BME280

A Linux device driver for the Bosch BME280 temperature, pressure, humidity sensor using the I2C protocol, written in C.

Setup on Raspberry Pi

This driver was tested on a Raspberry Pi 4B. To run on Raspberry Pi OS:

Run raspi config and enable I2C from Interface Options -> I2C.

Hook up the BME280 sensor to the Raspberry Pi and run i2cdetect to verify that it is available to interface:

sudo apt install i2c-tools # if not included
i2cdetect -y 1

The output of i2cdetect should be something like

     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 --                         

Which indicates that the sensor is available at 0x76.

Building and reading data

Build the driver:

cd driver && make

Upon successfully building, the kernel module bme280.ko will be created.

To initialize the driver, run:

sudo insmod bme280.ko

A device file should now be created in /dev/bme280. You can read continuous measurements as a stream by reading the device file:

chmod 666 /dev/bme280 # enable read access
cat < /dev/bme280

To remove the driver, run

sudo rmmod bme280

Data format

The data format of a single reading will be given as a single line in order of temperature, pressure, and humidity:

T2920P24874300H27597

To interpret this line:

• Temperature is in Celsius and is accurate to two decimal places: e.g. 2920->29.20C
• Pressure is in Pa and is obtained by dividing the value by 256, accurate to two decimal places, e.g. 24874300/256=97165.23 Pa
• Humidity is in percentage and is obtained by dividng the value by 1024, e.g. 27597/1024=25.9%

Running the example

The userspace example is a simple Rust program that reads the driver file as a stream and parses it. The driver is expected to be initialized already, or else reading the driver file will not work. To start it, run

cd user/ && cargo run

Here is a line of expected console output:

Temperature: 29.23C Pressure: 97290.80Pa Humidity: 26.35%