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LASER-BASED INTRUDER ALARM

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  • First published on: 5-4-2011

    LASER-BASED INTRUDER ALARM

    RAJ K. GORKHALI


    You can use this laser-based intruder alarm conveniently at the entrance of a hall or any other similar location to protect the same from unauthorised access as and when desired. Its range can be extended further to protect the perimeter of a building from unauthorised intrusion by using a cascade arrangement of multiple alarms.

    The circuit consists of a transmitter and a receiver. The transmitter circuit (shown in Fig. 1) is nothing but a laser diode (LD1) driven by a 9V PP3 battery. The output of IC1 is regulated 5V as long as its input remains equal to or more than 7.5V, thus ensuring a constant drive current for the laser diode. The battery (Batt1) is connected to the circuit through switch S1.



    Fig. 1: Transmitter circuit

    The laser diode (LD1) can be replaced with a laser pointer (torch) emitting red laser beam. The laser pointer itself can be used as a transmitter. The pointer has in-built series resistance, on/off switch and battery.

    The receiver circuit (shown in Fig. 2) is basically a current-to-voltage converter built around IC LM356 (IC3). The output of IC3 is fed to the monostable built around 555 timer (IC4). The high output of the monostable drives the piezobuzzer to sound an audio alarm.





    Fig. 2: Receiver circuit

    The receiver section operates off 5V DC generated from another 9V battery and voltage regulator IC 7805 (IC2). The battery (Batt.2) is connected to the circuit through switch S2.

    When the laser light transmitted through LD1 falls on phototransistor T1,the output of the op-amp (IC3) at its pin 6 remains high. In this condition, the output of IC4 remains low and the buzzer does not sound.

    When the laser beam falling on phototransistor T1 is interrupted by someone, the output of op-amp IC3 goes low and IC3 produces a pulse. This pulse triggers monostable IC4 and its output goes high to sound the alarm for a time period of about R8xC8.

    Assemble the transmitter and receiver circuits on separate general-purpose PCBs and enclose in suitable cabinets. Mount the transmitter and receiver units on opposite pillars of the entrance, aligning the two such that the laser beam from the transmitter directly falls on the phototransistor. Block the laser beam with your hand and measure the op-amp output. It should not be low. At pin 3 of IC4, you should get a positive-going pulse of one-second duration beginning with high-to-low edge of the trigger pulse appearing at pin 2 of IC4 or collector of transistor T2
    .


     

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    Post Comment | 25 Comments



    Raj   1299 days ago

    This could not possibly have been more helpufl
    Reply  
    himanshu dhoundyal   1296 days ago

    MY PHOTO TRANSISTOR IS NOT WORKING.HOW TO KNOW ABOUT ITS EMITTER BASE AND COLLECTORMY CIRCUIT IS NOT WORKING I MADE IT.........PLEASE ITS HURRY .REPLY ME
    Reply   1 Reply
    Chirayu   1121 days ago

    DEAR FRIEND I M HAVING THE SAME PROBLEM. HELP ME
    Reply  
    dinesh hemnani   1289 days ago

    check the notch and to test the working use a multi meter .. as far as i know emitter base is forward biased and collector base is reverse biased .. but it depends if its npn or pnp
    Reply   1 Reply
    Aashish   1221 days ago

    buddy whether a transistor is npn or pnp emitter base is always fb and collector base is always rb becoz transistor is most commonly operated in active region in analog electronics
    Reply  
    HIMANSHU   1282 days ago

    IT AINT WORKING I ALSO SHOW IT TO MY TEACHER EVERYTHING IS RIGHT........PHOTODIODE IS WORKING AND PHOTOTRANSISTOR IS ALSO WORKING...BUT WHEN I AM CREATING OBSTACLE IN BETWEEN SIGNAL NOTHING HAPPENS
    Reply   1 Reply
    Aashish   1221 days ago

    check your wires and op amps..
    Reply  
    vishal pandey   1256 days ago

    kindly tell me why when i design any ckt it shorts every time....
    Reply   1 Reply
    sathish chelliah   1159 days ago

    check the solderings it may be having excess led causing short
    Reply  
    Chirayu   1121 days ago

    MY PHOTOTRANSISTOR IS NOT WORKING . L14F1 WAS NOT AVAILABLE AND SO I BOUGHT L14G2 WHICH IS VERY SIMILAR. IS THERE ANY WAY TO TEST L14G2 ? PLZ HELP URGENT
    Reply  
    RAVINDRA SINGH BHATI   1055 days ago

    yar transmitter circuit is not working
    Reply  
    Sujay Joardar   1053 days ago

    but if i wants to calculate pulse from the same circuit what i have to do... and in case we use a micro controller then what to do
    Reply  
    Parth Patel   1035 days ago

    hey in my transmitter it works properly and in my receiver ckt i used lf356 which is similar to lm 356 and buzzer sounds continuosly give some idea to slove this problem
    Reply  
    Manasi   1001 days ago

    What is the main purpose of the diode in the circuit?
    Reply  
    Manasi   1001 days ago

    What is the purpose of the diode in the circuit?
    Reply  
    neethu   873 days ago

    where is the pcb layout of this ckt dagram
    Reply   1 Reply
    Efy Admin   843 days ago

    No PCB layout for this circuit, sorry. Note that all circuits published before January 2013 under Circuit Ideas section have no PCB layouts.
    Reply  
    rishi alen   834 days ago

    when we transmit laser beam in phototransistor then sound of buzzer is not stop...give me sol.
    Reply  
    monisankar shee   798 days ago

    my photo transistor is not work. how i will find emitter base & collector?
    Reply  
    ZAINABU   770 days ago

    i have got a problem of voltage drop at the lm356
    Reply  
    akshay reginold   741 days ago

    can u plz give me block diagaram of this ckt
    Reply  
    YOGESH   569 days ago

    Please send me the all theory of project laser based intruder alarm...........PLEASE........
    Reply  
    manzoor   492 days ago

    sir can u send me digital clock with 7segment display circuit ...plzzzzz sir
    Reply  
    SUBRAT KUMAR KAR   175 days ago

    I want to Know what will be cost of such system. I need to install such laser intruder protection system along my 100feet boundary wall.
    Reply  
    yash shinde   2 days ago

    my circuit is not working. what to do with the base photo transistor ? pls reply fast
    Reply  

     
     
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