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station-meteo/station-esp8266/lib-src/bme280_i2c.py

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# Author(s): Jonathan Hanson 2018
#
# This is more or less a straight read of the Bosch data sheet at:
# https://www.bosch-sensortec.com/bst/products/all_products/bme280
# and specifically:
# https://ae-bst.resource.bosch.com/media/_tech/media/datasheets/BST-BME280_DS001-12.pdf
#
# Modeled on the reference library Bosch Sensortec C library at:
# https://github.com/BoschSensortec/BME280_driver
#
# The development of this module was heavily guided by the prior work done
# by Peter Dahlberg et al at:
# https://github.com/catdog2/mpy_bme280_esp8266
from micropython import const
from ustruct import unpack, unpack_from
from utime import sleep_ms
# BME280 default address
BME280_I2C_ADDR_PRIM = const(0x76)
BME280_I2C_ADDR_SEC = const(0x77)
# Sensor Power Mode Options
BME280_SLEEP_MODE = const(0x00)
BME280_FORCED_MODE = const(0x01)
BME280_NORMAL_MODE = const(0x03)
# Oversampling Options
BME280_NO_OVERSAMPLING = const(0x00)
BME280_OVERSAMPLING_1X = const(0x01)
BME280_OVERSAMPLING_2X = const(0x02)
BME280_OVERSAMPLING_4X = const(0x03)
BME280_OVERSAMPLING_8X = const(0x04)
BME280_OVERSAMPLING_16X = const(0x05)
# Standby Duration Options
BME280_STANDBY_TIME_500_US = const(0x00) # Note this is microseconds, so 0.5 ms
BME280_STANDBY_TIME_62_5_MS = const(0x01)
BME280_STANDBY_TIME_125_MS = const(0x02)
BME280_STANDBY_TIME_250_MS = const(0x03)
BME280_STANDBY_TIME_500_MS = const(0x04)
BME280_STANDBY_TIME_1000_MS = const(0x05)
BME280_STANDBY_TIME_10_MS = const(0x06)
BME280_STANDBY_TIME_20_MS = const(0x07)
# Filter Coefficient Options
BME280_FILTER_COEFF_OFF = const(0x00)
BME280_FILTER_COEFF_2 = const(0x01)
BME280_FILTER_COEFF_4 = const(0x02)
BME280_FILTER_COEFF_8 = const(0x03)
BME280_FILTER_COEFF_16 = const(0x04)
# BME280 Chip ID
_BME280_CHIP_ID = const(0x60)
# Register Addresses
_BME280_CHIP_ID_ADDR = const(0xD0)
_BME280_RESET_ADDR = const(0xE0)
_BME280_TEMP_PRESS_CALIB_DATA_ADDR = const(0x88)
_BME280_HUMIDITY_CALIB_DATA_ADDR = const(0xE1)
_BME280_PWR_CTRL_ADDR = const(0xF4)
_BME280_CTRL_HUM_ADDR = const(0xF2)
_BME280_CTRL_MEAS_ADDR = const(0xF4)
_BME280_CONFIG_ADDR = const(0xF5)
_BME280_DATA_ADDR = const(0xF7)
# Register range sizes
_BME280_TEMP_PRESS_CALIB_DATA_LEN = const(26)
_BME280_HUMIDITY_CALIB_DATA_LEN = const(7)
_BME280_P_T_H_DATA_LEN = const(8)
class BME280_I2C:
def __init__(self, address: int = BME280_I2C_ADDR_PRIM, i2c=None):
"""
Ensure I2C communication with the sensor is working, reset the sensor,
and load its calibration data into memory.
"""
self.address = address
if i2c is None:
raise ValueError('A configured I2C object is required.')
self.i2c = i2c
self._read_chip_id()
self._soft_reset()
self._load_calibration_data()
def _read_chip_id(self):
"""
Read the chip ID from the sensor and verify it's correct.
If the value isn't correct, wait 1ms and try again.
If 5 tries don't work, raise an exception.
"""
for x in range(5):
mem = self.i2c.readfrom_mem(self.address, _BME280_CHIP_ID_ADDR, 1)
if mem[0] == _BME280_CHIP_ID:
return
sleep_ms(1)
raise Exception("Couldn't read BME280 chip ID after 5 attempts.")
def _soft_reset(self):
"""
Write the reset command to the sensor's reset address.
Wait 2ms, per the reference library's example.
