16x2 LCD（I2Cバックパック）を配線する

A 16x2 LCD shows two rows of sixteen characters each. It is the classic way to display readings without a computer attached. 📟

A bare LCD needs many pins to talk to your board. Wiring all those lines is fiddly and eats up most of your GPIO pins.

An I2C backpack is a tiny board soldered behind the LCD. It shrinks all those connections down to just four wires.

With the backpack you connect only four pins: power, ground, and two data lines. Much cleaner on a breadboard.

Wire VCC to 5V and GND to ground. These two power the display and its backlight, so get them right first.

SDA is the data line that carries the actual characters. On an Arduino Uno it goes to analog pin A4.

SCL is the clock line that keeps both devices in sync. On an Uno it connects to analog pin A5.

Many boards label SDA and SCL right on the header, so you do not have to remember A4 and A5. Look for those marked pins.

The backpack has a small blue potentiometer. Turn it to adjust contrast until the characters are clear and not just bright boxes. 🔧

Each backpack has an I2C address, often 0x27 or 0x3F. You need this number to talk to the correct display.

After wiring, plug in and look at the screen. A faint row of white blocks means power is good, even before you upload code.

You want fewer wires running to your LCD. What does the I2C backpack do?

You learned that an I2C backpack turns a 16x2 LCD into four simple wires: VCC, GND, SDA, and SCL. Now you are ready to drive it in code. ✅