Have anyone used MQ-9 Gas Sensor

Discussion in 'General Electronics Chat' started by divleelomo, Aug 4, 2011.

  1. divleelomo

    Thread Starter New Member

    Aug 4, 2011
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    MQ 9 is a Semiconductor Sensor for CO/Combustible Gas. For proper operation, it needs to supply 1.5V for 90s and then 5V for 60s according to the datasheet. However, my question is How can I do this. I have a MUC (8051), a step-up circuit with the chip ME2108 to generate 5V. What else do I need to build the circuit performing such function.

    Please Help!!

    I found
    http://webpages.iust.ac.ir/ali_reza...ing-MQ9/Carbon-Monoxie-Detector-using-MQ9.htm
    But I don't understand the method the website showed, it is very complicated.

    Can someone help me, please
     
  2. divleelomo

    Thread Starter New Member

    Aug 4, 2011
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    I want the voltage in the circuit can be changed automatically by the MCU not manually with a switch

    Please Help!!
     
  3. Jaguarjoe

    Active Member

    Apr 7, 2010
    770
    90
    Look at the bottom of page 22 of this data sheet:

    http://www.national.com/ds/LM/LM117.pdf

    The LM117/317 is a programmable voltage regulator. By using a circuit along the lines of what is shown on pg. 22, you can have numerous output voltages selected by your MCU. Note that the minimum output voltage is 1.2 volts.
     
  4. debe

    Well-Known Member

    Sep 21, 2010
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    This is how its done in a kit ive built. Q1 is turned on/off by the program in the PIC chip. This sensors heater is driven the same as the one you want to use.
     
  5. divleelomo

    Thread Starter New Member

    Aug 4, 2011
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    Thank You Jaguarjoe:):)

    But LM117/317 needs 3V ≤ (VIN − VOUT) ≤ 40V. That means if I need to get a 5v output, I need a 8v for VIN. The maximun voltage that I have is 5v. It is hard for me to use LM117/317. Also, I have a problem with the circuit along the lines of what is shown on pg. 22. how can I select the INPUTS for the VOUT and where do i put the GPIO pin which from the MCU to choose the VOUT??

    Please Help
     
  6. divleelomo

    Thread Starter New Member

    Aug 4, 2011
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    Thank You debe

    Is it 5V for on and 1.4V for off???
     
  7. divleelomo

    Thread Starter New Member

    Aug 4, 2011
    6
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    Can I use the method shown below to do what I want??:confused::confused:

    Please Help:):):)
     
  8. debe

    Well-Known Member

    Sep 21, 2010
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    184
    If you look at the circuit there is 2 resistors in series 75/10 ohms this gives 1.4V across the heater, this is when its sensing. The transistor Q1 is turned ON to bridge out the resistors giving 5V to the heater, this is to purge the sensor ready for the nex cycle of sensing.
     
  9. divleelomo

    Thread Starter New Member

    Aug 4, 2011
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    0
    Thank You Daryl

    I built the Co gas sensor circuit out (the orange part at the file I attached)with 2 resistors (75R and 10R) , a transistor (BC556B 338) and MQ7 gas sensor.
    I used another transistor (BC556B 338) instead of BC327. However, BC556B 338 is also a PNP transistor just like BC327.

    When I supplied 5V to the point E at the transistor and had no any input voltage for RB5 (I connected nothing to point RB5 to demonstrate the GOIP pin RB5 is low), the voltage across the H point at the sensor was around 1.4V which is GOOD ^^.

    However, when I supplied 5V to the point E at the transistor and 3.3V for for RB5 (it used to demonstrate the GOIP pin RB5 is high), the voltage across the H point was around 2.9V which is not I want ....(I want 5V)

    Do I need to use the same transistor (model name : BC327)??
    Why did I get 2.9V instead of 5V???

    Please Help
    Thank You
     
  10. debe

    Well-Known Member

    Sep 21, 2010
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    184
    Just took some voltage measurements on the unit i have. When RB5 is pulled down to .08V, there is 5V @ C on the transistor. When theres 5V @ RB5, C on the transistor is 1.4V. I suspect if you have the 1K resistor floating C will be1.4V. If you ground the 1K resistor the transistor turns on giving 5V @ C.
     
  11. debe

    Well-Known Member

    Sep 21, 2010
    947
    184
    Heres the circuit description as suplied with the Kit.
     
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