Expander 2

 

The Expander 2 unit was an acoustic modem for the VideoBrain.  An acoustic modem is a modem that uses sound signals to achieve a connection rather than through a direct electrical connection.  This meant that you needed to place your phone directly on the modem pad to connect, and then pray that no one in the room made a loud noise otherwise you'd lose your connection.  The Expander 2 was capable of achieving speeds of up to 300 baud.

The Expander 2 connected to the VideoBrain via the Expander 1 unit, rather than connecting directly.  The Expander 2 unit is incredibly rare, and only one cartridge (Timeshare) made use of it.