Re: Interesting Concept... or complete idiocy?

[Alan Shields <alan@xxxxxxx>]

take a look at 
http://www.cix.co.uk/~pplunkett/x10.htm

Alan Shields
alan@xxxxxxx
On Wednesday, February 20, 2002, at 06:34  pm, Ian Lowe wrote:

> 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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