What's the science on this gadget?

I picked up a few Sidekicks from Ran for my Propointers. I might add that he is great to deal with and has published the details of the build for those so inclined. I am fascinated by what happens when I play with this little gizmo. I am not an induction engineer, a hysteresis head or even a magnet maven so I can't wrap my head around how a tiny planar coil is undetectable when open, but becomes detectable when shorted! Please explain the magic. Before I mounted it to the pointer I played a bit. That is, I turned on the Propointer, held the sidekick board at the tip and it was not detected. As soon as I hit the button to short the coil, and it was then detected. How did the pointer not sense the copper in the tiny coil until I shorted it?

P.S. - FWIW - I think it's a great little gadget. Very clever.

Thanks folks,

Pete

I know the answer, I hope I can explain it...
The open loop of copper wire is not detected simply because there isn't anywhere near enough of it (less than 0.1 gram / 1 grain) and it is in wire form which is harder to detect than a solid pellet would.
Pinpointers like the Propointer detect metals' presence because the metal absorbs energy from the oscillator in the probe. Specifically, the Garrett looks at the drop in oscillation strength. The sidekicks' loop of wire actually behaves like a secondary winding on a transformer, the primary being inside the pointer. Like any transformer, if you put a load on the secondary winding, you put a load on the primary. The 'load' can be a resistor, a filament bulb, or in the case of the Sidekick, it's the resistance of the shorted-out wire loop (probably less than 0.2 ohms). This is a heavy load, quite easily picked up by the pointer.
If you were to open up a pointer (not just a Garrett) you would see the probe tip is a ferrite rod, wound with dozens of turns of copper wire, and the description of it as the primary winding of a transformer makes more sense.



Edited 2 time(s). Last edit at 11/30/2012 09:50AM by Pimento.

Many thanks Pimento. I can sleep now!

Pete