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First off all im a beginner with electricity. I'd like to know at all times when the door is open (5 meters away) at all times, and have it displayed with an LED. What kind of sensor I'd need and how much would it cost? Also is there any way of making it as hidden as possible, so that there wouldnt be a bunch of wiring around the door.

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closed as too broad by Matt Young, Joe Hass, Leon Heller, placeholder, Nick Alexeev May 13 '14 at 4:01

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    \$\begingroup\$ So you want a basic alarm system? \$\endgroup\$ – Passerby May 12 '14 at 21:04
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    \$\begingroup\$ It sounds like you have to start doing your research and learning about circuits. Do you want an optical sensor, or how do you plan to detect the door is open? What is the door 5 metres from? Are you saying you want it to light an LED or displayed on an LCD screen? Do you want to use a simple circuit or a micro-controller? These are all things you have to consider. As far as designing it, you either have to learn about circuits and what you want to do or pay someone to design this. \$\endgroup\$ – JFA May 12 '14 at 21:06
  • \$\begingroup\$ Well its not for that purpose. I'd figure it'd be pretty easy for you guys to answer me i dont know.. \$\endgroup\$ – user41740 May 12 '14 at 21:07
  • \$\begingroup\$ I dont know where Id learn what a micro-controller is, Id just like a simple LED lamp to go bright when the door is open, and while it stays open. I dont need it that urgently I just thought It'd be a good project to start on electricity with. The sensor and LED should be ~ 5 meters apart. \$\endgroup\$ – user41740 May 12 '14 at 21:11
  • \$\begingroup\$ Sounds like you want a magnet on the door and a reed switch on the wall. \$\endgroup\$ – Olin Lathrop May 12 '14 at 21:44
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As user30997 suggested, I would start with interfacing a simple LED. The idea is the same as in primitive alarms - use a magnet to close open a reed switch. There's an example I wound on google: enter image description here

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  • \$\begingroup\$ Yeah that's the idea, but where could I get two weak magnets that'd provide power when near by. Also this'd turn on LED when doors are closed \$\endgroup\$ – user41740 May 12 '14 at 21:31
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I did something like this when I was a kid by connecting a wire to the part of the bolt mechanism that is inside the door and another to the metallic hole that it fits into when the door is closed. Connecting the LED in series with this circuit and a current-limiting resistor (if your doorknob and wiring don't already provide plenty of impedance) is a quick-and-dirty way to do what you're up to. Of course, this setup lights up the LED when the door is closed. You'll have to get a little more complicated if you want to reverse the logic.

Most interior doors are hollow and the wiring can easily be run inside of it. To hide the wiring for the doorjamb, run it under the moulding. A Dremmel with a cutting disk makes this an easy job. Paint over the wire once you've pushed it into the groove.

I wonder if my wiring is still in place in that old house. =]

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  • \$\begingroup\$ Im very confused about most of things youre saying so hang on :D as I said im a noob and I dont know why I'd need a current limiting resistor (probably so LED doesnt burn up?) and I dont know why Id need impedance ?(wierd i know). Also couldnt you just buy a chip with NAND gates and invert output, for LED to light when door is open? What kinds of bolt mechanism are we talking about did you make it yourself is it visible..? \$\endgroup\$ – user41740 May 12 '14 at 21:29
  • \$\begingroup\$ There you go: you can use an input from the reed switch to your NAND gate. But now you have to learn about NAND gates too. )) \$\endgroup\$ – Nazar May 12 '14 at 21:38
  • \$\begingroup\$ Well I already know Exactly and I mean Excatly how NAND works, im actually a studdent of digital logic, but we have very little electonics and many Bolean logic gates. I still dont understand why I'd need impedance and how much does a proper magnet cost \$\endgroup\$ – user41740 May 12 '14 at 21:43
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    \$\begingroup\$ @user41740 No need for an inverter. You can get reed switches in either normally open (NO) or normally closed (NC) configurations. Most alarms would use a NC switch, so when the door is open, the switch closes and sets of the alarm. You would want a normally open (NO) one. \$\endgroup\$ – tcrosley May 13 '14 at 0:36
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A magnet, a C/O reedswitch, a battery and a buzzer springs to mind. If you need a led that's extra wiring and a resistor unless you went wireless but, by the sound of it thats one step too far.

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