Re: [mowbot] Active borders.

Bug Hunter (bughuntr nospam at
Tue, 25 May 1999 11:17:24 -0500 (CDT)

if you send a 20khz tone down the line, it can be picked up by a wire
loop and an amplifier, with a filter set for 20khz.

Or, try getting a touch-tone generator (like from radio shack) and a
touch-tone receiver, and decode a button. If you get a "1", then you know
you are near a wire.

Another possibility is the metal detectors. They can detect wire buried


On Tue, 25 May 1999 adamdb nospam at wrote:

> Having recently joined this list, I am sure this subject has been
> discussed before, but I wasn't around to hear it.
> Does anyone have any schematics or references for an "active border"
> system? (You know, kind of like the invisible dog fence, only for my
> mowbot). I am building my mowbot with the intention of using grass
> sensors to try and stay in the uncut grass, but just in case I would also
> like an active border so I don't mow down the wife's garden by accident.
> As I understand the concept, some kind of wire or wires are buried around
> the perimeter of the lawn, an AC signal is injected into the wire, and
> the mowbot has some form of sensor that will detect this signal. I would
> like to do this as cheaply and simply as possible.
> Any ideas?