Air Quality Sensor - SGP40 (Qwiic) Hookup Guide

2023-11-07 | By SparkFun Electronics

License: See Original Project

Courtesy of SparkFun

Guide by EL DUDERINO, MAKIN-STUFF

Introduction

The SparkFun Air Quality Sensor - SGP40 (Qwiic) is a robust metal oxide (MOx) based indoor air-‎quality measurement tool using the SGP40 gas sensor from Sensirion. The SGP40 is based on ‎Sensirion's CMOSens® technology that uses a MOx sensor with a temperature controlled micro ‎hotplate and a humidity-compensated indoor air quality signal. The SGP40 is highly responsive and ‎reports valid volatile organic compound (VOC) data within minutes of powering on the sensor.‎

SparkFun Air Quality Sensor - SGP40 (Qwiic)‎

The SGP40 outputs a digital value based on all VOC gases typically present in an indoor ‎environment and this value can be combined with Sensirion's VOC Index Algorithm to provide ‎responsive indoor air quality data. The SGP40 detects the relative intensity of VOC events in ‎relation to the average readings in a 24hr period but does not return specific concentrations of ‎VOC gases. Think of the SGP40 as a sensitive electronic nose for detecting VOCs in a room.‎

Users looking to measure specific gas concentrations may want to use the SparkFun Air Quality ‎Sensor - SGP30 (Qwiic) instead.‎

This guide will cover the SGP40 sensor and other hardware present on this breakout, how to ‎connect it to a microcontroller and use the Arduino and Python libraries so by the end you'll be able ‎to easily monitor VOC events indoors.‎

Required Materials

To follow along with this guide, you will need a microcontroller to communicate with the SGP40. ‎Below are a few options that come Qwiic-enabled out of the box:‎

If your chosen microcontroller is not already Qwiic-enabled, you can add that functionality with one ‎or more of the following items:‎

You will also need at least one Qwiic cable to connect your sensor to your microcontroller.‎

Suggested Reading

If you aren't familiar with the Qwiic system, take a look here for an overview.‎

qwiic_1

We also recommend taking a look at the following tutorials if you aren't familiar with the concepts ‎covered in them. If you are using one of the Qwiic Shields listed above, you may want to read ‎through their respective Hookup Guides as well before you get started with the SparkFun Air ‎Quality Sensor - SGP40 (Qwiic).‎

I2C: An introduction to I2C, one of the main embedded communications protocols in use today
Serial Terminal Basics: This tutorial will show you how to communicate with your serial devices ‎using a variety of terminal emulator applications
Qwiic Shield for Arduino & Photon Hookup Guide: Get started with our Qwiic ‎ecosystem with the Qwiic shield for Arduino or Photon
SparkFun Qwiic Shield for Arduino Nano Hookup Guide: Hookup Guide for the ‎SparkFun Qwiic Shield for Arduino Nano

Hardware Overview

In this section we'll cover the features and specifications of the SGP40 Air Quality Sensor as well as ‎highlight other hardware present on this Qwiic breakout.‎

SGP40 Gas Sensor

The SGP40 air quality gas sensor from Sensirion offers an easy-to-integrate indoor air quality ‎monitoring system with Sensirion's VOC Index. The SGP40 is an I²C device that outputs either a ‎raw digital signal of all typical VOC gases presents in an indoor environment or a processed VOC ‎index value.‎

air_2

The SGP40's broad spectrum of sensing means it does not measure specific concentrations of ‎individual VOC gases. Instead, the sensor outputs a digital signal sensitive to common indoor air ‎pollutants/VOC gases[¹]. Some common air pollutants the SGP40 detects are:‎

Acetone
Toluene
Ethanol
Hydrogen Sulfide & Volatile Sulfuric Compounds
Ammonia & Amines
Benzene & Nitrosamines

The raw signal can be read on its own but for best results, Sensirion's VOC Algorithm processes ‎the signal to output VOC Index data. The processed VOC Index value ranges from 0 to 500 index ‎points. The data is relative to the history of the monitored room where 100 is the average reading ‎reported over the last 24 hours. Values above 100 signify a VOC event or worse-than-average air ‎quality and values below indicate better-than-average air quality. The rate and intensity of change ‎help identify the severity of the event to trigger actions such as turning on fans to ventilate the area ‎until the signal stabilizes again.‎

