Fire Alarm Project Using Thermistor

In this alarm circuit project, a thermistor functions as the warmth sensor. At the point when temperature expands, its opposition diminishes, and the other way around. At ordinary temperature, the obstruction of the thermistor (TH1) is roughly 10 kilo-ohms, which diminishes to a couple of ohms as the temperature increases past 100°C. The circuit utilizes promptly accessible parts and can be effortlessly built on any universally useful PCB. Look at the fire sensor circuit.

Fire alarm circuit component:

R1 – 470Ω

R2 – 33K

R3 – 470Ω

R4 – 560Ω

R5 – 47K

R6 – 2.2K

R7 – 470Ω

C1 – 10μ 16V

C2 – 0.04μ

C3 – 0.01μ

D1 – 1N4001

T1 – BC548

T2 – BC558

T3 – SL100B

TH1 – Thermistor 10K

LS1 – 8Ω, 1W Speaker


IC1 – NE555

Fire Alarm Circuit Diagram :

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Fire Alarm Circuit Diagram


Timer IC NE555 (IC1) is wired as an astable multivibrator swaying in sound recurrence band. Exchanging semiconductors T1 and T2 drive multivibrator NE555 (IC1). The yield of IC1 is associated with npn semiconductor T3, which drives the amplifier (LS1) to produce sound. The recurrence of IC1 relies upon the estimations of resistors R5 and R6 and capacitor C2. To keep the thermistor from dissolving, envelop it with mica tape.


The home alarm framework works off a 6V-12V controlled force supply. LED1 is utilized to show that capacity to the circuit is turned on.

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