Environmental sensors

For my next little project I am thinking of making a good little environmental sensor box, mainly for CO₂ and temperature as they are the two things I have some control over.

ESP8266 based, why not. But I have been looking at the sensors you can get, and bought a few.

Are all CO₂ sensors crap?

Well, I tried a few, including this CJMCU module (CCS811 based) and this AppliedSensor module.

Sorry to say, but both are crap! And the detail is in the small print - they estimate CO₂ from other sensors, and are very easily confused. I have some isopropyl alcohol and you use that anywhere near them and they quickly say 18000ppm CO₂. Even without such factors they swing wildly all over the place.

It seems you need an NDIR based sensor, and I found this one which seems to actually work! This SCD30 sensor seems to be the business, with CO₂, temperature and humidity (floating point!) via I²C.

Next step - sort a suitable display and box.

I can then use the temperature to control the air-conditioning, and the CO₂ to control extractor fan speed.


  1. For temperature and humidity you can’t normally go wrong with the ds18b20 and dht22 (humidity only).

    1. Indeed, and even though that module has a temperature sensor I am thinking of using a DS18B20 anyway, so it can have the probe positioned where you want it exactly. I have a commercial PoE based sensor using an 18B20 now, and manage to keep room within 0.5C typically, and often even tighter.

  2. What about a particle sensor like the pms5003, then you could run the AC purely as an air scrubber since most AC have filters.

    1. The AC runs when I am in the room anyway, so not sure that helps. I may look at it anyway. Thanks.

  3. I love your blog and steal many of your ideas for my own home, but this project with your Daikin AC etc seems amazing yet also seems beyond me.

    I also have a Diakin AC, bought in 2016 after reading your AC related posts, and would bite your hand off if you ever decided to sell an "upgrade kit" to do this. Even if it were a couple of hundred pounds. The lack of temperature accuracy on the "auto" setting has always annoyed me.


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