# 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 BMP280 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.

## Class

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.

## Properties

### values = BME280.values

The `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
a `(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.

## Methods

### 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:

#### Integer formats:
* `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.

#### Float formats
* `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.

### read_raw_data(result)
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.

### Example

Copy `bme280_float.py` onto the board. Then:

``` python
#
# 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)
```