The SGP40 accepts a supply voltage between 1.7V and 3.6V with this breakout intended to run ‎at 3.3V to work with the Qwiic system. The SGP40 draws 34µA (typ.) while idling ‎and 2.6mA@3.3V (typ.) during operation. Power is provided either over the Qwiic interface or ‎through the pins labeled 3.3V and Ground on the 0.1"-spaced plated through hole (PTH) header.‎

I²C and Qwiic Interface

The SGP40 communicates via I²C so naturally we've routed that interface to a pair of Qwiic ‎connectors for easy integration into SparkFun's Qwiic system. For users who prefer a more ‎traditional interface, the SDA and SCL pins are routed to the same 0.1"-spaced PTH header as ‎the 3.3V and GND pins.‎

interface_3

The SGP40's I²C address is 0x59 and the IC supports both "standard-mode" and "fast-mode" with ‎max clock frequencies of 100 or 400kHz, respectively.‎

Solder Jumpers

If you have never worked with solder jumpers and PCB traces or would like a refresher, take a look ‎at our How to Work with Jumper Pads and PCB Traces tutorial.‎

This breakout has two solder jumpers labeled PWR and I2C. The PWR jumper completes the power ‎LED circuit and the I2C jumper pulls the SDA/SCL lines to 3.3V via a pair of 1kΩ resistors. Both ‎jumpers' default state is CLOSED.

jumpers_4 ‎

Disable the Power LED by severing the trace between the two pads. Opening this jumper helps ‎reduce the total current draw of the breakout for low-power applications. Similarly, disable the pull-‎up resistors for the SDA/SCL lines by severing the trace between the three pads.‎

Note: Recommended practice suggests to only have a single pair of pull-up resistors on an I²C bus ‎to avoid creating too strong of a parallel resistance on the bus. If these pull-ups are disabled, make ‎sure the entire bus is operating at the appropriate logic level (in this case, 3.3V) or the lines are ‎properly shifted to avoid damaging this or other devices on the bus.‎

Board Dimensions

The Air Quality Sensor - SGP40 (Qwiic) matches the 1.0" x 1.0" (25.4mm x 25.4mm) standard of ‎Qwiic breakouts and has two mounting holes that fit a 4-40 screw.‎

dimensions_5

‎1. Users looking to measure specific concentrations of VOC gases may want to consider using ‎the SparkFun Air Quality Sensor - SGP30 (Qwiic) instead. The SGP30 reports concentrations of

Hardware Assembly

With the SparkFun Qwiic system, assembling your sensor circuit is easy! All you need to do is ‎connect your SparkFun Air Quality Sensor - SGP40 (Qwiic) to your chosen development board with ‎a Qwiic cable or adapter cable. If you would prefer to not use the Qwiic connectors, you can ‎connect to the 0.1" header pins broken out on bottom of the board.‎

assembly_6

If you decide to use the PTH pins broken out on the Air Quality Sensor you need to solder to them ‎or if you want a temporary connection for prototyping, these IC Hooks are a great option to make ‎that connection. If you are not familiar with through-hole soldering, take a look at this tutorial:‎

solder_7

How to Solder: Through-Hole Soldering

This tutorial covers everything you need to know about through-hole soldering.‎

With the SGP40 connected to your microcontroller it's time to get some code uploaded and start ‎taking measurements!‎

SGP40 Arduino Library‎

Note: This library assumes you are using the latest version of the Arduino IDE on your desktop. If ‎this is your first time using Arduino, please review our tutorial on installing the Arduino IDE. If you ‎have not previously installed an Arduino library, please check out our installation guide.‎

We've written a simple Arduino library to quickly get started reading data from the SGP40. Install the ‎library through the Arduino Library Manager tool by searching for "SparkFun SGP40". Users who ‎prefer to manually install it can get the library from the GitHub Repository or download the ZIP by ‎clicking the button below:‎

SPARKFUN SGP40 ARDUINO LIBRARY (ZIP)‎

Library Functions

The list below outlines all of the functions of the library with some quick descriptions of what they ‎do.‎

Class

Construct the SGP40 object in the global scope. mySensor is used as the SGP40 object in the ‎example.‎

