Air Quality Sensor

[epierre]

@Yveaux you mean something like this ?

return ( (((float)RL_VALUE*(1023.0 - (float) raw_adc)) / (float) raw_adc));

I somehow forked the discussion on arduino.cc and sent an email in parallel do Davide Gironi for I would like to understand his formula as opposed to the curve approach.

[epierre]

This post is deleted!

[Yveaux]

@epierre something like that, yes. You could also feed it some artificial values in a debug build and see if the calculated values match your expectations.
It wouldn't be the first time that some calculations (divisions) are unexpectedly calculated as ints and always return either 0 or 1 instead of the expected fraction...

[epierre]

Hello,

Having sorted out how to make a power regression, I now have the sames values as Davide Gironi.

I applied this to MQ2, MQ6, MQ131, MQ135 and TGS2600 with resistance calibration at start.

MQ2    :LPG   :12ppm    CO    :0ppm    SMOKE :21ppm
MQ6    :LPG   :3ppm    CH4   :39ppm
MQ131  :CL2   :2ppm    O3    :3ppm
TGS2600:H2    :5191ppm    C2H5OH:8825ppm    C4H10 :16954ppm
MQ135  :CO2    :0ppm    CO    :0ppm    CH3    :0ppm    NH4    :0ppm
GP2Y1010AU0F Raw Signal Value (0-1023): 19 - Voltage: 0.09 - Dust Density: -84.23

the MQ135 is still doing its first heating period, do not care about its values.

Clearly the TGS shows abnormal values, I'm quite puzzled by this, using the previous method it was always 0...

[Yveaux]

@epierre I'm still a bit wondered by the way in which you present the values.
I, for instance, have an MQ135. Is "sensitive to noxious gas concentration. MQ135 sensor also sensitive to sulfide, benzene steam, smoke, etc". The logarithmic charts in the datasheet show the sensitivity to the various gases.
This sensor has a single analog output from which IMHO you cannot determine the fraction of individual gases. Yet you present them as individual values in your measurement data... How can you distinguish?

[epierre]

@Yveaux in fact it is a correlation, if you have a value from the analog, then from the curve you can guess it is one of the group, not one individually... it is the way they are designed...

[Yveaux]

@epierre That's exactly my point!

[epierre]

@Yveaux and there's worse : if you don't have the environment to calibrate it with real gas, it is just an indication... that is maybe why some projects that may have taken such sensor may hae a production process issue at the moment... In fact despite my researches, I've never found someone that said it made it to mesure correctly with gas sensors, mostly theory or just analog reading only...

An example: my MQ135 was silencious, I put its nose in the Aceton bottle:

Before:
Q2 :LPG :11ppm CO :0ppm SMOKE :18ppm
MQ6 :LPG :3ppm CH4 :36ppm
MQ131 :CL2 :2ppm O3 :3ppm
TGS2600:H2 :7602ppm C2H5OH:13706ppm C4H10 :26350ppm
MQ135 :CO2 :0ppm CO :0ppm CH3 :0ppm NH4 :0ppm
Dust :raw : 18 Voltage: 0.09 - Dust Density: -85.06

After:
MQ2 :LPG :208ppm CO :0ppm SMOKE :832ppm
MQ6 :LPG :44ppm CH4 :172ppm
MQ131 :CL2 :16ppm O3 :17ppm
TGS2600:H2 :7774ppm C2H5OH:13818ppm C4H10 :27274ppm
MQ135 :CO2 :999ppm CO :0ppm CH3 :484ppm NH4 :1904ppm
Dust :raw : 58 Voltage: 0.28 - Dust Density: -51.86

The MQ135 has reacted, but all others around...

[epierre]

doing the same on my basic sketch here what I have:

2014-08-03 11:29:57 3 0 1 24 -28393

looks like my old sketch needs some update...

