text: """read bme280 sensor data via i2c
  
  from here: https://randomnerdtutorials.com/micropython-bme280-esp32-esp8266/
  """
  from machine import I2C
  import time
  
  # BME280 default address.
  BME280_I2CADDR = 0x76
  
  # Operating Modes
  BME280_OSAMPLE_1 = 1
  BME280_OSAMPLE_2 = 2
  BME280_OSAMPLE_4 = 3
  BME280_OSAMPLE_8 = 4
  BME280_OSAMPLE_16 = 5
  
  # BME280 Registers
  BME280_REGISTER_DIG_T1 = 0x88  # Trimming parameter registers
  BME280_REGISTER_DIG_T2 = 0x8A
  BME280_REGISTER_DIG_T3 = 0x8C
  
  BME280_REGISTER_DIG_P1 = 0x8E
  BME280_REGISTER_DIG_P2 = 0x90
  BME280_REGISTER_DIG_P3 = 0x92
  BME280_REGISTER_DIG_P4 = 0x94
  BME280_REGISTER_DIG_P5 = 0x96
  BME280_REGISTER_DIG_P6 = 0x98
  BME280_REGISTER_DIG_P7 = 0x9A
  BME280_REGISTER_DIG_P8 = 0x9C
  BME280_REGISTER_DIG_P9 = 0x9E
  
  BME280_REGISTER_DIG_H1 = 0xA1
  BME280_REGISTER_DIG_H2 = 0xE1
  BME280_REGISTER_DIG_H3 = 0xE3
  BME280_REGISTER_DIG_H4 = 0xE4
  BME280_REGISTER_DIG_H5 = 0xE5
  BME280_REGISTER_DIG_H6 = 0xE6
  BME280_REGISTER_DIG_H7 = 0xE7
  
  BME280_REGISTER_CHIPID = 0xD0
  BME280_REGISTER_VERSION = 0xD1
  BME280_REGISTER_SOFTRESET = 0xE0
  
  BME280_REGISTER_CONTROL_HUM = 0xF2
  BME280_REGISTER_CONTROL = 0xF4
  BME280_REGISTER_CONFIG = 0xF5
  BME280_REGISTER_PRESSURE_DATA = 0xF7
  BME280_REGISTER_TEMP_DATA = 0xFA
  BME280_REGISTER_HUMIDITY_DATA = 0xFD
  
  
  class Device:
    """Class for communicating with an I2C device.
  
    Allows reading and writing 8-bit, 16-bit, and byte array values to
    registers on the device.
    """
  
    def __init__(self, address, i2c):
      """Create an instance of the I2C device at the specified address using
      the specified I2C interface object."""
      self._address = address
      self._i2c = i2c
  
    def writeRaw8(self, value):
      """Write an 8-bit value on the bus (without register)."""
      value = value & 0xFF
      self._i2c.writeto(self._address, value)
  
    def write8(self, register, value):
      """Write an 8-bit value to the specified register."""
      b=bytearray(1)
      b[0]=value & 0xFF
      self._i2c.writeto_mem(self._address, register, b)
  
    def write16(self, register, value):
      """Write a 16-bit value to the specified register."""
      value = value & 0xFFFF
      b=bytearray(2)
      b[0]= value & 0xFF
      b[1]= (value>>8) & 0xFF
      self.i2c.writeto_mem(self._address, register, value)
  
    def readRaw8(self):
      """Read an 8-bit value on the bus (without register)."""
      return int.from_bytes(self._i2c.readfrom(self._address, 1),'little') & 0xFF
  
    def readU8(self, register):
      """Read an unsigned byte from the specified register."""
      return int.from_bytes(
          self._i2c.readfrom_mem(self._address, register, 1),'little') & 0xFF
  
    def readS8(self, register):
      """Read a signed byte from the specified register."""
      result = self.readU8(register)
      if result > 127:
        result -= 256
      return result
  
    def readU16(self, register, little_endian=True):
      """Read an unsigned 16-bit value from the specified register, with the
      specified endianness (default little endian, or least significant byte
      first)."""
      result = int.from_bytes(
          self._i2c.readfrom_mem(self._address, register, 2),'little') & 0xFFFF
      if not little_endian:
        result = ((result << 8) & 0xFF00) + (result >> 8)
      return result
  
