Eric, you might want to take a look at the 8 July 99 issue of EDN.
As you are probably aware, there are major `battles' in the standards
process. I have a large house built in the early 1900's and I've been
wanting to do this for a long time but I'm waiting for the `dust to
settle' as I want compatibility. The EDN article will bring you up to
date as to where things are going as well as a `hands-on' project.

   - Tom

At 11:10 PM 7/29/99 -0500, Eric Oliver wrote:
>Well, someday I'm gonna build that dream house and, while I dream, I'm
>constantly coming up with new ways for complicating things.  I would like
>to build an RS485 based network to connect various gadgets throughout the
>house.  So I've been doing a little reading and I have a few questions. I
>thought I would post what I have in mind for review to make sure I'm on the
>right track.
>
>First, I figure I'll have a master node that provides the link between my
>PC and the RS485 net.  At this point, to keep it simple, I figure the
>master can poll slave nodes to avoid collisions. In addition, the master
>can store configuration data, etc. so that the network can operate without
>the PC.
>
>This brings up my first question.  Should I go with half duplex chips and
>forget about it, go with full duplex chips but use half duplex
>communication for now to keep my options open, or is there a simple means
>of implementing collision detection and do you think that I should bite the
>bullet and set it up as full duplex communication from the get go.
>
>The only thing I don't like about polling in a master/slave relationship is
>that it's kinda like a uC without interrupts. I don't mind using a
>master/slave setup, but I _would_ like a way for a slave to tell the master
>it needs attention. Maybe  I could use one pair for half duplex RS485 and
>the second pair as some sort of attention line ? Any ideas ?
>
>Next is the wiring. I am planning to use twisted pair CAT5 cable. As I
>understand it, I'll only need one pair for half duplex or two pair for full
>duplex. That leaves two unused pair. So my thoughts turned to using the
>extra wiring to carry power.  What are your thoughts on this ?
>
>There are some devices that will use 5V and some that will use 12V. Am I
>asking for trouble if I use a power supply that outputs both 5V and 12V and
>put them both on the unused wiring ?  What kinda of gotchas will get me <g>
>?
>
>This isn't mission critical stuff but, at the same time, I don't want to be
>working on it all the time either so I'd like to build reliability from the
>ground up.
>
>Any thoughts appreciated..
>
>Eric

------------------------------------------------------------------------
Tom Handley
New Age Communications
Since '75 before "New Age" and no one around here is waiting for UFOs ;-)