Microchip Technology

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  • Liquefied Petroleum Gas Detector

  • Created: Mar 20, 2017

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This reference design features a liquefied petroleum gas detector which utilizes a PIC16F18855 microcontroller and an MQ-5 sensor. Liquefied petroleum gas is an achromatic unscented liquid that easily evaporates into a gas. Its vapours can run for long distances along the ground and when it meets a source of ignition, it can burn or explode. By using a detector, the hazards of a liquefied petroleum gas leakage can be avoided.

The design consists mainly of a PIC16F18855 microcontroller, PIC18LF25K50 microcontroller, and an MQ-5 sensor. The MQ-5 sensor has a Tin Dioxide sensing layer which is suitable for detecting natural gas, town gas, and liquefied petroleum gas. It can detect liquefied petroleum gas concentration from 200ppm up to 10000ppm and outputs an analog voltage. For the sensor to function precisely, a 5V supply must be provided for its circuit and heater. The sensor needs to preheat for at least 24 hours to reach the right temperature. Since the resistance of the MQ-5 sensor changes depending on the kind of gas it detects and the level of concentration, a 10kΩ variable resistor is connected in parallel to its output so that its sensitivity can be adjusted. The output voltage from the sensor increases when the concentration of gas increases. The output of the sensor is connected to the ADC pin (RB0) of the PIC16F18855 micro controller.

The PIC16F18855 microcontroller reads the analog voltage across the sensor’s output and convert it to digital. The PIC18LF25K50 microcontroller acts as a USB-to-serial device that relays the digital output of the PIC16F18855 microcontroller to a PC, to monitor the reading of the MQ-5 sensor. It is also used to upload program to the PIC16F18855 microcontroller. The other GPIO pins of the PIC16F18855 microcontroller are connected to the 28-pin header (J1). The extra GPIO pins can be programmed to control external devices depending on the concentration of the liquefied petroleum gas.