## MQ7 & MQ135 Gas Sensors

lakindu93
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### MQ7 & MQ135 Gas Sensors

මට දැනගන්න පුළුවන් ද MQ7 සහ MQ135 ගෑස් Sensors පාවිච්චි කරලා කොහොමද CO(Carbon-monoxide) සහ CO2(carbon-dioxide) ගෑස් වර්ග දෙක වෙන වෙනම හදුනාගන්නේ කියල...

MQ7 - CO
MQ135 - CO2

මේ sensors දෙකම arduino compatible module එකක් විදිහට තියෙන්නේ...

මේ ගෑස් Sensors දෙකම එක ලග තියෙන්නේ... මොකක්හරි CO සහ CO2 mix වෙච්ච ගෑස් එකක්, ඒ ගෑස් sensors ලගට ලං කලාම ගෑස් දෙක වෙන වෙනම හදුනාගන්න ඕනි... එවගේ ම output result එක percentage එකක් විදිහට හෝ ppm value එකක් විදියට display කරගන්නත් ඕනි serial monitor එකේ...

නිකන් sensor එක arduino එකට ගහල, මොකක්හරි කොලයක් පත්තු කරලා එකෙන් එන දුම් ටික sensor එකට ලං කලාම analog reading එකක් එනවා එත් ඒ එන readings වලින් කොහොමද හරියටම co or co2 කියල කියන්නේ...

මේ sensors දෙකට තියෙන datasheet බැලුවට හරියටම තේරෙන්නේ නෑ නේ...
මේක කරගන්න මොනාහරි equations මොනාහරි තියෙනවා නම් සහ මේක කරගන්න හැටි පොඩ්ඩක් කියල දෙන්න කෝ.....
SemiconductorCat
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### Re: MQ7 & MQ135 Gas Sensors

If your application is automobil then you need oxygen sensor too. Because parameters would change due to oxygen
concentration.So this question is all about sensor calibration right ?

so it's sensitivity graph. And please note that it's x and y axes are on logarithmic scale.
So sounds like the the simple way to handle this situation using a look-up table and use a curve fitting
function, you could simply use matlab or octive like software [on computer] to generate such curve fitting
function so easily derive a polynomial based equation for that.ex -
http://en.wikipedia.org/wiki/Calibration_curve
$f(x) = a_0 x^0 + a_1 x^1 + a_2x^2 + ... + a_nx^n$

Even such polynominal based equations were used in older model ECU's may be [ Nazi Germany people's car just kidding there are no ECUs in nazi era ].

But modern sensor calibration is so complicated and it's not two dimensional either. In that case they have using neural
and PID methods to calibrate it dynamically. PID is enforced when there are sensor degeneration effects does exist.
PID's and neural nets are so complicated but if you asking the question would that fit on small microcontroller like ardiuno board ? The answer is yes, it's more than enough for this because real ECUS are also using same chips till recent days.

I could help you on the first curve fitting method. It would work most probably with more than enough acceptable accuracy for a simple project , but if you serious and this is for automotive industry , then your ECU design will broke your clients emission certificate.

lakindu93
Sergeant
Posts: 21
Joined: Wed Jun 26, 2013 12:45 pm
Location: Colombo

### Re: MQ7 & MQ135 Gas Sensors

SemiconductorCat wrote:If your application is automobil then you need oxygen sensor too. Because parameters would change due to oxygen
concentration.So this question is all about sensor calibration right ?

so it's sensitivity graph. And please note that it's x and y axes are on logarithmic scale.
So sounds like the the simple way to handle this situation using a look-up table and use a curve fitting
function, you could simply use matlab or octive like software [on computer] to generate such curve fitting
function so easily derive a polynomial based equation for that.ex -
http://en.wikipedia.org/wiki/Calibration_curve
$f(x) = a_0 x^0 + a_1 x^1 + a_2x^2 + ... + a_nx^n$

Even such polynominal based equations were used in older model ECU's may be [ Nazi Germany people's car just kidding there are no ECUs in nazi era ].

But modern sensor calibration is so complicated and it's not two dimensional either. In that case they have using neural
and PID methods to calibrate it dynamically. PID is enforced when there are sensor degeneration effects does exist.
PID's and neural nets are so complicated but if you asking the question would that fit on small microcontroller like ardiuno board ? The answer is yes, it's more than enough for this because real ECUS are also using same chips till recent days.

I could help you on the first curve fitting method. It would work most probably with more than enough acceptable accuracy for a simple project , but if you serious and this is for automotive industry , then your ECU design will broke your clients emission certificate.

Our application is monitoring and notification system for factory emission gasses. For this application we are going to use CO and CO2 gasses.
yes, my problem is calibrating the sensors...
we use Arduino Uno board to get the readings from the gas sensors...
Is there any easy way to do that? (I mean without getting the oxygen levels)
lakindu93
Sergeant
Posts: 21
Joined: Wed Jun 26, 2013 12:45 pm
Location: Colombo

### Re: MQ7 & MQ135 Gas Sensors

anyone having coding related to the MQ7 and MQ135 to get the ppm values from sensor readings...?
Neo
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Joined: Wed Jul 15, 2009 2:07 am
Location: Colombo

### Re: MQ7 & MQ135 Gas Sensors

Since the sensor was built to given a resistance to a certain pressure of CO, I'm not too sure it is possible to get an exact ppm value. Need to do a good literature survey on this. Most of the articles in the internet don't give direct information as well as the datasheet. However, I found following two articles little bit helpful.

https://forum.sparkfun.com/viewtopic.ph ... ide#p86747
http://forum.arduino.cc/index.php?PHPSE ... #msg399839

Once you are done, please be sure to update the topic here.
lakindu93
Sergeant
Posts: 21
Joined: Wed Jun 26, 2013 12:45 pm
Location: Colombo

### Re: MQ7 & MQ135 Gas Sensors

Neo wrote:Since the sensor was built to given a resistance to a certain pressure of CO, I'm not too sure it is possible to get an exact ppm value. Need to do a good literature survey on this. Most of the articles in the internet don't give direct information as well as the datasheet. However, I found following two articles little bit helpful.

https://forum.sparkfun.com/viewtopic.ph ... ide#p86747
http://forum.arduino.cc/index.php?PHPSE ... #msg399839

Once you are done, please be sure to update the topic here.
thanks lot...
SemiconductorCat
Major
Posts: 455
Joined: Mon Aug 22, 2011 8:42 pm
Location: currently in hyperspace

### Re: MQ7 & MQ135 Gas Sensors

Please note that in MQ6 datasheet, page 1 table 1.
That PL should be corrected to RL.
And there are grammar and English mistakes in sheet too.
It's clear it's poorly written, but let not be a complainer, let's see how could we correct the mistakes and
go forward. Let's see what we could do.