other components and requires through-hole
soldering.After assembly, this handheld device
has the SCD30 conveniently stacked on the
board, as shown in Figure
N
and on page 24. An
optional acrylic case diffuses the green, yellow,
and red LEDs so they’re visible across the room.
OPTION 3: Compact and Small CO
2
Devices
You can build a compact CO
2
monitor based on an
Adafruit Feather microcontroller with the sensor
stacked on top, mounted on a FeatherWing
board.Guido developed a FeatherWing board with
either the two-channel SCD30 (Figure
O
) or the
one-channel MHZ-19 CO
2
sensors.You can also,
as in Option 4, buy equivalent components from
Adafruit, Seeed Studios, or SparkFun.
The even smaller SCD40 sensor can also be
mounted on a FeatherWing, or piggybacked onto
Adafruit’s QT Py RP2040 ($10) or QT Py SAMD21
($8) or the Seeed Xiao SAMD21 ($6). (Note that
the RP2040 board can’t be programmed using
ArduBlock.) A Stemma/Qwiic display or others
can be used.You need to do a little soldering
of 2×8 header rows but it’s simple to build the
world’s smallest CO
2
device (Figure
P
). Guido
recently created a fun ruler PCB that also hosts a
QT Py and SCD40 (Figure
Q
).
Here’s a list of possible display options:
• LED matrix in different colors (Adafruit Feather
CharliePlex 15x7) — for universal output: text,
measured values, and trend graph
• 7-segment display in different colors (Adafruit
7-Segment FeatherWings) — easy-to-read LED
digits for measured value output
• NeoPixel matrix (Adafruit NeoPixelWing 4x8)
—widely visible signal lights (green, yellow, red)
• NeoPixel ring (Adafruit NeoPixel 24) and Grove
cable (male-jumper to Grove) — to display
measurement value (gauge) and traffic light
colors simultaneously. You could also use fewer
pixels — just increase the parameter delta in
the code if necessary (e.g. 200ppm/pixel) and
adjust size (e.g. 16 pixels).
OPTION 4: Stephan Schulz’s CO
2
Monitor
Stephan Schulz built a CO
2
device entirely from
Adafruit parts, as a portable battery-powered
monitor and data logger that his daughter could
take to school (Figure
S
).It’s based on a Feather
Guido Burger
FEATURE CO
2
Monitors vs. Covid
Q
SCD40 atop an Adafruit QT Py, connected to an
Adafruit FeatherWing 128×60 OLED display.
SCD40 and QT Py on Guido’s new ruler PCB.
P
32 makezine.com
N
O
The assembled CO
2
device with optional acrylic
housing on the left, and with Qwiic 7-segment
display on the right.
SCD30 sensor mounted on FeatherWing, for
stacking on a Feather microcontroller.
M78_024-35_CO2Monitor_F1.indd 32M78_024-35_CO2Monitor_F1.indd 32 7/13/21 9:50 AM7/13/21 9:50 AM
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