1. djsfantasi

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    Apr 11, 2010
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    I’m using the Sparkfun Music Maker shield, and I’m taking the line out output. The shield uses the VS1053 codec. Line output consist of a L & R output, plus an audio ground. For purposes of this discussion, I’m only concerned with the R channel.

    What happens if I tie the audio ground to circuit ground?

    If I don’t, then what does the R channel signal look like w.r.t. circuit ground?
     
  2. djsfantasi

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    I don’t believe have the equipment (oscilloscope) to measure one. I’ve considered writing a sketch to output the analog reads, but need to get additional microSD cards.. Until they come, I thought you guys could help.
     
  3. MrChips

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    You can always AC-couple the grounds using a 10μF caps.
     
  4. djsfantasi

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    So, add a 10μf cap between signal and circuit grounds?
     
  5. MrChips

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    Sure. This will couple your AC audio signal and not pass any DC.
     
  6. djsfantasi

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    The signal is already coupled with a 0.1μf cap. My concern is that the audio signal ground may be +1.1V above circuit ground. I’m sending the R channel into an op amp and I’m not sure of the input voltage range. Is it 0V-2.2V or ?-1.1V?
     
  7. BobTPH

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    Are you sure the audio ground isn’t already the same as ground? It would be an odd design if not.

    Bob
     
  8. djsfantasi

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    I thought I was sure. Now, not so much. The schematic for the Music Maker is unreadable.

    When I get home, I can check the voltage between the audio ground and circuit ground. If they’re the same, I should get 0V. If not, I expect something around 1.2V
     
  9. KeithWalker

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    Jul 10, 2017
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    I found the VS1053 datasheet, see the pdf below. It states:
    The common buffer GBUF can be used for common voltage (1.23 V) for earphones. This will eliminate
    the need for large isolation capacitors on line outputs, and thus the audio output pins from VS1053b may
    be connected directly to the earphone connector.
    GBUF must NOT be connected to ground under any circumstances. If GBUF is not used, LEFT and
    RIGHT must be provided with coupling capacitors. To keep GBUF stable, you should always have the
    resistor and capacitor even when GBUF is not used.

    Data Sheet:
    https://www.sparkfun.com/datasheets/Components/SMD/vs1053.pdf

    Have fun,
    Keith
     
  10. djsfantasi

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    Thanks for finding that! I’m reading through it now.

    I need to measure one channel’s output w.r.t. ground. Specifically the positive signal value relative to GBUF for one channel.

    I had a circuit that worked but no one had explained to me how. I may have input a negative voltage to the + input of a single supply op amp (should’ve blown it up) and I tied GBUF to ground (explicitly prohibited by the data sheet). But it has been working.

    What I’m looking for is how to obtain the + side of an audio signal. I’ve tried several approaches. Including adding a 1.2V offset to the signal. But if I can feel comfy with the voltage between the channel and ground...
     
  11. cmartinez

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    DJ, a few months ago, I bought this cheap-o scope and have been getting pretty decent results (considering its limitations of course) with it. And it only costs a little over $30.00 bucks in Amazon! And even less if you buy through Banggood.
     
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  12. KeithWalker

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    Try connecting the + audio out to the op amp input through a 10 uF capacitor.
     
  13. djsfantasi

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    @KeithWalker

    Please check out this post.
     
  14. djsfantasi

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    @cmartinez, I’ve ordered this ‘scope. Can’t wait to get it.
     
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  15. cmartinez

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    Can't wait to hear how it went... :)
     
  16. KeithWalker

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    If you already have a coupling capacitor, there will be no problem with dc offset.
     
  17. Yaakov

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    I have one too, it works very well. I bought a better probe for it, didn't cost much more.

    I am considering a slightly better one, ~$100 range for my tiny toolkit.
     
  18. djsfantasi

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    Came in the mail today. I’m waiting for some micro SD cards to set up a test.

    My first reaction. The one-page instruction sheet is printed so small that I need stronger readers or maybe scan it and blow up the image to where I can read it.
     
  19. cmartinez

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    Already did that myself ... here you go

    DSO188.jpg
     
  20. cmartinez

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    And, BTW. I've noticed that this place compresses original images even further, that's why the image in my previous post is not as clear as it should be. Here's the original, attached in a ZIP file so you can download it and see it with a little better resolution.
     
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