Hi Patrick,

I think I2C is probably your best bet. If you're implementing it in software, than it will eat processing time a bit, but it's not that bad. You will need a spare interrupt pin though. It was Phillips who developed I2C, and plenty of information can be found on their site (I would e-mail you the specification, but I'm in the North of England, and my computer is in the South right now, so I can't!). It should be noted that I2C was originally designed for communication between chips on the same board. I should think if you use the appropriate cable, you will get away with 1m between each node. There is a Phillips application-note on how you can extend I2C's range to several hundred meters, but of course the price you have to pay is a huge loss in speed. From the sound of your application, you won't be needing that fast a data-rate anyway.

Matt.