For various sensors, attached to Raspberry-Pi computers, I wrote small command-line tools to read the sensor values over the I2C connection. While you can do this with a Python script directly, I found using a compiled C or C++ program accessing the low-level device more reliable.

The program I publish today, reads temperature and humidity data from a SHT31 sensor. It outputs a simple JSON document you can parse in your script.

Usage

There are a number of arguments you can use:

Usage: read_sht31 [-h][-v]
 -h|--help   Display this help.
 -s          Get the sensor status.
 -t1 -t0     Enable/disable heater.
 -a0 -a1     Select the chip address. 0 is the default.
 -b0 -b1     Select the bus. 1 is the default.
 -d          Show debugging messages.

If you call the command, you will get JSON output:

$ read_sht32
{ "temperature_celsius": 24.8, "relative_humidity": 28.4 }

The idea is to call this command from your script and parse the returned JSON output.

Compile and Install

In order to compile and install the tool on your Raspberry-Pi, you need to install the compiler, CMake and the I2C-Tools first:

sudo apt install gcc cmake i2c-tools

Download the files of this git repository to a subdirectory in your home directory. In this example, I downloaded the files to the directory /home/pi/read_sht31.

Now create a separate build directory. In this example, I create the directory /home/pi/build_read_sht31.

Next switch to the build directory, execute cmake to create the build script. Build the executable with make and install the executable in your system with sudo make install.

cd build_read_sht31
cmake ../read_sht31
make
sudo make install

Download

Download or clone the files from GitHub:

License

The code is licensed under the GPL license version 3.

Available Sensors

The SHT31 sensor is available from various sources as breakout board. Here two examples:

• Adafruit Breakout
• Breakout from DFRobot

Conclusion

Hopefully this small tool will help with your next Raspberry-Pi project. 😄

If you have any questions, missed information, or simply want to provide feedback, feel free to comment below or contact me on Twitter. 😄