Fundamental Oscilliscope Usage - diyAudio
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Old 20th May 2012, 03:38 PM   #1
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Default Fundamental Oscilliscope Usage

I am using Visual Analyzer which is calibrated at 2v 60Hz power line. The same supply shows a square wave, when it should be a near perfect sine wave.

60HzWaveform.PNGI doubt the utility company switched over to square wave distribution, so it must be something on my end. It is my first attempt at using an Oscope.
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Old 20th May 2012, 04:04 PM   #2
DF96 is offline DF96  England
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Could it be clipping? Perhaps you are only seeing the first volt of 115V?
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Old 20th May 2012, 04:17 PM   #3
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Quote:
Originally Posted by DF96 View Post
Could it be clipping? Perhaps you are only seeing the first volt of 115V?
Thank you for replying.
The input is the secondary of a transformer, 2v rms. The gain is set at 50%. If set at 100% the same waveform appears.

Something is telling me Fourier Transformation is involved, but I am not sure precicely how that works.

Last edited by ITPhoenix; 20th May 2012 at 04:19 PM. Reason: Forgot Fourier
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Old 20th May 2012, 04:34 PM   #4
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What kind of hardware are you using to record that sine? Is recording gain set up correctly?
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Old 20th May 2012, 07:39 PM   #5
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Visual Analyzer; PC based software through the sound card. It works perfectly with an actual microphone input.
Visual Analyser details

Here is the capture settings:
CaptureSettingsTab.PNG
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Old 20th May 2012, 07:40 PM   #6
Simon B is offline Simon B  United Kingdom
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Quote:
Originally Posted by ITPhoenix View Post
Thank you for replying.
The input is the secondary of a transformer, 2v rms. The gain is set at 50%. If set at 100% the same waveform appears.

Something is telling me Fourier Transformation is involved, but I am not sure precicely how that works.

Have you checked the output of the transformer with a known good ac meter? As DF96 suggests, this looks like a clipped big sine wave - I hope you're soundcard is still ok...

Or, are you using a 'mic' rather than a 'line' input? You don't say what soundcard you're using - I think you'd see something like this feeding 2v RMS into a mic input, which expects much less signal. If you've got a line input, use that, otherwise I think you'll need a resistive divider attenuator.

What do you see if you set the gain to 10%, or 1%? If the clipping is happening before the software gain control this will make no difference. Perhaps try feeding through a pot, 1k, 5k, 10k are all ok, transformer to track ends, take soundcard input from wiper & ccw track end. Hopefully you should be able to confirm you're still on a sinewave supply.

Wrt Fourier, no, he doesn't come into this, you're still in the time domain. The Fourier transform goes between the time and frequency domains, eg turning a (time domain) waveform into a (frequency domain) spectrum.

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Old 20th May 2012, 08:17 PM   #7
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Soundcard is Asus DG. It is a low end but works good. The mic and line are combined. Looking at a Creative spec sheet, for one of their older cards, the max input is 2v for full range.

Transformer output is monitored with digital 5% voltmeter. I know this is correct since there is about 20 feet of magnet wire on the bench, and about 1/3 of the plastic spindle can be seen, there are so few windings. It used to be a 120/7.5v.

I originally started with 4v rms knowing the AD converter should handle at least 5. I repented after reading the Creative spec and recalibrated.

The same input was just tested recording from a mic. The playback is perfect, so I doubt the card is fried.
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Old 20th May 2012, 08:53 PM   #8
cbdb is offline cbdb  Canada
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Quote:
The same input was just tested recording from a mic
You probably have the sound card set for a mic , which needs a lot of gain. Check your card settings.
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Old 20th May 2012, 09:01 PM   #9
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Originally Posted by cbdb View Post
You probably have the sound card set for a mic , which needs a lot of gain. Check your card settings.
There is only one input option: mic/line. It is the same circuit.

I thought it was the line level inputs that need more gain. Well, they are not on this card, only the higher end ones.
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Old 20th May 2012, 09:19 PM   #10
DF96 is offline DF96  England
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Is the transformer saturating? This can happen with a cheap transformer when it is virtually unloaded.
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