Bosch BME280 3.3v 3-in-1 sensor Temperature Humidity and Air Pressure

#include <Wire.h>

const int BME280_ADDR = 0x76;

// BME280 registers
const uint8_t REG_CALIB_START = 0x88;
const uint8_t REG_ID = 0xD0;
const uint8_t REG_RESET = 0xE0;
const uint8_t REG_CTRL_HUM = 0xF2;
const uint8_t REG_STATUS = 0xF3;
const uint8_t REG_CTRL_MEAS = 0xF4;
const uint8_t REG_CONFIG = 0xF5;
const uint8_t REG_PRESS_MSB = 0xF7;

struct CalibrationData {
  uint16_t dig_T1;
  int16_t dig_T2;
  int16_t dig_T3;
  uint16_t dig_P1;
  int16_t dig_P2;
  int16_t dig_P3;
  int16_t dig_P4;
  int16_t dig_P5;
  int16_t dig_P6;
  int16_t dig_P7;
  int16_t dig_P8;
  int16_t dig_P9;
  uint8_t dig_H1;
  int16_t dig_H2;
  uint8_t dig_H3;
  int16_t dig_H4;
  int16_t dig_H5;
  int8_t dig_H6;
};

CalibrationData calib;
int32_t t_fine = 0;

void write8(uint8_t reg, uint8_t value) {
  Wire.beginTransmission(BME280_ADDR);
  Wire.write(reg);
  Wire.write(value);
  Wire.endTransmission();
}

uint8_t read8(uint8_t reg) {
  Wire.beginTransmission(BME280_ADDR);
  Wire.write(reg);
  Wire.endTransmission(false);
  Wire.requestFrom(BME280_ADDR, (uint8_t)1);
  return Wire.available() ? Wire.read() : 0;
}

void readBytes(uint8_t reg, uint8_t *buf, uint8_t len) {
  Wire.beginTransmission(BME280_ADDR);
  Wire.write(reg);
  Wire.endTransmission(false);
  Wire.requestFrom(BME280_ADDR, len);
  for (uint8_t i = 0; i < len && Wire.available(); i++) {
    buf[i] = Wire.read();
  }
}

bool initBME280() {
  uint8_t id = read8(REG_ID);
  if (id != 0x60) return false;

  write8(REG_RESET, 0xB6);
  delay(10);

  uint8_t calib1[26];
  readBytes(REG_CALIB_START, calib1, 26);
  calib.dig_T1 = (uint16_t)(calib1[1] << 8 | calib1[0]);
  calib.dig_T2 = (int16_t)(calib1[3] << 8 | calib1[2]);
  calib.dig_T3 = (int16_t)(calib1[5] << 8 | calib1[4]);
  calib.dig_P1 = (uint16_t)(calib1[7] << 8 | calib1[6]);
  calib.dig_P2 = (int16_t)(calib1[9] << 8 | calib1[8]);
  calib.dig_P3 = (int16_t)(calib1[11] << 8 | calib1[10]);
  calib.dig_P4 = (int16_t)(calib1[13] << 8 | calib1[12]);
  calib.dig_P5 = (int16_t)(calib1[15] << 8 | calib1[14]);
  calib.dig_P6 = (int16_t)(calib1[17] << 8 | calib1[16]);
  calib.dig_P7 = (int16_t)(calib1[19] << 8 | calib1[18]);
  calib.dig_P8 = (int16_t)(calib1[21] << 8 | calib1[20]);
  calib.dig_P9 = (int16_t)(calib1[23] << 8 | calib1[22]);
  calib.dig_H1 = calib1[25];

  uint8_t calib2[7];
  readBytes(0xE1, calib2, 7);
  calib.dig_H2 = (int16_t)(calib2[1] << 8 | calib2[0]);
  calib.dig_H3 = calib2[2];
  calib.dig_H4 = (int16_t)((calib2[3] << 4) | (calib2[4] & 0x0F));
  calib.dig_H5 = (int16_t)((calib2[5] << 4) | (calib2[4] >> 4));
  calib.dig_H6 = (int8_t)calib2[6];