"""
self.i2c.writeto_mem(self.address, _BME280_RESET_ADDR, bytearray([0xB6]))
sleep_ms(2)
def _load_calibration_data(self):
"""
Load the read-only calibration values out of the sensor's memory, to be
used later in calibrating the raw reads. These get stored in various
self.cal_dig_* object properties.
See https://github.com/BoschSensortec/BME280_driver/blob/bme280_v3.3.4/bme280.c#L1192
See https://github.com/BoschSensortec/BME280_driver/blob/bme280_v3.3.4/bme280.c#L1216
See https://github.com/catdog2/mpy_bme280_esp8266/blob/master/bme280.py#L73
"""
# Load the temperature and pressure calibration data
# (note that the first value of the humidity data is stuffed in here)
tp_cal_mem = self.i2c.readfrom_mem(self.address,
_BME280_TEMP_PRESS_CALIB_DATA_ADDR,
_BME280_TEMP_PRESS_CALIB_DATA_LEN)
(self.cal_dig_T1, self.cal_dig_T2, self.cal_dig_T3,
self.cal_dig_P1, self.cal_dig_P2, self.cal_dig_P3,
self.cal_dig_P4, self.cal_dig_P5, self.cal_dig_P6,
self.cal_dig_P7, self.cal_dig_P8, self.cal_dig_P9,
_,
self.cal_dig_H1) = unpack("<HhhHhhhhhhhhBB", tp_cal_mem)
# Load the rest of the humidity calibration data
hum_cal_mem = self.i2c.readfrom_mem(self.address,
_BME280_HUMIDITY_CALIB_DATA_ADDR,
_BME280_HUMIDITY_CALIB_DATA_LEN)
self.cal_dig_H2, self.cal_dig_H3 = unpack("<hB", hum_cal_mem)
e4_sign = unpack_from("<b", hum_cal_mem, 3)[0]
self.cal_dig_H4 = (e4_sign << 4) | (hum_cal_mem[4] & 0b00001111)
e6_sign = unpack_from("<b", hum_cal_mem, 5)[0]
self.cal_dig_H5 = (e6_sign << 4) | (hum_cal_mem[4] >> 4)
self.cal_dig_H6 = unpack_from("<b", hum_cal_mem, 6)[0]
# Initialize the cal_t_fine carry-over value used during compensation
self.cal_t_fine = 0
def get_measurement_settings(self):
"""
Return a parsed set of the sensor's measurement settings as a dict
These values include oversampling settings for each measurement,
the IIR filter coefficient, and the standby duration for normal
power mode.
See the data sheet, section 3 and 5
"""
mem = self.i2c.readfrom_mem(self.address, _BME280_CTRL_HUM_ADDR, 4)
ctrl_hum, _, ctrl_meas, config = unpack("<BBBB", mem)
return {
"osr_h": (ctrl_hum & 0b00000111),
"osr_p": (ctrl_meas >> 2) & 0b00000111,
"osr_t": (ctrl_meas >> 5) & 0b00000111,
"filter": (config >> 2) & 0b00000111,
"standby_time": (config >> 5) & 0b00000111,
}
def set_measurement_settings(self, settings: dict):
"""
Set the sensor's settings for each measurement's oversampling,
the pressure IIR filter coefficient, and standby duration
during normal power mode.
The settings dict can have keys osr_h, osr_p, osr_t, filter, and
standby_time. All values are optional, and omitting any will retain
the pre-existing value.
