text: #!/usr/bin/python
  #--------------------------------------
  #    ___  ___  _ ____
  #   / _ \/ _ \(_) __/__  __ __
  #  / , _/ ___/ /\ \/ _ \/ // /
  # /_/|_/_/  /_/___/ .__/\_, /
  #                /_/   /___/
  #
  #           bme280.py
  #  Read data from a digital pressure sensor.
  #
  #  Official datasheet available from :
  #  https://www.bosch-sensortec.com/bst/products/all_products/bme280
  #
  # Author : Matt Hawkins
  # Date   : 25/07/2016
  #
  # http://www.raspberrypi-spy.co.uk/
  #
  #--------------------------------------
  import smbus
  import time
  from ctypes import c_short
  from ctypes import c_byte
  from ctypes import c_ubyte
  
  DEVICE = 0x76 # Default device I2C address
  
  
  bus = smbus.SMBus(1) # Rev 2 Pi, Pi 2 & Pi 3 uses bus 1
                       # Rev 1 Pi uses bus 0
  
  def getShort(data, index):
    # return two bytes from data as a signed 16-bit value
    return c_short((data[index+1] << 8) + data[index]).value
  
  def getUShort(data, index):
    # return two bytes from data as an unsigned 16-bit value
    return (data[index+1] << 8) + data[index]
  
  def getChar(data,index):
    # return one byte from data as a signed char
    result = data[index]
    if result > 127:
      result -= 256
    return result
  
  def getUChar(data,index):
    # return one byte from data as an unsigned char
    result =  data[index] & 0xFF
    return result
  
  def readBME280ID(addr=DEVICE):
    # Chip ID Register Address
    REG_ID     = 0xD0
    (chip_id, chip_version) = bus.read_i2c_block_data(addr, REG_ID, 2)
    return (chip_id, chip_version)
  
  def readBME280All(addr=DEVICE):
    # Register Addresses
    REG_DATA = 0xF7
    REG_CONTROL = 0xF4
    REG_CONFIG  = 0xF5
  
    REG_CONTROL_HUM = 0xF2
    REG_HUM_MSB = 0xFD
    REG_HUM_LSB = 0xFE
  
    # Oversample setting - page 27
    OVERSAMPLE_TEMP = 2
    OVERSAMPLE_PRES = 2
    MODE = 1
  
    # Oversample setting for humidity register - page 26
    OVERSAMPLE_HUM = 2
    bus.write_byte_data(addr, REG_CONTROL_HUM, OVERSAMPLE_HUM)
  
    control = OVERSAMPLE_TEMP<<5 | OVERSAMPLE_PRES<<2 | MODE
    bus.write_byte_data(addr, REG_CONTROL, control)
  
    # Read blocks of calibration data from EEPROM
    # See Page 22 data sheet
    cal1 = bus.read_i2c_block_data(addr, 0x88, 24)
    cal2 = bus.read_i2c_block_data(addr, 0xA1, 1)
    cal3 = bus.read_i2c_block_data(addr, 0xE1, 7)
  
    # Convert byte data to word values
    dig_T1 = getUShort(cal1, 0)
    dig_T2 = getShort(cal1, 2)
    dig_T3 = getShort(cal1, 4)
  
    dig_P1 = getUShort(cal1, 6)
    dig_P2 = getShort(cal1, 8)
    dig_P3 = getShort(cal1, 10)
    dig_P4 = getShort(cal1, 12)
    dig_P5 = getShort(cal1, 14)
    dig_P6 = getShort(cal1, 16)
    dig_P7 = getShort(cal1, 18)
    dig_P8 = getShort(cal1, 20)
    dig_P9 = getShort(cal1, 22)
  
    dig_H1 = getUChar(cal2, 0)
    dig_H2 = getShort(cal3, 0)
    dig_H3 = getUChar(cal3, 2)
  
    dig_H4 = getChar(cal3, 3)
    dig_H4 = (dig_H4 << 24) >> 20
    dig_H4 = dig_H4 | (getChar(cal3, 4) & 0x0F)
  
    dig_H5 = getChar(cal3, 5)
    dig_H5 = (dig_H5 << 24) >> 20
    dig_H5 = dig_H5 | (getUChar(cal3, 4) >> 4 & 0x0F)
  
    dig_H6 = getChar(cal3, 6)
  
    # Read temperature/pressure/humidity
    data = bus.read_i2c_block_data(addr, REG_DATA, 8)
    pres_raw = (data[0] << 12) | (data[1] << 4) | (data[2] >> 4)
    temp_raw = (data[3] << 12) | (data[4] << 4) | (data[5] >> 4)
    hum_raw = (data[6] << 8) | data[7]
  
    #Refine temperature
    var1 = ((((temp_raw>>3)-(dig_T1<<1)))*(dig_T2)) >> 11
    var2 = (((((temp_raw>>4) - (dig_T1)) * ((temp_raw>>4) - (dig_T1))) >> 12) * (dig_T3)) >> 14
    t_fine = var1+var2
    temperature = float(((t_fine * 5) + 128) >> 8);
  
    # Refine pressure and adjust for temperature
    var1 = t_fine / 2.0 - 64000.0
    var2 = var1 * var1 * dig_P6 / 32768.0
    var2 = var2 + var1 * dig_P5 * 2.0
    var2 = var2 / 4.0 + dig_P4 * 65536.0
    var1 = (dig_P3 * var1 * var1 / 524288.0 + dig_P2 * var1) / 524288.0
    var1 = (1.0 + var1 / 32768.0) * dig_P1
    if var1 == 0:
      pressure=0
    else:
      pressure = 1048576.0 - pres_raw
      pressure = ((pressure - var2 / 4096.0) * 6250.0) / var1
      var1 = dig_P9 * pressure * pressure / 2147483648.0
      var2 = pressure * dig_P8 / 32768.0
      pressure = pressure + (var1 + var2 + dig_P7) / 16.0
  
    # Refine humidity
    humidity = t_fine - 76800.0
    humidity = (hum_raw - (dig_H4 * 64.0 + dig_H5 / 16384.0 * humidity)) * (dig_H2 / 65536.0 * (1.0 + dig_H6 / 67108864.0 * humidity * (1.0 + dig_H3 / 67108864.0 * humidity)))
    humidity = humidity * (1.0 - dig_H1 * humidity / 524288.0)
    if humidity > 100:
      humidity = 100
    elif humidity < 0:
      humidity = 0
  
    return temperature/100.0, pressure/100.0, humidity
  
  def main():
  
    (chip_id, chip_version) = readBME280ID()
    print "Chip ID     :", chip_id
    print "Version     :", chip_version
  
    temperature,pressure,humidity = readBME280All()
  
    print "Temperature : ", temperature, "C"
    print "Pressure : ", pressure, "hPa"
    print "Humidity : ", humidity, "%"
  
  if __name__=="__main__":
     main()
  