Computer Nerd Kev  wrote:
> bob prohaska  wrote:
>> Has anybody used a USB sound capture device for an audio frequency
>> oscilloscope on a Raspberry Pi? xoscope is available using apt,
>> but I can't find any reference to what sound devices, if any, it
>> can use over USB.
>
> Xoscope's webpage says it supports ALSA as an input source, so as
> long as a USB audio adapter is working with ALSA (the cheap Chinese
> ones seem to do so without issues) it should be fine.
>
Ok, that's a good hint. I'm looking at something like:
https://www.amazon.com/DIGITNOW-Capture-Grabber-Cassette-Converter/dp/B079CBGDS
T/ref=pd_rhf_dp_p_img_2?_encoding=UTF8&psc=1&refRID=YV3EVDFX4FWZF58TY2CW
There are reviews saying it works with Raspberry Pi, so maybe it'll work
with xoscope. It doesn't have to be good, just good enough to catch
sags and spikes on a timescale of milliseconds.

> It will have a series capacitor to block DC. You'll need to either
> remove this (might be difficult if it's a small indistinct-looking
> SMD part) or use a chopper circuit like this if you want to measure
> DC signals:
> http://lea.hamradio.si/~s57uuu/scdsp/CheapChop/cheapchop.htm
>
> For more sensible input impedence (so the behaviour of the circuit
> doesn't change when you probe it), the buffer circuit shown at the
> xoscope homepage would also be recommended:
> http://xoscope.sourceforge.net/hardware/hardware.html
>
Thank you for the link!

> Of course at this point you've got a significant amount of
> front-end circuitry for your "simple" sound card oscilloscope. For
> a data logging application that might be quite reasonable, but for
> basic troubleshooting maybe it would be easier to just buy an old
> CRO (Cathode Ray Oscilloscope), which has the added benefit of
> working outside the audio frequency range.
>

I'm experienced with analog 'scopes and don't want one. They aren't
useful for catching one-off transient events, which is what I'm looking
for. Something with a stop trigger is essential. A freestanding DSO
would be nice, but I won't use it enough to justify the cost and storage.

Thanks for writing,

bob prohaska

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