Ac Communication

Discussion in 'Wireless & RF Design' started by saleemsm, Jul 10, 2006.

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  1. saleemsm

    Thread Starter Active Member

    May 15, 2006
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    hello

    i am thinking over a project presently... i have designed the MC based hardware all i want it to communicate via an AC line can any one help...

    thanks in advance
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    Hi,

    You need to give more information before anyone can help. Be specific about things like data rate and what kind of modulation you wish to use. Also, what distances are involved? Have you checked to see if you are going to be legal doing this? If some company already uses AC power lines for data transmission, you could have legal problems for interfering with their stuff.
     
  3. Papabravo

    Expert

    Feb 24, 2006
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    Power lines are a very difficult communications medium to use. This is due to their low impedance and trunkline dropline geometry. Powerlines radiate like crazy because they are unshielded so most of your signal disappears into the ether so to speak. Impeadance matching is increasingly difficult as you go up in frequency to get more bandwidth. Several utility companies are involved in bitter disputes with licensed radio services over the interfernce potential of Broadband over Power Lines(BPL). You do not want to be on the wrong end of an interference complaint from a licesnsed user. The FCC will come after an individual much quicker than a utility.

    That said I would do a google search for powerline modems, but you should be prepared for disappointment.
     
  4. saleemsm

    Thread Starter Active Member

    May 15, 2006
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    hi papabravo and beenthere i don't want to interfere with those having the rights to use such a technology... and "beenthere" i don't know if it is possible to communicate via the AC power lines... by your explanations it is clear that we can. i want to know the extent to which we can communicate that is datarate, modulation technique, and distance... i want to know if this is feasible and to what extent... besides i don't know much about powerlines... and "papabravo" i need only signals of frequency like 200k- 1M or so... the problem is as we know AC lines are at freq 50-60 hz... if i use frequence modulation my carrier in the modulation will not be useless... actually that becomes my message signal right? so is this possible... besides i have heard of a project where communication was carried on in an AC powerline using Telephone... cool na? but mine is different... i want a digital data to be transmitted else where with the help of the AC lines. hope i am clear... it doesn't only mean digital signal using FSK we could also convert them if its easier?

    Thank you people for your reply.

    have a nice day!
     
  5. n9352527

    AAC Fanatic!

    Oct 14, 2005
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    It is certainly possible, although it is not easy, to do this. As far as I know, there's currently no allocation on the rights of using powerline as a communication medium as long as it is limited on your premise only. Although I'm sure that the power company would not regard this favourably for long distance communication.

    The implementations depend largely on your desired data rate. High data rate in the region of 50Mbps peak is possible for short distance (inside a house). I imagine the actual bit rate would be much lower than advertised.

    If you want to do this yourself, there are companies that make powerline modem chip. I've used an old Motorola chip for slow data rate, quite easy to design for non-demanding application. ST also had one (probably still has). There are also many new single-chip solution for powerline modems/ethernet, which I don't have any experience with. I imagine these would require some design effort.

    If you just need to control things around the house, then consider the X10 protocol. This is easy to implement and pretty robust. The data rate is very low and therefore only suitable for simple home automation applications.
     
  6. saleemsm

    Thread Starter Active Member

    May 15, 2006
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    ok will see into the X10 protocols and let you know if that is what i wanted... for now i know i can do this... but how can I????? that is the question... i will look through the protocol but i will need the idea behind it... i assumed that we cound modulate the message signal with the power signal with the message signal as the carrier... i want some ideas like this to implement the communication via the powerline... i found a strange thing in a site such things are already in progress... there are working models... but i want to think it my way... anyways i think i got the message straight... IDEAs are required on HOW TO communicate... will look through the X10 protocol and let you people know.
     
  7. Papabravo

    Expert

    Feb 24, 2006
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    In order to have a modulating signal with 1 MHz of bandwidth you need to have a carrier frequency which is much higher. Power lines will not propagate frequencies in the range that you need. The first transfomer you come to will knock your signal down to nothing. End of story. Try computing the inductive reactance of 100mH @ 100 MHz.(62 MOhms) It is hard to imagine how you can accomplish your goal, but "man's reach should exceed his grasp or what's a heaven for?"
     
