Air Quality Sensor

rollercontainer

So, obvious these are two variables. Wherefore is the mq135_ro? Is it the load resistor from signal to ground?

alexsh1

@rollercontainer let's start from the basic - which MQ-135 do you have? A bare unit or with a logic controller and a variable resistor?

rollercontainer

@alexsh1 I bought a breakout board and desoldered everything but the sensor and the 33Ohm resistor for the heating. Then I soldered a 10kOhm pulldown from analog signal out to ground.

alexsh1

@rollercontainer

Apologies for the confusion. @epierre did not use this library, but I have used MQ135.h library, but have not adopted it for MySensors and I did not like the sensor's reading jumping up and down.

In MQ135.h:

// Calibration resistance at atmospheric CO2 level
#define RZERO 394.5 //RZERO 76.63

I think the principle of RZERO is the same as mq135_ro

alexsh1

@rollercontainer I have do not done any changes to my breakout board. Just tuning the variable resistor and that's it.

One thing I noticed is that the sensor performs much better in enclosed premises (no windows and no doors). Alternatively, it has to be in the box or something. Any small light draft dramatically changing the readings.

rollercontainer

@alexsh1 I dont think so, in epierres sketch both values appear:

https://github.com/empierre/arduino/blob/master/AirQuality-MQ135.ino#L25
https://github.com/empierre/arduino/blob/master/AirQuality-MQ135.ino#L33

So, what the heck is mq135_ro? And what to tune to?

alexsh1

@epierre OK, I found a mistake in my Shinyei ppd42ns code. Basically, it produces pcs/0.01cf values (normally, anything from 2000 to 10000 per a 30 secs reading).

This sensor use counting method to test dust concentration but not weight method, and the unit it pcs/L or pcs/0.01cf.

This has to be converted into ug/m3 (the EPA standard)and then we can convert it into ppmv. I do not think dividing it by a volume factor is enough. Please see below updated code, which combines both ppd42ns and MH-Z14A sensors.

/**
 * The MySensors Arduino library handles the wireless radio link and protocol
 * between your home built sensors/actuators and HA controller of choice.
 * The sensors forms a self healing radio network with optional repeaters. Each
 * repeater and gateway builds a routing tables in EEPROM which keeps track of the
 * network topology allowing messages to be routed to nodes.
 *
 * Created by Henrik Ekblad <henrik.ekblad@mysensors.org>
 * Copyright (C) 2013-2015 Sensnology AB
 * Full contributor list: https://github.com/mysensors/Arduino/graphs/contributors
 *
 * Documentation: http://www.mysensors.org
 * Support Forum: http://forum.mysensors.org
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * version 2 as published by the Free Software Foundation.
 *
 *******************************
 * DESCRIPTION
 * 
 * Dust Sensor for Shinyei ppd42ns
 *  
 * 1 : COMMON(GND)
 * 2 : OUTPUT(P2)
 * 3 : INPUT(5VDC 90mA)
 * 4 : OUTPUT(P1)
 * 5 : INPUT(T1)･･･FOR THRESHOLD FOR [P2] - not used
 *
 * http://www.seeedstudio.com/wiki/images/4/4c/Grove_-_Dust_sensor.pdf
 * 
 *   connect the sensor as follows :
 *    Pin 4 of dust sensor PM1      -> Digital 6
 *    Pin 3 of dust sensor          -> +5V 
 *    Pin 2 of dust sensor PM25    -> Digital 3 
 *    Pin 1 of dust sensor          -> Ground
* Contributor: epierre and alexsh1
**/
  

#include <MySensor.h>  
#include <SPI.h>

// Define a static node address, remove if you want auto address assignment
#define NODE_ADDRESS_DUST   11
#define NODE_ADDRESS_CO2    13

#define CHILD_ID_DUST_PM10            0
#define CHILD_ID_DUST_PM25            1
#define CHILD_ID_DUST_PM10_MG_M3      2
#define CHILD_ID_DUST_PM25_MG_M3      3

#define DUST_SENSOR_DIGITAL_PIN_PM10  6
#define DUST_SENSOR_DIGITAL_PIN_PM25  3

#define CHILD_ID 0
#define CO2_SENSOR_PWM_PIN 2

unsigned long SLEEP_TIME = 30*1000; // Sleep time between reads (in milliseconds)
//VARIABLES
int val = 0;           // variable to store the value coming from the sensor
float valDUSTPM25 =0.0;
float lastDUSTPM25 =0.0;
float valDUSTPM10 =0.0;
float lastDUSTPM10 =0.0;
unsigned long duration;
unsigned long starttime;
unsigned long endtime;
unsigned long sampletime_ms = 30000;
unsigned long lowpulseoccupancy = 0;
float ratio = 0;
long concentrationPM25 = 0;
long concentrationPM10 = 0;
float concentration = 0;
float concentrationPM25_ugm3;
float concentrationPM10_ugm3;

int temp=273.5+22; //external temperature, if you can replace this with a DHT11 or better 
float ppmvPM25;
float ppmvPM10;

float valAIQ =0.0;
float lastAIQ =0.0;
unsigned long duration_co2;
long co2ppm;

