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DTMF over RTC

Discussion in 'Electronic Design' started by Fred Bartoli, Feb 6, 2006.

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  1. Fred Bartoli

    Fred Bartoli Guest

    That's not in my line but I've inherited an old project from where I
    previously worked.

    The system uses a PC+MODEM to manage some remote instrument.
    The modem is there only to get the phone line interface and dialog with the
    intrument through DTMF exchange.

    There were several thousands instruments installed and about 100 PC servers.
    Now the chosen modem doesn't exist anymore and we need to find a
    replacement.

    You'd think, any modem will do.
    Maybe. Anyway I remember we had problems with DTMF receiving (don't remember
    precisely which) and propagation time through all the windows layers.

    Any known good reference for a PCI modem?
     
  2. Joseph2k

    Joseph2k Guest

    Well, now you are in the specialty weird modem business. It may be possible
    to abuse current compliant modems to do what you want (no guaranties, it
    may well not be possible). Study the properties of the command set
    carefully.
     
  3. Joseph2k

    Joseph2k Guest

    Bloody mess. Come to think about it there were only a few DTMF
    gerenator/receiver chips ever made. I do not know of any still in
    production. However you may be able to buy a DSP which can do the job and
    any patented code for the process should be expired by now. It wouldn't
    take much of a DSP by todays standards either.
     
  4. David Harmon

    David Harmon Guest

    On Tue, 07 Feb 2006 06:09:54 GMT in sci.electronics.design, Joseph2k
    If I recall correctly, the author of the article in the current
    Circuit Cellar is doing it with a PIC.
     
  5. OBones

    OBones Guest

    As far as DTMF receiver are concerned, the 8870 is still made, I just
    bought a few recently.
     
  6. Nel

    Nel Guest

    hi fred,
    May be a custom design could solve your problem which can accept DTMF
    tones through telephone link and will send to the pc using some
    interface. If you can elaborate in some detail then may be we can help
    you !
     
  7. Fred Bartoli

    Fred Bartoli Guest

    "Fred Bartoli"
    Sure we could custom design something. Dead easy, but we won't have as many
    servers and they are connected to the phone network, so they have to have
    homologation, and this will be sold in many countries. Way too much hassle,
    cost and time.

    One way is to buy 50 modems at random and try. We're sure to find one
    suitable in the pile.
    Just thought somebody may already know for sure a suitable one.
     
  8. Guest

    You may have better luck with modems (possibly PCI, more likely little
    brick-like serial modules) sold for embedded applications - they cost a
    bit more than those found in flavor of the week store PCs, but are a
    bit more stable in their specifications and functionality.
     
  9. Fred Bartoli

    Fred Bartoli Guest

    Hmmm, good idea. Any brand (or better reference) on top of your head?
     

  10. Have you tried ebay? If they are discontinued, people tend to dump
    them into the surplus channels.

    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  11. Rich Grise

    Rich Grise Guest

    All of the modems I've seen only use DTMF for dialing. Are all of these
    things supposed to be able to talk to each other, or is there one "master"
    and 99 "slaves?"

    If you're going computer-to-computer, then you don't even need modems -
    just serial interfaces. There might be something called a "short-haul
    modem", but you'd have to look that up - I saw one about 20 years ago, and
    don't know if they make them any more either.

    What are you trying to accomplish? Do you have to replace a bunch of
    adapters or modems? Why not just make it all ethernet?

    Thanks,
    Rich
     
  12. Fred Bartoli

    Fred Bartoli Guest

    No, 100 masters, 10000s slaves (custom instruments part of which is already
    installed), dispersed all over the world.
    My guess is ethernet or serial interfaces won't do over 5000 km.

    I guess I've now found the *key* word: answering machine. I've now
    identified 2 modems that (should) provide the functionality if it works.
    None of these directly available in France.

    Now I have to hope they'll work. At $10-15 some modems seem, not
    surprisingly, to not work as advertised.
     
  13. OBones

    OBones Guest

    An OLITEC PCI card, can do answering machine, they do it with the
    provided software.
    And if configured correctly, it can detect ringtones and record the
    received sound, but not send at the same time, it's only half duplex.
    There are whole bunch of APIs under Win32 for this, it's a bit complex,
    but it works.
     
  14. Zak

    Zak Guest

    Some 'winmodems' show up as an audio device in Windows - they can
    actually be another channel to the sound card on cheapo modems.

    DTMF decoding in software shouldn't be too hard.


    Thomas
     
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