Installation and Calibration
Install your CO
2
monitor about 1.5m (5') high,
away from direct sunlight, windows, and wind
gusts. Use a permanent power supply to
keep it running 24/7 to see if the room needs
active ventilation, and to learn about baseline
ventilation, for example during a weekend.
Calibration is automatic. If 420ppm is
not shown outdoors, then you can use the
calibrations block manually, as auto calibration
doesn’t work in all cases.
A Real-Time Dashboard
Guido built a real-time air quality dashboard
(Figure
T
) using the open source Grafana data
visualization app and MQTT messaging.This
requires connecting the device to the internet.
Notice there is not one but five traffic lights: CO
2
,
temperature, humidity, VOCs, and PAX (number of
people in the room). “Dry air allows the aerosols
to stay even longer in the air,” Guido explained.
Testing Devices in Classrooms
Guido set up seven identical CO
2
devices in seven
classrooms for one week in one school.In the
chart on page 25, we see CO
2
rising and falling
daily from Monday through Friday; school is off
Saturday and Sunday. “So you see the values of
CO
2
are declining slowly, but as we have seen on
the weekend, we are around 400ppm,said Guido.
“We have this blue one being an exception.Looks
like the blue one still needs to be calibrated.
In Figure
U
, we see the seven classrooms on
a Monday, and in Figure
V
we look at just one
of them. “Now, the class starts here at 7:30, so
the kids are moving in and you see how quickly
we are going from a fresh air condition to an
alarm situation,” Guido explained. “Thats literally
happening in, let’s say 20 minutes. We have the
first alarm because the CO
2
reaches 1100ppm.
Because this room is equipped with a CO
2
traffic
alarm system, the teacher sees a yellow light and
opens the windows and door.We see how quickly
this value drops down to around 500ppm. Then
the teacher closes the window and you see its
going back up again.
These graphs can help a person see how
changes in ventilation in the room occur over
time, impacted by the actions of people in the
FEATURE CO
2
Monitors Fight Covid
The CO
2
Ring
Guido Burger used the tiny SCD40 CO
2
sensor and a NeoPixel ring to create the
CO
2
Ring the world’s smallest air-
quality wearable detecting CO
2
and VOCs
at the same time.
His SCD40 circuit board also features
a BME688 VOC sensor and a single
NeoPixel. This is stacked on top of a QT
Py RP2040 microcontroller, wired to a
12-element NeoPixel ring, and its all
powered by a coin cell battery.
The CO
2
Canary
Guido Burger, Moritz Metz
Berlin audio journalist and maker Moritz
Metz (netzbasteln.de) presented a
particularly beautiful version of the CO
2
Traffic Light: He took Guido’s project as
inspiration for his CO
2
-Narienvogel (CO
2
-
nary), which tips off the shelf when the air
is bad, like the canary in the coal mine.
Code shared at github.com/netzbasteln/
co2narienvogel. —Helga Hansen
34 makezine.com
M78_024-35_CO2Monitor_F1.indd 34M78_024-35_CO2Monitor_F1.indd 34 7/13/21 9:50 AM7/13/21 9:50 AM
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