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really old magazine article on diy modem

Discussion in 'Electronic Design' started by Brad, Nov 14, 2006.

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  1. Brad

    Brad Guest

    Hi all,
    I'm trying to find an article I read about 30 years ago or so. It was
    a diy project for a low speed modem. It was in Byte, Kilobaud or
    Popular Electronics. Do any of you happen to know where this article
    might have been?

    If I recall, the modem was like 300 baud or maybe only 110. I'm doing
    a little project that could use a dirt cheap modem, and signalling
    speed is not an issue. Slow is fine, cheap is better :)

    Or, if anyone has a more up to date approach I'd be glad to look at
    that too. I've come across a few half-way described implementations of
    modems using PICs, but I don't have the time to figure out the missing

    Regards, Brad
  2. IIRC it was Popular Electronics and it was an acoustic coupler.

    Look on eBay for an old Radio Shack modem.
  3. Tom Bruhns

    Tom Bruhns Guest

    Google "modem IC" and you'll get quite a few hits. Search for "Bell
    103 modem IC" and you'll get things more targeting what you are asking
    for. There are other ways to phrase the search that will become
    obvious from the hits you get on those. I suppose some of the slow
    modem ICs are still available. MM74HC943 seems to not be made by
    National now, but perhaps someone has stock.

  4. Ross Herbert

    Ross Herbert Guest

    If cheap is what you want there will be literally thousands of unused
    dial-up modems lying around which can be had for a few dollars if not
    for free. These are tried and proven so you won't have to spend time
    developing and proving a design either... why re-invent the wheel?
  5. Eeyore

    Eeyore Guest

    Heck, even I've given some away and I'm the ultimate hoarder. I'm sure I must
    have a rather nice 33.6k one somewhere still around.

  6. Jeff Findley

    Jeff Findley Guest

    I've found old RS-232 modems (often 9600 baud and higher) at places like
    Goodwill, garage sales, and etc. for $5 or so. You might even try eBay.
    You can get just about anything on eBay.

  7. GregS

    GregS Guest

    36 years ago I was troubleshooting modems made from 7400 series
    chips. I didn't really know how the whole thing worked but I could fix
    bad logic. That was at DEC.

  8. IIRC I have 5 of the RadShack 300 baud models NIB.
  9. Brad

    Brad Guest

    I appreciate the advice and offers of cheap modems. I am not
    interested in obtaining a modem. I am interested in information
    presented in that specific article.

    So, if anyone knows where the article was, I'm still looking......
  10. Early '80's IIRC.
  11. I have a memory of an article like this, when the AM7910 was fairly new.
    Possibly in EDN?.

    Best Wishes
  12. You're paying too much. I paid five dollars for my used 2400 baud external
    modem back in 1995.

    I paid ten dollars for an external 33.6K modem some years back. And I
    got my 56K external modem for five dollars last year.

  13. Your vague reference means nothing. DO you really think there was
    only one modem described in all those magazines? Do you really think
    it matters that much whether or not you get the very same article if
    all you need is a modem? Do you really think that you can build a 30
    year old design without having to dig to get the ICs that it used?

    IN the very first issues of Byte magazine, in the fall of 1975, there
    was a series of excerpts from Don Lancaster's "TV Typewriter Cookbook".
    I can't recall whether those covered building modems, but the book does,
    even if they aren't construction projects.

    There is nothing special about a modem, and so some of those early schemes
    for saving programs to cassette tape were basically modems. There was
    an article, I think it was in "73", that used the Digital Group cassette
    interface as a teletype modulator/demodulator for use on radio, and it
    was a modem minus the interface circuitry.

    Lee Felsenstein described his "Pennywhistle" modem in early 1976 in Popular

    Steve Ciarcia eventually described a modem, using PLLs, in his "Circuit
    Cellar" column in Byte. ANd then some years later, revisited the topic
    once or twice as ICs became available that provided the whole modem
    function in one package.

    It goes on and on.


  14. Find a large library with old magazines on microfilm, and start
    looking. There were dozens of those articles, and most used now
    obsolete ICs. There is a company in Ann Arbor, Michigan that made those
    microfilms. I think it was connected to the university. They used to
    advertise in '70s and '80s magazines.

    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
  15. Mark Zenier

    Mark Zenier Guest

    "Build the Pennywhistle - a hobbyists modem"
    Lee Felsenstein*
    Popular Electronics, March 1976

    *(the desiger of the SOL computer).

    As I remember it, it didn't have a great reputation.

    In ham radio circles, Buzzwords would be "RTTY" and "Terminal Unit".
    Try looking up the XR-2211 FSK receiver chip.

    Mark Zenier
    Googleproofaddress(account:mzenier provider:eskimo domain:com)
  16. Ross Herbert

    Ross Herbert Guest

    It sounded awfully like you wanted to obtain or build one;

    "I'm doing a little project that could use a dirt cheap modem, "
  17. TCM3105 100% integrated 300 Baud modem, used for amateur packet radio.
    Needs a 4.43 MHz xtal :)

    This is a very good chip though, even with bad signals, build in filtering,
    carrier detect, hardly any external components.
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