Is a preamp needed for a PIC

Discussion in 'Embedded Systems and Microcontrollers' started by JDR04, Oct 15, 2014.

  1. JDR04

    Thread Starter Active Member

    May 5, 2011
    339
    4
    Hi Folks, my project involves using a 16F688 PIC and a electret microphone.

    I would like the circuit to be sensitive enough to detect a normal conversation in a quiet room.

    My question is, does the PIC require a preamp and amp so that the signal can be detected?

    Any suggestions or circuits will be most welcome.

    Thanks a lot......JDR04
     
  2. lightingman

    Senior Member

    Apr 19, 2007
    374
    22
    Basically, yes.

    The electret mic will need a pre-amp and a supply to it via the pre-amp.

    Daniel.
     
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    A PIC16F688 when combined with a microphone (amplified, of course) has sufficient resources to make a device such as a clapper. (Clap on, Clap off, Clap on clap off... the clapper!)

    I cannot grab any other intelligence out of a normal conversation in a quiet room.
     
  4. JDR04

    Thread Starter Active Member

    May 5, 2011
    339
    4
    Thanks lightingman.
     
  5. JDR04

    Thread Starter Active Member

    May 5, 2011
    339
    4
    Hi ErnieM, thanks for the info. Can you or anybody else suggest a circuit with minimum parts as I am limited for space. The quality of the audio is not important in this instance.

    Thanks a lot....JDR04
     
  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Just google 'microphone preamp schematic'.
     
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  7. MrChips

    Moderator

    Oct 2, 2009
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    A simple one-transistor amplifier will do. Google MPF102 preamp.

    Or something like this should work:

    [​IMG]
     
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  8. JDR04

    Thread Starter Active Member

    May 5, 2011
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    Thanks MrChips, appreciate your time.
     
  9. Markd77

    Senior Member

    Sep 7, 2009
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    Where it says output to next stage you will want a voltage divider between Vdd and Vcc, maybe two 100K resistors (I don't know how to work out the ideal values) because otherwise you will be driving the PIC input below 0V.
     
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  10. JDR04

    Thread Starter Active Member

    May 5, 2011
    339
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    Thanks Markd77. I'll give it a bash next week and let you guys know how it workeed out.

    Thanks again to everyone.......JDR04
     
  11. MrChips

    Moderator

    Oct 2, 2009
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    If you want to connect the output of the preamp to a microcontroller ADC input, power the preamp from the MCU supply and eliminate C2 in the schematic.
     
  12. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Ouch, I would not do that. A biased gain stage like this will have an output around 1/2 the supply voltage, or around 2.5 V in a PIC running off 5V.

    That should ONLY be input to an analog input. Using a digital input may result in damage to the PIC.

    As the device you are looking at cannot handle voice the best you can hope for is a clap on, clap off thing, which is implying digital.

    You would have to move up to a PIC24 in the "DS" range to hope to get a 5KHz sample bandwidth, which is what a telephone can do on a good day.
     
  13. MrChips

    Moderator

    Oct 2, 2009
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    I had assumed that the signal was going into an ADC or comparator input.
     
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