Air Quality Sensor

[AtmosCheme]

@epierre

Thank you for the reply epierre.

I was going off of the SainSmart website that says the range for their module is 10 ppb to 200 ppm. That would cover 10 ppb to 200,000 ppb.

http://www.sainsmart.com/sensors/eco/sainsmart-mq131-gas-sensor-ozone-module-for-arduino-uno-mega2560-r3-raspberry-pi.html

The values keep dropping down as more and more ozone is added, I'm not thinking it is a problem with range as much as a problem with resolution. I have gone as high as around 50,000 ppb and continue to get response from the sensor.

Ive thought of using mapping functions in my code as well as resolution functions. But I just wasn't sure if there was a component I could add to the circuit to improve resolution.

In my latest sketch I have used a calibration code that analog reads the sensor for 6 minutes, and then remaps the min and max values observed during that time. I though this would get a broader range of values. The problem is that the longer the sensor is on it becomes stable so the min and max values become the same and there is nothing to map. So the longer it runs the smaller the range of values in the serial monitor.

[epierre]

@AtmosCheme said:

I was going off of the SainSmart website that says the range for their module is 10 ppb to 200 ppm. That would cover 10 ppb to 200,000 ppb.

check their datasheet (or ask for it !)

The values keep dropping down as more and more ozone is added, I'm not thinking it is a problem with range as much as a problem with resolution. I have gone as high as around 50,000 ppb and continue to get response from the sensor.

yes it should be possible but you don't know from the datasheet the value. On a power regression you make an estimation with error, but that may change outside of know datapoints.

Ive thought of using mapping functions in my code as well as resolution functions. But I just wasn't sure if there was a component I could add to the circuit to improve resolution.

some as the Particle Photon has a better ADC that goes up to 4096

[jnewton957]

Hi,

I just try to connect 7 sensors to an nano.
MQ-2, MQ-3, MQ-4,MQ-6, MQ-7,MQ-9, MQ-135

With sketch form robosensor https://forum.mysensors.org/topic/1595/mq2-sensor-w-airquality-sketch/2

I get data like MQ-7:1020 ,MQ135: 294, MQ-2:191

So it looks really good.
As i would like to have also the correct names an value names of the sensor and a correct calibration I think I should use a sketch like AirQuality-Multiple_Gas_Sensor1_4.ino
But I only see 3 of my 7 sensors in this sketch.

What would be a good sketch for my 7 sensors ??

Thanks
Jorg

[walk_porto]

Hello everybody,

I am working with an Arduino Uno and a MQ135 module arduino : http://www.sainsmart.com/sainsmart-mq135-sensor-air-quality-sensor-hazardous-gas-detection-module-arduino.html

I can get back data from this sensor, I got 100 ppm when I launched serial terminal after compiling and uploading this code below.

int sensorValue;

void setup()
{
  Serial.begin(9600);      // sets the serial port to 9600
}

void loop()
{
  sensorValue = analogRead(0);       // read analog input pin 0
  Serial.println(sensorValue, DEC);  // prints the value read
  delay(100);                        // wait 100ms for next reading
}

But, I would like to get back data from gases like NH3, NOx, alcohol, benzene, smoke and CO2 . I read a lot of topics and the datasheets of the sensor but I don't see how to do.

If someone could help me, it will be great.

Thanks.

[AtmosCheme]

@walk_porto

I think that the only way you are going to be able to distinguish between different gases is to have a known concentration of that gas and adjust load resistance. This sensor will detect all of these gase because of cross sensitivity to the gases mentioned in the filament. You can not use just one MQ135 sensor and get readings for all of the gases.

[Thanh-Viet]

Hi Guys,

Nice work. I'm based in Hong Kong, and what matters to us is PM2.5, NO2 and Ozone (and indoor CO2/VOC).

Have you guys checked the laser based particle sensors like the Plantower G1-G3-G5, Innovafitness SDS011/021 ?
http://aqicn.org/sensor

[alexsh1]

@Thanh-Viet Hello. Yes, I have Plantower G3 on order from Aliexpress and won't be able to test it before September. I think adopting it for MySensors is going to be easy

[paqor]

Hello, there are statements if the values increase the MQ135 when a room ventilated, without people and is furnished? I I have several rooms here an increase over time. Perhaps this is also by the increase in temperature, sunlight or gases from the furniture. I have not found any literature on this. Is this behavior with other users as well?

[paqor]

Has the type of installation (horizontal or vertical) have an impact on the values of MQ135? I have found no photos of built-in sensors already exist in the data sheet a statement.

[alexsh1]

@paqor yes, in fact my MQ-135 was so unreliable that I had to move on to a different sensor

[paqor]

Those interested in a 4 sensors Sketch FHEM (CO2, Temp, Hum, Motion) has ...

[A Former User]

@paqor
I'm interested, but i'm using mysensors 2.0. Can you update your sketch?

