I2C is a two-wire, low-speed serial communications format that was originally developed by Phillips (now NXP) in 1982. Although its original use was to allow integrated circuits in televisions to communicate with one another it has evolved into a standard communications method used by a myriad of devices.
I2C works with the concept of “Master” and “Slave” devices. The master device provides the clock signal and initiates communications with the slaves. An I2C bus can have multiple masters and slaves, but only one master can be active at any given time.
I2C Part 1 - Using 2 Arduinos
How I2C Communication Works and How To Use It with Arduino
I2C Devices
GY80 : Multi Sensor Board - 3 Axis Gyro -3 Axis Accelerometer - 3 Axis Magnetometer (Magnetic Compass) and Pressure sensor
GY521 : 3-axis gyroscope, a 3-axis accelerometer, a digital motion processor (DMP), and a temperature sensor.