Quick and dirty bear perimeter alarm

[Bob Gross]

"18vdc x 3 sirens = way hella loud"

You have to decide the purpose of the alarm sound. Is it to wake up the human inside the tent, or to scare the bear outside of the tent?

My design doesn't require anything in ground conductivity, and it does work pretty good if you have the ground covered in bushes or tall grass.

Mercury switches were nice thirty years ago, but mercury is getting to be a banned substance now. Maybe you can continue to use mercury, but only if you have hair samples from the local bears proving that there is no heavy metal uptake.

–B.G.–

[peter vacco]

" You have to decide the purpose of the alarm sound. Is it to wake up the human inside the tent, or to scare the bear outside of the tent? "

no need to decide. if loud enough, it will do both. handily.

" Mercury switches were nice thirty years ago, but mercury is getting to be a banned substance now. "

banned (in theory) only as if installed in a newly manufactured product. still quite available (like, from Fry's) in the aftermarket. a 3 year old with a credit card can get mercury switches delivered to his house. it's not a problem.
and .. they still work great ! (Fry's Philmore brand good. the chinese ones off ebay work as expected)

the replacement device most often substituted for a mercury switch in tilt switch applications contains a metal ball. this works ok (not great, just ok) but is far too touchy for bear fence use, and will not solidly conduct if mounted to a pole in the the wind. even the switch manufacturer recommends using some form of buffering circuit to reduce false signals. such mystery of circuits is far beyond my electronic capacity.

i am jones'ing after your hair-thin wire. my first effort got fitted with 65' of instrument probe lead (fantastic stuff ! ), but omg … the mass of it was… oh lordy, it was just way up there.
so then i toned it down to 20ga stranded (much lighter) and modified banana plugs.
that was better, but still too heavy.
next time around we have 24ga wire, and .093" moldex connector fittings, and That will be about right.
too wussy a wire, and i'm not seeing it will handle decently wearing gloves.
the weight difference between 20ga and 24ga is something you can readily feel if you have a 100' roll of each in your hand. is like 1/4 pound or something.

base plates did not work made of carbon fiber. too flexy and hard to work with if you form it yourself.
so it ended up being .030" aluminum, with some belled holes and the edges broke. they feel stiff enough. stiff is good .. as it wants to be herky enough to pull the wire connections apart.

the work continues. i could stop right now, and it would not matter. it's going on a sled anyway.

cheers,
v.

[Dale Wambaugh]

Now in know how Dr. Frankenstein felt. I can hear the villagers at the gates…..

[Bob Gross]

"such mystery of circuits is far beyond my electronic capacity."

It's not so bad. The Army unit that I had was in use in 1970, so the electronic circuit couldn't be too complex by modern standards. The one that I designed a few years later used a single CMOS gate, so the battery consumption was nearly zero when it was in standby.

The wire gauge was phenomenally tiny: two conductors, insulated, in something the size of a human hair. I can't remember exactly, but it seemed like the Army unit had a wire spool a little larger than a common spool of thread, and that was a quarter mile of two conductors. It was so fine and easy to break that we were told never to try to recover it. We were told to walk back and forth through the area, and that would break the remaining wire into less and less usable pieces.

–B.G.–

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