    def readS16(self, register, little_endian=True):
      """Read a signed 16-bit value from the specified register, with the
      specified endianness (default little endian, or least significant byte
      first)."""
      result = self.readU16(register, little_endian)
      if result > 32767:
        result -= 65536
      return result
  
    def readU16LE(self, register):
      """Read an unsigned 16-bit value from the specified register, in little
      endian byte order."""
      return self.readU16(register, little_endian=True)
  
    def readU16BE(self, register):
      """Read an unsigned 16-bit value from the specified register, in big
      endian byte order."""
      return self.readU16(register, little_endian=False)
  
    def readS16LE(self, register):
      """Read a signed 16-bit value from the specified register, in little
      endian byte order."""
      return self.readS16(register, little_endian=True)
  
    def readS16BE(self, register):
      """Read a signed 16-bit value from the specified register, in big
      endian byte order."""
      return self.readS16(register, little_endian=False)
  
  
  class BME280:
    def __init__(self, mode=BME280_OSAMPLE_1, address=BME280_I2CADDR, i2c=None,
                 **kwargs):
      # Check that mode is valid.
      if mode not in [BME280_OSAMPLE_1, BME280_OSAMPLE_2, BME280_OSAMPLE_4,
                      BME280_OSAMPLE_8, BME280_OSAMPLE_16]:
          raise ValueError(
              'Unexpected mode value {0}. Set mode to one of '
              'BME280_ULTRALOWPOWER, BME280_STANDARD, BME280_HIGHRES, or '
              'BME280_ULTRAHIGHRES'.format(mode))
      self._mode = mode
      # Create I2C device.
      if i2c is None:
        raise ValueError('An I2C object is required.')
      self._device = Device(address, i2c)
      # Load calibration values.
      self._load_calibration()
      self._device.write8(BME280_REGISTER_CONTROL, 0x3F)
      self.t_fine = 0
  
    def _load_calibration(self):
  
      self.dig_T1 = self._device.readU16LE(BME280_REGISTER_DIG_T1)
      self.dig_T2 = self._device.readS16LE(BME280_REGISTER_DIG_T2)
      self.dig_T3 = self._device.readS16LE(BME280_REGISTER_DIG_T3)
  
      self.dig_P1 = self._device.readU16LE(BME280_REGISTER_DIG_P1)
      self.dig_P2 = self._device.readS16LE(BME280_REGISTER_DIG_P2)
      self.dig_P3 = self._device.readS16LE(BME280_REGISTER_DIG_P3)
      self.dig_P4 = self._device.readS16LE(BME280_REGISTER_DIG_P4)
      self.dig_P5 = self._device.readS16LE(BME280_REGISTER_DIG_P5)
      self.dig_P6 = self._device.readS16LE(BME280_REGISTER_DIG_P6)
      self.dig_P7 = self._device.readS16LE(BME280_REGISTER_DIG_P7)
      self.dig_P8 = self._device.readS16LE(BME280_REGISTER_DIG_P8)
      self.dig_P9 = self._device.readS16LE(BME280_REGISTER_DIG_P9)
  
      self.dig_H1 = self._device.readU8(BME280_REGISTER_DIG_H1)
      self.dig_H2 = self._device.readS16LE(BME280_REGISTER_DIG_H2)
      self.dig_H3 = self._device.readU8(BME280_REGISTER_DIG_H3)
      self.dig_H6 = self._device.readS8(BME280_REGISTER_DIG_H7)
  
      h4 = self._device.readS8(BME280_REGISTER_DIG_H4)
      h4 = (h4 << 24) >> 20
      self.dig_H4 = h4 | (self._device.readU8(BME280_REGISTER_DIG_H5) & 0x0F)
  
      h5 = self._device.readS8(BME280_REGISTER_DIG_H6)
      h5 = (h5 << 24) >> 20
      self.dig_H5 = h5 | (
          self._device.readU8(BME280_REGISTER_DIG_H5) >> 4 & 0x0F)
  
    def read_raw_temp(self):
      """Reads the raw (uncompensated) temperature from the sensor."""
      meas = self._mode
      self._device.write8(BME280_REGISTER_CONTROL_HUM, meas)
      meas = self._mode << 5 | self._mode << 2 | 1
      self._device.write8(BME280_REGISTER_CONTROL, meas)
      sleep_time = 1250 + 2300 * (1 << self._mode)
  
