File content as of revision 0:010b908e2187:

/*
Arduino-MAX30100 oximetry / heart rate integrated sensor library
Copyright (C) 2016  OXullo Intersecans <x@brainrapers.org>
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#ifndef MAX30100_FILTERS_H
#define MAX30100_FILTERS_H

// http://www.schwietering.com/jayduino/filtuino/
// Low pass butterworth filter order=1 alpha1=0.1
// Fs=100Hz, Fc=6Hz
class  FilterBuLp1
{
    public:
        FilterBuLp1()
        {
            v[0]=0.0;
        }
    private:
        float v[2];
    public:
        float step(float x) //class II
        {
            v[0] = v[1];
            v[1] = (2.452372752527856026e-1 * x)
                 + (0.50952544949442879485 * v[0]);
            return
                 (v[0] + v[1]);
        }
};

// http://sam-koblenski.blogspot.de/2015/11/everyday-dsp-for-programmers-dc-and.html
class DCRemover
{
public:
    DCRemover() : alpha(0), dcw(0)
    {
    }
    DCRemover(float alpha_) : alpha(alpha_), dcw(0)
    {
    }

    float step(float x)
    {
        float olddcw = dcw;
        dcw = (float)x + alpha * dcw;

        return dcw - olddcw;
    }

    float getDCW()
    {
        return dcw;
    }

private:
    float alpha;
    float dcw;
};

#endif