The MQ-3 ethanol detection alarm kit is mainly an alarm control circuit composed of a gas sensor MQ-3. When the sensor MQ-3 is surrounded by alcohol vapor, the conductivity of the sensor will increase with the concentration of the alcohol vapor. increase and increase. By measuring the series partial voltage between the sensor and the fixed resistor, the alcohol content in the environment can be judged. If the alcohol content is greater than the set threshold, the buzzer will sound an alarm, indicating that the alcohol content exceeds the standard. In the design of this kit, the knowledge of the two courses of “analog electronic technology” and “digital electronic technology” is used to comprehensively complete the course design. It can be used for the teaching and training of electronic technology foundation and skills, for electronic enthusiasts and beginners, and to enhance the comprehensive practical ability.
Kit parameters:
Product model: TJ-56-276
Power supply voltage: DC5~7.5V (DC power supply)
Board size: 62*36mm
Circuit principle:
This circuit can be powered by a 5-75 volt DC power supply, the switch S1 is the power switch, the resistor R1 and the light diode D1 is used for power indication. The inside of the sensor MQ-3 needs to be heated to a certain temperature when it is working, so a section of heating wire is installed inside it. The resistor R4 is the current-limiting resistance of the heating wire. It is normal for MQ-3 to heat up after power on. When MQ-3 does not detect alcohol vapor, its internal resistance is large, the voltage drop of R3 and RW is very low, the voltage of pin 2 of NE555 is lower than the trigger voltage (VCC/3), its pin 3 outputs a high level, and D2 goes out , the buzzer does not sound, and the relay does not act. When MQ-3 detects alcohol vapor, the internal resistance drops, the voltage of R3 and RW rises, the voltage of pin 2 of NE555 is higher than the trigger voltage, pin 3 becomes low level, D2 turns on and lights up, and the buzzer flows The current starts to sound, and the electromagnetic coil in the relay is energized to attract the switch action. In order to realize the detection and alarm function. The adjustable resistor RW is used to adjust the detection sensitivity. This circuit uses the second comparator inside the NE555 to detect voltage changes, and uses its internal flip-flop to debounce. NE555’s pin 7 and pin 5 are not used and are suspended. The output terminal J3 of the relay can be used to control other electrical appliances, such as the exhaust fan, to start the exhaust fan when the alcohol concentration exceeds the standard, and to turn off the exhaust fan after the alcohol concentration drops to realize automatic control. Diode D3 is used to eliminate the induced electromotive force generated when the relay coil is turned on and off. The power supply interface can be a DC plug, or you can use a line directly at the J2 position, pay attention to the positive and negative signs, the DC plug power supply is positive on the inside and negative on the outside.
Instructions for use:
1. Under normal circumstances, adjust the potentiometer so that there is no alarm, and the sensitivity is the highest.
2. You can put some wine in a cup, put the sensor probe on the top of the cup, or blow the volatile gas of alcohol to the sensor for sensing.
3. The output switch has a switching function. It has no voltage output, the relay is closed, and the two pads are connected. It can be used to control the on and off of other circuits or the switch of electrical appliances.
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