I have examined several topics related to this sensor. However, my lack of English understanding has left me quite confused in following the steps and advice on those forums. Therefore, I kindly request corrections on my plan to convert ADC into ppm units that I will undertake in using the MICS 6814 sensor module (the purple one, without I2C, with analog pins, CJMCU):
Using a 5V power source for both CJMCU and Arduino Nano.
Adding a variable resistor of 10k ohms in series with the previous resistor. This follows advice from feu ([CJMCU-6814 adapter board with MICS-6814 CO/NH3/NO2-sensor - #9 by feu]) to obtain a value of 2.5V or 511 (ADC) as a reference value. This value needs to be obtained by placing the sensor in a clean air environment.
Question related to step 3:
If I am measuring NO2, can I directly convert ADC = 511 to 0.05 ppm & ADC = 1023 to 10 ppm?
I still don't understand the rationale behind normalizing the output to 2.5V. Why not directly use the voltage range of 0-1023 (in other words, 0 to 5V)? Thus, achieving finer resolution?
The second question above, of course, requires a calibrator and statistical equations, such as regression for example (to consider temperature and humidity value comparisons). If I don't have a calibrator, can I just use the map() function between ADC 0-1023 and the sensor range of 0.05 - 10 ppm? Lastly, how can I obtain conditions of clean air environment? Is it sufficient to place the sensor in a clean box? Or are there other methods?
You should probably explain what you mean by "calibration", and describe the environment where the sensor will be used.
Since each of the individual sensors responds to several different gases, is there a plan for discriminating between the gases, or does that even matter?
Will you be using gas mixtures of known composition for the calibration?
I will only be using this sensor to measure the concentration of CO and NO2, not measuring other gases. Additionally, I am unsure if I have the knowledge and access to use gas mixtures with specific compositions for calibration purposes. Therefore, before attempting to compare the ADC values of the CJMCU MICS 6814 (CO & NO2) with a reference device or system that can provide actual gas concentration, I am inquiring about the schematics configuration and method/concept of conversion through programming first.
Also, the sensor will be used in a traffic environment
Explain the purpose of your measurements? IF you ever have to defend your measurement in court, you must always do calibration BEFORE making a measurement.
Then what should I do with the effects of other gasses? Right now i am planning to add step 4 to collect ADC CJMCU-6814 value of CO and NO2 with actual concentration of those gasses using calibrator to determine the conversion equation. Please, please, all I want is the correction of my plan on schematic and method using this sensor. It could really helpful if anyone can provide comprehensive/summary to use CJMCU MICS-6814.
To accurately and reliably measure CO and NO2 in a traffic environment, two sensors are generally required, one completely specific for CO and the other completely specific for NO2.
There are also very expensive, laboratory grade multichannel gas analyzers that will handle both at the same time.
Here is the procedure, based on the nitrogen generation machine I bought, once. The tech attempted to calibrate the oxygen sensor,
First you can calibrate a SINGLE sensor for a SINGLE gas! DO you get that?
Required equipment includes an enclosure for your sensor that can be purged of all gas, except your calibration gas. DO you have that enclosure?
Now you need canisters of the single calibration gas, plus nitrogen so you can purge your enclosure of all air can fill it only with your test gas.
Then let the sensor soak in the gas until a stable reading is given. Now you have a single calibration point for that single sensor in that single gas.
Do you understand how to calibrate a gas sensor?