Sounds like an interesting project, we'd love to hear more! At a high level, it sounds like what you're looking for is a high order band pass filter of some kind. Assuming the biopotential (or body signal) that you're looking at is EMG, then it also sounds like you're mostly focused on the very low end of that spectrum. The DEVLPR (an Arduino shield we make) measures across the entire spectrum of EMG (10ish-500Hz). It uses AC coupling to create an effective high pass filter, removing that voluntary movement signal that is right around 0Hz. If you're curious, this is the reference circuit (page 171) we used and a longer explanation. Then you're left with the low pass side of the problem, and there should be a lot of good software solutions for that. We could also work with you to generate some filter coefficients or something along those lines if that's something you think would be helpful. So I would say measure EMG, do filtering/digital signal processing to make sure you're measuring the frequency band you care about, and then you could do a Fourier Transform or a Wavelet Transform to confirm your work. Hopefully that helps, and if not don't hesitate to tell me where I got it wrong. 😉