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I am totally new to hardware.

Recently I bought this MQ-2 module, but I couldn't figure how to get it to work, the on the ship worked but where is the output? I mean the place where I place the voltmeter?

This is a picture of it:

enter image description here

It has 5 connections (+5v, GND, NO, COM, NC ).

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  • \$\begingroup\$ It's worth posting a datasheet or a link to product information for that particular module. Guessing from the connections it only offers a relay output presumably when a pre-set limit is exceeded, although if you want a voltage output they'll be a pin somewhere on the board you can connect to. \$\endgroup\$ – PeterJ Feb 13 '14 at 9:57
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As Peter says in a comment, there's a relay on that board. The output connections include COM, NO and NC connections that are usable as follows ...

schematic

simulate this circuit – Schematic created using CircuitLab

1

So set your multimeter to resistance (ohms) and connect it from COM to NC. When there is enough gas to trigger the relay the resistance will increase from 0 to infinity (or at least to "out of range" - some multimeters show that as -1)

You could use the COM and NO connections to switch on a large and loud siren and/or strobe-light.

2

The board also contains an indicator LED. You can connect a voltmeter across the resistor next to it. When the LED is turned on the voltage across the resistor will rise from 0 to perhaps a few volts.

3

The board has an LM358 op-amp, I guess this is processing the MQ-2 output signal, it might be interesting to put a voltmeter on it's output. See LM358 data sheet for pinout

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  • \$\begingroup\$ @user2514409: If you find the answer useful, consider upvoting it and/or accepting it using the icons to the left of the top of the answer. \$\endgroup\$ – RedGrittyBrick Feb 13 '14 at 10:40
  • \$\begingroup\$ i accepted it put i cant up vote until i get 15 reputation :( \$\endgroup\$ – user2514409 Feb 13 '14 at 10:48
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VCC to 5V+ and GRD on negative, that's all you need to do to run this module. On the relay you, you can use it as normally open or normally close, use it as how you would use a switch on a basic circuit like to turn on an AC lightbulb whenever it detects gas. The other pin which are the analog 0 A0 and Digital output DO. You have to get micro controller to use those pins

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Yes the board contains an LM358 op amp to amplify the signal output from the heater element of the MQ2 sensor, this way when it is exposed to LPG/CO2 gases,

The output coming out from the sensor also varies, and LM358 op amp is configured as a comparator, thus it drives the relay directly or using a BJT.

Note:The heater element which can be seen with steel mesh, does not rapidly varies while exposed to LPG, it takes some time to change in its output signal.

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