#coding: utf-8
import time
ADDR=0x77
# this value is necessary to calculate the correct height above sealevel
# its also included in airport weather information ATIS named as QNH
# unit is hPa
QNH=1020
# power mode
# POWER_MODE=0 # sleep mode
# POWER_MODE=1 # forced mode
# POWER_MODE=2 # forced mode
POWER_MODE=3 # normal mode
# temperature resolution
# OSRS_T = 0 # skipped
# OSRS_T = 1 # 16 Bit
# OSRS_T = 2 # 17 Bit
# OSRS_T = 3 # 18 Bit
# OSRS_T = 4 # 19 Bit
OSRS_T = 5 # 20 Bit
# pressure resolution
# OSRS_P = 0 # pressure measurement skipped
# OSRS_P = 1 # 16 Bit ultra low power
# OSRS_P = 2 # 17 Bit low power
# OSRS_P = 3 # 18 Bit standard resolution
# OSRS_P = 4 # 19 Bit high resolution
OSRS_P = 5 # 20 Bit ultra high resolution
# filter settings
# FILTER = 0 #
# FILTER = 1 #
# FILTER = 2 #
# FILTER = 3 #
FILTER = 4 #
# FILTER = 5 #
# FILTER = 6 #
# FILTER = 7 #
# standby settings
# T_SB = 0 # 000 0,5ms
# T_SB = 1 # 001 62.5 ms
# T_SB = 2 # 010 125 ms
# T_SB = 3 # 011 250ms
T_SB = 4 # 100 500ms
# T_SB = 5 # 101 1000ms
# T_SB = 6 # 110 2000ms
# T_SB = 7 # 111 4000ms
CONFIG = (T_SB <<5) + (FILTER <<2) # combine bits for config
CTRL_MEAS = (OSRS_T <<5) + (OSRS_P <<2) + POWER_MODE # combine bits for ctrl_meas
# print ("CONFIG:",CONFIG)
# print ("CTRL_MEAS:",CTRL_MEAS)
REGISTER_DIG_T1 = 0x88
REGISTER_DIG_T2 = 0x8A
REGISTER_DIG_T3 = 0x8C
REGISTER_DIG_P1 = 0x8E
REGISTER_DIG_P2 = 0x90
REGISTER_DIG_P3 = 0x92
REGISTER_DIG_P4 = 0x94
REGISTER_DIG_P5 = 0x96
REGISTER_DIG_P6 = 0x98
REGISTER_DIG_P7 = 0x9A
REGISTER_DIG_P8 = 0x9C
REGISTER_DIG_P9 = 0x9E
REGISTER_CHIPID = 0xD0
REGISTER_VERSION = 0xD1
REGISTER_SOFTRESET = 0xE0
REGISTER_CONTROL = 0xF4
REGISTER_CONFIG = 0xF5
REGISTER_STATUS = 0xF3
REGISTER_TEMPDATA_MSB = 0xFA
REGISTER_TEMPDATA_LSB = 0xFB
REGISTER_TEMPDATA_XLSB = 0xFC
REGISTER_PRESSDATA_MSB = 0xF7
REGISTER_PRESSDATA_LSB = 0xF8
REGISTER_PRESSDATA_XLSB = 0xF9
class signed_int(int):
def __new__(self, number, bits=16):
if number & ( 1 << ( bits - 1 ) ):
number -= 1 << bits
return int.__new__(self, number)
class bmp280(object):
def __init__(self, i2c_bus=None, addr=ADDR):
object.__init__(self)
self._temperature = 0
self._pressure = 0
self.addr = addr
self.i2c_bus = i2c_bus
self._is_setup = False
if getattr(i2c_bus, "write_byte_data", None) is None or getattr(i2c_bus, "read_byte_data", None) is None:
raise TypeError("Object given for i2c_bus must implement write_byte_data and read_byte_data methods")
def _write_byte(self, register, value):
self.i2c_bus.write_byte_data(self.addr, register, value)
def _read_byte(self, register):
return self.i2c_bus.read_byte_data(self.addr, register)
def _read_word(self, register):
return self.i2c_bus.read_word_data(self.addr, register)
def _read_signed_word(self, register):
word = self._read_word(register)
return signed_int(word)
def _read_unsigned_word(self, register):
return self._read_word(register)
def temperature(self):
"""Return the current temperature.
Note: This value may be affected by nearby sources of heat, including the Pi itself.
"""
self.update()
return self._temperature
def pressure(self):
"""Return the current air pressure."""
self.update()
return self._pressure
def altitude(self, qnh=QNH):
"""Return the current approximate altitude.
