Source: https://mokxi.com/parts/lcd1602i2c Updated: 2026-09-27 Part # Character LCD with I2C backpack The same two rows on four wires, through the PCF8574 backpack at 0x27. Mind the backlight bit. or see every part - 4 pins - 2 properties Drawn live by the editor's own code, at the size you see it. Reference ## Every one of its 4 pins Pin What it does GND VCC SDA SCL This part ## What it does This is the 16x2 character LCD with a PCF8574 backpack on the back, which turns sixteen pins into four: SDA, SCL, power and ground. The display itself is the same HD44780 controller as the plain module, with its character shapes in ROM, so a sketch sends characters rather than pixels. The backpack is an eight-bit port expander wired to the controller’s control lines, four data lines and the backlight, and every byte the board sends appears on those pins. That has one famous consequence, modeled here: the backlight is a single bit in that byte, and a driver that forgets it gets a display that works and cannot be read. The address is 0x27 by default and is a property, since some backpacks answer at 0x3F. The LiquidCrystal_I2C calls tutorials use compile on every board, and on an Uno they use A4 and A5. How to use it ## How to use an I2C LCD with an Arduino SDA to A4, SCL to A5, VCC to 5 V, GND to GND. Create a LiquidCrystal_I2C with the address and the size, call init() and backlight() in setup(), and print. If the screen stays empty, the address is the first suspect: most backpacks answer at 0x27 and some at 0x3F. To update a number without flicker, overwrite the line and pad it with spaces rather than calling clear() every time. Part pin Board pin SDA A4 SCL A5 VCC 5 V GND GND LiquidCrystal_I2C compiles on every board here, on whichever pins Wire.begin() uses on that board. Click to open it in the editor This is the simulator itself, running here. Click anything to open it in the editor. Open this project in the editor Read the full tutorial A first I2C LCD sketch Reference ## The 2 properties you can set Property Default What it means address 39 contrast 0.75 How it is modeled ## What is true about the Character LCD with I2C backpack, here ### Not modeled Reads of any kind. The busy flag, the address counter and DDRAM read back nothing, so a driver that polls the busy flag instead of waiting will hang. Wait instead; that is what every real library does anyway. Also not modeled: the 5x10 font a one-line module can select, and the viewing angle. The busy timings are the datasheet's two typical numbers (37 microseconds for a write and 1.52 milliseconds for clear and home), used as exact values. A real HD44780's timing scales with whatever its internal oscillator happens to be running at, so those figures move by tens of percent between parts and with temperature, and the 4-bit nibble timing (the minimum E pulse width and the hold after it) is not checked here at all: a driver can clock E as fast as it likes. A byte arriving while the controller is busy is dropped. That is a choice the model makes so the fault is visible and repeatable; on a real part the outcome is undefined and more often a corrupted character than a lost one. On the backpack, the PCF8574 never stretches the clock and acknowledges every byte sent to it. There is no read of the expander's port, no NACK and no bus error of any kind, and the backlight transistor is bit 3 and nothing else: no current, no brightness. Contrast on the backpack is a property rather than the trimmer's actual divider. See it: Thermometer on an I2C LCD for the backpack, and Thermometer in the templates for the six-wire hookup. If an I2C LCD stays blank, shows blocks or prints leftovers, Arduino I2C LCD not working goes through the causes by symptom. From The 16x2 character LCD, in full. Projects ## See the Character LCD with I2C backpack in a project Shown here on: Arduino Uno R3, ESP32-C3-DevKitM-1 Learn ## Where it turns up in a lesson ### In a learn article - Arduino I2C LCD 16x2: Wiring and Code - Arduino DHT22 Temperature and Humidity Sensor - I2C Explained: Addresses, Pull-Ups and a Scanner - Arduino I2C LCD Not Working: Blank, Blocks, No Text More parts ## The rest of the bench Every one of these is drawn and simulated the same way. Full-size breadboard A real 0.1 inch grid with the rails and the center channel, 63 columns wide. Jumper wires Drag from any pin or hole to any other. Corners snap, and you can drag them. Power A supply rail at the voltage you choose. Ground The other end of every circuit. LED Lights when current flows. Five colors, and the brightness is what your eye would see. Resistor Any value you like, with the color bands drawn to match. ESP32-C3-DevKitM-1 A RISC-V board that runs your firmware at 160 MHz on the real memory map. Pushbutton A 12 mm tactile switch. Hold it while the simulation runs. Raspberry Pi Pico The RP2040 board on our own Cortex-M0+ core. Pick a program and press Run. Raspberry Pi Pico W Raspberry Pi Pico W (RP2040). The same board and the same pinout as a Pico, with the CYW43439 on it. The WiFi is simulated (no radio, no real internet), and the on-board LED, which hangs off that chip rather than off GP25, is driven through the same path. Everything else is the Pico. STM32F411 Black Pill The Black Pill on our own Cortex-M4 core. Pick a program and press Run. BBC micro:bit V2 The nRF52833 board with its 5x5 LED matrix, buttons A and B and a speaker. Wire the rings to a breadboard. See every part ## Wire up the Character LCD with I2C backpack Open the editor and push it into the breadboard. It is free, and it runs on your own machine. Start building Open the editor