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So I am thinking of building an device to measure CO2 levels in the air DIY fashion as premade equipment costs upwards of 100$. I have found some information on how to build such a device using Arduino and a MQ-135 Gas Sensor.

Seeing how the MQ-135 sensor is about 5 bucks I was wondering if it would be able to actually measure CO2 parts in the air, as other CO2 specific sensors I have found are more in the hundreds of dollars price range.

Has the MQ-135 Gas Sensor already been used for projects like this?

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  • \$\begingroup\$ It looks like the sensor you're talking about is sensitive to quite a few different gases, so no, you can't get an accurate measure of CO₂ concentration using this sensor alone. \$\endgroup\$
    – Hearth
    Commented Jan 28, 2019 at 15:40
  • \$\begingroup\$ In a classic indoors environment are the variations of the other gases significant enough be bias the results? If it measures benzene, alcohol and smoke (as mentioned by @evildemonic below) wouldn't those be rather constant in general? \$\endgroup\$
    – A.D
    Commented Jan 28, 2019 at 15:59

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The general answer to your question is no. Although the sensor responds somewhat to CO2, it responds highly to other things in the air and this will dominate your signal. This sensor is made for benzene, alcohol, and smoke. The output of this sensor will not track with CO2 levels in a way that is usable.

Here is a link to a project where somebody tried unsuccessfully to use this sensor for CO2.

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  • \$\begingroup\$ Ok just as I suspected... Are there any other sensors that go for a reasonable price that can successfully measure (not necessarily too accurately) co2 parts? \$\endgroup\$
    – A.D
    Commented Jan 28, 2019 at 15:57
  • \$\begingroup\$ This site isn't for specific product recommendations, and I can't judge what you find a reasonable price. That said, something like a Sensirion SCD30 should set your expectations for the type of sensors you will find at the low-end (around $50us). \$\endgroup\$
    – evildemonic
    Commented Jan 28, 2019 at 16:27
  • \$\begingroup\$ Sorry for going a little off into specific products ;) (I'll check the SCD30 out thanks) \$\endgroup\$
    – A.D
    Commented Jan 28, 2019 at 16:35

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