It's easy to use the SCD-4x with Python or CircuitPython, and the Adafruit CircuitPython SCD4x module. This module allows you to easily write Python code that reads CO2, temperature, and humidity from the SCD-4x sensor.

You can use this sensor with any CircuitPython microcontroller board or with a computer that has GPIO and Python thanks to Adafruit_Blinka, our CircuitPython-for-Python compatibility library.

CircuitPython Microcontroller Wiring

First wire up a SCD-4x to your board exactly as shown below. Here's an example of wiring a Feather M4 to the sensor with I2C using one of the handy STEMMA QT connectors:

  • Board 3V to sensor VIN (red wire)
  • Board GND to sensor GND (black wire)
  • Board SCL to sensor SCL (yellow wire)
  • Board SDA to sensor SDA (blue wire)

You can also use the standard 0.100" pitch headers to wire it up on a breadboard:

  • Board 3V to sensor VIN (red wire)
  • Board GND to sensor GND (black wire)
  • Board SCL to sensor SCL (yellow wire)
  • Board SDA to sensor SDA (blue wire)

Python Computer Wiring

Since there's dozens of Linux computers/boards you can use, we will show wiring for Raspberry Pi. For other platforms, please visit the guide for CircuitPython on Linux to see whether your platform is supported

Here's the Raspberry Pi wired to the sensor using I2C and a STEMMA QT connector:

  • Pi 3V to sensor VIN (red wire)
  • Pi GND to sensor GND (black wire)
  • Pi SCL to sensor SCL (yellow wire)
  • Pi SDA to sensor SDA (blue wire)

Finally here is an example of how to wire up a Raspberry Pi to the sensor using a solderless breadboard:

  • Pi 3V to sensor VIN (red wire)
  • Pi GND to sensor GND (black wire)
  • Pi SCL to sensor SCL (yellow wire)
  • Pi SDA to sensor SDA (blue wire)

Python Installation of SCD4x Library

You'll need to install the Adafruit_Blinka library that provides the CircuitPython support in Python. This may also require enabling I2C on your platform and verifying you are running Python 3. Since each platform is a little different, and Linux changes often, please visit the CircuitPython on Linux guide to get your computer ready!

Once that's done, from your command line run the following command:

  • pip3 install adafruit-circuitpython-scd4x

If your default Python is version 3, you may need to run pip instead. Make sure you aren't trying to use CircuitPython on Python 2.x, it isn't supported!

CircuitPython Usage

To use with CircuitPython, you need to first install the SCD4x library, and its dependencies, into the lib folder on your CIRCUITPY drive. Then you need to update with the example script.

Thankfully, we can do this in one go. In the example below, click the Download Project Bundle button below to download the necessary libraries and the file in a zip file. Extract the contents of the zip file, and copy the entire lib folder and the file to your CIRCUITPY drive.

Your CIRCUITPY/lib folder should contain the following folder and file:

  • adafruit_bus_device/
  • adafruit_scd4x.mpy

Python Usage

Once you have the library pip3-installed on your computer, copy or download the following example to your computer, and run the following, replacing with whatever you named the file: python3

Example Code:

# SPDX-FileCopyrightText: 2020 by Bryan Siepert, written for Adafruit Industries
# SPDX-License-Identifier: Unlicense
import time
import board
import adafruit_scd4x

i2c = board.I2C()  # uses board.SCL and board.SDA
# i2c = board.STEMMA_I2C()  # For using the built-in STEMMA QT connector on a microcontroller
scd4x = adafruit_scd4x.SCD4X(i2c)
print("Serial number:", [hex(i) for i in scd4x.serial_number])

print("Waiting for first measurement....")

while True:
    if scd4x.data_ready:
        print("CO2: %d ppm" % scd4x.CO2)
        print("Temperature: %0.1f *C" % scd4x.temperature)
        print("Humidity: %0.1f %%" % scd4x.relative_humidity)

If running CircuitPython: Once everything is saved to the CIRCUITPY drive, connect to the serial console to see the data printed out!

If running Python: The console output will appear wherever you are running Python.

Here is a quick explanation of the code and library features.

First, you import the necessary modules and library, and initialize the I2C connection with the sensor. Next, you print the serial number.

Then, you start measuring data with start_periodic_measurement().

Now you're ready to read values from the sensor using these properties:

  • data_ready - Check the sensor to see if new data is available.
  • CO2 - The CO2 concentration in PPM (parts per million).
  • temperature - The current temperature in degrees Celsius.
  • relative_humidity - The current relative humidity in %rH.

That's all there is to using the SCD-40 and SCD-41 with CircuitPython!

This guide was first published on Aug 26, 2021. It was last updated on Jul 11, 2024.

This page (Python & CircuitPython) was last updated on Jul 11, 2024.

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