MG811 Carbon Dioxide Sensor measures gaseous carbon dioxide levels by monitoring the amount of infrared (IR) radiation absorbed by carbon dioxide molecules. This type of sensor is used in monitoring indoor air quality, landfills, process control, and controlled environment horticulture. Useful for greenhouses and medical projects. Sends an analog signal that decreases as the concentration of CO2 increases. This module also includes a digital output pin with TTL output. The Potentiometer on board is used to set the Digital Output Setpoint. After setting the potentiometer threshold, once that threshold is reached, an LED on the sensor will illuminate and the digital pin will give a HIGH voltage signal.