Define perimeter with underground RF signal - Page 1
Forum section: electronics / beginners

author: mattruwe
author_rank: Newbie
timestamp: August 22, 2015, 03:25:20 am
content: I would like to setup a perimeter to define the area that a robot is allowed to travel inside of. This will be outside in an odd shaped "fence" and I need accuracy down to about 1-2 feet (30-60 cm). Given these requirements, I don't think GPS will allow me to reliably achieve my goal, but if someone thinks otherwise, I'm certainly open to that idea.Instead I'm thinking that an underground wire that transmits on a very low power/frequency (e.g. in the kilohertz range) and a receiver on the robot that can detect this signal at the appropriate distance would be a good solution. This is basically the same idea as an invisible fence for a pet. My problem is that I don't know much about how to build the transmitter / receiver combo and everywhere I look I see people saying that it's a very difficult thing to do and that other solutions should be tried. I get that it might be hard to do, but I don't want that to stop me. This (http://www.philohome.com/sensors/filoguide.htm) is basically what I'm looking to do, but I'm not sure how to scale / change that solution to a defines a perimeter around a ~8,000 square foot area.I'm looking for one or more of the following:a) a nudge in the right direction to help me understand what I need to dob) suggestions on books to read that can help me get started in the RF space. My current level is a hobbyist who understand the basic principals of how RF works but I need to go deeper. I don't have any practical experience building RF devicesc) a prebuilt device that could accomplish the same goal - although I prefer not a hack an invisible fence dog collar since that feels kind of like cheating to me. Ultimately, having something that is capable of delivering an electrical shock isn't something I want as a part of my solution.d) suggestions on tools that I will need to learn and build this solution (e.g. should I invest in a spectrum analyzer etc?). I already have a fairly basic Oscilloscope, is that enough?e) other items that I should be thinking about but don't know to ask aboutThanks!

author: Richard Crowley
author_rank: Super Contributor
timestamp: August 22, 2015, 03:37:27 am
content: That scheme is rather popular for containing pets without building a fence.https://en.wikipedia.org/wiki/Pet_fenceThe technology is already developed and available off-the-shelf.It would be trivial to adapt it to use with a robot.Simply connect the pet-collar receiver to your robot control circuit.

author: mattruwe
author_rank: Newbie
timestamp: August 22, 2015, 03:52:31 am
content: Thanks for your response, and I agree that hacking a dog collar wouldn't be too bad, but I would really like to understand how to build something using more discrete components than a fully functional dog collar. Also, the shocking components are something that I'd really like to avoid. I'm not suggesting that I need to fully understand the RF principles behind what I'm building (although I'm certainly not opposed to learning them), but I would like to gain some level of RF understanding in the process.

author: Richard Crowley
author_rank: Super Contributor
timestamp: August 22, 2015, 07:35:56 am
content: The principles are very basic. But the practice of implementing RF circuits is NOT beginner territory. Learning about RF is a major project itself that could completely eclipse your robot project.You need only the receiver part of the dog collar, you can discard the shocking components. If you attempt to make a working receiver from scratch, you may never get to your robot.

author: mattruwe
author_rank: Newbie
timestamp: August 22, 2015, 11:33:32 am
content: Quote from: Richard Crowley on August 22, 2015, 07:35:56 amThis is 100% consistent with the messaging I've received from others. Iunderstandandbelieveyou, but I'm willing to take the time to learn. In my mind the robot is an application I can use to learn about RF. It's a simple application of RF that doesn't even require modulation. It's low power, low frequency. Is there another better way to learn about RF?I've learned enough difficult things in my life to understand that when you don't know about something you have more confidence that you'll be able to learn it. Whereas after learning months or years later you realize that if you had known what it would take that you might never have started down the path. I have an advantage by not knowing what I need to know. I just want to take it one step at a time.Even a journey of 1,000 miles has to begin with a single step. Who will help me prepare for my journey and take the first steps?

author: Richard Crowley
author_rank: Super Contributor
timestamp: August 22, 2015, 01:34:43 pm
content: Certainly, go for it. You don't need our permission. If I were doing it, I would at least start out by finding what frequency they use. Unless you want to completely re-invent the wheel.A quick Google revealed this anecdote which seems to indicate that they are using AM broadcast band frequencies, in this case 600 KHz...http://www.instructables.com/id/How-to-find-a-break-in-an-invisible-dog-fence/That doesn't seem like a very good idea to me, but I'm not going to argue with success.

author: amyk
author_rank: Super Contributor
timestamp: August 22, 2015, 01:46:32 pm
content: A similar mechanism is used to prevent shopping carts from leaving the vicinity of the store.http://hackaday.com/2011/02/28/reverse-engineering-shopping-cart-security/