microphone for heart sound

Can anyone suggest the appropiate microphone for capturing heart sound ??

I once tried the same thing, with several microphones. None picked up an audible heartbeat.

The stethoscope has a diaphragm which is pressed against the skin. I believe that is the key. A larger area of detection.

If you put a tiny mic in the stethoscope tube, it might give an audible heartbeat.

Actually We have already made an arrangement for stethoscope and microphone. But the thing is Signal we are getting is quite noisy. we need to find exact location at which S1 and S2 sound is occurring and some signal processing on that.
I just need some high sensitivity microphone(name or specification ) with which S1 and S2 sounds are clearly visible.
We have a general purpose microphone with frequency response extending upto 20KHz due to which it is picking lot of unwanted signal(50Hz n it's harmonics)

I fixed an electronic stethoscope project that had errors so it didn't work.
I took a cheap electret microphone and mounted it in the lid of a jar of peanut butter. The rim of the lid sealed a sound chamber that picked up my heartbeats very well and blocked background sounds.

My fixed circuit uses an inverting opamp as a preamp because the original circuit had it but its input impedance is low and it loads down the level from the mic a little. it should be a non-inverting preamp circuit with a high input impedance.
The next opamp is a Sallen-Key Butterworth lowpass filter to reduce sounds above 103Hz.
The output uses an LM386 little power amplifier IC to drive headphones that can have a low impedance. if a speaker is used then there will be acoustical feedback howling.
There is a 741 opamp that is used to blink an LED with each heartbeat.

EDIT: The shielded audio cable that connects the mic to the preamp blocks mains hum pickup. If the preamp is built on a solderless breadboard then the strips of contacts and many wires all over the place are antennas that pickup mains hum. Use a printed circuit board.

Electret microphones are not designed for frequencies below ~20 Hz. Try to use a dynamic earphone or a small dynamic speaker with a soft membrane. The low-frequency audio circuit as described will work but try to avoid the cable and install all around the microphone in a small metal case. Use a 9V battery for DC power.

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Using a stereo headphones is also not the best solution due to their poor frequency response to < 20 Hz as needed. Use a small oscilloscope to see the pattern of heartbeat.

jiripolivka said:

Electret microphones are not designed for frequencies below ~20 Hz. Try to use a dynamic earphone or a small dynamic speaker with a soft membrane.

Click to expand...

I disagree. Electret mics have an extremely lightweight diaphragm so they do not resonate like dynamic mics and produce frequencies VERY low.

Using a stereo headphones is also not the best solution due to their poor frequency response to < 20 Hz as needed. Use a small oscilloscope to see the pattern of heartbeat.

Click to expand...

I used on-the-ear headphones that came with a Kenwood CD player and heard my heartbeats perfectly. Headphones vary in frequency response. Good ones are excellent.

Physicians use the diaphragm side for high frequencies and good skin contact. The bell side (if it has one) is used for lower frequencies and lighter skin contact.

John

Thank you sir. That helped a lot