I am trying to get a useable wave from a pulse oximeter, but there is a pesky DC bias that keeps changing every now and then, so I cannot simply subtract the DC bias from it and get useable results for long. I also tried to take an appropriate sampled running average, and subtract that from my wave, and it gave me much better results than before.
However, I am told that a DSP high pass filter will work even better, and I am trying to implement that. I am not an electrical engineer and do not have much knowledge about filters, and absolutely no knowledge of DSP. I found this great website that lets me design a DSP filter and gives me a C++ library to use that filter in my code.
The problem is, I want to design a filter that cuts below 1Hz and lets through any frequencies above 1Hz or 1.3Hz max. My oximeter wave is 1.4Hz. But the design tool I mentioned above seems to indicate that it is not possible.
Any help in this would be highly appreciated.
I have finally managed to make it work a bit, but the DC bias is still there. (red line is the data filtered from the filter from that website, blue line is moving average subtracted from incoming signal)