SGP40 mySensor;‎

Device Setup and Settings

bool SGP40::begin(TwoWire &wirePort); - Initialize I²C communication with the SGP40 on the ‎defined port. If no port is specified, Wire is used. This function also initializes the VOC index ‎parameters
void enableDebugging(Stream &debugPort = Serial); - Turn debug printouts and select the ‎Serial port used for prints. If no port is defined, Serial is used
SGP40ERR measureTest(void); - Run a self-test of the SGP40 chip. Returns SUCCESS (0) on ‎pass or specific error code on fail when debugging prints are enabled. Primarily used during ‎manufacturing but can be helpful for debugging
SGP40ERR softReset(void); - Trigger a soft reset of the SGP40. Returns SUCCESS (0) if reset ‎is successful with debugging enabled
SGP40ERR heaterOff(void); - Turn the heater off. Returns SUCCESS (0) if heater is ‎successfully disabled with debugging enabled

SGP40 VOC Data

Both of these data outputs have default values set for relative humidity percentage and temperature ‎‎(in °C) that can be adjusted to new static values or fed a live humidity and temperature data from an ‎external sensor.

SGP40ERR measureRaw(uint16_t *SRAW_ticks, float RH = 50, float T = 25); - Returns the ‎raw signal from the SGP40 in SRAW_ticks. If debugging statements are on, returns SUCCESS ‎‎(0) on pass
int32_t getVOCindex(float RH = 50, float T = 25); - Return the processed VOC index ‎data from the SGP40. Returns -100 on error. Refer to the VOC Index app note document for ‎more information on the Sensirion VOC Index

Arduino Example

The SGP40 Arduino Library includes a single example demonstrating how to get the processed ‎VOC Index data from the sensor. Let's take a closer look at this example.‎

Example 1 - Get VOC Index

Open this example by navigating to File > Examples > SparkFun SGP40 Arduino Library > ‎Example1_GetVOCIndex. Next, open the Tools menu and select the Board (in our ‎case, SparkFun RedBoard) and the Port the board enumerated on.‎

Upload the code and open the Arduino Serial Monitor with the baud set to 115200. The code starts ‎both the Wire and Serial ports and initializes the SGP40 on the I²C bus. If the SGP40 is not ‎detected at the default address, the code will print out SGP40 not detected. Check connections. ‎Freezing... and will stop. If this error prints, double check the connections between the breakout ‎and development board and reset it.‎

After initializing, the code calls the getVOCIndex(); function and prints out the value every second. ‎The SGP40 takes about 30 to 60 seconds to warm up and return valid VOC readings. The printed ‎data starts at "0" and increases for about a minute as it acclimates to the room and stabilizes around ‎‎100 VOC index. Also, the SGP40 refers to VOC Index readings from the history of the room over ‎the past 24 hours so the longer the sensor remains running in the room, the more accurate the data ‎becomes.‎

Try creating VOC events by putting something like isopropyl alcohol or a permanent marker near ‎the sensor and then pull it away after a few seconds. The VOC Index should rise significantly ‎depending on the intensity of the event and after a couple of minutes the output should drop back ‎towards 100 as the gases dissipate.‎

SGP40 Python Package

Note: This package and the included examples assume you are using the latest version of Python 3. ‎If this is your first-time using Python or I²C hardware on a Raspberry Pi, these tutorials can help you ‎get started:‎

The SparkFun SGP40 Python package is a simple module to get you started getting VOC data from ‎the sensor. The Sensirion VOC Index algorithm is written for C/C++ so the Qwiic SGP40 Python ‎package uses a similar algorithm for Python from DFRobot.‎

The package is hosted on PyPi so it can be installed using the command interface with some simple ‎commands. If you prefer to manually install the package you can find it on the Github repository or ‎download the ZIP of it by clicking the button below:‎

DOWNLOAD THE SPARKFUN QWIIC SGP40 PACKAGE (ZIP)‎

‎(*Please be aware this package depends on the Qwiic I2C Driver. You can also check out the ‎repository documentation page, hosted on Read the Docs.)‎

Qwiic SGP40 Py Installation

Now let's go over both ways of installing the Qwiic SGP40 Python package.‎

Note: Don't forget to double check that the hardware I²C connection is enabled on your Raspberry ‎Pi or other single board computer. The Raspberry Pi tutorials linked in the note above cover how to ‎enable the Pi's I²C bus.‎

PyPi Installation

Since this repository is hosted on PyPi installation is simple on systems that support PyPi installation ‎via pip3 (use pip for Python 2). Open a command interface and install the package using the ‎following commands:‎

For all users (The user must have sudo privileges):‎

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sudo pip3 install sparkfun-qwiic-sgp40

For the current user:‎

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pip3 install sparkfun-qwiic-sgp40

Local Installation

Follow these instructions for a local installation. Make sure to install the setuptools package prior to ‎installing the Qwiic SGP40 package.‎

