I2C LCD Hello World
Drive an LCD through a modeled PCF8574 backpack using only SDA and SCL.
Wire it up
Disconnect power before changing connections. Follow terminal names rather than wire colors.
| From | To | Why it matters |
|---|---|---|
| I²C LCD 16×2 (lcd1) · GND | Uno · GND.1 | Ground reference |
| I²C LCD 16×2 (lcd1) · VCC | Uno · 5V | Power connection |
| I²C LCD 16×2 (lcd1) · SDA | Uno · A4 | Match this terminal to the sketch |
| I²C LCD 16×2 (lcd1) · SCL | Uno · A5 | Match this terminal to the sketch |
The complete sketch
#include <LiquidCrystal_I2C.h>
LiquidCrystal_I2C lcd(0x27, 16, 2);
void setup() {
lcd.init(); lcd.backlight();
lcd.print("Hello Circuitera");
lcd.setCursor(0, 1); lcd.print("I2C at 0x27");
}
void loop() {}
The launch buttons use this same code and a matching saved circuit.
Build it step by step
Open a complete project
Launch in Simulator creates a separate Uno sketch and its matching wired circuit. Existing sketches are preserved. Press Run to compile and execute.
Explore the live circuit
Run and compare its four external wires with the parallel LCD project.
Try it on hardware
Disconnect power while wiring. Match terminal names in the table, select the exact board, Verify, then connect and upload. Check component ratings and power requirements first.
Understand the sketch
Address and backpack mapping
The project uses address 0x27 and the simulator’s P0 RS / P1 RW / P2 E / P3 backlight / P4–7 data mapping. Other backpacks may use a different address or mapping.
If something is different
Nothing displays
Keep the inspector address at 39 decimal (0x27), use A4 for SDA and A5 for SCL, and check the physical backpack mapping.
Expected output and tested scope
The modeled I2C backpack drives Hello Circuitera onto the character display.
Version 1 · Last source- and build-matched test: 2026-10-25. Actual shipped AVR-GCC WASM compilation and Uno AVR engine execution; no physical hardware test.
Supported tutorial target: Arduino Uno R3 / ATmega328P. Compile: PASS · Modeled execution: PASS. Other boards require a separate review of pins, voltage, libraries and the exact build profile.