David Schleef writes:
> Hmmm... bad idea. Sound cards have a few properties that make them
> good sound cards, but bad data acquisition cards.
> - input is generally heavily filtered, with unknown filters, but
> generally cut out anything below 20 Hz, around 50 or 60 Hz (depending
> on your local line frequency), and above 10 kHz. The <20 Hz
> filter is nasty, since it makes DC measurements impossible.
Reminds me. I do have a ComputerBoards PCI-DAS1602-16 board. Currently
I use it as a plain single channel D/A converter :-( to generate a
voltage ramp.)
The voltage of this ramp (or simply a constant output) shows very
prominent 50 Hz -- though not all time ! Some days it is not visible
on a 1 mV scale (the lowest setting of my bread-and-butter scope) and
as such is good enough (for me). Most days I do have problems with my
application due to the 50 Hz though (because is is big, like 10 mV
p-t-p, or such). The shape isn�t exactly sinus-like, it�s almost a
(bad) rectangular wave.
(... I am pretty sure this is not a software problem, sorry for the
off-topic posting :-)
Are others out here seeing similar problems with D/A conversion ? What
are you doing to avoid/nihilitate/minimize such problems ?
I assume I simply see the line-frequency somewhat modulated by the
card. The converters itself are hosted in a small Faraday-box (at
least I hope it is one) on the card. Still, are such noises induced by
e-smog inside the PC, through the PCI bus, or both ?
I appreciate any hints,
Jochen
--
Heinrich-Heine-Universit�t, Institut f�r Physikalische Chemie I
Universit�tsstr. 1, Geb. 26.43 Raum 02.29
40225 D�sseldorf, Germany phone ++49-211-8113681
http://www.Jochen-Kuepper.de fax ++49-211-8115195
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