This is a  compressed natural gas (CNG) sensor, suitable for sensing  natural gas (composed of mostly Methane [CH4]) concentrations in the air. The MQ-4 can detect natural gas concentrations anywhere from 200 to 10000ppm.

This sensor has a high sensitivity and fast response time. The sensor's output is an analog resistance. The drive circuit is very simple; all you need to do is power the heater coil with 5V, add a load resistance, and connect the output to an ADC.
This sensor comes in a package similar to our MQ-3 alcohol sensor, and can be used with the breakout board below.

For more information of this product, please visit theWiki PAGE

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Wiring Example