A/D conversion by PC sound card?

B

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

Best regards,
Boki.

NoSpam@daqarta.com (Bob Masta) wrote in message news:<416e6f30.1922132@news.itd.umich.edu>...
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
Click to expand...
 
John <look@sig.net> wrote in message news:<9b2um0hlmmomrhfms3b5mcd45mh60erbq9@4ax.com>...
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
Click to expand...
: )

Thank you very much for information.

Best regards,
Boki.
 
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