Problem with Infrared CO2 Sensor V1.1 - Gravity - SEN0219

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1

Bonjour,
I have implemented this CO2 sensor on an Arduino UNO.
Reading are not conform.
For 1 mn, just after preheat, they are at 153pp to 368ppm (sensor value is 92 to 106, voltage : 449 to 512 mV).
And then, they are always at arround 1500 ppm (sensor : arround 185, voltage : arround 909 mV).

I have checked power supply : 4,95 V, constant. And after several hours (but less than 1 day), problem is the same.

I have seen (https://www.dfrobot.com/forum/viewtopic.php?t=3128) that I may have to waite for 1 day in a room where CO2 is suposed to be constant at arround 400 ppm, and that the value will then be automatically corrected.
But could anyone tell me :

1/ assuming I put the sensor 1 long day - powered on on my arduino card - in a room outside with CO2 stabilised at outside CO2 value (arround 400 ppm), if I disconnect the power supply, should I wait another day with sensor powered? or does the sensor remind previous initialisation?

2/ If I want to use this sensor "as is", can I consider that I have only a shifted estimation of CO2? (in my case, as sensor tells me : 1500 ppm in a room w/o any human in it, I only have to remove 1500 ppm to all the following readings?)

3/ In understand that we can short pins 8 and 20 to 0V for more than 7 sec - after 20mn in a room outside. ( https://www.dfrobot.com/forum/viewtopic.php?t=3128 ). Is it a relable procedure?

Thanks in advance,

2

I may have some answers to my own questions ...

I have connected pins 8 and 20 to the ground of my Arduino for a couple of seconds (sensor being active).
Values measured have switched immediatly to normal values : sensor arround 107 / voltage 523mV / CO2 concentration 381ppm ( link to and electrical schema : Dropbox - CO2 sensor - how to reset it.jpg - Simplify your life ).

I have also powered Arduino and sensor off for 1 or 2 minutes. After power on, reading where still good (arround 381 ppm). So, power off seems not to erase the off-set setting.

In addition, i give you the details of concenration calculation :

  • n = 0 ---> 1023 (sensor values stored in Arduino after conversion by the 10 bits analog to binary convertor).

  • V = 0 ---> 5 V (range of voltage coming from sensor, if Arduino VDD = 5 V. Put 3,3V if VDD = 3,3V ).
    so, V = n * (5.0 / 1023) // in volts
    or, V = n * (5000.0 / 1023) // in milli-volts

  • Correspondance between Voltage measured by Arduino and CO2 concentration
    V = 0,4 V ---> 2,0 V
    c = 0 ppm ---> 5000 ppm (CO2 concentration)
    so, ( c - 0 ) / ( v - 0,4 ) = ( 5000 - 0 ) / ( 2,0 - 0,4 )
    so, c = ( V - 0,4 ) * 5000.0 / 1,6 (ppm of CO2) (if V in volts)
    or c = ( V - 400 ) * 5000.0 / 1600 (ppm of CO2) (if V in millivolts)

CO2 sensor - how to reset it.jpg
CO2 sensor - how to reset it.jpg1049×600 45.6 KB

3

All inexpensive sensors have to be calibrated against known standards, if the current output value is to be meaningful.

Otherwise, just use them to detect changes in gas concentration.

4

Sure.
I only expect to have an idea of the evolution of CO2 in a room. I hope values are true at 30%...
Anyway,it is only to train students on sensors for CO2 and air quality.
Thanks.