Re: soundcard as oscilloscope
- From: "Abstract Dissonance" <Abstract.Dissonance.hotmail.com>
- Date: Thu, 26 Jan 2006 21:10:25 -0600
"Joerg" <notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx> wrote in message
news:04fCf.14546$_S7.13462@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> Could you give us your real name? First name would be nice.
>
>
>> I can control the amplitude of the wave form pretty easy by controlling
>> either a variable resistor or the variac... the problem is that that the
>> wave form looks like crap and I can't rectify it in any way(I put a
>> rectifier as the first component).
>>
>> Heres a shot of the oscilloscope:
>>
>> http://www.geocities.com/abstract_dissonance/osc.JPG
>>
>
> Doesn't look too bad except for some clipping and a wee distortion.
heh, looks like crap to me. I'd expect the mains to be more like a sinusoid
than a triangle?
>>
>> I've used several resistor ratios from 10M's down to 50k but nothing
>> seems to work. I'm not sure if it has something to do with the sound
>> card(it should have no problem sampling 60hz mcuh better than it is?) or
>> if its just the wave form is crap cause of the variac or what ;/
>>
>> Anyone have any ideas?
>>
>
> AFAIK the impedance of some sound cards is pretty low, in the tens of kohm
> range or so. Also, there may be a bias voltage for an electret microphone
> on its input. Best would be to post a schematic of what you have wired up
> so far.
>
> Regards, Joerg
>From what I could gather the input impedence is 47kOhms with 2Vpp max and I
have no idea bout the current.
As I said, I'm simply using a voltage divider(I've did it more complex at
first but didn't work well so I just used two resistors in series and took
the voltage off the smaller resistor). I tried for many combinations and
such...
since I'm using a variac I can choose the voltage so I basically worked from
200Vpp and 20Vpp (so I did like 10M and 250k and 1M and 250k and it allows
me to stay ~ within 2Vpp(well, max 5Vpp but)) then I tried other
combinations that gave me the ~ the same pp values(all the way down to 50k).
I tried capacitively coupling the "probe"(which is just one mono channel of
the stereo input) but it didn't do anything.
The thing I don't like is that you can see the sampling going on... I don't
like that blocky look.
>
> http://www.analogconsultants.com
thanks,
AD
.
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