Open Source Power Line Communication

Power Line Communication Filtering

 

Since we all have wires running throughout our houses to provide mains power, there’s a number of devices that piggyback on mains lines for communication. For his thesis project, [Haris Andrianakis] developed his own power line communication system.

The basic principle of the system is to inject a signal onto the power lines at a much higher frequency than the 50 or 60 Hz of the AC power itself. Using both active and passive filters, the signal can be separated from the AC power and decoded. This system uses frequency-shift keying to encode data. This part is done by a ST7540 modem that’s designed for power line applications. The modem is controlled over SPI by an ATmega168 microcontroller.

[Haris]‘ write up goes into detail about some of the challenges he faced, and how to protect the device from the high voltages present. The final result is a remote display for a weigh scale, which communicates over the power line. Schematics, PCB layout, and software are all available.

Comments

  1. Truth says:

    I hate this whole category of device, so much RF interference is generated by them. The commercial ones as well, I’m not picking on this project. I just hate the RF generated by what is in effect a high frequency variable oscillator hooked up to a huge piece of metal, with no grounded shielding.

    • nelsontb says:

      I have no ideia how this is legal in anyway

      • tekkieneet says:

        Pretty much sure that it is under FCC part 15.3 part f, so there are regulated signal level over the spectrum that a device has to meet. So it is not free for all DIY project without a proper Spectrum analyzer and a LISN setup to make sure that it is okay. (Need FCC certification if you want to sell it.)

        http://www.arrl.org/part-15-radio-frequency-devices

        >Carrier-current system: § 15.3 (f) Carrier current system. A system, or part of a system, that transmits radio frequency energy by conduction over the electric power lines. A carrier current system can be designed such that the signals are received by conduction directly from connection to the electric power lines (unintentional radiator) or the signals are received over-the-air due to radiation of the radio frequency signals from the electric power lines (intentional radiator).

        In additional there are safety standards to follow and you are on your own if it is the cause of a fire that burn down your house or get someone injured. etc

    • Dan Julio says:

      Interesting. Do you have any of your own research online or can you point to other people’s research documenting this RF interference? There are several FCC qualified (in the US) devices out there now and I imagine that as the automated home becomes a reality with the IoT there will more and more of devices communicating over the power line.

      • tekkieneet says:

        Just because there are products that do something doesn’t mean that everyone esle is allowed to do that without proper FCC certification. See my post above on FCC 15.3 part f.

      • Truth says:

        No, but here are some links that may be useful from 2010, It looks like these issues are known but being ignored.

        http://www.theregister.co.uk/2011/04/05/ofcom_plt_response/

        • Truth says:

          This site has a lot of information about the problems http://www.ban-plt.org.uk/

        • Dan Julio says:

          Interesting again. Thanks. I have a pair of Netgear ethernet over power adapters I’m not using. Maybe I’ll do some experiments. I still think that there will be a lot of companies trying to bring to market products that communicate over the powerlines since these are so ubiquitous. I know Maxim has a line of parts they want to see integrated into power meters so utility companies can read them remotely without even having to send vans around to read the low-power RF interface devices they have now.

        • Mike Lu says:

          There’s a big difference between the high speed wideband used for BPL and low speed narrowband as described in the article. He’s only using a 72kHz carrier, so there really should be no interference to others assuming the transmitter is well designed. On the contrary, that frequency is right where interference from switching supplies would be a common problem.

          • DainBramage1991 says:

            “assuming the transmitter is well designed”…

            They never are. Anyone trying to do weak signal work in the proximity of these devices is completely out of luck.

            As for switching supplies, the poor quality ones tend to splash awful signals out in harmonics across the entire range of LF, MF, HF, and sometimes even VHF frequencies. I’ve seen it with my own radio equipment, and chased down the offending supplies.

    • Pinky's Brain says:

      Not very high frequency in this case, we’re talking about kilometer waves here.

  2. Simon says:

    Now just to implement some encryption so your neighbours can’t sniff all your traffic (without even having to plug into the wall because the emitted RF is so bad!)

  3. Biomed says:

    Excuse me. But how many of you have sniffed the AC mains coming into your home looking for neighbor’s automation signals. I mean… .stuck a scope on there or other test equip and actually looked? Show of hands please. I’ll be first… IMy hand is up. have while looking for spurious interference… and never saw any control signals. How about you?

    • pcf11 says:

      I know that there are signals on my power lines. My power company pioneered the technology. We have this gadget called a beat the peak meter that is like a 3 color night lite that they control from their central office. They also offer another program where they can shut down heavy power consuming appliances that customers can sign up for. Something also screws with my X-10 home automation equipment sometimes. I figure it is the power company. But it is so intermittent you’d have to watch your test equipment for months to see a signal. Oh yeah, I have a smart meter too.

