I am very curious how to disrupt an induction loop, much like the ones used at traffic lights. I understand that they detect current changes that occur when a conductor enters the induction field, such as when a large axle enters the field. I seek a portable method of disrupting the field thus triggering the device that monitors the field (so carrying around a large axle to a ford F150 in my back pocket is kind of out of the question ). I have read that using strong rare earth metal magnets can disrupt the field, but it seems that using a magnet to disrupt a magnetic field will not work and is just a myth. I was thinking more along the lines of using a battery powered oscilloscope connected to a circuit to detect the field, then using that info to build a counter field to disrupt the existing on which should set off the trigger. Any ideas? Is it possible to build such a small circuit that I can transport and use at will? Is it versatile, i feel like my idea will only create a method of disrupting one specific field.

2/14/2009 10:15:15 AM

http://www.thelightchanger.com/

2/14/2009 10:24:35 AM

all you need is a strong electromagnet

2/14/2009 11:31:01 AM

I initially attempted to disrupt the field using 3 HDD magnets; no luck. How much stronger of a magnet would I need?

2/14/2009 1:10:13 PM

I'm guessing it's an RF oscillator that is triggered by the detuning of the tank when a metal is in the coil of the inductor

I believe you'd need an alternating magnetic field on the close order of the frequency of the oscillator and in anti-phase, as a constant magnetic field would have a net 0 effect and in-phase would detune it in the wrong direction

however, you could probably use a loop placed near the inductor, causing it to act as a transformer with a shorted turn

2/14/2009 2:01:58 PM

actually the rare earth magnets work great, as well as technique on a motorcycle, you gotta go at an angle to the light a cross the field twice, works every time

2/14/2009 8:58:11 PM

magnets work great.

2/14/2009 9:37:23 PM

well ok a moving magnet would probably work too

2/15/2009 12:24:20 AM

So today i tried to use a 4x2x2 N50 neodymium magnet. I ran over the loop in every way possible; traced the perimeter and crossed in and out of the bounded area. This magnet has a pulling power of over 250 lbs and it would not disrupt the loop. I even pulled my golf clubs out of the car, laid them across the loop, then ran the magnet across the ground. Nothing has worked. How can i disrupt this loop?

Would wrapping the magnet in wire and hooking it to a battery make an electromagnet? If so, how should I wrap the wire to increase the pre-existing field; parallel to the magnetic face or perpendicular/over the face.


[Edited on February 25, 2009 at 10:48 PM. Reason : q]

2/25/2009 10:32:12 PM

how do you make a rare-earth magnet into an electro-magnet? I thought the whole point of electro magnets is that they didn't require magnetic material, per se, but just some plain old metal, wire, and electricity?

Would an electro-magnet made out of a rare-earth magnet be more powerful than one made out of metal/wire?

2/25/2009 10:38:22 PM

I'm not sure; I'm wondering the same thing. I seem to remember reading that you can use a "soft", or nonmagnetic core, or a "hard", magnetic, core.

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

^ it will actually make the device a transformer or inductor.

[Edited on February 25, 2009 at 10:52 PM. Reason : q]

2/25/2009 10:50:31 PM

^^ you still need a ferrous material to use as the core of the electromagnet

2/25/2009 11:00:51 PM

so by me turning the magnet into an inductor, I would actually need to design it such that the field created by my inductor is in anti-phase with the one I want to disrupt. How would I accomplish this task?

2/25/2009 11:05:33 PM

lol did you try using a shorted loop of wire? it'd be a lot easier if it worked

also, the magnet isn't being turned into an inductor. there's already an inductor in the ground, that's what the induction loop is. a capacitor, an inductor, a frequency detector, and some logic to switch the output on or off based on the frequency of the oscillation between the capacitor and inductor. to trigger the logic, you need to change the resonant frequency of the LC oscillator. this is why a permanent magnet shouldn't work as I understand it, unless it was perhaps fired from a bullet. over a full cycle of the AC wave, the net effect of the constant magnetic field is 0.

it seems that usually the metal of a vehicle magnetically couples with the coil of the inductor to increase the inductance and shift the resonant frequency of the LC oscillator lower. I suspect that you can detune in the other direction and still trigger the sensor, without the mass of a vehicle, by introducing a shorted turn to reduce the inductance and raise the resonant frequency.

2/26/2009 3:14:28 AM

my electronics knowledge is very limited. How can I construct and introduce this shorted wire you speak of?

2/26/2009 5:50:05 PM

well... start with a loop of wire



strip the ends and twist them together. you now have a single shorted turn

2/26/2009 6:11:28 PM

so you think me hovering a loop of wire over the detector in the ground will trigger it, because it sounds like you want me to introduce the loop physically to the inductance loop? Physically shorting the loop is not possible b/c it is buried underground. I'll try it, but it seems too easy.

also, Do i need to introduce any power source to the loop?


[Edited on February 26, 2009 at 6:19 PM. Reason : q]

2/26/2009 6:15:44 PM

you shouldn't need any power source, and yes I suspect that'll be adequate.

what I'm proposing is not to short the buried loop directly, but kind of indirectly. placing the shorted loop near the induction loop should should cause the shorted loop to act as the secondary winding of an air-core transformer, with the induction loop itself being the primary winding.

I really don't know if it'll work, but it's worth a shot

2/26/2009 9:12:10 PM

ok, I'll try it tomorrow. What gauge wire do you recommend and what length of wire should I use to make the loop?

[Edited on February 26, 2009 at 9:49 PM. Reason : q]

2/26/2009 9:48:07 PM

whatever's laying around, lower gauge is probably better but not necessary. 14 gauge would be a good value, I guess?

2/26/2009 9:51:57 PM

congratulations, you were correct. Thank you!

2/27/2009 10:51:47 PM

wow, i'm surprised that a single coil is all it took

2/28/2009 12:56:07 AM

1$ for the part

10,000$ to tell you were to put it

3/1/2009 5:04:14 PM