Wich Sound card oscilloscope probe circuit?

[samsagaz]

Hey guys, i want to purchase an external USB Sound Card to use as simple oscilloscope to use soft like multiintruments. Want to know if can someone recommend me some circuits to have protection circuit ensures its output to be less than 2-3V at all time.

[xtoffer]

I seem to recall making something similar as well before I got a "proper" scope. To clip the input you can use a few diodes in series (https://en.wikipedia.org/wiki/Clipper_(electronics)). On a sound card you normally have mic or line input (or both). Line input can take the highest voltage but 2-3V still seem a bit high to me.

Ok I had a look at Wikipedia, line level for "consumer audio" is listed as 0.894 Vpp and for "professional" 3.472 Vpp. Mic input will be even lower I believe.

Mine was rather minimalistic, I think I put a resistive divider followed by diodes for the protection and buffered it with opamps before and after. Could maybe have used some filtering as well...

Otherwise there are a lot of circuits out there if you search around.

[tggzzz]

Protection against all overvoltage sources is non-trivial. See

http://in.tek.com/dl/3AW_19134_2_MR_Letter.pdf
http://www.tek.com/dl/51W_10640_1.pdf

You might decide to specify protection against a subset of overvoltage conditions.

[EntropyWizard]

I built one of these http://xoscope.sourceforge.net/hardware/hardware.html and it seemed to work ok with a regular PC sound card. I only used it very briefly though since I acquired an old analog scope, and haven't had much use for the sound card one since.

[LaserSteve]

Some of the 5.1 and 7.1 19$ USB sound modules can be modified for direct coupling by adding an adjustable 1.2V offset to your signal.
Just remove the electrolytic caps.

The trick is adjusting the setup software to turn off the audio signal processing, echos, depth cue phasing,  and "surround sound".

We used them mainly for DC coupled high speed outputs, but input is also possible..

CM series chipsets were the ones we had success with...

While my application was control of a mechanically scanned RGB projection graphics system,  this fellow uses them for DAQ work,,

Reviews:

http://www.daqarta.com/dw_gguu.htm

Mods:

http://www.daqarta.com/dw_ggmm.htm

You really do need to protect your PC when you do this, a failure of the motherboard USB hub goes right in to "soft tissue" near the processor on the motherboard...


Steve