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What is I2C

I2C (Inter-Integrated Circuit) is a serial protocol using just two wires — SDA (data) + SCL (clock). It is the most common way to connect sensors and displays to Arduino/ESP32.

Why I2C​

  • Only 2 wires regardless of device count
  • Up to 127 devices on one bus (each with unique 7-bit address)
  • Built into virtually every MCU

How It Works​

  1. Master sends START + 7-bit device address + R/W bit
  2. Target acknowledges
  3. Data exchanged byte-by-byte, each byte ACKed
  4. Master sends STOP

Quick Example (Arduino)​

#include <Wire.h>
void setup() { Wire.begin(); Serial.begin(9600); }
void loop() {
  Wire.beginTransmission(0x68);
  Wire.write(0x00);
  Wire.endTransmission();
  Wire.requestFrom(0x68, 2);
  while (Wire.available()) {
    Serial.println(Wire.read());
  }
  delay(1000);
}

Common Pitfalls​

  • Device not found — wrong address; run I2C scanner sketch
  • Garbage data — missing pull-up resistors; add 4.7k on SDA/SCL
  • Bus hang — device holding SDA low; power-cycle