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Newbie Help

  1. Mar 19, 2009 #1
    Hey guys. Can someone help me with this circuit?
    http://www.discovercircuits.com/H-Corner/secwireloop.htm

    Where it says "beeper" do they mean a speaker or do they mean a buzzer?

    And can I replace the 2N7000 transistor with a 2N3906?
     
  2. jcsd
  3. Mar 19, 2009 #2
    Simpler question: What does the D G S mean around the transistor?

    Shouldn't it say E B C?
     
  4. Mar 19, 2009 #3
    D G S means drain gate source. The 2N7000 is an N channel FET (field effect transistor). Type in "2N7000 datasheet" in Google search to find one. The beeper is one of those units that beep when you apply a dc voltage. You could use a transistor instead of a FET, but the current to power the base will be more, so the drain current from the battery will be more.. The circuit is laid out for a NPN; the 2N3906 is a PNP.
     
  5. Mar 21, 2009 #4
    Will someone help explain how this circuit works? I don't understand what the transistor does.
     
  6. Mar 21, 2009 #5

    dlgoff

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    Gold Member

    Hey Inspiron1,

    The security loop wire grounds (neg. side of battery) the gate keeping the transistor from conducting. When it is opened (breach of security), the gate voltage goes to 9 volts which causes a current to flow through the buzzer via the transistors drain to source conduction.
     
  7. Mar 21, 2009 #6
    It can be a speaker or a naked piezo element. When the loop is broken, the circuit will oscillate with the capacitor on the gate.
     
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