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bme280.py
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bme280.py
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"""
MicroPython driver for Bosh BME280 temperature, pressure and humidity I2C sensor:
https://www.bosch-sensortec.com/bst/products/all_products/bme280
Authors: Nelio Goncalves Godoi, Roberto Colistete Jr
Version: 3.1.2 @ 2018/04
License: MIT License (https://opensource.org/licenses/MIT)
"""
import time
from ustruct import unpack, unpack_from
from array import array
# BME280 default address
BME280_I2CADDR = 0x76
# BME280_I2CADDR = 0x77
OSAMPLE_0 = 0
OSAMPLE_1 = 1
OSAMPLE_2 = 2
OSAMPLE_4 = 3
OSAMPLE_8 = 4
OSAMPLE_16 = 5
BME280_REGISTER_STATUS = 0xF3
BME280_REGISTER_CONTROL_HUM = 0xF2
BME280_REGISTER_CONTROL = 0xF4
BME280_REGISTER_CONTROL_IIR = 0xF5
FILTER_OFF = 0
FILTER_2 = 1
FILTER_4 = 2
FILTER_8 = 3
FILTER_16 = 4
CELSIUS = 'C'
FAHRENHEIT = 'F'
KELVIN = 'K'
class BME280(object):
def __init__(self,
temperature_mode=OSAMPLE_2,
pressure_mode=OSAMPLE_16,
humidity_mode=OSAMPLE_1,
temperature_scale=CELSIUS,
iir=FILTER_16,
address=BME280_I2CADDR,
i2c=None):
osamples = [
OSAMPLE_0,
OSAMPLE_1,
OSAMPLE_2,
OSAMPLE_4,
OSAMPLE_8,
OSAMPLE_16]
msg_error = 'Unexpected {} operating mode value {0}.'
if temperature_mode not in osamples:
raise ValueError(msg_error.format("temperature", temperature_mode))
self.temperature_mode = temperature_mode
if pressure_mode not in osamples:
raise ValueError(msg_error.format("pressure", pressure_mode))
self.pressure_mode = pressure_mode
if humidity_mode not in osamples:
raise ValueError(msg_error.format("humidity", humidity_mode))
self.humidity_mode = humidity_mode
msg_error = 'Unexpected low pass IIR filter setting value {0}.'
if iir not in [FILTER_OFF, FILTER_2, FILTER_4, FILTER_8, FILTER_16]:
raise ValueError(msg_error.format(iir))
self.iir = iir
msg_error = 'Unexpected temperature scale value {0}.'
if temperature_scale not in [CELSIUS, FAHRENHEIT, KELVIN]:
raise ValueError(msg_error.format(temperature_scale))
self.temperature_scale = temperature_scale
del msg_error
self.address = address
if i2c is None:
raise ValueError('An I2C object is required.')
self.i2c = i2c
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 = unpack("<hB", dig_e1_e7)
e4_sign = unpack_from("<b", dig_e1_e7, 3)[0]
self.dig_H4 = (e4_sign << 4) | (dig_e1_e7[4] & 0xF)
e6_sign = unpack_from("<b", dig_e1_e7, 5)[0]
self.dig_H5 = (e6_sign << 4) | (dig_e1_e7[4] >> 4)
self.dig_H6 = unpack_from("<b", dig_e1_e7, 6)[0]
self.i2c.writeto_mem(
self.address,
BME280_REGISTER_CONTROL,
bytearray([0x24]))
time.sleep(0.002)
self.t_fine = 0
self._l1_barray = bytearray(1)
self._l8_barray = bytearray(8)
self._l3_resultarray = array("i", [0, 0, 0])
self._l1_barray[0] = self.iir << 2
self.i2c.writeto_mem(
self.address,
BME280_REGISTER_CONTROL_IIR,
self._l1_barray)
time.sleep(0.002)
self._l1_barray[0] = self.humidity_mode
self.i2c.writeto_mem(
self.address,
BME280_REGISTER_CONTROL_HUM,
self._l1_barray)
def read_raw_data(self, result):
self._l1_barray[0] = (
self.pressure_mode << 5 |
self.temperature_mode << 2 | 1)
self.i2c.writeto_mem(
self.address,
BME280_REGISTER_CONTROL,
self._l1_barray)
osamples_1_16 = [
OSAMPLE_1,
OSAMPLE_2,
OSAMPLE_4,
OSAMPLE_8,
OSAMPLE_16]
sleep_time = 1250
if self.temperature_mode in osamples_1_16:
sleep_time += 2300*(1 << self.temperature_mode)
if self.pressure_mode in osamples_1_16:
sleep_time += 575 + (2300*(1 << self.pressure_mode))
if self.humidity_mode in osamples_1_16:
sleep_time += 575 + (2300*(1 << self.humidity_mode))
time.sleep_us(sleep_time)
while (unpack('<H',
self.i2c.readfrom_mem(
self.address,
BME280_REGISTER_STATUS, 2))[0] & 0x08):
time.sleep(0.001)
self.i2c.readfrom_mem_into(self.address, 0xF7, self._l8_barray)
readout = self._l8_barray
raw_press = ((readout[0] << 16) | (readout[1] << 8) | readout[2]) >> 4
raw_temp = ((readout[3] << 16) | (readout[4] << 8) | readout[5]) >> 4
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):
""" Get raw data and compensa the same """
self.read_raw_data(self._l3_resultarray)
raw_temp, raw_press, raw_hum = self._l3_resultarray
var1 = ((raw_temp >> 3) - (self.dig_T1 << 1)) * (self.dig_T2 >> 11)
var2 = (raw_temp >> 4) - self.dig_T1
var2 = var2 * ((raw_temp >> 4) - self.dig_T1)
var2 = ((var2 >> 12) * self.dig_T3) >> 14
self.t_fine = var1 + var2
temp = (self.t_fine * 5 + 128) >> 8
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:
pressure = 0
else:
p = 1048576 - raw_press
p = (((p << 31) - var2) * 3125) // var1
var1 = (self.dig_P9 * (p >> 13) * (p >> 13)) >> 25
var2 = (self.dig_P8 * p) >> 19
pressure = ((p + var1 + var2) >> 8) + (self.dig_P7 << 4)
h = self.t_fine - 76800
h = (((((raw_hum << 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
humidity = h >> 12
if result:
result[0] = temp
result[1] = pressure
result[2] = humidity
return result
return array("i", (temp, pressure, humidity))
@property
def values(self):
temp, pres, humi = self.read_compensated_data()
temp = temp/100
if self.temperature_scale == 'F':
temp = 32 + (temp*1.8)
elif self.temperature_scale == 'K':
temp = temp + 273.15
pres = pres/256
humi = humi/1024
return (temp, pres, humi)
@property
def formated_values(self):
t, p, h = self.values
temp = "{} "+self.temperature_scale
return (temp.format(t), "{} Pa".format(p), "{} %".format(h))
@property
def temperature(self):
t, _, _ = self.values
return t
@property
def pressure(self):
_, p, _ = self.values
return p
@property
def pressure_precision(self):
_, p, _ = self.read_compensated_data()
pi = float(p // 256)
pd = (p % 256)/256
return (pi, pd)
@property
def humidity(self):
_, _, h = self.values
return h
def altitude(self, pressure_sea_level=1013.25):
pi, pd = self.pressure_precision()
return 44330*(1-((float(pi+pd)/100)/pressure_sea_level)**(1/5.255))