  8. saleemsm

    Thread Starter Active Member

    May 15, 2006
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    n9352527 your suggestion was bulls eye... ya the protocol is very helpful i am doing deep study into it to understand the concepts will let you people know if i have any doubt...

    and Papabravo you misunderstood or overlooked what i tried to say... i have said in my previous replys that i assumed we could transmit the message (200k-1M) as carrier and the regular AC line frequency (50-60) as the message you understood??? reverse modulation... after modulating my signal with the AC line freq i want to retrieve the Carrier rather than the message... hope i was clear. But i don't know if it is possible its just my thought... well as n9352527 has given me the lead for X10 protocols i feel i should learn it and implement it myself... lets see would let you people know about my status...

    thanks for now everyone... especially n9352527
    take care
    have a nice day!
     
  9. Papabravo

    Expert

    Feb 24, 2006
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    The problem here is that you are unable to clearly articulate your ideas. There is no such thing as reverse modulation where your signal is the carrier.

    Now listen to me. For all modulation schemes the carrier frequency must be greater than the modulating signal. If you have a data signal in the range of 200 kHz. to 1 MHz. Then you need a carrier frequency that is much greater than that. When you try to couple that modulated signal onto the power lines they will radiate and attenuate your signal dramatically as a function of distance. When your signal gets to the first utility company transformer your signal will be knocked down to zero.

    X10 is a well know home control system. I don't believe it is designed to go outside the home. I also believe that the data rates available are rather low. If it suits your needs that is fine and wondeful. I think you have greater aspirations for the system that you want to design. You just need to be aware of the obstacles, and you might want to think about taking some smaller steps on the way to your goal.
     
  10. saleemsm

    Thread Starter Active Member

    May 15, 2006
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    hi people!
    hi n9352527

    i went through the websites citing X10 and understood very little... can you explain it to me in plain words... that is what X10 is actually doing with an example... also from the site below
    http://www.x10.com/support/technology1.htm

    i found the theory behind X10 but not able to understand it either... can you explain it as it is in the article. or someother site where a better layman explanation is given?

    hi papabravo
    sorry for the late reply i was actually thinking of correlating X10 with my idea it suits well but i am not able to understand its working...
    and about my inarticulate ideas!! well that was a good way to reprimand my behaviour.
    the assumtion i made was that consider a signal AsinWt which is the message and a signal Bsinft which is the carrier... both having different frequencies... W and f respectively... now modulating them in any technique... say FM we obtain the modulated signal right??? now using a highpass filter in the receiver what can we obtain??? as W<f we obviously get Bsinft in the output right??? this is what i thought... i don't know whether it is feasible but it was only an assumed theory i didn't mean to lay a new theory called reverse modulation... this is from the theory of modulation. and i clearly understood that my data signal will not travel the distance when i use the regular scheme as you said. And one more thing i don't plan to NATIONALIZE my idea... i only want to use it in my premises... i think i will not face any rights/patents issue here right? and besides that i think X10 will suffice my idea but i will not copy it... will
    create my style of X10 :) and i am sure that you ppl will help me with the obstacles and remind me when to come back to earth when i just float off...

    thanks for your interests!
    have a nice day!
     
  11. hgmjr

    Moderator

    Jan 28, 2005
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    Greetings saleemsm,

    You may be interested in the material on Wikipedia's website on the topic of X10. Taken together, the material that you have already found and the wikipedia material may shed a brighter light on the overall topic.

    http://en.wikipedia.org/wiki/X10_%28industry_standard%29#Weak_points_and_limitations

    One thing to be aware of is that the X10 baud rate (factoring in the overhead of a certain amount of duplicated transmission) works out to around 20 bits per second. Rather slow by normal data speed standards but plenty fast for the type of simple control applications for which X10 was designed.

    hgmjr
     
  12. saleemsm

    Thread Starter Active Member

    May 15, 2006
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    greetings hgmjr

    now i think i understand X10 better... now i know that we can Transmit signals in the powerline but have to design another system... but before that i need to know the exact working of X10 which i could neither understand from the previous site nor WIKIPEDIA... can you people shed some light on it??? all i know is that there is a transmitter and a receiver for controlling the switches... and controls can be passed from a suitable position else where near by. i understood that we need to transmit signals in bursts... and RF bursts are used... but why 120kHz? why the 200micro second delay between pulses? not at all clear in those areas... please explain in lay mans' terms...

    thank you for your support.
     
