The iAQ Sensor Wing Makes for a Compact Indoor Air Quality Measurement Platform

This FeatherWing provides a practical platform for air quality measurements.

Tom Fleet
a month agoEnvironmental Sensing / Sensors

One of the hot topics in the world of sensors and measurment lately has been that of the quality of the air we breathe.

Pollution is on the up and up, and while we can't do a lot about the air we are breathing when we venture outside, we still have some control on the air we breathe when indoors. We can open a window in a stuffy room, or we can think twice about leaving that smelly solvent bottle open on our work bench.

If you wanted to track and monitor the quality of air within an a space, there are a few options you could take. Electrochemical cells are one popular option, but can be tricky to interface, and are fairly chunky.

The last few years have seen the release of tiny, solid state CMOS MEMS MOX iAQ VOC sensors. That's a lot of acronyms, so let's break down the buzzwords

  • CMOS - Complimentatry metal oxide semiconductor
  • MEMS - Micro-electromechanical structures
  • MOX - Metal oxide, in this case, in the form of a Chemiristor
  • iAQ - Indoor air quality
  • VOC - Volatile organic compound

In a nutshell, the sensor is a tiny MOX chemiristor sensor, that is heated by a MEMS hotplate, to a temperature where its resistivity is affected by changes in the composition of the atmospheric gas it is exposed to.

The chemical composition, and temperature of the hotplate can be tuned to offer selective response to certain chemical groups, and certain combinations are now offered by manufacturers to target the typical components that affect the quality of the air we breathe.

Air Quality Feather

Jared Wolff has designed a really neat, compact platform, based around one such sensor, the ams CCS811 digital VOC sensor, and coupled it with a Silicon Labs Si7021 temperature and relative humidity sensor, to provide a suite of readings to help you characterize the air in your space.

The board also has the ability to connect an optional HPMA115S0 particulate sensor and provides the necessary voltage regulator for when running off battery power.

This sensor board has taken care of all the tricky layout guidelines, and picky assembly procedures found with sensor ICs, to produce a sensing platform that is easy to integrate into your favourite hardware stack.

There is a Feather-compatible pinout for direct connection to your MCU of choice.

A 8-pin JST connector is used to provide an interface to the HPMA115S0 dust sensor, allowing the measurement of dust particulate in the air, at both PM10 and PM2.5 levels.

The iAQ data from the CCS811, and the temperature / relative humidity data from the Si7021 sensors is available over I2C, and a single 3.3V supply eases hardware requirements.

An application note from ams also provides example code to compensate the iAQ readings against possible errors due to offset introduced to the measurement by extreme ambient temperature / humidity — something to be sure to check your driver/library supports!

CCS811 iAQ Sensor

  • Complete, all-in-one digital iAQ / VOC sensor
  • Provides complete integration of MEMS hotplate control, and sensor digitization / conversion
  • I2C interface and 3.3V supply for ease of integration

Si7021 Temp & RH Sensor

  • Complete, all-in-one digital temperature and relative humidity sensor
  • Accuracy of ± 3% RH (max), 0–80% RH, and ±0.4 °C (max), –10 to 85 °C
  • I2C interface and 1.8-3.3V supply

The combination of temperature, relative humidity, tVOC, eCO2 and PM2.5/PM10 levels provides you with a complete suite of measurements from which to form an analysis of the air in and around your space.

If you are keen to explore the air around you, Jared Wolff has a product page, and the Air Quality Feather Wing (rev5) featured in this article is due for release very soon.

If you are interested in the design of the sensor wing, hardware design files are available here, and a comprehensive documentation can be found here.

Follow along with Jared Wolff on Twitter and GitHub.

Tom Fleet
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