Getting my robot to stay in a specific area (Buried cable)

eyyYo

Hello! I have built and programmed my robot. I have built it from scratch and everything (kinda proud, since its my first project). Now i wounder how i can make it stay in a specific area. My plan is to bury a cable (12V or something going through), and get the robot to sence if its near this cable, and then turn. Now, im completely lost on how to do this "sensing"-part. Any ideas from someone that have done it?

Thanks in advance.

D Faust

Have you looked at how electric dog fences work?

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eyyYo

ah, of course.. didnt think of that [noparse]:)[/noparse] im going to the store on monday and getting one, so i can take a better look at it [noparse]:)[/noparse]

eyyYo

Unfortunately, i havent been able to find any good documentation about how electric dog fences work If anyone can help me here, i would greatly appreciate it!

Thanks

kjennejohn

A quick Google using "dog fence" found an article about containing rambunctious dogs. Here is the relevant part:
QUOTE:
An invisible dog fence is also an option to inexpensively contain dogs in a very large area, often up to 25 acres. A wire is buried 3 inches underground and attached in a loop to the transmitter for the fencing system. The electric dog fence is completed with a receiver collar properly fitted to your dog. The collar then receives signals from the wire underground and warns and/or corrects your dog as it approaches the defined boundaries.
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There is nothing about frequency or power level. I think should think a signal of a few milliwatts through a cable lying on the surface would do it. If you bury the cable you will have to increase the power output, of course.
Perhaps you could use a broad colored line to keep your bot corralled. Use an optical sensor with a glass or plastic filter "tuned" to that color to force the bot to turn away.

FWIW,
kenjj

eyyYo

Yes, i know that power creates a magnetic field. I will simply start from scratch, reinvent the wheel, if you know what i mean [noparse]:)[/noparse] Much more fun, learning more [noparse]:)[/noparse] I will start with a cable (24V), and a coil, and some meassure devices (osciloscope is one of them), and research a bit [noparse]:)[/noparse] Thanks for the answers, i will post anything i discover here, in case anyone else is doing/going to do the same thing.

eyyYo

Okey, now i know that the coil "produces" power, when its near the cable (induction). Now, is there a component avalible for the stamp, that sends like pulses or something to a pin, when a magnetic field is in range? [noparse]:)[/noparse] I wounder about sending the power to the cable in pulses, like power on in 4 ms, power off in 16 ms, power on in 4 ms, and so on. And then check with the stamp if the magnetic field occurs in 4 ms, then is off in 16 ms, you know what i mean. Is this easy to do?

Thanks

D Faust

Hall Effect sensor?

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eyyYo

Isnt hall-effect sensors creating their own magnetic fields, and detecting rotation on axes? I want something that detects the magnetic field [noparse]:)[/noparse] Sorry if im wrong.

Thanks.

D Faust

A hall effect sensor senses a magnetic field (pretty sure).· Many people mount a magnet to a rotating object so that the magnet will pass by the sensor and use it as an encoder·(positive)· Do a wikipedia search on hall effect or hall effect sensor.

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eyyYo

Oh darn, now i feel stupid >.< Thank you very much for the help, i appreciate it! [noparse]:)[/noparse]

Dgswaner

I'm kinda just taking a wild stab here I have no background with this... but how about measuring the Voltage produced by a coil passing by the line guessing it's minimal. Then find a transistor or optoisolater that will work with the measured voltage. Setting a pin high when voltage is produced.

Added:

Somebody said...
I think should think a signal of a few milliwatts through a cable lying on the surface would do it. If you bury the cable you will have to increase the power output, of course.

Mythbusters did a test about stealing power by putting a coil next to a power line, and it was supposedly enough to power a house. in actuality it was barely detectable. I think it will need to be quite the opposite, I think you'll want to power the line with a high voltage source. (low amperage). you are essentially making a Transformer (as I understand it) which would also mean that you would need to use AC Voltage.

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A complex design is the sign of an inferior designer. - Jamie Hyneman, Myth Buster

Post Edited (Dgswaner) : 10/8/2007 8:56:11 PM GMT

crgwbr

You would basically be building a transformer. This means you need to run AC power (try household 120v) through the underground coil. Then, the coil on your robot, will (hopefully) produce a small AC voltage when near the underground coil. You should be able to then run this voltage through a bridge rectifier, across a couple small caps, and into the LED side of an opto-isolater. I'm sure you can figure out the rest.

Regards,
Craig

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