Two Lock Rule?

In article ,
"RST Engineering" wrote:

The electronics would always have been trivial to implement for an
undergrad IC circuit designer; the needed fiber optics components are
now at the Radio Shack level; and the remote signalling would be
trivial with Wi-Fi or Bluetooth technology.

I won't argue what RF technology would be best for remote signalling. I
argue that small current loops (on the order of microamperes) is much more
efficient of power AND money than optics. I'm not really sure how you
"scrape off the insulation" when the "wire" can be the chain (or better yet,
cable) itself.

My argument would be that if the wire is a current loop and is
physically accessible (and of course if the protected item is valuable
enough) a moderately competent thief can literally shave the insulation
off the side of the wire with a razor blade or Exacto knife; attach a
longer bypass wire that doesn't encircle the protected goods with a
couple of alligator clips; snip the original wire; and be home free.

This might fail -- that is, the alarm might still go off -- if the
electrical signals in the wire are high frequency enough, or the
measurement of the impedance of the wire itself, or the capacitance from
wire to ground, is sensitive enough, or . . .

But if you're using techniques that sophisticated, then the alarm is
also likely to be triggered by temperature changes, or by some large
object going by (a fork lift in a hangar), or by EMF from a nearby radio
or computer, or by . . .

A fiber loop would (in my judgment) be much less sensitive to all of the
above problems, and I believe the optical source, detector, and fiber
technology involved is now really cheap and simple.

As for the power consumption question, well, I have an optical mouse on
my desk that's been in use (putting out a lot of light, as well as
communicating constantly with the Bluetooth adaptor on my laptop) for
8-10 hours/day for many weeks now, and never turned off 24/7, on just a
couple of AA batteries.

AES -

If you aren't going into business - somebody should. I think it is a
neat idea although it would need a way to detect that the electronic
box is being crunched or shot at etc etc.

Cool------

The easy way to do that is with a positive signal system. That is, the
little transmitter chirps once every couple of seconds when things are
"good". When it stops chirping (batteries low, shot, crunched, or alarm
triggered) you light the alarm fuse.

Jim




"nrp" wrote in message
oups.com...
AES -

If you aren't going into business - somebody should. I think it is a
neat idea although it would need a way to detect that the electronic
box is being crunched or shot at etc etc.

Cool------

RST Engineering wrote:
The easy way to do that is with a positive signal system. That is, the
little transmitter chirps once every couple of seconds when things are
"good". When it stops chirping (batteries low, shot, crunched, or alarm
triggered) you light the alarm fuse.

That's not very expandable. If the system gets popular, you'd need lots of
frequencies; otherwise your alarm might fail to sound when your item is stolen
because someone else close by is on the same frequency.

George Patterson
"Naked" means you ain't got no clothes on; "nekkid" means you ain't got
no clothes on - and are up to somethin'.

Then you chirp a digital code. A simple 16 bit code gives you 64K discrete
addresses. Ain't that many airplanes on the field at Oshkosh at one time.

Jim


"George Patterson" wrote in message
news:EPTie.9665$E05.6247@trndny09...
RST Engineering wrote:
The easy way to do that is with a positive signal system. That is, the
little transmitter chirps once every couple of seconds when things are
"good". When it stops chirping (batteries low, shot, crunched, or alarm
triggered) you light the alarm fuse.

That's not very expandable. If the system gets popular, you'd need lots of
frequencies; otherwise your alarm might fail to sound when your item is
stolen because someone else close by is on the same frequency.

George Patterson
"Naked" means you ain't got no clothes on; "nekkid" means you ain't
got
no clothes on - and are up to somethin'.

"George Patterson" wrote

That's not very expandable. If the system gets popular, you'd need lots of
frequencies; otherwise your alarm might fail to sound when your item is
stolen
because someone else close by is on the same frequency.

Nah, yah gotta think digital. It has to be chirping your digital code, not
just frequencies.
--
Jim in NC

On Thu, 19 May 2005 00:20:04 -0400, "Morgans"
wrote:


"George Patterson" wrote

That's not very expandable. If the system gets popular, you'd need lots of
frequencies; otherwise your alarm might fail to sound when your item is
stolen
because someone else close by is on the same frequency.

Nah, yah gotta think digital. It has to be chirping your digital code, not
just frequencies.

And when you get two on the same frequency is it possible for one to
swamp the other. If you use something like WiFi to set off an alarm,
or call home, that's different as the networking *should* take care of
collissions and multiple systems can coexist on the same frequency.


Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

In article .com,
"nrp" wrote:

AES -

If you aren't going into business - somebody should. I think it is a
neat idea although it would need a way to detect that the electronic
box is being crunched or shot at etc etc.

Cool------

Thanks!

One could also get more complicated and have the lock and the remote
system in continuous wireless communication, to make sure the lock is
still intact -- but then there are more ways for the false alarm rate to
go up.