I2Cが2本の線で通信する仕組み

I2C lets many chips share just two wires, so you can add sensors and screens without running out of pins. 🔌

I2C uses two lines: SDA carries the data, and SCL carries the clock pulses that keep both sides perfectly in step.

The SCL clock line ticks like a metronome. Every tick tells devices exactly when to read the next bit on the data line.

Your Arduino is the master: it starts every conversation. Sensors and displays are slaves that only answer when called.

Each chip on the bus owns a unique address, usually a 7-bit number. The master uses it to talk to exactly one device. 📬

The master sends a start signal, then the target address. The matching device replies, and the rest stay quiet on the shared lines.

I2C lines need pull-up resistors to 3.3V or 5V. Without them the bus floats and your devices simply will not respond.

On an Arduino Uno, SDA is pin A4 and SCL is pin A5. Many breakout boards include their own pull-ups already.

Arduino talks I2C through the built-in Wire library. One include line gives you everything you need to start communicating.

Call Wire.begin() in setup to join the bus as master. After that you can send to any device by its address.

Because devices share two lines, I2C keeps wiring simple and your pins free. That is why so many modules use it.

Which two lines does I2C use to communicate?

You learned that I2C shares two wires, SDA and SCL, with a master, addressed slaves, and pull-ups. Two wires, many devices. ✅