LCD
Interfacing LCD2004 I2C with Arduino Uno
What is the LCD2004 I2C?
The LCD2004 is a 20-column, 4-row character LCD, built on the same HD44780-family controller as the smaller LCD1602 and almost always sold with the identical PCF8574 I2C backpack. That means the wiring, the library, and the code are essentially the same as the LCD1602 — the only real difference is passing 20, 4 instead of 16, 2 into the constructor. If a project's status screen or menu has outgrown two lines of 16 characters, this is the natural next step up rather than a different technology to learn.
Like the LCD1602, it only displays fixed-width text characters (plus up to 8 custom 5x8 glyphs), not arbitrary graphics — for pixel-level graphics, look at a display like the SSD1306 OLED instead.
Specifications
| Display | 20 characters × 4 lines, fixed-width text (HD44780-family controller) |
| Backpack | PCF8574 I2C I/O expander (converts the LCD's 6-wire parallel interface to I2C) |
| Operating voltage | 5 V DC (most common); some 3.3V-tolerant backpacks exist but are less common |
| I2C address | 0x27 default on most PCF8574 backpacks, 0x3F on some clones — scan to confirm |
| Interface | I2C, up to 100 kHz typical |
| Backlight | LED backlight, on/off controllable over I2C |
| Custom characters | Up to 8 user-defined 5×8 pixel glyphs |
LCD2004 I2C Pinout
| Pin | Name | Description |
|---|---|---|
| 1 | GND | Ground |
| 2 | VCC | Power, 5V DC |
| 3 | SDA | I2C data line |
| 4 | SCL | I2C clock line |
Identical wiring considerations to the LCD1602: the PCF8574 backpack's I2C pull-ups reference VCC, and the panel needs 5V for proper contrast/brightness, so on 3.3V-only boards you're typically feeding VCC from a 5V rail while accepting 5V-level I2C signaling (or adding a level shifter if you want to be strict). If text looks like solid blocks or is invisible, adjust the contrast potentiometer on the back of the backpack first. If the bus doesn't respond at all, run an I2C scanner sketch to confirm whether the address is 0x27 or 0x3F before touching your code.
Setting Up LCD2004 I2C with Arduino Uno
Library
LiquidCrystal I2C by Frank de Brabander
Arduino IDE → Tools → Manage Libraries → search "LiquidCrystal I2C" by Frank de Brabander → Install
Wiring
| Component pin | Arduino Uno pin | Note |
|---|---|---|
| VCC | 5V | — |
| GND | GND | — |
| SDA | A4 | Uno's hardware I2C data pin. |
| SCL | A5 | Uno's hardware I2C clock pin. |
Example code
- If the backlight is on but no text appears, adjust the contrast potentiometer on the back of the backpack before assuming it's a code problem.
lcd.print()does not auto-wrap between rows or clear a line first — always pad with trailing spaces if a new value might be shorter than the old one.- The extra two rows compared to the LCD1602 are genuinely useful for showing a label plus a live value plus a status line simultaneously, without needing to scroll or alternate screens.
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