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OEM Cellular Modems - Non-Internet - Models, Prices, Experiences ???

Discussion in 'Embedded' started by B1ackwater, Jan 7, 2008.

  1. B1ackwater

    B1ackwater Guest

    I'm looking for a relatively simple (and hopefully
    inexpensive) OEM-style cellular modem that can work
    in conjunction with a PIC-based remote data-acquisition

    Data transmission speed doesn't have to be very
    high at all, 2400 baud would be more than enough.
    The data only needs to be sent maybe twice a day,
    preferably by calling the cell-modem to wake up the
    PIC device and initiate transmission.

    I've looked into using 'smartphones', but the phone
    companies always insist on selling you an expensive
    internet-access subscription (that's where they
    really make their money). Non-'smart' phones require
    a Winders-based PC and drivers to serve as a modem.

    Yea, a PIC can be linked through and/or operated by
    one of those phones over USB or bluetooth, but the
    whole thing is *serious* overkill. As I intend to
    install twenty or thirty stations right off the bat,
    internet-access rates would just *destroy* the budget.
    I don't NEED an interactive web page at every site.

    I've seen a few such modems on the net, but they
    never list prices ... apparently they want to get
    you on the phone for the big sales speil. I'd be
    interested in hearing from anyone who's bought
    and used these things - price, performance and
    gotcha issues.

    Something like Global-Datas 'StarPoint' or OEM
    units are what I have in mind :


    Any info helpful.
    B1ackwater, Jan 7, 2008
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  2. You can consider the following approach: connect to a regular cellphone
    via the hands-free connector. Make calls and generate a modem signal
    into the voice path with PIC. This is kinda partisan solution, however
    you don't have to care about the internets, OEM modems and subscriptions.

    It is simple enough to get the bit rate of 600bps via the voice path; it
    is possible to obtain much higher speed with some sophistication.

    Vladimir Vassilevsky
    DSP and Mixed Signal Design Consultant
    Vladimir Vassilevsky, Jan 7, 2008
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  3. Look here:


    Where are you located? What mobile network standards are available?

    Mit freundlichen Grüßen

    Frank-Christian Krügel
    Frank-Christian Kruegel, Jan 7, 2008
  4. B1ackwater

    B1ackwater Guest

    I finally found some data about the MultiTech MTCBA-G-F2-NAM /
    MTCBA-G-F4-NAM cell modems. They can be had for under $200 US
    and employ GSM/GPRS technology compatible with our local carrier.
    All that's needed is the appropriate SIM-card.

    I'd looked into using a hands-free connector also. Hands-free
    can PLACE the call, but ANSWERING a call would be more of a
    pain - you really need the "Ring Detect" output from a 'real'
    modem or something similar to tell the PIC board that someone
    wants a download.

    Bluetooth could likely be pressed into service, as well as
    a USB connection, but the abovementioned unit is conveniently
    set up for RS-232 and that's a breeze to connect to any
    microcontroller nowdays. Also comes in a nice industrial-
    looking box with flashing lights, screw-on connector for
    high-gain antennas and stuff to impress the client :)

    I ordered an 'F2' to play with although it's soon to be
    discontinued, replaced by the 'F4'. I'm not sure what
    the big difference is. The F4s are only ten dollars more
    however so if I need 29 more units I won't go broke.

    As a lot of 'real' phones will cost you over $200 nowdays,
    the price of the MultiTech units ain't bad ... and they've
    got exactly the connectors you'd want. There's also a USB
    model ... I think my MikroPascal compiler can do those too.

    Anyhow, an 18x PIC with a serial EEPROM to hold the datasets
    and I'm in business. Easy to hang analog and digital sensors
    off of that, and I've ordered a s-EEPROM/RTC combo chip so
    I can timestamp the data too. The remaining obstacle was
    sending the data out ...
    B1ackwater, Jan 7, 2008
  5. B1ackwater

    B1ackwater Guest

    GSM/GPRS ... AT&T/Cingular.
    The AC-45 looks interesting ... I'll have to see what it

    I ordered a MultiTech MTCBA-G-F2-NAM (soon to be replaced
    by the 'F4') to experiment with. These units are under $200
    US, needing only a SIM-card from the local carrier. Convenient
    RS-232 as well. Draws 10 mA in standby mode however ... and my
    app is to be solar powered. The Siemens says 25 mA in "idle mode".

    Anyway, with units like these, it should be easy to interface
    any microcontroller. Prices seem to have dropped considerably
    since the last time I checked on these things. Anything from
    DTMS to SMS to TCP and several other data transmission options
    will be availible depending on how much you want to spend on
    the monthly service.

    I'm encouraged. I thought I'd have to bluetooth to a
    Winders 'smartphone' - lots of places to go astray
    there - but it looks as if a PIC plus s-EEPROM/RTC
    chip, the cell modem and a serial cable is all I need.
    The cells really seem superior to the olde-tyme method
    of dedicated high-powered radio links. Effectively
    unlimited range, no special licences and, due to
    volume & competition, CHEAP.
    B1ackwater, Jan 7, 2008
  6. B1ackwater

    John Temples Guest

    If you intend to use this on AT&T, be advised that they probably won't
    provision your account with the necessary feature to place modem calls
    (CSD) unless you pay an additional monthly fee.
    John Temples, Jan 8, 2008
  7. B1ackwater

    B1ackwater Guest

    As expected, alas. Of course they ARE in it for
    the money after all ...

    I'll just have to find out if adding the CSD option
    is cheaper than the "full internet" package they
    sell for their smartphones.

    Well ....... there's always the OTHER option for
    people who need to move data, but not MUCH data ...
    just use DTMF tones. I've got a nice DTMF decoder
    I could use at the base station - and my PIC can
    produce the necessary tones at the remote end.

    16 baud ... what the hey - it's cheap ! :)
    B1ackwater, Jan 8, 2008
  8. B1ackwater

    jetmarc Guest

    Hi B1ackwater,

    I looked for a similar modem, and eventually settled for a GSM-based
    module: TER-GX110 (see http://www.roundsolutions.com/uk_products.htm).

    This device has an RS232 port, which is easily interfaced to a
    microcontroller. It supports both GPRS (for "internet" connection),
    and SMS (text messages with up to 160 chars).

    If your data set is small enough for transmission via SMS, you can
    omit the internet service plans. Just use a prepaid SIM card without
    monthly fees ("pay as you go") and send an SMS upon receiving incoming
    calls as trigger.

    jetmarc, Jan 9, 2008
  9. Just one minor point in case someone's thinking of sending binary data
    via SMS and that is that it's actually 160 _7-bit_ characters, or only
    140 _8-bit_ characters per SMS message.

    Simon Clubley, Jan 9, 2008
  10. B1ackwater

    BigJohn Guest


    Did you manage to get a price per unit on the AC45?
    BigJohn, Mar 5, 2008
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