The new version of DIY CO2 meter for home and office use.

Displays current CO2 level with alarm indicator.
Automatic display brightness. Powered from accumulator. USB charging.

Components inside (all from aliexpress):

• LGT8F328P LQFP32 MiniEVB 5V pro-mini
• SCD40 CO2 sensor
• BMP180 pressure sensor
• TM1637 display
• TP4056 charging board
• 18650 accumulator
• SS12F15 G6 1P2T switch
• 5516 photoresistor and 10K resistor
• 3 mm. led and 330 Ohm resistor
• Dupont wires

Arduino firmware and schematics at my github

More info at my website in Russian or translated to English.

Anet ET4 Titan Aero

No

Yes

0.3

20%

Some parts may require sanding for best fit.
Round display frame may be fixed with superglue if needed.
All other stuff fixed with 7 M3x6 and 2 M2x4 screws.