EYE on NPI – Sensirion SCD40 and SCD41 Compact CO2 Air Sensors

Adafruit Industries

This week's EYE ON NPI is a timely one - the Sensirion SCD4X (SCD40 and SCD41) a fantastic upgrade to the Sensirion SCD30 (https://www.digikey.com/en/products/detail/sensirion-ag/SCD30/8445334). Sensirion were clearly working on this sensor for a few years, but got some excellent timing as they finished and released it right when demand for CO2 sensors skyrocketed. Carbon dioxide, aka CO2, is a gas that is an essential part of the Earth's atmosphere and life in general. However, while essential, it can have negative effects when concentrations exceed certain levels. It can impact the entire planet via global warming. But it can also have very local effects, for example on indoor air quality. Elevated levels of CO2 can lead to reduced cognitive ability and other health related concerns. Therefore, monitoring CO2 levels of inside air can be useful as a part of gauging general air quality. Folks have had CO2 air-quality sensors in buildings and homes for a long time, but now they're extremely popular because CO2 levels are correlated with air freshness. Outdoor air is about 400 ppm CO2. Us humans love to breathe in air, extract the O2 and fill rooms with CO2. That means when there's poor ventilation to the outdoors, and lots of humans, the air is going to get higher and higher CO2. (https://theconversation.com/how-to-use-ventilation-and-air-filtration-to-prevent-the-spread-of-coronavirus-indoors-143732) We consider under 1000 ppm to be 'good' but really we want to keep it under 600 ppm if we can since that has been shown to reduce transmission of airborne disease (https://onlinelibrary.wiley.com/doi/full/10.1111/ina.12639) First, let's talk about the SCD-30, since this the next generation sensor. The SCD-30 is an NDIR sensor, which is a 'true' CO2 sensor that will tell you the CO2 PPM (parts-per-million) composition of ambient air. Unlike the SGP30, this sensor isn't approximating it from VOC gas concentration - it really is measuring the CO2 concentration! That means it's a lot bigger and more expensive than eCO2 sensors, but it is the real thing. Perfect for environmental sensing, scientific experiments, air quality and ventilation studies, and more. However, its...kinda chunky and requires hand-soldering. Thus the awesome introduction of the SCD4X series which comes in four part numbers: SCD-D-R1 (https://www.digikey.com/en/products/detail/sensirion-ag/SCD40-D-R1/13684001), SCD-D-R2 (https://www.digikey.com/en/products/detail/sensirion-ag/SCD40-D-R2/13684003), SCD41-D-R1 (https://www.digikey.com/en/products/detail/sensirion-ag/SCD41-D-R1/13684000) and SCD41-D-R2 (https://www.digikey.com/en/products/detail/sensirion-ag/SCD41-D-R2/13684005). The SCD40 and SCD41 differ in price and precision. SCD40 is base accuracy, with a specified range of 400 to 2000 ppm for continuous measurements, good for vast majority of indoor measurements. SCD41 is high accuracy, specified range 400 to 5,000 ppm, with both continuous and single shot mode supported: perhaps better for scientific or industrial or low-power use cases. Both have the same instructions and footprint so you could swap them easily on the PCBs. It was really easy for us to get an Arduino demo going with the SCD4x because Sensirion has written drivers for Arduino, Raspberry Pi, Python and even MakeCode! (https://github.com/Sensirion/?q=scd4&type=&language=&sort=) Add to that, there's a cute breakout board with JST-PH connector and breakout pads so you can quickly wire it up and get data into your favorite platform. (https://www.digikey.com/en/products/detail/sensirion-ag/SEK-SCD41-SENSOR/13684004?s=N4IgTCBcDaIM4GMAmAWEBdAvkA) The sensor can run from 3 to 5V but we've noted that it needs very low ripple - so use the quietest power supply you have access to. With built-in humidity and temperature sensing as well, it's an all-in-one air measurement sensor about the size of a skittle. You can pick up SCD40 and SCD41 sensors at Digi-Key. (https://www.digikey.com/en/products/filter/gas-sensors/530?s=N4IgTCBcDaIMoGEAiAWEBdAvkA) Note that at this moment they're out of stock, but they will be restocked in a few weeks so sign up to be notified or place on backorder. There are breakout boards available now (https://www.digikey.com/en/products/detail/sensirion-ag/SEK-SCD41-SENSOR/13684004?s=N4IgTCBcDaIM4GMAmAWEBdAvkA) - order today so you can start sensing tomorrow! See on Digi-Key at https://www.digikey.com/short/r5p31vrh