HC-SR04 + LCD 1602 Distance Meter with ESP32

The HC-SR04 is one of the most popular ultrasonic distance sensors in the maker world — cheap, accurate to within a few millimetres, and dead simple to wire. Pair it with a 16x2 LCD display and an ESP32, and you have a compact, self-contained distance meter that shows live readings without needing a computer or serial monitor. This is a great beginner project that teaches you PWM timing, I2C displays, and clean real-time output all in one build.

Components for This Project

How the HC-SR04 Works

Before writing any code, it helps to understand what is happening at the hardware level.

The HC-SR04 uses sound to measure distance — the same principle as a bat or a car parking sensor. Here is the sequence:

1. Your microcontroller sends a short 10 µs HIGH pulse to the TRIG pin
2. The sensor fires a burst of 8 ultrasonic pulses at 40 kHz
3. The sound bounces off the nearest object and returns to the sensor
4. The sensor holds the ECHO pin HIGH for exactly as long as the round-trip took
5. You measure that pulse duration and convert it to distance

The conversion formula uses the speed of sound (~343 m/s at 20°C):

textcode
1distance (cm) = pulse duration (µs) / 58.0

Or equivalently:

textcode
1distance (cm) = (pulse duration (µs) * 0.0343) / 2

Effective range: 2 cm to 400 cm. Objects closer than 2 cm may not return a reliable echo. Objects further than 4 m or with soft/angled surfaces (like fabric or carpet at 45°) can give inconsistent readings.

What You Will Need

Why the I2C LCD? The standard LCD 1602 without I2C requires 6 data pins plus power — nearly half your ESP32's GPIO pins just for a display. The I2C backpack solves this with just 2 data wires (SDA + SCL). If you only have a parallel LCD, you can add an PCF8574 I2C expander module for under RM 2.

Wiring Guide

HC-SR04 to ESP32

The ECHO pin outputs 5V on many HC-SR04 modules. The ESP32 GPIO pins are 3.3V tolerant only. Use a voltage divider (2x resistors) or a logic level shifter to protect the ESP32.

Simple voltage divider for ECHO (1kΩ + 2kΩ):

textcode
1HC-SR04 ECHO ──── 1kΩ ──── ESP32 GPIO (safe 3.3V)
2                      |
3                     2kΩ
4                      |
5                     GND

LCD 1602 I2C to ESP32

I2C Address: Most PCF8574-based I2C LCD modules use address

textcode

10x27

. Some use

textcode

10x3F

. If the display stays blank after uploading, try

textcode

10x3F

in the code.

Installing Required Libraries

You need two libraries. Install both via Arduino IDE > Tools > Manage Libraries:

1LiquidCrystal I2C

1pulseIn()

The Code

cppcode
1#include <Wire.h>
2#include <LiquidCrystal_I2C.h>
3
4// ── Pin Definitions ───────────────────────────────────────────────────────────
5#define TRIG_PIN  5    // HC-SR04 trigger
6#define ECHO_PIN  18   // HC-SR04 echo (use voltage divider from 5V to 3.3V)
7
8// ── LCD Setup ─────────────────────────────────────────────────────────────────
9// Parameters: I2C address, columns, rows
10// Try 0x3F if 0x27 does not work
11LiquidCrystal_I2C lcd(0x27, 16, 2);
12
13// ── Measure distance in centimetres ───────────────────────────────────────────
14float measureDistance() {
15  // Send 10 µs trigger pulse
16  digitalWrite(TRIG_PIN, LOW);
17  delayMicroseconds(2);
18  digitalWrite(TRIG_PIN, HIGH);
19  delayMicroseconds(10);
20  digitalWrite(TRIG_PIN, LOW);
21
22  // Read echo pulse duration (timeout = 30 ms → ~5 m max)
23  long duration = pulseIn(ECHO_PIN, HIGH, 30000);
24
25  if (duration == 0) return -1;   // no echo received (out of range)
26
27  return duration / 58.0;         // convert to cm
28}
29
30void setup() {
31  Serial.begin(115200);
32
33  pinMode(TRIG_PIN, OUTPUT);
34  pinMode(ECHO_PIN, INPUT);
35
36  // Initialise LCD
37  lcd.init();
38  lcd.backlight();
39
40  // Splash screen
41  lcd.setCursor(0, 0);
42  lcd.print("  Distance Meter");
43  lcd.setCursor(0, 1);
44  lcd.print(" HC-SR04 + ESP32");
45  delay(2000);
46  lcd.clear();
47}
48
49void loop() {
50  float distance = measureDistance();
51
52  // ── Print to Serial Monitor ────────────────────────────────────────────────
53  if (distance < 0) {
54    Serial.println("Out of range");
55  } else {
56    Serial.printf("Distance: %.1f cm\n", distance);
57  }
58
59  // ── Update LCD ─────────────────────────────────────────────────────────────
60  lcd.setCursor(0, 0);
61  lcd.print("Distance:       ");   // trailing spaces clear old characters
62
63  lcd.setCursor(0, 1);
64  if (distance < 0 || distance > 400) {
65    lcd.print("Out of range    ");
66  } else {
67    // Format: "123.4 cm        "
68    String display = String(distance, 1) + " cm";
69    // Pad to 16 chars to overwrite previous longer values
70    while (display.length() < 16) display += " ";
71    lcd.print(display);
72  }
73
74  delay(200);   // update 5 times per second
75}

