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DC powerline communication at 2Mbit/s

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scrat:
Hi all, after a long time I'm back to the forum, just to ask for advice  :-[.

A friend asked my though about a bidirectional communication link at about 2Mbit/s over a short (5 meters) 24 Vdc power line (up to 10A load) that he needs to make at work.
The number of pieces they will use is certainly low (1-10).

Since I think this could be quite a common specification, I looked around for standard implementations of DC powerline communication, but to my surprise I didn't find one. Many of the most common solutions are limited to the 100kbit/s range.

A commercial solution I found seems suitable: a 5Mbit/s LinkSprite module (http://www.linkspritedirect.com/product_info.php?products_id=4). This is quite expensive (50$/piece), and another problem in this case could be the fact this is designed for AC power lines, where there aren't any large parallel capacitors as terminations, as happens in a DC line instead.

I also found this forum page http://e2e.ti.com/support/interface/industrial_interface/f/142/t/75687.aspx, where the advice (in the schematic) is to use RS-485 (encoded or modulated) and differential mode chokes at the two line ends. This looks like a custom solution that could be quite long to set up and hardly reusable in the future (for example, with a longer line).

What would you say to my friend? Are there any standard ways to do the job?

Many thanks,
Sandro

sacherjj:
I know there are powerline based ethernet modules to jump a wired network along home wiring.  I don't remember the speed, but I'm almost 100% sure it is over 2 mbit.  Not sure if that would help in this situation.

scrat:
Thanks for your replies...


--- Quote from: Dave.S on February 23, 2012, 07:30:25 pm ---A well-designed highpass ?

And heavy filtering for the DC .

--- End quote ---
Well, the solution in the TI forum link I posted is on that way, but they use transformers at both DC sides. Simply filtering the DC will result in shunting the "HF" signal too. This also requires some kind of modulation or encoding, so which one would you choose?


--- Quote from: sacherjj on February 23, 2012, 08:18:56 pm ---I know there are powerline based ethernet modules to jump a wired network along home wiring.  I don't remember the speed, but I'm almost 100% sure it is over 2 mbit.  Not sure if that would help in this situation.

--- End quote ---
Yes, in fact, AFAIK the LinkSprite I mentiond (5Mbit/s) should be one of those, or very similar (it's HomePlug complaint, and HomePlug should one of the most adopted standards in this field).
It seems too much for a 5meters link on a fixed line configuration (much simpler than a power grid)...

There must be a common solution to this quite common need!

T4P:
Interleave the signal on top of the DC voltage at the transmitter then parallel decouple the DC and one highpass for the AC , then another output low pass for the DC .

scrat:

--- Quote from: Dave.S on February 24, 2012, 11:57:38 am ---Interleave the signal on top of the DC voltage at the transmitter then parallel decouple the DC and one highpass for the AC , then another output low pass for the DC .

--- End quote ---

I think I've understood what you mean. High- and low- pass filtering could be done by using inductors, since the DC line has to pass 10A, so resistors are not an option at all. Moreover, a differential signalling would be more robust. In fact, this is the approach posted in the TI's forum.
The problem is still in the choice for the modulation (imagine a digital serial data source). I wanted to check for past experiences and possible common solutions. If there is no standard, there would be complete freedom.

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