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dukedevil

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Posts posted by dukedevil

  1. Electronic Stethoscope

    in Projects Q/A

    Posted

    I was also wondering if you might be able to post a picture of the mic and it's holder.  Where is the rubber grommet placed?  The noise I hear is a small intermittant bursts of static.  It's difficult for me to tell whether I'm hearing a heart beat or whether all I'm hearing is noise.  Is the gain of your entire circuit about 10*20 or 200? Thanks.

  3. Electronic Stethoscope

    in Projects Q/A

    Posted

    Hi again,
      I was just curious what the sensitivity and signal to noise ratio of your microphone was.  I have the circuit built, but I'm having a hard time distinguising between possible heart beats and random noise.  Is there anything I might do to help with this?  I was also wondering if the gains of the circuit are enough to magnify the signal enough to be audible.  From my calculations given a microphone with a sensitivity of -35 dB, I find that heart sounds would only produce outputs at the microphone of around 10 microvolts.  To magnify this to the audible range, it seems like a total gain of 1000 or more would be necessary.  Thanks for any help you can give me.

  4. Electronic Stethoscope

    in Projects Q/A

    Posted

    Hi again,
      I was just curious what kind of voltages are output from the microphone from a heart beat.  I ask because I haven't bought a microphone yet and I just wanted to input a sine wave to make sure the circuit works.  I'd like to know what voltage to input into the circuit.  Thanks for any help you can provide.

  5. Electronic Stethoscope

    in Projects Q/A

    Posted

    Thanks a lot for a quick response!! Since I have to build this circuit for a class and justify why each component is a certain value, I was wondering if there is a certain reason for the gains in the circuit (for example, why does U1a have a gain of 3.9 and U1b have a gain of 1.6?)  Thanks again!

  6. Electronic Stethoscope

    in Projects Q/A

    Posted

    Dear all,
      I am just starting to work on this project for a design course.  I was trying to understand the uses of each of the components in the circuit diagram.  What are the uses of R1, C1, and R16?  Do they create a voltage divider?  If so, what is the output voltage supplied to the mic?  Thanks for all of your help!

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