[epierre]

Doing the same on the basic sketch :

 Vrl / Rs / ratio:4.21 3731.17 0
 CO ppm :inf

Then:

Vrl / Rs / ratio:4.21 3731.17 0
CO ppm :inf

[epierre]

and now ethanol/isopropylène (bike chain cleaning product):

MQ2    :LPG   :247ppm   CO    :0ppm    SMOKE :1053ppm
MQ6    :LPG   :3527ppm    CH4   :2160ppm
MQ131  :CL2   :10ppm    O3    :12ppm
TGS2600:H2    :7891ppm C2H5OH:14279ppm C4H10 :27751ppm
MQ135  :CO2   :0ppm    CO    :0ppm     CH3   :0ppm    NH4    :0ppm
Dust   :raw   : 206    Voltage: 1.01 - Dust Density: 71.00

[epierre]

and now eveyone through aceton:

MQ2    :LPG   :25ppm   CO    :0ppm    SMOKE :48ppm
MQ6    :LPG   :19677ppm    CH4   :3010ppm
MQ131  :CL2   :71ppm    O3    :51ppm
TGS2600:H2    :8448ppm C2H5OH:15007ppm C4H10 :28738ppm
MQ135  :CO2   :840ppm    CO    :0ppm     CH3   :400ppm    NH4    :1474ppm
Dust   :raw   : 728    Voltage: 3.55 - Dust Density: 504.30

remark that dust sensor goes up ! and TGS2600 goes down afterward:

MQ2    :LPG   :8ppm   CO    :0ppm    SMOKE :11ppm
MQ6    :LPG   :1264ppm    CH4   :1194ppm
MQ131  :CL2   :27ppm    O3    :24ppm
TGS2600:H2    :4966ppm C2H5OH:8407ppm C4H10 :16227ppm
MQ135  :CO2   :840ppm    CO    :0ppm     CH3   :400ppm    NH4    :1474ppm
Dust   :raw   : 165    Voltage: 0.81 - Dust Density: 36.96

[epierre]

@hek I now have the netatmo CO2 xml and json, they are based on the generic sensor.

But I don't have mysensors running on my vera...

I would need from you:

• the device and variable type
• an icon, but maybe I can reuse the other one

maybe
CO2 = {22, "urn:schemas-micasaverde-com:device:CO2Sensor:1", "D_CO2Sensor.xml", "CO2 "}
CO2 = {36, "urn:micasaverde-com:serviceId:CO2Sensor", "Concentration", "396" },

S_CO2Sensor.json D_CO2Sensor.xml D_CO2Sensor.json

P.S. there's the icon from Nest plugin too: http://cocu.la/vera/nest/nest_co.png

[epierre]

About initial calibration, just a warning from this graph:

chart.png

you can see high levels around july 21 then dropping in august... the sensor has been restarted... that is what the call clean air...

this automatic reading at the start should be stored in the sketch and not reclaculated at each reboot or you would loose all reference on your data...

[epierre]

This post is deleted!

[epierre]

This post is deleted!

[Yveaux]

@epierre did you just post the same reply 3 times or is the forum software showing yet another bug?

[epierre]

@Yveaux don't know, I did post once...

[korttoma]

I wanted to get acquainted with the MQ2 AirQuality Sensor so I took a look at the sketch from github.
One thing I noticed was that there is some sleep-time defined, is this just to make the sensor report the value every 30 seconds?
I guess it is not for saving power so you can run it on batteries because my understanding is that it needs to be hot in order to function correctly and that will drain the battery fast.

Does not look like the calibration during setup takes in account the preheating time either, maybe it is a good idea to add a delay before the calibration so the sensor gets hot enough.

Please correct me if I'm wrong.

[epierre]

@hek Here is a first list from the most commons:

• Carbon Monoxide – CO
• Carbon Dioxide – CO2
• Oxygen – O2
• Methane – CH4
• Hydrogen – H2
• Ammonia – NH3
• Isobutane – C4H10
• Ethanol – CH3CH2OH (aka C2H5OH or C2H60)
• Toluene – C6H5CH3
• Hydrogen Sulfide – H2S
• Nitrogen Dioxide – NO2
• Ozone – O3
• Hydrocarbons – VOC
• Chlorine CL2
• Ammonium NH4
• Ethanol CO2H50H
• Methyl CH3
• Acetone CH3_2CO
• LPG (both C3H8 C4H10)