Teoría sobre I2C y SPIhttp://quick2wire.com/articles/i2c-and-spi/Conectar por USB GPOI I2Chttp://blog.oscarliang.net/connect-raspberry-pi-and-arduino-usb-cable/http://blog.oscarliang.net/raspberry-pi-and-arduino-connected-serial-gpio/http://blog.oscarliang.net/use-gpio-pins-on-raspberry-pi/ http://blog.oscarliang.net/raspberry-pi-arduino-connected-i2c/ Instalación I2C en Raspberry PIhttp://learn.adafruit.com/adafruits-raspberry-pi-lesson-4-gpio-setup/configuring-i2chttp://www.skpang.co.uk/blog/archives/575 Conectar y comunicar mediante I2Chttp://tronixstuff.com/tutorials/http://tronixstuff.com/2010/10/20/tutorial-arduino-and-the-i2c-bus/http://tronixstuff.com/2010/10/29/tutorial-arduino-and-the-i2c-bus-part-two/ Librería Wire.h para comunicación I2C e info sobre Arduino Mega 2560http://mindstormsyarduino.blogspot.com.es/2011/03/arduno-y-la-comunicacion-i2c-libreria.html  Libreria wire (twowire)http://arduino.cc/en/Reference/Wire