The Clock Plug adds a real-time clock to a JeeNode:
A demo for setting it and reading it out follows:
Unfortunately, there seems to be a problem with it – it does not start up reliably, and connecting the backup battery makes it stop?
Oh, wait – the DS1307 is specified for a 4.5 .. 5.5V power supply, and I’m driving it from the 3.3V line! And yes, sure enough, it works fine when powered from 5V.
Time to look for another chip. Ah, looks like there is a pin-compatible one which does work at 3.3V – here’s a post from someone who fell into the same trap.
Update – the DS1340Z works fine, see this followup post.