See the data sheet, section 3 and 5
"""
self._validate_settings(settings)
self._ensure_sensor_is_asleep()
self._write_measurement_settings(settings)
def _validate_settings(self, settings: dict):
oversampling_options = [
BME280_NO_OVERSAMPLING, BME280_OVERSAMPLING_1X,
BME280_OVERSAMPLING_2X, BME280_OVERSAMPLING_4X,
BME280_OVERSAMPLING_8X, BME280_OVERSAMPLING_16X]
filter_options = [
BME280_FILTER_COEFF_OFF, BME280_FILTER_COEFF_2,
BME280_FILTER_COEFF_4, BME280_FILTER_COEFF_8,
BME280_FILTER_COEFF_16]
standby_time_options = [
BME280_STANDBY_TIME_500_US,
BME280_STANDBY_TIME_62_5_MS, BME280_STANDBY_TIME_125_MS,
BME280_STANDBY_TIME_250_MS, BME280_STANDBY_TIME_500_MS,
BME280_STANDBY_TIME_1000_MS, BME280_STANDBY_TIME_10_MS,
BME280_STANDBY_TIME_20_MS]
if 'osr_h' in settings:
if settings['osr_h'] not in oversampling_options:
raise ValueError("osr_h must be one of the oversampling defines")
if 'osr_p' in settings:
if settings['osr_h'] not in oversampling_options:
raise ValueError("osr_p must be one of the oversampling defines")
if 'osr_t' in settings:
if settings['osr_h'] not in oversampling_options:
raise ValueError("osr_t must be one of the oversampling defines")
if 'filter' in settings:
if settings['filter'] not in filter_options:
raise ValueError("filter filter coefficient defines")
if 'standby_time' in settings:
if settings['standby_time'] not in standby_time_options:
raise ValueError("standby_time must be one of the standby time duration defines")
def _write_measurement_settings(self, settings: dict):
# Read in the existing configuration, to modify
mem = self.i2c.readfrom_mem(self.address, _BME280_CTRL_HUM_ADDR, 4)
ctrl_hum, _, ctrl_meas, config = unpack("<BBBB", mem)
# Make any changes necessary to the ctrl_hum register
if "osr_h" in settings:
newval = (ctrl_hum & 0b11111000) | (settings['osr_h'] & 0b00000111)
self.i2c.writeto_mem(self.address, _BME280_CTRL_HUM_ADDR, bytearray([newval]))
# according to the data sheet, ctrl_hum needs a write to
# ctrl_meas in order to take effect
self.i2c.writeto_mem(self.address, _BME280_CTRL_MEAS_ADDR, bytearray([ctrl_meas]))
# Make any changes necessary to the ctrl_meas register
if "osr_p" in settings or "osr_t" in settings:
newval = ctrl_meas
if "osr_p" in settings:
newval = (newval & 0b11100011) | ((settings['osr_p'] << 2) & 0b00011100)
if "osr_t" in settings:
newval = (newval & 0b00011111) | ((settings['osr_t'] << 5) & 0b11100000)
self.i2c.writeto_mem(self.address, _BME280_CTRL_MEAS_ADDR, bytearray([newval]))
# Make any changes necessary to the config register
if "filter" in settings or "standby_time" in settings:
newval = config
if "filter" in settings:
newval = (newval & 0b11100011) | ((settings['filter'] << 2) & 0b00011100)
if "standby_time" in settings:
newval = (newval & 0b00011111) | ((settings['standby_time'] << 5) & 0b11100000)
self.i2c.writeto_mem(self.address, _BME280_CONFIG_ADDR, bytearray([newval]))
def get_power_mode(self):
"""
Result will be one of BME280_SLEEP_MODE, BME280_FORCED_MODE, or
BME280_NORMAL_MODE.
See the data sheet, section 3.3
"""
mem = self.i2c.readfrom_mem(self.address, _BME280_PWR_CTRL_ADDR, 1)
return (mem[0] & 0b00000011)
def set_power_mode(self, new_power_mode: int):
"""
Configure the sensor's power mode (BME280_SLEEP_MODE,
BME280_FORCED_MODE, or BME280_NORMAL_MODE)
Note that setting to forced mode will immediately set the sensor back
to sleep mode after taking a measurement.
See the data sheet, section 3.3
"""
if new_power_mode not in [BME280_SLEEP_MODE, BME280_FORCED_MODE, BME280_NORMAL_MODE]:
raise ValueError("New power mode must be sleep, forced, or normal constant")
self._ensure_sensor_is_asleep()
# Read the current register, mask out and set the new power mode,
# and write the register back to the device.
mem = self.i2c.readfrom_mem(self.address, _BME280_PWR_CTRL_ADDR, 1)
newval = (mem[0] & 0b11111100) | (new_power_mode & 0b00000011)
self.i2c.writeto_mem(self.address, _BME280_PWR_CTRL_ADDR, bytearray([newval]))
def _ensure_sensor_is_asleep(self):
"""
If the sensor mode isn't already "sleep", then put it to sleep.
This is done by reading out the configuration values we want to keep,
and then doing a soft reset and writing those values back.
"""
if self.get_power_mode() != BME280_SLEEP_MODE:
settings = self.get_measurement_settings()
self._soft_reset()
self._write_measurement_settings(settings)
def get_measurement(self):
"""
Return a set of measurements in decimal value, compensated with the
sensor's stored calibration data.