  // Humidity oversampling x1, temperature oversampling x1, pressure oversampling x1, normal mode
  write8(REG_CTRL_HUM, 0x01);
  write8(REG_CTRL_MEAS, 0x27);
  // Standby 1000 ms, filter off
  write8(REG_CONFIG, 0xA0);

  return true;
}

int32_t readTemperatureRaw() {
  uint8_t data[8];
  readBytes(REG_PRESS_MSB, data, 8);
  int32_t adc_T = ((int32_t)data[3] << 12) | ((int32_t)data[4] << 4) | (data[5] >> 4);
  return adc_T;
}

int32_t readPressureRaw() {
  uint8_t data[8];
  readBytes(REG_PRESS_MSB, data, 8);
  int32_t adc_P = ((int32_t)data[0] << 12) | ((int32_t)data[1] << 4) | (data[2] >> 4);
  return adc_P;
}

int32_t readHumidityRaw() {
  uint8_t data[8];
  readBytes(REG_PRESS_MSB, data, 8);
  int32_t adc_H = ((int32_t)data[6] << 8) | data[7];
  return adc_H;
}

float compensateTemperature(int32_t adc_T) {
  int32_t var1 = ((((adc_T >> 3) - ((int32_t)calib.dig_T1 << 1))) * ((int32_t)calib.dig_T2)) >> 11;
  int32_t var2 = (((((adc_T >> 4) - ((int32_t)calib.dig_T1)) * ((adc_T >> 4) - ((int32_t)calib.dig_T1))) >> 12) * ((int32_t)calib.dig_T3)) >> 14;
  t_fine = var1 + var2;
  float T = (t_fine * 5 + 128) >> 8;
  return T / 100.0f;
}

float compensatePressure(int32_t adc_P) {
  int64_t var1 = ((int64_t)t_fine) - 128000;
  int64_t var2 = var1 * var1 * (int64_t)calib.dig_P6;
  var2 = var2 + ((var1 * (int64_t)calib.dig_P5) << 17);
  var2 = var2 + (((int64_t)calib.dig_P4) << 35);
  var1 = ((var1 * var1 * (int64_t)calib.dig_P3) >> 8) + ((var1 * (int64_t)calib.dig_P2) << 12);
  var1 = (((((int64_t)1) << 47) + var1) * (int64_t)calib.dig_P1) >> 33;
  if (var1 == 0) return 0;
  int64_t p = 1048576 - adc_P;
  p = (((p << 31) - var2) * 3125) / var1;
  var1 = ((int64_t)calib.dig_P9 * (p >> 13) * (p >> 13)) >> 25;
  var2 = ((int64_t)calib.dig_P8 * p) >> 19;
  p = ((p + var1 + var2) >> 8) + (((int64_t)calib.dig_P7) << 4);
  return p / 256.0f;
}

float compensateHumidity(int32_t adc_H) {
  int32_t v_x1_u32r = t_fine - 76800;
  v_x1_u32r = (((((adc_H << 14) - (((int32_t)calib.dig_H4) << 20) - (((int32_t)calib.dig_H5) * v_x1_u32r)) + 16384) >> 15) * (((((((v_x1_u32r * ((int32_t)calib.dig_H6)) >> 10) * (((v_x1_u32r * ((int32_t)calib.dig_H3)) >> 11) + 32768)) >> 10) + 2097152) * ((int32_t)calib.dig_H2) + 8192) >> 14));
  v_x1_u32r = v_x1_u32r - (((((v_x1_u32r >> 15) * (v_x1_u32r >> 15)) >> 7) * ((int32_t)calib.dig_H1)) >> 4);
  if (v_x1_u32r < 0) v_x1_u32r = 0;
  if (v_x1_u32r > 419430400) v_x1_u32r = 419430400;
  return (v_x1_u32r >> 12) / 1024.0f;
}

void setup() {
  Serial.begin(115200);
  while (!Serial) {}

  Wire.begin();

  Serial.println("BME280 canonical example");
  if (!initBME280()) {
    Serial.println("BME280 not found. Check wiring and that CSB is tied high for I2C mode.");
    while (1) {
      delay(1000);
    }
  }
  Serial.println("BME280 initialized.");
}

void loop() {
  int32_t rawT = readTemperatureRaw();
  int32_t rawP = readPressureRaw();
  int32_t rawH = readHumidityRaw();

  float temperature = compensateTemperature(rawT);
  float pressurePa = compensatePressure(rawP);
  float humidity = compensateHumidity(rawH);

  Serial.print("Temperature: ");
  Serial.print(temperature, 2);
  Serial.print(" °C, Humidity: ");
  Serial.print(humidity, 2);
  Serial.print(" %, Pressure: ");
  Serial.print(pressurePa / 100.0f, 2);
  Serial.println(" hPa");

  delay(2000);
}