# Updated 2018 and 2020
# This module is based on the below cited resources, which are all
# based on the documentation as provided in the Bosch Data Sheet and
# the sample implementation provided therein.
#
# Final Document: BST-BME280-DS002-15
#
# Authors: Paul Cunnane 2016, Peter Dahlebrg 2016
#
# This module borrows from the Adafruit BME280 Python library. Original
# Copyright notices are reproduced below.
#
# Those libraries were written for the Raspberry Pi. This modification is
# intended for the MicroPython and esp8266 boards.
#
# Copyright (c) 2014 Adafruit Industries
# Author: Tony DiCola
#
# Based on the BMP280 driver with BME280 changes provided by
# David J Taylor, Edinburgh (www.satsignal.eu)
#
# Based on Adafruit_I2C.py created by Kevin Townsend.
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.
#
import time
from ustruct import unpack, unpack_from
from array import array
# 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_REGISTER_CONTROL_HUM = 0xF2
BME280_REGISTER_STATUS = 0xF3
BME280_REGISTER_CONTROL = 0xF4
MODE_SLEEP = const(0)
MODE_FORCED = const(1)
MODE_NORMAL = const(3)
BME280_TIMEOUT = const(100) # about 1 second timeout
class BME280:
def __init__(self,
mode=BME280_OSAMPLE_8,
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_OSAMPLE_1, BME280_OSAMPLE_2, BME280_OSAMPLE_4,'
'BME280_OSAMPLE_8, BME280_OSAMPLE_16'.format(mode))
self._mode = mode
self.address = address
if i2c is None:
raise ValueError('An I2C object is required.')
self.i2c = i2c
self.__sealevel = 101325
# load calibration data
dig_88_a1 = self.i2c.readfrom_mem(self.address, 0x88, 26)
dig_e1_e7 = self.i2c.readfrom_mem(self.address, 0xE1, 7)
self.dig_T1, self.dig_T2, self.dig_T3, self.dig_P1, \
self.dig_P2, self.dig_P3, self.dig_P4, self.dig_P5, \
self.dig_P6, self.dig_P7, self.dig_P8, self.dig_P9, \
_, self.dig_H1 = unpack("<HhhHhhhhhhhhBB", dig_88_a1)
self.dig_H2, self.dig_H3, self.dig_H4,\
self.dig_H5, self.dig_H6 = unpack("<hBbhb", dig_e1_e7)
# unfold H4, H5, keeping care of a potential sign
self.dig_H4 = (self.dig_H4 * 16) + (self.dig_H5 & 0xF)
self.dig_H5 //= 16
# temporary data holders which stay allocated
self._l1_barray = bytearray(1)
self._l8_barray = bytearray(8)
self._l3_resultarray = array("i", [0, 0, 0])
self._l1_barray[0] = self._mode << 5 | self._mode << 2 | MODE_SLEEP
self.i2c.writeto_mem(self.address, BME280_REGISTER_CONTROL,
self._l1_barray)
self.t_fine = 0
def read_raw_data(self, result):
""" Reads the raw (uncompensated) data from the sensor.
Args:
result: array of length 3 or alike where the result will be
stored, in temperature, pressure, humidity order
Returns:
None
"""
self._l1_barray[0] = self._mode
self.i2c.writeto_mem(self.address, BME280_REGISTER_CONTROL_HUM,
self._l1_barray)
self._l1_barray[0] = self._mode << 5 | self._mode << 2 | MODE_FORCED
self.i2c.writeto_mem(self.address, BME280_REGISTER_CONTROL,
self._l1_barray)
# Wait for conversion to complete
for _ in range(BME280_TIMEOUT):
if self.i2c.readfrom_mem(self.address, BME280_REGISTER_STATUS, 1)[0] & 0x08:
time.sleep_ms(10) # still busy
else:
break # Sensor ready
else:
raise RuntimeError("Sensor BME280 not ready")
# burst readout from 0xF7 to 0xFE, recommended by datasheet
self.i2c.readfrom_mem_into(self.address, 0xF7, self._l8_barray)
readout = self._l8_barray
# pressure(0xF7): ((msb << 16) | (lsb << 8) | xlsb) >> 4
raw_press = ((readout[0] << 16) | (readout[1] << 8) | readout[2]) >> 4
# temperature(0xFA): ((msb << 16) | (lsb << 8) | xlsb) >> 4
raw_temp = ((readout[3] << 16) | (readout[4] << 8) | readout[5]) >> 4
# humidity(0xFD): (msb << 8) | lsb
raw_hum = (readout[6] << 8) | readout[7]
result[0] = raw_temp
result[1] = raw_press
result[2] = raw_hum
def read_compensated_data(self, result=None):
""" Reads the data from the sensor and returns the compensated data.
