Perimeter alarm ideas ...
Beau Schwabe
Posts: 6,566
So we are about to move to a new house that sits on 10 Acres of land and I was curious for ideas on a perimeter alarm.
One method I thought of was to have a single loop wire that would "look" like a conventional electric fence, but instead of putting high voltage on the wire I would treat it as an inductor. A person touching the wire would act like a capacitor to ground and you could perhaps detect where along the perimeter of the fence it was being touched. <-- I need to test this theory, but I was wondering if there were any other ideas someone else might have.
BTW) That's about 4 thousand feet of fence wire to make the perimeter.
One method I thought of was to have a single loop wire that would "look" like a conventional electric fence, but instead of putting high voltage on the wire I would treat it as an inductor. A person touching the wire would act like a capacitor to ground and you could perhaps detect where along the perimeter of the fence it was being touched. <-- I need to test this theory, but I was wondering if there were any other ideas someone else might have.
BTW) That's about 4 thousand feet of fence wire to make the perimeter.
Comments
In my opinion, 4000' is a lot of wire for a touch sensor and will be costly.
How about a similar idea to what I had about the peeping tom catcher, with make or break circuits?
Let's say that you place various wireless reporting stations around the perimeter, with each of these stations monitoring two make or break circuits. Now picture each make or break circuit similar to the insertion contact of a barrel connector (basically just a spring that makes contact against the edge of a barrel). All you would need is the contacts (springs) and plungers (barrel). A pair of plungers being tethered by 50-100 lb transparent fishing line, with the fishing line being supported by eyelets around the perimeter on stakes.
The plungers make the various circuit checkpoints, but when enough force is put against the fishing line, a plunger is extracted from the contacts of a checkpoint, thus breaking the supervisory circuit.
Well, when I say "last thing" I did actually deliberately touch an electric fence when I was about nine years old. One has to try these things right? When my arm flew backwards violently, having never been shocked before, my immediate thought was that one of my friends behind me had hit me in the shoulder with a cricket bat or some such. Took me a few seconds to realize that was an electric shock!
I hope you have no high voltage power lines overhead. On a friends farm they used to run a long electric fence cable down the middle of a field with no "ticker" box driving it. The overhead power cables induced quite enough power into that cable to keep the cows from wanting to go near it.
Lol, people have been fined for stealing power in a similar fashion.
In this case though I don't think the power company would want to go to court and have to explain how they are forcing dangerously high voltages into the farmers perfectly legitimate cow fence. The power consumption was of course tiny.
Anyway, point was that 4000ft of wire, insulated from the ground, makes a great antenna and can pick up all kind of things.
swamp everything I think.
You might be able to use time-domain reflectometry though, if very persistent and determined.
Use two parallel strands of wire, about 6 inches apart, which will act as a transmission line. In fact
send out two of these that meet at the far corner of the property, so only 2000' long, and terminate
each with the right resistance (typically 600 to 1k ohms depending on geometry of cross section
of the twin wire.
Keep the wires both well away from the ground or other conductors. Send 20ns balanced pulses
down each set and look for reflected signals. Someone climbing the wire will cause a small disturbance
in the relevant part of the reflected signal, but it will be a bit like tuning a LIGO sensor to get this
to work!!
More sensibly run a wire at 50V or so and monitor leakage current to ground - if its not raining
this will probably spot someone (but you'll have to bandwidth limit to avoid all the noise and hope
they elect to touch it rather than ignore it).
I think its a great excuse to build a patrol robot!
I was thinking more along the lines of a transmission line with proper termination at each end and where a known capacitor value was dropped to ground every so many feet. ... burning laser is probably not going to happen, sorry erco.
That's too easy. Put a box near your gate with some GPS-enabled cell phones that you can track, and a sign that says, "Take one." Then when someone grabs one and crosses into your property, you'll know exactly where they are! Plus, if instead they try to abscond with a phone, you can track them down and retrieve it.
Please email me your mailing address so I can invoice you for my minimum consulting fee.
Thanks,
-Phil
Fine, so we're back to a patrol bot.
"I guess your not covering the whole 10 acre perimeter since 10 acres is 435,600 square feet... "
...No that's the entire perimeter... think of a rectangle 330x1320 ... the Area is 435600, however the perimeter is 330x2 + 1320x2 = 3300 ... 4000 was figured for overage.
Field-dropper caps is sounding complicated.
To have contact changes measurable, you probably want lowest overall C.
I think there are commercial Electric Fence designs that use Time Domain Reflectometer measurements, for fence failure isolation (usually growth, or damage).
You could use both - alternate between resonant-loop check, where frequency can measure to ppm levels, for highest sensitivity, and maybe a TDR, to isolate where.
What is the terrain and vegetation like, and what intrusion type exactly are you looking for ?
Cameras are hard to beat, and they give important recorded information.
Set them up carefully enough, and you can capture nocturnal animals, which are probably more frequent and interesting than intruders anyway
Or, how about going "old style" and using one of those cattle fence 10,000V chargers?
Ken Gracey
As far as "old-style" it is a log-cabin :-) I have in the past made an electric fence charger for a friend of mine several years ago that had 1 mile of fence. The commercial units were too wimpy at that distance so I found a circuit that used 120VAC to drive a cheap 12V automotive coil that did the trick.... without a load (the 1 mile of fence) the Automotive coil would arc 3-inches out of the top of the coil and to the side of the case. With the load of the fence, the arcs were about 1/4 inch with his particular setup. I think he had about 10 Acres also, but the perimeter cut in a few times, making the linear feet of required fence longer.
http://www.bscircuitdesigns.com/Misc/House1.jpg
http://www.bscircuitdesigns.com/Misc/House2.jpg
On my brother-in-laws property he has sheep, alpaca and horses. He has chickens although they are restricted, and of course the farmers pest... the foxes. I don't know how you would manage those animals touching the fence. The animals are always pushing against his fence causing a maintenance nightmare. Fortunately he only has about 10 acres. Pity those farmers with millions of acres!
We have ducks ...
http://www.bscircuitdesigns.com/Misc/Duck.jpg
... and potentially a couple of horses.
The BIG picture with lots of ambition in my mind, one day I will own one of those million acre farms. This is just a stepping stone to get there. Now I have a "playground" that is conducive to design and express one of my biggest dreams, I can finally get started.
I have a similar issue, albeit on a much smaller scale.
1.4 acres, 95x650
I am planning on setting up a solar farm in the back if it works economically.
At a minimum, a decent 120-150w panel with some DIY New-Edison batteries
(http://www.earthineer.com/blog/29533/the-idiot-edison-battery-diy)
using cheap PIR sensors (http://www.eastmachinery.com/product/wired-wideangle-wall-mouted-passive-pir-detector-ls8183_12555.html?pay=usd&state=US&gclid=CPDAsL6w_ssCFcNahgodviAGIw)
Probably throw an ESP8266 on each one to signal a remote camera to start videoing the deer by the pond or the odd arch nemesis...
OR, I'd think of something more along the line of a simple mesh thing.
Run thin wire for power in a shallow trench around the perimeter.
Have LOS posts with an ESP8266, IR receiver and laser diode.
Each post reads the laser from the previous post, and laser it next upstream neighbor.
When a post detects lost laser on its receiver, it ping Master Control that something has intruded or exfiltrated.
Topic was labeled perimeter alarm, not control.