The Expander Plug is a small board with 8 general-purpose digital I/O lines. Each of the lines can be configured individually as input (with optional 100 kΩ pull-ups) or as output. The 2×6-pin connection carries the 8 I/O signals, +3.3V and ground, as well as the raw PWR voltage and the IRQ line.
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.
The two address solder jumpers on the board allow up to four Expander Plugs to be used together on the same I2C bus.
As a bonus, a small “Breadboard Connector” is included with each plug, to make it easy to hook the Expander Plug up to a breadboard.
The Pre-assembled version has the SMD-sized MCP23008 expander chip and decoupling capacitor already soldered onto the board. Note that no 4-pin or 6-pin headers are included.
The PCB only variant contains just the board for the Expander Plug plus the board for the Breadboard Connector. No parts, no headers.
As connectors you can use a Plug Headers set with 10 male and 10 female 6-pin headers, which makes it easy to connect multiple plugs and JeeNodes in a “standard” way. Or you can solder the board directly in place for more permanent use.
The documentation and full design details are freely available.