RE: heart beat detector
I have had some experience with cardiac monitors and what you are trying to do is no simple task.
First remember that these Holter monitors are not recording the heart rate but rather the actual heart electrical activity (waveform). The heart is much like a piezo device in that its mechanical activity produces an electrical output (EKG). Similarly, electrical pulse to the heart produces mechanical motion (defibrillator).
Next be advised that the EKG signal is typically 1 millivolt but may be much smaller. Many things affect the amplitude including the particular body chemistry as well as skin pigmentation when using external 'pads'. Also the amplitude can change with body position, standing vs prone. You will need to become familiar with EKG lead configurations such as I,II,III,aVR.etc as well as the lead placement. You will need electronic amplifiers with low noise and high common mode rejection.
And lastly, and not to descourage you, but your device will have to be submitted to the FDA for approval under 510K as this device has already been marketed in principal.
I recently has to wear one of those Holter devices and your right they are no fun to sleep with. Mama is much better.
Personally I encourage you to continue.
TomB