The Plug Shield allows using I2C-based JeePlugs with any Arduino or compatible clone. It acts as an interface between the hardware I2C port and the plugs. There is a level converter on board, as well as a 3.3V regulator to supply power to the plugs. The reset button and ISP signals are duplicated on the shield.
The Plug Shield can be used with just an Arduino, or stacked between other shields. The only requirement is that the A4 and A5 lines be used for hardware I2C. All other I/O lines and pin headers can be used in the same way as without a Plug Shield.
There is room for up to 5 port headers – these are all connected in parallel to allow using multiple plugs. Plugs with additional connectors on them, such as the Expander Plug and the UART Plug, can point outwards so they don’t interfere with other shields stacked on top of the Plug Shield.
The pre-assembled version comes with SMD-sized components and reset button already soldered onto the board. All the port headers and stacking headers are included (not soldered on).
The PCB only variant contains just the board for the Plug Shield. No parts, no headers. Use this and add a few wire jumpers if you want to run plugs at 5V (note that not all plugs are 5V-tolerant).
The documentation and full design details are freely available.