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Newbie Help

  1. Mar 19, 2009 #1
    Hey guys. Can someone help me with this circuit?

    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


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    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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