Portable CO2 sensor

CO2 sensors may be used to estimate the Covid-19 aerosol risk.

This design of this CO2 sensor focuses on reduced size for portability. It requires some soldering skills.

In its simplest form it uses a Wemos/NodeMCU (ESP8266 board), a CO2 NDIR sensor, and a 1" OLED display. It is powered over micro-USB. A case can be 3D-printed. Size (without battery) is 20x35x55mm (0.8"x1.4"x2.2").

The display shows current CO2 value, and a graph showing CO2 value development during the past hour (Y-axis range 400-1000ppm, dashed indicator line at 600ppm). Optional are a Li-ion battery (with voltage indication), LED and on/off switch, making it convenient to use at school, at work, or in supermarkets.

The LED starts to blink above 600ppm (short pulses), changes pattern above 800ppm (longer pulses), and remains on above 1000ppm.

The CO2 NDIR sensor element can be either a Winsen MH-Z19B (~20 Euro/$ 25), a SenseAir S8-LP (~30 Euro/$ 35), or a (dual-channel NDIR, so no concerns on calibrati