Last Modified: February 10, 2014, at 01:26 PM
By: robtillaart

This very simple sketch scans the I2C-bus for devices. If a device is found, it is reported to the Arduino serial monitor.

This sketch is the first step to get the I2C communication working.

The sketch shows the 7-bit addresses of the found devices as hexadecimal values. That value can be used for the "Wire.begin" function which uses the 7-bit address. Some datasheets use the 8-bit address and some example sketches use decimal addresses.

Interesting links

The Arduino Wire Reference.

I2C Bi-directional Level Shifter about level shifting, pull-up resistors and connecting 3.3V devices.

Nick Gammon's page about I2C : http://gammon.com.au/i2c (the page also has a "I2C Scanner").

robtillaart made a "Multispeed I2C Scanner" that scans with different I2C speeds. If you use longer wires or libraries that use higher I2C speeds, the Multispeed I2C Scanner is very useful.


Open a new sketch and copy the sketch below into it. Upload it to the Arduino and open the serial monitor. Every found device on the I2C-bus is reported.

You can change the wires, and plug-in I2C devices while the i2c_scanner is running.

The output of the serial monitor will look like this:

Please do not change the sketch. If you have improvements, add your improved sketch to this page.

// --------------------------------------
// i2c_scanner
// Version 1
//    This program (or code that looks like it)
//    can be found in many places.
//    For example on the Arduino.cc forum.
//    The original author is not know.
// Version 2, Juni 2012, Using Arduino 1.0.1
//     Adapted to be as simple as possible by Arduino.cc user Krodal
// Version 3, Feb 26  2013
//    V3 by louarnold
// Version 4, March 3, 2013, Using Arduino 1.0.3
//    by Arduino.cc user Krodal.
//    Changes by louarnold removed.
//    Scanning addresses changed from 0...127 to 1...119,
//    according to the i2c scanner by Nick Gammon
//    http://www.gammon.com.au/forum/?id=10896
// Version 5, March 28, 2013
//    As version 4, but address scans now to 127.
//    A sensor seems to use address 120.
// This sketch tests the standard 7-bit addresses
// Devices with higher bit address might not be seen properly.

#include <Wire.h>

void setup()

  Serial.println("\nI2C Scanner");

void loop()
  byte error, address;
  int nDevices;


  nDevices = 0;
  for(address = 1; address < 127; address++ )
    // The i2c_scanner uses the return value of
    // the Write.endTransmisstion to see if
    // a device did acknowledge to the address.
    error = Wire.endTransmission();

    if (error == 0)
      Serial.print("I2C device found at address 0x");
      if (address<16)
      Serial.println("  !");

    else if (error==4)
      Serial.print("Unknow error at address 0x");
      if (address<16)
  if (nDevices == 0)
    Serial.println("No I2C devices found\n");

  delay(5000);           // wait 5 seconds for next scan