Lighting LEDs from Sound.

Discussion in 'The Projects Forum' started by arfarfarfarf, Mar 13, 2012.

  1. arfarfarfarf

    Thread Starter New Member

    Mar 10, 2012
    17
    0
    Hi, i have this project where I should light 20 LED's in response to an input from the microphone. as the electret microphone detects sound, the LED's light up. do you have a schematic for this? thanks!
     
  2. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Here is a schematic that has not been built yet.
    Don't use a little 9V battery because it will not last long.
     
  3. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
  4. arfarfarfarf

    Thread Starter New Member

    Mar 10, 2012
    17
    0
    Thanks again audioguru! I would just like to ask, if there are only 2 LED's in that given circuit, will a 9V battery last? What is the minimum number of LEDs to make the circuit work with a 9V battery?
     
  5. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The battery life with only 2 LEDs instead of 20 LEDs is more than 10 times longer. Maybe 15 times longer. The circuit can use only 1 LED if you re-calculate the value of the current-limiting resistor.
     
  6. arfarfarfarf

    Thread Starter New Member

    Mar 10, 2012
    17
    0
    I already made the circuit and it works, though the mic is not that sensitive. It does not recognize speech but reacts to clapping. What adjustments should i make? Plus when i tested the circuit, only one led is bright. The other one is dimmer. :)
     
  7. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Try another 10uF input coupling capacitor and another electret mic.

    If both LEDs are the same and their current-limiting resistors are the same then they should have the same brightness.
     
  8. KJ6EAD

    Senior Member

    Apr 30, 2011
    1,425
    363
    You should also make sure that the 10k pot is connected correctly so you can adjust the input sensitivity.
     
  9. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Yes, the 10k pot adjusts the sensitivity but it was designed to adjust the DC bias voltage. If it is turned down too low then the input signal must be very high to light the LEDs.
     
  10. KJ6EAD

    Senior Member

    Apr 30, 2011
    1,425
    363
    That's exactly why I mentioned it as a potential cause for the symptom of the circuit only reacting to loud sounds. A pot connected the wrong way may be always "turned down too low". It's also a common trap for neophytes.
     
  11. arfarfarfarf

    Thread Starter New Member

    Mar 10, 2012
    17
    0
    I think I connected the pot correctly, though. Its middle pin is connected to pin #2 right?
    Also, with regards to the mic, how do I test if an electret mic is working? I think I broke my mic since it took too much heat when I soldered a wire to it.

    What if, instead of using an Ic, I use a transistor?
     
  12. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    With no signal when the pot is turned down to near zero then the LEDs should light at half brightness.
    Then slowly turn up the pot and the LEDs will get dimmer and dimmer. When the LEDs are barely turned off then the pot is set correctly for the most sensitivity.

    The LM386 in that circuit has a voltage gain of 200 so it is sensitive. A single transistor with many resistors and a few capacitors will have a voltage gain and sensitivity that is half as much or less.

    I have soldered circuits for about 54 years and have never gave anything "too much heat". If the soldering iron is clean, tinned and not too hot then use rosin core solder and each joint takes 1 second to do perfectly.
     
  13. KJ6EAD

    Senior Member

    Apr 30, 2011
    1,425
    363
    The pot connection sounds right. The easiest way to test the microphone is with a known working amplifier. Most multimeters can't discern it's tiny signal from noise.
     
  14. arfarfarfarf

    Thread Starter New Member

    Mar 10, 2012
    17
    0
    That same thing happened to me while adjusting the pot, Yet I don't know why it's not that much reactive to the microphone. I really think the microphone is at fault,

    Anyway, I found this sound activated circuit but I haven't tried it yet. Any insights?
    [​IMG]
     
  15. arfarfarfarf

    Thread Starter New Member

    Mar 10, 2012
    17
    0
    That same thing happened to me while adjusting the pot, Yet I don't know why it's not that much reactive to the microphone. I really think the microphone is at fault,

    Anyway, I found this sound activated circuit but I haven't tried it yet. Any insights?
    [​IMG]
     
  16. ishaan3731

    Member

    Jun 23, 2011
    43
    1
  17. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Your new circuit is horrible:
    1) There is no current-limiting resistor in series with each LED so if the output transistor turns on the LEDs will instantly burn out if the battery is any good.
    2) The first transistor has a very low base resistor that turns it on as hard as it can go.
    I doubt that the microphone is strong enough to turn it off (so that the output transistor can turn on).
    Usually an electret mic drives 50k ohms, not the 1k resistor R2 in parallel with the input resistance of the first transistor.
     
  18. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    NO!!!!!
    This new circuit is much more sensitive than the last one because the 10nF capacitor provides positive feedback.
    It also instantly burns out its LED.

    It does not have a "condenser mic". Instead it has an electret mic.
    It does not drive a motor and the weak little transistor it uses probably will burn out if it tries to drive a motor or 20 LEDs.
     
  19. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    For those who don't really understand LEDs I wrote this tutorial. I kind of bloomed from there.

    LEDs, 555s, Flashers, and Light Chasers

    It also has circuits showing how to make LEDs responsive to sounds.
     
  20. arfarfarfarf

    Thread Starter New Member

    Mar 10, 2012
    17
    0
    I see. How about this one? There is a FET so that the current will increase. [​IMG]
     
Loading...