The port expander board uses serial to parallel IO expander ICs (datasheet) to run 8 behaviour ports from a single behaviour port on the breakout board. The port expander must be connected to a behaviour port that supports I2C serial communication (ports 3 and 4 on breakout 1.2).
!!! Electrical safety !!!
The port expander can draw power either from the the behaviour port or from a 12V power supply connected to the expander board using the 2.1mm barrel plug. See more