BME280 Micropython driver for the BME280 sensor
This is a driver for the Bosch BME280 temperature/pressure/humidity sensor, for use with MicroPython on Pycom of ESP8266 boards. It is also compatible with the BMP180 which provides the same interface but temperature + pressure only.
Two different variants of the library are supplied. bme20_int.py uses integer arithmetic, bme280_float.py uses float arithmetic for the compensation of the raw values. The results are (almost) the identical, but the format of the returned values differs.
About the BME280
The Bosch BME280 Environmental Sensor is a combined temperature, pressure and humidity sensor. It can communicate via I2C or SPI; this driver uses I2C.
See the datasheet at https://www.bosch-sensortec.com/media/boschsensortec/downloads/datasheets/bst-bme280-ds002.pdf for details.
bme = BME280(mode=BME280_OSAMPLE_8, address=BME280_I2CADDR, i2c=i2c)
mode is the setting for oversampling of the humidity value. It must be either a single
int or a tuple of 3 ints, specifying (mode_hum, mode_temp, mode_pressure).
address is the i2c
address used, and i2c must be a I2C object.
values = BME280.values
values property is a convenience function that provides a tuple of
human-readable string values to quickly check that the sensor is working.
In practice, the method to use is
read_compensated_data() which returns
(temperature, pressure, humidity)-tuple
altitude = bme.altitude
Altitude in m. The altitude is calculated based on the value given to the property sealevel (see below). Obviously, this value does not have to be the sealevel pressure, but any pressure you may select, for instance to measure altitude difference in general.
bme.sealevel = sealevel
sealevel = bme.sealevel
Setting and getting the pressure for altitude calculation. The default is 101325 Pa, but you can use your local QNH in Pa, or set a local pressure to determine altitude difference.
dew_point = bme.dew_point
Returns the dew_point temperature (°C) calculated from the actual temperature and humidity.
values = read_compensated_data(result = None)
Values is an array of either integers (bme280_int.py) of floats (bme280_float.py), holding the values of temperature, pressure and humidity. The format differs for integers and floats:
temperature: the temperature in hundredths of a degree Celsius. For example, the value 2534 indicates a temperature of 25.34 degrees.
pressure: the atmospheric pressure. This 32-bit value consists of 24 bits indicating the integer value, and 8 bits indicating the fractional value. To get a value in Pascals, divide the return value by 256. For example, a value of 24674867 indicates 96386.2Pa, or 963.862hPa.
humidity: the relative humidity. This 32-bit value consists of 22 bits indicating the integer value, and 10 bits indicating the fractional value. To get a value in %RH, divide the return value by 1024. For example, a value of 47445 indicates 46.333%RH.
temperature: the temperature in degree Celsius.
pressure: the atmospheric pressure in Pascal.
humidity: the relative humidity in percent.
If the parameter result is supplied as an array of the appropriate type, The return values will in addition be stored in that array, and the array will be returned.
Store the raw sensor data into the array result, which must provide space for three
32 bit integers, as provided for instance by
array("i", [0, 0, 0]). This
method is used internally.
bme280_float.py onto the board. Then:
# # this script for the rp2040 port assumes the I2C connections at # GPIO8 and 9. At the RPi Pico, these are the board pins 11 and 12 # Please check that pull-up resistors are in place at sda and scl. # import machine, Pin import bme280_float as bme280 i2c = machine.I2C(0, sda=machine.Pin(8), scl=machine.Pin(9)) bme = bme280.BME280(i2c=i2c) print(bme.values)