On Sat, 16 Dec 1995, Chris Smolinski wrote:

>I'm having a new house built, and what to put some "intelligence" in it. I
>haven't decided exactly what and how yet, but I am going to run a lot of
>wiring in the walls, so at least I will have that in place.


Why don't use directly the current home wires. You can add on the power line
a FM signal (about 110-160 KHZ). Try to check the LM1893 application note. I
think there is no need of high speed communication in a home network.

With  LM1893 you will be able to send and receive logical signal up to 4800
Bauds. This circuit have a PLL and FM demodulator to recieve, a FM modulator
and power output stage.
If you want to get something as small as possible, you need also to get
power directly from the power line via a step-down-converter (see also MAXIM
product).

* if your design have a very low consumption (<15mA), and want to connect
directly to a light, you can steal some current through the light to get
power. This is realize with a TRIAC by open the gate a very little time,
just enought to charge a capacitor and just enought to get the light "turn
off". When the light is on, the same system can be use.

LM 1893 is not the only solution, you can also build yourself a
transmitter/receive with a 4046, some OP and power stage ... The main
problem with LM1893 is it need +12V ...

I know there is also some hybrid module wich are able to transmit and
receive data on a power line, try also to check ECHELON circuits.

The hard job is to define exactly the communication protocol. I think OSI
model is a good starting point ( just follow level 1,2 and 3). In my mind,
the best way to define such a protocol is like token ring, with a busy/free
flag on the current frame.

Regards,
                Philippe.