Some questions

[22MarioZ]

I'm looking to your code and I have few questions. I'm interesting in MQ135 for CO2 measure, but when using your code I get results which are not in line with typical results.

1. Different code between Gassensors_calibration and arduino codes:

• arduino code for MQ135
  RL_VALUE_MQ135 (1) //define the load resistance on the board, in kilo ohms
  RO_CLEAN_AIR_FACTOR_MQ135 (3.59)

• calibration code
  RL_VALUE_MQ135 19
  RO_CLEAN_AIR_FACTOR_MQ135 3.59

2. After calibration I get Ro so I should replace Ro and disable calibration for future usage?

3. The results I get are very low values (18 - 20 ppm) which is to low as we have in normal air (outside) the value of CO2 around 410 ppm?

4. If you know what is the range of MQ135? From data sheet is 10-200 ppm, but I assume this must be interpolated to real values.

Thank you for your responses.