How to Scan I2C Address of Sensors with Arduino

Why Finding I2C Address Matters

I2C communication requires specifying the device address before sending data. Multiple devices on the same bus are distinguished by their unique addresses. This is why you need to know the I2C address before using any sensor or module.

Hardware Wiring

For Arduino Uno, I2C uses pin A4 (SDA) and A5 (SCL). Check the table below for wiring details:

Requirements:

• Arduino Uno
• I2C Module or Sensor to scan
• 4 Jumper wires (male-to-female)

I2C Scanner Code

This code scans addresses from 8 to 119 and displays found addresses on the Serial Monitor.

#include <Wire.h>

void setup() {
  Serial.begin(115200);
  
  // Wait for serial connection (for Leonardo/Micro)
  while (!Serial);
  
  Serial.println("I2C Scanner Starting...");
  
  Wire.begin();
  byte deviceCount = 0;
  
  // Scan addresses 8-119 (0x08 - 0x77)
  for (byte address = 8; address < 120; address++) {
    Wire.beginTransmission(address);
    byte response = Wire.endTransmission();
    
    // Response = 0 means device responded
    if (response == 0) {
      Serial.print("Found address: ");
      Serial.print(address, DEC);
      Serial.print(" (0x");
      Serial.print(address, HEX);
      Serial.println(")");
      deviceCount++;
      delay(10);
    }
  }
  
  Serial.println("Scan Complete");
  Serial.print("Total devices found: ");
  Serial.println(deviceCount);
}

void loop() {
  // Nothing to do
}

Step-by-Step Instructions

Step 1 Connect I2C wires according to the table above. Make sure VCC connects to 5V (unless your device supports only 3.3V)

Step 2 Upload the I2C Scanner code to Arduino

Step 3 Open Serial Monitor and set Baud Rate to 115200

Step 4 Press the Reset button on Arduino once, then wait for results

Reading the Results

If wiring is correct, Serial Monitor displays output like this:

I2C Scanner Starting...
Found address: 39 (0x27)
Scan Complete
Total devices found: 1

The address appears in both Decimal and Hexadecimal formats. For actual coding, use the Hexadecimal value such as 0x27

Practical Example

After finding the address, use it with libraries. Here’s an example with I2C LCD:

#include <Wire.h>
#include <LiquidCrystal_I2C.h>

// Use the address you scanned
LiquidCrystal_I2C lcd(0x27, 16, 2);

void setup() {
  lcd.begin();
  lcd.print("Hello I2C");
}

void loop() {}

[image: Circuit diagram showing Arduino Uno connected to I2C LCD 1602 Module with all 4 wires connected]

Summary

Finding the I2C address is a fundamental step before using any I2C device. Keep in mind that some devices have jumpers to change the address. When connecting multiple devices on the same bus, make sure each device has a unique address.