Need help with LM3914 VU Meter

Discussion in 'The Projects Forum' started by AlessandroS, Jan 25, 2014.

  1. AlessandroS

    Thread Starter New Member

    Jan 25, 2014
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    0
    Hello all,

    I recently picked up a LM3914 to play around with before I started designing a VU meter. I want to simultaneously drive a speaker or headphones, so I need to mitigate the loading effect of putting a relatively small resistance in parallel with the input of the LM3914.

    I figured a unity gain buffer would do it, but for some reason, it simply causes all the LEDs to light up. Anyone able to perhaps explain why that's happening, or suggest an alternative? My circuit was working fine until I tried this.

    Also, this is hard to describe, but is there a way to "smooth out" the output? I tried a peak detector, which again didn't do anything.

    Thank you,
    AlessandroS
     
    Last edited: Jan 25, 2014
  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    3,686
    Sound (audio) power is a log, not linear measurement. Use the lm3915 for audio.

    The lm3914 is linear
     
  3. AlessandroS

    Thread Starter New Member

    Jan 25, 2014
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    Thank you for the suggestion, I take it that the LM3915 is a solution to my second issue?
     
  4. bertus

    Administrator

    Apr 5, 2008
    15,634
    2,342
    Hello,

    Take a look at the following project of ESP:
    http://sound.westhost.com/project60.htm

    You can also have a look at the LM3916, wich is specialy made to create a VU meter.
    The attached datasheet will give a number of schematics.

    Bertus
     
    Last edited: Jan 26, 2014
  5. ericgibbs

    Senior Member

    Jan 29, 2010
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  6. AlessandroS

    Thread Starter New Member

    Jan 25, 2014
    3
    0
    Thanks everyone!
    I think I'll go with that ESP link, then maybe try a 5 or 10 band version once I've completed that.
     
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