11-01-2015, 04:10 PM
please show report on the investigatory project "fire Alarm" full report
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abstract for fire alarm using thermistor
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please show report on the investigatory project "fire Alarm" full report
07-04-2017, 03:35 PM
In this fire alarm circuit, a thermistor functions as the heat sensor. When the temperature increases, its resistance decreases, and vice versa. At normal temperature, the resistance of the thermistor (TH1) is approximately 10 kilo-ohms, which is reduced to a few ohms as the temperature increases beyond 100 ° C. The circuit uses readily available components and can be easily constructed On any general purpose PCB.
![[Image: 1E6_nov_1_efy.png]](http://electronicsforu.com/wp-contents/uploads/2016/04/1E6_nov_1_efy.png)
The IC timer NE555 (IC1) is wired as an astable multivibrator that oscillates in the audio frequency band. Switching transistors T1 and T2 Multivibrator NE555 (IC1). The output of IC1 is connected to transistor npn T3, which drives the loudspeaker (LS1) to generate sound. The frequency of IC1 depends on the values of resistors R5 and R6 and capacitor C2.
When the TH1 thermistor is heated, it provides a low resistance path for extending the positive voltage to the base of the transistor T1 through the diode D1 and the resistor R2. The capacitor C1 charges up to the positive voltage and increases the activation time of the alarm. The greater the value of capacitor C1, the greater the direct voltage applied to the base of transistor T1 (BC548).
Since the collector of transistor T1 is connected to the base of transistor T2, transistor T2 provides a positive voltage to reset pin 4 of IC1 (NE555). The resistor R4 is used in such a way that IC1 remains inactive in the absence of positive voltage. Diode D1 stops the discharge of capacitor C1 when the thermistor connected to the positive supply cools and provides a high resistance (10 kilo-ohm) path. It also stops driving T1. To prevent the thermistor from melting, wrap it in mica tape.
The circuit operates with a regulated 6V-12V power supply. LED1 is used to indicate that the circuit power is on.
The IC timer NE555 (IC1) is wired as an astable multivibrator that oscillates in the audio frequency band. Switching transistors T1 and T2 Multivibrator NE555 (IC1). The output of IC1 is connected to transistor npn T3, which drives the loudspeaker (LS1) to generate sound. The frequency of IC1 depends on the values of resistors R5 and R6 and capacitor C2.
When the TH1 thermistor is heated, it provides a low resistance path for extending the positive voltage to the base of the transistor T1 through the diode D1 and the resistor R2. The capacitor C1 charges up to the positive voltage and increases the activation time of the alarm. The greater the value of capacitor C1, the greater the direct voltage applied to the base of transistor T1 (BC548).
Since the collector of transistor T1 is connected to the base of transistor T2, transistor T2 provides a positive voltage to reset pin 4 of IC1 (NE555). The resistor R4 is used in such a way that IC1 remains inactive in the absence of positive voltage. Diode D1 stops the discharge of capacitor C1 when the thermistor connected to the positive supply cools and provides a high resistance (10 kilo-ohm) path. It also stops driving T1. To prevent the thermistor from melting, wrap it in mica tape.
The circuit operates with a regulated 6V-12V power supply. LED1 is used to indicate that the circuit power is on.
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