A/D conversion by PC sound card?

>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.

> On 13 Oct 2004 23:26:57 -0700, bokiteam@ms21.hinet.net (boki) wrote:
>
> >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.
>
> 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

>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.

> On 13 Oct 2004 23:26:57 -0700, bokiteam@ms21.hinet.net (boki) wrote:
>
> >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.
>
> 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