MH-Z19 CO₂ Sensor~

#ifndef USE_MHZ19 
#define USE_MHZ19       // Add support for MH-Z19 CO2 sensor (+2k code)
#endif

The MH-Z19 sensor is manufactured by Winsen Lt., China and the measurement method used is based on the non-dispersive infrared (NDIR) principle to detect the existence of CO₂ in the air.

Key features according to the manufacturer are:

• good sensitivity
• non-oxygen dependent
• long life
• built-in temperature compensation
• UART serial interface and Pulse Width Modulation (PWM) output

Principle of operation:
The main components of an NDIR sensor are an infrared source (lamp), a sample chamber or light tube, a light filter and an infrared detector. The IR light is directed through the sample chamber towards the detector. In parallel there is another chamber with an enclosed reference gas, typically nitrogen. The gas in the sample chamber causes absorption of specific wavelengths according to the BeerñLambert law, and the attenuation of these wavelengths is measured by the detector to determine the gas concentration. The detector has an optical filter in front of it that eliminates all light except the wavelength that the selected gas molecules can absorb.

Wiring~

In some situations if you only get 0 ppm displayed it may be necessary to set "TX GPIO1" to "MHZ Rx" and "RX GPIO3" to "MHZ Tx" and correspondingly reverse the cabling for RX/TX. See here for more details.

Tasmota Settings~

In the Configuration -> Configure Module page assign:

1. RX to MHZ Tx
2. TX to MHZ Rx

After a reboot the driver will detect MH-Z19 automatically and display measurements.

Measure range can be selected with command:

• sensor15 1000 for 1000 ppm range
• sensor15 2000 for 2000 ppm range
• sensor15 3000 for 3000 ppm range
• sensor15 5000 for 5000 ppm range

Full commands list for the sensor

Model Comparison~

Available from AliExpress