Off late I did lots of research on this for my IVRS and here is the
abstract.
1. Internal modem and sound cards have a dsp (digital signal processor)
2. The only difference is that internal modem has telephone line interface
also which combines (or splits up) mic/spk signal of dsp in to the telephone
line.
3. On the net there are some references to using sound card for modem, but I
feel it is very old.
4. Prices of internal modem( soft one ) have dropped to Rs.1100 with one
month satyam unlimited (from vintron) thrown in.
5. The vintron internal modem uses cirrus logic chip set and has driver ( In
alpha) for linux.
If you still want to use your sound card as modem, go ahead. Built the
telephone line interface, and write a driver, but that would amount to
reinventing the wheel.
BTW me too is Electronic Engineer.
Best Regards,
M.S.Deshmukh,
Director.
Beta Computronics Pvt. Ltd.
Web Site - http://betacomp.com
-----Original Message-----
From: sreangsu acharyya <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED]
<[EMAIL PROTECTED]>
Date: Monday, August 14, 2000 12:33 PM
Subject: [LIH] newbie: sound card as a modem (LONG)
>
>hi people,
>
>DISCLAIMER:
> i am not an electronics engineer, so please dont flame me if the
>following does not make sense.
>
> Thinking of ways to surf net for free, i thought of having a
>call-back system at my office. ( they will probably fire me if I actually
>do it...but no harm romanticising.)The 1st hurdle, is the office machine
>do not have a modem.
>
> I reasoned that, tone dialing is done by feeding "tones" into the
>receiver. Moreover these are certainly in our audible range 16-20k Hz,
>thus reproducible by the sound card.
>
> Thus given proper driver support wouldnt it be possible to use the line
>out of the sound card to dial some number. Upto this it seems ok, but
>what if i use the sound card as a modem. I sure can "hear" data packets on
>a connected line...but are all of them within our audible range or more
>precisely reproducible by the sound card.
>
> There are many issues however, getting the frequency right is ok, but
>the voltage output of the soundcard should be comparable to the one used
>on phone lines. About these values i have no idea.Moreover the speed would
>also be quite low if a sound card is used.
>
> The reasoning seems pretty elementary, and i am sure some one has
>thought about it. I searched linmodem.org and google.com/linux but couldnt
>get anything substantial.
> Please respond if you have any ideas.
> sreangsu
>
>
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