Air Quality Sensor

epierre

@Heinz so bad I don't have a MQ135 running anymore to compare, here are the MH-Z14 curves I have near my desk.

chart(6).png

epierre

IN MiCS 2614 , sensitivity factor is defined by "Rs at 100 ppb of O3 divided by Rs at 50 ppb of O3". From where you measured Rs at 100 ppb or 50 ppb.???

this is just to tell you how much a double concentration scales up, here they just say it is somehow linear at ratio 2

Rasenheizung

@Heinz very nice work :+1: (wie heisst du im FHEM Forum?)

Does someone have the values a MQ-07 needs to perform properly? I rally don't know how to gather the right values from the description.... :)

Thank you

epierre

@Rasenheizung if you base yourself on my template here https://github.com/empierre/arduino/blob/master/AirQuality-Multiple_Gas_Sensor1_4.ino

H2
1.3 50
0.8 100
0.28 400
0.16 1000
0.05 4000

y = 73.59123879 x-1.355617483
Residual Sum of Squares: rss = 87393.44418
H2Curve[3] = {73.5912, -1.355617};

CO
1.6 50
1 100
0.39 400
0.21 1000
0.09 4000

y = 99.27731641 x-1.513643469
Residual Sum of Squares: rss = 43168.87424
COCurve[3] = {99.27731, -1.51364};

CO is a dangerous gas, the MQ7 is very sensitive to many things and no calibration too... for a serious work please think about using the MICS-6814 that is calibrated, includes 3 gases out of the box, and is very low consumption (can run on battery !)
https://github.com/empierre/arduino/blob/master/AirQuality-CO-NO2-NH3.ino

bhavika

What is the pre-heating time for TGS2442???

epierre

@bhavika said:

What is the pre-heating time for TGS2442???

from datasheet: "the sensor’s resistance reaches to 90% of its final value in less than one minute"

bhavika

So what is the conditioning period for testing in it??? It is two days.. What does it mean??

epierre

@bhavika said:

So what is the conditioning period for testing in it??? It is two days.. What does it mean??

on this kind maybe to have it powered for a full two days to burn out the production "dusts" that may remain in.

those sensors are not good science, see the correlation of gases they are reported for in the datasheet

epierre

Hello,

a very sensitive HCHO module you can see a demo here: http://www.seeedstudio.com/recipe/379-a-handheld-hcho-detector.html?utm_source=EDM&utm_medium=EDM&utm_campaign=EDM20150930

https://github.com/empierre/arduino/blob/master/AirQuality-HCHO.ino

paqor

I have a question for the MQ135. Do not always be above 500 ppm, the measured values? I also get values of 0. I suspect that it is due to the conversion. The values vary greatly. Is that normal? I get the values with an ordinary power supply. mq135 werte.PNG

paqor

This post is deleted!

Heinz

Looks strange, could you supply your code?
Btw the sensor draws a lot of current, the power supply should be able to deliver 1A. Did you burn in the sensor for 12-24 hours?

paqor

I have used the code from epiere. Baking I have not done. I use different power supplies (USB, Samsung and a large controllable power supply). I sometimes feel that contacts do not function properly. But the sensor draws but only about 100 mA = 0.1 A? Then it seems to be on branding. I have three new sensors. Mostly we read that it is only an attempt here is to measure the CO2 content. When I check the values with a measuring instrument with which agree the details here https://olimex.wordpress.com/2015/05/26/experimenting-with-gas-sensors-and-arduino/ Branding should work outdoors? Can you show me a chart or values?

paqor

This post is deleted!

Heinz

I used this library:
https://github.com/GeorgK/MQ135

Together with this description:
https://hackaday.io/project/3475-sniffing-trinket/log/12363-mq135-arduino-library

Simple to use and very good explanations.

paqor

I've read about. It sounds interesting.

I stand a little hard with the development. Is there a skit for MQ135.h and MYSENSORS?

I will test this afternoon.

Heinz

Hi @paqor,
I wrote a little sketch which you could use as a start, it uses the MQ135 library.
I also used a timer library, but this could be replaced by a simple sleep, too.

RZERO should be changed when calibrating the sensor, this can be done at compile-time or during runtime by sending the value to the sensor via the gateway.

Unfortunately I could not test the sketch yet, but it should help you getting started.
If you have a second sensor which provides humidity and temperature then you can also get the corrected ppm from the library,...

good luck!

