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Alcohol concentration alarm, when the ambient alcohol gas solubility exceeds the set threshold, the buzzer will alarm, the red light will be on, and the relay will act. This circuit is mainly an alarm control circuit composed of the gas-sensing sensor group MQ-3. When there is alcohol vapor in the environment where the sensor MQ-3 is located, the conductivity of the sensor will increase as the alcohol vapor concentration increases. By measuring the partial pressure in series between the sensor and the fixed resistor, the alcohol content in the environment can be determined.
The probe needs to be warmed up for 1 minute, so it will work normally after 1 minute of power-on.
Working voltage: 5-7.5V DC
Main components: MQ3 smoke sensor, LM358 integrated chip
Module size: 36 * 59mm (length * width)
This circuit can be powered by 5-7.5 volt DC power supply, resistor R5 and light-emitting diode D2 are used for power indication. The sensor U1 (MQ3) needs to be heated to a certain temperature during work, so a piece of heating wire is installed inside it. It needs to be warmed up for 1 minute after power on, and then it works normally after 1 minute, so it is normal for MQ-3 to generate heat after power on. Resistor R9 is the current-limiting resistance of the heating wire. When MQ-3 does not detect alcohol vapor, its internal resistance is very large, and the pressure drop of R6 and R7 is very low. The voltage of pin 5 of LM358 is lower than the voltage of pin 6, and the voltage of pin 7 of the LM358 outputs low level. Q1 is not turned on. D1 is off, the buzzer does not sound, and the relay does not operate. When MQ3 detects alcohol vapor, the internal resistance decreases, and the voltages of R6 and R7 increase. The voltage of pin 5 of LM358 is higher than the voltage of pin 6, and pin 7 becomes high level. The Q1 transistor is turned on and D1 is turned on to emit light. The buzzer starts to sound when the current flows, and the solenoid coil in the relay is energized to attract the switch. So as to realize the detection alarm function. The adjustable resistor R7 is used to adjust the detection sensitivity. The output terminal J3 of the relay can be used to control other electrical appliances, such as exhaust fans. When the alcohol concentration exceeds the standard, the exhaust fan is started.
Turn off the exhaust fan after the concentration decreases to achieve automatic control.
1 x MQ-3 Sensor Alcohol Detector Tester Kit