New pinpointer

   I'm still looking for that old radio. I wound a coil 350uH on a piece of ferrite then the darn thing fell and broke in half so I placed the two pieces on top of one another as it was only 6mm by 8mm thick and wound another coil but it will only detect a coin at 1in my BFO probe use to detect the same coin at 3in also using a piece of ferrite (small). I must get it to work is there a specific thickness for that ferrite rod?

Regards Xavier



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Xavier

Hi GD

I was under the impression that the ferrite rod had to be about 10mm in diameter and that detection would be more than 1in so what detection distance should I expect?  that ferrite rod that I stupidly broke came from one of them pocket radios but was rather thin a bit like a pencil.

Regards Xavier 

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Xavier

		Quote:			Posted by xavier
	Hi GD I was under the impression that the ferrite rod had to be about 10mm in diameter and that detection would be more than 1in so what detection distance should I expect?  that ferrite rod that I stupidly broke came from one of them pocket radios but was rather thin a bit like a pencil. Regards Xavier

The size of the coil determines the size of the field maximum. There are limits to how big a field can get based on the diameter of the entire coil irrespective of the ferrite rod. Take the same number of windings on a plastic core (which is the same as an air core) and you will have a radically different inductance value. The ferrite rod focuses the field into a flattened toroid around the coil body with the ferrite being the center plane. With an air coil of the same dimensions, the field shape is larger in the side dimension.

I would expect an absolute maximum of 2 inches from the coil end. Don't forget, if the coil is too close to the PC board, the metal in the parts will attenuate the field making your distances even shorter. This is why I recommend a 10 inch piece of coax for distance.

Because the Surf PI uses 8 AA batteries and the PC board is long, I don't really believe it will be a practical pinpointer but the smaller coil will help to troubleshoot the building of the device.

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ApBerg and I have been playing with the surf Pi as a pinpointer
with various ferrite coils, single, 3 pieces of ferrite bound together, we cannot get beyond 10cm
6-10cm is easy with almost all coils

It is not ideal, as stated above, with 8 x AA and the board in 32mm tubing it is a bit on the large side

A new battery solution is required to reduce the size - suggestions ?

I'm am working with someone on a surf pi SMD board - watch this space
first draft is 150x15mm

A long way off yet but anyone with smd knowledge is welcome to join in the project



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I have a piece of ferrite approx 60mm x 10mm - 22swg copper wire wound until approx 300uH, sorry can't remember the no. of turns
Although I have made a few - shorter ferrite, litz wire, 26swg - all should give 6-10cm if adjusted ok


It is ok as pinpointer and better than my current commercial one for distance, but not ideal - a bit big and as a motion detector sometimes when searching the sides of a hole a non motion would be better

Lets not forget this is a normal detector and best with a 8-10 inch coil - pinpointing is a by product

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