It's easy to use the SGP40 with Python or CircuitPython, and the Adafruit CircuitPython SGP40 module. This module allows you to easily write Python code that reads gas measurements from the SGP40 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 SGP40 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 VCC (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 VCC (red wire)
  • Pi GND to sensor GND (black wire)
  • Pi SCL to sensor SCL (yellow wire)
  • Pi SDA to sensor SDA (blue wire)

CircuitPython Installation of SGP40 Library

You'll need to install the Adafruit CircuitPython SGP40 library on your CircuitPython board.

First make sure you are running the latest version of Adafruit CircuitPython for your board.

Next you'll need to install the necessary libraries to use the hardware--carefully follow the steps to find and install these libraries from Adafruit's CircuitPython library bundle.  Our CircuitPython starter guide has a great page on how to install the library bundle.

Before continuing make sure your board's lib folder or root filesystem has the adafruit_SGP40.mpy file and adafruit_bus_device folder copied over. Your CIRCUITPY drive should look like this:

Next connect to the board's serial REPL so you are at the CircuitPython >>> prompt.

Python Installation of SGP40 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:

  • sudo pip3 install adafruit-circuitpython-sgp40

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

CircuitPython & Python Usage

To demonstrate the usage of the sensor we'll initialize it and read the raw gas measurements from the board's Python REPL.

Run the following code to import the necessary modules and initialize the I2C connection with the sensor:

import board
import busio
import adafruit_sgp40

i2c = busio.I2C(board.SCL, board.SDA)
sgp = adafruit_sgp40.SGP40(i2c)

Now you're ready to read values from the sensor using the raw property to read the raw gas measurements.

print("Raw Gas: ", sgp.raw)

These measurements rare the raw values from the VOC-sensitive resistor. They aren't quite 'resistance' but they're related. The number is affected by VOC as well as humidity.

Example Code

# SPDX-FileCopyrightText: 2020 by Bryan Siepert for Adafruit Industries
#
# SPDX-License-Identifier: Unlicense
import time
import board
import adafruit_sgp40

# If you have a temperature sensor, like the bme280, import that here as well
# import adafruit_bme280

i2c = board.I2C()  # uses board.SCL and board.SDA
sgp = adafruit_sgp40.SGP40(i2c)
# And if you have a temp/humidity sensor, define the sensor here as well
# bme280 = adafruit_bme280.Adafruit_BME280_I2C(i2c)

while True:
    print("Raw Gas: ", sgp.raw)
    # Lets quickly grab the humidity and temperature
    # temperature = bme280.temperature
    # humidity = bme280.relative_humidity
    # compensated_raw_gas = sgp.measure_raw(temperature = temperature, relative_humidity = humidity)
    print("")
    time.sleep(1)

This guide was first published on Dec 30, 2020. It was last updated on Dec 30, 2020.

This page (Python & CircuitPython) was last updated on Oct 22, 2021.

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