Test Equipment: Oscillocopes

[Brian516]

My computer makes for the WORST FG of all time!  The only thing that actually looks the way it should from the PC is a sine wave...
Square wave looks like a cross between sawtooth and square wave... and none of the others look good at all.  I need to get my Arduino working as an FG, or maybe the Dell desktop that I picked up from storage set up and loaded with Linux and an FG since I have decent sound cards for it.  Maybe running the output thru my yamaha stereo amp would help?  I know it's not the scope, and It'd be nice to have a semi-decent FG to use until I get a real one.
I'm going to upload a few pics as soon as I get this camera/sd card issue resolved and add them to this post. They are pics of the diagonal line, circle, etc, and one or two of my horrible looking other waveforms.


After watching the Youtube video YouScope & Oscillofun and seeing what the song is supposed to look like on the scope, I realized that what I am seeing is definitely not correct. I made a vid showing what I see for most of the song. I hope it's just an issue with my PC soundcard but I somehow doubt that's the case. Whatever it is is likely the cause of my distorted waveforms (other than the sine wave).

https://www.youtube.com/watch?v=sPkQEFfGOfM


Here are some test waveforms (standard and XY) off my scope and PCFG.

http://i1081.photobucket.com/albums/j347/Brian_Bloom/1khzSawtooth-PCFG_zpsydiaz5rz.jpg
http://i1081.photobucket.com/albums/j347/Brian_Bloom/1khzSQ-PCFG_zpspmukkzwp.jpg
http://i1081.photobucket.com/albums/j347/Brian_Bloom/1khzSine-PCFG_zpsv7xrk0tq.jpg
http://i1081.photobucket.com/albums/j347/Brian_Bloom/1khzSineXY-PCFG_zps4ekkrzib.jpg
http://i1081.photobucket.com/albums/j347/Brian_Bloom/1khzSineXY-45OOF-PCFG_zpsuwkgcmjo.jpg
http://i1081.photobucket.com/albums/j347/Brian_Bloom/1khzSineXY-90OOF-PCFG_zpskllfhqko.jpg
http://i1081.photobucket.com/albums/j347/Brian_Bloom/1khzSquareXY-90OOF-PCFG_zpsvrcpsucv.jpg
http://i1081.photobucket.com/albums/j347/Brian_Bloom/10khzSquareXY-90OOF-PCFG_zpsch524ueb.jpg
http://i1081.photobucket.com/albums/j347/Brian_Bloom/20khzSquareXY-90OOF-PCFG_zpsq19blots.jpg
http://i1081.photobucket.com/albums/j347/Brian_Bloom/20khzSineXY-90OOF-PCFG_zpsp6kpnhsm.jpg
http://i1081.photobucket.com/albums/j347/Brian_Bloom/10khzSineXY-PCFG_zpsxqajwnrf.jpg

Time to crash. Goodnight everyone.


Just realized, it has to be a PC sound card problem, right? I mean, I get a good, clean square wave off the calibrator.... Right?? Or am I totally missing something, again?

[TinselKoala]

Well, the Sine waves look really clean and the 90 degree oop circle is perfect. Yes, I think your sound card is probably introducing distortion for the ramp and square wave signals and the "oscillofun" FLAC file. I'm puzzled as to why you need to turn it up all the way, though. I ran "oscillofun" just at normal volume in my speakers and at the same time took the headphone output directly from the front panel headphone jack into the 10x attenuated probes and was able to see the shapes fairly cleanly, with much less distortion than your video shows.
So like I said I'm puzzled. You should be able to just use the V/div scales to set the scope at more sensitive amplification and run the sound card at normal volume, and I don't see why you can't run the speaker output and the headphone output at the same time. I'm running a seven year old Asus motherboard with onboard sound, no separate soundcard. The probes shouldn't be loading the soundcard much at all, certainly not as much as headphones would. If you run the sound card at 70 percent volume you should get much less distortion from it, and if the scope's V/div settings won't display it at that output level I'd say that there is something wrong somewhere.

[MarkE]

PNGs always seem to display, TIFs don't seem to display.  My scope puts out TIFs.

Your scope seems to be working OK.  The fuzzy signals look like a high impedance in the probe ground.  The awful square waves look possibly like an open ground connection.

[TinselKoala]

Yep. I thought also perhaps some distortion from running the sound card all the way up. This may have been necessary due to a high impedance in the ground connection also.


I just made a video playing the two sound files into the 2213a. Direct from the headphone output, volume at about 75 percent, speakers going too (with separate VC on the speakers). 10x probe attenuation, V/div settings 500 mV/div mostly, increasing to 200 mV/div at another segment (I misspoke in the video, was reading the "1x" position on the knob by mistake, but I inserted correction titles in the vid, the 500 and 200 mV numbers are correct.)

It will take half an hour or so to process and upload the video. It is much cleaner than what Brian showed, so I think that better connections and perhaps different settings will also work to clean up his display of the files as well. (I downloaded the files and played them directly using the Ubuntu native "movie player" app rather than playing them from the YT video player on the video I linked earlier.)


One weirdness for me is that the text in the "youscope.wav" file is displaying in mirror-image or backwards or something. Nothing I've tried has corrected that. Swapping channels makes the text run vertically instead of horizontally and inverting one channel makes it upside down, but still it appears backwards instead of straight.

[TinselKoala]

My video of the Youscope and Oscillofun audio files on the Tek 2213a is ready at:

http://www.youtube.com/watch?v=FoSPK1qRhSY