Library allows to read and calibrate modules based on CO2 sensor.
VCC- stabilized voltage (5V for TGS4166 and 6V for MG811)GND- groundAOUT- link to an analog input of Arduino.DOUT- digital value indicates whether current concentration exceeds some thretshold value (can be adjusted by potentiometer)TCM- temperature compensation (I have no details)
Before calibration it is necessary to refresh the room. Then we treat concentration of co2 as 400 ppm.
Sensor provides a value (voltage between 0 and 5 V) which we need to convert to a concentration value by formula:
c=d^((a-v)/b)
where
c- co2 concentration inppmd- some constant. 400 in our case.v- input fromAOUTinmillivoltsa- a parameter which we'll change during calibration. (Initially 1500)b- a constant. 600 in our case
In order to calibrate we should modify a value using this formula
a := v + b*(Ln(c1)/Ln(d))
where
c1 - is the current real concentration value. For example for well refreshed room it will be 400 ppm.
Actually we always take d = c1 in such case our calculation will be simpler and we do not need calculate Ln. Then actual adjustment formula is just
a := v + b
If we decide to change c1 then we should change b and d constants using such formulas
d := c1b := 100*Ln(c1)
The module contains 2 potentiometers.
- Left - adjusts threshold of DOUT
- Rigth - hardware sensor calibration
Class constructor accepts one parameter - analog input of arduino. Specify the number of analog input linked to AOUT of the module (A0, A1, A2 etc)
The example of arduino sketch is here.
From here