Help with circut design - A noise (sound) indication box.

Discussion in 'The Projects Forum' started by ward257, Jul 16, 2015.

  1. ward257

    Thread Starter New Member

    Jul 16, 2015
    1
    0
    Hello all,

    Im currently working on a project to design my own circuit but i am struggling.... alot!!

    The circuit i wish to design is the following.
    A noise (sound) indication box. There will be two lights on the box one green and one red.
    The green light will illuminate if the sound is under 79dB.
    If the noise goes to 80dB or over the red LED will illuminate.

    I understand i will need a transducer to monitor the sound then the sound needs to be conditioned then converted to a digital format.

    Any designs/ideas are welcome.

    Thanks for taking the time to look.
     
  2. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,170
    395
    Microphone or hi Z speaker, AC amplifier to give about 3 V PP signal, rectifier, filter, 2 comparators, 2 LED's.
     
  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    How complex is the sound? You likely need some "weighting" network that responds to the ratio of peaks to average levels. It is not simple.

    What is the application?
     
  4. #12

    Expert

    Nov 30, 2010
    16,247
    6,739
    LM3915 VU meter chip.
    and/or
    Microphone, amplifier, precision rectifier, comparator, LED
    where the LM3915 chip might or might not be used for the comparator function.
     
    absf likes this.
  5. #12

    Expert

    Nov 30, 2010
    16,247
    6,739
    Buy a sound level meter, set it for the correct range, attach to its output connector, comparator, LED.
     
  6. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,515
    1,246
    IF you want to build something from scratch
    AND IF the lights can be simple low power LEDs
    AND IF you don't care about precision measurement, weighting factors, etc.

    THEN:
    Microphone > 1/2 LM358 opamp as preamp > diode, cap, resistor > 1/2 LM358 opamp as level detector > current limit resistor > Green LED to Vcc, Red LED to GND.

    OR:
    Microphone > 1/2 LM393 comparator as preamp > cap, resistor > 1/2 LM393 comparator as level detector > Red LED > Green LED to GND, current limit resistor to Vcc.

    Power = 9 V battery.

    ak
     
    Last edited: Jul 17, 2015
    absf likes this.
Loading...