---- START NEW MESSAGE --- Received: from cherry.ease.lsoft.com [209.119.0.109] by dpmail10.doteasy.com with ESMTP (SMTPD32-8.05) id ACF3D20007E; Sun, 01 Feb 2004 20:07:15 -0800 Received: from PEAR.EASE.LSOFT.COM (209.119.0.19) by cherry.ease.lsoft.com (LSMTP for Digital Unix v1.1b) with SMTP id <20.00CC8476@cherry.ease.lsoft.com>; 1 Feb 2004 22:58:18 -0500 Received: from MITVMA.MIT.EDU by MITVMA.MIT.EDU (LISTSERV-TCP/IP release 1.8e) with spool id 8017 for PICLIST@MITVMA.MIT.EDU; Sun, 1 Feb 2004 22:58:12 -0500 Received: from MITVMA (NJE origin SMTP@MITVMA) by MITVMA.MIT.EDU (LMail V1.2d/1.8d) with BSMTP id 1466; Sun, 1 Feb 2004 22:57:28 -0500 Received: from smtp2.globo.com [200.208.9.169] by mitvma.mit.edu (IBM VM SMTP Level 430) via TCP with ESMTP ; Sun, 01 Feb 2004 22:57:28 EST X-Warning: mitvma.mit.edu: Host smtp2.globo.com claimed to be mail.globo.com Received: from user88l53zxzyb (200.158.164.177) by mail.globo.com (6.0.053) id 40076DB00019D520 for PICLIST@MITVMA.MIT.EDU; Mon, 2 Feb 2004 01:57:29 -0200 References: <401A9A93.20071.28A7C0C@localhost> <006201c3e75d$14b7f200$0301a8c0@user88l53zxzyb> <401BD419.7050908@ubasics.com> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2600.0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2600.0000 Message-ID: <004e01c3e949$127b22d0$0301a8c0@user88l53zxzyb> Date: Mon, 2 Feb 2004 01:57:26 -0300 Reply-To: pic microcontroller discussion list Sender: pic microcontroller discussion list From: Pedro Drummond Subject: Re: [EE]: Challenge for keen minds To: PICLIST@MITVMA.MIT.EDU Precedence: list X-RCPT-TO: Status: U X-UIDL: 371856801 Interesting ! But wouldn't 2 thick metal walls invalidate this ? (one for each device, on each door). ----- Original Message ----- From: "M. Adam Davis" To: Sent: Saturday, January 31, 2004 1:13 PM Subject: Re: [EE]: Challenge for keen minds > Since this is a double door, you need to be aware of either door being > open (ie, they could simply close the one with the sensor but leave the > other open) > > Consider welding two boxes of aluminum on each door opposite each other > very close together. When the door opens they are unaligned and/or far > apart. In one box you put the data logger with a small metal detector > type coil set at a specific frequency. > > The other box contains another coil and capacitor which, when close to > the detector side, modifies the oscillation frequency significantly. By > monitoring the actual frequency you can not only get a good idea of when > they move apart, but how far apart they are. Since they can be > completely sealed inside a metal box (does affect frequency change and > sensitivty, but it would still work well) then they could only defeat it > if they also had such a coil. > > The kicker is that they would not only have to have such a coil, but it > would have to modify the frequency the same way both your coil and the > metal box does. Fuirthermore they'd have to somehow move their coil in > synchronization with the door so that your receiver didn't detect the > drop and rise in frequency. Since this is all mounted on the inside it > would be nearly impossible without quite a bit of additional equipment > (measuring the field, etc) and very good reflexes, if possible at all > without an active external transmitter. > > Truck vibration and movement wouldn't affect it. Temperature would, so > you may want to look at a temperature sensor so you can compensate for > capacitor values changing a bit. > > Additional security could be provided by using different frequency coils > so no one solution could work for all boxes. The circuit could be > calibrated when installed, or for higher sensitivity every time the box > is sealed/opened/logging data read. > > Of course, you realize that you should also put in a GSM or GPRS module > so it can call or page you when a box is opened with its serial number. > Better still, attach a GPS as well and log its movement, transmitting > location and time information to your pager when it's opened. Attach a > small digital camera and send yourself a picture. Etc, etc, etc. > > -Adam > > Pedro Drummond wrote: > > >Thank you all for the help and interest. > > > >Ok, time for more data: > > > >The space being protected is a metallic box, the size of an elevator, that > >will be towed by small trucks. Its metallic "door" (actually a double door) > >is the gate I mentioned. During long trips, these boxes are commonly moved > >from truck to truck, with long periods waiting for the next one, with no > >guards nearby. Although there is a very strong lock, theft was detected at > >final destination in locked boxes (i.e., someone opened it, took some goods, > >and somehow relocked it). A redesign of the metal box is being made, but it > >will be a long time until all of them are replaced. It is enough for now to > >help the insurance company in detecting WHEN and for HOW LONG it was opened, > >so the responsible will be known. > >I do not mind reading its information only when the gate is open, and I > >cannot modify the gate, only add some small device close to the door. > > > > > >To comment some of the group ideas: > > > >Using a contact method for data transfer - I am afraid of dust, grease, etc. > >But maybe. > >RFID - cheap tag, but expensive sensor (I guess). > >Gyro/acceleration sensors - can't do, since it will be towed by a truck. > >Hinge sensored - can't alter the hinge. > > > > > >BTW, special thanks to Russel ! > > > >-- > >http://www.piclist.com#nomail Going offline? Don't AutoReply us! > >email listserv@mitvma.mit.edu with SET PICList DIGEST in the body > > > > > > > > > > > > -- > http://www.piclist.com hint: To leave the PICList > mailto:piclist-unsubscribe-request@mitvma.mit.edu > -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads .