2B -Fire alarm
This is a multi purpose project . Now a days the possibility of catching fire has increased tremendously due to increase in the electrical appliances in the todays age of electronics . Fire alarm is very useful item for shops and workshops etc.
TECHNICAL DESCRIPTION AND WORKING
This project has been developed and tested O.K. in our TV Engineers Technical Lab. The components and PCB used in the projects published in our books are available for sale at resonable price.
Todays in electronic age the use of electronic / electrical appliances is increasing day by day creating more chances of catching fire in the big building and residential areas . In this project sensing the fire an alarm is sounded . This is a multipurpose project .
In this a popular IC 555 is used . It is a timer IC and used in both analog as well as digital circuit .Its input and output impedance can be matched of any TTL and , CMOS logic circuits. The most important part of this circuit is germanium diode , which is very sensitive to heat . At room temperature the diode reverse resistance is very high and allow transistor Q1 to conduct. The reset pin of IC 555 remains at the ground potential . Due to fire the temperature near the diode increases and lower the reverse resistance of diode.
At the temperature of 70 degree C the resistance of diode is less than 1K and transistor Q1 stops conducting . On account of the reset pin no.5 of IC555 becomes positive due to 1K resistance and alarm starts ringing . You can place the alarm at three or four different places and also keep germanium diodes connecting in parallel at separate places . If fire catches at any spot , diode will sense it and alarm will be sounded.
PRECAUTIONS WHILE ASSEMBLING THE PROJECT :-
While ASSEMBLING THE PROJECT :-
Don’t solder diode (fire sensor) on PCB . Keep it away from PCB otherwise there is possibility of parts getting spoiled on PCB.
While soldering transistor check the collector , base and emmiter with multimeter .
While soldering diode pay attention towards anode and cathode of the diode.
Don’t solder IC directly on the PCB. There is possibility of parts getting spoiled due to leakage current from the soldering iron.
LIST OF COMPONENT
PCB [Code 5TP11]=1
1K=1, 4K7=2, 56K=2, 100K Preset =1
0.04pf=1, 0.1pf=1, 220mfd/16V=1, 10mfd/25V =1
IC555=1, TR. 547 =1, DR25 DIODE=1, IC Base [8 Pin]=1
CABINET=1, Candle =1