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# BME280 Micropython driver for the BME280 sensor # BME280 Micropython driver for the BME280 sensor
This is a driver for the Bosch BME280 temperature/pressure/humidity 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 for use with MicroPython on Pycom of ESP8266 boards. It is also compatible with
the BMP280 which provides the same interface but temperature + pressure only. the BMP180 which provides the same interface but temperature + pressure only.
Two different variants of the library are supplied. bme20_int.py uses integer 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 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 raw values. The results are (almost) the identical, but the format of the
returned values differs. returned values differs.
## About the BME280 ## About the BME280
The Bosch BME280 Environmental Sensor is a combined temperature, pressure and The Bosch BME280 Environmental Sensor is a combined temperature, pressure and
humidity sensor. It can communicate via I2C or SPI; this driver uses I2C. humidity sensor. It can communicate via I2C or SPI; this driver uses I2C.
See the datasheet at https://ae-bst.resource.bosch.com/media/_tech/media/datasheets/BST-BME280_DS002.pdf See the datasheet at https://ae-bst.resource.bosch.com/media/_tech/media/datasheets/BST-BME280_DS002.pdf
for details. for details.
## Class ## Class
bme= BME280(i2c=i2c, mode=BME280_OSAMPLE_8, address=BME280_I2CADDR) bme = BME280(i2c=i2c, mode=BME280_OSAMPLE_8, address=BME280_I2CADDR)
mode is the setting for oversampling of the humidity value, address the i2c mode is the setting for oversampling of the humidity value, address the i2c
address used. address used.
## Properties ## Properties
### values = BME280.values ### values = BME280.values
The `values` property is a convenience function that provides a tuple of The `values` property is a convenience function that provides a tuple of
human-readable string values to quickly check that the sensor is working. human-readable string values to quickly check that the sensor is working.
In practice, the method to use is `read_compensated_data()` which returns In practice, the method to use is `read_compensated_data()` which returns
a `(temperature, pressure, humidity)`-tuple a `(temperature, pressure, humidity)`-tuple
### altitude = bmp.altitude ### altitude = bme.altitude
Altitude in m. The altitude is calculated based on the value given to 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 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 sealevel pressure, but any pressure you may select, for instance to measure
altitude difference in general. altitude difference in general.
### bmp.sealevel = sealevel ### bme.sealevel = sealevel
### sealevel = bmp.sealevel ### sealevel = bme.sealevel
Setting and getting the pressure for altitude calculation. Setting and getting the pressure for altitude calculation.
The default is 101325 Pa, but you can use your local The default is 101325 Pa, but you can use your local
QNH in Pa, or set a local pressure to determine altitude difference. QNH in Pa, or set a local pressure to determine altitude difference.
### dew_point = bmp.dew_point ### dew_point = bme.dew_point
Returns the dew_point temperature (°C) calculated from the actual temperature and humidity. Returns the dew_point temperature (°C) calculated from the actual temperature and humidity.
## Methods ## Methods
### values = read_compensated_data(result = None) ### values = read_compensated_data(result = None)
Values is an array of either integers (bme280_int.py) of floats (bme280_float.py), Values is an array of either integers (bme280_int.py) of floats (bme280_float.py),
holding the values of temperature, pressure and humidity. holding the values of temperature, pressure and humidity.
The format differs for integers and floats: The format differs for integers and floats:
#### Integer formats: #### Integer formats:
* `temperature`: the temperature in hundredths of a degree Celsius. For example, * `temperature`: the temperature in hundredths of a degree Celsius. For example,
the value 2534 indicates a temperature of 25.34 degrees. the value 2534 indicates a temperature of 25.34 degrees.
* `pressure`: the atmospheric pressure. This 32-bit value consists of 24 bits * `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 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 a value in Pascals, divide the return value by 256. For example, a value of
24674867 indicates 96386.2Pa, or 963.862hPa. 24674867 indicates 96386.2Pa, or 963.862hPa.
* `humidity`: the relative humidity. This 32-bit value consists of 22 bits * `humidity`: the relative humidity. This 32-bit value consists of 22 bits
indicating the integer value, and 10 bits indicating the fractional value. 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 To get a value in %RH, divide the return value by 1024. For example, a value of
47445 indicates 46.333%RH. 47445 indicates 46.333%RH.
#### Float formats #### Float formats
* `temperature`: the temperature in degree Celsius. * `temperature`: the temperature in degree Celsius.
* `pressure`: the atmospheric pressure in Pascal. * `pressure`: the atmospheric pressure in Pascal.
* `humidity`: the relative humidity in percent. * `humidity`: the relative humidity in percent.
If the parameter result is supplied as an array of the appropriate type, The 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 return values will in addition be stored in that array, and the array will be
returned. returned.
### read_raw_data(result) ### read_raw_data(result)
Store the raw sensor data into the array result, which must provide space for three 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 32 bit integers, as provided for instance by `array("i", [0, 0, 0])`. This
method is used internally. method is used internally.
### Example ### Example
Copy `bme280_float.py` onto the board. Then: Copy `bme280_float.py` onto the board. Then:
``` python ``` python
# #
# this script assumes the default connection of the I2C bus # this script assumes the default connection of the I2C bus
# On pycom devuces that is P9 = SDA, P10 = scl # On pycom devuces that is P9 = SDA, P10 = scl
# #
import machine import machine
import bme280_float as bme280 import bme280_float as bme280
i2c = machine.I2C() i2c = machine.I2C()
bme = bme280.BME280(i2c=i2c) bme = bme280.BME280(i2c=i2c)
print(bme.values) print(bme.values)
``` ```