Control signal over 12V DC power.
and...@unconfigured.xvnews.domain
I am looking for way to "inject" a control signal onto a pair of 12V power
lines. I want to take a serial bit stream, and use the existing cabling
to carry the data, and then have a controller extract the data.
A bit like X10 but not over AC power lines.
TIA Andrew
--
-----------------------------------------------------------------------------
God put me on earth to accomplish a certain number of things
Right now I am so far behind I will never die
-----------------------------------------------------------------------------
Andrew Holt email: andre...@uk.sun.com
Technical Consultant -----------------------------------------------------------------------------
Charlie Allen
can use the sort of tricks used to communicate between DBS antennas and
the receiver box ----- they simply bounce the voltage back and forth.
If your data bit rate needs are low, simply set up your UART for 300
baud, and switch your "12V" back and forth between 10V and 14V. You
recover the data at the other end with a simple 12V threshold
comparator.
-------------------------------
On the other hand, if the data source is at the 12V LOAD, then what you
can do is to switch in and out a low value resistor to make a dramatic
change in load current. Then you recover the data at the other side by
monitoring the total load current. This is a bit more trouble, but it
is a lot simpler than putting fancy modulations onto the supply lines.
Charlie
--
!!!
/o o\ Charlie Allen charli...@usa.net
( > ) ph 408-736-3815 fax 408-732-7613
\ - /
_] [_
EWMCo
the load after you extract the data? Then you wouldn't have to worry about
whether the load can tolerate the voltage variation..
-Scott Burgess
Everett M. Greene
In article <19981106084345...@ng66.aol.com> ew...@aol.com (EWMCo) writes:
> >IF the load on the 12V power lines can accept some voltage variation you
> >can use the sort of tricks used to communicate between DBS antennas and
> >the receiver box ----- they simply bounce the voltage back and forth.
> >
> >If your data bit rate needs are low, simply set up your UART for 300
> >baud, and switch your "12V" back and forth between 10V and 14V. You
> >recover the data at the other end with a simple 12V threshold
> >comparator
> the load after you extract the data? Then you wouldn't have to worry about
> whether the load can tolerate the voltage variation..
Couldn't you use a smaller modulation voltage at a high
frequency and let the filter caps get rid of the "noise"?
Extracting the modulation from the regular noise may be
a problem though.
Christian G. Taranti
and...@unconfigured.xvnews.domain wrote:
> Hi All,
>
> I am looking for way to "inject" a control signal onto a pair of 12V power
> lines. I want to take a serial bit stream, and use the existing cabling
> to carry the data, and then have a controller extract the data.
>
> A bit like X10 but not over AC power lines.
>
> TIA Andrew
>
> --
> -----------------------------------------------------------------------------
> God put me on earth to accomplish a certain number of things
> Right now I am so far behind I will never die
>
> -----------------------------------------------------------------------------
> Andrew Holt email: andre...@uk.sun.com
> Technical Consultant -----------------------------------------------------------------------------
I'm assuming here that you 12V line is reasonably clean. A capacitor is essentially a short for high frequency and a
short for DC. You can inject your signal though a capacitor on the 12V line an then use another on the other end to
recover it. If you can, try to modulate your signal using a simple AM scheme. The larger the modulation frequency, the
smaller the capacitor. And even 2V of modulation on your load probably won't be a problem (espetially if it is an
electromecanical device).
Tell us how things are going,
Christian
David R Brooks
:Hi All,
:
:I am looking for way to "inject" a control signal onto a pair of 12V power
:lines. I want to take a serial bit stream, and use the existing cabling
:to carry the data, and then have a controller extract the data.
:
There is a system like this used in some model railway setups, where
you modulate by reversing the power polarity. Naturally, the "slave"
(receiver) has a bridge rectifier in its power circuit.
Of course, this only carries data one way (from power source to
load).
-- Dave Brooks <http://www.iinet.net.au/~daveb>
PGP public key via <http://www.iinet.net.au/~daveb/crypto.html>, or servers
Charlie Allen
>
> There is a system like this used in some model railway setups, where
> you modulate by reversing the power polarity. Naturally, the "slave"
> (receiver) has a bridge rectifier in its power circuit.
> Of course, this only carries data one way (from power source to
> load).
This is awesome in its simplicity! Polarity reversal is much easier to
implement than my earlier suggestion of bouncing the 12V supply voltage
up and down with the data.
Too often the solutions posted on the NG are unecessarily
complicated.
Charlie Allen charli...@usa.net
Baytech Electronics
Mike Hardwick
> I am looking for way to "inject" a control signal onto a pair of 12V power
> lines. I want to take a serial bit stream, and use the existing cabling
> to carry the data, and then have a controller extract the data.
