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
    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.


    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.


  2. R!f@@

    AAC Fanatic!

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


    Mar 24, 2008
    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
  5. mikecrockett

    Thread Starter New Member

    Jul 15, 2010
    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


    Mar 24, 2008
    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.