What are the principles of implementing Ethernet over power lines ? Is it reasonable/possible to create an Arduino shield which will provide both power & network ? (properly isolate the "dangerous parts") Mains is 220V 50Hz where I live.
\$\begingroup\$ I'm talking about something similar to this: dealextreme.com/details.dx/sku.24489 \$\endgroup\$– AtrigenJul 22, 2010 at 9:13
\$\begingroup\$ That shield will need an enclosure to keep fingers out... \$\endgroup\$– Toby JaffeyJul 22, 2010 at 11:34
\$\begingroup\$ Rather than Ethernet data over AC mains power, many people prefer DC power and Ethernet data over CAT5 cable (PoE) \$\endgroup\$– davidcaryApr 13, 2011 at 23:10
\$\begingroup\$ It's tricky. To have an idea, you'll need to handle problems like transmission line reflections since your network won't have terminal resistors, which means each wall plug or interruptor or anything hooked up becomes a reflection source. I think that's the worst part. \$\endgroup\$– PDuarteMar 2, 2016 at 22:46
In a nutshell, you add a high-frequency, low amplitude signal to the low-frequency, high amplitude AC signal. Powered devices don't care about the added noise, and filtering can extract the high frequency signal without the low frequency component.
Probably due to the dangerous nature of mains power, I haven't seen any blogs or tech notes on how to implement it. However, an Amazon search for "Power Line Communication" yields 325 books, of which most appear pertinent to your question, and by much more qualified persons than myself.
It is possible. However, if you're using an Arduino, you likely don't have the expertise to create a well-isolated and well-insulated shield. No offense intended, I would be hesitant to try it myself, and I've had some training on the topic at a university. Also, an Arduino is meant to be handled, and, as Joby pointed out, it will definitely need a well-designed enclosure.
All things considered, you'll have a much more flexible, easier to create, cheaper, and more robust system if you simply use an Ethernet shield and buy a powerline ethernet adapter like the one you linked to. Do some searching, they're available for less than $30.
Slightly off-topic, but I would consider Power over Ethernet to be much more within the reach of an Arduino shield. National has a decent appnote/FAQ on their LM507X series of powered device controllers. This is something I'd like to try once I get some free time....
The big question here is what is your objective? If it's to DIY your own powerline ethernet adapters, I'd say don't bother. Working with mains voltages and working out how to make power line carrier work at those speeds is probably not worth it. Additionally, the cost of the whole thing will end up being way more than it would cost you for those DX adapters.
If, on the other hand, you've got some other lower data rate application in mind and PLC is your only way to get the signal from point A to point B then you could give it a shot. There might even be some preexisting chipsets/modules you could work with to bootstrap the process.
For a good general overview of PLC, check out: http://en.wikipedia.org/wiki/Power_line_communication
Standard mains voltage disclaimers applies. Be careful, don't get shocked.
\$\begingroup\$ You didnt really answer the question now, did you ? \$\endgroup\$– AtrigenJul 22, 2010 at 11:18
\$\begingroup\$ He answered it, but the answer wasn't what you wanted to hear. He gave a link to some principles of PLC, which is an answer to your first question, and said that it's probably not reasonable for most applications, which is an answer to your second question. \$\endgroup\$ Jul 22, 2010 at 13:09
\$\begingroup\$ I think Atrigen has made it clear he wants to take the time to DIY. He also wants to do Ethernet over power-lines, there is some info here, but if the question asker feels like his question was avoided, and it reads the same to me, I think he is right. I will not downvote, a good answer, just not what he was wanting. \$\endgroup\$– KortukJul 22, 2010 at 14:21