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Data over power — Parallax Forums

Data over power

bnikkelbnikkel Posts: 104
in Propeller 1
I need someone to please point me in the right direction. old thread, link to an article, or any helpful info at all. I have two propellers about ten feet apart both being powered by a 12v 77A DC power supply and I want to send data over the power line similar to a phone line, half duplex is fine if that's all that is possible.

Thanks in advance for any help.

Comments

  • kwinnkwinn Posts: 8,697
    This might be a good place to start.

    https://www.smarthome.com/sc-what-is-x10-home-automation

    You can also search the internet and this forum for X10, which is the the first popular communication protocol over power lines. Still in use today. There are also power line modems available.

  • RS_JimRS_Jim Posts: 1,753
    Bnikkel,
    The power line you are referring to is 12VDC? Correct? If so you might be able to couple your data signals into the power with DC blocking Caps. How fast is your data going to run?
    Jim
  • bnikkelbnikkel Posts: 104
    yes the power line is 12vDC, it powers both propellers, right now I have them talking to each other over 2.4ghz transceivers but I would like them to communicate over the power line.
  • bnikkelbnikkel Posts: 104
    9600baud right now,
  • kwinnkwinn Posts: 8,697
    bnikkel wrote: »
    yes the power line is 12vDC, it powers both propellers, right now I have them talking to each other over 2.4ghz transceivers but I would like them to communicate over the power line.

    Your first post mentions the current is 77A. Is that correct or is it a typo? Is it the supply rating or actual current draw?

    I ask because I designed a relatively simple power line comm for a long conveyor that may work for you.
  • bnikkelbnikkel Posts: 104
    its the supply rating.
  • bnikkelbnikkel Posts: 104
    actual is under 1A
  • jmgjmg Posts: 15,144
    edited 2018-11-19 19:15
    bnikkel wrote: »
    actual is under 1A

    That's quite a difference - 77A to 1A ?
    The main challenge with power+data is to raise the impedance enough at some frequency, to get enough voltage swing to measure...
    A series inductor for each end is common, but it needs to be rated at the supplied current.
    IrDA has examples of Serial to pulse and pulse to serial usage, there is bound to be some IrDA code for P1.


    The other issue, is what does the current draw by the system look like, frequency wise. You want to avoid lots of energy where you are trying to send data ....
  • bnikkelbnikkel Posts: 104
    im sorry if I said that incorrectly, the available current is 77A I am only drawing about 1A.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    bnikkel wrote:
    im sorry if I said that incorrectly, the available current is 77A I am only drawing about 1A.
    But jmg's admonition still stands. If the supply is capable of delivering 77A, it has a very low impedance. So you will need to remedy that either with series inductors or, since your actual draw is so low, resistors -- assuming you don't need exactly 12V -- to increase the impedance to AC.

    -Phil
  • kwinnkwinn Posts: 8,697
    Phil and jmg are right about both the impedance and possible noise frequency from the power supply. At 77A it is almost certainly a switcher so there will be some noise. A fairly large inductor between the PS and the two Propeller boards should take care of both the noise and impedance problems.
  • kwinnkwinn Posts: 8,697
    Attached the schematic and waveforms plus description of the circuit I used to communicate over a 24V power line with a master and five slave stations. Ran at 1200 baud and was tested to work at up to 4800.
    Comparator circuit description.jpg
    805 x 542 - 54K
    Power line comm.jpg
    1214 x 639 - 61K
  • kwinnkwinn Posts: 8,697
    Only caveat is that the propeller boards had to have switching regulators to keep the line current and voltage drop down.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    You might consider using my Bell 202 modem software for your communication needs:

    http://forums.parallax.com/discussion/110918/bell-202-modem-1200-baud-afsk-object/p1

    It's only 1200 baud, though.

    -Phil
  • Mark_TMark_T Posts: 1,981
    edited 2018-11-22 22:47
    A transformer is a standard approach, you both provide the HF isolation, adapt the impedance
    and inject the signal in one component. PoE does this with beefed up magnetics for instance.
    And you get isolation of course.

    Getting the right transformer is crucial, it has to handle the DC bias current without saturating.
    The AC signal needs to use a DC-free modulation technique.

    For low voltage other approaches using RFCs and capacitor injection may be cheaper - you still need to handle
    the DC current without saturating, you get less isolation, you need DC-free modulation. This
    may be easier to source.
  • Clock LoopClock Loop Posts: 2,069
    edited 2018-11-22 23:47
    DCC made for model railroads is a pretty refined data over power standard..
    Check it out, i have adapted the method to make my own data over power in the past, simple hbridge pushed by serial output , two wires, ...etc..
    My dcc equiptment can be set to 12v. I doubt op needs 77amps tho?

    https://www.nmra.org/beginners-guide-command-control-and-dcc

    https://www.nmra.org/sites/default/files/standards/sandrp/pdf/s-9.1_electrical_standards_2006.pdf



    serveimage?url=http:%2F%2Fusuaris.tinet.cat%2Ffmco%2Fimages%2FcompletoDCC.gif&sp=367fe294a725151b5138c51a81a891b4
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