Sound Activated LED

Discussion in 'General Electronics Chat' started by Dlong88, Nov 9, 2010.

  1. Dlong88

    Thread Starter New Member

    Nov 9, 2010
    26
    0
    This is my first post on here and I am new to electronics, for I am a programmer and lack the knowledge of the electrical engineering.

    With this is mind I have created a circuit to light a LED from the input of a mic element. The circuit works correctly for if the sound is soft or loud the brightness of the LED reflects it.

    Problems:
    - Since this circuit will eventually be running on batteries, and the batteries will lose voltage, the resistance set from the potentiometer will need to be constantly be readjusted.
    - The LED does not get bright enough unless it is right in the mouth of the speaker.

    Is there a better way of achieving this?
    Thanks for your help.

    Here is the circuit diagram-----
    [​IMG]
     
    Last edited: Nov 9, 2010
  2. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
    201
    Put LED in series with the resistor, not across the transistor.

    Don't know what kind of mike that is but some work could be done there as well.
     
  3. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
  4. Dlong88

    Thread Starter New Member

    Nov 9, 2010
    26
    0
    Well if i run the LED in series with the 150 transistor it does the opposite effect. It is constant lit when sounds enters, it then dims. Was I supposed to run with the 10 resistor?
     
  5. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Depends on what you are after. Typically you want LED light with sound, but this isn't a must or a given. The amplitude of the signal from a mic is going to be small, so you need to increase it, and possibly make it variable gain.
     
  6. Dlong88

    Thread Starter New Member

    Nov 9, 2010
    26
    0
    Ok well the desired effect is to have it light with sounds so running across the resistor worked. What was the purpose of being in series with resistor?
     
  7. Dlong88

    Thread Starter New Member

    Nov 9, 2010
    26
    0
    I have looked at chapter 12 of the link provided. I see that that i should create the throbbing effect with the mic as the input to the 555? Also I am using 3 volts not 9 so would the resistance then be different?
     
  8. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    You are referring to PWM. It doesn't have to use a 555 (see the RGB LED driver). PWM is good for large currents. I'd put your circuit as very comparable to the single transistor I put in there. For both you need a simple audio amp boosting the signal level (preferably with a volume control).
     
  9. Dlong88

    Thread Starter New Member

    Nov 9, 2010
    26
    0
    What drives volume besides the volume of the actual speaker. How can I amplify the output signal of this mic which is a 34H4S.
     
  10. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    That is the million dollar question. There are quite a few options, I tend toward a class of chips called op amps. I'll have to get back with you with a schematic, assuming someone else doesn't beat me to it.
     
  11. Dlong88

    Thread Starter New Member

    Nov 9, 2010
    26
    0
    great! I appreciate your help.
     
  12. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
  13. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Google has never heard of your 34H4S microphone. What type is it (electret or dynamic) and who makes it?
     
  14. Dlong88

    Thread Starter New Member

    Nov 9, 2010
    26
    0
    Sure the price on the speaker seems fine. The mic I am using is from my Dads collection from god knows when so the only info i can give you about it is what is engraved around it, which I have already provided. As far as i can see just from appearance it looks like a standard mic element. I guess it is so old it cant be found HA, which holds true then for most of my equipment unfortunately...
     
  15. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Nothing wrong with old equipment. The speaker I referenced could be any junk box speaker for this experiment.

    The reason it matters is there are several different types of microphones, and they require different types of biasing. If you included a picture of the mic AG could probably give good advise on how to bias it. I tend to use magnetic types of microphones (which speakers can be considered a subclass of).

    If you have a pile of parts let use know what you have, I can probably cobble something together schematic wise. Do you have a breadboard similar to the picture below, or are you soldering this together on a perfboard?

    [​IMG]
     
  16. Dlong88

    Thread Starter New Member

    Nov 9, 2010
    26
    0
    Yes i have a breadboard, also I have a multimeter, and I also have an oscilloscope. As far as materials I have a Radio shack right down the street if I'm missing something needed.

    This is what my mic looks like. I will take a picture of mine if needed, but my camera is with a friend... Does this help?
    [​IMG]
    [​IMG]
     
    Last edited: Nov 13, 2010
  17. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    A speaker, especially a cheap little one has a strong resonance that causes very poor sound when used as a microphone. A dynamic microphone also has a voice coil and magnet but does not have a strong resonance.

    An electret mic is small, inexpensive and has excellent sound quality. It needs to be biased with 0.5mA to power its Jfet inside.
     
  18. Dlong88

    Thread Starter New Member

    Nov 9, 2010
    26
    0
    Ok so getting a electret mic will solve my brightness issue. Still I have this resistance problem. Hooked up to the breadboard of course has a constant voltage while if I were to power by battery they will soon start to spend their energy thus needing a readjustment of the pot to get resistance at the ideal lvl again.
     
    Last edited: Nov 13, 2010
  19. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Your LED is not bright because your mic is missing a preamp. Even an electret mic needs a preamp. You posted the photo of an electret mic. One pin connects to its metal case and should connect to the (-) of the battery. The other pin is the output signal that connects to the resistor that powers it and to the input of a preamp.
     
  20. Dlong88

    Thread Starter New Member

    Nov 9, 2010
    26
    0
    Ahh so that is what Mr.Marsden is designing the preamp. Yes i have looked up many circuits that amp but they don't seem they are designed for this simple circuit.
     
Loading...