Welcome to Tutorial 2 of our exciting TinkerCad series! A display shows data from your Arduino—like sensor values, messages, or status updates—in real time.
We need displays to interact visually with our projects instead of just guessing what’s happening. A 16×2 LCD is common but requires 6 pins, which limits space for other components. An I2C LCD module reduces this to just 2 pins (SDA and SCL) using the PCF8574 chip. This saves wiring space and simplifies your design—great for compact or complex projects. It also includes a contrast knob and backlight control for better visibility.
With the LiquidCrystal_I2C library, coding becomes beginner-friendly and fast. You can display temperature, distance, time, or any sensor data.
Perfect for robotics, weather stations, and any smart IoT display system. In short: fewer wires, more freedom, and smarter Arduino outputs!
What is I2C?
I2C (Inter-Integrated Circuit) is a serial communication protocol that allows multiple devices to communicate with just two shared lines:
- SDA (Serial Data)
- SCL (Serial Clock)
On the Arduino Uno:
- SDA connects to pin A4
- SCL connects to pin A5
Each I2C device on the bus has a unique address, enabling the Arduino to talk to many devices using just two data lines.
🔌 I2C LCD Pin Details
An I2C LCD module typically has 4 pins, located on the I2C adapter board mounted on the back of the LCD. Here’s what each pin does:
| Pin | Label | Description |
| 1 | GND | Connects to Arduino GND (Ground) |
| 2 | VCC | Connects to 5V power supply (from Arduino) |
| 3 | SDA | Serial Data Line – connects to A4 |
| 4 | SCL | Serial Clock Line – connects to A5 |
These four pins replace the need for 6 to 10 separate wires required in a traditional LCD setup, making the build neater and more manageable.
⚙️ Software Integration
To use the I2C LCD in your Arduino project, you’ll typically install the LiquidCrystal_I2C library. Once initialized with the correct I2C address (commonly 0x27 or 0x3F) and display dimensions, you can easily control the screen to:
- Display text and numbers
- Move the cursor
- Clear or scroll the screen
- Define and show custom characters
The I2C interface allows these operations with simple function calls, providing a clean programming experience.
🧪 Use Cases
I2C LCDs are used across a wide range of real-world projects:
- Showing sensor readings like temperature, humidity, distance, or voltage
- Display Name or Specific Text
- Providing system status for automation setups (e.g., “Running”, “Error”, “Standby”)
- Giving feedback in robotics, such as battery level, movement direction, or object detection
- Acting as user interfaces in interactive devices using buttons or rotary encoders
- Offering on-the-spot debugging information without the need for a serial monitor
I2C LCD modules provide an efficient, space-saving way to add a display to any Arduino project. With just 4 connection pins (GND, VCC, SDA, SCL) and a supporting library, these displays offer powerful capabilities with minimal wiring. Whether you’re working with a compact 16×2 or a larger 20×4 module, I2C makes integration easy, scalable, and clean—ideal for robotics, automation, and real-time monitoring.
To connect a standard character LCD to an Arduino using just two data lines, an I2C LCD Adapter is used. This small circuit board is typically soldered directly to the back of the LCD and serves as a bridge between the I2C communication protocol and the parallel signals required by the LCD controller.
🧠 PCF8574 – The Core Chip
At the heart of the I2C adapter is the PCF8574, an 8-bit I/O expander chip manufactured by NXP. Its job is to convert the serial I2C data from the Arduino into the parallel signals needed by the LCD (such as RS, E, and the data lines D4 to D7).
This chip allows you to control the LCD with just two Arduino pins (SDA and SCL), significantly simplifying hardware wiring—especially useful in projects that require multiple sensors or modules.
🎚️ Contrast Adjustment via Trimpot
The adapter board includes a small trimpot (or variable resistor), typically blue and square-shaped. This component lets you adjust the contrast of the characters on the screen. Turning it clockwise or counterclockwise changes the voltage sent to the LCD contrast pin, helping make the text either darker or lighter depending on lighting and viewing angle.
This adjustment is essential when first setting up the LCD, as the characters might appear too dim or completely invisible if the contrast isn’t set properly.
💡 Backlight Control and LED Jumper
Most I2C LCD adapters include a jumper that supplies constant power to the LCD’s backlight. This jumper is usually labeled and located near the corner of the adapter.
- If the jumper is in place, the backlight is always on at full brightness.
- If you remove the jumper, you can control the backlight brightness manually by supplying voltage through the pin labeled ‘LED’. This opens the door to dimming the display or switching the backlight on/off dynamically using external circuitry or a transistor controlled by the Arduino.
Let’s Make Virtual Circuit with ThestemGuy using TinkerCad
Conclusion:
n this project, we successfully demonstrated how to connect an I2C LCD display to an Arduino board and display basic text such as a name. Using the I2C interface greatly simplified the wiring by reducing the number of connections to just four: VCC, GND, SDA, and SCL. We also utilized the LiquidCrystal_I2C library, which made it easy to send text commands to the LCD. This project is a great starting point for beginners learning about Arduino and display modules, and it lays the foundation for more advanced applications like sensor readouts, menus, or real-time data displays.