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bme280.py
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bme280.py
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import smbus
bus_number = 1
i2c_address = 0x76
bus = smbus.SMBus(bus_number)
digT = []
digP = []
digH = []
t_fine = 0.0
def write_reg(reg_address, data):
bus.write_byte_data(i2c_address, reg_address, data)
def get_calib_param():
calib = []
for i in range(0x88, 0x88 + 24):
calib.append(bus.read_byte_data(i2c_address, i))
calib.append(bus.read_byte_data(i2c_address, 0xA1))
for i in range(0xE1, 0xE1 + 7):
calib.append(bus.read_byte_data(i2c_address, i))
digT.append((calib[1] << 8) | calib[0])
digT.append((calib[3] << 8) | calib[2])
digT.append((calib[5] << 8) | calib[4])
digP.append((calib[7] << 8) | calib[6])
digP.append((calib[9] << 8) | calib[8])
digP.append((calib[11] << 8) | calib[10])
digP.append((calib[13] << 8) | calib[12])
digP.append((calib[15] << 8) | calib[14])
digP.append((calib[17] << 8) | calib[16])
digP.append((calib[19] << 8) | calib[18])
digP.append((calib[21] << 8) | calib[20])
digP.append((calib[23] << 8) | calib[22])
digH.append(calib[24])
digH.append((calib[26] << 8) | calib[25])
digH.append(calib[27])
digH.append((calib[28] << 4) | (0x0F & calib[29]))
digH.append((calib[30] << 4) | ((calib[29] >> 4) & 0x0F))
digH.append(calib[31])
for i in range(1, 2):
if digT[i] & 0x8000:
digT[i] = (-digT[i] ^ 0xFFFF) + 1
for i in range(1, 8):
if digP[i] & 0x8000:
digP[i] = (-digP[i] ^ 0xFFFF) + 1
for i in range(0, 6):
if digH[i] & 0x8000:
digH[i] = (-digH[i] ^ 0xFFFF) + 1
def read_data():
data = []
for i in range(0xF7, 0xF7 + 8):
data.append(bus.read_byte_data(i2c_address, i))
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]
return compensate_t(temp_raw), compensate_h(hum_raw), compensate_p(pres_raw)
def compensate_p(adc_p):
global t_fine
v1 = (t_fine / 2.0) - 64000.0
v2 = (((v1 / 4.0) * (v1 / 4.0)) / 2048) * digP[5]
v2 = v2 + ((v1 * digP[4]) * 2.0)
v2 = (v2 / 4.0) + (digP[3] * 65536.0)
v1 = (((digP[2] * (((v1 / 4.0) * (v1 / 4.0)) / 8192)) / 8) + ((digP[1] * v1) / 2.0)) / 262144
v1 = ((32768 + v1) * digP[0]) / 32768
if v1 == 0:
return 0
pressure = ((1048576 - adc_p) - (v2 / 4096)) * 3125
if pressure < 0x80000000:
pressure = (pressure * 2.0) / v1
else:
pressure = (pressure / v1) * 2
v1 = (digP[8] * (((pressure / 8.0) * (pressure / 8.0)) / 8192.0)) / 4096
v2 = ((pressure / 4.0) * digP[7]) / 8192.0
return (pressure + ((v1 + v2 + digP[6]) / 16.0)) / 100
def compensate_t(adc_t):
global t_fine
v1 = (adc_t / 16384.0 - digT[0] / 1024.0) * digT[1]
v2 = (adc_t / 131072.0 - digT[0] / 8192.0) * (adc_t / 131072.0 - digT[0] / 8192.0) * digT[2]
t_fine = v1 + v2
return t_fine / 5120.0
def compensate_h(adc_h):
global t_fine
var_h = t_fine - 76800.0
if var_h != 0:
var_h = (adc_h - (digH[3] * 64.0 + digH[4] / 16384.0 * var_h)) * (
digH[1] / 65536.0 * (1.0 + digH[5] / 67108864.0 * var_h * (1.0 + digH[2] / 67108864.0 * var_h)))
else:
return 0
var_h = var_h * (1.0 - digH[0] * var_h / 524288.0)
if var_h > 100.0:
var_h = 100.0
elif var_h < 0.0:
var_h = 0.0
return var_h
def setup():
osrs_t = 1 # Temperature oversampling x 1
osrs_p = 1 # Pressure oversampling x 1
osrs_h = 1 # Humidity oversampling x 1
mode = 3 # Normal mode
t_sb = 5 # Tstandby 1000ms
filter = 0 # Filter off
spi3w_en = 0 # 3-wire SPI Disable
ctrl_meas_reg = (osrs_t << 5) | (osrs_p << 2) | mode
config_reg = (t_sb << 5) | (filter << 2) | spi3w_en
ctrl_hum_reg = osrs_h
write_reg(0xF2, ctrl_hum_reg)
write_reg(0xF4, ctrl_meas_reg)
write_reg(0xF5, config_reg)