"""
uncompensated_data = self._read_uncompensated_data()
# Be sure to call self._compensate_temperature() first, as it sets a
# global "fine" calibration value for the other two compensation
# functions
return {
"temperature": self._compensate_temperature(uncompensated_data['temperature']),
"pressure": self._compensate_pressure(uncompensated_data['pressure']),
"humidity": self._compensate_humidity(uncompensated_data['humidity']),
}
def _read_uncompensated_data(self):
# Read the uncompensated temperature, pressure, and humidity data
mem = self.i2c.readfrom_mem(self.address, _BME280_DATA_ADDR, _BME280_P_T_H_DATA_LEN)
(press_msb, press_lsb, press_xlsb,
temp_msb, temp_lsb, temp_xlsb,
hum_msb, hum_lsb) = unpack("<BBBBBBBB", mem)
# Assemble the values from the memory fragments and return a dict.
#
# Note that we're calling temperature first, since it sets the
# cal_t_fine value used in humidity and pressure.
return {
"temperature": (temp_msb << 12) | (temp_lsb << 4) | (temp_xlsb >> 4),
"pressure": (press_msb << 12) | (press_lsb << 4) | (press_xlsb >> 4),
"humidity": (hum_msb << 8) | (hum_lsb),
}
##
# Float Implementations
##
# def _compensate_temperature(self, adc_T: int) -> float:
# """
# Output value of “25.0” equals 25.0 DegC.
#
# See the floating-point implementation in the reference library:
# https://github.com/BoschSensortec/BME280_driver/blob/bme280_v3.3.4/bme280.c#L884
# """
# temperature_min = -40
# temperature_max = 85
#
# var1 = (adc_T / 16384.0) - (self.cal_dig_T1 / 1024.0)
# var1 = var1 * self.cal_dig_T2
#
# var2 = (adc_T / 131072.0) - (self.cal_dig_T1 / 8192.0)
# var2 = var2 * var2 * self.cal_dig_T3
#
# self.cal_t_fine = int(var1 + var2)
#
# temperature = (var1 + var2) / 5120.0
#
# if temperature < temperature_min:
# temperature = temperature_min
# elif temperature > temperature_max:
# temperature = temperature_max
#
# return temperature
# def _compensate_pressure(self, adc_P: int) -> float:
# """
# Output value of “96386.0” equals 96386 Pa = 963.86 hPa
#
# See the floating-point implementation in the reference library:
# https://github.com/BoschSensortec/BME280_driver/blob/bme280_v3.3.4/bme280.c#L912
# """
# pressure_min = 30000.0
# pressure_max = 110000.0
#
# var1 = (self.cal_t_fine / 2.0) - 64000.0
#
# var2 = var1 * var1 * self.cal_dig_P6 / 32768.0
# var2 = var2 + (var1 * self.cal_dig_P5 * 2.0)
# var2 = (var2 / 4.0) + (self.cal_dig_P4 * 65536.0)
#
# var3 = self.cal_dig_P3 * var1 * var1 / 524288.0
#
# var1 = (var3 + self.cal_dig_P2 * var1) / 524288.0
# var1 = (1.0 + var1 / 32768.0) * self.cal_dig_P1
#
# # avoid exception caused by division by zero
# if var1:
# pressure = 1048576.0 - adc_P
# pressure = (pressure - (var2 / 4096.0)) * 6250.0 / var1
# var1 = self.cal_dig_P9 * pressure * pressure / 2147483648.0
# var2 = pressure * self.cal_dig_P8 / 32768.0
# pressure = pressure + (var1 + var2 + self.cal_dig_P7) / 16.0
#
# if pressure < pressure_min:
# pressure = pressure_min
# elif pressure > pressure_max:
# pressure = pressure_max
#
# else:
# # Invalid case
# pressure = pressure_min
#
# return pressure
# def _compensate_humidity(self, adc_H: int) -> float:
# """
# Output value between 0.0 and 100.0, where 100.0 is 100%RH
#
# See the floating-point implementation in the reference library:
# https://github.com/BoschSensortec/BME280_driver/blob/bme280_v3.3.4/bme280.c#L952
# """
# humidity_min = 0.0
# humidity_max = 100.0
#
# var1 = self.cal_t_fine - 76800.0
#
# var2 = self.cal_dig_H4 * 64.0 + (self.cal_dig_H5 / 16384.0) * var1
#
# var3 = adc_H - var2
#
# var4 = self.cal_dig_H2 / 65536.0
#
# var5 = 1.0 + (self.cal_dig_H3 / 67108864.0) * var1
#
# var6 = 1.0 + (self.cal_dig_H6 / 67108864.0) * var1 * var5
# var6 = var3 * var4 * (var5 * var6)
#
# humidity = var6 * (1.0 - self.cal_dig_H1 * var6 / 524288.0)
#
# if humidity > humidity_max:
# humidity = humidity_max
# elif humidity < humidity_min:
# humidity = humidity_min
#
# return humidity
##
# 32-Bit Integer Implementations
##
def _compensate_temperature(self, adc_T: int) -> float:
"""
Output value of “25.0” equals 25.0 DegC.
