The RTC Plug is a small board containing a low power real-time clock with battery backup. It continues to track the time with second by second resolution while the attached node is sleeping (or even powered off with optional battery inserted).
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 pre-assembled version comes with the SMD-sized DS1340 chip, crystal, battery holder and decoupling capacitor already soldered onto the board. The CR1220 battery is not included. Note that no 6-pin headers are included.
Add a 3 V Lithium Battery for continuous time keeping without power to the board.
The PCB only variant is just the board for the RTC Plug. No parts, no headers, no battery.
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.