Subject:
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Re: Land mine robot
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Newsgroups:
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lugnet.robotics
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Date:
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Wed, 15 Jan 2003 11:59:08 GMT
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Original-From:
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PeterBalch <PETERBALCH@COMPUSERVE.COMnomorespam>
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Viewed:
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981 times
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Metal detectors are subtle things. Good ones can distinguish between an
aluminium ringpull and a gold coin; bad ones get confused by damp soil.
The simplest and cheapest design I've seen used a PIC12C508, a hand-wound
coil, a resistor and a couple of caps. On a good day, it can just see a
coin at 5cm. It uses the coil and a few pF cap as the resonator of the PICs
clock oscillator. Then it measures how long it takes to charge/discharge a
resistor/capacitor (a constant time). If the coil inductance changes
(because it's near metal) the oscillator changes freq and the number of
clock counts to charge/discharge the R/C changes. A simple program in the
PIC allows self-calibration and can produce a yes/no signal. All for a cost
of $2. There's a Microchip Application Note describing it with sample code
(try searching their web site www.microchip.com).
But why not just buy one of those devices that hardware shops sell for
finding nails in joists and gas pipes behind walls? Discounted, they're
$10-$20.
Peter
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