The ones I am familiar with work primarily on physical effects. Its
like comparing the effect of a metallic object in an resonant
(oscillator) circuit. One coin is placed in a reference coil, and its
characteristics are learned (how much this coin changes the frequency
etc). The one to being tested falls through another coil; if its fall
causes effects identical (within limits) to the reference, the coin
is accepted. Most of the work is spent slowing the fall of the coin so
the effect can be carefully examined.

Having designed metal detectors in my youth (er.. day before yesterday)
I have always been fascinated by how they work so well.

US coins (like most coins) no longer have ANY precious metal, and in
order to obtain an effect similar to real coins, are layered with an inner
core of copper to more closely match the solid, precious-metal coins
they mimic.

Try looking up http://www.windtrax.com/featured_products/

--Bob


At 08:40 AM 7/29/2003 +0400, you wrote:
>Guys,
>has anybody good links to practical aspects of the
>coin-comparators design (schematic, theory etc.)?
>I googled, but didn't find anything.
>
>Thanks in advance.
>Mike.
>
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