SoundCard Oscilloscope free software and simple clipper.

[blueroomelectronics]

Something I came across, thought it might be a cheap & cheerful way to see waveforms on low frequency projects <20,000Hz. I'm testing it now and if it works I'll use it as part of my Lab tutorial for the Firefly kit I sell. Attached is a schematic for a simple adjustable voltage limiter for your soundcard.
**broken link removed**
**broken link removed**

 

[Sceadwian]

Might I suggest learning something about LTspice instead? It's free and while not real time it can take .wav files as voltage or current sources and you can do significantly more processing with it (feed the .wav's into simulated analog/digital systems). Another pieces of software I'd recommend is Spectrum lab which is ostensible for amateur radio experimenters which allows real time FFT (and FFT filtering) of incoming audio signals (including demodulation of common HAM protocols)

 

[Sceadwian]

Mind you sound card oscopes are without hardware modifications only AC coupled and usually have filtering stages in between. Another thing to think about is modern PC's have sound cards built in and there is usually a LOT of nasty noise on the various line and wave in/outs that can further distort readings. You'd be amazed at the crosstalk an audio processor will pick up when closely coupled with a PCI/USB or high speed processor interconnects.

 

[blueroomelectronics]

It's not meant as a serious instrument, but mostly to see pwm width, digital signals (square waves) and the price is right. Most soundcards are A/C coupled so DC is out of the question.

Is spectrum lab free, or student version available?

 

[Sceadwian]

Free, that's why I use it. Awesome software. https://www.qsl.net/dl4yhf/spectra1.html
I've been gradually shifting all the hacked or pirate software I use to use to the free domain. I don't think I currently run any pirate software on my system.

 

[blueroomelectronics]

Very nice, I'll play with it.

 

[Sceadwian]

Just to warn you, it likes a LOT of horsepower. Realtime FFT and reverse FFT is very processor demanding.

 

[blueroomelectronics]

Well the freeware scope software works...
1. the signal is inverted.
2. the A/C coupling rounds the squarewaves

on the plus side the frequency measurement was spot on, and the signal was quite useable for what it was.

 

[Nigel Goodwin]

2. the A/C coupling rounds the squarewaves

No, the lack of any bandwidth rounds the squarewaves - AC coupling isn't a problem, except for very low frequency ones.

 

[blueroomelectronics]

Now I wonder why it's inverted? Are all sound cards inverted?

 

[Nigel Goodwin]

Now I wonder why it's inverted? Are all sound cards inverted?

Why not?, it makes no difference to sound - audio amplifers don't concern themselves with inverting or not. Certainly it would be trivial for the scope software to invert the image if needed.

 

[Sceadwian]

Inverting amplifiers have higher input impedance than non-inverting amplifiers don't they? They probably feed the line/mic input directly from the cap into an inverting amplifier used as a voltage follower for the ADC stage. My sound card has a fixed 20db gain stage on the mic (I think a lot do) so if you want real high precision make sure you're using the mic in with the boost. Keep in mind the noise is really pretty bad but can be averaged out. I pick up all sorts of cross talk (non audiable) when I use that FFT software.

 

[Sam Jelfs]

Why not?, it makes no difference to sound - audio amplifers don't concern themselves with inverting or not. Certainly it would be trivial for the scope software to invert the image if needed.

Err... it does if you are using the signal as a sound source in a multi-point system... less so in stereo and 5.1, but when you start to deal with clustered speaker sources, ambisonics and the like, phase and polarity can start to make huge differences to how the sound is perceived by the listener. electronically it might make no difference, but it does when you listen to it.

 

[ericgibbs]

hi,

The 'sense' of the audio signals must be the same on all the audio channels.

You would get poor quality sound on a stereo system with channels in opposite phases.

 

[Nigel Goodwin]

Err... it does if you are using the signal as a sound source in a multi-point system... less so in stereo and 5.1, but when you start to deal with clustered speaker sources, ambisonics and the like, phase and polarity can start to make huge differences to how the sound is perceived by the listener. electronically it might make no difference, but it does when you listen to it.

The phase makes no difference whatsoever, as long as all are in the same phase.