RE: Interesting Concept... or complete idiocy?

["Ian B" <Ian@xxxxxxx>]

Have a look at the home brew appliance module that Phil et al has been
playing with. This will go some way towards your answer. Phil can n doubt
provide the url.

Ian

-----Original Message-----
From: Ian Lowe [mailto:ian@xxxxxxx]
Sent: 20 February 2002 18:35
To: UKHA Mailing List
Subject: [ukha_d] Interesting Concept... or complete idiocy?


I am fishing for the views of experts before comitting time to something
that's obviouslly flawed.

As I understand it, X-10 signalling is basically this:

You place (and detect) a 1ms wide pulse of 120khz with an amplitude of as
little as .1v 20ms or so after the zero crossing, such that after an agreed
pre-amble, a burst means "1" and no burst means "0"
this transmits house
code, unit code, command a couple of times for redundancy.

Now, I saw some articles about improving X-10 range and reliability, which
all centred around improving how accurately the reciever circuit was tuned
to 120khz, and this got me thinking..

It started as "what if the 120khz oscillator was *very* precise?"
I figured
a PIC Chip with an XTAL clock could be that precise, and then I figured,
why
bother?

Why not just use the ADC in the PIC chip to analyse the powerline as an
analog signal, and watch for a burst of "noise" in the right
place on the
wave?

I figure if I used a large resistor to limit the current, and used some
circuit arrangement to "crop" the powerline "signal" so
that I was only
looking at the segment from -10 to +10 I would be able to do some simple
DSP
on the line to watch for firstly, the zero cross, then a pulse of
"something
kinda like 120khz" in the right place.

As i recall, if you want to recognise (and replicate) a signal, your sample
rate needs to be at least double the signal rate. so, for a 120khz signal,
you would want to be sampling at 240khz. Given that even the fairly basic
PIC12C jobs have a 10Mz clock, I'm sure sampling at 240khz wouldn't be
stressing things too much!

Just wondering if you could implement a basic X-10 module with very little
in the way of components?

Does this seem deeply ridiculous? or just technically too bothersome? or
might it even work?

Ian.



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