BME280 Sensor Driver
====================
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Interfacing a Bosch BME280 digital sensor module (capable of sensing
temperature, humidity and pressure) in Python 2 or 3 using I2C on the Raspberry
Pi. The particular kit I bought can be acquired for a few pounds from `eBay
<http://www.ebay.co.uk/itm/311728184519>`_. Further technical details for the
BME280 sensor can be found in the `datasheet
<https://raw.githubusercontent.com/rm-hull/bme280/master/doc/tech-spec/BME280.pdf>`_
[PDF].

.. image:: https://raw.githubusercontent.com/rm-hull/bme280/master/doc/bme280-sensor.jpg
   :alt: mounted

GPIO pin-outs
-------------
The BME280 is an I2C device, so connecting to the RPi is very straightforward:

P1 Header
^^^^^^^^^
For prototyping, the P1 header pins should be connected as follows:

========== ====== ============ ======== ==============
Board Pin  Name   Remarks      RPi Pin  RPi Function  
========== ====== ============ ======== ==============
1          VIN    +3.3V Power  P01-1    3V3           
2          GND    Ground       P01-6    GND           
3          SCL    Clock        P01-5    GPIO 3 (SCL)  
4          SDA    Data         P01-3    GPIO 2 (SDA)  
========== ====== ============ ======== ==============

Pre-requisites
--------------
Ensure that the I2C kernel driver is enabled::

  $ dmesg | grep i2c
  [    4.925554] bcm2708_i2c 20804000.i2c: BSC1 Controller at 0x20804000 (irq 79) (baudrate 100000)
  [    4.929325] i2c /dev entries driver

or::

  $ lsmod | grep i2c
  i2c_dev                 5769  0
  i2c_bcm2708             4943  0
  regmap_i2c              1661  3 snd_soc_pcm512x,snd_soc_wm8804,snd_soc_core

If you have no kernel modules listed and nothing is showing using ``dmesg`` then this implies
the kernel I2C driver is not loaded. Enable the I2C as follows:

#. Run ``sudo raspi-config``
#. Use the down arrow to select ``9 Advanced Options``
#. Arrow down to ``A7 I2C``
#. Select **yes** when it asks you to enable I2C
#. Also select **yes** when it asks about automatically loading the kernel module
#. Use the right arrow to select the **<Finish>** button
#. Select **yes** when it asks to reboot

After rebooting re-check that the ``dmesg | grep i2c`` command shows whether
I2C driver is loaded before proceeding.

Optionally, to improve permformance, increase the I2C baudrate from the default
of 100KHz to 400KHz by altering ``/boot/config.txt`` to include::

  dtparam=i2c_arm=on,i2c_baudrate=400000

Then reboot.

Then add your user to the i2c group::

  $ sudo adduser pi i2c

Install some packages::

  $ sudo apt-get install i2c-tools python-pip

Next check that the device is communicating properly (if using a rev.1 board,
use 0 for the bus not 1)::

  $ i2cdetect -y 1
         0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
    00:          -- -- -- -- -- -- -- -- -- -- -- -- --
    10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
    20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
    30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
    40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
    50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
    60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
    70: -- -- -- -- -- -- 76 --

Installing the Python Package
-----------------------------
For python2, from the bash prompt, enter::

  $ sudo python setup.py install

This will install the Python files in ``/usr/local/lib/python2.7``
making them ready for use in other programs.

Alternatively for python3, type::

 $ sudo python3 setup.py install

Cheeseshop install
^^^^^^^^^^^^^^^^^^
Alternatively, a version on PyPi is available, just do::

  $ sudo pip install RPi.bme280

Software Driver - Example Usage
-------------------------------
Once installed, confirm the I2C address (see prerequisites, it will most 
likely be 0x76 or 0x77) and port.

Then in a python script or REPL:

.. code:: python

  import smbus2
  import bme280

  port = 1
  address = 0x76
  bus = smbus2.SMBus(port)

  calibration_params = bme280.load_calibration_params(bus, address)

  # the sample method will take a single reading and return a
  # compensated_reading object
  data = bme280.sample(bus, address, calibration_params)

  # the compensated_reading class has the following attributes
  print(data.id)
  print(data.timestamp)
  print(data.temperature)
  print(data.pressure)
  print(data.humidity)

  # there is a handy string representation too
  print(data)

This then should print something like::

  ee50df9c-3aa3-4772-8767-73b6bb74f30f
  2016-11-18 17:33:28.937863
  20.563
  980.91
  48.41
  compensated_reading(id=ee50df9c-3aa3-4772-8767-73b6bb74f30f, 
      timestamp=2016-11-18 17:33:28.937863, temp=20.563 °C, 
      pressure=980.91 hPa, humidity=48.41 % rH)

For a data-logger like application, periodically call ``bme2.sample(bus, address, calibration_params)`` to
get time-based readings.

See the `weatherstation project <https://github.com/rm-hull/weatherstation>`_ for
a more complete example usage.

References
----------
> TODO

License
-------
The MIT License (MIT)

Copyright (c) 2016-2020 Richard Hull

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
