MG811 CO2 Carbon Dioxide Gas Sensor Module - Analog & Digital Output

The MG811 module requires a stable 6V DC power supply. This voltage is specifically needed to power the internal heater circuit of the metal-oxide sensor element, bringing it to the high operating temperature necessary for proper CO2 sensitivity. Using a lower voltage may result in incorrect readings or sensor failure.

The analog output (AOUT) provides a voltage signal that inversely correlates with CO2 concentration: voltage decreases as ppm increases. The digital output (DOUT) is a TTL signal that goes HIGH (and lights the onboard LED) when the CO2 level exceeds a threshold you set using the onboard potentiometer. This allows for both precise measurement and simple alarm functionality.

You can use the digital output directly with the Raspberry Pi's GPIO pins. However, to use the analog output, you will need an external Analog-to-Digital Converter (ADC) chip or module (like an MCP3008) because the Raspberry Pi lacks built-in analog input pins. For Arduino boards with analog inputs, no additional hardware is needed for the AOUT pin.

As a metal-oxide sensor, the MG811 may require baseline calibration in fresh air (approximately 400 ppm CO2) for accurate relative measurements. Its analog output can drift over time and is sensitive to temperature/humidity changes. It is best suited for applications requiring trend monitoring rather than absolute, precision measurement, which would require a more stable NDIR sensor.