Driving a 16x2 character LCD over I2C with ESP8266 and Arduino

The 16x2 character LCD (two rows of sixteen characters) is the classic beginner display: cheap, readable, and everywhere. The annoyance is wiring — in parallel mode it eats six or more GPIO pins. An I2C backpack reduces that to two wires. This repository is my maintained LiquidCrystal_I2C library, compatible with both ESP8266 boards and classic Arduinos.

What I2C is, in one paragraph

I2C is a two-wire bus: one clock line (SCL) and one data line (SDA). Any number of devices can share it, each with an address. The LCD backpack contains a small expander chip at address 0x27 (sometimes 0x3F); your sketch talks to that address, and the chip wiggles the LCD's many parallel pins for you.

Quick start

#include <LiquidCrystal_I2C.h>

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

void setup() {
  lcd.begin();          // ESP8266: default pins 4 (SDA), 5 (SCL); Arduino Uno: A4/A5
  lcd.backlight();
  lcd.setCursor(0, 0);
  lcd.print("Hello, world!");
}

void loop() {}

On the tiny ESP-01 module there are almost no free pins, so the library also supports lcd.begin(0, 2) to use GPIO0 as SDA and GPIO2 as SCL — the two pins that are otherwise unusable anyway.

Code structure

• LiquidCrystal_I2C.h/.cpp — the library itself: initialisation sequences, cursor control, scrolling, custom characters.
• examples/ — four sketches: HelloWorld, BlinkingCursor, CustomChars (defining your own pixel symbols), and SerialDisplay (echo whatever arrives on the serial port to the screen).
• keywords.txt — makes the IDE syntax-highlight the library's methods.

I tested it on ESP-12 (LoLin), ESP-01 and Arduino Uno. The repository is a cleaned-up fork of the well-known fdebrabander library, with the ESP8266 pin handling that actually matches real boards. Get it at github.com/bobhuang1/LiquidCrystal_I2C.