i2c scanner

    /**
     * I2CScanner.pde -- I2C bus scanner for Arduino
     *
     * 2009, Tod E. Kurt, http://todbot.com/blog/
     *
     */

    #include "Wire.h"
    extern "C" {
    #include "utility/twi.h"  // from Wire library, so we can do bus scanning
    }

    // Scan the I2C bus between addresses from_addr and to_addr.
    // On each address, call the callback function with the address and result.
    // If result==0, address was found, otherwise, address wasn't found
    // (can use result to potentially get other status on the I2C bus, see twi.c)
    // Assumes Wire.begin() has already been called
    void scanI2CBus(byte from_addr, byte to_addr,
                    void(*callback)(byte address, byte result) )
    {
      byte rc;
      byte data = 0; // not used, just an address to feed to twi_writeTo()
      for( byte addr = from_addr; addr <= to_addr; addr++ ) {
        rc = twi_writeTo(addr, &data, 0, 1, 0);
        callback( addr, rc );
      }
    }

    // Called when address is found in scanI2CBus()
    // Feel free to change this as needed
    // (like adding I2C comm code to figure out what kind of I2C device is there)
    void scanFunc( byte addr, byte result ) {
      Serial.print("addr: ");
      Serial.print(addr,DEC);
      Serial.print( (result==0) ? " found!":"       ");
      Serial.print( (addr%4) ? "\t":"\n");
    }


    byte start_address = 1;
    byte end_address = 100;

    // standard Arduino setup()
    void setup()
    {
        Wire.begin();

        Serial.begin(9600);
        Serial.println("\nI2CScanner ready!");

        Serial.print("starting scanning of I2C bus from ");
        Serial.print(start_address,DEC);
        Serial.print(" to ");
        Serial.print(end_address,DEC);
        Serial.println("...");

        // start the scan, will call "scanFunc()" on result from each address
        scanI2CBus( start_address, end_address, scanFunc );

        Serial.println("\ndone");
    }

    // standard Arduino loop()
    void loop()
    {
        // Nothing to do here, so we'll just blink the built-in LED
        digitalWrite(13,HIGH);
        delay(300);
        digitalWrite(13,LOW);
        delay(300);
    }