Sound card oscilloscope probe circuit

juantravel

May 14, 2010
41
I was thinking of making my own oscilloscope probe based on a pc sound card. I was wondering if the following circuit would work to limit the voltage going to the sound card. the circuit is attached.

Attachments

• circuit_limiter.bmp
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(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,507
Ground is normally shown at the bottom rather than at the top.

Have you checked the specs for your sound card? If it allows an input of 0 to 5V then that is fair enough, however the range may be smaller.

This circuit also means that your signals must have the same ground level as your computer, which may be a problem.

juantravel

May 14, 2010
41
?

It utilizes the mic input. The probe ground will be on the circuit ground. and the signal from the circuit will feed into mic input. the ground is up top becuase the circuit also had another zener.

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,507
the ground is up top becuase the circuit also had another zener.

That's not an excuse.

Drawing things in ways that defy convention is a quick way to ensure that people misinterpret your diagrams.

It doesn't matter what input it uses, you should determine the maximum required input voltage. I would suggest that you'd be looking at a very small voltage and a pair of diodes to limit the amplitude to about 1.5V would be a better solution.

Last edited:

55pilot

Feb 23, 2010
434
Audio card based scope generally does not work because most sound cards are AC coupled and so you can not measure the input DC level.

---55p

Tesla

May 10, 2010
165
This one runs on Windows (and Linux also I think). I couldn't find the suggested hardware schematic though:
http://gitorious.org/osqoop

This one is Linux only and someone made some nice hardware:

I was going to give it a shot until I saw that speed was defined in Khz instead of Mhz. I think I need (want ) something around 40 Mhz minimum.

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,507
Yes, audio card oscilloscopes are limited to audio frequencies. The sampling rate determines how many data points you'll get too.

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