🖥️ ESP32 I2C Display Tutorial – Using OLED and LCD 1602 with I2C

In this tutorial, you will learn how to use I2C communication on ESP32 to control two commonly used displays:

We’ll also explain what I2C is, how it works, and how to connect multiple devices using just two wires.

🧠 Principle: What is I2C?

I²C (Inter-Integrated Circuit) is a communication protocol that allows microcontrollers like the ESP32 to talk to multiple peripherals (like sensors or displays) using only two wires:

Line Function
SDA Serial Data Line (data transfer)
SCL Serial Clock Line (sync the data transfer)

✅ I2C Key Features:

🧠 I2C in Real Life

Think of I2C like a school classroom:

⛓️ This shared communication saves GPIO pins and makes I2C great for expanding your system.

⚙️ Circuit Connection

Device SDA Pin SCL Pin I2C Address
OLED Display GPIO 19 GPIO 20 0x3C
LCD1602 Display GPIO 19 GPIO 20 0x27

📝 On ESP32 DevKit, default I2C pins are typically SDA = 21, SCL = 22
But you can define any two GPIOs using Wire.begin(SDA, SCL);

🧪 Code: Display “Hello World” on OLED and LCD

Here’s a full working example to test both I2C displays:

#include <SPI.h>
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SH110X.h>
#include <LiquidCrystal_I2C.h>

// Define I2C pins for ESP32 S3 (customizable)
const int SDAPin = 19;
const int SCLPin = 20;

// OLED Setup
#define oled_address 0x3C
#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
#define OLED_RESET -1
Adafruit_SH1106G oled_display = Adafruit_SH1106G(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);

// LCD1602 Setup
#define lcd_address 0x27
#define CHAR_NUM 16
#define LINE_NUM 2
LiquidCrystal_I2C lcd_display(lcd_address, CHAR_NUM, LINE_NUM);

void setup() {
  Serial.begin(9600);

  // Initialize I2C bus
  Wire.begin(SDAPin, SCLPin);

  // LCD init
  lcd_display.init();
  lcd_display.clear();
  lcd_display.backlight();

  lcd_display.setCursor(2, 0);
  lcd_display.print("LCD Display");

  lcd_display.setCursor(2, 1);
  lcd_display.print("at 0x27");

  // OLED init
  delay(250); // Power up delay
  oled_display.begin(oled_address, true);
  oled_display.display();
  delay(2000);

  oled_display.clearDisplay();
  oled_display.setTextSize(2);
  oled_display.setTextColor(SH110X_WHITE);
  oled_display.setCursor(0, 0);
  oled_display.println("OLED");

  oled_display.setCursor(0, 18);
  oled_display.println("Display1");

  oled_display.setCursor(0, 36);
  oled_display.println("at 0x3C");

  oled_display.display();
}

void loop() {
  // Nothing here – everything is shown in setup
}

🔍 How It Works

Part Explanation
Wire.begin(SDA, SCL); Initialize I2C bus with custom pins
Adafruit_SH1106G.begin(address) Starts OLED display at I2C address 0x3C
LiquidCrystal_I2C.init() Starts LCD display at I2C address 0x27
setCursor() Moves the print position
print() Prints text on screen
display() Sends the OLED buffer to screen

🛠 How to Scan I2C Devices

If you’re unsure which address your display is using, upload this I2C scanner:

#include <Wire.h>

void setup() {
  Wire.begin(19, 20); // SDA, SCL
  Serial.begin(115200);
  Serial.println("Scanning I2C...");

  for (byte i = 1; i < 127; i++) {
    Wire.beginTransmission(i);
    if (Wire.endTransmission() == 0) {
      Serial.print("I2C device found at 0x");
      Serial.println(i, HEX);
    }
  }
}

void loop() {}

📦 Organizing Arduino Libraries: .h and .cpp Files

In Arduino development, libraries like LiquidCrystal_I2C are usually made up of two files:

File Type Purpose
.h (Header file) Contains declarations of classes, functions, constants, and variables
.cpp (Source file) Contains actual implementations of the functions declared in .h

🧠 Why Use .h and .cpp?

This modular structure makes your code:

🗂 How to Add a Custom Library Manually

If you’re not installing through the Library Manager, you can:

  1. Download the LiquidCrystal_I2C.h and LiquidCrystal_I2C.cpp files
  2. Create a new Arduino sketch (e.g. MyLCDTest.ino)
  3. Save your sketch to a folder — Arduino will create one automatically
  4. Place both .h and .cpp files inside that folder

Now in your .ino file, you can simply use:

#include "LiquidCrystal_I2C.h"

⚠️ If you use angle brackets like #include <LiquidCrystal_I2C.h>, Arduino looks in the global libraries folder. If you use quotes "", it looks in your sketch folder first.

🧰 LiquidCrystal_I2C Function Overview

After including the library, here are the most commonly used functions:

Function Description
LiquidCrystal_I2C(addr, cols, rows) Constructor to create LCD object. e.g. 0x27, 16, 2
init() Initializes the LCD
clear() Clears the screen
home() Moves cursor to top-left
backlight() / noBacklight() Turns backlight on/off
print() Prints text on the LCD
setCursor(col, row) Moves the cursor to position (starting from 0,0)
leftToRight() / rightToLeft() Sets text display direction
cursor() / noCursor() Shows/hides cursor
blink() / noBlink() Makes the cursor blink or not
display() / noDisplay() Turns screen on/off (content remains)

📘 Example Usage Recap

LiquidCrystal_I2C lcd(0x27, 16, 2); // Address 0x27, 16 columns, 2 rows

void setup() {
  lcd.init();          // Initialize the LCD
  lcd.backlight();     // Turn on the backlight
  lcd.setCursor(0, 0); // Move cursor to top-left
  lcd.print("Hello!");
}

This will display “Hello!” on the first line of your LCD.

📚 Useful Resources