> The gizmo described in that Si-chip article used a hand-
> wound sensor coil, so not really practical. Basically, it was
> a metal detector cct like you go after nuggets with

As they say in the article, the coil is thousands of fine turns
on a soft iron core and impractical to wind youself, so it's
supplied ready-made with the kit. The difference between
what SC did and a metal detector is that their coil is passive,
and relies on the disturbance of the Earth's magnetic field
to cause voltage in the coil. They call it a low-power system
(70mA, though I can see room for improvement in the circuit)
but I've no idea how that compares with a typical metal
detector

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