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Bme280.py
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Bme280.py
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#!/usr/bin/python3
# Torben:
# This is from https://www.raspberrypi-spy.co.uk/2016/07/using-bme280-i2c-temperature-pressure-sensor-in-python/
# my modifications:
# converted to Python3 syntax
# converted to class
# install requirements
# sudo apt-get install python-smbus python3-smbus python-dev python3-dev i2c-tools
# --------------------------------------
# ___ ___ _ ____
# / _ \/ _ \(_) __/__ __ __
# / , _/ ___/ /\ \/ _ \/ // /
# /_/|_/_/ /_/___/ .__/\_, /
# /_/ /___/
#
# bme280.py
# Read data from a digital pressure sensor.
#
# Official datasheet available from :
# https://www.bosch-sensortec.com/bst/products/all_products/bme280
#
# Author : Matt Hawkins
# Date : 21/01/2018
#
# https://www.raspberrypi-spy.co.uk/
#
# --------------------------------------
import smbus
import time
from ctypes import c_short
class Bme280:
def __init__(self, verbose: bool = False):
self.verbose = verbose
if self.verbose:
print("Bme280: verbose = True")
self.DEVICE = 0x76 # Default device I2C address
self.bus = smbus.SMBus(1) # Rev 2 Pi, Pi 2 & Pi 3 uses bus 1
# Rev 1 Pi uses bus 0
def getShort(self, 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(self, data, index):
# return two bytes from data as an unsigned 16-bit value
return (data[index + 1] << 8) + data[index]
def getChar(self, data, index):
# return one byte from data as a signed char
result = data[index]
if result > 127:
result -= 256
return result
def getUChar(self, data, index):
# return one byte from data as an unsigned char
result = data[index] & 0xFF
return result
def readBME280ID(self):
# Chip ID Register Address
REG_ID = 0xD0
(chip_id, chip_version) = self.bus.read_i2c_block_data(
self.DEVICE,
REG_ID,
2,
)
return (chip_id, chip_version)
def readBME280All(self):
# Register Addresses
REG_DATA = 0xF7
REG_CONTROL = 0xF4
REG_CONTROL_HUM = 0xF2
# Oversample setting - page 27
OVERSAMPLE_TEMP = 2
OVERSAMPLE_PRES = 2
MODE = 1
# Oversample setting for humidity register - page 26
OVERSAMPLE_HUM = 2
self.bus.write_byte_data(self.DEVICE, REG_CONTROL_HUM, OVERSAMPLE_HUM)
control = OVERSAMPLE_TEMP << 5 | OVERSAMPLE_PRES << 2 | MODE
self.bus.write_byte_data(self.DEVICE, REG_CONTROL, control)
# Read blocks of calibration data from EEPROM
# See Page 22 data sheet
cal1 = self.bus.read_i2c_block_data(self.DEVICE, 0x88, 24)
cal2 = self.bus.read_i2c_block_data(self.DEVICE, 0xA1, 1)
cal3 = self.bus.read_i2c_block_data(self.DEVICE, 0xE1, 7)
# Convert byte data to word values
dig_T1 = self.getUShort(cal1, 0)
dig_T2 = self.getShort(cal1, 2)
dig_T3 = self.getShort(cal1, 4)
dig_P1 = self.getUShort(cal1, 6)
dig_P2 = self.getShort(cal1, 8)
dig_P3 = self.getShort(cal1, 10)
dig_P4 = self.getShort(cal1, 12)
dig_P5 = self.getShort(cal1, 14)
dig_P6 = self.getShort(cal1, 16)
dig_P7 = self.getShort(cal1, 18)
dig_P8 = self.getShort(cal1, 20)
dig_P9 = self.getShort(cal1, 22)
dig_H1 = self.getUChar(cal2, 0)
dig_H2 = self.getShort(cal3, 0)
dig_H3 = self.getUChar(cal3, 2)
dig_H4 = self.getChar(cal3, 3)
dig_H4 = (dig_H4 << 24) >> 20
dig_H4 = dig_H4 | (self.getChar(cal3, 4) & 0x0F)
dig_H5 = self.getChar(cal3, 5)
dig_H5 = (dig_H5 << 24) >> 20
dig_H5 = dig_H5 | (self.getUChar(cal3, 4) >> 4 & 0x0F)
dig_H6 = self.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 = self.bus.read_i2c_block_data(self.DEVICE, 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
temperature = temperature / 100.0
pressure = pressure / 100.0
if self.verbose:
print("Temperature %.1f C" % temperature)
print("Pressure %.3f hPa" % pressure)
print("Humidity %.3f %% " % humidity)
return temperature, pressure, humidity
def test():
bme280 = Bme280(verbose=True)
(chip_id, chip_version) = bme280.readBME280ID()
print("Chip ID :", chip_id)
print("Version :", chip_version)
print("I2C Device :", bme280.DEVICE)
temperature, pressure, humidity = bme280.readBME280All()
if __name__ == "__main__":
test()