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BME280.py
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BME280.py
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import smbus
import time
from ctypes import c_short
from ctypes import c_byte
from ctypes import c_ubyte
DEVICE = 0x76 # Default device I2C address
bus = smbus.SMBus(1)
def getShort(data, index):
# return two bytes from data as a signed 16-bit value
return c_short((data[index+1] << 8) + data[index]).value
def getUShort(data, index):
# return two bytes from data as an unsigned 16-bit value
return (data[index+1] << 8) + data[index]
def getChar(data,index):
# return one byte from data as a signed char
result = data[index]
if result > 127:
result -= 256
return result
def getUChar(data,index):
# return one byte from data as an unsigned char
result = data[index] & 0xFF
return result
def readBME280ID(addr=DEVICE):
# Chip ID Register Address
REG_ID = 0xD0
(chip_id, chip_version) = bus.read_i2c_block_data(addr, REG_ID, 2)
return (chip_id, chip_version)
def readBME280All(addr=DEVICE):
# Register Addresses
REG_DATA = 0xF7
REG_CONTROL = 0xF4
REG_CONFIG = 0xF5
REG_CONTROL_HUM = 0xF2
REG_HUM_MSB = 0xFD
REG_HUM_LSB = 0xFE
# Oversample setting - page 27
OVERSAMPLE_TEMP = 2
OVERSAMPLE_PRES = 2
MODE = 1
# Oversample setting for humidity register - page 26
OVERSAMPLE_HUM = 2
bus.write_byte_data(addr, REG_CONTROL_HUM, OVERSAMPLE_HUM)
control = OVERSAMPLE_TEMP<<5 | OVERSAMPLE_PRES<<2 | MODE
bus.write_byte_data(addr, REG_CONTROL, control)
# Read blocks of calibration data from EEPROM
# See Page 22 data sheet
cal1 = bus.read_i2c_block_data(addr, 0x88, 24)
cal2 = bus.read_i2c_block_data(addr, 0xA1, 1)
cal3 = bus.read_i2c_block_data(addr, 0xE1, 7)
# Convert byte data to word values
dig_T1 = getUShort(cal1, 0)
dig_T2 = getShort(cal1, 2)
dig_T3 = getShort(cal1, 4)
dig_P1 = getUShort(cal1, 6)
dig_P2 = getShort(cal1, 8)
dig_P3 = getShort(cal1, 10)
dig_P4 = getShort(cal1, 12)
dig_P5 = getShort(cal1, 14)
dig_P6 = getShort(cal1, 16)
dig_P7 = getShort(cal1, 18)
dig_P8 = getShort(cal1, 20)
dig_P9 = getShort(cal1, 22)
dig_H1 = getUChar(cal2, 0)
dig_H2 = getShort(cal3, 0)
dig_H3 = getUChar(cal3, 2)
dig_H4 = getChar(cal3, 3)
dig_H4 = (dig_H4 << 24) >> 20
dig_H4 = dig_H4 | (getChar(cal3, 4) & 0x0F)
dig_H5 = getChar(cal3, 5)
dig_H5 = (dig_H5 << 24) >> 20
dig_H5 = dig_H5 | (getUChar(cal3, 4) >> 4 & 0x0F)
dig_H6 = getChar(cal3, 6)
# Wait in ms (Datasheet Appendix B: Measurement time and current calculation)
wait_time = 1.25 + (2.3 * OVERSAMPLE_TEMP) + ((2.3 * OVERSAMPLE_PRES) + 0.575) + ((2.3 * OVERSAMPLE_HUM)+0.575)
time.sleep(wait_time/1000) # Wait the required time
# Read temperature/pressure/humidity
data = bus.read_i2c_block_data(addr, REG_DATA, 8)
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]
#Refine temperature
var1 = ((((temp_raw>>3)-(dig_T1<<1)))*(dig_T2)) >> 11
var2 = (((((temp_raw>>4) - (dig_T1)) * ((temp_raw>>4) - (dig_T1))) >> 12) * (dig_T3)) >> 14
t_fine = var1+var2
temperature = float(((t_fine * 5) + 128) >> 8);
# Refine pressure and adjust for temperature
var1 = t_fine / 2.0 - 64000.0
var2 = var1 * var1 * dig_P6 / 32768.0
var2 = var2 + var1 * dig_P5 * 2.0
var2 = var2 / 4.0 + dig_P4 * 65536.0
var1 = (dig_P3 * var1 * var1 / 524288.0 + dig_P2 * var1) / 524288.0
var1 = (1.0 + var1 / 32768.0) * dig_P1
if var1 == 0:
pressure=0
else:
pressure = 1048576.0 - pres_raw
pressure = ((pressure - var2 / 4096.0) * 6250.0) / var1
var1 = dig_P9 * pressure * pressure / 2147483648.0
var2 = pressure * dig_P8 / 32768.0
pressure = pressure + (var1 + var2 + dig_P7) / 16.0
# Refine humidity
humidity = t_fine - 76800.0
humidity = (hum_raw - (dig_H4 * 64.0 + dig_H5 / 16384.0 * humidity)) * (dig_H2 / 65536.0 * (1.0 + dig_H6 / 67108864.0 * humidity * (1.0 + dig_H3 / 67108864.0 * humidity)))
humidity = humidity * (1.0 - dig_H1 * humidity / 524288.0)
if humidity > 100:
humidity = 100
elif humidity < 0:
humidity = 0
return temperature/100.0,pressure/100.0,humidity
def main():
#(chip_id, chip_version) = readBME280ID()
# print "Chip ID :", chip_id
#print "Version :", chip_version
temperature,pressure,humidity = readBME280All()
#print "Temperature : ", temperature, "C"
#print "Pressure : ", pressure, "hPa"
#print "Humidity : ", humidity, "%"
def airtemp():
temperature,pressure,humidity = readBME280All()
return temperature
def airhumi():
temperature,pressure,humidity = readBME280All()
return humidity
def airpress():
temperature,pressure,humidity = readBME280All()
return pressure