S8 CO2 reading of -2

Full disclosure, I don’t have a real applied knowledge of EMI, but I ran a couple more tests. The sensor is my bedroom was reading CO2 fine. I walked to the kitchen, which shares a circuit with my bedroom and turned on the 1000W blender. Went back to my room and the CO2 was reading -1. I repeated the test with a 1500W electric kettle that sits next to the blender. 2-5 minutes later after each device was off CO2 was back to reading correct values. I guess I don’t understand how that would be related to EMI unless the current is impacting EMI how. Or don’t understand how “noise” is the culprit. For reference, the blender and kettle were about 12 feet away in another room through a wall.

@KnowPassFilter interesting. Could you run the monitor from a usb power bank and try the same experiment again. This would identify if the interference is coming through the mains or the air.

Oh this is a great idea. I will give it a go soon and report back here.

FINALLY got mine working!! Had to play around alot but finally got there…
I can confirm noisey power supplied are NOT good for the S8. @KnowPassFilter you could add an electrolytic capacitor between +5V and GND, that will remove any high freq noise from the power.

I also found that I have to supply ~5.15V to get the S8 to work reliably . +5.00V and it wont work.

The -2 message means you are not reading anything from the sensor.
The -1 means you are reading from the sensor and there is an error, so if your getting -1’s it is a better sign than reading -2’s.

As you can see in my photo posted above, it works quite well down to 3.73 volts if you have a properly built board.

In that post you can download the gerber files for the board that I am running that on and have it made for yourself.

1 Like

I checked every single solder point… swapped usb cables… used a high quality power supply…
I keep getting “-2” with the S8 CO2 sensor (when all sensors and screen are attached)

please advise - I don’t know what else to try!

I do have a slightly different D1 board:

  • ESP8266 ESP-12 ESP-12F CH340G CH340 V2 USB WeMos D1 Mini PRO V 3.0.0 WIFI Development Bord NodeMCU Lua IOT Bord 3,3 V with Pins

Another FUN fact:
WITHOUT the screen and pm sensor - the CO2 sensor works!
…well… sometimes.

The CO2-SIMPLE Example works perfectly… as long as I disconnect the PM sensor.
It is not enough to not activate it in the code - it has to be physically disconnected!
This makes no sense to me!!!

Does the D1 Pro need more power and therefore fails to power both sensors??

Can anyone help me please?

This somehow looks like you could have some shorts on the board. Can you post photos from both sides of the board here?