MQ2 Sensor w/AirQuality Sketch

[gigaguy]

I bought a gas sensor MQ2 from ebay. trying to figure out how to connect it, and use the Air Quality Sketch.

http://www.ebay.com/itm/371194045196?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Ive got the analog connection on A0, not sure if i need to connect the digital pin too or not.

I am getting a reading of 0ppm for all the measurements in the sketch.

Any ideas? TIA.

[robosensor]

I'm using similar sensors, this test sketch works fine for me, but I'm using raw readings from this sensors.
8 sensors connected to A0-A7 pins on arduino nano directly to analog output pin on each sensor board.

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

unsigned long SLEEP_TIME = 10000; // Sleep time between reports (in milliseconds)

#define NODE_ID										4

MySensor gw;
MyMessage msg(0, V_VAR1);

int lastLightLevel[8] = {0};
unsigned long lastRefreshTime = 0;

void setup()
{
	pinMode(13, OUTPUT);
	// warm up sensors (3 minutes)
	for (int i = 0; i < 180; i++)
	{
		digitalWrite(13, HIGH);
		delay(250);
		digitalWrite(13, LOW);
		delay(250);
		digitalWrite(13, HIGH);
		delay(250);
		digitalWrite(13, LOW);
		delay(250);
	}
	gw.begin(NULL, NODE_ID);

	gw.sendSketchInfo("GasSensors", "1.5");

	gw.present(1, S_AIR_QUALITY, false, "MQ-2");
	gw.present(2, S_AIR_QUALITY, false, "MQ-3");
	gw.present(3, S_AIR_QUALITY, false, "MQ-4");
	gw.present(4, S_AIR_QUALITY, false, "MQ-6");
	gw.present(5, S_AIR_QUALITY, false, "MQ-7");
	gw.present(6, S_AIR_QUALITY, false, "MQ-8");
	gw.present(7, S_AIR_QUALITY, false, "MQ-9");
	gw.present(8, S_AIR_QUALITY, false, "MQ-135");
}

void loop()
{
	gw.wait(100);
  
	boolean bNeedRefresh = (millis() - lastRefreshTime) > SLEEP_TIME;
	if (bNeedRefresh)
	{
		lastRefreshTime = millis();
	}
	for (int i = 0; i < 8; i++)
	{
		int lightLevel = 0;
		for (int j = 0; j < 32; j++)
			lightLevel += analogRead(i);
		lightLevel = (lightLevel / 32);

		int nDifference = lastLightLevel[i] - lightLevel;
		if ((abs(nDifference) > 5) || bNeedRefresh)
		{
			gw.send(msg.setSensor(i + 1).set(lightLevel));
			lastLightLevel[i] = lightLevel;
		}
	}
}

Raw ADC readings are 20-80 (differs from sensor to sensor) for fresh outdoor air.

[epierre]

you can find the curves for the MQ2 here: https://github.com/empierre/arduino/blob/master/AirQuality-Multiple_Gas_Sensor1_4.ino

Check the thread about gas sensors: http://forum.mysensors.org/topic/147/air-quality-sensor/83

Regarding having 6 electolithic sensors on a nano, check ths out about powering them :

Arduino Mega is given at : DC Current per I/O Pin 40 mA, so at 5V I have P=5*0,04=0,2w

When I list all the gases sensors I have this:

MQ2          5V     0,8 w
MQ6          5V     0,75w
MQ131      6V     1,1 w
MQ135      5V     0,8 w
MQ138      5V     0,85w
MS2610    2.35V  0,09w
TGS2600  5V     0,21w
TGS2602  5V     0,28w
HCHO       5V     NA

[gigaguy]

@robosensor What is on pin 13? In the Setup() warmup part?
btw, I am getting a value of 1 or 2, after warmup.

[robosensor]

@gigaguy pin 13 connected to board's led :)
Warm up is just 3-minute pause (with led blinking) between power up and start of main loop measurements transmission. Cold sensors shows very big measurements, so I heating them up for 3 minutes.

[robosensor]

@gigaguy
example response of sensors for natural gas (left) and alcohol (right):

[epierre]

@robosensor this graph shows well the limit ofg the MQ gas sensors, they somehow all react to the same gases, and thus are not one gas specific.

[robosensor]

@epierre in general, you are right, but there are exceptions.

This measurements, but one sensor per graph:

And 6-day graph of all sensors:

[epierre]

@robosensor sure, but people need to know not to rely for their life on these classes of sensors.

[Viper_Scull]

is it normal that the reads of my MQ-2 sensor are 0ppm in fresh air?
If I use a lighter to throw some gas, the reads skyrocket and then without gas they go back to zero.
Should I adjust the sensitivity?

[epierre]

@Viper_Scull If you follow my method, it considers clean air has no toxic gas so it should be 0.

If you are able to do a calibration, you could change that, but I would recommend to keep the straight lean air way if you cannot do that.

[Viper_Scull]

@epierre said:

@Viper_Scull If you follow my method, it considers clean air has no toxic gas so it should be 0.

If you are able to do a calibration, you could change that, but I would recommend to keep the straight lean air way if you cannot do that.

@epierre I use the AirQualitySensor example in the MySensors library that I believe is your work indeed. Happy now to know that it's ok 0ppm for clean air.

One thing I noticed on the sketch is that last_mq inital value is 0. If we are in clean air, no value is send to the gateway when connected because val_mq = last_mq, so the controller would have no data to display unless it sets it to zero by default or gas is present.

By the way, I can't get domoticz to recognize this sensor. It receives the name of the sketch and the version, but although I can see that the sensor sends the value, there's no sign of it in the log of domotic and no device is recognized.

[epierre]

@Viper_Scull I have someone else reporting this, you should ask @GizMoCuz for him to support it

[Viper_Scull]

@epierre, already asked. Turns out, domoticz doesn't support V_VARs. Changing V_VAR1 in the sketch for V_DUST_LEVEL works.

[Moshe Livne]

@Viper_Scull Domoticz supports V_VARs, just not as a viewable or modifiable value on the controller. It will store and return the V_VARs values for the sketch, nothing more.