So, I'm looking to build an autonomous robot of a sort and want to know what sensors / MCU packages would be good for dealing with lined boundaries?

These would be similar to how dog collars work. Lay a ground line beneath the ground, power it up, and use a sensor (magnet?) of some sort to detect the boundary.

Another way could be to use wireless beaming of a kind (above ground) but would have to work without LOS (Line of Sight).

What are my options? Any suggestions would be helpful too.

Some options explored or being thought about:

Hall effect sensor:
What is a low voltage (approx 5v) hall sensor that could detect up to 8". I came across: A3144 but spec says it's a discontinued product since 2005.

Inductive sensor.
The few that I could find were around $3 but could only provide up to about 4mm of distance.

AM radio and receiver:
After more research perhaps the best way to go about this would be using a similar setup of how dog collars work. From what I understand the ground line basically acts as a small AM frequency antenna and the receiver (on the bot) picks up that signal when it gets close. By fine tuning the power going to the antenna / receiver, you can have a fairly accurate type of boundary system.

Now only to find what kind of MCU/receiver would be best for the job.

Another part of the problem that I forgot to mention is that there will be a 9DOF MPU-9150 package onboard (or something similar, Perhaps GY-271 HMC5883L). How will the magnetic field affect this? I imagine it's possible to fine tune the ground boundary wire to output as minimal of a field as possible.

  • \$\begingroup\$ I'm guessing UV-phosphorescent paint would be out? \$\endgroup\$ Commented Aug 16, 2013 at 19:23
  • \$\begingroup\$ Yes, this would mostly be an embedded system behind plastic with the boundary line being beneath the surface. \$\endgroup\$ Commented Aug 16, 2013 at 19:35
  • \$\begingroup\$ what about going the other way: Putting some sensor in the floor (e.g. a capacity sensor) and sending the signal via rc to the µC, when the sensor recognized a change? \$\endgroup\$
    – Tobi
    Commented Apr 14, 2014 at 23:22
  • \$\begingroup\$ One of the bigger reasons of why I don't want to put the sensor in the "floor" is because I'd have to make many modifications to the project. One being that I'd like to use the same mechanism for two of my projects, one being indoor - the other being outdoor. ;) \$\endgroup\$ Commented Apr 15, 2014 at 20:29
  • 1
    \$\begingroup\$ I can't post an answer because of the protection, but this might be valuable for anyone coming here in the future: RobotShop now has kits with perimeter signal generator and sensor. robotshop.com/community/blog/show/… \$\endgroup\$ Commented Dec 20, 2018 at 15:08

1 Answer 1


A few suggestions:

Lets assume that there is only a wire/ metal strip buried beneath the ground (not very deep) as the 'invisible' boundary.

(1) The wire/strip has a direct current passing through it.

You could detect the magnetic field around the wire with a Hall sensor.

(2) The wire/strip has a low frequency alternating current.

Hall sensor or pick up coil (detecting AC 'hum')

(3) The wire/strip has a high frequency alternating current

Tuned LC circuit - probably with a ferrite rod to localize signal.

(4) The wire/strip is carrying a pulse signal (e.g. output of a square wave generator)

as per solution (3) but doesn't need to be tuned (detects wideband 'noise') - similar to electric cable detector in walls.

(5) The wire/strip is not connected to anything

Some form of metal detector.

  • \$\begingroup\$ All very valid ideas. Hmm. Seeing as how I'd eventually like the boundary line to be solar panel driven or battery - I'd like to stick to DC current. So looks like I'll be doing more research into hall sensors. \$\endgroup\$ Commented Aug 16, 2013 at 19:50
  • \$\begingroup\$ Battery means alternating current, unless you want to drain the battery quickly (via a modified "Joule Thief"). \$\endgroup\$ Commented Aug 16, 2013 at 19:56
  • \$\begingroup\$ As far as I know, batteries provide DC current. Unless you mean the discharge rate of the battery, which would need to be addressed obviously. Probably with a DC-to-AC converter, but then the hall effect sensor is out. \$\endgroup\$ Commented Aug 16, 2013 at 19:58
  • \$\begingroup\$ Batteries provide DC, but if you oscillate the DC you get DC-biased AC. \$\endgroup\$ Commented Aug 16, 2013 at 20:00
  • \$\begingroup\$ That's what I thought you meant. As of this moment, running the ground boundary line off batteries isn't the priority. \$\endgroup\$ Commented Aug 16, 2013 at 20:01

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