Fire Alarm Circuit Using 555 IC

Posted on Feb 4, 2014

This is a design for fire alarm circuit. This circuit is based on a LDR and lamp pair for sensing the fire. The alarm will works by sensing the smoke produced during fire. The circuit produces an audible alarm when the fire breaks out with smoke. This is the circuit of the circuit. For operation the circuit will work when there is no smoke the lig

Fire Alarm Circuit Using 555 IC
Click here to download the full size of the above Circuit.

ht from the bulb will be directly falling on the LDR. The LDR resistance will be low and so the voltage across it (below. 6V). The transistor will be OFF and nothing happens. When there is sufficient smoke to mask the light from falling on LDR, the LDR resistance increases and so do the voltage across it. Now the transistor will switch to ON. This gives power to the IC1 and it outputs 5V. This powers the tone generator IC UM66 (IC2) to play a music. This music will be amplified by IC3 (TDA 2002) to drive the speaker. The diode D1 and D2 in combination drops 1. 4 V to give the rated voltage (3. 5V) to UM66. UM 66 cannot withstand more than 4V. The speaker that can be used for this circuit is a 8 ohm tweeter. The POT R4 can be used to adjust the sensitivity of the alarm circuit. The POT R3 can be used for varying the volume of the alarm. There are general purpose NPN transistor (like BC548, BC148, 2N222) can be used for Q1. The circuit can be powered from a 9V battery or a 9V DC power supply. Instead of bulb you can use a bright LED with a 1K resistor series to it.

Leave Comment

characters left:

Related Circuits

  • New Circuits



    Popular Circuits

    Lantern with dimmer and flasher
    74C164 8 bit shift register work as a heart for car LED light sequencer
    low power switching regulator
    50 MHz range frequency counter using ATtiny45 microcontroller
    autotronics injector circuit
    long delay timer schematics
    Alarms and security related schematics
    elp needed making changes circuit
    8051 Development System Circuit Board 3
    Three of the five band equalizer circuit transistor