/** \file algorithm.cpp ****************************************************** * * Project: MAXREFDES117# * Filename: algorithm.cpp * Description: This module calculates the heart rate/SpO2 level * * * -------------------------------------------------------------------- * * This code follows the following naming conventions: * * char ch_pmod_value * char (array) s_pmod_s_string[16] * float f_pmod_value * int32_t n_pmod_value * int32_t (array) an_pmod_value[16] * int16_t w_pmod_value * int16_t (array) aw_pmod_value[16] * uint16_t uw_pmod_value * uint16_t (array) auw_pmod_value[16] * uint8_t uch_pmod_value * uint8_t (array) auch_pmod_buffer[16] * uint32_t un_pmod_value * int32_t * pn_pmod_value * * ------------------------------------------------------------------------- */ /******************************************************************************* * Copyright (C) 2016 Maxim Integrated Products, Inc., All Rights Reserved. * * Permission is hereby granted, free of charge, to any person obtaining a * copy of this software and associated documentation files (the "Software"), * to deal in the Software without restriction, including without limitation * the rights to use, copy, modify, merge, publish, distribute, sublicense, * and/or sell copies of the Software, and to permit persons to whom the * Software is furnished to do so, subject to the following conditions: * * The above copyright notice and this permission notice shall be included * in all copies or substantial portions of the Software. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. * IN NO EVENT SHALL MAXIM INTEGRATED BE LIABLE FOR ANY CLAIM, DAMAGES * OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR * OTHER DEALINGS IN THE SOFTWARE. * * Except as contained in this notice, the name of Maxim Integrated * Products, Inc. shall not be used except as stated in the Maxim Integrated * Products, Inc. Branding Policy. * * The mere transfer of this software does not imply any licenses * of trade secrets, proprietary technology, copyrights, patents, * trademarks, maskwork rights, or any other form of intellectual * property whatsoever. Maxim Integrated Products, Inc. retains all * ownership rights. ******************************************************************************* */ #include "Arduino.h" #include "spo2_algorithm.h" #if defined(__AVR_ATmega328P__) || defined(__AVR_ATmega168__) //Arduino Uno doesn't have enough SRAM to store 100 samples of IR led data and red led data in 32-bit format //To solve this problem, 16-bit MSB of the sampled data will be truncated. Samples become 16-bit data. void maxim_heart_rate_and_oxygen_saturation(uint16_t *pun_ir_buffer, int32_t n_ir_buffer_length, uint16_t *pun_red_buffer, int32_t *pn_spo2, int8_t *pch_spo2_valid, int32_t *pn_heart_rate, int8_t *pch_hr_valid) #else void maxim_heart_rate_and_oxygen_saturation(uint32_t *pun_ir_buffer, int32_t n_ir_buffer_length, uint32_t *pun_red_buffer, int32_t *pn_spo2, int8_t *pch_spo2_valid, int32_t *pn_heart_rate, int8_t *pch_hr_valid) #endif /** * \brief Calculate the heart rate and SpO2 level * \par Details * By detecting peaks of PPG cycle and corresponding