DIYEFI.org Forum

Having probably fixed the injection timing issues that have been present for a known reason the whole time I would now like to view the signals and confirm that they look as they should.

If any of you have used such software, throw me your recommendations.

I'll have a search/look around and see what I can find to do the job. If I find anything good, I'll post about it here :-)

Admin.

I've used Audacity to record signals with my soundcard scope.
http://audacity.sourceforge.net/

Thanks, I have audacity, and was thinking of playing with that :-)

I found this, it appears to be the only one :

http://xoscope.sourceforge.net/

Just playing now trying to get any input at all, I've never managed an input on this machine. In fact, the last time I recorded sound on a PC was on a mac colour classic about 12 years ago! lol

Admin.

I've had zero luck with my sound input device :-(

both audacity and xoscope only see one channel with tiny noise on it, and nothing on the other channel.

If i run xoscope first, audacity whinges, so they are using the same device for it.

I've tried all sorts.

Any Linux gurus have any clues of things to try? I'm somewhat out of ideas :-(

Admin.

I take that back, my "alsamixer" skills were a bit lacking. Apparently you have to turn on the sound input...

I have now seen "The Doors" on a scope. Hooray.

Time to wire up my device and see if the code is any good :-)

Admin.

xoscope is good :-)

Capacitive coupling inside sound card :







Denso 24/2 minimum speed :



max speed :



normal speed :



break up just above max speed :



60-2 :



36-1 :



I've identified a bug in the code with it, and I'll try to fix that before bed tonight.

Admin.

A few people have asked about the strange slopes present in the scope images. The decay's are caused by capacitive input coupling which is present on most audio equipment worth the copper it's made from. The reason that it's not instantly present is most likely that the voltage present at the input is far higher than the maximum ADC signal voltage. Thus, its just reading max till it decays below that level.

Also visible are some artifacts around the end of each square wave. To understand those you probably need to read up on this :

http://en.wikipedia.org/wiki/Fourier_series

You can see them on the edges of this wave form (look at the corners) :



The way a square wave is represented with a sound device is a sum of sign waves. I'll try to find an illustration for you :

http://en.wikipedia.org/wiki/Square_wave



If I was using a real scope, these artifacts would not be present at all. The consequence is that I can't see any high frequency noise that might be present, but (as I should anyway) I can code around it.

Enjoy :-)

Admin.

I took this one just for the curious in this thread :



It's a bit more obvious there.

Admin.

Wow, that's pretty funny.

Er, so why not dedicate a sound card (bet you could find one for $5-10) and jump over the caps? You'd want a nice reference ground, but I think you'd be ok. Might be worth it...

Two main reasons :
I don't have 50 bucks anymore (donations accepted)
And I only have a laptop, so it would be pcmcia/cardbus/usb which might be tricky to bridge (also, usb is a problem for me, I have acpi bugs... = usb causes crashes sometimes)

Also, what does it matter? we aren't watching analog forms, we are watching digital forms and they are at a sufficiently low frequency that the sound card samples them just fine :-)