Understanding the Code

The

textcode

1measureDistance()

Function

This is the heart of the project. It drives TRIG LOW briefly to clean up any noise, then pulls it HIGH for 10 µs to fire the ultrasonic burst.

1pulseIn(ECHO_PIN, HIGH, 30000)

Clearing Old Characters on the LCD

LCD displays do not auto-clear when you write shorter text over longer text. For example, writing

1"9.5 cm"

1"123.4 cm"

1"9.5 cmcm"

The Update Rate

1delay(200)

1delay(50)

1delay(100)

Serial Monitor Output

Open Tools > Serial Monitor at 115200 baud and press the RESET button. You should see:

textcode
1Distance: 14.3 cm
2Distance: 14.4 cm
3Distance: 14.2 cm
4Distance: 14.3 cm
5Out of range
6Distance: 28.7 cm

This is useful for debugging — if the LCD shows garbage but the Serial Monitor looks correct, the issue is with the LCD address or wiring.

Calibration and Accuracy Tips

The HC-SR04 is reasonably accurate for most DIY purposes, but there are a few things that affect readings:

1distance = duration * (331.3 + 0.606 * tempC) / 20000.0

Averaging for Stability

For smoother readings, take multiple samples and average them:

cppcode
1float stableDistance() {
2  const int SAMPLES = 5;
3  float total = 0;
4  int valid = 0;
5  for (int i = 0; i < SAMPLES; i++) {
6    float d = measureDistance();
7    if (d > 0 && d <= 400) {
8      total += d;
9      valid++;
10    }
11    delay(15);
12  }
13  return valid > 0 ? total / valid : -1;
14}

Replace

1measureDistance()

1stableDistance()

Troubleshooting

10x3F

Taking It Further

Once your distance meter is working, there are many directions to expand it:

• Proximity alert — add a buzzer that beeps faster as objects get closer, like a car parking sensor
• Water level monitor — mount the sensor facing down into a tank; calculate water level from
  textcode

  1tank_height - distance

• People counter — place the sensor in a doorway and count when the reading drops below a threshold
• Robot obstacle avoidance — mount on a motor car chassis and steer away when distance drops below 20 cm
• Wi-Fi dashboard — use the ESP32's Wi-Fi to POST readings to a local Node-RED or web dashboard every second
• Temperature-compensated distance — add a DS18B20 for accurate speed-of-sound correction

Wrapping Up

You have built a complete real-time distance meter using an HC-SR04 ultrasonic sensor, a 1602 LCD display, and an ESP32. Along the way you learned how ultrasonic ranging works, how to protect ESP32 GPIO pins from 5V signals, how to drive an I2C LCD, and how to keep display output clean and readable.

Browse our HC-SR04 sensors, LCD displays, and ESP32 boards in the store — all the components for this project ship together.

Happy building!