Microphone question

Discussion in 'Homework Help' started by FBorges22, Jan 13, 2010.

  1. FBorges22

    Thread Starter Active Member

    Sep 11, 2008
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    Greetings,

    I have a question about the standard PC microphone. What are the voltage range (min and max ) of the audio output pin?

    Thanks,
    FBorges22
     
  2. retched

    AAC Fanatic!

    Dec 5, 2009
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    I believe it is 0w to .25w min to max
     
  3. Audioguru

    New Member

    Dec 20, 2007
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    Microphones are not rated in Watts.
    The output is about 10mV (0.01V) RMS when you speak in a normal voice about 20cm away. Electret mics have a FET transistor inside that needs to be powered from a few volts DC through a resistor of 3.3k to 10k ohms.
     
  4. retched

    AAC Fanatic!

    Dec 5, 2009
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    you are correct sir. I was recalling a spec for a mic preamp input stating do not exceed 1/4 watt on input.
     
  5. FBorges22

    Thread Starter Active Member

    Sep 11, 2008
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    I have another question... the sound card microphone input accept what voltage range?

    I am trying to use the pc sound card as a data acquisition system. Is that possible? I think that signal conditioning at lower voltages is a little bit hard...
     
  6. Audioguru

    New Member

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    You will need to attenuate the output of your circuit for it to feed the mic input of a sound card. A mic has an output of 10mV and might be overloaded if the signal is 50mV.
     
  7. FBorges22

    Thread Starter Active Member

    Sep 11, 2008
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    Let me see if I understood correctly... The microphone input only accept an input ranging from 0V to 10mV RMS? That will be very hard to make the signal conditioning at these voltages...
     
  8. Audioguru

    New Member

    Dec 20, 2007
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    The mic input is from 0V to maybe 50mV. The low noise preamplifier on the sound card works perfectly from such a low signal level.

    What signal conditioning do you need and where will it be done? Can't the pc use Audacity or another software for signal conditioning?
     
  9. FBorges22

    Thread Starter Active Member

    Sep 11, 2008
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    Well... basically I need to measure a high voltage signal using the pc sound card. This signal has 14VAC and I am trying to see the waveform and make some measures in him.
     
  10. Audioguru

    New Member

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    Two series resistors will attenuate the 14VAC down to 10mV.
     
  11. FBorges22

    Thread Starter Active Member

    Sep 11, 2008
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    However, the PC sound card does not accept negative voltage values? I need to dislocate this AC signal to the 0V->50mV range? Also it may be necessary to implement a active filter to reduce some of the input noises?
     
  12. Audioguru

    New Member

    Dec 20, 2007
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    A mic input on a pc is usually biased at a positive voltage for an electret mic. Use a coupling capacitor to feed it your attenuated AC signal.
    Remove hum and hiss noises with active filters before you attenuate the signal.
     
  13. FBorges22

    Thread Starter Active Member

    Sep 11, 2008
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    Ok... I will try to project the signal conditioner using those parameters...
    Thanks
     
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