Gravity: CCS811 Air Quality Sensor

Why should we get the baseline? Because once get it, we can show the air quality quickly after the sensor warm-up by inputting the baseline. Otherwise, it will cost a long time to read correctly when startup in polluted air. During the first week of running the sensor, it is recommended to save a new baseline every 24 hours. After 1 week of operation, it can be saved every 1-28 days

Input the baseline value to the function `sensor.writeBaseLine();`If you don't want to set the baseline, please disable this function in the sample program. The sensor will automatically calibrate the baseline, but it would be a pretty long process. after the function uploaded to UNO, open the serial port monitor to check the carbide dioxide concentration and TVOC concentration.

Input the baseline value to the function `sensor.writeBaseLine();` Upload it to UNO, when the CO2 concentration moves from the current range (low, medium, high) to another range (more than 50 ppm), an interruption is generated and the current CO2 value will be printed. **NOTE: This example requires the INT pin of the sensor to be connected to the corresponding interrupt pin on the main board (in the sample, D2 of UNO is selected).**