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[SOLVED] Heart beat sound detection.

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Gautam Kumar

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Hello Everyone,
Below is the circuit that I have simulated in the LT-Spice.
Acoustic Ckt.jpg



graph.jpg



Here for the power supply (+11v and -11v), I have used Boost converter.

Here the problem is at real time implementation.

The input to the circuit is being given using contact microphone and output is being taken using earphone (The Moto is to detect the heart beat sound).

When I am recording the signal in laptop and then listening it, I am able to detect the heart beat sound, whereas in real-time when I am trying to listen the sound (without recording), I am not able to hear on my earphone.

The circuit after the node out1 has been used to amplify the signal.

Please suggest any solution to this problem.

Thank you.
 

KlausST

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Hi,

I can't see where the difference is between recording and direct earphone listening. (Did you tell?)
Thus I can't help.

But your circuit is extremely complicated for what it does.
I'd say 1/5 (or may be less) parts could do the same, or even better. Less effort, less cost...

Klaus
 

Gautam Kumar

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Hi,

I can't see where the difference is between recording and direct earphone listening. (Did you tell?)
Thus I can't help.

But your circuit is extremely complicated for what it does.
I'd say 1/5 (or may be less) parts could do the same, or even better. Less effort, less cost...

Klaus


Previously I have used Class AB amplifier in simulation after the instrumentation amplifier and filter to amplify the low amplitude signal, but didn’t have better result, that’s why I am trying with this complex circuit.

Here in the simulation I am getting better result than before, but the problem is in real time implementation.

In real time when I am giving high amplitude sound to the microphone, it is responding well i.e. I am able to listen it, but when taking the microphone at chest to listen the heart beat sound, at that time not able to listen it.

Means here the problem is with very low amplitude signal.

Please suggest any way to sort out this problem.

Thanks
 

Audioguru

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Your input signal is very low then the amplifiers need a lot of gain. Your output amplifier has a gain of only 1+ (50k/5k)= 11 times but it needs a gain of maybe 200 times like a simple LM386 amplifier with a capacitor between its pin 1 and pin 8.

Your instrumentation amplifier has one input grounded then it might pickup a lot of mains hum.
You are overloading the microphone with your 2.2k ohms input resistor. Its datasheet for the mic shows a load of 100M ohms and the extremely high input resistance of a Mosfet.

Your schematic has its parts so far apart that the symbols and text are tiny and impossible to see.
 

Gautam Kumar

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Your input signal is very low then the amplifiers need a lot of gain. Your output amplifier has a gain of only 1+ (50k/5k)= 11 times but it needs a gain of maybe 200 times like a simple LM386 amplifier with a capacitor between its pin 1 and pin 8.

Your instrumentation amplifier has one input grounded then it might pickup a lot of mains hum.
You are overloading the microphone with your 2.2k ohms input resistor. Its datasheet for the mic shows a load of 100M ohms and the extremely high input resistance of a Mosfet.

Your schematic has its parts so far apart that the symbols and text are tiny and impossible to see.
Thanks for the suggestion , now i am able to hear the heart beat sound.
 

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