Sound Activated LED

Discussion in 'The Projects Forum' started by uday159, Apr 25, 2012.

  1. uday159

    Thread Starter New Member

    Apr 25, 2012
    9
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    Hey guys

    I need some help with a circuit i am looking to build for school.

    I want to power a circuit that i have previously built that currently has a switch, but i want to replace that switch with something to make it sound activated.

    I am really new to circuits so I would really appreciate the most information I could get.

    The circuit has 2 leds that flash in sequence and i want them to flash when the circuit detects sound. I understand that I need an electret mic, but I dont know how to make the preamp and how it should connect to my circuit.
     
  2. russpatterson

    Member

    Feb 1, 2010
    351
    16
    If you Google 'electret mic circuit' you'll get a bunch of ideas.

    Looks like a straight forward schematic using an op-amp here:

    http://www.alanmacek.com/usb/

    Then put the output to an analog input pin on your uC and then trigger when you read a value over 128, or whatever works for what you want (sound level).
     
  3. uday159

    Thread Starter New Member

    Apr 25, 2012
    9
    0
    Could you explain the last part in simpler terms. This is literaly my 3rd circuit project and have mostly only used transistors capcitors and LEDs.

    Or could you send me a link for how I could do this. Im really new to this stuff.
     
  4. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
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    Post the schematic of your existing flasher.
     
  5. uday159

    Thread Starter New Member

    Apr 25, 2012
    9
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    Will do tommorow.

    Gotta get it from my laptop and its in my locker at school.

    I can take a picture of the circuit, dont know how much it will help

    Ill post it here soon.

    *Edit* Cant take a picture not neat at all. Anyone know a circuit maker program online?
     
  6. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
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    Actually we may not need the schematic. Post the operating voltage and whether the flashing is switch operated. If so, is it High side or low side switching.
     
  7. uday159

    Thread Starter New Member

    Apr 25, 2012
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    0
    The operating voltage for the circuit is 6V (4 AA Batteries). The flashing is just continuous as long as a power source is connected which in this case is the 4 AA batteries. What I want to do is make a sound activated switch that will activate the flashing when it picks up noise and stop the flashing when their is no more sound
     
  8. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
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    You're also going to want something to convert the audio to a pulse that's stretched. A 555 would be a good choice for this. A single NPN AF Amp/Trigger stage should work fine with an electret mic.
     
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  9. #12

    Expert

    Nov 30, 2010
    16,298
    6,809
    You might take parts of this circuit to make what you want.

    One advantage is that it doesn't require an IC to get the mic to work.
     
  10. uday159

    Thread Starter New Member

    Apr 25, 2012
    9
    0
    Alright thanks.

    By any chance, would you happen to have a diagram of this?

    So the basic idea of what you told me will give me 6V too right and I can connect the output to my resistors on my other circuit?

    Thanks for the help.
     
  11. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    I'll draw one up for you. Your current flasher circuit and the Mic interface will be powered by the same batteries.
     
  12. uday159

    Thread Starter New Member

    Apr 25, 2012
    9
    0
    Thanks man, could really use that diagram.

    This thing is due either tommorow or monday so its really appreciated.
     
  13. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    Whoa thar pardner! That statement tells me this is your homework. I can't do your homework for you. It's against AAC policy and mine too.

    Sooo, here's the deal. In an hour or two I'll be posting a schematic but YOU will have to fill in most of the component values.
     
  14. uday159

    Thread Starter New Member

    Apr 25, 2012
    9
    0
    Oh this isnt homework. Im just adding this to my circuit to make it better. The flasher is actually the homework and that is already done. So technically this isnt homework just using it to improve.

    BTW im in grade 10 im just trying to improve and want to try to add this.
     
  15. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    Check your flasher circuit to see if it'll operate on 4V. As you can see from this plot the 555 will output about 4.6V. If you absolutely need the full battery voltage of 6V then we'll have to add another transistor stage to the output of the 555.

    For other members that are curious how 181mV is turning on an unbiased BJT, it isn't. I didn't have an Electret Mic in my library so a made an Electret macro. That mic is actually a Piezo Mic driving a JFET. The signal you see is the input to the FET's gate. The FET outputs over 1V.
     
    Last edited: Apr 27, 2012
  16. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The output of an electret mic is about 14mV peak with voices nearby which is not enough to turn on your transistor.
     
  17. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    AG, thanks for your input but I find your statement Odd. Electrets are amplified elements. I've always believed they put out more juice than any other types, crystal, dynamic, carbon, Piezo etc. When I was in the marine electronics business I replaced many dynamic Mic elements with Electrets with no problem at all. Besides, the OP didn't state a range requirement and range can be improved with a simple hearing horn (ear trumpet) design. This way he gets to combine old technology with the new. :D

    The specs on this one seems to confirm my belief.
     
  18. Audioguru

    New Member

    Dec 20, 2007
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    The sound level for 1 Pa is pretty loud at 94dB. Then the output of the electret mic you posted is only 5.9mV. Of course a preamp with a fairly high gain is needed.

    The electret mic you posted is a little more sensitive than a Shure SM58 vocals dynamic mic.
     
  19. uday159

    Thread Starter New Member

    Apr 25, 2012
    9
    0
    So i already handed in the project and couldnt add in the sound activated to the blinker.

    Can you tell me the values of R1, R2, R4 and C3 because i still really want to build this. Also what is the Trig? Im really new to this stuff so help is very appreciated.
     
  20. Audioguru

    New Member

    Dec 20, 2007
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    The IC is an NE555 or LM555 timer. There are hundred of tutorials about it on the web and its datasheet also tells all about it.

    R1 powers the Jfet inside the electret mic with about 0.5mA of current.
    TRIG is the pin 2 Trigger input of the 555 timer IC.
     
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