/*
MQ135 MySensor
A0      white
D0      black
GND     brown
5V      red
*/

#include <SPI.h>
#include <MySensor.h>
#include <MQ135.h>
#include "Timer.h"

Timer timer;

// 30 seconds
#define TEMP_UPDATE_INTERVAL 30000

// MQ135
#define CHILD_ID_CO2 0
#define CHILD_ID_R0 1

#define CO2_SENSOR_ANALOG_PIN 0

/// Calibration resistance at atmospheric CO2 level
#define RZERO 300.0
#define EEPROM_R0 0

MQ135 gasSensor = MQ135(CO2_SENSOR_ANALOG_PIN, RZERO);
int lastC02;
float lastR0;

//-----------------------------------------------------------------------------
// MySensor
MySensor gw;
MyMessage msgCO2(CHILD_ID_CO2, V_VAR1);
MyMessage msgR0(CHILD_ID_R0, V_VAR1);

//-----------------------------------------------------------------------------
void setup()
{
    gw.begin(incomingMessage, AUTO, true);
    gw.sendSketchInfo("MQ135 Sensor", "1.0");
    gw.present(CHILD_ID_CO2, S_AIR_QUALITY);
    gw.present(CHILD_ID_R0, S_CUSTOM);
    
    uint8_t R02 = gw.loadState(EEPROM_R0);

    // get R0 from EEPROM
    float R0 = R02 * 2;

	// do a plausibility check
    if (R0 > 1.0 && R0 < 400.0) 
    {
        Serial.print(F("Setting R0 from EEPROM: "));
    }
    else
    {
        Serial.print(F("Setting default R0: "));
        R0 = RZERO;
    }

    Serial.print(R0);
    Serial.println(F(""));

    gasSensor.setR0(R0);
    
    timer.every(TEMP_UPDATE_INTERVAL, timerHandler);
}


bool MQ135Changed()
{
    bool changed = false;

    lastR0 = gasSensor.getRZero();
    Serial.print(F("R0: "));
    Serial.println(lastR0);

    {
        float ppm = gasSensor.getPPM();

        Serial.print(F("CO2 ppm: "));
        Serial.print(ppm);


        int roundedPpm = (int)ppm;
        Serial.print(F(" --> "));
        Serial.println(roundedPpm);

        if (roundedPpm != lastC02)
        {
            lastC02 = roundedPpm;
            changed = true;
        }
    }

    return changed;
}


void timerHandler()
{
    bool airQualityChanged = MQ135Changed();
    if (airQualityChanged)
    {
        gw.send(msgCO2.set(lastC02));
        gw.send(msgR0.set(lastR0, 2));
    }
}


void loop()
{
    gw.process();
    timer.update();
}


// Gets the R0 value from the gw passes ot to the lib and stores it into the EEPROM.
void incomingMessage(const MyMessage& message)
{
    Serial.println(F("Incoming Message:"));

    if (message.isAck())
    {
        Serial.println(F("This is an ack from gateway"));
    }

    uint8_t sensor = message.sensor;
    if (sensor == CHILD_ID_R0)
    {
        float R0 = message.getFloat();

        Serial.print(F("Incoming R0: "));
        Serial.print(R0);
        Serial.println(F(""));

        gw.saveState(EEPROM_R0, (uint8_t)(R0/2));
        gasSensor.setR0(R0);
        gw.send(msgR0.set(R0, 2));
    }
}

paqor

I have compiled from various sources themselves something. The result is https://gleisnetze.de/2015/12/25/das-erste-kleine-programm/ described herein. The most plausible values I received with the MQ135.h library. For that I have then added the transfer after MySensors / FHEM.

Bildschirmfoto vom 2015-12-25 07-53-25.png

bhavika

Hello

In MiCS 2614 or in any gas sensor. what should be the value of R0... Because in datasheet they mentioned that value is measured in ambient condition. Any default value for that??

epierre

@bhavika said:

Hello

In MiCS 2614 or in any gas sensor. what should be the value of R0... Because in datasheet they mentioned that value is measured in ambient condition. Any default value for that??

The datasheed propose the "clean air calibration": "Sensing resistance in air R0 is measured under controlled ambient conditions, i.e. synthetic air at 23 ±5°C and 50 ± 10% RH. Sampling test."
so you should go outside and mesure the defautl R0 value in your environment.

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