最近爆火的電子血氧儀是什么原理？測的準嗎？

max30102_Bus_Write(REG_INTR_ENABLE_1,0xc0);  // INTR settingmax30102_Bus_Write(REG_INTR_ENABLE_2,0x00);max30102_Bus_Write(REG_FIFO_WR_PTR,0x00);    //FIFO_WR_PTR[4:0]max30102_Bus_Write(REG_OVF_COUNTER,0x00);    //OVF_COUNTER[4:0]max30102_Bus_Write(REG_FIFO_RD_PTR,0x00);    //FIFO_RD_PTR[4:0]max30102_Bus_Write(REG_FIFO_CONFIG,0x0f);    //sample avg = 1, fifo rollover=false, fifo almost full = 17max30102_Bus_Write(REG_MODE_CONFIG,0x03);    //0x02 for Red only, 0x03 for SpO2 mode 0x07 multimode LEDmax30102_Bus_Write(REG_SPO2_CONFIG,0x27);    // SPO2_ADC range = 4096nA, SPO2 sample rate (100 Hz), LED pulseWidth (400uS)  max30102_Bus_Write(REG_LED1_PA,0x24);     //Choose value for ~ 7mA for LED1max30102_Bus_Write(REG_LED2_PA,0x24);     // Choose value for ~ 7mA for LED2max30102_Bus_Write(REG_PILOT_PA,0x7f);     // Choose value for ~ 25mA for Pilot LED

void maxim_max30102_read_fifo(uint32_t *pun_red_led, uint32_t *pun_ir_led){  uint32_t un_temp;  unsigned char uch_temp;  char ach_i2c_data[6];  *pun_red_led=0;  *pun_ir_led=0;
  //read and clear status register  maxim_max30102_read_reg(REG_INTR_STATUS_1, &uch_temp);  maxim_max30102_read_reg(REG_INTR_STATUS_2, &uch_temp);
  IIC_ReadBytes(I2C_WRITE_ADDR,REG_FIFO_DATA,(u8 *)ach_i2c_data,6);
  un_temp=(unsigned char) ach_i2c_data[0];  un_temp<<=16;  *pun_red_led+=un_temp;  un_temp=(unsigned char) ach_i2c_data[1];  un_temp<<=8;  *pun_red_led+=un_temp;  un_temp=(unsigned char) ach_i2c_data[2];  *pun_red_led+=un_temp;
  un_temp=(unsigned char) ach_i2c_data[3];  un_temp<<=16;  *pun_ir_led+=un_temp;  un_temp=(unsigned char) ach_i2c_data[4];  un_temp<<=8;  *pun_ir_led+=un_temp;  un_temp=(unsigned char) ach_i2c_data[5];  *pun_ir_led+=un_temp;  *pun_red_led&=0x03FFFF;  //Mask MSB [23:18]  *pun_ir_led&=0x03FFFF;  //Mask MSB [23:18]}

