I've been working on a remote control thermostat "Cricket" and more, I
recently posted "Elephant" which is a very inexpensive HA server (my
web pages run on it) and I'm working on perl scripts to control the
serial port. Although the Green Elephant uses a recycled PC I would
recommend a VIA EPIA PD 6000 (fanless) for the mainboard (4 serial
ports and 2 Ethernet ports) It's tiny as it's a Mini-ITX and has plenty
of 12V power options.
I'm thinking of hooking up an 80W 12V solar panel and large 24AH
GelCell to run it and the cable modem.