MAX30100_SpO2Calculator.cpp

00001 /*
00002 Arduino-MAX30100 oximetry / heart rate integrated sensor library
00003 Copyright (C) 2016  OXullo Intersecans <x@brainrapers.org>
00004 This program is free software: you can redistribute it and/or modify
00005 it under the terms of the GNU General Public License as published by
00006 the Free Software Foundation, either version 3 of the License, or
00007 (at your option) any later version.
00008 This program is distributed in the hope that it will be useful,
00009 but WITHOUT ANY WARRANTY; without even the implied warranty of
00010 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00011 GNU General Public License for more details.
00012 You should have received a copy of the GNU General Public License
00013 along with this program.  If not, see <http://www.gnu.org/licenses/>.
00014 */
00015 
00016 #include <math.h>
00017 
00018 #include "MAX30100_SpO2Calculator.h"
00019 
00020 // SaO2 Look-up Table
00021 // http://www.ti.com/lit/an/slaa274b/slaa274b.pdf
00022 const uint8_t SpO2Calculator::spO2LUT[43] = {100,100,100,100,99,99,99,99,99,99,98,98,98,98,
00023                                              98,97,97,97,97,97,97,96,96,96,96,96,96,95,95,
00024                                              95,95,95,95,94,94,94,94,94,93,93,93,93,93};
00025 
00026 SpO2Calculator::SpO2Calculator() :
00027     irACValueSqSum(0),
00028     redACValueSqSum(0),
00029     beatsDetectedNum(0),
00030     samplesRecorded(0),
00031     spO2(0)
00032 {
00033 }
00034 
00035 void SpO2Calculator::update(float irACValue, float redACValue, bool beatDetected)
00036 {
00037     irACValueSqSum += irACValue * irACValue;
00038     redACValueSqSum += redACValue * redACValue;
00039     ++samplesRecorded;
00040 
00041     if (beatDetected) {
00042         ++beatsDetectedNum;
00043         if (beatsDetectedNum == CALCULATE_EVERY_N_BEATS) {
00044             float acSqRatio = 100.0 * log(redACValueSqSum/samplesRecorded) / log(irACValueSqSum/samplesRecorded);
00045             uint8_t index = 0;
00046 
00047             if (acSqRatio > 66) {
00048                 index = (uint8_t)acSqRatio - 66;
00049             } else if (acSqRatio > 50) {
00050                 index = (uint8_t)acSqRatio - 50;
00051             }
00052             reset();
00053 
00054             spO2 = spO2LUT[index];
00055         }
00056     }
00057 }
00058 
00059 void SpO2Calculator::reset()
00060 {
00061     samplesRecorded = 0;
00062     redACValueSqSum = 0;
00063     irACValueSqSum = 0;
00064     beatsDetectedNum = 0;
00065     spO2 = 0;
00066 }
00067 
00068 uint8_t SpO2Calculator::getSpO2()
00069 {
00070     return spO2;
00071 }