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Topic: CONVERTING ANALOG OUT OF MQ-7 TO PPM (Read 3048 times) previous topic - next topic

vhenamae

Hi guys..
Can somebody help me how to convert the voltage out of MQ-7 to ppm? I already do the cycle time,interface it in arduino board and received a analog out from the sensor.But the problem is i dont know to convert those output to a useful one or ppm values.can somebody help me or give me an idea?

RIDDICK

hi!

is it this one:
http://www.sparkfun.com/datasheets/Sensors/Biometric/MQ-7.pdf
?

did u heat it properly?

then u need to measure the resistance of the A and B pins...
u can do it in 2 ways:
1.
send a known current through it (e. g. 50uA) and measure the voltage at the A and B pins...
2.
send a known voltage via a known series restistor through it (e. g. 100kOhm) and measure the voltage at the A and B pins...

have fun...  :)
-Arne

vhenamae

yes.im using that one.you mean preheating the sensor in 5v(60sec) and 1.4v(90sec)? or preheating it with 5v in less than 48 hours? the A and B pins of the sensor? thanks for your reply.. :)

RIDDICK

1.
i think for moderate accuracy preheating with 60sec@5V should be sufficient...
2.
yo... A and B...
-Arne

vhenamae

thanks. do you have any code?or idea? coz i will display it in LCD.

RIDDICK

hm
i never did it myself...

maybe this works fine:
hardware:
+5V(from arduino) -- pin A
GND(from arduino) -- ~10kOhm resistor -- pin B
it seems like the heating voltage affects the resistance between pin A and pin B...

software:
measure the voltages at pin B with an analog pin... http://arduino.cc/en/Reference/AnalogRead
regarding the LCD: http://arduino.cc/en/Reference/LiquidCrystal?from=Tutorial.LCDLibrary

interpretation of the readings:
u will need reference concentrations...
but be careful: CO is dangerous to humans and animals...
so u should possibly do it together with a teacher who smokes (cigarette smoke contains CO)... but: smoking is not necessarily healthy... :)
then u should c a change of voltage...
but then u wouldnt know how much CO it was... :-)
maybe u know a firefighter? they might have calibrated CO meters...
-Arne

vhenamae

thanks again.. i already have the conversion code and i was able to display it in lcd.but the main problem there is that i dont know if the reading is accurate. :) so same with your suggestion i used a cigarette. :) i will try another method

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