Author Topic: EMF detector with substituted components not working; could it be the substituti  (Read 946 times)

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Offline seanspotatobusinessTopic starter

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I'm trying to cobble together an EMF detector to trace electrical wiring in a wall. I have a live wire detector but it's a POS. The circuit I'm attempting to improvise is below. I had to substitute a few components and it's not working; I'd like to know whether my substitutions are the reason. Can I use an LM158 instead of a LF351? I also substituted a 1.9 M resistor for the 2.2 M and a 220 uF capacitor for the 150 uF capacitor. I've no idea how suitable my chosen inductor is. It's all crammed together on a breadboard so it could also be a lose connection or a short circuit (obviously I've endeavoured to eliminate any). I've also used a ready-made audio amplifier instead of making one.



 

Online Andy Watson

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L1 appears to be a toroid (?), i.e. for all practical purposes it has a closed magnetic path - and therefore very little interaction with an external field.
 

Offline Brumby

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L1 appears to be a toroid (?), i.e. for all practical purposes it has a closed magnetic path - and therefore very little interaction with an external field.

Yes.  Your "detector coil" could not be any worse.

Imagine you have a slinky.  The magnetic path runs down the middle of the slinky.  If you have a slinky with nose to tail (like a donut), the magnetic path runs around in a circle, not interacting with the outside world very much.

What you need is a slinky just sitting flat - the way it came in the box - with two open ends.  The magnetic path runs through the middle of the slinky (just as before) but now has to turn around and wrap outside the slinky to get back to the other end - and this hugely interacts with the outside world.

In short, you need a flat coil (a very short slinky).
 

Offline seanspotatobusinessTopic starter

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Thanks very much. I've replaced the coil but it still doesn't seem to work. I tried putting the coil next to a CFL lamp cable and next to a 2.5 mW Bluetooth amplifier. Could I connect the coil leads to something to test if that gives a signal?

 


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