Use the following command for direct installation at the command line (use python for Python 2):‎

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python3 setup.py install

To build a package for use with pip3:‎

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python setup.py sdist

This builds and places a subdirectory called "dist". Install the package using pip3 with this command ‎making sure to fill in the correct version number:‎

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langauge:bash
cd dist
pip3 install sparkfun_qwiic_sgp40-<version>.targ.gz

Qwiic SGP40 Python Package Operation

A complete overview of all the functions included in the Qwiic SGP40 Py is hosted on ‎the ReadtheDocs. You can also take a look at the source code.‎

Upgrading the SGP40 Python Package

In case the package is updated in the future, you may need to upgrade it. Upgrade the package ‎using the following commands:‎

For all users (The user must have sudo privileges):‎

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sudo pip3 install --upgrade sparkfun-qwiic-sgp40

For the current user:‎

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pip3 install --upgrade sparkfun-qwiic-sgp40

Python Example

The Qwiic SGP40 Python package includes one example to demonstrate how to get VOC Index ‎data from the sensor. Open the example from the Qwiic SGP40 Py location or copy the code into ‎your preferred Python interpreter.‎

Example 1 - VOC Index

This simple example initializes the SGP40 on the I²C bus and uses the get_VOC_index() function to, ‎well, get the VOC index from the sensor. Take note, polling the VOC index should occur at 1Hz ‎‎(once per second) for accurate results.‎

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from __future__ import print_function
import qwiic_sgp40
import time
import sys

def run_example():

    print("\nSparkFun Qwiic Air Quality Sensor - SGP40, Example 1\n")
    my_sgp40 = qwiic_sgp40.QwiicSGP40()

    if my_sgp40.begin() != 0:
        print("\nThe Qwiic SGP40 isn't connected to the system. Please check your connection", \
            file=sys.stderr)
        return

    print("\nSGP40 ready!")

    while True:

        print("\nVOC Index is: " + str(my_sgp40.get_VOC_index()))

        time.sleep(1)

if __name__ == '__main__':
    try:
        run_example()
    except (KeyboardInterrupt, SystemExit) as exErr:
        print("\nEnding Example 1")
        sys.exit(0)

Run the example and let the sensor warm up for ~60 seconds and the readings should stabilize to ‎around 100. Try creating VOC events by putting something like isopropyl alcohol or a permanent ‎marker near the sensor and then pull it away. You should see the VOC index rise significantly and ‎then return back to the "norm" of ~100 after a minute or so. For the best results, let the SGP40 run ‎for 24hrs to generate a "history" of the average VOC gas concentration in the room.‎

Troubleshooting

VOC Index Data

The example in the Arduino library returns values processed through Sensirion's VOC Index which ‎returns qualitative data based on the history of the room. While the sensor reports valid VOC ‎readings within a minute of power up, leaving it running to gain a "history" of the room will provide ‎more accurate data from the sensor when VOC events occur. In our testing we found the longer ‎the SGP40 remains in the room it monitors, the more reliable the data becomes.‎

After acclimating to the room, it is monitoring, the SGP40 should report "100" or close to it for the ‎normal VOC Index for the room. Values below that indicate a lower concentration and values above ‎indicate a higher concentration. Refer to Sensirion's VOC Index for Experts document as well as ‎the SGP40 Datasheet for more information on how to interpret and use that data in your air quality ‎measurement application.‎

Quick SGP40 Test

If you're looking for more accurate testing than using common household items like isopropyl ‎alcohol or a permanent marker, Sensirion has a quick test document for testing the SGP40 is ‎operating within specifications here: SGP40 Quick Testing Guide.

General Troubleshooting and Technical Support

Not working as expected and need help? ‎

If you need technical assistance and more information on a product that is not working as you ‎expected, we recommend heading on over to the SparkFun Technical Assistance page for some ‎initial troubleshooting.

SPARKFUN TECHNICAL ASSISTANCE PAGE‎ ‎

If you don't find what you need there, the SparkFun Forums are a great place to find and ask for ‎help. If this is your first visit, you'll need to create a Forum Account to search product forums and ‎post questions.

Resources and Going Further

That wraps up this Hookup Guide for the SparkFun Air Quality Sensor - SGP40 (Qwiic). For further ‎information regarding this breakout, take a look at the links below:‎

Looking for some inspiration for an air quality sensing project or an air quality sensor that monitors specific gases and concentrations? Check out these tutorials:

sgp30