[paqor]

@gieljnssns said:

@paqor
I'm interested, but i'm using mysensors 2.0. Can you update your sketch?

Yes, sure but I need time. I'm not a good programmer and need a lot of testing. My Englich is not particularly good. As some patience please, because I have to house, garden, woman and taking care of animals. :two_men_holding_hands:

[paqor]

@gieljnssns said in Air Quality Sensor:

@paqor
I'm interested, but i'm using mysensors 2.0. Can you update your sketch?

@paqor
https://gleisnetze.de/2016/08/07/sensoren4sketch/

• v0.8 korrigierte Lib von RSTOICA
• EEPROM set R0Cor
• amended mq135.h required!
• Temp, Hum --> CO2Cor
• Api 2.0
• Motion is not yet tested
• Auto base value set r0corr if Co2cor <390
• R0Cor set by TextField runs (incoming message)
• Redesign

[paqor]

@paqor
Probably one should not speak of a sensor CO2 value as well as responding to many other particles at the MQ135. The most accurate CO2 measurement we certainly be possible only with a MH-Z14. I now have to buy me a part and will then calibrate the MQ135 so. With the MQ135 can z. B. only say something about the air quality in relation to the outside air. It is rather a relative value.

Here the comparison of MH-14T (yellow) and MQ135 (red). One sees the calibration and as yet are both curves to each other.
[https://smarthome.gleisnetze.de/38-mhz-14-erste-erfahrungen-mit-dem-co2-sensor-fuer-mysensors-arduino-fhem]

Wahrscheinlich sollte man beim MQ135 nicht von einem CO2 Wert sprechen da der Sensor auch auf viele andere Partikel reagiert. Die genaueste CO2 Messung wir sicher nur mit einem MH-Z14 möglich sein. Ich habe mir jetzt so ein Teil bestellt und werde dann den MQ135 damit kalibrieren. Mit dem MQ135 lässt sich z. B. nur etwas zur Luftgüte im Verhältnis zur Außenluft sagen. Es ist also eher ein relativer Wert.

[ysinh]

@tuimanso
There seems a general misunderstanding about how those gas sensors really work: the "heater" must be switched on (5v) and "off"(1.4v) for the air sample going in and out of the sensor, when heating the air sample expands and goes out of the sensor, then in the cool down period the remaining air contracts and sucks in a new sample.
Those boards with mq... sensors only provide fixed 5v heating, so this can never work reliable
the 1.4v is needed to keep the sensor on a minimum temperature,example 40'c for the catalyst to react, the 5v will heat it up to example 80'c, to clean the catalyst and air flows out of the sensor
http://i49.tinypic.com/2rzdqgn.png something like this will work
Soon I will report my results together with a modified sketch for mysensors 2.0

[bezeefly]

@epierre I am working on a dust sensor project using Samyoung DSM501A. I am confused with the identical calculation formula used in the Samyoung DSM501A and Shinyei PPD42NS dust sketch.

concentration = 1.1pow(ratio,3)-3.8pow(ratio,2)+520*ratio+0.62;

My understanding is that the formula is based on the specific product's data sheet curve. Is the formula for DSM501A, PPD42NS, or both?

[epierre]

@bezeefly said:

Samyoung DSM501A and Shinyei PPD42NS

This is formula for Shinyei, you're right, I'searched back but don't know if a formula was made out : https://groups.google.com/forum/#!topic/airqualityegg/A1F9padoW10

strangely here it is used too : http://learn.linksprite.com/arduino/shields/use-dust-sensor-dsm501-with-arduino/

a formula by Chris Nafis here: https://github.com/OSBSS/Samyoung_Dust_Sensor/blob/master/Samyoung_Dust_Sensor.ino

[bezeefly]

@epierre I obtained the following equation by polynomial fit the low ratio vs particle (pcs/283ml) graph in the DSM501 datasheet.

concentration = (0.1 * pow(ratio, 2)) + (619 * ratio) + 50;

Please help to check whether the equation is correct.

[epierre]

@bezeefly said:

@epierre I obtained the following equation by polynomial fit the low ratio vs particle (pcs/283ml) graph in the DSM501 datasheet.

concentration = (0.1 * pow(ratio, 2)) + (619 * ratio) + 50;

Please help to check whether the equation is correct.

looks correct for the red curve

using http://www.xuru.org/rt/PR.asp with:
4 2500
8 5000
12 7500
16 10000
20 12500
22 15000
gives =7,613212955POWER(B3;2) + 467,3617082B3 + 631,9862425

a bit better ;-)

and on the previous one datasheet http://www.mouser.com/ds/2/744/Seeed_101020012-838657.pdf:
2 1000
3.9 2000
5.8 3000
7.2 4000
9 5000
10 6000
11.3 7000
12.6 8000
y = 19.09464953 x2 + 383.1041412 x + 174.9189116