalWrite(TRIG, LOW);

  // Measure echo duration
  long duration = pulseIn(ECHO, HIGH, 30000); // 30ms timeout

  // Distance = (duration * speed of sound) / 2
  // Speed = 0.0343 cm/us
  return duration * 0.0343 / 2;
}

void loop() {
  long cm = measureCm();
  if (cm > 0 && cm < 400) {
    Serial.print("Distance: ");
    Serial.print(cm);
    Serial.println(" cm");
  } else {
    Serial.println("Out of range");
  }
  delay(100);
}

Add a 16x2 LCD display

Show the distance on an LCD using the LiquidCrystal_I2C library.

// Install: Library Manager -> Search "LiquidCrystal I2C" -> Install
#include <Wire.h>
#include <LiquidCrystal_I2C.h>

LiquidCrystal_I2C lcd(0x27, 16, 2);  // Address 0x27 is most common

const int TRIG  = 9;
const int ECHO  = 10;
const int BUZZ  = 6;

void setup() {
  lcd.init();
  lcd.backlight();
  pinMode(TRIG, OUTPUT);
  pinMode(ECHO, INPUT);
  pinMode(BUZZ, OUTPUT);
  lcd.print("Distance Meter");
  delay(1500);
  lcd.clear();
}

long measureCm() {
  digitalWrite(TRIG, LOW);  delayMicroseconds(2);
  digitalWrite(TRIG, HIGH); delayMicroseconds(10);
  digitalWrite(TRIG, LOW);
  long d = pulseIn(ECHO, HIGH, 30000);
  return d * 0.0343 / 2;
}

void loop() {
  long cm = measureCm();

  lcd.setCursor(0, 0);
  lcd.print("Distance:       ");
  lcd.setCursor(0, 1);

  if (cm > 0 && cm < 400) {
    lcd.print(cm);
    lcd.print(" cm   ");

    // Beep faster when closer
    int beepDelay = constrain(cm * 5, 50, 1000);
    tone(BUZZ, 2000, 50);
    delay(beepDelay);

  } else {
    lcd.print("Out of range    ");
    noTone(BUZZ);
    delay(300);
  }
}

💡 Tip: If your LCD shows nothing or only black squares, it is a contrast issue. Turn the small blue potentiometer on the I2C module until the characters appear. If the I2C address 0x27 does not work, try 0x3F.

🎉 You Did It!

An HC-SR04 costs about $1 and can measure anything from 2 cm to 4 m. This same sensor is used in robot obstacle avoidance, parking sensors, water level monitors, and automatic door openers.

Browse More Tutorials

📡 Build an Ultrasonic Distance Meter with Arduino

🎯 What You'll Build

📋 What You'll Need

Understand how the HC-SR04 works

Add a 16x2 LCD display

🎉 You Did It!

📡 Build an Ultrasonic Distance Meter with Arduino

🎯 What You'll Build

📋 What You'll Need

Understand how the HC-SR04 works

Add a 16x2 LCD display

🎉 You Did It!

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