Heart Rate Monitor

#include <Arduino.h>
#include <Wire.h>
#include <LiquidCrystal_I2C.h>
#include "MAX30105.h"
#include "heartRate.h"


// Forward declarations
void writeLine(uint8_t row, const String &text, String &previous);
void updateDisplay();

constexpr uint8_t I2C_SDA_PIN = 21;
constexpr uint8_t I2C_SCL_PIN = 22;
constexpr uint8_t LCD_ADDRESS = 0x27;
constexpr uint32_t FINGER_THRESHOLD = 50000;
constexpr uint32_t DISPLAY_INTERVAL_MS = 250;

MAX30105 particleSensor;
LiquidCrystal_I2C lcd(LCD_ADDRESS, 16, 2);

uint32_t lastBeatMs = 0;
uint32_t lastDisplayMs = 0;
float bpm = 0.0F;
float averagedBpm = 0.0F;
uint8_t bpmSamples[4] = {0, 0, 0, 0};
uint8_t sampleIndex = 0;
bool fingerPresent = false;
String lastLine1;
String lastLine2;

void writeLine(uint8_t row, const String &text, String &previous) {
  String padded = text;
  while (padded.length() < 16) {
    padded += ' ';
  }
  padded = padded.substring(0, 16);
  if (padded != previous) {
    lcd.setCursor(0, row);
    lcd.print(padded);
    previous = padded;
  }
}

void updateDisplay() {
  if (!fingerPresent) {
    writeLine(0, "Place finger", lastLine1);
    writeLine(1, "on MAX30102", lastLine2);
    return;
  }

  writeLine(0, "Heart rate", lastLine1);
  if (averagedBpm >= 30.0F && averagedBpm <= 220.0F) {
    writeLine(1, String((int)(averagedBpm + 0.5F)) + " BPM", lastLine2);
  } else {
    writeLine(1, "Measuring...", lastLine2);
  }
}

void setup() {
  Serial.begin(115200);
  Wire.begin(I2C_SDA_PIN, I2C_SCL_PIN);

  lcd.init();
  lcd.backlight();
  writeLine(0, "MAX30102 monitor", lastLine1);
  writeLine(1, "Starting...", lastLine2);

  if (!particleSensor.begin(Wire, I2C_SPEED_STANDARD)) {
    writeLine(0, "MAX30102 error", lastLine1);
    writeLine(1, "Check I2C wires", lastLine2);
    while (true) {
      delay(1000);
    }
  }

  particleSensor.setup(60, 4, 2, 100, 411, 4096);
  particleSensor.setPulseAmplitudeRed(0x1F);
  particleSensor.setPulseAmplitudeIR(0x1F);
  particleSensor.setPulseAmplitudeGreen(0);
  updateDisplay();
}

void loop() {
  const long irValue = particleSensor.getIR();
  fingerPresent = irValue > FINGER_THRESHOLD;

  if (fingerPresent && checkForBeat(irValue)) {
    const uint32_t now = millis();
    if (lastBeatMs != 0) {
      bpm = 60.0F / ((now - lastBeatMs) / 1000.0F);
      if (bpm >= 30.0F && bpm <= 220.0F) {
        bpmSamples[sampleIndex] = (uint8_t)bpm;
        sampleIndex = (sampleIndex + 1) % 4;
        uint16_t total = 0;
        uint8_t count = 0;
        for (uint8_t i = 0; i < 4; i++) {
          if (bpmSamples[i] > 0) {
            total += bpmSamples[i];
            count++;
          }
        }
        if (count > 0) {
          averagedBpm = (float)total / count;
        }
      }
    }
    lastBeatMs = now;
  }

  if (!fingerPresent) {
    averagedBpm = 0.0F;
    lastBeatMs = 0;
    for (uint8_t i = 0; i < 4; i++) {
      bpmSamples[i] = 0;
    }
  }

  if (millis() - lastDisplayMs >= DISPLAY_INTERVAL_MS) {
    lastDisplayMs = millis();
    updateDisplay();
  }
}