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){    uint32_t un_ir_mean ,un_only_once ;    int32_t k ,n_i_ratio_count;    int32_t i, s, m, n_exact_ir_valley_locs_count ,n_middle_idx;    int32_t n_th1, n_npks,n_c_min;          int32_t an_ir_valley_locs[15] ;    int32_t an_exact_ir_valley_locs[15] ;    int32_t an_dx_peak_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, n_x_dc_max_idx;     int32_t an_ratio[5],n_ratio_average;     int32_t n_nume,  n_denom ;    // remove DC of ir signal        un_ir_mean =0;     for (k=0 ; k    un_ir_mean =un_ir_mean/n_ir_buffer_length ;    for (k=0 ; k
    // 4 pt Moving Average    for(k=0; k< BUFFER_SIZE-MA4_SIZE; k++){        n_denom= ( an_x[k]+an_x[k+1]+ an_x[k+2]+ an_x[k+3]);        an_x[k]=  n_denom/(int32_t)4;     }
????//?get?difference?of?smoothed?IR?signal????    for( k=0; k        an_dx[k]= (an_x[k+1]- an_x[k]);
    // 2-pt Moving Average to an_dx    for(k=0; k< BUFFER_SIZE-MA4_SIZE-2; k++){        an_dx[k] =  ( an_dx[k]+an_dx[k+1])/2 ;    }
    // hamming window    // flip wave form so that we can detect valley with peak detector    for ( i=0 ; i        s= 0;        for( k=i; k            s -= an_dx[k] *auw_hamm[k-i] ;                      }        an_dx[i]= s/ (int32_t)1146; // divide by sum of auw_hamm ????}
    n_th1=0; // threshold calculation    for ( k=0 ; k        n_th1 += ((an_dx[k]>0)? an_dx[k] : ((int32_t)0-an_dx[k])) ;    }    n_th1= n_th1/ ( BUFFER_SIZE-HAMMING_SIZE);    // peak location is acutally index for sharpest location of raw signal since we flipped the signal             maxim_find_peaks( an_dx_peak_locs, &n_npks, an_dx, BUFFER_SIZE-HAMMING_SIZE, n_th1, 8, 5 );//peak_height, peak_distance, max_num_peaks 
    n_peak_interval_sum =0;    if (n_npks>=2){        for (k=1; k            n_peak_interval_sum += (an_dx_peak_locs[k]-an_dx_peak_locs[k -1]);        n_peak_interval_sum=n_peak_interval_sum/(n_npks-1);        *pn_heart_rate=(int32_t)(6000/n_peak_interval_sum);// beats per minutes        *pch_hr_valid  = 1;    }    else  {        *pn_heart_rate = -999;        *pch_hr_valid  = 0;    }
    for ( k=0 ; k????????an_ir_valley_locs[k]=an_dx_peak_locs[k]+HAMMING_SIZE/2;?
    // raw value : RED(=y) and IR(=X)    // we need to assess DC and AC value of ir and red PPG.     for (k=0 ; k        an_x[k] =  pun_ir_buffer[k] ;         an_y[k] =  pun_red_buffer[k] ;     }
    // find precise min near an_ir_valley_locs    n_exact_ir_valley_locs_count =0;     for(k=0 ; k        un_only_once =1;        m=an_ir_valley_locs[k];        n_c_min= 16777216;//2^24;        if (m+5 <  BUFFER_SIZE-HAMMING_SIZE  && m-5 >0){            for(i= m-5;i                if (an_x[i]                    if (un_only_once >0){                       un_only_once =0;                   }                    n_c_min= an_x[i] ;                   an_exact_ir_valley_locs[k]=i;                }            if (un_only_once ==0)                n_exact_ir_valley_locs_count ++ ;        }    }    if (n_exact_ir_valley_locs_count <2 ){       *pn_spo2 =  -999 ; // do not use SPO2 since signal ratio is out of range       *pch_spo2_valid  = 0;        return;    }    // 4 pt MA    for(k=0; k< BUFFER_SIZE-MA4_SIZE; k++){        an_x[k]=( an_x[k]+an_x[k+1]+ an_x[k+2]+ an_x[k+3])/(int32_t)4;        an_y[k]=( an_y[k]+an_y[k+1]+ an_y[k+2]+ an_y[k+3])/(int32_t)4;    }
    //using an_exact_ir_valley_locs , find ir-red DC andir-red AC for SPO2 calibration ratio    //finding AC/DC maximum of raw ir * red between two valley locations    n_ratio_average =0;     n_i_ratio_count =0; 
    for(k=0; k< 5; k++) an_ratio[k]=0;    for (k=0; k< n_exact_ir_valley_locs_count; k++){        if (an_exact_ir_valley_locs[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 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_exact_ir_valley_locs[k+1]-an_exact_ir_valley_locs[k] >10){            for (i=an_exact_ir_valley_locs[k]; i< an_exact_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_exact_ir_valley_locs[k+1]] - an_y[an_exact_ir_valley_locs[k] ] )*(n_y_dc_max_idx -an_exact_ir_valley_locs[k]); //red            n_y_ac=  an_y[an_exact_ir_valley_locs[k]] + n_y_ac/ (an_exact_ir_valley_locs[k+1] - an_exact_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_exact_ir_valley_locs[k+1]] - an_x[an_exact_ir_valley_locs[k] ] )*(n_x_dc_max_idx -an_exact_ir_valley_locs[k]); // ir            n_x_ac=  an_x[an_exact_ir_valley_locs[k]] + n_x_ac/ (an_exact_ir_valley_locs[k+1] - an_exact_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*20)/n_denom ; //formular is ( n_y_ac *n_x_dc_max) / ( n_x_ac *n_y_dc_max) ;  ///*************************n_nume原來是*100************************//                n_i_ratio_count++;            }        }    }
    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 ratio is out of range        *pch_spo2_valid  = 0;     }}