From: Joerg Hansmann (info_at_jhansmann.de)
Date: 2001-05-19 00:39:53
Hi,
----- Original Message -----
From: <jiva_at_humboldt1.com>
To: <buildcheapeeg_at_yahoogroups.com>
Sent: Friday, May 18, 2001 8:02 PM
Subject: [buildcheapeeg] Re: Sound Card-Phase II
...
> I'm still not following Joerg's explanation all that well.
> (my lack of tech skills, not his lack of explanation)
>
> Why he opted to put two VCOs on one channel further
> confuses me.
...
One reason is to eliminate a second optocoupler for the second
channel and another reason is to reduce the amount of data
that is sampled into the PC - and has to be processed.
On the other hand frequency demodulation could be made
very simple if only one frequency per physical channel were used.
The sinewave could be transformed into a rectangle wave
with 2 thesholds (for hysteresis) and then the number of samples
between two low to high transitions are counted. The reciproce
of the count gives the frequency. Subtract the center frequency
and then multiply with dV/df of the modulator VCO.
Because this demodulation is very simple, a very high soundcard
sample rate (BTW. what is the maximum sample rate available on
normal sound cards ?) could be used to increase the resolution
(number of bits).
Regards,
Joerg
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