SV: Re: SV: [sdiy] scope recommendations wanted (or even "wtb: scope in england")

[Karl Ekdahl]

Personally i simply don't have space for an
oscilloscope (anyone want to buy a TEK?) and builded a
souncard based. It works okay, but of course, the DC
problem persists since i have a laptop and don't
really want to go in and modify anything. But, i was
thinking of simply doing a little modulation source
that is basically a waveform with fixed pitch that has
it's amplitude modulated with the signal being
measured, so just a low-impedance VCA. Does this sound
stupid btw.?

Karl


--- Seb Francis <seb at burnit.co.uk> skrev:

> 
> WeAreAs1 at aol.com wrote:
> 
> >Unfortunately, soundcard-based scopes will only
> measure AC signals.  This is 
> >because all soundcards are AC-coupled at the inputs
> (with coupling capacitors, 
> >which block all incoming DC).
> >  
> >
> 
> Of course this is something that can be fixed by
> modifying the soundcard 
> and adding a small external circuit..
> http://www.qsl.net/om3cph/sb/dcwithsb.htm
> 
> In any case when using a soundcard you should at
> least have an external 
> buffer circuit since the impedance of a soundcard is
> very low compared 
> to a scope and will tend to influence what you are
> trying to measure.
> 
> Seb
> 
> 
>