Sensirion Raspberry Pi I2C SCD4x Driver

This document explains how to set up the SCD4x sensor to run on a Raspberry Pi using the provided code.

Click here to learn more about the SCD4x sensor and the SCD41 Evaluation Kit Board.

Setup Guide

Connecting the Sensor

Your sensor has the four different connectors: VCC, GND, SDA, SCL. Use the following pins to connect your SCD4x:

Raspberry Pi

• Install the Raspberry Pi OS on to your Raspberry Pi
• Enable the I2C interface in the raspi-config
• Download the driver from the Sensirion GitHub Page and extract the .zip on your Raspberry Pi

• Compile the driver

  1. Open a terminal
  2. Navigate to the driver directory. E.g. cd ~/raspberry-pi-i2c-scd4x

  3. Run the make command to compile the driver

     Output:

     rm -f scd4x_i2c_example_usage
     cc -Os -Wall -fstrict-aliasing -Wstrict-aliasing=1 -Wsign-conversion -fPIC -I. -o scd4x_i2c_example_usage  scd4x_i2c.h scd4x_i2c.c sensirion_i2c_hal.h sensirion_i2c.h sensirion_i2c.c \
     sensirion_i2c_hal.c sensirion_config.h sensirion_common.h sensirion_common.c scd4x_i2c_example_usage.c

• Test your connected sensor

  • Run ./scd4x_i2c_example_usage in the same directory you used to compile the driver.

    Output:

    serial: 0xbff79f073b51
    CO2: 799
    Temperature: 20.92
    Humidity: 35.95
    CO2: 900
    Temperature: 20.92
    Humidity: 36.47
    CO2: 926
    Temperature: 20.81
    Humidity: 36.85
    ...

Troubleshooting

Building driver failed

If the execution of make in the compilation step 3 fails with something like

-bash: make: command not found

your RaspberryPi likely does not have the build tools installed. Proceed as follows:

$ sudo apt-get update
$ sudo apt-get upgrade
$ sudo apt-get install build-essential

Initialization failed

If you run ./scd4x_i2c_example_usage but do not get sensor readings but something like this instead

Error executing scd4x_get_serial_number(): -1
Error executing scd4x_start_periodic_measurement(): -1
Error executing scd4x_read_measurement(): -1

then go through the below troubleshooting steps.

• Ensure that you connected the sensor correctly: All cables are fully plugged in and connected to the correct pin.
• Ensure that I2C is enabled on the Raspberry Pi. For this redo the steps on "Enable the I2C interface in the raspi-config" in the guide above.
• If running the same command as root with sudo ./scd4x_i2c_example_usage works then your user is likely missing access permissions for the I2C interface. See the next chapter how to solve this.

Missing I2C permissions

If your user is missing access to the I2C interface you should first verfiy the user belongs to the i2c group.

$ groups
users input some other groups etc

If i2c is missing in the list add the user and restart the Raspberry Pi.

$ sudo adduser your-user i2c
Adding user `your-user' to group `i2c' ...
Adding user your-user to group i2c
Done.
$ sudo reboot

If that did not help you can make globally accessible hardware interfaces with a udev rule. Only do this if everything else failed and you are reasoably confident you are the only one having access to your Pi.

Go into the /etc/udev/rules.d folder and add a new file named local.rules.

$ cd /etc/udev/rules.d/
$ sudo touch local.rules

Then add a single line ACTION=="add", KERNEL=="i2c-[0-1]*", MODE="0666" to the file with your favorite editor.

$ sudo vi local.rules