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Sound Reactive LEDs

Discussion in 'LEDs and Optoelectronics' started by Sizer, Nov 6, 2012.

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  1. Sizer


    Nov 6, 2012
    Firstly Hi!...noob here....

    Im trying to do a project with my two lads and don't know a great deal about electronics but I do know what we want to achieve

    We want:

    10 LED's to light up to music (all at the same time not a bar type thing).
    To be able to turn it off and on.
    To be able to turn off the light syncing leaving "all LED's" lit.
    To be able to adjust the Electret Microphone Sensitivty.
    To Run off USB.

    At the moment I believe the power from the Microphone needs to be amplified but I dont know how or how much to amplify it by.

    The Mic :
    (0dB = 1V/µbar at 1kHz, Vcc = 4.5V, Rl = 1kΩ) 60dB ±3dB

    Done a bit more digging around and found these circuits which I mocked up in iCurcuit....

    Source for the left one :
    Source for the right one (with video) :

    They both seem to work when simulated so was hoping for some input on wether they will actually work, which ones better or if there is a better solution.

    Any help appreciated.

    Attached Files:

  2. Sizer


    Nov 6, 2012
    After some advice from other forums, Ive now updated the curcuit...what do you think?

  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Why the resistor in series with the battery, and what is that thing with the red dot near the battery and kinda in parallel with it?

    Is there supposed to be an input to this? And you realise that all the LEDs will come on at once. That doesn't seem to be what you want.

    If I were you, I'd look up the LM3914 / LM3915. They probably do what you're after.
  4. Sizer


    Nov 6, 2012
    The resistor, i cant rememebr lol..(i think it was to control the input to the op-amp, a voltage divider iirc.)
    Based on this

    The red dot is a electret mic, thats how it comes up in the app.

    And yes i do want all leds to light up at the same time with in response to the mic.

  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    OK, then the electret is shown connected entirely the wrong way.

    Remove the electret and 1k pot (entirely) and remove the other 1k resistor so that the anode of the LED(s) connects directly to the battery.

    Now you're going to have to redesign an input circuit to make the electret feed into the op-amp.

    Oh, and the op-amp is biased to ground. This isn't especially bad as long as your op-amp allows this. But it does mean your input level needs to ne relative to ground. Probably easier to have a capacitor to block the DC offset from the electret.

    I'm far from anything I can draw and/or scan a diagram, so maybe someone else can help.
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