Hi Stan,
points taken, though I don't necessarily agree with all of it (but that's what this forum is for, to discuss different approaches and points of view, right?!). About two years ago I spent quite a while researching those soundcard based scope offerings (I wanted to use it at home as a simple scope for tinkering), but finally gave up. While the screenshots and descriptions all looked good on the web, the actual performance was just dismal for all of them (I went through about 10 different ones, all Freeware or demo); unstable triggering / unstable picture, poor sensitivity, questionable user interface were usual breaking points. Even when if would have worked well, 20 kHz sample rate is just barely enough to function as a logic analyzer (that tells you high/low) for the Picaxe - forget doing accurate timing or level measurements. And I tried those scope programs on three different computers (one fast desktop and two good laptops, all different manufacturers). Level accuracy versus. frequency of the sound cards is usually horrible, too (1dB is not much in terms of voulme difference, but means over 10% error in level - no self-respecting scope is even that bad. And run-of-the-mill sound cards fall of MUCH more than 3 dB even below 20 kHz).
But what's more important, feed in a few Volts too much and you can fry your whole computer (yes, one could get a cheap used laptop or desktop but for me that kills the "zero overhead" aspect of those scopes). And from my own experience I can tell that many sound cards are horribly sensitive to static electricity (sometimes I am brave and work without a grounded wriststrap when I am tinkering at home, and twice I killed a phone input or line ine on those cards that way).
Good scopes are more forgiving, especially with a good passive probe in front (which doesn't work well with sound card inputs because then the signal becomes too small).
As to PC based scopes (a little hardware box hooked up to serial port or USB), they are quite a bit better and I agree, you get storage function, Fourier transform and other goodies virtually for free (and it's super-easy to load/save/print waveforms). One frequent complaint is that the cheaper units often have only a single input channel, so you can't trigger on one signal and look at another. Which makes them virtually useless for most serious work. The higher-end pico scopes look pretty decent (I looked at them around the same time as the sound card scopes) but for a steep price. The lower end are almost a joke (in my opinion anyway!) given their poor bandwidth. (even a simple RS-232 based system could go to close to 100kHz). And I do think you need several MHz to make sense in the long run.
Finally, but that is of course personal taste, nothing can beat the intuitive feel of real knobs and pusbuttons when operating such an instrument. Fiddling with a mouse on "virtual buttons" just does not cut it - because it's much slower.
As I said in the beginning, but probably good to repeat, those are just my 2 cents! Like to hear other opinions, too!
Wolfgang
Edited by - womai on 13/06/2006 07:36:18
