The JeeLabs Output Plug is a small board containing an 8-bit I/O expander plus NPN darlington array. Each pin can sink up to 500 mA @ 50V. Clamping diodes are included, so that relays and small inductive loads may also be connected.
An I2C bus running at 3.3V is used as interconnect, with all the power and signal lines brought out to to both sides of the board to allow daisy-chaining with other I2C-conformant boards.
TheAssembled Output Plug comes with the SMD-sized ULN2803 and MCP23008 chips, as well as the decoupling capacitor already soldered onto the board. Headers for this and all other JeeLabs plugs can be found here (straight) and here (right angle).
The PCB Only version contains just the printed circuit board for the Output Plug. No parts, no headers.