MySensor gw;
MyMessage dustMsgPM10(CHILD_ID_DUST_PM10, V_LEVEL);
MyMessage msgPM10(CHILD_ID_DUST_PM10_MG_M3, V_LEVEL);
MyMessage dustMsgPM25(CHILD_ID_DUST_PM25, V_LEVEL);
MyMessage msgPM25(CHILD_ID_DUST_PM25_MG_M3, V_LEVEL);

MySensor gw1;
MyMessage msg(CHILD_ID, V_LEVEL);

void setup()  
{
  gw.begin(NULL,NODE_ADDRESS_DUST,false);

  // Send the sketch version information to the gateway and Controller
  gw.sendSketchInfo("Dust Sensor PPD42NS", "1.5");
  
  // Register all sensors to gateway (they will be created as child devices)
  gw.present(CHILD_ID_DUST_PM10, S_DUST);
  //gw.send(msgPM10.set("ppm"));  
  gw.present(CHILD_ID_DUST_PM25, S_DUST);  
  //gw.send(msgPM25.set("ppm"));
  gw.present(CHILD_ID_DUST_PM10_MG_M3, S_DUST);
  gw.present(CHILD_ID_DUST_PM25_MG_M3, S_DUST);
  
  pinMode(DUST_SENSOR_DIGITAL_PIN_PM10,INPUT);
  pinMode(DUST_SENSOR_DIGITAL_PIN_PM25,INPUT);

  gw1.begin(NULL,NODE_ADDRESS_CO2,false);
  gw1.sendSketchInfo("AIQ Sensor CO2 MH-Z14A", "1.0");
  // Register all sensors to gateway (they will be created as child devices)
  gw1.present(CHILD_ID, S_AIR_QUALITY);  
  
  pinMode(CO2_SENSOR_PWM_PIN, INPUT);
 
  
}

void loop()      
{    

  //get PM 2.5 density of particles over 2.5 μm.
  concentrationPM25=(long)getPM(DUST_SENSOR_DIGITAL_PIN_PM25);
  Serial.print("PM25: ");
  Serial.print(concentrationPM25);
  Serial.println(" pcs/0.01cf");
  concentrationPM25_ugm3 = conversion25(concentrationPM25);
  Serial.print("PM25: ");
  Serial.print(concentrationPM25_ugm3);
  Serial.println(" ug/m3");
  Serial.print("\n");   
  //ppmv=mg/m3 * (0.08205*Tmp)/Molecular_mass
  //0.08205   = Universal gas constant in atm·m3/(kmol·K)
  ppmvPM25=((concentrationPM25_ugm3) * ((0.08205*temp)/28.97));
 
  if ((concentrationPM25 != lastDUSTPM25)&&(concentrationPM25>0)) {
      gw.send(dustMsgPM25.set(ppmvPM25,2));
      gw.send(msgPM25.set(concentrationPM25_ugm3,2));
      lastDUSTPM25 = ceil(concentrationPM25);
  }
 //get PM 1.0 - density of particles over 1 μm.
  concentrationPM10=getPM(DUST_SENSOR_DIGITAL_PIN_PM10);
  Serial.print("PM10: ");
  Serial.print(concentrationPM10);
  Serial.println(" pcs/0.01cf");
  concentrationPM10_ugm3 = conversion10(concentrationPM10);
  Serial.print("PM10: ");
  Serial.print(concentrationPM10_ugm3);
  Serial.println(" ug/m3");
  Serial.print("\n");
  //ppmv=mg/m3 * (0.08205*Tmp)/Molecular_mass
  //0.08205   = Universal gas constant in atm·m3/(kmol·K)
  ppmvPM10=((concentrationPM10_ugm3) * ((0.08205*temp)/28.97));
  
  if ((ceil(concentrationPM10) != lastDUSTPM10)&&((long)concentrationPM10>0)) {
      gw.send(dustMsgPM10.set(ppmvPM10,2));
      gw.send(msgPM10.set(concentrationPM10_ugm3,2));
      lastDUSTPM10 = ceil(concentrationPM10);
  }

  while(digitalRead(CO2_SENSOR_PWM_PIN) == HIGH) {;}
  //wait for the pin to go HIGH and measure HIGH time
  duration_co2 = pulseIn(CO2_SENSOR_PWM_PIN, HIGH, 2000000);
  co2ppm = 5000 * ((duration_co2/1000) - 2)/1000;
  Serial.print("CO2: ");
  Serial.print(co2ppm);
  Serial.print(" ppm");
  Serial.print("\n");
  if ((co2ppm != lastAIQ)&&(abs(co2ppm-lastAIQ)>=10)) {
      gw1.send(msg.set((long)ceil(co2ppm)));
      lastAIQ = ceil(co2ppm);
  }
  //sleep to save on radio
  gw.sleep(SLEEP_TIME);
  gw1.sleep(SLEEP_TIME);
  
