LED light organ with Mic

Discussion in 'The Projects Forum' started by Kieiks, Aug 24, 2014.

  1. Kieiks

    Thread Starter New Member

    Jul 21, 2014
    3
    0
    Hello all,

    I´ve been reading quite a lot about different circuits on how to make a mic signal or jack signal turn into blinking leds.

    I like to understand what I'm doing when following the schematics from other people, so I can in the end, build on my own.

    I tried different things, when I came up with the following solution attached below.
    I imagined I could use my TIP31 transistor to amplify a first time the signal and take this to the LM386, giving another 20x and send it to the LEDs.

    Could someone help me debugging it? When I turn on the power, the Leds are constantly bright and the mic signal has no effect into it.

    Thanks!
     
  2. ronv

    AAC Fanatic!

    Nov 12, 2008
    3,292
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    What kind of microphone are you using? If it is electret you will need to bias it. The 386 is a single supply op amp so the output will be at 1/2 the supply voltage or 4.5 volts, so you need the capacitor like in the data sheet. If I remember correctly the 368 is capable of a gain of 200 so you may not need the extra amplifier in front of it.
    Take a look at the circuits in the data sheet for some circuits.
    http://www.mouser.com/ds/2/405/snas545a-56527.pdf
     
    Last edited: Aug 24, 2014
  3. Kieiks

    Thread Starter New Member

    Jul 21, 2014
    3
    0
    Will the capacitor remove this 4,5V and leave only the amplified signal?
    I don't have a 250 uF (on the datasheet), do you think a 1000 uF or a 500 uF (using in series) would work as well?

    I'll try it!
    Thanks
     
  4. Kieiks

    Thread Starter New Member

    Jul 21, 2014
    3
    0
    For the microphone, I have an electrec mic which I connect to the 9V through a 10k resistor.

    I tried to add the capacitor on the output of the LM386, and then instead of having it all bright, the LEDs just turn down and don't blink even screaming at it =)

    I also tried only the LM386 with 200 gain, same issue. With capacitor I got no lights at all, without it, LEDs always bright.

    I have two mics, but none gives any reaction to sound. Don't have any way to test them tough =(
     
  5. to3metalcan

    Member

    Jul 20, 2014
    228
    23
    The LM386 automatically biases at 50% of the supply rail...it's continuously outputting 4.5V DC. I suspect your problem comes from not taking this into account. That voltage is turning the led's on continuously. When you add the cap, it is blocking this voltage, which turns them all off. It diesn't sound like your amplifier is passing any microphone signal at all.

    Start with the connections at the inverting input...What is the purpose of that voltage divider? All it's doing is putting .3V or so at the inverting input.

    (Also, you can omit R6 and C3 at the output...they're helpful for protecting speakers from high-frequencies, but aren't really necessary here.)
     
  6. ronv

    AAC Fanatic!

    Nov 12, 2008
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    Try this one:
    This is not the best way to do it.... but..;)
     
  7. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,176
    397
    Put Bill's index, in find box, upper right, this page. Down to LEDs 555s, Flashers, light chasers----, ch 12,Special effects, fig 12.4, ex B.
    Biggest difference is in rectifing & lightly filtering the signal to give just the envelope of the signal to drive the LEDs.
     
    Last edited: Aug 26, 2014
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