Simple (incomplete) example of how to detect beats from data given by a MAX30102 sensor

MAX30102.cpp

  unsigned long sensorValue = particleSensor.getIR();
  if ( sensorValue > 50000)
  {
    if ( usePlotter )
    {
      Serial.println(sensorValue); //Send raw data to plotter
    } else {
      int diff = lastSensorValue - sensorValue;
      if ( diff > 80  ) // we may have a beat!
      {
        unsigned long now = millis();
        if (lastCount != 0) // ignore the first
        {
          int possibleValue = now - lastCount;
          if ( possibleValue > 400 && possibleValue < 1500 )
          {
            heartbeats[ index ] = possibleValue;
            //Serial.print("Saving: ");
            //Serial.println(heartbeats[ index ]);
            index++;
          }
        }
        lastCount = now;

        if ( index > BEATS ) {
          index = 0;

          // calc and output the average
          int i, total;
          for (i = 0; i < BEATS; i++)
          {
            total += heartbeats[ i ];
          }
          float average = (float)total / BEATS;

          float bpm = 60000 / average;
          Serial.print("Average ms between heartbeats: ");
          Serial.print(average);
          Serial.print(" BPM: ");
          Serial.println((int)bpm);

          display.clearDisplay();
          display.setTextSize(2);
          display.setTextColor(WHITE);
          display.setCursor(40, 40);
          display.println((int)bpm);
          display.display();
        }

        digitalWrite(LED_BUILTIN, HIGH);
        delay(50);
        digitalWrite(LED_BUILTIN, LOW);
      }
    }
  }
  lastSensorValue = sensorValue;