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# dukedevil

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1. ## Electronic Stethoscope

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.
2. ## Electronic Stethoscope

I did build project 2 and I didn't substitute any parts. Do you know what the specifications are for your microphone?
3. ## Electronic Stethoscope

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

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

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

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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