See the integer implementation in the data sheet, section 4.2.3
And the reference library:
https://github.com/BoschSensortec/BME280_driver/blob/bme280_v3.3.4/bme280.c#L987
"""
temperature_min = -4000
temperature_max = 8500
var1 = (((adc_T // 8) - (self.cal_dig_T1 * 2)) * self.cal_dig_T2) // 2048
var2 = (((((adc_T // 16) - self.cal_dig_T1) * ((adc_T // 16) - self.cal_dig_T1)) // 4096) * self.cal_dig_T3) // 16384
self.cal_t_fine = var1 + var2
temperature = (self.cal_t_fine * 5 + 128) // 256
if temperature < temperature_min:
temperature = temperature_min
elif temperature > temperature_max:
temperature = temperature_max
return temperature / 100
def _compensate_pressure(self, adc_P: int) -> float:
"""
Output value of “96386.0” equals 96386 Pa = 963.86 hPa
See the 32-bit integer implementation in the data sheet, section 4.2.3
And the reference library:
https://github.com/BoschSensortec/BME280_driver/blob/bme280_v3.3.4/bme280.c#L1059
Note that there's a 64-bit version of this function in the reference
library on line 1016 that we're leaving unimplemented.
"""
pressure_min = 30000
pressure_max = 110000
var1 = (self.cal_t_fine // 2) - 64000
var2 = (((var1 // 4) * (var1 // 4)) // 2048) * self.cal_dig_P6
var2 = var2 + ((var1 * self.cal_dig_P5) * 2)
var2 = (var2 // 4) + (self.cal_dig_P4 * 65536)
var3 = (self.cal_dig_P3 * (((var1 // 4) * (var1 // 4)) // 8192)) // 8
var4 = (self.cal_dig_P2 * var1) // 2
var1 = (var3 + var4) // 262144
var1 = ((32768 + var1) * self.cal_dig_P1) // 32768
# avoid exception caused by division by zero
if var1:
var5 = 1048576 - adc_P
pressure = (var5 - (var2 // 4096)) * 3125
if pressure < 0x80000000:
pressure = (pressure << 1) // var1
else:
pressure = (pressure // var1) * 2
var1 = (self.cal_dig_P9 * (((pressure // 8) * (pressure // 8)) // 8192)) // 4096
var2 = (((pressure // 4)) * self.cal_dig_P8) // 8192
pressure = pressure + ((var1 + var2 + self.cal_dig_P7) // 16)
if pressure < pressure_min:
pressure = pressure_min
elif pressure > pressure_max:
pressure = pressure_max
else:
# Invalid case
pressure = pressure_min
return pressure
def _compensate_humidity(self, adc_H: int) -> float:
"""
Output value between 0.0 and 100.0, where 100.0 is 100%RH
See the floating-point implementation in the reference library:
https://github.com/BoschSensortec/BME280_driver/blob/bme280_v3.3.4/bme280.c#1108
"""
humidity_max = 102400
var1 = self.cal_t_fine - 76800
var2 = adc_H * 16384
var3 = self.cal_dig_H4 * 1048576
var4 = self.cal_dig_H5 * var1
var5 = (((var2 - var3) - var4) + 16384) // 32768
var2 = (var1 * self.cal_dig_H6) // 1024
var3 = (var1 * self.cal_dig_H3) // 2048
var4 = ((var2 * (var3 + 32768)) // 1024) + 2097152
var2 = ((var4 * self.cal_dig_H2) + 8192) // 16384
var3 = var5 * var2
var4 = ((var3 // 32768) * (var3 // 32768)) // 128
var5 = var3 - ((var4 * self.cal_dig_H1) // 16)
if var5 < 0:
var5 = 0
if var5 > 419430400:
var5 = 419430400
humidity = var5 // 4096
if (humidity > humidity_max):
humidity = humidity_max
return humidity / 1024
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