---
+ Post New Thread
Results 1 to 4 of 4
  1. #1
    Newbie level 2
    Points: 462, Level: 4

    Join Date
    May 2010
    Posts
    2
    Helped
    0 / 0
    Points
    462
    Level
    4

    Wishing to read rf signal broadcast from home water meter

    Hello. I found this forum on Google. I hope someone can give me some tips on where to start.

    I am not an engineer or even a hobbiest in this area. Just a guy wanting to do a specific thing.

    My home has an AMR (automatic meter reading) water meter. It broadcasts its serial number, meter reading, and some other data via its RF transmitter so that the utility can drive by and read it monthly without having to get out of the vehicle. In the interest of monitoring and lowering my water usage (we live in a semi-desert area), I would like to make use of that data in (more-or-less) real time. For example, to monitor for leaks without discovering it on my bill 4-8 months later.

    This is the water meter: http://neptunetg.com/userfiles/file/products/E-Coder)R900i/Product%20Sheet_EN.pdf

    It says it uses 910 to 920 Mhz spread spectrum.

    I found AMR modules from china that specify this:
    Carrier frequency: 433mhz, options of 868/915mhz;
    I don't really know how spread spectrum works... so does the fact the receiver operates at 915mhz, and the transmitter has a range with 915 exactly in the middle mean these should be compatible?

    Or am I on the wrong track. Is what I want to do possible? If so, how might I go about it? Thanks.

    - Steven

    •   Alt20th May 2010, 19:34

      advertising

        
       

  2. #2
    FvM
    FvM is offline
    Super Moderator
    Points: 171,406, Level: 98
    Awards:
    1st Helpful Member

    Join Date
    Jan 2008
    Location
    Bochum, Germany
    Posts
    27,774
    Helped
    8760 / 8760
    Points
    171,406
    Level
    98

    Re: Wishing to read rf signal broadcast from home water mete

    Spread spectrum involves a special coding of data using pseudo random codes. It most likely can't be received by a standard fixed frequency
    915 MHz band receiver. Apart from decoding spread spectrum modulation, you also have to understand the representation of data in the
    protocol implemented by the manufacturer. A communication expert would be most likely able to reverse engineer the protocol, if actually
    motivated. But I guess, you don't know how.

    I'm not aware of a protocol specification undisclosed by Neptune. But you surely can buy receiver equipment from them, unless they have
    granted exclusive data access or individual protocol features to utility companies.



    •   Alt20th May 2010, 21:48

      advertising

        
       

  3. #3
    Newbie level 2
    Points: 462, Level: 4

    Join Date
    May 2010
    Posts
    2
    Helped
    0 / 0
    Points
    462
    Level
    4

    Wishing to read rf signal broadcast from home water meter

    Thanks for the reply.

    I've learned that the signal isn't true spread spectrum. The unit broadcasts identical data across 8 frequencies (why?) between 910 and 920.

    I wouldn't think they're doing anything for security reasons... it is very basic, non sensitive data. I think whatever they're doing, its going to be for costs savings and (more important) reliability. It appears, from some of the searching I've done, that the readers these companies sell can read other brand meters and vice versa.

    It seems as recently as December 2009 there was an OpenAMR.org project going, but it is currently down.


    The readers from Neptune (and similar) cost like $5k :) again, I don't think that's to keep people like me out... I think its just economics and the fact that they don't have a large market for readers.

    Anyway, I'll keep searching.


    Oh, and I did just stumble upon something that discourages me a little. I realize now that the unit broadcasts every 14 seconds, but only updates what it broadcasts every hour. So the resolution of data isn't what I had hoped. I wanted to be able to have the software recognize, for example, when a toilet flushed. But with hourly updates that's not possible. Still, monitoring my usage hourly is still better than quarterly!

    Did you know that if my irrigation blows a line (happened twice in the past 5 years before we got metered) it can pump out $142 per day worth of water!?!

    A leaky toilet can cost some $200 a month and you might never know it until you're a grand in the hole.

    That's (part of) my motivation.



    •   Alt20th May 2010, 22:07

      advertising

        
       

  4. #4
    FvM
    FvM is offline
    Super Moderator
    Points: 171,406, Level: 98
    Awards:
    1st Helpful Member

    Join Date
    Jan 2008
    Location
    Bochum, Germany
    Posts
    27,774
    Helped
    8760 / 8760
    Points
    171,406
    Level
    98

    Re: Wishing to read rf signal broadcast from home water mete

    The main reason for using spread spectrum (or whatever it actually is) can be found in FCC 15.245 to 15.249, that allow considerably
    higher output power for frequency hopping and similar modulation methods. Using only 8 frequencies would however not comply to this
    rules. And it has of course to do with avoiding possible interferences.

    The hourly logging timescale is suggested by storage economy and sufficient for most applications, I think. In any case, I wonder, if it
    wouldn't be easier to install a second meter with electronical readout. Of course, every manufacturer would love to sell a 5k$ data acquisition
    system. He even more loves customers, that can be convinced it would necessary to pay this amount for basic instrumentation. Otherwise,
    he'll quickly discover, that an acceptable solution can be made for a few 100 $ as well.



+ Post New Thread
Please login

LinkBacks (?)

  1. 1st November 2010, 13:15