      • Biomed says:

        filters are available to block your outbound X-10 commands as well as the neighbors that are incoming.

      • John says:

        Norweb in the UK pioneered this technology starting in 1991. They hold the base patents, that actually expire this year, for use of HF signals on power lines. Currently those patents are leased to a company in MA who are, at the moment, concentrating on smart grid. There is a huge amount of crap talked about the radiation, mostly by radio amateurs who would be happiest if everyone else stopped using radio waves at all.

        • DainBramage1991 says:

          No, we just don’t like it when other people destroy the RF spectrum with illegal and /or unintentional transmissions.

          How many times do the neighbors have to piss in your pool before you start to complain about it?

          • pajog says:

            I won’t complain, I’ll just go take a dump in theirs.

          • John says:

            It’s not “your pool”, that is the whole point.

          • DainBramage1991 says:

            @John: Not mine personally, but the very small slices of spectrum allocated to amateur radio use by worldwide treaty are very small slices indeed. When someone comes along and ruins nearly all of them because they want to look at cat pictures without all of the huge inconvenience of setting up a router or, perish the thought, running a wire, it’s worth complaining about.

            By the way, many of the frequency allocations in question here are bands where amateur radio is considered the primary user. So technically, it is our pool. Legally (in most places that go by ITU rules, including the US), all other services are not allowed to interfere with amateur radio operation in those bands. There are bands where we are secondary users and must accept interference from primary users. However, in most cases, BPL and similar services would be considered tertiary users on those bands.

            One of the things amateur radio operators need to learn before getting their licenses are some of the finer points of RF rules, regulations, and laws.

          • John says:

            Homeplug should never have been approved. You cannot stop severe radiation because of the properties of in house wiring. I was involved in the formulation of the Homeplug standard in the early days as a consultant for Cisco. We built a complete frame of a house and wired it as one would a normal house with sockets and spurs etc inside a massive Faraday cage up in Cambridge or somewhere North of NY South of Boston IIRC. Ran loads of tests on every powerline chip that was available at that time (2000 or so) to see which ones performed best, radiated least and so on. Out of that work came the Homeplug standard which completely sucks and should be declared illegal because powerline doesn’t work in house and it releases so much spuria it is hard to believe. During my research in the 90s (pre OFDM) we involved the UK authorities and they wobbled up to the test site and lab with lots of mag loops and network / spectrum analysers, took loads of readings of every sort and wrote a report that actually showed there was not much leakage from the underground MV, slightly more from LV (less deep) and that steel lampposts did not radiate, someone in the media took that to mean that concrete lampposts did radiate and it got all over the papers at that time. I still get people quoting to me that powerline radiates from lampposts, it gets tiring does that one.

            Whatever powerline does and doesn’t do is kind of irrelevant really, you only have to look at GSM phones to realise that if the powers deem it to be good it will get approved.

  4. Shakipu says:

    Another way to turn your entire house into a gigantic microwave :p

  5. Harvie.CZ says:

    And what about connecting WiFi devices to mains using some safety capacitors?

  6. Doug says:

    Electric utilities have been using Power Line Carrier (PLC) since at least the 40’s, when they used tube transmitters and receivers to do the job. I work with PLC devices almost daily, operating at frequencies spanning 16-500 KHz. on transmission lines approaching 80 miles long. They’re used to send status signalling data (on-off keying), voice audio (phones and intercoms), metering information (telemetry) and even have been running SCADA control systems over PLC since the 70’s. I just took one of those 70’s systems out of service a few years ago: 17-24 KHz band, 1200 baud, full-duplex, 10W. Never had to work on it because it was just that over-built. Currently I’m working on getting over 400 PLC units certified for PRC-005 compliance this year, with another 350 to be certified next year. And that’s just at one company. PLC is everywhere and has been for years. Projects like this are amusing, but hardly thesis material. It’s just a re-hash of technologies that are already well-known and documented

    • John says:

      IIRC the first was a telephone system way before that, 1910s 20s or so. It was patented but no one looked at it again for a long time after that. I think that I have designed and installed the biggest HF install in the world with 130 sq km of wifi coverage over 120km of MV line giving broadband to about 7 small villages in central Greece. It has been running now for about 5 years or so. As far as I know there isn’t a bigger one anywhere.

  7. Jan says:

    On his site: “The filter was first designed and simulated in spice software.”

    He did quite a good job in designing the filter, as there is exactly the same schematic in the application note AN2451.

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