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Fax detection

Discussion in 'Electronic Design' started by Patrick, Oct 25, 2007.

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  1. Patrick

    Patrick Guest


    I'm looking for a way of detecting if a fax is making my phone ring or
    if it is a voice call. I'd like to have only one phone number,
    therefore one unique ringtone. So far I thought about building a
    device that would answer any calls after 5 rings. After it answers I
    would like it to determine if this is a voice call or a fax calling.
    Maybe this is impossible, or maybe there is no precise way of doing
    this but I am hoping that all faxes send somekind of handshake within
    the first second after the call is answered (that way I could wait
    1sec for the handshake, and if I don't get any, route to answering

    Anyone could tell me if there is such a mechanism?
  2. PeterD

    PeterD Guest

    Troll... Try google!

    Peter's Troll-o-Meter

    Not Troll Troll
    0 1 2 3 4 5 6 7 8 9 10

    (Pegged the needle!)
  3. Jim Thompson

    Jim Thompson Guest


    There are boxes you can buy that sense the fax tones and switch to
    your fax, or ring the phones if it's voice.

    I had one years ago before there were PC's ;-)

    ...Jim Thompson
  4. Joerg

    Joerg Guest

    Multi-Function printers also do that nicely, such as the MFC-7820N here
    in the office. Connect its fax jack to the phone jack, plug the
    answering machine into the jack labeled "Answering Machine", done.
  5. Phil Hobbs

    Phil Hobbs Guest

    With you around, I imagine it's up around 9 or 10 all the time.


    Phil Hobbs
  6. mpm

    mpm Guest

    It's a logarithmic scale.
  7. mpm

    mpm Guest

    If your fax accepts distrinctive ring, that's another possibility.
    We just yanked our business fax line out.
    I think we were getting something on the order of 3 faxes a year (2 of
    those were junk mortgage offers).

    Everything's email now. (Except attorneys, of course.)
  8. Joerg

    Joerg Guest

    Until the Internet goes out for a day or some web master thinks he is
    smarter than all the others and blocks a whole domain to reduce spam.
    Happened numerous times. Boy was I grateful for that backup fax machine
    (and so were others here that used it). Internet will never reach the
    reliability of POTS, it's not as well organized and AFAICT never will be.
  9. Joerg wrote:

    I wish it could be a phone blackist similar to SPAMCOP, DSBL, ORDB or
    like. So the phone spamwhores could be rejected automatically.
    Unfortunately, the business phone numbers can't be on the non-call list.
    Also, non-call lists do not help against the so-called non-profit
    Probably true.

    Vladimir Vassilevsky
    DSP and Mixed Signal Design Consultant
  10. Ross Herbert

    Ross Herbert Guest

    As far as the PSTN is concerned a fax machine is no different from an
    ordinary telephone handset when originating a call.

    Only after the receiving end answers a call does the fax machine send
    its signature tone, and that is the only time it is possible to
    determine whether a call originates from a fax machine or not.

    Some fax machines (auto mode) work on the principle that when an
    incoming call remains unanswered (by a human) after X number of rings,
    the call should be answered by itself. If, after answering, the fax
    machine does not hear any tone from an originating fax, it assumes the
    call is from a telephone and it then activates its own incoming call
    sounder once more to try to attract the attention of a human to take a
    voice call. However, this procedure usually takes so long that by the
    time a human (if present) hears the second incoming call sounder the
    originating caller has hung up.
  11. Robert Baer

    Robert Baer Guest

    ** The Federal DNC list, for me, is almost useless.
    I get calls from marketeers ranging from unleaded gas futures, to
    FOREX futures - and many of them are illegally unregisterd.
    And the so-called securities regulatory agencies refuse to do anything.
    And no, i have never done business with any of these assholes, i have
    been on the Fed DNC list for over 2 years, and have an unlisted number.
  12. Joerg

    Joerg Guest

    Mine does it differently. It switches to the answering machine right
    away but cuts that off again when it detects a fax tone. The answering
    machine then thinks it was a hang-up. Since the fax tone (usually) comes
    much earlier than the beep of the answering machine the result is
    exactly what I want: A fax in the tray and no message indicated on the
  13. LVMarc

    LVMarc Guest

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  14. Wim Ton

    Wim Ton Guest

    I'm looking for a way of detecting if a fax is making my phone ring or

    Not really, AFAIR. According to the CCITT standard (T30??), the called party
    has to say first: "I am a fax". instead of the caller saying "I am a fax".
    At my office we had a fax that strickly followed CCITT and always had
    trouble with automatic fax switches.

  15. Jim Thompson

    Jim Thompson Guest

    All the internal fax modems that I know of begin sending the query
    tone just as soon as they complete the dialing, irrespective of
    whether the called end has yet answered.

    ...Jim Thompson
  16. Rich Grise

    Rich Grise Guest

    I heard about some guy who, when the telemarketer called, he'd say, "Oh,
    good. May I have the name and billing address of your company, your
    name, and your supervisor's name? I must inform you that our charge for
    the use of our private equipment in the conduct of your business is
    $100.00 per minute."

    He didn't say if he got any takers. ;-)

  17. mpm

    mpm Guest

    This is my experience as well.
    I would add that my "all-in-one" printer/fax also send tones
    immediately after dialing (outbound fax).

  18. krw

    krw Guest

    Even they've converted to email. I've been emailing signatures back
    and forth to patent attorneys for a couple of months. They send the
    forms, I print, sign, scan, and email back. I've been doing the same
    with my real estate agent. Everyone still wants the original
    signatures by snail-mail though.

    I was thinking about getting a fax, but since I have no phone line...
  19. krw

    krw Guest

    If it's on the DNC list it's not unlisted. ;-/

    I think I've only gotten one unsolicited call in three or four years.
    Cell phones have benefits, other than the obvious. Even politicians
    don't call them. :)
  20. Robert Baer

    Robert Baer Guest

    Not too bad, but some just hang up when asked for the required info.
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