John Fields
Guest
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 Posted:
Wed Feb 16, 2005 4:17 am Post subject:
Re: OEM chips for X-10 available? |
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On Tue, 15 Feb 2005 17:05:02 +0000 (UTC), Andrew Burgess
<aab@athlon.cichlid.com> wrote:
| Quote: | John Fields <jfields@austininstruments.com> writes:
As far as getting the signal on the line goes, it's pretty simple;
just capacitively couple a high-frequency tone burst signal onto the
mains using a frequency far enough displaced from the mains frequency
that the capacitor looks like a very large reactance to the mains
frequency while being small enough to let your signalling frequency
pass, like this:
Can you do this without a transformer?
|
Yes:
MAINS>--+-----+-------------/ /-----+-----+------------------
| | | |
| [C] | [C]
| | | |
| +--+--+ | +--+--+
+--| TX | +--| RX |--[LOAD]--+
| | | | |
+--| | +--| |----------+
| +-----+ | +-----+
| |
| |
MAINS>--+------------------/ /------+------------------------
Looking at the caps connected to the mains, if inside the TX box we
have something like this,:
MAINS>----+----------+
| |
+--+--+ [C1]
|TONE | |
|BURST+-------+
| GEN | |
+--+--+ [R1]
| |
MAINS>----+----------+
what we'll want to do is keep the 170V peak AC from damaging the tone
burst generator, while at the same time allowing the generator to
couple bursts of a high frequency tone to the mains. Just for grins,
let's say that we'd like to keep the 60Hz down to about +/- a volt at
the R1C1 junction, and we'd like R1 to be about 100 ohms. That means
that we'll have to limit the 60Hz current through R1 to
E 1V
I = --- = ------ = 0.01A
R 100R
With 170V on the mains, that means that the impedance of R1C1 has to
look like:
170V
Z = ------- = 17000 ohms
0.01A
Now, since
Z = sqrt (R² + Xc²)
and we need to find the value of C1, we can rearrange to get the
reactance of C1:
Xc = sqrt (Z² - R²) = sqrt (17000² - 100²) ~ 17000R
And the capacitance will be:
1
C = ---------- ~ 0.156µF
2pi f Xc
So now we have this:
MAINS>----+----------+
| |
+--+--+ [0.15µF]
|TONE | |
|BURST+-------+
| GEN | |
+--+--+ [100R]
| |
MAINS>----+----------+
and we want to place a signal on the mains. First we'll choose a nice
high frequency (say 100kHz) so that the reactance of C1 will be nice
and low to it, allowing it to pass through and onto the mains without
attenuating it too much.
At 100kHz the reactance of 0.15µF will be
1
Xc = --------- ~ 10 ohms
2pi f C
So that looks pretty good, and the last thing that needs to be done is
to decide on the output amplitude of the tone burst generator.
If we say that our receiver has a sensitivity threshold of 100mV at
100kHz during the mains zero-crossings, and we want the receiver to
work with a 10kW load on the mains, then our circuit starts to look
like this:
MAINS>----+----------+-------+
| | |
+--+--+ [10R] |
|TONE | | |
|BURST+-------+ [1.44R]
| GEN | | |
+--+--+ [100R] |
| | |
MAINS>----+----------+-------+
Which is essentially this:
+-----+
|TONE |
|BURST+-------+--------+---E1
| GEN | | |
+--+--+ [100R] [10R]R1
| | |
| | +---E2
| | |
| | [1.44R]R2
| | |
+----------+--------+
In order to have E2 be 0.1V, we'll need E1 to be
(R1 + R2)
E1 = E2 ----------- = 0.794V
R2
and the generator will have to pump current into the impedance formed
by everything across the mains, which reduces to:
+----------+
| |
| [10R]
[100R] |
| [1.44R]
| |
+----------+
and, finally, to:
|
[10.26R]
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which is close enough to 10 ohms for our purpose, which is to
determine how much current the tone burst generator has to supply into
10 ohms to get a drop of 0.794 across it, and since
E 0.79V
I = --- = ------- = 0.079A ~ 80mA
R 10R
it'll be eminently doable, and as a matter of fact, upping it to 1V
would get us better receiver operation and only require 100 mA out of
the tone burst generator.
--
John Fields
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Eduardo Gimeno
Guest
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| Posted:
Thu Feb 17, 2005 9:25 pm Post subject:
Re: OEM chips for X-10 available? |
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John, thanks for your calculation for the adapter part. Maybe I will
have to use them in short (converted to 50Hz and 220 V...)
Some comments about the replies:
1.-Cabling all the house with Ethernet would be the most profitable
solution, but would also involve making a really big project of the
design, and filling the tubes up with lots of cables. Suppose I need
to have control over ALL the lamps and from all the switches. My house
(2 floors) would have several hubs/switches at given places, and some
tubes would carry more cables than expected due to design of network
(avoid more switches)
2.-I don't know yet the legal problems I would have here in Spain if I
modify the electrical installation, or from the assurance company in
case of fire... I should ask about it before doing anything.
3.-I think I will consider two choices:
a) Using a dedicated cable with a low level protocol, i.e. with
RS485, and a top level protocol of my own in a PIC, for example. The
cable would only have to go through all the switches one time, like a
bus.
b) Using a home-made X10-like protocol, with the indications from
John Fields. Positive: I would avoid using the dedicated cable.
Negative: I would have to train for a while until building the right
"interface" module.
Once again, thanks to everyone for all the replies and help!
Eduardo. |
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