Args:
result: array of length 3 or alike where the result will be
stored, in temperature, pressure, humidity order. You may use
this to read out the sensor without allocating heap memory
Returns:
array with temperature, pressure, humidity. Will be the one
from the result parameter if not None
"""
self.read_raw_data(self._l3_resultarray)
raw_temp, raw_press, raw_hum = self._l3_resultarray
# temperature
var1 = (raw_temp/16384.0 - self.dig_T1/1024.0) * self.dig_T2
var2 = raw_temp/131072.0 - self.dig_T1/8192.0
var2 = var2 * var2 * self.dig_T3
self.t_fine = int(var1 + var2)
temp = (var1 + var2) / 5120.0
temp = max(-40, min(85, temp))
# pressure
var1 = (self.t_fine/2.0) - 64000.0
var2 = var1 * var1 * self.dig_P6 / 32768.0 + var1 * self.dig_P5 * 2.0
var2 = (var2 / 4.0) + (self.dig_P4 * 65536.0)
var1 = (self.dig_P3 * var1 * var1 / 524288.0 + self.dig_P2 * var1) / 524288.0
var1 = (1.0 + var1 / 32768.0) * self.dig_P1
if (var1 == 0.0):
pressure = 30000 # avoid exception caused by division by zero
else:
p = ((1048576.0 - raw_press) - (var2 / 4096.0)) * 6250.0 / var1
var1 = self.dig_P9 * p * p / 2147483648.0
var2 = p * self.dig_P8 / 32768.0
pressure = p + (var1 + var2 + self.dig_P7) / 16.0
pressure = max(30000, min(110000, pressure))
# humidity
h = (self.t_fine - 76800.0)
h = ((raw_hum - (self.dig_H4 * 64.0 + self.dig_H5 / 16384.0 * h)) *
(self.dig_H2 / 65536.0 * (1.0 + self.dig_H6 / 67108864.0 * h *
(1.0 + self.dig_H3 / 67108864.0 * h))))
humidity = h * (1.0 - self.dig_H1 * h / 524288.0)
# humidity = max(0, min(100, humidity))
if result:
result[0] = temp
result[1] = pressure
result[2] = humidity
return result
return array("f", (temp, pressure, humidity))
@property
def sealevel(self):
return self.__sealevel
@sealevel.setter
def sealevel(self, value):
if 30000 < value < 120000: # just ensure some reasonable value
self.__sealevel = value
@property
def altitude(self):
'''
Altitude in m.
'''
from math import pow
try:
p = 44330 * (1.0 - pow(self.read_compensated_data()[1] /
self.__sealevel, 0.1903))
except:
p = 0.0
return p
@property
def dew_point(self):
"""
Compute the dew point temperature for the current Temperature
and Humidity measured pair
"""
from math import log
t, p, h = self.read_compensated_data()
h = (log(h, 10) - 2) / 0.4343 + (17.62 * t) / (243.12 + t)
return 243.12 * h / (17.62 - h)
@property
def values(self):
""" human readable values """
t, p, h = self.read_compensated_data()
return ("{:.3f}".format(t), "{:.3f}".format(p/100),
"{:.3f}".format(h))