I2C PIO 8574AT

The Arduino has a special Bus, called I2C with that you can connect several bricks. The 8574 is a brick with  that you can recieve additional 8 in and outpus and therefore extend the IO-ports easily. The I2C uses adresses for the bricks that you can change mechanically to use mamximum 8 of those bricks. Here is the 8574AT type used.