In the previous guide of MAX30102, we have shown a test code with the MAX30102 module build/sold by Maker Focus mounted on a MH-ET LIVE breakout board. Our two challenges are – ESP32 is not exactly same as Arduino UNO and the good looking MH-ET LIVE breakout board is not same as the MAX30102 module sold by Sparkfun. As we commonly use the MAX30102 sensor library by Sparkfun, we need to guess which code evokes IR and RED LED. The MAX30105 module has a GREEN LED as well.
Tweak the MAX30102 MH-ET LIVE breakout board
You’ll notice that the back of MAX30102 MH-ET LIVE breakout board has PCB jumper at it’s back. The jumpers are like :
1V8
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3.3V
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You have to solder the 3.3v with the middle one. After soldering, test with a multimeter (resistance measurement settings) whether they are connected and also avoid to short-circuit with 1V8. This is not just easy work unless you are used with soldering PCB mounted components.
Secondly, put the MAX30102 MH-ET LIVE breakout board inside a thing plastic bag. I have used the plastic cover of cigarette pack as a “bag” of the MAX30102 MH-ET LIVE breakout board. A lot of box packages have such thin plastic wraps. Wrap of a cigarette pack is an example of how thin it should be.
Third, as the pressure determines the Gamma value, you should not apply too much pressure with your finger (on the sensors) to avoid false high reading. You can use a tape, or velcro or a cloth clip to apply uniform pressure.
Forth, the code is designed to start after pressing the reset button of ESP32. Also, it will halt after a period of sampling and upon error. You need to press reset button of ESP32 in such case.
Fifth, open the serial plotter of Arduino IDE after some seconds of attaching the sensor. Close the serial plotter of Arduino IDE after it faces a halt, press reset button of ESP32, wait for a while and then open the serial plotter of Arduino IDE.
Working Code for Local Use
The below code is for testing with Arduino IDE’s plotter. Thankfully, I found that coniferconifer did the works we required for building a basic pulse oximeter with ESP32 and MAX30102 (MH-ET LIVE breakout board). I can tell you that finding that code was not closest to easy but he did the best work of working with all possible projects so far I know.
The green plotting line is of SpO2.
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#include <Wire.h> #include "MAX30105.h" //sparkfun MAX3010X library MAX30105 particleSensor; //#define MAX30105 //if you have Sparkfun's MAX30105 breakout board , try #define MAX30105 #define USEFIFO void setup() { Serial.begin(115200); Serial.println("Initializing..."); // Initialize sensor if (!particleSensor.begin(Wire, I2C_SPEED_FAST)) //Use default I2C port, 400kHz speed { Serial.println("MAX30102 was not found. Please check wiring/power/solder jumper at MH-ET LIVE MAX30102 board. "); while (1); } //Setup to sense a nice looking saw tooth on the plotter byte ledBrightness = 0x7F; //Options: 0=Off to 255=50mA byte sampleAverage = 4; //Options: 1, 2, 4, 8, 16, 32 byte ledMode = 2; //Options: 1 = Red only, 2 = Red + IR, 3 = Red + IR + Green //Options: 1 = IR only, 2 = Red + IR on MH-ET LIVE MAX30102 board int sampleRate = 200; //Options: 50, 100, 200, 400, 800, 1000, 1600, 3200 int pulseWidth = 411; //Options: 69, 118, 215, 411 int adcRange = 16384; //Options: 2048, 4096, 8192, 16384 // Set up the wanted parameters particleSensor.setup(ledBrightness, sampleAverage, ledMode, sampleRate, pulseWidth, adcRange); //Configure sensor with these settings } double avered = 0; double aveir = 0; double sumirrms = 0; double sumredrms = 0; int i = 0; int Num = 100;//calculate SpO2 by this sampling interval double ESpO2 = 95.0;//initial value of estimated SpO2 double FSpO2 = 0.7; //filter factor for estimated SpO2 double frate = 0.95; //low pass filter for IR/red LED value to eliminate AC component #define TIMETOBOOT 3000 // wait for this time(msec) to output SpO2 #define SCALE 88.0 //adjust to display heart beat and SpO2 in the same scale #define SAMPLING 5 //if you want to see heart beat more precisely , set SAMPLING to 1 #define FINGER_ON 30000 // if red signal is lower than this , it indicates your finger is not on the sensor #define MINIMUM_SPO2 80.0 void loop() { uint32_t ir, red , green; double fred, fir; double SpO2 = 0; //raw SpO2 before low pass filtered #ifdef USEFIFO particleSensor.check(); //Check the sensor, read up to 3 samples while (particleSensor.available()) {//do we have new data #ifdef MAX30105 red = particleSensor.getFIFORed(); //Sparkfun's MAX30105 ir = particleSensor.getFIFOIR(); //Sparkfun's MAX30105 #else red = particleSensor.getFIFOIR(); //why getFOFOIR output Red data by MAX30102 on MH-ET