How Can You Build a Locker Alarm That Activates When Wires Separate?

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Discussion Overview

The discussion revolves around designing a locker alarm that activates when two wires separate, as part of a high school AP Physics project. Participants explore various circuit designs and components, including transistors and relays, while addressing specific project requirements and constraints.

Discussion Character

  • Technical explanation
  • Homework-related
  • Exploratory

Main Points Raised

  • The original poster (OP) seeks assistance in designing a locker alarm that activates upon wire separation, as required by the project guidelines.
  • Some participants suggest using a transistor circuit to sense when the wire circuit is opened, indicating a potential approach to meet the project requirements.
  • Others propose using a double-pole (dp) relay to break the alarm circuit when the wires are closed and complete it when the wires separate, suggesting this might be a simpler solution for the OP.
  • The OP expresses a need for clarification on the dp relay and mentions the components provided by the teacher, including a NPN transistor, which must be used in the project.
  • One participant highlights the advantage of using a transistor for lower power consumption in the circuit.
  • The OP requests further explanation about the dp relay and shares personal details, indicating a casual tone in the discussion.

Areas of Agreement / Disagreement

Participants generally agree on the use of either a transistor or a dp relay as potential solutions, but there is no consensus on the best approach, and the discussion remains exploratory.

Contextual Notes

The OP's project has specific requirements, including the necessity to use a transistor and other provided components, which may limit the design options discussed.

Who May Find This Useful

Students working on similar electronics projects, educators looking for examples of circuit design discussions, and hobbyists interested in alarm systems may find this discussion relevant.

EllBe
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Please help me with my school project!

I'm in AP Physics in High School right now, and the teacher just assigned our class to design a locker alarm. It must turn on when the locker is opened and turn off when the locker is closed. However, there's a restriction: the alarm must turn on when 2 wires separate, not when they come together. I'm pretty stuck with this project because of the restriction...anyone has any idea on how to build the alarm in a way that would satisfy the restriction?? Thank you very much!
 
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EllBe said:
I'm in AP Physics in High School right now, and the teacher just assigned our class to design a locker alarm. It must turn on when the locker is opened and turn off when the locker is closed. However, there's a restriction: the alarm must turn on when 2 wires separate, not when they come together. I'm pretty stuck with this project because of the restriction...anyone has any idea on how to build the alarm in a way that would satisfy the restriction?? Thank you very much!

Welcome to the PF.

It's your school project, so we can only offer small hints.

Are you familiar with transistor circuits yet? You could have a transistor "sense" when the input "2-wire" circuit is opened...
 


You could use a dp relay and wire it up so the relay breaks the alarm circuit when the wires are closed and completes the alarm circuit when the wires break.
 


rollcast said:
You could use a dp relay and wire it up so the relay breaks the alarm circuit when the wires are closed and completes the alarm circuit when the wires break.

Good hint. That's probably simpler for him if he's not familiar with transistors.

Let's all wait for the OP to come back with a reply. They should be able to get quite far with the relay hint.
 


Thank you for the hints! :)

The teacher didn't tell us much about the transistors though we have to use one for this project. She provided us with resistors, a NPN transistor, LED, buzzer, wire, battery and the battery connector; and we have to use all of them.

Can you explain for me what's the dp relay?? xD is it the differential protective relay?? ty
and I'm a girl btw :P
 


EllBe said:
Thank you for the hints! :)

The teacher didn't tell us much about the transistors though we have to use one for this project. She provided us with resistors, a NPN transistor, LED, buzzer, wire, battery and the battery connector; and we have to use all of them.

Can you explain for me what's the dp relay?? xD is it the differential protective relay?? ty
and I'm a girl btw :P

A DP relay is a double-pole relay:

http://en.wikipedia.org/wiki/Electrical_relay

It's good that you can use a transistor -- the circuit will be lower power that way (the standby/off power consumed).

Do you have an example circuit of an NPN transistor being used to drive your buzzer? That should be pretty easy to find in the buzzer datasheet or by doing a Google Images search...
 

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