Setup Info:

MQ135 + Arduino+16x2LCD+ESP8266+ThinkSpeak.

Hi All, I have just bought a MQ135 . I started arduino basics with LED blinking , interfacing and then started with my real project. e I have seen in the data sheet of MQ135 that it can measure Ammonia, Sulfide,CO2 and Benze steam. It can also be used to detect smoke and alert.

But in the Arduino uno Serial monitor, I can see only one value 408.

Now, I dont know how to differentiate it in all different values of required gases and trigger smoke alarm

Also, my friend suggested to calibrate this sensor for which I found really good material and started with 24 Hours on test after dumping a code to read data from it. Now I read 1836 which was 1795 , about half an hour back.

Kindly reply and let me know what info or input is required from My side. This is my first of my many uno projects to come.

Regards, Sillicon https://forum.arduino.cc/index.php?topic=535401.msg3649205#msg3649205

  • you already posted at forum.arduino.cc .... why are you posting again here? ..... you have not asked a specific question.
    – jsotola
    Commented Mar 15, 2018 at 22:29
  • Yup, I intend to notify the same and look for unique solution to solve this problem Commented Mar 15, 2018 at 23:11

1 Answer 1


Now, I dont know how to differentiate it in all different values of required gases and trigger smoke alarm

This sensor does not differentiate between the various gases that it is sensitive to.

  • I dont recollect but I have seen coders showing off different values of CO2 , Ammonia on a 16X2 screen using MQ135. Commented Mar 15, 2018 at 23:13
  • If you’ve seen it, show it. Commented Mar 16, 2018 at 3:07
  • youtube.com/watch?v=GT8dNNRWNOY Visit this please Commented Mar 18, 2018 at 8:04
  • I watched the video. The fact that values are displayed for different gases does not mean the values displayed are accurate. There are values shown for "Smoke" and for CO when it's clear nothing is being burned/combusted. Commented Mar 19, 2018 at 1:18

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