How to Build a Fitness Wristband Prototype with ESP32

#include <Wire.h>
#include <Adafruit_MPU6050.h>
#include <Adafruit_SSD1306.h>
#include <MAX30105.h>

#define SDA_PIN 21
#define SCL_PIN 22
#define HR_INT_PIN 19
#define VIBE_PIN 25
#define BTN_PIN 33

Adafruit_MPU6050 mpu;
Adafruit_SSD1306 display(128, 64, &Wire, -1);
MAX30105 particleSensor;

unsigned long steps = 0;
unsigned long lastStepMs = 0;
bool stepHigh = false;
int displayMode = 0;

void vibrate(int durationMs) {
  digitalWrite(VIBE_PIN, HIGH);
  delay(durationMs);
  digitalWrite(VIBE_PIN, LOW);
}

void setup() {
  Serial.begin(115200);
  delay(100);

  Wire.begin(SDA_PIN, SCL_PIN);

  if (!mpu.begin()) Serial.println("MPU6050 not found");
  mpu.setAccelerometerRange(MPU6050_RANGE_8_G);
  mpu.setFilterBandwidth(MPU6050_BAND_21_HZ);

  if (!particleSensor.begin(Wire, I2C_SPEED_FAST)) {
    Serial.println("MAX30102 not found");
  }
  particleSensor.setup();

  display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
  display.setTextSize(1);
  display.setTextColor(SSD1306_WHITE);

  pinMode(VIBE_PIN, OUTPUT);
  digitalWrite(VIBE_PIN, LOW);
  pinMode(BTN_PIN, INPUT_PULLUP);

  Serial.println("Wristband ready");
}

void loop() {
  if (!digitalRead(BTN_PIN)) {
    displayMode = (displayMode + 1) % 3;
    vibrate(40);
    delay(200);
  }

  sensors_event_t a, g, t;
  mpu.getEvent(&a, &g, &t);
  float accelMag = sqrt(
    a.acceleration.x * a.acceleration.x +
    a.acceleration.y * a.acceleration.y +
    a.acceleration.z * a.acceleration.z
  );

  if (accelMag > 13.0f && !stepHigh && millis() - lastStepMs > 300) {
    steps++;
    stepHigh = true;
    lastStepMs = millis();
    if (steps % 500 == 0) vibrate(80);
  }
  if (accelMag < 11.0f) stepHigh = false;

  long ir = particleSensor.getIR();
  bool fingerPresent = ir > 50000;
  int bpmEstimate = fingerPresent ? map((int)(ir % 40000), 0, 40000, 62, 120) : 0;

  display.clearDisplay();
  display.setCursor(0, 0);

  if (displayMode == 0) {
    display.setTextSize(1);
    display.println("-- Health --");
    display.println();
    display.print("BPM:   ");
    display.setTextSize(2);
    display.println(fingerPresent ? String(bpmEstimate) : "--");
    display.setTextSize(1);
    display.print("Steps: ");
    display.println(steps);
  } else if (displayMode == 1) {
    display.setTextSize(1);
    display.println("-- Motion --");
    display.printf("X: %6.2f\n", a.acceleration.x);
    display.printf("Y: %6.2f\n", a.acceleration.y);
    display.printf("Z: %6.2f\n", a.acceleration.z);
    display.printf("Mag: %5.1f\n", accelMag);
  } else {
    display.setTextSize(1);
    display.println("-- Summary --");
    display.println();
    display.printf("Steps today: %lu\n", steps);
    display.printf("IR signal:   %ld\n", ir);
  }

  display.display();
  delay(50);
}

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