i need help in my project. i made a electronic stethoscope but theres too much noise in the output. i need to reduce this noise but dnt know how. secondly i have to implement the adc block in hardware. need help there too. i used this circcuit http://www.aaroncake.net/circuits/steth.asp
Or noises from the actual stethoscope head such as rubbing? A stethoscope is a very high gain instrument whether it be mechanical or electronic. It's always going to produce a lot of other noise.
As for the ADC, what are you trying to accomplish? Measure the beats? In that case you already have an ADC in the form of the sound hardware on your computer/tablet/phone. Just write the software.
main problem with noises 1. on oscilloscope there's a lot of noise even when there is no input. 2. there's a constant hissing noise when i record it. 3. as i have to implement the adc block using pic then all this noise is a problem for me. plus i forgot to mention the amplifier IC i am using is NE5532.
It is a cheap simple circuit so it uses a fairly noisy and cheap LM386 power amp IC. There are a few low noise expensive audio power amp ICs available that can be used instead.
The NE5532 is low noise but I do not know if you are also using the noisy LM386. The LM386 is used to drive low impedance headphones. Do not use the LM386 if you do not have low impedance headphones.
i am using LM386. what should i use instead? i have to give this signal to pic16f877a for adc part and will be the serial input to my lappy for where ill transmit it to the other end using LAN. so noise is a big problem
Since you do not use low impedance headphones then the noisy LM386 power amp IC is not needed. Use a low noise opamp instead. The gain of the LM386 is only 20.
whats the overall gain of this circuit? the pre-amp is providing 21 gain. filter 1.6 and lm386 20. so the overall gain is 672. i read somewhere that the gain is divided by 2. now i am confused
whats the overall gain of this circuit? the pre-amp is providing 21 gain.
No it is not because the electret mic has a fairly high output impedance that is in series with R2. The gain of the preamp is somewhere from 3.9 to about 9.6 when fed from an electret mic.
quote:The gain of the filter is 1.6.
Yes.
quote:The gain of the lm386 is 20.
Yes.
quote:so the overall gain is 672.
No. It is somewhere from 124.8 to 307.2.
quote:i read somewhere that the gain is divided by 2.
I know this thread is old, but I was wondering if there was a way to hook this circuit up to a computer to record the sounds. The way it is now leaves a lot of distortion and noise in the recording. I think it has something to do with the biasing of the microphone/line in jack on the computer. The computer I am using has a bias of of about 2.8volts. thanks!
the output of this project is line level that is about 22 times too high since the audio input on a computer is microphone level. Only two resistors are needed to make an attenuator.
The bias voltage for an electret mic can be removed by using a coupling capacitor to the mic input of a computer.
Some computers record only speech so they have poor response to the very low frequency from heartbeats.
I am now using the line in on the computer and I have bypassed the LM324 going straight from the TL072. It's obviously a little quieter but you can definitely hear the heartbeat.
Would you recommend switching it back to the mic and trying to get it to work that way? Or am I on the right track? thanks!
I am now using the line in on the computer and I have bypassed the LM324 going straight from the TL072. It's obviously a little quieter but you can definitely hear the heartbeat.
The circuit does not have an LM324 quad opamp. It uses an old 741 single opamp to blink the LED.
quote:Would you recommend switching it back to the mic and trying to get it to work that way? Or am I on the right track?
Switch what back? The output of the volume control R11 can feed the line level input of a computer.
i need help sir. i made electronic stethoscope circuit but there is a noise at output sir n mic is not picking up heart beat sounds n which type of wire we should use for mic sir. why i am not geting output sir. plz help me sir
You did not describe the noise. Is it low frequency hum because you did not use shielded audio cable from the electret mic to the circuit? Is it high frequency hiss because you did not use a TL072 low noise dual opamp?
Electronic stethoscope
Posted - Jul 20 2013 : 03:42:17 AM