AC/DC of red/infra-red signal, the an_ratio for the SPO2 is computed. * Since this algorithm is aiming for Arm M0/M3. formaula for SPO2 did not achieve the accuracy due to register overflow. * Thus, accurate SPO2 is precalculated and save longo uch_spo2_table[] per each an_ratio. * * \param[in] *pun_ir_buffer - IR sensor data buffer * \param[in] n_ir_buffer_length - IR sensor data buffer length * \param[in] *pun_red_buffer - Red sensor data buffer * \param[out] *pn_spo2 - Calculated SpO2 value * \param[out] *pch_spo2_valid - 1 if the calculated SpO2 value is valid * \param[out] *pn_heart_rate - Calculated heart rate value * \param[out] *pch_hr_valid - 1 if the calculated heart rate value is valid * * \retval None */ { uint32_t un_ir_mean; int32_t k, n_i_ratio_count; int32_t i, n_exact_ir_valley_locs_count, n_middle_idx; int32_t n_th1, n_npks; int32_t an_ir_valley_locs[15] ; int32_t n_peak_interval_sum; int32_t n_y_ac, n_x_ac; int32_t n_spo2_calc; int32_t n_y_dc_max, n_x_dc_max; int32_t n_y_dc_max_idx = 0; int32_t n_x_dc_max_idx = 0; int32_t an_ratio[5], n_ratio_average; int32_t n_nume, n_denom ; // calculates DC mean and subtract DC from ir un_ir_mean =0; for (k=0 ; k60) n_th1=60; // max allowed for ( k=0 ; k<15;k++) an_ir_valley_locs[k]=0; // since we flipped signal, we use peak detector as valley detector maxim_find_peaks( an_ir_valley_locs, &n_npks, an_x, BUFFER_SIZE, n_th1, 4, 15 );//peak_height, peak_distance, max_num_peaks n_peak_interval_sum =0; if (n_npks>=2){ for (k=1; k BUFFER_SIZE ){ *pn_spo2 = -999 ; // do not use SPO2 since valley loc is out of range *pch_spo2_valid = 0; return; } } // find max between two valley locations // and use an_ratio betwen AC compoent of Ir & Red and DC compoent of Ir & Red for SPO2 for (k=0; k< n_exact_ir_valley_locs_count-1; k++){ n_y_dc_max= -16777216 ; n_x_dc_max= -16777216; if (an_ir_valley_locs[k+1]-an_ir_valley_locs[k] >3){ for (i=an_ir_valley_locs[k]; i< an_ir_valley_locs[k+1]; i++){ if (an_x[i]> n_x_dc_max) {n_x_dc_max =an_x[i]; n_x_dc_max_idx=i;} if (an_y[i]> n_y_dc_max) {n_y_dc_max =an_y[i]; n_y_dc_max_idx=i;} } n_y_ac= (an_y[an_ir_valley_locs[k+1]] - an_y[an_ir_valley_locs[k] ] )*(n_y_dc_max_idx -an_ir_valley_locs[k]); //red n_y_ac= an_y[an_ir_valley_locs[k]] + n_y_ac/ (an_ir_valley_locs[k+1] - an_ir_valley_locs[k]) ; n_y_ac= an_y[n_y_dc_max_idx] - n_y_ac; // subracting linear DC compoenents from raw n_x_ac= (an_x[an_ir_valley_locs[k+1]] - an_x[an_ir_valley_locs[k] ] )*(n_x_dc_max_idx -an_ir_valley_locs[k]); // ir n_x_ac= an_x[an_ir_valley_locs[k]] + n_x_ac/ (an_ir_valley_locs[k+1] - an_ir_valley_locs[k]); n_x_ac= an_x[n_y_dc_max_idx] - n_x_ac; // subracting linear DC compoenents from raw n_nume=( n_y_ac *n_x_dc_max)>>7 ; //prepare X100 to preserve floating value n_denom= ( n_x_ac *n_y_dc_max)>>7; if (n_denom>0 && n_i_ratio_count <5 && n_nume != 0) { an_ratio[n_i_ratio_count]= (n_nume*100)/n_denom ; //formular is ( n_y_ac *n_x_dc_max) / ( n_x_ac *n_y_dc_max) ; n_i_ratio_count++; } } } // choose median value since PPG signal may varies from beat to beat maxim_sort_ascend(an_ratio, n_i_ratio_count); n_middle_idx= n_i_ratio_count/2; if (n_middle_idx >1) n_ratio_average =( an_ratio[n_middle_idx-1] +an_ratio[n_middle_idx])/2; // use median else n_ratio_average = an_ratio[n_middle_idx ]; if( n_ratio_average>2 && n_ratio_average <184){ n_spo2_calc= uch_spo2_table[n_ratio_average] ; *pn_spo2 = n_spo2_calc ; *pch_spo2_valid = 1;// float_SPO2 = -45.060*n_ratio_average* n_ratio_average/10000 + 30.354 *n_ratio_average/100 + 94.845 ; // for comparison with table } else{ *pn_spo2 = -999 ; // do not use SPO2 since signal an_ratio is out of range *pch_spo2_valid = 0; } } void maxim_find_peaks( int32_t *pn_locs, int32_t *n_npks, int32_t *pn_x, int32_t n_size, int32_t n_min_height, int32_t n_min_distance, int32_t n_max_num ) /** * \brief Find peaks * \par Details * Find at most MAX_NUM peaks above MIN_HEIGHT separated by at least MIN_DISTANCE * * \retval None */ { maxim_peaks_above_min_height( pn_locs, n_npks, pn_x, n_size, n_min_height ); maxim_remove_close_peaks( pn_locs, n_npks, pn_x, n_min_distance ); *n_npks = min( *n_npks, n_max_num ); } void maxim_peaks_above_min_height( int32_t *pn_locs, int32_t *n_npks, int32_t *pn_x, int32_t n_size, int32_t n_min_height ) /** * \brief Find peaks above n_min_height * \par Details * Find all peaks above MIN_HEIGHT * * \retval None */ { int32_t i = 1, n_width; *n_npks = 0; while (i < n_size-1){ if (pn_x[i] > n_min_height && pn_x[i] > pn_x[i-1]){ // find left edge of potential peaks n_width = 1; while (i+n_width < n_size && pn_x[i] == pn_x[i+n_width]) // find flat peaks n_width++; if (pn_x[i] > pn_x[i+n_width] && (*n_npks) < 15 ){ // find right edge of peaks pn_locs[(*n_npks)++] = i; // for flat peaks, peak location is left edge i += n_width+1; } else i += n_width; } else i++; } } void maxim_remove_close_peaks(int32_t *pn_locs, int32_t *pn_npks, int32_t *pn_x, int32_t n_min_distance) /** * \brief Remove peaks * \par Details * Remove peaks separated by less than MIN_DISTANCE * * \retval None */ { int32_t i, j, n_old_npks, n_dist; /* Order peaks from large to small */ maxim_sort_indices_descend( pn_x, pn_locs, *pn_npks ); for ( i = -1; i < *pn_npks; i++ ){ n_old_npks = *pn_npks; *pn_npks = i+1; for ( j = i+1; j < n_old_npks; j++ ){ n_dist = pn_locs[j] - ( i == -1 ? -1 : pn_locs[i] ); // lag-zero peak of autocorr is at index -1 if ( n_dist > n_min_distance || n_dist < -n_min_distance ) pn_locs[(*pn_npks)++] = pn_locs[j]; } } // Resort indices int32_to ascending order maxim_sort_ascend( pn_locs, *pn_npks ); } void maxim_sort_ascend(int32_t *pn_x, int32_t n_size) /** * \brief Sort array * \par Details * Sort array in ascending order (insertion sort algorithm) * * \retval None */ { int32_t i, j, n_temp; for (i = 1; i < n_size; i++) { n_temp = pn_x[i]; for (j = i; j > 0 && n_temp < pn_x[j-1]; j--) pn_x[j] = pn_x[j-1]; pn_x[j] = n_temp; } } void maxim_sort_indices_descend( int32_t *pn_x, int32_t *pn_indx, int32_t n_size) /** * \brief Sort indices * \par Details * Sort indices according to descending order (insertion sort algorithm) * * \retval None */ { int32_t i, j, n_temp; for (i = 1; i < n_size; i++) { n_temp = pn_indx[i]; for (j = i; j > 0 && pn_x[n_temp] > pn_x[pn_indx[j-1]]; j--) pn_indx[j] = pn_indx[j-1]; pn_indx[j] = n_temp; } }