LIVE breakout board ir = particleSensor.getFIFORed(); //why getFIFORed output IR data by MAX30102 on MH-ET LIVE breakout board #endif i++; fred = (double)red; fir = (double)ir; avered = avered * frate + (double)red * (1.0 - frate);//average red level by low pass filter aveir = aveir * frate + (double)ir * (1.0 - frate); //average IR level by low pass filter sumredrms += (fred - avered) * (fred - avered); //square sum of alternate component of red level sumirrms += (fir - aveir) * (fir - aveir);//square sum of alternate component of IR level if ((i % SAMPLING) == 0) {//slow down graph plotting speed for arduino Serial plotter by thin out if ( millis() > TIMETOBOOT) { float ir_forGraph = (2.0 * fir - aveir) / aveir * SCALE; float red_forGraph = (2.0 * fred - avered) / avered * SCALE; //trancation for Serial plotter's autoscaling if ( ir_forGraph > 100.0) ir_forGraph = 100.0; if ( ir_forGraph < 80.0) ir_forGraph = 80.0; if ( red_forGraph > 100.0 ) red_forGraph = 100.0; if ( red_forGraph < 80.0 ) red_forGraph = 80.0; // Serial.print(red); Serial.print(","); Serial.print(ir);Serial.print("."); if (ir < FINGER_ON) ESpO2 = MINIMUM_SPO2; //indicator for finger detached Serial.print(ir_forGraph); // to display pulse wave at the same time with SpO2 data Serial.print(","); Serial.print(red_forGraph); // to display pulse wave at the same time with SpO2 data Serial.print(","); Serial.print(ESpO2); //low pass filtered SpO2 Serial.print(","); Serial.print(85.0); //reference SpO2 line Serial.print(","); Serial.print(90.0); //warning SpO2 line Serial.print(","); Serial.print(95.0); //safe SpO2 line Serial.print(","); Serial.println(100.0); //max SpO2 line } } if ((i % Num) == 0) { double R = (sqrt(sumredrms) / avered) / (sqrt(sumirrms) / aveir); // Serial.println(R); SpO2 = -23.3 * (R - 0.4) + 100; //http://ww1.microchip.com/downloads/jp/AppNotes/00001525B_JP.pdf ESpO2 = FSpO2 * ESpO2 + (1.0 - FSpO2) * SpO2;//low pass filter // Serial.print(SpO2);Serial.print(",");Serial.println(ESpO2); sumredrms = 0.0; sumirrms = 0.0; i = 0; break; } particleSensor.nextSample(); //We're finished with this sample so move to next sample //Serial.println(SpO2); } #else while (1) {//do we have new data #ifdef MAX30105 red = particleSensor.getRed(); //Sparkfun's MAX30105 ir = particleSensor.getIR(); //Sparkfun's MAX30105 #else red = particleSensor.getIR(); //why getFOFOIR outputs Red data by MAX30102 on MH-ET LIVE breakout board ir = particleSensor.getRed(); //why getFIFORed outputs IR data by MAX30102 on MH-ET LIVE breakout board #endif i++; fred = (double)red; fir = (double)ir; avered = avered * frate + (double)red * (1.0 - frate);//average red level by low pass filter aveir = aveir * frate + (double)ir * (1.0 - frate); //average IR level by low pass filter sumredrms += (fred - avered) * (fred - avered); //square sum of alternate component of red level sumirrms += (fir - aveir) * (fir - aveir);//square sum of alternate component of IR level if ((i % SAMPLING) == 0) {//slow down graph plotting speed for arduino IDE toos menu by thin out //#if 0 if ( millis() > TIMETOBOOT) { float ir_forGraph = (2.0 * fir - aveir) / aveir * SCALE; float red_forGraph = (2.0 * fred - avered) / avered * SCALE; //trancation for Serial plotter's autoscaling if ( ir_forGraph > 100.0) ir_forGraph = 100.0; if ( ir_forGraph < 80.0) ir_forGraph = 80.0; if ( red_forGraph > 100.0 ) red_forGraph = 100.0; if ( red_forGraph < 80.0 ) red_forGraph = 80.0; // Serial.print(red); Serial.print(","); Serial.print(ir);Serial.print("."); if (ir < FINGER_ON) ESpO2 = MINIMUM_SPO2; //indicator for finger detached Serial.print((2.0 * fir - aveir) / aveir * SCALE); // to display pulse wave at the same time with SpO2 data Serial.print(","); Serial.print((2.0 * fred - avered) / avered * SCALE); // to display pulse wave at the same time with SpO2 data Serial.print(","); Serial.print(ESpO2); //low pass filtered SpO2 Serial.print(","); Serial.print(85.0); // Serial.print(","); Serial.print(90.0); //warning SpO2 line Serial.print(","); Serial.print(95.0); //safe SpO2 line Serial.print(","); Serial.println(100.0); //max SpO2 line //#endif } } if ((i % Num) == 0) { double R = (sqrt(sumredrms) / avered) / (sqrt(sumirrms) / aveir); // Serial.println(R); SpO2 = -23.3 * (R - 0.4) + 100; //http://ww1.microchip.com/downloads/jp/AppNotes/00001525B_JP.pdf ESpO2 = FSpO2 * ESpO2 + (1.0 - FSpO2) * SpO2; // Serial.print(SpO2);Serial.print(",");Serial.println(ESpO2); sumredrms = 0.0; sumirrms = 0.0; i = 0; break; } particleSensor.nextSample(); //We're finished with this sample so move to next sample //Serial.println(SpO2); } #endif } |
As usually, I kept the above code in my GitHub account as a repository. In the next guide, we will send the data to IBM Watson IoT platform.
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