Have you considered LIN protocol?  I guess it could be cheap and robust
solution.

www.microchip.com/download/appnote/pic16/00729a.pdf

Igor

-----Original Message-----
From: pic microcontroller discussion list [mailto:PICLIST@MITVMA.MIT.EDU]On
Behalf Of Lyle Hazelwood
Sent: Thursday, June 05, 2003 12:55 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [PIC]: Home Automation with PICs


>On Behalf Of Ruben vd Merwe
>Subject: Re: [PIC]: Home Automation with PICs
>
>Thanks for all the feedback.
>
>I am just starting to build a new home and I am building it with HA in
>mind, meaning that all electrical systems would be able to be wired up.
>I have been investigating all the different systems, and I must agree
>that X-10 is way out there.
>
>I have currently got a system that I made which is working fine, but the
>problem is that is a parallel bus system. So all the connected items
>have to be wired back to the control system. Where a serial system can
>have controllers all over the place and devices just wired to the
>closest controller.

CAN is not quite that easy. It is serial, but there is a single run that
includes all nodes. There can be no "forks" in the line, and only two
endpoints. star configuration is not possible as far as I know.

>I am keen on I2c and maybe CAN, and I like the IP idea, but as pointed
>out, expense in doing so.

I am not very familiar with I2C for this kind of application. I believe
it was designed for connecting chips within a product. I am skeptical of
how well it could handle the noise you might pick up if you wired it around
the house. I considered IP, but the cost per node, cost of hubs, and higher
levels of "software overhead" made it less attractive.

Some advantages of CAN: Most of the protocol overhead is built into the
18Fxx8 PICs. Only an 8 pin line driver is required at each node for
interface.
CAN was designed to work in noisy environments. Automatic priority
arbitration.
Flexible addressing scheme. Well documented interface. 2 wire
bi-directional.
Automatic error detection and re-transmission, simple twisted pair wiring.
Faulty nodes are automatically "kicked off" the bus.

Disadvantage of CAN: maximum 8 byte packets.

>Some more input welcome. Thanks for all the cool replies so far!

>Ruben

I should mention here that wireless CAN is available. Mr. Danmeyer has
created
http://www.autoartisans.com/products/index.htm
in case you need to go wireless. I have not used these (yet), but it's nice
to know.

There are many projects using CAN on the web. Example code for a CAN node
and
a CAN bootloader are available from the Microchip "Application Maestro". I'm
working with this now, though I haven't made it to the CAN code yet.

Good Luck,
Lyle

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