The oxygen molecules get attached to the surface of the sensor. This charged layer attracts oxygen from the atmosphere to its surface. The tin oxide layer gets charged when the sensor is heated by the coil. Platinum wires are connected to the tin oxide layer which forms the sensing layer. A heating coil of nickel-chromium is used to heat the sensor. Inside the MQ2 sensor, there is an aluminum oxide Al2O3 based ceramic having a coating of tin oxide SnO2. Due to this, the LEDs will eventually glow and buzzer will start, indicating that Gas has been leaked in the surroundings. With the presence of LPG or any other petroleum gas, the output of the sensor will start rising and it will cross the threshold voltages. In the absence of any Gas (LPG, butane, methane) or smoke the output of the MQ2 Gas sensor will be below 4V. Use trimmers to set the required threshold voltage. In this circuit, the three opamps in lm339 ic are set at 4V, 4.25V, and 4.5V respectively. To know how an opamp works in open-loop read working of the opamp as comparator.Īs already said that the trimmers are used to set a reference voltage. This Gas detector circuit works on the open-loop configuration of the opamp. Working of the Gas sensor circuit: MQ2 Gas Sensor Circuit Diagram You can use this 5-volt power supply to power this circuit or use a battery pack. The color of the LED will indicate the danger level of gas.Īlso, a Buzzer is connected to the output of the opamp which will start ringing when the output of the sensor crosses a threshold value set by the trimmer. The output of the three OPAMPs is given to the three LEDs having Red Orange and yellow colors. We are using three voltage divider circuits, you can use three trimmers to set the reference voltage at the non-inverting terminal of the opamp. Pinout of LM339 ic is as shown in the figureĪ voltage divider circuit is used to set a reference voltage at the non-inverting terminal of the opamp. The output of the MQ2 sensor is given to the inverting terminal of the three OPAMPs in the quad opamp lC.ģrd pin of the IC is connected to the +Vcc and 12 is the ground terminal. The remaining pin is the output pin of the sensor. On the other side, one terminal is pulled to the ground via a 470k ohm resistor, and the middle pin is connected to the ground. Out of 6 terminals, 3 terminals of the gas sensors are connected to +Vcc which are at one side. Gas sensor circuit: Mq2 gas sensor circuit diagram Explanation of MQ2 Gas Sensor circuit:Ī Gas sensor circuit is as shown, it contains an MQ2 Gas sensor, LM339 opamp IC, LED lights, and a Buzzer. Three LED lights Red, Orange, and yellow.In this project, we are using the LM339 quad opamp comparator IC. We can use any gas sensors like MQ2, MQ6. Connect the middle pin to the ground and the remaining pin is the output pin.Ī simple gas sensor and alarm circuit are as shown in the figure. On the other side connect the first pin to the ground via a resistor. To use this sensor simply connect all three pins at one side to +Vcc. one pin is connected to pulled to the ground using a resistor and the other act as an analog output pin. The H pins are connected to the supply voltage. It has three pairs of pin namely A, B, and H pin. It is round and somewhat pyramid-like having a base on which the sensor is mounted and a protective forged. MQ2 sensor is a 6 pin semiconductor device that sens gas and smoke. A gas leak can causes really very big fire, blasts, loss of lives, and big property damage at places where gases are used for either cooking or other commercial purposes. Gas leakage is a very dangerous situation it can cause breathing problems, headache, and other physical problems. MQ2 gas sensor can sense butane, LPG, Smoke, Alcohol, Propane, Hydrogen, Methane and Carbon Monoxide. MQ2 Gas sensor circuit diagram is as shown in the figure. In this project, we will use the MQ2 Gas sensor circuit to detect Methane, Butane, LPG, Smoke which is released into the environment at the time of the gas leak.
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