  13. saleemsm

    Thread Starter Active Member

    May 15, 2006
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    to be precise:

    :eek: "This digital data is encoded onto a 120 kHz carrier" :eek: which is transmitted as bursts during the relatively quiet zero crossings of the 50 or 60 Hz AC alternating current waveform. One bit is transmitted at each zero crossing.

    why is it encoded onto a 120kHz carrier?

    and

    In the 60 Hz AC power flow, :eek:a Binary Digit (bit) 1 is represented by a 1 millisecond burst of 120 kHz at the zero crossing point (0-o, but certainly within 200 microseconds of the zero crossing point:eek:), immediately followed by the absence of a pulse. And a Binary 0 by the absence of 120 kHz at the zero crossing points (pulse), immediately followed by the presence of a pulse. All messages are sent twice to reduce false signaling. After allowing for retransmission, line control, etc, data rates are around 20 bit/s, making X10 data transmission so slow that the technology is confined to turning devices on and off or other very simple operations.

    why is binary 1 represented by 1msec burst?

    why certainly within 200 microseconds?

    and "binary 0 is represented by the absence of 120kHz at the zero crossing" is what is said how is this controlled? does the receiver search for a signal every zero crossing?

    hope i am articulate now papabravo?

    have a nice day!!!
     
  14. hgmjr

    Moderator

    Jan 28, 2005
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    Greetings saleesman,

    I think you have caught on to the X-10 technique.

    I am pretty sure that the 120KHz frequency was chosen to be well above any harmonics that might be present in the 60Hz. Another possible reason is along the lines that papabravo has stressed. As he has pointed out, transformers located throughout the AC distribution system are going block frequencies above 10Khz or so. By making the frequency high enough, it is fairly certain that the X10 controlled stuff located in your house is not going to be inadvertantantly affected by your neighbor's X10 system. As you can see they have added another element into the X10 message protocol called "house code" to make it possible to avoid accidentally controlling something in your neighbor's house. This is probably more of a problem in an apartment complex where there is a higher likelihood that adjacent apartments share the same AC power feed.

    The duration of the burst was chosen to make it reasonably easy to detect with simple circuitry while at the same time being long enough in duration so that it is clearly differentiable from all the other trash that is most certainly present on the AC power lines.

    By controlling the relative time between the zero-crossing and the 120KHz burst, it is easier to pick out the zeros which as you have figured out are indicated by the absence of the 120KHz burst. It means that the detection circuitry only has to look at the 200uS window following a zero crossing to clearly determine that there is no 120KHz burst.

    Yes, The receiver detects the zero crossing and begins its search for the presense or absense of the 120KHz burst during the 200uS window that follows.

    In the link that you provided earlier in the thread, the initial figure threw me at first until I realized that X10 protocol takes into account the existence of 3-phase AC and so it has to send the same message so that it is present at the zero-crossing of each of the three phases. That is why the first figure shows 120KHz burst that don't appear to be aligned with the zero crossing.

    hgmjr
     
  15. saleemsm

    Thread Starter Active Member

    May 15, 2006
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    thanks hgmjr

    That was exactly what i wanted... now i understand X10 clearly... but i am need some time to think on my decisions... will surely need further help from all of you...

    thanks once again.

    have a nice day!
     
  16. hgmjr

    Moderator

    Jan 28, 2005
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    We look forward to hearing your follow-up ideas once you have fully digested the comments and suggestions of all responders to your original posting.

    hgmjr
     
  17. saleemsm

    Thread Starter Active Member

    May 15, 2006
    36
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    hello everyone!

    a new cryptex 4 all of u;

    i am looking 4 steganography over the internet but not able to find any good reference.

    caN u ppl shed some light over this tech and also give me some ref;

    and one more thing i need to know what is cryogenics, and ref 4 that to...

    sry 4 disturbing so much.

    hope u don't mind.

    have a nice day!
     
  18. pebe

    AAC Fanatic!

    Oct 11, 2004
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    Hi Saleemsm,
    It would help (me, at least) if you didn't write in gobbledegook! The extra keystrokes would only take fractions of a second longer.
     
  19. saleemsm

    Thread Starter Active Member

    May 15, 2006
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    hi pebe!

    I m sry 4 tat; wil be short and straight. hv a nc day!
     
  20. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Greetings saleemsn,

    Here is a link to the Wikipedia page containing some information on the subject of steganography. You can also search the Wikipedia's website for cryogenics while you are there.

    http://en.wikipedia.org/wiki/Steganography

    Keep in mind that information contained in Wikipedia's database is supplied and edited by the general public and is therefore subject to the occasional error. Still it can serve as useful source of information to be pooled with other sources to build up a complete understanding of the specific subject you are investigating.

    To echo Pebe's comment, I would encourage you to use all of the keys on your keyboard when posting here. Since AAC serves the International community, there are many members of the forum for whom English is their second, third, or fourth language. Unfortunately, English is difficult enough to understand when one's grammar and spelling is flawless.

    Good Luck,
    hgmjr
     
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