ALLNET Brick'R'knowledge 2x1 I2C Port Textender
The Arduino has a special bus, called I2C, with which you can connect additional bricks. The 8574 is a component with which you get an additional 8 input or output ports and can therefore easily expand the number of IO ports on the Arduino. The I2C uses addresses for the blocks, which can be set in the brick in order to be able to use a maximum of 8 such blocks. The 8574AT type is used here