What I did until now is summarized here:
I bought a fetal Doppler from Amazon and tested it on myself.

I found there is no need for gel, and that it is quite easy to find my own heart. It is probably much more difficult to find the heart of a baby in the womb. Future mothers must be warned that it is not a magic tool, my heart is probably one hundred times bigger than a fetus heart. In retrospect those fetal Doppler are impressive!

I acquire my heart sounds and transfered them on a Linux box. There I studied their spectrum and other characteristics.

Next I studied the Physionet Cinc 2016 challenge in order to train their most successful software on my heart sounds.

Alas I do not have bought the Matlab libraries that are needed and an attempt to use Octave (open source alternative) gives no satisfactory outcome.

Anyway as my goal is to implement this on a low cost processor of the Arm family or even less powerful, Matlab/Octave was out of question.

As I can program in Java I wrote my own program, which mimics the winning physionel 2016 code. I have great confidence that I can translate this Java code in machine language (I used to work on a small Java machine long ago). And the Java code could be a reference implementation.