Air Gradient Pro - CO2 below 400ppm

Hi all - my first post to the forum since buying an AirGradient Pro and 3 of the basic boards.

I have a few questions and notes;

  1. My CO2 sensor doesn’t seem to be very reliable. If I open the window and place the unit on the windowsill I’d expect the unit to self-calibrate back to 420 (or at least a baseline of 400). Instead, it’s been down to 114 and recently risen (in the space of around 20 seconds) to 205 (at the time of writing this).
    I’ve left it there for a few hours on a stable power supply with nothing else plugged in on that socket and have avoided moving it as much as possible.

  2. I’ve tried using the “Request CO2 calibration” check box on the app, and I assumed that it would be advisable to place the unit in the fresh air whilst this was carried out - it doesn’t appear to be doing anything.

  3. Is there a way of manually telling the device that it’s outside, and to calibrate itself to a baseline of 400?

  4. Is there a timeframe for calibration (do I need to leave this outside under a cover for 24 hours to get this calibration to work)

Notes: I even tried unplugging the device for a few hours to see if any cached errors might have been causing issues - after powering back up - same issues as before…

UK based - fairly cold at the moment

*No LEDs installed. *

*Sensor information still has 'current boot count: ’ (as in there is no data next to it in the AirGradient App
Calibration Request in Progress is under it - has been there for I think 3 days since I found the box to tick to request it…

It looks like your sensor is not calibrated. The CO2 calibration from the dashboard is not yet implemented for the DIY monitors and thus it is not working.

There are two options.

a) you let it run for about a week and then the automatic baseline calibration will kick in. Make sure that within this week it has been exposed to ambient CO2 levels for at least 30 minutes.

b) you can flash some code to force a manual calibration and then flash the AirGradient code back

Two things:

  1. How do I flash it manually?

  2. An entire week for a baseline is too long, I’d suggest taking that down to a maximum of three days. Can you explain the rationale behind a 1 week period? Is the device really logging an entire weeks worth of data to work out a base point?

Does it have to be an entire week without a reboot \ power failure? Or would a power failure restart the count?

I think reboots do not pose a problem but try to keep it connected as much as possible.

If you pull the CAL pin low for between 4 and 8 seconds it puts the sensor into calibration mode assuming 400ppm CO2. See for the pinout and more on the background calibration process.