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    First published on: 1-3-2003



    This reliable and easy-to-operate electronic security system can be used in banks, factories, commercial establishments, houses, etc.

    The system comprises a monitoring system and several sensing zones. Each sensing zone is provided with a closed-loop switch known as sense switch. Sense switches are fixed onthedoors of premises under security and connected to the monitoring system. As long as the doors are closed, sense switches are also closed. The monitoring system can be installed at a convenient central place for easy operation.

    Fig. 1 shows the monitoring circuit only for zone 1 along with the common alarm circuit. For other zones, the monitoring circuit is identical, with only the prefixes of components changing as per zone number. Encircled points A, B, and C of each zone monitoring circuit need to be joined to the corresponding points of the alarm circuit (upper half of Fig. 1).

    Fig. 1: Monitoring circuit along with the alarm circuit

    When zone 1 sensing switch S11, zone  switch S1 are all on, pnp transistor T12 reverse biases to go in cut-off condition, with its collector at around 0 volt. When the door fitted with sensor switch S11 is opened, transistor T12 gets forward biased and it conducts. Its collector voltage goes high, which forward biases transistor T10 via resistor R10 to turn it on. (Capacitor C10 serves as a filter capacitor.) As a result, the collector voltage of transistor T10 falls to forward bias transistor T11, which conducts and its collector voltage is sustained at a high level. Under this latched condition, sensor switch S11 and the state of transistor T12 have no effect. In this state, red LED11 of the zone remains lit.

    Simultaneously, the high-level voltage from the collector of transistor T11 via diode D10 is applied to VDD pin 5 of siren sound generator IC1 (UM3561) whose pin 2 is grounded. Resistor R3 connected across pins 7 and 8 of IC1 determines the frequency of the in-built oscillator. As a result, IC1 starts generating the audio signal output at pin 3. The output voltage from IC1 is further amplified by Darlington pair of transistors T1 and T2. The amplified output of the Darlington pair drives the loudspeaker whose output volume can be controlled by potentiometer VR1. Capacitor C1 serves as a filter capacitor.

    Fig. 2: Physical layout of sensors and monitoring alarm system

    You can alter the alarm sound as desired by changing the connections of IC1 as shown in the table.

    The circuit continues to sound the alarm until zone door is closed (to close switch S11) and the reset switch is pressed momentarily (which causes transistor T10 to cut off, returning the circuit to its initial state).

    The system operates off a 3V DC battery or recharging battery with charging circuit or battery eliminator. If desired, more operating zones can be added. Initially keep the monitoring system switch S1 off. Keep all the zone doors fixed with sensing switches S11, S21, S31, S41, etc closed. This keeps the sensing switches for respective zones in closed position. Also keep zone slide switches S12, S22, S32, S42, etc in ‘on’ position. This puts the system in operation, guarding all the zone doors.Now, if the door of a particular zone is opened, the monitoring system sounds an audible alarm and the LED corresponding to the zone glows to indicate that the door of the zone is open. The alarm and the LED indication will continue even after that particular door with the sensing switch is immediately closed, or even if that switch is removed/damaged or connecting wire is cut open. Any particular zone in the monitoring system can be put to operation or out of operation by switching on or switching off the corresponding slide switch in the monitoring system.


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    commentPost Comment | 15 Comments

    HARSHITA BANSAL   1332 days ago

    please sent report of electronic security system and further detail of this project.
    naga suresh   1325 days ago

    nice construction.i use this project in my college project expo.thanq efy
    commentReply   1 Reply
    siddharth   1100 days ago

    hey dude i also wann dis as my clg project but im ltil bt confuse will u plz give m the whole dtal of dis on my email plzzzzzzzzzz
    Murtala   1246 days ago

    pls is there any subtitude for the IC UM3561 and transistor BEL 187.
    david   1224 days ago

    Arun B   1186 days ago

    good i will use this in my home
    kkkkk   1172 days ago

    sir please send me the pcb layout of this project
    commentReply   1 Reply
    Efy Admin   1169 days ago

    This circuit was published under Circuit Ideas section. We don't provide PCB layout for this section.
    Nandhini   1130 days ago

    please sent project report and further details about this project
    MD HEDAYATULLAH   1115 days ago

    please send me full report along with circuit diagram and how to connect and performance of the circuit
    shivam kumar   1045 days ago

    sir i have choosed this project for my college and i have no idea about this so please send me the simple diagram and how to connect it please send me soon plessssssssssssssssssssssssssssssssss
    priyanka   1041 days ago

    plz send me electronics security system pcb layout and its complete joining circuit diagram
    SARAVANAN   1014 days ago

    madhuri   967 days ago

    hi..pls can u send circuit diagramprogram for home security system for gas detection using 8051 to my id???
    kritika rajput   591 days ago

    can you plz tell me the name of all components quantity wise.

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