Help with Secured Wire Loop Circuit - 2N7000/2N3906 Transistor Questions

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Discussion Overview

The discussion revolves around a secured wire loop circuit involving transistors, specifically the 2N7000 and 2N3906. Participants seek clarification on component functions, circuit operation, and potential substitutions within the circuit design.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions whether "beeper" refers to a speaker or a buzzer in the circuit.
  • Another participant asks about the meaning of D G S in relation to the transistor, suggesting it should be E B C instead.
  • It is noted that D G S stands for drain, gate, source, and that the 2N7000 is an N channel FET. A datasheet is suggested for further information.
  • One participant mentions that while a transistor could replace a FET, it would require more current to power the base, affecting the drain current from the battery.
  • A participant explains the function of the transistor in the circuit, stating that it controls current flow through the buzzer when the security loop is breached.
  • Another participant suggests that the beeper could be a speaker or a naked piezo element and mentions the circuit's oscillation when the loop is broken.

Areas of Agreement / Disagreement

Participants express varying interpretations of component roles and circuit behavior, indicating that multiple competing views remain on certain aspects of the circuit design and function.

Contextual Notes

There are unresolved questions regarding the suitability of substituting the 2N7000 with the 2N3906, as well as the implications of using different types of sound-producing components.

Who May Find This Useful

Individuals interested in circuit design, particularly those working with transistors and security systems, may find this discussion relevant.

Inspiron1
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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?
 
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Simpler question: What does the D G S mean around the transistor?

Shouldn't it say E B C?
 
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.
 
Will someone help explain how this circuit works? I don't understand what the transistor does.
 
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.
 
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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