Electret Microphone Amplifier to Low pass filter

Discussion in 'General Electronics Chat' started by timobg, Jun 19, 2014.

  1. timobg

    Thread Starter New Member

    Nov 30, 2013
    2
    0
    How can I amplify an electret microphone to use the signal into a low pass filter like this?
    [​IMG]



    :)
     
  2. wmodavis

    Well-Known Member

    Oct 23, 2010
    737
    150
    You can do that by hooking the electret microphone output signal to the input of an amplifier. Be sure to provide the bias voltage required for the electret microphone to operate.
     
  3. crutschow

    Expert

    Mar 14, 2008
    13,055
    3,245
    That's a simple first-order filter with no gain. A simple passive RC low-pass filter would give the same response.
     
  4. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    5,003
    745
    Change R2 to 20k to increase the gain.
     
  5. timobg

    Thread Starter New Member

    Nov 30, 2013
    2
    0
    Thank you all for your help. My purpose is to build a glass-break detector that want to put the voltage after the filter in A2D input of a microcontroller.
    I doubt if I need to add something else to the circuit after the filter.


    Thank you very much.
    Timóteo
     
  6. crutschow

    Expert

    Mar 14, 2008
    13,055
    3,245
    It would seem that for a glass-break detector you want to record high frequency sounds and thus suppress the low frequency sounds with a high-pass filter, not a low-pass filter. :confused:
     
  7. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,546
    1,252
    Actually, there is a strong low freq, even subsonic component to a glass pane break. But beyone that:

    1. The opamp output will be bipolar, swinging above and below GND. Make sure the uC input can handle that.

    2. The more gain you add to this circuit, the more DC error there will be at the output. This is the input offset voltage times the circuit gain.

    How did you come up with 360 Hz as the cutoff freq?

    ak
     
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