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. Further technical details for the BME280 sensor can be found in the datasheet [PDF].
The BME280 is an I2C device, so connecting to the RPi is very straightforward:
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) |
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 --
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
Alternatively, a version on PyPi is available, just do:
$ sudo pip install RPi.bme280
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:
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 for a more complete example usage.
> TODO
The MIT License (MIT)
Copyright (c) 2016 Richard Hull
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