      sleep_time = sleep_time + 2300 * (1 << self._mode) + 575
      sleep_time = sleep_time + 2300 * (1 << self._mode) + 575
      time.sleep_us(sleep_time)  # Wait the required time
      msb = self._device.readU8(BME280_REGISTER_TEMP_DATA)
      lsb = self._device.readU8(BME280_REGISTER_TEMP_DATA + 1)
      xlsb = self._device.readU8(BME280_REGISTER_TEMP_DATA + 2)
      raw = ((msb << 16) | (lsb << 8) | xlsb) >> 4
      return raw
  
    def read_raw_pressure(self):
      """Reads the raw (uncompensated) pressure level from the sensor."""
      """Assumes that the temperature has already been read """
      """i.e. that enough delay has been provided"""
      msb = self._device.readU8(BME280_REGISTER_PRESSURE_DATA)
      lsb = self._device.readU8(BME280_REGISTER_PRESSURE_DATA + 1)
      xlsb = self._device.readU8(BME280_REGISTER_PRESSURE_DATA + 2)
      raw = ((msb << 16) | (lsb << 8) | xlsb) >> 4
      return raw
  
    def read_raw_humidity(self):
      """Assumes that the temperature has already been read """
      """i.e. that enough delay has been provided"""
      msb = self._device.readU8(BME280_REGISTER_HUMIDITY_DATA)
      lsb = self._device.readU8(BME280_REGISTER_HUMIDITY_DATA + 1)
      raw = (msb << 8) | lsb
      return raw
  
    def read_temperature(self):
      """Get the compensated temperature in 0.01 of a degree celsius."""
      adc = self.read_raw_temp()
      var1 = ((adc >> 3) - (self.dig_T1 << 1)) * (self.dig_T2 >> 11)
      var2 = ((
          (((adc >> 4) - self.dig_T1) * ((adc >> 4) - self.dig_T1)) >> 12) *
          self.dig_T3) >> 14
      self.t_fine = var1 + var2
      return (self.t_fine * 5 + 128) >> 8
  
    def read_pressure(self):
      """Gets the compensated pressure in Pascals."""
      adc = self.read_raw_pressure()
      var1 = self.t_fine - 128000
      var2 = var1 * var1 * self.dig_P6
      var2 = var2 + ((var1 * self.dig_P5) << 17)
      var2 = var2 + (self.dig_P4 << 35)
      var1 = (((var1 * var1 * self.dig_P3) >> 8) +
              ((var1 * self.dig_P2) >> 12))
      var1 = (((1 << 47) + var1) * self.dig_P1) >> 33
      if var1 == 0:
        return 0
      p = 1048576 - adc
      p = (((p << 31) - var2) * 3125) // var1
      var1 = (self.dig_P9 * (p >> 13) * (p >> 13)) >> 25
      var2 = (self.dig_P8 * p) >> 19
      return ((p + var1 + var2) >> 8) + (self.dig_P7 << 4)
  
    def read_humidity(self):
      adc = self.read_raw_humidity()
      # print 'Raw humidity = {0:d}'.format (adc)
      h = self.t_fine - 76800
      h = (((((adc << 14) - (self.dig_H4 << 20) - (self.dig_H5 * h)) +
           16384) >> 15) * (((((((h * self.dig_H6) >> 10) * (((h *
                            self.dig_H3) >> 11) + 32768)) >> 10) + 2097152) *
                            self.dig_H2 + 8192) >> 14))
      h = h - (((((h >> 15) * (h >> 15)) >> 7) * self.dig_H1) >> 4)
      h = 0 if h < 0 else h
      h = 419430400 if h > 419430400 else h
      return h >> 12
  
    @property
    def temperature(self):
      "Return the temperature in degrees."
      t = self.read_temperature()
      ti = t // 100
      td = t - ti * 100
      return "{}.{:02d}".format(ti, td)
  
    @property
    def pressure(self):
      "Return the temperature in hPa."
      p = self.read_pressure() // 256
      pi = p // 100
      pd = p - pi * 100
      return "{}.{:02d}".format(pi, pd)
  
    @property
    def humidity(self):
      "Return the humidity in percent."
      h = self.read_humidity()
      hi = h // 1024
      hd = h * 100 // 1024 - hi * 100
      return "{}.{:02d}".format(hi, hd)
  