Smoking warning device 2

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The smoking warning device described in this example can be used in places where smoking is not appropriate (eg hospitals, conference rooms, etc.). When someone smokes, the smoking reminder will issue a "Please do not smoke!" language warning to remind the smoker to consciously stop smoking.
Circuit Operation The smoking alarm circuit consists of a smoke detector, a monostable trigger, a language generator, and a power amplifier circuit, as shown in Figure 9-154.

The smoke detector is composed of a potentiometer RP1, a resistor R1 and a gas sensor.
The monostable flip-flop is composed of a time base integrated circuit ICl, a resistor R2, a capacitor C1 and a potentiometer RP2.
The speech generator circuit is composed of a voice integrated circuit IC2, a resistor R3-R5, a capacitor C2, and a Zener diode VS.
The audio power amplifying circuit is composed of a transistor V, a boosting power amplifier module IC3, resistors R6 and R7, capacitors C3 and C4, and a speaker BL.
When the gas sensor detects smoke, the resistance of the two ends of A and B is larger, the 2 pin of ICl is high level (higher than 2Vcc/3), the output of 3 feet is low level, and the voice generator The circuit and audio power amplifier circuit do not work, and BL does not sound.
When someone smokes and the gas sensor detects smoke, the resistance values ​​of the two ends of A and B become smaller, causing the voltage of pin 2 of ICl to drop. When the voltage of the foot drops to Vcc/3, the one-shot is triggered. Flip, IC1's 3 pin changes from low level to high level. After high level R3 current limit, C2 filtering and VS voltage regulation, it generates 4.2V DC voltage and supplies to voice integrated circuit IC2 and transistor V. After the power is turned on, the lC2 outputs a voice electrical signal. After the electrical signal is amplified by V and IC3, the BL is urged to issue a "Please do not smoke!" voice warning sound.
The nuclear smoking reminder can also be used as a smoke alarm to detect fires or as a detection alarm for harmful gases and flammable gases.
Adjusting the resistance of RPl can change the heating current of the gas sensor (generally about 130M).
Adjusting the resistance of RP2 can change the sensitivity of the monostable trigger circuit action.
Component selection
Rl-R7 uses 1/4W carbon film resistor or metal film resistor.
Small linear potentiometers or variable resistors are available for RPl and RP2.
Cl, C2 and C4 are all made of aluminum electrolytic capacitors with a withstand voltage of 16V; C3 is a monolithic capacitor.
VS selects 1/2W, 4.2V silicon Zener diode.
V selects S9013 or C8050 type silicon NPN transistor for use.
ICl selects NE555 type time base integrated circuit; IC2 selects voice integrated circuit with "Please do not smoke!" voice information; IC3 selects WH68 type boost power amplifier thick mode integrated circuit.
BL uses 8Ω, 1-3W electric speakers.
The gas sensor is a MQK-2 type sensor.