Re: [mowbot] Buried cable

Dave Everett (deverett nospam at
Mon, 04 Aug 1997 19:00:13 +1000

At 08:31 PM 8/1/97 -0500, you wrote:
> I'm sorry the message keeps getting lost. Its cuts off right
>before the stuff I write, so maybe if I do a straight compose you'll see
>the whole thing. Anyway you mentioned finding some info on these things
>on the net. I was asking if you could post the net addresses for us.
>Hope this one gets through

It did :-)

Here are 2 sites I found that sell pet containment systems.

Both describe there systems enough to show they could be adapted for this
type of application.

I have started developing my own, but I have very limited experience in

The first experiment used a standard aerial rod as is found in cheap pocket
AM radios, the rods, consisting of a ferrite rod with 2 coils wound on it
are available from most electronics stores here.

I did some coarse experiments with a .01uf and a 60-160pf trimmer and
determined that an 82pf and a 5-30pf trimmer in parallel with the coil
would give me about .5v P-P when the coil was placed on the boundary wire
(the boundary wire is about 5 metres in this experiment, I am using a
550khz sine to drive a 5w line transformer.) The problem with this is that
the best pickup is with the ferrite cutting across the boundary wire, when
the coil is inline with the boundary wire the signal is not very good.
Since the robot might find the wire at any angle it is important for the
deflection to be uniform.

I have just started some new experiments using a standard former with a
ferrite core and a base that allows the coil to hang downward, thus keeping
the coil orientation the same no matter what angle the robot might engage
the boundary. The response is far from satisfactory yet, I get about 60mv
at the closest position, however I have been able to drop the freq of the
boundary wire down to 88khz and hopefully I will be able to drop it further.

Dave Everett.