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Sending data through water with acoustics — Parallax Forums

Sending data through water with acoustics

ArchiverArchiver Posts: 46,084
edited 2001-09-28 01:40 in General Discussion
Hi,

Rather than deal with all the problems associated with running a cable to
the surface from an instrument at 100m seawater depth, I'm interested in
sending some data using acoustics. Baud rate could be around 300 as I am
only sending short strings of data every ten minutes or so.

Can anyone suggest methods or possible ways I could attempt this, or if it
is feasible? What frequency or transducer is best?

Cheers,
Bill

Comments

  • ArchiverArchiver Posts: 46,084
    edited 2001-09-27 06:28
    There are a couple manufacturers of underwater communications gear.
    They all use radio waves modulated to a certain frequency. I know
    Uwatec is one, but there are a couple others. That might be one way to
    go.

    Nathan

    Original Message
    From: Bill Sherwood [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=n4wEtN2EvP38m4103yTTNkpoylMwTsWSt_tPi2ieXqkyYeVStvTt30g2RWjfhklCa6t05RqC01erp6CHweFwTFo]bill.sherwood@p...[/url
    Sent: Wednesday, September 26, 2001 9:27 PM
    To: basicstamps@yahoogroups.com
    Subject: [noparse][[/noparse]basicstamps] Sending data through water with acoustics


    Hi,

    Rather than deal with all the problems associated with running a cable
    to
    the surface from an instrument at 100m seawater depth, I'm interested in

    sending some data using acoustics. Baud rate could be around 300 as I
    am
    only sending short strings of data every ten minutes or so.

    Can anyone suggest methods or possible ways I could attempt this, or if
    it
    is feasible? What frequency or transducer is best?

    Cheers,
    Bill


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  • ArchiverArchiver Posts: 46,084
    edited 2001-09-27 18:05
    Hi Bill,

    Kynar piezofilms have a good acoustic match to water:
    http://www.msiusa.com/piezo/index.htm
    I hesitate to use loud acoustics for that purpose, due to their
    possible effect on fish and marine mammals. Greenpeace has been
    actively protesting the Navy project that generates underwater sound
    at >140dbm. I really don't know what sound levels you would need in
    order to transmit only 100m. Probably not much if it could be
    focussed up.

    I saw an article once that used "rf" at less than 100 hz for
    communication in seawater, with very widely spaced antenna nodes.
    Low EM frequencies penetrate seawater better than high frequencies.
    The Navy uses an ELF antenna in the U.P. of Michigan (coupled to
    magnetic geological formations there) to communicate to submarines at
    about 70 hz and low information rates.

    -- regards,
    Tracy Allen
    electronically monitored ecosystems
    mailto:tracy@e...
    http://www.emesystems.com



    >Hi,
    >
    >Rather than deal with all the problems associated with running a cable to
    >the surface from an instrument at 100m seawater depth, I'm interested in
    >sending some data using acoustics. Baud rate could be around 300 as I am
    >only sending short strings of data every ten minutes or so.
    >
    >Can anyone suggest methods or possible ways I could attempt this, or if it
    >is feasible? What frequency or transducer is best?
    >
    >Cheers,
    >Bill
    >
    >
    >To UNSUBSCRIBE, just send mail to:
    > basicstamps-unsubscribe@yahoogroups.com
    >from the same email address that you subscribed. Text in the
    >Subject and Body of the message will be ignored.
    >
    >
    >Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
  • ArchiverArchiver Posts: 46,084
    edited 2001-09-27 19:13
    I have been researching a similar application, and I'm at a loss as to why
    there's not much info available on underwater communications.
    Scores of SCUBA equipment manufacturers make units that read a pressure
    transducer on an air tank and transmit through the water to a device on the
    diver's wrist or console for calculation and display. I am wanting to expand
    on this concept, and I am finding tight lips on the subject....
    There must be someone in here who knows this field!....
    Well???

    Chris

    >
    Original Message
    > From: Bill Sherwood [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=ldYJ7NWKwhFhKwoDCh3lf96tY30ml9z6rploBe5hrFPA_NR87aup2lUlMubnNj_xZ2urNRcR28U9D8QhOKzKMDUIVQ]bill.sherwood@p...[/url
    > Sent: Thursday, September 27, 2001 12:27 AM
    > To: basicstamps@yahoogroups.com
    > Subject: [noparse][[/noparse]basicstamps] Sending data through water with acoustics
    >
    >
    > Hi,
    >
    > Rather than deal with all the problems associated with
    > running a cable to
    > the surface from an instrument at 100m seawater depth, I'm
    > interested in
    > sending some data using acoustics. Baud rate could be around
    > 300 as I am
    > only sending short strings of data every ten minutes or so.
    >
    > Can anyone suggest methods or possible ways I could attempt
    > this, or if it
    > is feasible? What frequency or transducer is best?
    >
    > Cheers,
    > Bill
    >
    >
  • ArchiverArchiver Posts: 46,084
    edited 2001-09-27 20:08
    At 09:26 PM 9/26/2001 , you wrote:
    >Hi,
    >
    >Rather than deal with all the problems associated with running a cable to
    >the surface from an instrument at 100m seawater depth, I'm interested in
    >sending some data using acoustics. Baud rate could be around 300 as I am
    >only sending short strings of data every ten minutes or so.
    >
    >Can anyone suggest methods or possible ways I could attempt this, or if it
    >is feasible? What frequency or transducer is best?
    >
    >Cheers,
    >Bill

    Bill,
    An excellent idea! I don't believe there is anything special about crafting
    your
    own transducer. Maybe a waterproof piezo transducer or mylar cone speaker
    would work. I believe acoustic waves move through water at about 9600 fps.
    You'll have to do your homework on frequency, that is, you may need to send a
    tone burst or serial "clicks" . A stamp based instrument at the bottom could
    send a series of different frequencies or clicks from its transducer to a
    surface
    based transducer. Radio shack sells a flat plate piezoelectric microphone
    that might work for that. As amplitude is measured at the surface you should
    be able to determine the best zone for both transmission and reception. I'd be
    interested in hearing more about this project!
    Greg Hensley
    Lawrence Livermore National Laboratory
    Defense Sciences Engineering Division
    7000 East Avenue Mail Stop L-369
    Livermore, CA 94550
    Phone: (925) 423-4850
    Fax: (925) 422-2118
    Email: hensley1@l...
  • ArchiverArchiver Posts: 46,084
    edited 2001-09-28 01:40
    Quoting Greg Hensley <hensley1@l...>:

    > At 09:26 PM 9/26/2001 , you wrote:
    > >Hi,
    > >
    > >Rather than deal with all the problems associated
    with running a cable to
    > >the surface from an instrument at 100m seawater
    depth, I'm interested in
    > >sending some data using acoustics. Baud rate could
    be around 300 as I am
    > >only sending short strings of data every ten minutes
    or so.
    > >
    > >Can anyone suggest methods or possible ways I could
    attempt this, or if it
    > >is feasible? What frequency or transducer is best?
    > >
    > >Cheers,
    > >Bill
    >

    I have seen several designs on the web for underwater
    acoustic modems.

    Bob
    nienhuis@w...
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