02-02-2012, 12:47 PM
AUTOMATED ALARM CIRCUITS
ACKOWLEDGEMENT
Through perseverance and enthusiasm combined with effort in the right direction can bring forth the thing called success but the realization of the harsh reality that the path towards success is full of myriads, temptations, impediments and pitfalls often proves to be disheartening in such situation, it is the able guidance of knowledgeable persons that steers one through difficulties and help her achieve success.
We are highly obliged to express our deep sense of great gratitude and grateful thanks to our erudite Prof. Dhankar and Prof. Thawri for their valuable guidance and support which led to the successful and timely completion of our project
Secondly, thanks to our Head of the Dept. ELECTRONICS ENGINEERING, Prof. M. Bhongade for his encouraging guidance.
Last but not the least, we deeply appreciate the cheerful encouragement of all the staff members of our department and our friends.
Thanking You..
Introduction
The world is no longer a safe place..........simple thefts have stirred in the minds of people.... what could be done to make robbery and thieving stop once and for all...for this engineers have fabricated simple electronic alarm circuits which could be used to catch thieves or robbers in action.......
Simple ICs, diodes, resistors, capacitors, light emitting diodes....when fabricated together.........can be used to trigger the alarm circuit......and when this circuit is connected to a loudspeaker- a very loud sound is generated....in this case......a police siren
Such circuits find great applications when security is concerned...they are used in household, banks, offices......
AUTOMATED
ALARM CIRCUIT
Operating Principle/Working of circuit:-
The control unit is built around two ICs CD4047 AND CD4027. IC4047 (IC1) is wired in positive-edge-triggering monostable multivibrator mode to set and reset IC 4027(IC2). The output pulse width of IC1 depends on the values of the capacitor C2 and resistor R3 connected to pins 1,2,and 3
Normally, when the door is closed, reed switch S1 is closed, transistor T1 conducts and the monostable multivibrator(IC1) remains in standby mode with ‘low’ output at pin 10.
When the door is closed, reed switch S1 gets disconnected, T1 stops conducting and low-to-high pulse at pin 8 of IC1 triggers the monostable and a short-duration positive pulse of about 10 seconds is available as Q output at pin 10. At the same time, complementary output Q goes low at pin 11. The output from IC1 is used to set and reset IC2.
IC2 is a low-power, dual J/K master flip-flop having independent J, K, set, reset and clock inputs. The flip-flops change states on the positive-going transition of the clock pulses. IC2 is wired such that its Q output turns “high” when reset pin 4 receives a high, Q output goes low and complementary Q goes high. This lights up LED2 and drives transistor T2(BC548), which enables the alarm circuit.
The output at point A is used to enable the alarm tone generator circuit consisting of two IC555 timer ICs marked as IC1 &IC2. The R-C network determines the frequency of the sound produced. The triangular wave-form of the astable-multivibrator is taken out from the junction pins 2 and 6 of IC3. This waveform is fed as the control voltage at pin 5 of IC4 through resistor. The output received from pin 3 of IC4 is fed through base of transistor T3 to drive an 8-ohm loudspeaker which generates a police siren.
ADVANTAGES:-
1. A simple 9V battery excites the entire circuit
thereby reducing power consumption.
2.The sound generated by the speaker is very large
3.It is economical, portable, convenient and compact.
DISADVANTAGES/ LIMITATIONS
1. Loose connections can burn up the entire circuit.
2.Precise specifications of the components needs to be met
2. Time period is very short