:param qnh: Your local value for atmospheric pressure adjusted to sea level.
"""
return 44330.0 * (1.0 - pow(self.pressure() / (qnh*100), (1.0/5.255))) # Calculate altitute from pressure & qnh
def update(self):
"""Update stored temperature and pressure values.
This function is called automatically when calling temperature() or pressure().
"""
if not self._is_setup:
if self._read_byte(REGISTER_CHIPID) == 0x58: # check sensor id 0x58=BMP280
self._write_byte(REGISTER_SOFTRESET,0xB6) # reset sensor
time.sleep(0.2) # little break
self._write_byte(REGISTER_CONTROL,CTRL_MEAS) #
time.sleep(0.2) # little break
self._write_byte(REGISTER_CONFIG,CONFIG) #
time.sleep(0.2)
self.dig_T1 = self._read_unsigned_word(REGISTER_DIG_T1) # read correction settings
self.dig_T2 = self._read_signed_word(REGISTER_DIG_T2)
self.dig_T3 = self._read_signed_word(REGISTER_DIG_T3)
self.dig_P1 = self._read_unsigned_word(REGISTER_DIG_P1)
self.dig_P2 = self._read_signed_word(REGISTER_DIG_P2)
self.dig_P3 = self._read_signed_word(REGISTER_DIG_P3)
self.dig_P4 = self._read_signed_word(REGISTER_DIG_P4)
self.dig_P5 = self._read_signed_word(REGISTER_DIG_P5)
self.dig_P6 = self._read_signed_word(REGISTER_DIG_P6)
self.dig_P7 = self._read_signed_word(REGISTER_DIG_P7)
self.dig_P8 = self._read_signed_word(REGISTER_DIG_P8)
self.dig_P9 = self._read_signed_word(REGISTER_DIG_P9)
else:
raise IOError("bmp280 not found on address {:x}".format(self.addr))
self._is_setup = True
raw_temp_msb=self._read_byte(REGISTER_TEMPDATA_MSB) # read raw temperature msb
raw_temp_lsb=self._read_byte(REGISTER_TEMPDATA_LSB) # read raw temperature lsb
raw_temp_xlsb=self._read_byte(REGISTER_TEMPDATA_XLSB) # read raw temperature xlsb
raw_press_msb=self._read_byte(REGISTER_PRESSDATA_MSB) # read raw pressure msb
raw_press_lsb=self._read_byte(REGISTER_PRESSDATA_LSB) # read raw pressure lsb
raw_press_xlsb=self._read_byte(REGISTER_PRESSDATA_XLSB) # read raw pressure xlsb
raw_temp=(raw_temp_msb <<12)+(raw_temp_lsb<<4)+(raw_temp_xlsb>>4) # combine 3 bytes msb 12 bits left, lsb 4 bits left, xlsb 4 bits right
raw_press=(raw_press_msb <<12)+(raw_press_lsb <<4)+(raw_press_xlsb >>4) # combine 3 bytes msb 12 bits left, lsb 4 bits left, xlsb 4 bits right
var1=(raw_temp/16384.0-self.dig_T1/1024.0)*self.dig_T2 # formula for temperature from datasheet
var2=(raw_temp/131072.0-self.dig_T1/8192.0)*(raw_temp/131072.0-self.dig_T1/8192.0)*self.dig_T3 # formula for temperature from datasheet
temp=(var1+var2)/5120.0 # formula for temperature from datasheet
t_fine=(var1+var2) # need for pressure calculation
var1=t_fine/2.0-64000.0 # formula for pressure from datasheet
var2=var1*var1*self.dig_P6/32768.0 # formula for pressure from datasheet
var2=var2+var1*self.dig_P5*2 # formula for pressure from datasheet
var2=var2/4.0+self.dig_P4*65536.0 # formula for pressure from datasheet
var1=(self.dig_P3*var1*var1/524288.0+self.dig_P2*var1)/524288.0 # formula for pressure from datasheet
var1=(1.0+var1/32768.0)*self.dig_P1 # formula for pressure from datasheet
press=1048576.0-raw_press # formula for pressure from datasheet
press=(press-var2/4096.0)*6250.0/var1 # formula for pressure from datasheet
var1=self.dig_P9*press*press/2147483648.0 # formula for pressure from datasheet
var2=press*self.dig_P8/32768.0 # formula for pressure from datasheet
press=press+(var1+var2+self.dig_P7)/16.0 # formula for pressure from datasheet
press/=100 # convert to hPa
self._temperature = temp
self._pressure = press