Originally Posted by narco
my first thought is find a sample
second thought is go to a medical institute, maybe somewhere like a school of medicine where they be more likely to do something outside the call of duty, maybe a midwife, they have machines for listening to heart beats.
third thought is use a piezo pickup, if you can't find one, rip one out of an acoustic guitar and tape it to your chest, might work..
Don't go tearing up your guitar. You can get piezoelectric elements at any electronic parts supplier for a buck or two. Then you just have to build an appropriate preamplifier, so... SMash that guitar!
or, just as seriously, and without having tried it, if you have an old unused dynamic mic, preferably with a busted diaphragm, try substituting a crystal onto the mic's circuit, and feed that into your board. Then tell me if it works.
Or, if you're that ambitious, most modern stethoscopes are electronic instruments, meaning that they've already gone to the trouble of transducing the sound from an audio signal to an electric one, so you should really only have to tap a wire in, and move that analogous electrical signal into some other equipment. Again, talk to a hospital, and see if they have an old electrical stethoscope they're getting rid of.