• SENSIRION SCD30 is a nondispersive infrared
(NDIR) optical sensor that costs about $50.Shown
in Figures
C
and
D
, this Swiss-made sensor
has two channels or tubes that use infrared light
to detect CO
2
in the air. The infrared light that's
emitted is absorbed by the CO
2
molecules. “The
more CO
2
in the tube, the less infrared light is
detected,” said Guido.The SCD-30 also measures
temperature and humidity. It’s available on
breakout boards including Seeed’s Grove and
Adafruit’s Feather format.
• SENSIRION SCD40 is a newer, miniature
photoacoustic CO
2
sensor. It’s not dual channel,
so it might show a bit more drift in the long run,
but it’s more rugged and much smaller than the
SCD30. Shown in Figure D (it’s the tiny cube),
it costs about $37. Digi-Key stocks the SCD40
and a breakout board; Guido also makes a tiny
breakout, and a larger Feather breakout that
accepts either SCD40 or SCD30.
• WINSEN MH-Z19C is a Chinese CO
2
NDIR
optical sensor with a single channel (Figure
E
).
It costs around $35. The advantage of having two
channels is greater accuracy —the two readings
can be compared — and reliability. But for a low-
cost option the MH-Z19 sensor can be used in
place of the SCD-30.
• SENSEAIR S8 LP — A Swedish NDIR optical
sensor (Figure
F
) with the same single channel
and footprint as the MH-Z19C but slightly higher
price and quality, and better calibration firmware.
Sensirion, Guido Burger, WinSen
FEATURE CO
2
Monitors vs. Covid
SHT31 + comp. engine
CO
2
measurement
channel
Reference channel Optical cavity
Light source
The Sensirion SCD30 (left) and SCD40 (center) CO
2
sensors, shown here mounted on Guido’s Feather
breakout board (right).
C
D
E
F
28 makezine.com
M78_024-35_CO2Monitor_F1.indd 28M78_024-35_CO2Monitor_F1.indd 28 7/13/21 9:49 AM7/13/21 9:49 AM
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