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A/D conversion by PC sound card?

Discussion in 'Electronic Basics' started by boki, Oct 14, 2004.

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  1. boki

    boki Guest

    Dear All,
    I want to implement a simple A/D conversion by PC sound card
    input channel(Line in / MIC in), therefore I can employ it as a high
    resolution A/D processor :D ?

    What is the limit/problem in hardware?

    Thank you very much for your comments.

    Best regards,
    Boki.
     
  2. Bob Masta

    Bob Masta Guest

    There are several limits. The most important one
    is that sound cards do not go down to DC; they
    are AC coupled with cutoffs at a few Hz. So if
    you want to make general measurements like
    DC voltage, temperature, pressure, or many
    other real-world quantities you need to provide
    external modulators to convert them to AC,
    and some sort of software demodulation to
    recover the original values. In theory you
    might be able to modify the card to go to DC,
    but the problem is that these cards are usually
    operated from a single supply voltage and if
    you remove the input capacitor then your
    input signal must be biased up to half the
    card's supply voltage somehow... not trivial,
    if you expect to maintain any sort of DC accuracy.

    Another problem is timing. Under Windoze, you
    have to be very careful when you are trying to
    correlate measurements with timing events in
    your program. Windows and the sound card
    don't start conversions exactly when you give
    a command... there is a variable and unknown
    delay that can't simply be calibrated away.
    Same thing for outputs. So if you need to
    know what your data looks like at the time of
    some event, you should record that event
    on the second channel of the stereo card...
    even if you created the event yourself in
    software and sent it to the D/A.

    Finally, there is the fact that most sound cards
    have only 2 A/D channels, and those that
    have more must use non-standard drivers
    that you would have a hard time finding how to
    program for.

    If you will discuss exactly what you are trying
    to observe, perhaps we can come up with a
    good recommendation.

    Best regards,



    i
    Bob Masta
    dqatechATdaqartaDOTcom

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    www.daqarta.com
     
  3. John

    John Guest

    You will probably be better served by a device made for the purpose.

    http://www.dataq.com/194.htm

    This a 4 channel, 10 bits/channel D/A converter with software for
    $25US
     
  4. boki

    boki Guest

    Dear Bob,
    I can say nothing. :D thank you so much.
    if any new, I will post it.

    Best regards,
    Boki.
     
  5. boki

    boki Guest

    : )

    Thank you very much for information.

    Best regards,
    Boki.
     
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