[time-nuts] Off topic project sort of heart rate monitor NEED BEATS PRE MINUTE TO ANALOG VOLTAGE

[Ed Breya]

If you only need cardiac pulse rate, an optical pulse-oximeter type 
interface - but without the oximetry part - would be much simpler than 
an ECG system, and it doesn't need galvanic connection. If you need more 
than that, then ECG methods should suffice.

Back in the 1970s, there was a lot of interest in biofeedback and TM 
techniques, using ECG and EEG. Common feedback signals were sound and 
light related to the detected physiological signals. A chart display is 
a good visual feedback with dynamics too, and it records the events for 
further study, so you can investigate the QRST details and whatever else 
is interesting. Detecting and processing the signals is nearly trivial 
now with modern electronics - it wasn't even that hard back then. If you 
study what's transpired over the last forty years, you'll get a pretty 
good idea of the whole history of the field, and the technologies 
involved. Nowadays of course, the PC can take care of most of the 
processing and feedback/indicator functions.

For a DIY, I'd recommend for each channel run the high-gain 
instrumentation amplifier into a V-F or FM converter to translate the 
signal into a workable frequency range like a few hundred Hz, then use a 
sound card and SW to post-process. Copy front-end interface ideas from 
the real stuff - professional medical equipment - to make sure it's safe 
to hook up to your own hide. If you don't need absolute details, you can 
AC-couple the physiological signals into the V-F process with 
appropriate time constants, to avoid the drift, and average in SW.

I doubt that interest in this area has waned over the decades, so it's 
likely there are all kinds of cooler, newer stuff available off-shelf, 
so you may be able to find it ready to go - and even way beyond what you 
had in mind.

Ed