5 LED Sound Level Meter

Discussion in 'The Projects Forum' started by mikecrockett, Jul 16, 2010.

  1. mikecrockett

    Thread Starter New Member

    Jul 15, 2010
    2
    0
    Hi Guys

    I built the circuit below as it pretty much met my requirements and expected, even with my little knowledge of electronics to modify it fairly easily, but have failed.

    [​IMG]

    I have replaced the LEDs with 3 high intensity LEDs in series on each channel and upped the supply voltage to 9 volts so they reach maximum brightness.

    As standard, at minumum sensitivity FSD is around 90dB and I need to increase this to 120dB but still leave maximum sensitivity FSD at around 75db, which it is a present.

    Additionally the spread from LED1 to LED5 is around 15dB and I need to reduce this to around 7.5dB.

    Any help would be greatly appreciated.

    Thanks

    Mike
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,739
    759
    you will need comparators and a lot more components than that to do ur job
     
  3. Wendy

    Moderator

    Mar 24, 2008
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    The LM 3914 or LM3915 is probably what you need. It is an IC that is a lot more programmable and designed for the job.

    Basically you are using the natural voltage drops of the devices to step up. I have a similar circuit (a lot simpler and less usuable) in my LEDs, 555s, Flashers, and Light Chasers, Chapter 3
     
    Last edited by a moderator: Jul 16, 2010
  4. campeck

    Active Member

    Sep 5, 2009
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  5. mikecrockett

    Thread Starter New Member

    Jul 15, 2010
    2
    0
    Thanks for the replys and for the great blog Bill.

    The reasons I used this circuit were that it was a kit with a ready made PCB saving me the trouble if making my own and it was cheap. I was aware of the LM3914 etc but couldnt find a cheap kit with PCB.

    From Bill's blog I guess that I can solve the voltage spread problem by selecting different values for R5 - R9.

    Any suggestions on how to get more variation on the amplifier gain? I tried changing RV1 for a 2meg but it didn't make enough difference.
     
  6. Wendy

    Moderator

    Mar 24, 2008
    20,764
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    Nope, that is the problem, you can't move the values around. They are set in stone because they depend on basic values of the semiconductors. I just came across a blog on another site that will calculate a LM3914 and LM3915 values for you. I believe these chips can be tweaked to what you need, but I have never used the calculators.

    Dual LM3914 V3.0 Calculator

    Basic LM3915 Calculator V3.0

    Hope it works for you.
     
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