My first sensor hub is going to be based on an Arduino Mega. I'm going to build it in shield form and then if it's successfull I might attempt to integrate an arduino directly into it.
It is going to have 4 link ports tied to hardware serial ports to connect to adjacent hubs. These wires are going to be cat5 with data in rs-485 format and the remaining 4 wires used for power. The shield is going to have a stepdown DC to DC chip so that 48v power can be sent over the line and stepped down to the 5v required for the arduino and sensors.
To connect sensors, there are goingto be 4 more cat5 jacks with pin devoted to power, analog sensors, i2c, and digital i/0
(sketches coming soon)
Next week I will order parts to start breadboarding the hub