Newsgroups: sci.electronics.misc
Subject: Re: using voice input of pc
References: <[email protected]>
"kkrish"  writes:

> Hi all,
>         Is it possible to  use the mic input of a pc to capture an
> analog signal and convert it into digital signal using the voide
> processing circuit of the PC?

The answer is yes if your signal you have and/ot part you are 
interrested in is within the sound card supported frequency 
range. generally frequencies from few hundred Hz to few kHz
be recorded more or less at useable quality on mic input 
but the frequency response might not be flat
(outside this the signals the signal ca attenuate considerably). 

When usign line input you generally get around 20 Hz to 20 kHz 
with pretty flat frequency response.  

> I browsed the net and asked the question
> in arch.embedded but I did not get any specific answer.Is it not
> possible to convert analog signals of frequency other than the voice
> frequency into digital form?

Soundcards are not detected to handle frequencies outside normal 
audio frequencies (20 Hz to 20 kHz). Those higher and lower frequencies  
are intentionally filtered out on soundcard circuitry before 
actual analogue to digital conversion. 

With some hardware modifications at least some sound cards 
can be adapted to accept frequencies down to DC: 
 
Sound card based multimeter 
http://www.qsl.net/om3cph/sb/dcwithsb.htm
This web page describes how to modify Sound Blaster AWE-64 and SB16 to
accept DC signals into their A/D-converter. With suitable software
this allows a sound card to be used as a simple multimeter or
oscilloscope that can measure also DC signals. There ideas described
here sould be also adaptable to other sound card models as well.

-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/