Secret metal detector

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Surprisingly there are quite a lot of places in the world where metal detecting is not allowed. Even if you lose an item while on the beach or playing some sort of sport. Metal detecting is banned. Its not only places you would expect, ruled by oppressive regimes either. Quite a lot of modern European places ban metal detecting. Like Ireland or Portugal to name just two.

Using these plans will enable you at very low cost to build a concealed metal detector that could be abandoned or discarded if it were about to be discovered. At no great expense to the user.

The walking stick above was purchased by me from Ebay for £9 including post. And would be available most places where they have Ebay/Paypal etc. It is of excellent quality and made in China as you would expect.

To build this detector you will need to make a very narrow circuit board 100mm long by 20mm wide. You can print out the artwork I will supply, but you may have to adjust it some way to get the exact size ( does not have to be to exact actually) just have to fit inside the main tube. You could make a board using copper clad board and drawing the artwork with a fine tipped brush and paint. Or reproduce the artwork using pre sensitive copper clad board and etching with Ferric Chloride. All depends what facilities you have. You could also use strip board.

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With the board made correctly you will be able to read the word "SAXON" on the surface. Also note the two cut outs carefully filed on the edges to take the reference coil windings.

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After removing a metal plate and screws I unscrewed the foot from the walking stick. Then I drilled a small hole so that I could pass through from the inside the .25mm enameled copper wire and wound on 14 turns. This is the search coil and is about 9cm diameter. Other makes of walking stick may vary in size. The bigger the better. This coil oscillated at about 105 khz .5 volt p to p.

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The reference coil; is wound directly on to the circuit board and is tuned by a brass olive sliding on the outside of the main plastic tube, The reference coil here in made from 80 turns .25 enameled copper wire, and oscillates at about 103 khz. This increases to about 108 khz as the olive is moved over the coil.

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