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FIRE ALARM DETECTOR: FIRE ALARM USING LM741: Here is another small project on fire alarm. When a fire accident is happened in home or office, it will detect the fire (intensity of fire in the room) at instant and give the alarm so we can be ready and act accordingly. Here is another small project on fire alarm. When a fire accident happens in home or office, it will detect the fire (intensity of fire in the room) at instant and give the alarm so we can be ready and act accordingly.
COMPONENTS USED: THERMISTOR LM741 NE555 LED CAPACITORS(0.01mf;100f RESISTORS(100!"4.7!"100!"##! SPEA!ER
MAIN COMPONENTS:
The thermistor is the main component which detects the fire by sudden change in the room temperature because of the heat generated by the fire. The thermistor will detect the heat and give the information to the L!"# $%&'%. The op& will mae the *+++ to generate pulse which has been given to a buer to bu. Thermistor -
The resistance of the thermistor will change according to the temperature. There are two types of thermistors of which one type of thermistor will increase its resistance with increase in temperature called as positive temperature coefficient and the other type of thermistor will decrease its resistance with increase in temperature called as negative temperature coefficient. n this project, we use the thermistor which will have lower resistance with respect to the temperature (negative temperature coefficient thermistor). Thermistor has large applications in consumer electronics, food preservation sectors etc. LM741-
L!"# is an operational amplifier which will wor according to the difference in the input voltages. L!"# has following features lie high current driving, voltage gain, noise amplification and also provide low output impedance. L!"# can also used as a short circuit protection.
BLOC! DIAGRAM OF FIRE ALARM CIRCUIT:
CIRCUIT DIAGRAM:
CIRCUIT E%PLANATION: There are two modes in this project•
ode #- How the circuit will wor if there is no fire
•
ode /- How the circuit will wor if there is fire.
INDEPTH STUD& OF MODES: •
MODE 1:
When there is no fire- The thermistor will have high resistance and there will be no difference in the voltages coming to the L!"# at pin/ and pin0 so there will be no output which will help to trigger the timer. •
MODE #:
When 1ire started- The thermistor resistance will go down to the heat produced by the fire and the resistor 20. 'nd thermistor will act as a potential divider circuit resulting a low voltage at pin/ of L!"# as the temperature goes high. The reference voltage is given by the 2" to the pin0 when there is a difference in the voltage. The pin3 will trigger the timer configured as a stable multi vibrator. *+++ timer will activate the speaer which maes the alarm. The variable resistor 2+ will vary according to the difference in the voltage of the op amp. 'ccording to the resistor 2+, the timer will generate pulse. f temperature goes high, the speaer will mae high noise.
APPLICATION:
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1ire alarms can be used in any place lie pars, theatres , hotels, restaurants, boats, ships, etc.
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1ire alarms can be also used as temperature sensors in some applications, when the temperature goes up abruptly it can inform.
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1ire alarm can be used in our home for safety purpose and it is a very good precautionary measure.
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