free soundcard PC oscilloscope software?

[JBeale]

My daughter's 4th grade class is introducing electronic circuits and invited me to talk to them on the subject. I thought it would be fun to demonstrate some sensors, and I wanted to show something like a live scope trace to the class, but my regular scopes don't have a video output.  I just want to show a basic low-voltage, low-audio-range signal as voltage vs. time live on a big screen for the whole class to see.  They have a video projector you can connect to a laptop.

I think there are some software programs that act like an oscilloscope using the soundcard input. Seems like that should work. Does anyone have any suggestions for such software (ideally as a free download)?  I don't want to spend much money as this is just a one-off demo.

[JBeale]

Ah, nevermind. It looks like this program should do what I want:
https://www.zeitnitz.eu/scope_en

[Ian.M]

Yep. I was going to recommend that one.

Its got a reasonably simple UI that looks very much like a low end CRO, and has X-Y mode, a spectrum analyser, and can concurrently use the sound card as a signal generator.

Note: its *NOT* freeware, but the free licence explicitly permits your intended usage

    * The use of the software and of the documentation is granted free of charge for private and non-commercial use in educational institutions
    * Any commercial application requires a corresponding license (see below)
    * Distribution and sale of the program is prohibited. Contact the author in order to obtain a resale license.

N.B. any soundcard scope is *NOT* DC coupled.  Although its possible to hack a USB soundcard to remove the coupling caps and add OPAMP level shifters (+ generate a negative rail) to make it DC coupled, that's a lot of work when you can get a 2 channel usb scope for as little as $30.

For showing sensors without confusion, you may actually be better off mounting a webcam on a selfie stick to the top of your usual bench scope.  It will certainly help you *not* to be fumbling with unfamiliar scope controls during the presentation.

[NiHaoMike]

This is the best ready-to-use signal analysis software for sound card that I can find, even though its last release is pretty old:
http://www.baudline.com/
I would suggest using a webcam and a proper scope since a sound card is not at all a good scope. Namely its limitation of AC coupling only is going to be quite a disadvantage.

[JBeale]

Thanks for the suggestions. I had not thought about a webcam pointed at the scope, but that could be the best idea, and I don't have to worry about the DC-coupling problem.

[JBeale]

Followup: I brought a little Tek TDS 210 scope to the class and put it on the table facing straight up, underneath their document camera, which projected a view of it on the big screen. This worked well and everyone could see it.  So as it turned out, there was no extra setup needed at all from my end.

What I was showing was the output of a HB100 microwave motion sensor ($3 doppler radar module).  I waved my hand in front of it, and it made a wavy line on the scope.  Then I looked up and every single kid in the class was waving both arms enthusiastically.  That was a fun moment!  (I also asked how much they think this sensor cost- they figured hundreds or thousands of $, and were amazed that it cost less than one hot lunch at their cafeteria).

Among other things I put a Fluke 77 DVM under the camera, so everyone could see the output of some AA batteries drop down one millivolt at a time, while they powered up a light bulb.  Hopefully the morning inspired some kids to learn what circuits are about.