}

float conversion25(long concentrationPM25) {
  double pi = 3.14159;
  double density = 1.65 * pow (10, 12);
  double r25 = 0.44 * pow (10, -6);
  double vol25 = (4/3) * pi * pow (r25, 3);
  double mass25 = density * vol25;
  double K = 3531.5;
  return (concentrationPM25) * K * mass25;
}

float conversion10(long concentrationPM10) {
  double pi = 3.14159;
  double density = 1.65 * pow (10, 12);
  double r10 = 0.44 * pow (10, -6);
  double vol10 = (4/3) * pi * pow (r10, 3);
  double mass10 = density * vol10;
  double K = 3531.5;
  return (concentrationPM10) * K * mass10;
}


long getPM(int DUST_SENSOR_DIGITAL_PIN) {

  starttime = millis();

  while (1) {
  
    duration = pulseIn(DUST_SENSOR_DIGITAL_PIN, LOW);
    lowpulseoccupancy += duration;
    endtime = millis();
    
    if ((endtime-starttime) > sampletime_ms)
    {
    ratio = (lowpulseoccupancy-endtime+starttime)/(sampletime_ms*10.0);  // Integer percentage 0=>100
    concentration = 1.1*pow(ratio,3)-3.8*pow(ratio,2)+520*ratio+0.62; // using spec sheet curve
    Serial.print("lowpulseoccupancy:");
    Serial.print(lowpulseoccupancy);
    Serial.print("\n");
    Serial.print("ratio:");
    Serial.print(ratio);
    Serial.print("\n");
    //Serial.print("PPDNS42:");
    //Serial.println(concentration);
    //Serial.print("\n");
    
    lowpulseoccupancy = 0;
    return(concentration);    
    }
  }  
}

Please see the terminal printout below. The lowpulseoccupancy and ratio are correct. um/m3 to ppmv conversion is correct as well. I had to dive into physics and a bit of googling to find out how to convert pcs/0.01cf into ug/m3 - this is a tricky one!

send: 11-11-0-0 s=1,c=1,t=37,pt=7,l=5,sg=0,st=ok:5.39
send: 11-11-0-0 s=3,c=1,t=37,pt=7,l=5,sg=0,st=ok:6.45
lowpulseoccupancy:3339978
ratio:11.03
PM10: 6751 pcs/0.01cf
PM10: 10.53 ug/m3

send: 11-11-0-0 s=0,c=1,t=37,pt=7,l=5,sg=0,st=ok:8.80
send: 11-11-0-0 s=2,c=1,t=37,pt=7,l=5,sg=0,st=ok:10.53
CO2: 960 ppm
send: 13-13-0-0 s=0,c=1,t=37,pt=4,l=4,sg=0,st=ok:960
lowpulseoccupancy:1983280
ratio:6.51
PM25: 3527 pcs/0.01cf
PM25: 5.50 ug/m3

send: 11-11-0-0 s=1,c=1,t=37,pt=7,l=5,sg=0,st=ok:4.60
send: 11-11-0-0 s=3,c=1,t=37,pt=7,l=5,sg=0,st=ok:5.50
lowpulseoccupancy:3430970
ratio:11.34
PM10: 7008 pcs/0.01cf
PM10: 10.93 ug/m3

send: 11-11-0-0 s=0,c=1,t=37,pt=7,l=5,sg=0,st=ok:9.13
send: 11-11-0-0 s=2,c=1,t=37,pt=7,l=5,sg=0,st=ok:10.93
CO2: 960 ppm
lowpulseoccupancy:1789340
ratio:5.86
PM25: 3141 pcs/0.01cf
PM25: 4.90 ug/m3

send: 11-11-0-0 s=1,c=1,t=37,pt=7,l=5,sg=0,st=ok:4.09
send: 11-11-0-0 s=3,c=1,t=37,pt=7,l=5,sg=0,st=ok:4.90
lowpulseoccupancy:3271804
ratio:10.80
PM10: 6563 pcs/0.01cf
PM10: 10.23 ug/m3

send: 11-11-0-0 s=0,c=1,t=37,pt=7,l=5,sg=0,st=ok:8.55
send: 11-11-0-0 s=2,c=1,t=37,pt=7,l=5,sg=0,st=ok:10.23
CO2: 970 ppm
send: 13-13-0-0 s=0,c=1,t=37,pt=4,l=4,sg=0,st=ok:970

I still have not connected the BMP280 to get the pressure and temp readings into the equation.

