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wire break sensor alarm circuit schematic

Wire Break Sensor Alarm

Circuit of a loop sensor based simple security alarm is described here. The sensor loop is nothing but a short length of thin enamelled copper wire, which bridges two input points of the electronic alarm circuit. When the loop is opened the alarm circuit fires an active electric/electronic hooter to raise an ear-splitting audio alert signal. The circuit requires 12 volt dc supply for proper working.

When the loop is closed, anode terminal of diode D1 is at ground level and transistor T1 is off. When the loop opens, capacitor C1 is quickly charged via resistor R1 and diode D1, whereupon mosfet T1 comes on so that the hooter (BZ1) is switched on. If the loop is closed again, initial condition is maintained by grounding the anode of D1 and this stops the charging of C1. However, C1 is disharged fairly slowly via R2, so that T1 is not switched off immediately! This ensures that the alarm remains active for a little more time and then goes out slowly. This timeout can be changed by varying the value of R1,R2 and C1. Mosfet T1 may be one of many types of popular n-channel power mosfet, but it should be able to handle the selected 12V hooter of your choice.

Wire break alarm circuit schematic

wire break sensor alarm circuit schematic

37 Comments

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  • SkyNet

    Hello,
    P. Marian,
    you have same circuit in low current (3v/5v.)?

    What i do, the same circuit work in 3v.?
    I already made This circuit.

    SkyNet

  • jerry rani

    Sir,
    Can you please let me know what’s the purpose of the Capacitor C2??

  • حاشير نيشار

    MY WIRE BREAK SENSORS ALARM CIRCUIT IS WORKING SUCCESSFUL .

    Very very very Thank you,
    ELECTRO SCHEMATIC
    P. MARIAN

  • 007

    Alarm circuit that works?
    Sensor wire break after the alarm rings for how long?
    Please give your answer soon.

  • Hasir nisar

    Can i use
    TRANSFORMSLESS / TRANSFORM BASED POWER SUPPLY
    12v. 100mA
    for alarm circuit proper(24×7) work.
    Or
    # 12v. (how)?mA.
    HN….

    • Arindam Ray

      Hi, Hasir nisar

      Thanking You for your kind cooperation.

      I am facing some problem.

      As some components are not available in the
      Local market,I went for some compatible components
      Described by the author,but in fact the circuit is not
      Working at all.
      I’ve replaced BUZ74 with IRF820,10uF/25V with 10uF/63V,
      1N4001 with 1N4007,
      But the circuit is not working.
      Please advice.

    • Hasir Nisar

      Hey Arindam,
      your circuit works ?

      My circuit successful working but
      sound is LOW.
      What i do for high sound?
      YOU KNOW WHAT PROBLEM .

      Rply please. HN..

    • Hasir Nisar

      Hello,
      Arindam.
      I have an idea for you.
      Increase the battery power with
      15v. DC
      OR
      My question is pending
      r2=4M7
      meaning of ‘M’ ?
      HN..

    • P. Marian

      4M7 = 4.7MΩ

    • Hasir Nisar

      In
      4.7R
      (Ohm denote by ‘R’)

      4.7K
      (Kilo Ohm denote by ‘K’)

      4.7M
      (What is denote by ‘M’)
      HN..

  • Hasir nisar

    Hey,
    Arindam Ray,
    thanx for share your problem.
    I have circuit’s all same components are available
    but
    R2 confused me?:|
    > R2=4M7,
    what stand for “M”.
    Your New friend,
    HASIR NISAR. (DELHI)
    hasir_nisar@rediffmail.com

  • Hasir nisar

    Dear sir,
    what is the value of
    R2=4M7
    in this circuit?

    And one more question,

    what used of c2?
    C2’s + point connect to battery wire,
    and (-) point where connect?

    Pleas answer me………..
    HN..:)

    • Wayne Rickertsen

      R2 is 4.7 megohm. In the realm of resistance we measure in ohms, kilohms, and last but not least megohms.

    • Arindam Ray

      Hey Hasir nisar ! I have same problem as u faced,I simply grounded the C2′s – point,but end of all,the circuit is not working.you can see my previous query to the author about the changes/problems I faced.plz reply if u find some solution.

  • Arindam Roy

    Dear Sir,
    I’ve replaced BUZ74 with IRF820,10uF/25V with 10uF/63V,1N4001 with 1N4007,as the mentioned parts are not available locally.But the circuit is not working.Please advice.

  • A.Ray

    Dear Sir,
    I’ve replaced BUZ74 with IRF820,10uF/25V with 10uF/63V,1N4001 with 1N4007,as the mentioned parts are not available locally.But the circuit is not working.Please advice.

  • soumya

    sir …….can u plz send me the information why r3=100k is used.plz plz do reply sir

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