On Mon, Nov 29, 2010 at 3:54 PM, Bill Unruh <unruh@physics.ubc.ca> wrote:
On Mon, 29 Nov 2010, Sathishkumar Duraisamy wrote:

Dear all,

I am new to the list and to the alsa library. In my application, I have to
collect data from outside world in the form of voltage, and then plot. I
have done the plotting and GUI parts of the application. Now I have to use
an ADC to collect the data.

My question: Is it possible to use the ADC of audio input and alsa lib to
get the sample from the outside world. Have anyone tried like this. If it so
can you please guide me how I can get started?

Sure. Just use the source code for arecord as a sample. But there are some limitations. Almost all audio cards do not go down to DC
intpu level but have a low frequency cutoff of about 10Hz. Thus if your
project requires low frequency levels, you are out of luck. Also most sound cards have a pretty hard cutoff about about 20KHz since this
is the highest sound humans can hear and corresponds to the upper
frequencymeasurable by a 44.1 frequncy card. If you allow in higher
frequencies you get distortion int hat the high frequencies are floded over
into the low frequency band. The tird problem is normaisation-- ie you really
have to put in a test signal of a known voltage to calibrate your card's
amplitude -voltage characteristic.


Thanks Unruh. superb explanation. Now I started to analyse things with specification. I shall update regarding  this and share my experience. 


Now I have been looking at this
http://www.alsa-project.org/main/index.php/Tutorials_and_Presentations.

With thanks
Sathishkumar


--
William G. Unruh   |  Canadian Institute for|     Tel: +1(604)822-3273
Physics&Astronomy  |     Advanced Research  |     Fax: +1(604)822-5324
UBC, Vancouver,BC  |   Program in Cosmology |     unruh@physics.ubc.ca
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