This is the model of a homemade CO2 meter which measures the CO2 gas concentration in a room in ppm (particles per million). The CO2 concentration is useful to estimate when it is recommended to air the room in order to keep a healthy air quality.

This project has been made using the following materials (find in brackets the items I have used):

• Arduino UNO or compatible (https://es.aliexpress.com/item/32680845470.html)
• IPS round screen (https://es.aliexpress.com/item/1005002229915644.html)
• MH-Z19C CO2 monitor (https://es.aliexpress.com/item/1005001883572051.html)
• 2x green LEDs and 2x red LEDs
• 4x 220 Ohm resistors
• Some cables and a tin soldering iron

Recommended printing parameters:Layer height: 0.2mmInfill: 20%

An Arduino project has been added as an example, which controls the screen and the LEDs depending on the measurements read by the CO2 monitor. In this example a CO2 concentration over 800ppm has been considered harmful for the health and therefore the background colour as well as the LEDs colour changes from green to red over this threshold value.Hardware connection information and code examples can be found in the following sources:

• https://www.waveshare.com/wiki/1.28inch_LCD_Module (wiki of the round screen)
• MHZ19 library for Arduino (includes examples for running the CO2 monitor)
• LEDs have been connected to pins 0 and 1 for the green LEDs and 2 and 4 for the red LEDs

This is not a medical device and is not intended for so, read the datasheet of the MH-Z19C CO2 monitor for more details about the precision on the measurements.