about the mq2 / mq7 sensor

Using Arduino Sensors
1

hi, i hope i got the right place asking a question here,

so, recently, i have a school project about arduino, and i want to create a simple gas driven project,

so, i follow this link to connect the mq2 / mq7 gas sensor,
http://nootropicdesign.com/projectlab/2010/09/17/arduino-breathalyzer/

yet, no matter how many times i tried, the readings are so strange and i have no idea of what i could deal with the problem

here is some readings
23
0
0
0
0
1023
1023
1023
0
0
0
0
1023
1023
1023
0
0
0
285
1023
1023
327
0
0
1023
1023
1023
0
0
0
622
1023

anyone could help??

2

Post your code please?

3

int sensorValue = 0;
int sensorPin = 9;

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

void loop()
{
sensorValue = analogRead(sensorPin); // read analog input pin 9
Serial.print(sensorValue); // prints the value read
Serial.print(" "); // prints a space between the numbers
delay(1000); // wait 100ms for next reading
}

4

pinMode(9, INPUT) will set Digital I/O pin 9 to be a digital input.
analogRead(9) will read Analog Input pin 9 ?!? Do you have an Arduino that has more than the usual 6 analog input pins (0-5)?!?

5

thx for reply first,

actually, i have try to connect into analogue A0 at the bottom right of the arduino,
yet, the outcome is also almost the same, strange readings

6

From the readings it appears that you may have a bad connection somewhere or some bad noise in the input. When you hook a multimeter between the input pin and ground do you get a nice steady voltage reading?

7

thx again, and i have checked immediately, i have gaineded steady voltage reading, and i have also checked the data sheet, http://www.winsensor.com/english/products/sms/jsq.asp?filename=MQ7.pdf, so, i am sure i am supplying 5.2 - 5.4 voltage to the circuit correctly, and the readings are still not ok ...

btw, is it necessary to pre-heat this sensor? i have found one point in the datasheet saying that it takes 2 days to re-heat the sensor,
so does it mean i have to supply 5 volt to the circuit for 2 days for reasonable readings?

sorry, i have a fairly ok knowledge only, thx for your patience, thxthxthx

8

btw, is it necessary to pre-heat this sensor? i have found one point in the datasheet saying that it takes 2 days to re-heat the sensor,
so does it mean i have to supply 5 volt to the circuit for 2 days for reasonable readings?

IIRC it is needed for calibration (only once). To use this sensor you have to apply 60sec 5Volts and then 90sec 1.4 Volts. Can be done with PWM. Measure at the end of a 1.4V cycle. So one reading every 2.5 minutes is possible.

This thread may be helpfull - http://arduino.cc/forum/index.php/topic,55780.0.html - Contact cronus as you learn about the same sensor.

9

sorry... i am still clueless of what i could do after i have tried several times...

so, now, how to wiring the sensor to give it a 60sec 5Volts and then 90sec 1.4 Volts?

10

fakeid:
sorry... i am still clueless of what i could do after i have tried several times...

so, now, how to wiring the sensor to give it a 60sec 5Volts and then 90sec 1.4 Volts?

since i don't have the breakout kit.. i don't have TOG Pin from sensor board, but six PINs AHA, BHA............

omg

11

Hi guys.. anyone knows how to convert the analog input of mq-7 to ppm?

12

Hello all,
I have exact the same problem, and readings as you. Did you managed to make it work? or does anyone has a solution for this?

13

Try 10 K Resistor between Analog IN and GND.