Re: Inductive Loops

"jc" <jack@xxxxxxxxx> wrote:
I have been looking for a circuit to build an inductive loop, that is
easily installed like the 'electronic dog fence' things, around my
yard. I also need a corresponding sensor to keep my 'bot in the yard.

Any idea where I can find such a circuit?

I know that the Friendly Robotics mowers use this technology.

I also remember YEARS (like in the 1960's) an article in Mechanics
Illustrated or some such to put a coil around your living room then
have wireless headphones to listed to your TV or whatever.

Thanks ... JC

I could be wrong, but I suspect those systems are nothing but standard
radio transmitters and receivers. They are just tuned to activate only
when the signal is strong enough - which only happens when you are within a
foot or two of the transmitting wire. Signal strength goes up
exponentially as you get closer to the transmitter so it's simple to pick a
level that will allow you to detect distance to the transmitter when you
are close to the antenna.

You can probably make it work by using nearly any radio transmitter and
receiver set with the correct power levels. I don't think you would need
any type of fancy antenna or anything. The simplest would just be a
constant wave transmitter, and a receiver that outputs an analog voltage
relative to the power level received - a simple L/C tuned circuit with a
diode and filter capacitor might be all you need (no power needed for the
receiver - like a crystal radio - you won't even need an antenna). Run
that to an A/D input on your robot and calibrate it for the effect you
want. Something along that level of complexity I would guess should work
fine to keep the bot in the yard. Plus, with the A/D, you get a signal
strength reading that lets you know how close you are to the wire and
whether you are getting closer to it or moving away. That might help you
write code to correctly stay away from the wire.

If you just search for science fair circuits for a simple radio transmitter
and receiver you can probably find something that work.

I can't say I've tried this, so it might not work as well I would suspect,
but it wouldn't cost much to build a very cheap circuit and try it.

--
Curt Welch http://CurtWelch.Com/
curt@xxxxxxxx http://NewsReader.Com/
.

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