What do you think?

alexsh1

@rollercontainer said:

@alexsh1 I dont think so, in epierres sketch both values appear:

https://github.com/empierre/arduino/blob/master/AirQuality-MQ135.ino#L25
https://github.com/empierre/arduino/blob/master/AirQuality-MQ135.ino#L33

So, what the heck is mq135_ro? And what to tune to?

I think https://github.com/empierre/arduino/blob/master/AirQuality-MQ135.ino#L25

is identical to

https://github.com/GeorgK/MQ135/blob/master/MQ135.h#L27 multiplied by a factor is 1000

Maybe @epierre can clarify it?

rollercontainer

Hm, in the loop, mq135_ro will be read and used. As written in line 78, the MQ135_DEFAULTRO can be overwritten by the messured mq135_ro. Ok, but where is the 10kOhm voltage divider in this calculation? Included in the measurement of mq135_ro?
https://github.com/empierre/arduino/blob/master/AirQuality-MQ135.ino#L78

alexsh1

@rollercontainer you are correct - mq135_ro is overwritten in the loop and I do not see a point in float mq135_ro = 10000.0; unless the mq135_ro function is deactivated during calibration. However, #define MQ135_DEFAULTRO 68550 this is the parameter you should change during the calibration process. Try to calibrate with the function mq135_ro and deactivating it though I am sure the result will be the same.

tantt2810

Hi all,

I have my library for reading sensor. It is open source and its name is OpenSensor. I think that it's useful for every body.

Besides, I have my a monitoring system in real time using Arduino, MQ2, MQ135, MG811, GP2Y10 sensors and shield wifi ESP8266. It use OpenSensor library to read value from sensor and push it to database of WebServer by ESP826.

This is link: https://github.com/tantt2810

Hoping it helpful for all,

Good job,

alexsh1

@tantt2810 Thanks

#define RSRO_CLEAN_AIR_FACTOR        3.7                                    //The value of Rs/Ro in clean air. According chart in datasheet.
#define RL_VALUE                     20                                     //The value of the load resistance on the board, in kilo ohms.
#define GET_RO_SAMPLE_TIMES          10                                     //The times of calibrating 
#define GET_RS_SAMPLE_TIMES          10

Can you please elaborate on how to calibrate the sensor?
Also how do you connect it if it comes on the board like this?

http://i.ebayimg.com/00/s/NjAwWDYwMA==/z/vMIAAOxycD9TTOVW/$_1.JPG

epierre

@alexsh1 said:

Also how do you connect it if it comes on the board like this?
http://i.ebayimg.com/00/s/NjAwWDYwMA==/z/vMIAAOxycD9TTOVW/$_1.JPG

easy here, the AOUT is the one you will put on an analog one.

the DOUT (Digital OUT) is just an alarm linked to a level you could change on the board)

alexsh1

@epierre said:

the DOUT (Digital OUT) is just an alarm linked to a level you could change on the board)

So DOUT is not used. Just AOUT?

epierre

@alexsh1 said:

@epierre said:

the DOUT (Digital OUT) is just an alarm linked to a level you could change on the board)

So DOUT is not used. Just AOUT?

yes !

alexsh1

@epierre For the air quality purpose which sensor would you recommend TSG-2600 or TS2602? They are slightly different, but both detect aiir contaminants (based on ppm of H2 and EtOH).

So far, I got MH-Z14A and the Dust sensor working with OLED screen and Domoticz and I just want to add 1-2 sensors to finish the project.

epierre

@alexsh1 well any I would think for they are similar technology

alexsh1

@epierre What about MICS-4514 or MICS-5524?

I am thinking ordering this board:
https://sgx.cdistore.com/ProductDetail/MICSVZ86F-SGX-Sensortech-Limited-formerly-e2v/556306/#.V2Bw7jVUmec

Tore André Rosander

How do i get the Airquality sensor to show in domoticz? I use the AirQuality example from the library and MQ2.
I can see that it works in the serial, and it shows as a node under the mysensors hardware, but nothing in log or the device list when i expose it for gas.

0_1466081228162_upload-0f9ebe47-10d5-446c-a3bd-24c1649c94c1

epierre

@Tore-André-Rosander said:

ut nothing in log or the device list when i expose it for gas.

huh you're on which version of mysensors ? have you tried the console (in arduino programmer) to see if there are some readings or a good wiring ?

Air Quality Sensor

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