---- START NEW MESSAGE --- Received: from cherry.ease.lsoft.com [209.119.0.109] by dpmail10.doteasy.com with ESMTP (SMTPD32-8.05) id AA811F40280; Fri, 30 Jan 2004 21:17:53 -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 <0.00CC61EE@cherry.ease.lsoft.com>; Sat, 31 Jan 2004 0:17:40 -0500 Received: from MITVMA.MIT.EDU by MITVMA.MIT.EDU (LISTSERV-TCP/IP release 1.8e) with spool id 3078 for PICLIST@MITVMA.MIT.EDU; Sat, 31 Jan 2004 00:17:31 -0500 Received: from MITVMA (NJE origin SMTP@MITVMA) by MITVMA.MIT.EDU (LMail V1.2d/1.8d) with BSMTP id 1864; Sat, 31 Jan 2004 00:16:18 -0500 Received: from cassiopeia.email.starband.net [148.78.247.122] by mitvma.mit.edu (IBM VM SMTP Level 430) via TCP with ESMTP ; Sat, 31 Jan 2004 00:16:18 EST X-Comment: mitvma.mit.edu: Mail was sent by cassiopeia.email.starband.net Received: from pacific.net (vsat-148-63-152-126.c189.t7.mrt.starband.net [148.63.152.126]) by cassiopeia.email.starband.net (8.12.10/8.12.9) with ESMTP id i0V58FZs032302; Sat, 31 Jan 2004 00:08:25 -0500 User-Agent: Mozilla/5.0 (Windows; U; Win98; en-US; rv:1.4) Gecko/20030624 Netscape/7.1 (ax) X-Accept-Language: en-us, en MIME-Version: 1.0 References: <200401310417.i0V4Hs3c022718@mailfilter.pacific.net> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Message-ID: <401B3A1C.3070905@pacific.net> Date: Fri, 30 Jan 2004 21:16:12 -0800 Reply-To: pic microcontroller discussion list Sender: pic microcontroller discussion list From: Brooke Clarke Subject: [EE]: Challenge for keen minds Comments: cc: Pedro Drummond To: PICLIST@MITVMA.MIT.EDU In-Reply-To: <200401310417.i0V4Hs3c022718@mailfilter.pacific.net> Precedence: list X-RCPT-TO: Status: U X-UIDL: 371856642 Hi Pedro: This sounds like a classic burglar alarm scenario. I would recommend using a strong box that's outside the cage, maybe mounted on one of the doors or on the side of the box near the doors. This box needs to have a way to open it and lock it. It will contain the logging equipment. Drill two small holes in this box and fit them with insulating sleeves. Now run a piece of wire, Nicrome would work thread the wire through an insulated hole in the left side of the box, in and out of the left gate, in and out of the right gate and through an insulated hole in the right side of the box and back inside the strong box through the other insulated sleeve. Now measure the resistance of the wire and if it goes either up or down by more than some % of the nominal value log a door opening. You will probably not log a door closing, but that really doesn't matter in this case. If there are large temperature variations yo could use cut two lengths of insulated wire. One would be used in the detection loop and the other would be inside the strong box connected in a bridge configuration in such a way as to balance out the delta R due to temperature. Even if the temp did not have a large range, using a bridge like this would allow sensing smaller resistance variations, making it harder ot defeat. If you used a short loop of wire that just went around the center posts of the two doors it could be defeated by someone sawing a cut thorough one of the posts so that they could open the doors without breaking the wire. That's why the threading across both doors and looping though the box walls. This could still be defeated by cutting all the gate posts and gate bars, but would take a very long time. Have Fun, Brooke Clarke, N6GCE http://www.PRC68.com >Date: Fri, 30 Jan 2004 15:12:35 -0300 >From: Pedro Drummond >Subject: Re: [EE]: Challenge for keen minds > >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 hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu .