Sound card oscilloscopes

[laserpon3]

Before I got professional high resolution DAC's to controll my laser projectors I used to use a 5.1 sound card as a DAC (modified with a correction board to work for laser equipment).
Worked really well.

Anyway I found this: http://www.automata.hk/projects/scope
It might be already known here, I'm not sure.
As safety I would likely use a external usb sound card.

I know that Dave's advice is: don't bother with the digital crap, get yourself a proper analog oscilloscope (hell I would not bother with these chinese oscilloscopes at all seeing how horrible results they give).
But On top of this being extremely portable it's also very cheap.

I was wondering about the accuracy and range of these things.
And if they are horrible: would there be a way to improve this by adding extra components to the sound card attachement? (that being said if its not because of the limits of a sound card itself).

[alm]

Issues are no DC coupling, very limited input protection and limited range. Good luck using it for 5V logic, for example. Apart from the obvious issues like bandwidth (quite low for something like I2C or RS-232). Accuracy is usually quite poor (who cares about their volume drifting by a few dB, especially in consumer audio).

You can build an external attenuator (preferably variable, unlike the link you gave) with BNC connectors and circuit protection, but this will defeat the portable and cheap advantage. Especially by the time you bought a dedicated sound card. I wouldn't bother, but don't let that stop you from experimenting if you have plenty of time and no funds/space for a real (even used analog) scope.

[PhynixViking]

AH!!! HAHAHHA!! YES!~ I am going to do the same thing!!!
I found some simpler program (the thing is like written in 16bit and 150kb...) but has the basics and seems to work.
I have a programer friend that makes really amazing things... I gave the program to him and asked if he could modify it (or write me a new one) and I'm going to be making a "probe circuit" and yes using a USB sound card. ^___^

I don't think it will have "much" range even with all my modifications... and accuracy I was going to have a calibration menu in the software.

If we end up rebuilding the program from scratch and all works well I'll try to convince him to have it as freeware and include schematic with it.

[laserpon3]

I happen to have an unmodified usb 5.1 surround sound card laying here which also wasn't expensive.
no DC coupling is certainly too bad.

The problem with the used analog scopes is that there are none to be found on ebay which are close to my location.
Scopes are heavy and large.
Shipping costs are immense.

[T4P]

(hell I would not bother with these chinese oscilloscopes at all seeing how horrible results they give).

Interesting. Every rigol is a "chinese" oscilloscope. Stereotype much? Rigol, Owon, Hantek they make great oscilloscopes for the money
Horrible results? Really?

[Lightages]

A nice freeware oscilloscope program I have is from a dead website. Luckily it is true freeware and the license says it is free to distribute.

Actually I found the website that now has the programs. Many other good ones too.
http://infinitespectra.com/freeware/

More fun:
http://www.analog.com/library/analogDialogue/archives/45-11/soundcard.html

[BravoV]

For PC sound card based measurement software, look no further, it has scope, spectrum analyzer, waev form generator, freq meter, impedance meter/ZRLC (this particular feature is my favorite) and tons of others features, its just too many to list here.

Don't worry, its freeware  -> Visual Analyser

[Harvs]

With a high precision sound card like the ASUS Xonar Essence you can do very well in the audio range.  I know of several people who bypassed the ac-coupling caps on their sound card to get DC-coupling.

But as already discussed, with a max sample rate of 192KHz, not much use as an oscilloscope in my mind.  Excellent, cheap tool for audio analysis, but no substitute for a scope.

PS Visual Analyser is awesome...

[grenert]

If you're interested in protecting your soundcard/computer, there are some DIY interfaces out there.  A relatively cheap and simple one was published in Silicon Chip and available as a kit:
http://www.siliconchip.com.au/cms/A_30518/article.html
http://www.jaycar.com.au/productView.asp?ID=KA1811 (not quite the same project as the SC article, but very close)

This design is pretty similar to the SC one and easy to build, but lacks input dividers (not hard to add):
http://xoscope.sourceforge.net/hardware/hardware.html

A very fancy DIY option is available from audio designer Pete Millett:
http://www.pmillett.com/ATEST.htm

As alm says, however, these all have the problem of no DC coupling.

[jancumps]

With a high precision sound card like the ASUS Xonar Essence you can do very well in the audio range.  I know of several people who bypassed the ac-coupling caps on their sound card to get DC-coupling.

...

Does the ADC capture that DC signal?

[peter.mitchell]

I am curious as to how a soundcards frequency response would lay into this?

[Harvs]

My understanding is it does.  I haven't actually done it myself, but having said that I've got an old card sitting around there I could try it with and get back to you. I'll see if I get the time tonight.

EDIT: Fail before I even started.  Put the card into my PC and to get some base level readings and it's kaput.   Drawing lots of power and getting very hot...

[PhynixViking]

I just thought of something that will probably be VERY IMPORTANT!!!

Mic input VS Line-In inputs are completely different!!!

SO! I bet one way will work or not... OR... work better or worse.

I will have to at one point devote this stack of 50 sound cards to figuring out which is what... LOL
(and make a video about it.)

[T4P]

Mic input is intended for condenser mics and therefore will have a DC bias voltage which i'm not sure of and i'm not sure how much input impedance it's gonna have either
Line input is most likely 1kohm input impedance for dynamic mics and other "line out"
Sometimes you might even get a 3.5mm that looks like nothing but is actually a line out/spdif but the last time i've seen that is on a HP laptop (Frankly they make terrible laptops but you get all sorts of oddities, like the failed wacom touchscreen or the biometric reader which is pointless and holed touchpads which is a terrible thing)