MH-Z19

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mra2ko
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MH-Z19

#1 Post by mra2ko » 06 Dec 2021, 08:38

Hi,
I use ESP Easy Mega (ESP_Easy_mega_20211105_normal_ESP8266_4M1M Nov 5 2021) and have connectet MH-Z19. Data count, but I have still aroud 400.
What is the exact calibration procedure ?

I test disable abc, get outside, connect HD to GND and still have around 400 inside and outisde too :/

Thak

TD-er
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Re: MH-Z19

#2 Post by TD-er » 06 Dec 2021, 08:50

How is the sensor connected?
You should not need to perform a calibration as the sensor should be calibrated from the factory.

Can you see any information in the log regarding the MH-Z19?

What voltage do you supply to the sensor? It needs 5V.

A very simple check to see if the sensor is working, is simply breathing on it.
This should increase the measured CO2 values quite a lot.

mra2ko
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Re: MH-Z19

#3 Post by mra2ko » 06 Dec 2021, 09:09

Sensor is connected on short cables 10cm, direct to D1 mini to TX/RX pins, VCC is 5V
Yes, if I breathe on the sensor, the value changes, but after 10s. But in normal conditions in the room is around 410 which is nonsense.


303718: MHZ19: PPM value: 395 Temp/S/U values: 21/0/0.00
304689: MHZ19: PPM value: 395 Temp/S/U values: 21/0/0.00
305689: MHZ19: PPM value: 395 Temp/S/U values: 21/0/0.00
306689: MHZ19: PPM value: 395 Temp/S/U values: 21/0/0.00
307689: MHZ19: PPM value: 395 Temp/S/U values: 21/0/0.00
308690: MHZ19: PPM value: 395 Temp/S/U values: 21/0/0.00
309691: MHZ19: PPM value: 395 Temp/S/U values: 21/0/0.00
310689: MHZ19: PPM value: 395 Temp/S/U values: 21/0/0.00
311689: MHZ19: PPM value: 395 Temp/S/U values: 21/0/0.00
312689: MHZ19: PPM value: 395 Temp/S/U values: 21/0/0.00

after breathing

445690: MHZ19: PPM value: 619 Temp/S/U values: 21/0/0.00
446690: MHZ19: PPM value: 619 Temp/S/U values: 21/0/0.00
447689: MHZ19: PPM value: 619 Temp/S/U values: 21/0/0.00
448689: MHZ19: PPM value: 705 Temp/S/U values: 21/0/0.00
449692: MHZ19: PPM value: 705 Temp/S/U values: 21/0/0.00
450690: MHZ19: PPM value: 705 Temp/S/U values: 21/0/0.00
451689: MHZ19: PPM value: 705 Temp/S/U values: 21/0/0.00
452716: MHZ19: PPM value: 705 Temp/S/U values: 21/0/0.00
453689: MHZ19: PPM value: 725 Temp/S/U values: 21/0/0.00
454689: MHZ19: PPM value: 725 Temp/S/U values: 21/0/0.00
455690: MHZ19: PPM value: 725 Temp/S/U values: 21/0/0.00
456689: MHZ19: PPM value: 725 Temp/S/U values: 21/0/0.00
457689: MHZ19: PPM value: 725 Temp/S/U values: 21/0/0.00
458690: MHZ19: PPM value: 688 Temp/S/U values: 21/0/0.00
459689: MHZ19: PPM value: 688 Temp/S/U values: 21/0/0.00
460690: MHZ19: PPM value: 688 Temp/S/U values: 21/0/0.00
461689: MHZ19: PPM value: 688 Temp/S/U values: 21/0/0.00
462689: MHZ19: PPM value: 688 Temp/S/U values: 21/0/0.00
463702: MHZ19: PPM value: 618 Temp/S/U values: 21/0/0.00
464689: MHZ19: PPM value: 618 Temp/S/U values: 21/0/0.00

TD-er
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Re: MH-Z19

#4 Post by TD-er » 06 Dec 2021, 10:34

OK, so the sensor does respond, which makes it clear it is working.
Just to be sure, please also check the settings page of that sensor and have a look at the statistics to see if there are lots of checksum errors detected.
If there are none (or next to no errors) then we can leave that for now.

Is this sensor new, thus with fresh factory calibration?
Or has it been used in other projects too?

You could try to have it running for over 24h with ABC enabled to see if it will show a bit more "believable" values.
The ABC period of this sensor is 24h, which is a bit impractical short.
This means that if it was running for 24h in a room with not enough ventilation, it will re-set the 400 ppm level to some higher level like maybe 600 or 700 or whatever was the lowest seen concentration in the past ABC window.
If after that (incorrect) adjustment the room is ventilated, the CO2 value may "clip" to 400 ppm for a large part of the day until the next ABC period has passed.
I think something like this is happening since the rise to only 700 ppm is unlikely low if you directly breathe on it.
The CO2 concentration of the air you breathe out is upto 40'000 ppm when leaving your mouth.
Of course then it dilutes very quickly, but still you should be able to get it well over 1000 ppm when breathing on it for a few seconds (which it seems like you did based on the log)

mra2ko
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Location: Czech Republic

Re: MH-Z19

#5 Post by mra2ko » 07 Dec 2021, 11:35

Problem solved. I dont know why, but I had to recalibrate 2x. Afther them work fine. The sensor was never used again
Thank to all!

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