> Wire length. Impeadance. other nasty stuff. Better would probably be send
15V
> unregulated down the line and regulate at the node.
>
> BAJ
>

What about 18 or 24 VAC?  I, too, have been considering this type of home
setup, and am just starting  ( with the sprinkler systems).  I plan to have
"smart" nodes that communicate with a Linux box which contains the "home
management" logic.  To get the sprinklers up and working, I'm going to just
use RS-232, but will be converting to '485 next.

Plans include:
  Temperature Sensing - each living area, attic, basement (eventually will
be finished into individual rooms, first things first, ya know <g>)
outdoors, and garage.
  Underground sprinklers - automatic start / stop, skipping days when not
necessary.
  Security - door and window open / closed status indicators, garage door
monitoring, perimeter detection, video camera control, while-away monitoring
  Remote Access - Telnet into my Linux box and be able to check temperatures
inside the house, adjust A/C or heat, control sprinklers, etc.

-- Mitch