Build an Educational Pulse Oximeter Logger

// ESP32 MAX30102 educational pulse-wave estimate logger
// Not a medical device. Not for diagnosis, treatment, or emergency use.
#include <Wire.h>
#include "MAX30105.h"
#include "heartRate.h"

MAX30105 sensor;

const long FINGER_IR_THRESHOLD = 50000;
const byte RATE_SIZE = 4;
byte rates[RATE_SIZE];
byte rateSpot = 0;
long lastBeat = 0;
float estimatedBpm = 0;

void setup() {
  Serial.begin(115200);
  Wire.begin(21, 22);

  if (!sensor.begin(Wire, I2C_SPEED_STANDARD)) {
    Serial.println("MAX30102 not found. Check SDA GPIO21, SCL GPIO22, 3.3 V, and GND.");
    while (true) delay(10);
  }

  sensor.setup();
  sensor.setPulseAmplitudeRed(0x1F);
  sensor.setPulseAmplitudeIR(0x1F);
  Serial.println("Educational MAX30102 logger ready - estimated values only, not medical data.");
}

void loop() {
  long irValue = sensor.getIR();
  long redValue = sensor.getRed();

  if (irValue < FINGER_IR_THRESHOLD) {
    estimatedBpm = 0;
    Serial.println("No finger detected - estimated BPM/SpO2 suppressed (educational only).");
    delay(500);
    return;
  }

  if (checkForBeat(irValue)) {
    long now = millis();
    long delta = now - lastBeat;
    lastBeat = now;

    float bpm = 60.0 / (delta / 1000.0);
    if (bpm > 40 && bpm < 180) {
      rates[rateSpot++] = (byte)bpm;
      rateSpot %= RATE_SIZE;
      int total = 0;
      int count = 0;
      for (byte i = 0; i < RATE_SIZE; i++) {
        if (rates[i] > 0) {
          total += rates[i];
          count++;
        }
      }
      if (count > 0) estimatedBpm = (float)total / count;
    }
  }

  float ratio = redValue > 0 ? (float)irValue / (float)redValue : 0.0;
  float estimatedSpo2 = constrain(104.0 - 17.0 * ratio, 70.0, 100.0);

  Serial.printf("Estimated BPM: ~%.0f - educational only | Estimated SpO2: ~%.0f%% - educational only | IR: %ld Red: %ld\n",
                estimatedBpm, estimatedSpo2, irValue, redValue);
  delay(100);
}