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We've got a mouse in the house. I want to setup traps in the attic, but I don't want to go up there to check them. My thought is to use a simple circuit that uses the trap itself as a switch. I think it needs two circuits: a path for the electricity when the trap is set (circuit A) and a path when the trap has gone off (circuit B).

I think:

  • Circuit A should be nothing except a resistor. (If it was just metal, the battery would run down real quick... plus... you know... hot).
  • Circuit B should have a resistor and an LED (and a long pair of wires so we can hang the LED out the attic door and it is visible from the hallway.

When the trap is set, circuit A will have less resistance than circuit B, and thus short circuit the light. When the trap goes off, circuit A will break, and B will then be the only path for the electricity thus lighting up the LED.

Questions: How do I calculate out what resistors to use? In terms of power, how do I decide on 9V? 5V? 1.5V?

DrDamnit
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    There are literally hundreds of questions about how to calculate a resistor for a led. Use the "search" function. – Eugene Sh. Aug 08 '17 at 14:14
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    Why don't you just use the trap itself as a switch to close the circuit to the LED. So the battery isn't providing any power while the LED is off and the trap unactivated, then once the trap is activated, it closes the switch and provides power to your LED and resistor circuit? Battery will last much longer that way... – MrPhooky Aug 08 '17 at 14:15
  • Rat traps are extremely violent. I am not confident the switch will actually close. Especially if there is a dead rat in there. – DrDamnit Aug 08 '17 at 14:17
  • @EugeneSh. I did search, but my terms weren't good because I'm a neophyte here. I appreciate you finding that one, and I'll delete this question in favor of the one you posted. – DrDamnit Aug 08 '17 at 14:18
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    With the comment about the switch not closing - if you don't want to use something like a microswitch a bit of steel wool should work well to close the circuit without interfering with the travel. – PeterJ Aug 08 '17 at 14:22
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    Better use a LED to show when the trap is set. If the LED does not light, it can mean two things: Either you forgot to set the trap, or the trap is sprung. In either case, a lit LED will mean that everything is OK, and a dark LED means that you need to check on your trap. – Dampmaskin Aug 08 '17 at 14:28
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    Best solution for the mouse - throw a cat up in the attic : 10 minutes of WWIII and sorted, and yes I have done this - it works a treat... – Solar Mike Aug 08 '17 at 14:28
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    Cats are unreliable devices, and not all of them work as advertised. – Dampmaskin Aug 08 '17 at 14:29
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    don't get the "Garfield" type - farm mousers are the best... – Solar Mike Aug 08 '17 at 14:30
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    @DrDamnit: You don't need to delete the question as your application is odd enough that someone else will find it, the redirect and the both sensible and amusing comments useful. – Transistor Aug 08 '17 at 14:47

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