>
> A bit like X10 but not over AC power lines.
Andrew,
I've done this a couple of ways...
[1] Modulate your supply current with a switched load resistor, then use
a current sensing circuit to recover the modulation. Maxim makes a chip
that works really well for this job; the MAX471. It's actually intended
for battery monitoring, but if you read the data sheet (between the
lines), you will discover the method...
[2] Insert a series choke and a shunt data modulation transistor to pull
the supply voltage to ground during active bit times. Sounds crazy, I
know, but the choke prevents your power source from seeing the brief
short-circuit intervals. At the receiving end, insert another series
choke to keep your filter capacitor from shunting away the modulation,
and use a simple voltage comparator to recover the modulation. One
caveat: The supply voltage on the line flies up to a value substantially
higher than the standing voltage after each modulation pulse. It's OK,
if the system (including the modulation transistor) can stand the higher
voltage, but you can kill it by adding commutation diodes.
Mike Hardwick
Marty
> and...@unconfigured.xvnews.domain wrote:
>
> > Hi All,
> >
> > I am looking for way to "inject" a control signal onto a pair of 12V power
> > lines. I want to take a serial bit stream, and use the existing cabling
> > to carry the data, and then have a controller extract the data.
> >
> > A bit like X10 but not over AC power lines.
> >
> > TIA Andrew
> >
> > --
> >
-----------------------------------------------------------------------------
> > God put me on earth to accomplish a certain number of things
> > Right now I am so far behind I will never die
> >
> >
-----------------------------------------------------------------------------
> > Andrew Holt email:
andre...@uk.sun.com
> > Technical Consultant
-----------------------------------------------------------------------------
Well, two things come to mind...
Motorola has a CMOS device, I think is called an Addressable UART.
I forget the number, but it was something like MC144XX.
If you can find a data sheet on the part, it has some schemes for sending
data over the same lines as the power.
We once built a device that used ASK carrier on a 12 volt power line.
At the time, we used a device made by Signetics/Phillips called
a NE5050. This chip is a modem chip for power line carrier applications.
As I recall, we used a 120 KHz carrier.
The important thing that I have not seen mentioned in this thread, is to
isolate the power supply with an inductor. Also, use an inductor at
each of the remote points (we called these RIMS or Room Interface Modules).
Pick off the ASK before the inductor on the power bus, and filter the
DC on the module side of the inductor. The power bus has a high impedance
at 120 KHz, but low at DC.
Marty
Saddle
controller, but why don't you send the power down the lines as AC instead of
DC and rectify it at the controller end. FM modulate the AC power to send
the required data to it. It doesn't have to be a sinewave, squarewaves are
easy to generate and rectify and the frequency shift doesn't have to be
much to be detectable.
Hope this helps,
Saddle (In the land of OZ)
and...@unconfigured.xvnews.domain wrote in message
<71pufk$i...@flonk.uk.sun.com>...
aja...@kencomp.net
> > and...@unconfigured.xvnews.domain wrote:
> >
> > > Hi All,
> > >
> > > I am looking for way to "inject" a control signal onto a pair of 12V power
> > > lines. I want to take a serial bit stream, and use the existing cabling
> > > to carry the data, and then have a controller extract the data.
> > >
> > > A bit like X10 but not over AC power lines.
> > >
> > > TIA Andrew
> > >
> > > --
> > >
> -----------------------------------------------------------------------------
> > > God put me on earth to accomplish a certain number of things
> > > Right now I am so far behind I will never die
> > >
> > >
> -----------------------------------------------------------------------------
> > > Andrew Holt email:
> andre...@uk.sun.com
> > > Technical Consultant
The simplest way I believe to achieve this is to use a diode and large
reservoir cap to power your line circuit then put a small resistor to in
series with your line before the diode. Then use your serial data line to
drive a transistor to pull the supply line down by a volt or two in sync with
your data. At the receiving end you can then use a level comparator to
reconstitute the signal. A similar circuit at the other end will allow
bi-directional data streams. The only disadvantages I have found are the
reduction in your supply volts, compensated by using say a 15V supply instead
and regulating the remote supply down to 12V, and losses if the remote device
draws a large current, however my application only uses around 100ma, so the
losses are acceptable I am currently testing this idea for use in an
industrial application, as two core cable is cheaper than 4 or 6.
I hope this gives you an idea, otherwise try a dedicated FSK transmitter,
which can be a bit expensive, compared to a transistro and comparator!!
Best regards,
Alistair James
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