Boundry/buried wire sensing

Have any of you been successful in building a boundary/buried wire detection system? I am thinking like the dog perimeter fences. Were the dog wears a
collar and when he approaches the buried wire it beeps. I know RoboMow uses this in the robot lawn mower to keep it in the yard. I would like to build one for my lawn mower robot.
Thanks for any ideas.
Tim
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detection
a
uses
build one

I haven't done it, but I imagine one technique would be to excite the underground wire with a particular AC frequency and make it radiate. The robot detects it, or maybe a harmonic of the frequency. The detected signal strength indicates how far from the wire you are. Or modulate the signal on the wire and demodulate in the robot.
Buy one of the dog collars and take it apart to see how it works. Maybe you can adapt it for use it on your mower.
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Trkeenan wrote:

Check out http://www.betuwe.net/~mowbot/Mowing/New_UDO_5/Electronics_UDO_5/electronics_udo_5.html
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