Air Quality Sensor

[bhavika]

I am confused with MiCS 4514 sensor. What I had done is :

using MiCS quick start evaluation board, measured ADC value
calculated Vout and from that calculated R0.
Rs/R0 concentration gives me high value, which is not possible, My data is as follows
clean air file is used for the purpose of R0 value
https://drive.google.com/file/d/0B8sF8a6FHoseWjhWOHRoYzIxakk/view?usp=sharing
and Polluted file is used to calculate the actual pollution
https://drive.google.com/file/d/0B8sF8a6FHoseR1BnclhCUHdibEU/view?usp=sharing

I am confused. Please help me

[epierre]

@tantt2810 said:

@epierre
Thank you. Your mean is Vcc->5V, GND->GND, Dout->Digital pin, Aout->Analog pin. Is it right?
But I don't know the tcm pin connect with ? I have read datasheet but I don't find any info about tcm pin. Please help me. Thank you so much !!!

do not use the digital pin !!! it only reacts with the potentiometer in on/off mode, so useless... you need to power the device with Vcc/Gnd, and read the output with Aout (A stands for analog). The last one forget it.

[epierre]

@alexsh1 is that raw ADC output or with a calculation ? normaly this should go up or down but not in sucha drastic way

[alexsh1]

@epierre

This is a value gw.send(msg.set(MQ135_DEFAULTPPM+(int)ceil(valAIQ))) reported to Domoticz.
It does not make any sense to me at all.

[tantt2810]

@epierre
Thanks you so much !!! Good job, Good boy =)).

[epierre]

@alexsh1 said:

@epierre

This is a value gw.send(msg.set(MQ135_DEFAULTPPM+(int)ceil(valAIQ))) reported to Domoticz.
It does not make any sense to me at all.

same for mle, sometime it is good to have two piece to compare their behavior... I have 3 o them ...

[alexsh1]

@epierre do you think it is a faulty sensor though?

[tantt2810]

Hello,

Can I use pinMode(digitalpin, OUTPUT) to turn off sensor? Or Is there any way to wirte a function that turn off sensor?

I want to remote it on web to turn on or off it.

Thank you so much !!!

[supersjimmie]

For those who are trying to use an MQ135 module from e-bay or other sellers, on a small pcb with a chip, LED and potmeter:
It took me a while until I figured out that the little chip has a very big influence on the value that you read on the A-out pin.
Only after removing the connection between the A-out pin and the little chip, I got normal measurements.

I also replaced the small resistor marked "102" with a 10k resistor, to make measurements more compatible with code that uses a 10k pull down resistor. But that was already a known issue, found on many other places.

[epierre]

@tantt2810 said:

Hello,

Can I use pinMode(digitalpin, OUTPUT) to turn off sensor? Or Is there any way to wirte a function that turn off sensor?

I want to remote it on web to turn on or off it.

Thank you so much !!!

well no, powering is through Vcc/GND, so you whould use a switch on this. Digital pins do not gives enough power for such sensors.

[epierre]

@alexsh1 said:

@epierre do you think it is a faulty sensor though?

coud be, hard to know without possibility to compare to another one.

[alexsh1]

@epierre

This is what I discovered. When nobody is around the sensor 'settles' on a particular value. However, when there is anyone around in the room, the sensor reading goes up and down - see the snapshot attached. Any idea what the problem may be?

[epierre]

@alexsh1 hard to say, could be something moving inside if someone makes vibration around and thus this strange reaction... the down curve at the end is correct, the in between not

[Elfnoir]

Hi,
Can you check the reception level?
I had same behaviour with an old temperature/humidity module; need to move it to another place in the room, and works perfectly now :-)

[epierre]

@Elfnoir said:

; need to move it to another place in the room, and works perfectly now

temp/hum are "less" sensitive on environment, here the sensors heats up to 40-60° (or more) so temp/hum is not the most impacting (I can be wrong anyway ;-)

[alexsh1]

@epierre I wonder if you looked at this sensor Figaro TGS8100:

http://www.figarosensor.com/products/entry/tgs8100.html

Looks like it is perfect for a low-powered platform.

[epierre]

@alexsh1 said:

@epierre I wonder if you looked at this sensor Figaro TGS8100:

http://www.figarosensor.com/products/entry/tgs8100.html

Looks like it is perfect for a low-powered platform.

as a replacement for MQ in low power yes could be... the bad part is how to get one ?

[alexsh1]

@epierre said:
the bad part is how to get one ?

How about http://www.soselectronic.com/?str=371&artnum=170939&name=figaro-tgs8100 ?

[Vir]

Hi, It all make sense, I am just confused that in your code once your multiply and once you divide...

case CO:
{
if(ratio1 < 0.01) ratio1 = 0.01;
if(ratio1 > 3) ratio1 = 3;
//c = pow(10, 0.6) / pow(ratio1, 1.2);
** c = pow(ratio1, -1.179)4.385; //mod by jack*
break;
}
case NO2:
{
if(ratio2 < 0.07) ratio2 = 0.07;
if(ratio2 > 40) ratio2 = 40;
//c = ratio2 / pow(10, 0.8);
** c = pow(ratio2, 1.007)/6.855; //mod by jack**
break;
}
SO, what is the actual formula?

Vir

@epierre said:

I'm now testing the MICS-6814 (3 sensors in one) given for :
Carbon monoxide CO 1 -1000ppm
**Nitrogen dioxide NO2 0.05 –10ppm **
Ethanol C2H5OH 10 –500ppm
Hydrogen H2 1 –1000ppm
Ammonia NH3 1 –500ppm
Methane CH4 >1000ppm
Propane C3H8 >1000ppm
Iso-butane C4H10 >1000ppm

Datasheet maionly speaks on CO, NO2 and NH3:
http://www.seeedstudio.com/wiki/images/1/10/MiCS-6814_Datasheet.pdf

Here is are scripts:
http://www.seeedstudio.com/wiki/Grove_-_Multichannel_Gas_Sensor

http://www.seeedstudio.com/wiki/images/1/10/MiCS-6814_Datasheet.pdf

Some readings:

The concentration of NH3 is 0.99 ppm
The concentration of CO is 1.20 ppm
The concentration of NO2 is 0.15 ppm
The concentration of C3H8 is 1000.04 ppm
The concentration of C4H10 is 999.98 ppm
The concentration of CH4 is 2991.14 ppm
The concentration of H2 is 1.09 ppm
The concentration of C2H5OH is 1.40 ppm

I guess I'll make a script soon...

[Vir]

What does 37143 represents, Rs? and -3.178 is a second value from your regression method, but what about the first value?
Can you elaborate on ppm line, please
Vir

here the formula is a simplification of this:

float Vrl = val * ( 5.00 / 1024.0 ); // V
float Rs = 20000 * ( 5.00 - Vrl) / Vrl ; // Ohm
int ratio = Rs/Ro;
ppm = 37143 * pow (ratio, -3.178);