Re: [Phys-l] Oscilloscope Software that uses USB Soundcards?

["John SOHL" <jsohl@weber.edu>]

I have played around with several of these. (Sorry don't recall which ones and I've since reformatted this machine for other reasons.) General experiences:
 
1. The biggest problem is that they do NOT do DC or close to DC signals. All the sound cards I played with have a high pass filter at the input and that removes anything slower than about 15 to 20 Hz. 
 
2. The FFT applications work great. Select the software based on your need. I tried a few before I found one that had an FFT display that I liked for the task at hand. (I was trying to help a student do a science fair project involving sound and he wanted to know what frequencies were contained in various whistle blasts.) 
 
3. If you use an external sound card the USB cable will protect your computer as long as you don't lose your ground or put in really high voltages (like 500V or something). I'd try it first with an old computer that you don't care about. Most schools and colleges have a property control department that takes care of surplus computers, you can get an old one from them and try it for free.) 
 
4. You can always open up the sound card and solder a surge protector across the inputs. For example you can place a 25 cent varistor across the input leads such as:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=P7285-ND 
This will shunt any larger voltages to the ground lead and short out the input. 
5. I did use the function generator feature of a couple of the ones that I played with and it worked just fine as long as you didn't want something outside of audible frequencies. 
 
6. Square waves at higher frequencies were a bit of a problem since the sound card couldn't respond fast enough to give good square edges (think about Fourier components here). 
 
If you are not demanding too much and don't want DC signals these sound card oscilloscopes work just fine. 
 
Another option are the USB oscilloscopes that have actual BNC connections and the like. They will do pretty much anything a real scope will do but for only $300 or so. Not free but not wildly expensive either. Basically they are a cheap oscilloscope where you don't have to pay for the screen and controls because you supply those via the software and your computer. 
 
John 
 
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John E. Sohl, Ph.D.
Professor of Physics
Weber State University
2508 University Circle
Ogden, UT 84408-2508

voice: (801) 626-7907, fax: (801) 626-7445
cell: (801) 476-0589
e-mail: jsohl@weber.edu

> > > "Ann Reagan" <areagan@csmd.edu> 8/29/2010 4:06 PM >>>
This week I have found several software programs that claim to allow the use of an ordinary home computer as a low-frequency (less than 20 kHz) oscilloscope, by using the microphone input jack on a sound card (embedded or USB) for A to D conversion and/or data acquisition. Each package provides a graphical user interface that makes the computer screen "look" like an oscilloscope, with most of the standard controls and knobs as sliders. Functionality includes Fourier analysis, timing, voltage measurement, plotting of signals from one or two channels, and use as a signal generator. While all the packages warn of potential harm to the computer/soundcard from excess voltage, the idea of using a free or cheap piece of software instead of buying a $700 oscilloscope is attractive.

1) Does anyone on this list use any such software? 

2) Which one? Why? How? Pros/Cons? Please tell.

3) Would buying a cheap USB soundcard be sufficient to protect the computer from voltage spikes, or would additional controls and conditioning be advised? What kind? How much?

4) Ant other thoughts, ideas, warnings, or suggestions?

Thanks!

- Ann R.

Dr. Ann M. Reagan
Adjunct Faculty
Department of Math/Physics/Engineering
College of Southern Maryland, Leonardtown Campus