Take a look at how X10 stuff works (at the AC voltage zero crossings). You might be able to adapt some existing chipsets and other hardware.
--
Paul Hovnanian mailto:Paul@Hovnanian.com
------------------------------------------------------------------
Hanlon\'s Razor:
Never attribute to malice that which is adequately explained by
stupidity.
Just OTTOMH - brute-force baseband (9600 HZ Manchester, DTMF, ?) through a current transformer?
It's just I'm thinking "modulation", with a transmission line impedance of
0.2 - 1 ohm, 60 HZ "carrier" - or just superimpose your data stream, coded at your leisure. What kind of noise and crap are we dealing with here?Good Luck! Rich
Maybe pass the power wire through a low-mu core and inject the signal in series, rather than in parallel? Ditto receive end.
If there are any bridge rectifiers in the system, the line parallel impedance will be modulated by diode conduction!
John
A little one-off (at the moment) G-job here:
I'm interested in doing carrier current communication over 12VAC power. Total AC current will probably be in the 10-50A range, and I'd like to get 4800 or 9600 baud, but less would be acceptable. There could be a couple hundred feet of wire, and I don't control the source impedance.
So, a fat choke (or the secondary of a transformer) in series with the line and couple the carrier in capacitively or inductively?
Looks like there's some advantage in keeping the fundamental frequency low if this is ever to have to deal with FCC etc. standards.
Maybe the AM IF frequency of 455kHz, making a ceramic filter for the receiver easy?
Any other suggestions?
Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
Hello Spehro,
A resonant circuit would make for a smaller device to isolate the RF path. At 50A a choke can become rather bulky.
I would go much lower, below 150kHz, but avoid any Loran ranges. X10 operates on 120kHz and AFAIK they blast several volts onto the mains line.
Stay away from simple AM on-off protocols. That is one of the downsides of X10. It should at least be FM or something even more reliable. Your protocol may have to be fault tolerant against missed or misinterpreted bits. FEC and all that sort of things.
As to receiver filtering you can't use crystals at 9600bps. But LC is pretty stable below 150kHz. Another upside of staying under 150kHz is the abundance of ferrites that are suitable.
Using frequencies that others already have can yield FCC advantages similar to what FDA 510(k) does in medical: Prior art, less scrutiny. The downsides may be patent issues and the like.
Regards, Joerg
Hello Paul,
We have some X10 and I don't find this AM protocol all that reliable. It is also very slow.
Regards, Joerg
"Is also rejected"? Some sort of Royal decree?
John
Maybe think about transmitting the comms as a common-mode voltage. The 24Vac system can be connected to Ground at 60Hz (or have stray-C to ground), just devise something that makes that connection a high impedance at (and above) the comms carrier frequency.
-- Tony Williams.
That's one of three possibilities of selecting two of three terminals for the signal transmission , but for some reason it is forbidden for safety reasons. Also, the current carrier method of inducing a signal via transformer with secondary in series with line is also rejected- probably too much bulk required there.
I like it better than that execrable term "deemed".
Best regards, Spehro Pefhany
-- "it's the network..." "The Journey is the reward" snipped-for-privacy@interlog.com Info for manufacturers:
The one I hate is "good engineering practice" which usually means "I always do it that way but can't actually explain why."
John
I use the term "good engineering practice" to indicate to the client that, if they'd done it my way, they wouldn't be in ka-ka-land right now ;-)
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
I should have added... I told a client more than two weeks ago, "your design failed because....".
They vehemently denied it could happen, that I was totally wrong, how could I be so wrong, all their simulations showed it was stable, etc.
Guess who's kissing my ass today ?:-)
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Or they just don't like the looks of something innovative, therefore it doesn't conform to "good engineering practice".
Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
The only problem is that you can't gloat and rub it in, it drives the clients away.
So all I can do is laugh with the wife over a glass of wine ;-)
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
How about using the GND and Neutral? No series inductors needed, and no line voltage to worry about.
The GND and neutral are joined at the source, so the driver has to deliver current into a short circuit. A few dozen feet of wire will give enough impedance to develop a useful signal.
Hot +-------------------- Black ------------------+
60Hz supply Load +-------------+------ White -----+------------+ | | GND +-------------|---+-- Green -+---|------------+ | | | | C1=== | | ===C2 | | | | Tx RxCarrier current often uses wideband FM to reduce noise. The frequencies may be around 300KHz or so.
In fact, now that I think of it, I may have a use for this. Thanks!
Mike Monett
. * L1 50A,60Hz * L2 . +-----/////---+----+---->--------+--/////----+ . 60Hz supply ===== | '--||--, | ===== Load . +-----/////-------+-------+--+------/////----+ . * | | oops! | | * . C1=== | | ===C2 . | | | | . Tx Rx .
What about high-frequency capacitive loading by other stuff that's plugged into the AC mains? Another thing, L1 would have to be a big beast, handling the entire AC main branch.
--
Thanks,
- Win
Right. You can prove that you're smarter than them, or you can get repeat business, but not both.
John
Speff said it was 'low voltage' which doesn't sound 'utility' to me; I got the impression it might be some 'private' low-voltage system. And you can slip a split-core ferrite over even an insulated conductor.
A low-mu core with a high-ratio winding, resonated on the primary, clamped with a couple of zeners, won't have any spike problems. Making a voltage connection into a utility line takes about as many resonating and transient protection components.
Agree on that one. FSK or PSK makes more sense.
John
Except for needing four windings in series with the 50-amp circuit. Those will be huge transformers and nasty connections.
Why not
| tx | | rx | | | | | +---/////---+ +---/////---+
where the trannies are 1-turn primaries, just cores slipped over the insulated power conductors?
John
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