PIC16F84A Gas Detector

This is a gas detecting circuit capable of sensing many different types of gases. The sensor used is the GH-312 and from the datasheet it is capable of sensing gases like smoke, liquefied gas, butane and propane, Methane, alcohol, hydrogen, etc. I've used a 9V battery for this project because the sensor requires a 9V input. The output when the sensor is triggered is always 5V which is perfect for a direct connection to any microcontroller. Although I've used a 9V battery, any 12V power supply ( a small wall transformer for example ) will work perfectly since the sensor can handle from 9V up to 20V and the microcontroller's voltage is regulated by a 7805 regulator.
PIC16F84A Gas Detector - schematic

It's a pretty cheap and easy to assemble circuit. To test the sensor I used my portable gas soldering iron with the gas coming out pointed to the sensor. The sensor is able to detect the gas and the microcontroller will trigger a flashing led warning and sound. The sound is produced by a small piezo and the display show the message "Found Gas". Does not require too many parts and the microcontroller is very easy to find ( the famous 16F84A from microchip ). When the air is clean again and the sensor does not sense any gas, the circuit will return to it's normal state turning off both led and piezo sound. Since it's used a small lcd ( 8x2 ) this project can be portable. Also this sensor senses several types of gas and it's pretty stable.

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