---- START NEW MESSAGE --- Received: from cherry.ease.lsoft.com [209.119.0.109] by dpmail10.doteasy.com with ESMTP (SMTPD32-8.05) id AFD6A580068; Fri, 30 Jan 2004 13:42:46 -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 <8.00CC53AD@cherry.ease.lsoft.com>; Fri, 30 Jan 2004 15:50:04 -0500 Received: from MITVMA.MIT.EDU by MITVMA.MIT.EDU (LISTSERV-TCP/IP release 1.8e) with spool id 5268 for PICLIST@MITVMA.MIT.EDU; Fri, 30 Jan 2004 15:29:22 -0500 Received: from MITVMA (NJE origin SMTP@MITVMA) by MITVMA.MIT.EDU (LMail V1.2d/1.8d) with BSMTP id 9411; Fri, 30 Jan 2004 15:28:12 -0500 Received: from *unknown [64.4.26.195] by mitvma.mit.edu (IBM VM SMTP Level 430) via TCP with ESMTP ; Fri, 30 Jan 2004 15:27:40 EST X-Warning: mitvma.mit.edu: Could not confirm that host [64.4.26.195] is hotmail.com Received: from mail pickup service by hotmail.com with Microsoft SMTPSVC; Fri, 30 Jan 2004 12:22:27 -0800 Received: from 67.65.155.200 by bay8-dav60.bay8.hotmail.com with DAV; Fri, 30 Jan 2004 20:22:27 +0000 X-Originating-IP: [67.65.155.200] X-Originating-Email: [jsears2027@hotmail.com] X-Sender: jsears2027@hotmail.com References: <401A9A93.20071.28A7C0C@localhost> <006201c3e75d$14b7f200$0301a8c0@user88l53zxzyb> <008101c3e767$6673d1e0$0301a8c0@user88l53zxzyb> <401AB450.90D8D861@UALBERTA.ca> 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 6.00.2800.1158 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1165 X-OriginalArrivalTime: 30 Jan 2004 20:22:28.0015 (UTC) FILETIME=[C7BFA3F0:01C3E76E] Message-ID: Date: Fri, 30 Jan 2004 14:22:25 -0600 Reply-To: pic microcontroller discussion list Sender: pic microcontroller discussion list From: James Nick Sears Subject: Re: [EE]: Challenge for keen minds To: PICLIST@MITVMA.MIT.EDU Precedence: list X-RCPT-TO: Status: U X-UIDL: 371856570 ----- Original Message ----- From: "Robert Rolf" To: Sent: Friday, January 30, 2004 1:45 PM Subject: Re: [PICLIST] [EE]: Challenge for keen minds > Properly arranged, there should be NO glitches in a reed switch > caused by truck movement. This should definitely be possible - either with a mechanical or a reed switch except in the case where the box gets severely deformed (as in the case of an accident). If the box is so flimsy that the sensor or switch bounces out of contacting range when the truck hits a bump, then I think you need a new box anyway if theft is such a major concern. Think also about a limit switch which has a long paddle on it that when released is open, then it moves a portion of its throw and closes and then can move farther without damage while remaining closed. I think Omron is a popular manufacturer of such switches. Then "bias" the switch so that it would take a catastrophic jolt to move it all the way out of the closed throw range while making sure that if the door is cracked enough to get something in to manipulate the switch that it has already opened and been recorded. I would say that this isn't a place for a debounced (at least not heavily so) switch. If it flips open even for a brief instant you should know about it, and also you will know when it closes again. If for whatever reason errant switch openings are a problem you can always then filter them out later in PC software or even just by looking at a graph. If something is gone even if you have a few times where the switch opens for 200ms and one where it opens for 1 or 2s you should be able to deduce where the problem occured. Better to have the noise + potential signal at your disposal -- you can get rid of noise later but you can't recover the ignored pulse. Of course you could still sleep the PIC to save power and use the wake on port change interrupt feature so that you would always sleep except at the moment the door opens or closes and long enough to store the timestamp. In any case I agree with Robert that with a proper switch arrangement it should be rock solid. Maybe even look into the spring loaded switches that turn on the dome light when you open your car door. By the way, what about just using an inverter with a cheap security cam system so that you not only know when the entry happened but who did it? Seems like while they are going to the trouble they would want to catch the guy with more than circumstantial evidence. Besides it would be fun to see his face drop the first time he popped it open and found the camera staring him in the face. Nick > > Have two sensors. One obvious, to be disabled/bypassed. One hidden, > that logs the 'real' activity. > > If the box is normally dark, a light sensor (CdS cell) > hooked to one of the self contained Dallas data logger > chips should work with minimal effort. The crooks are going > to need light to see what they're stealing. And if they think > they've disabled the detector, they're more likely to turn on > the lights. > > And you could always put a floor switch at the entrance, hidden under > under a mat. > > And why not put a disposable camera in a box over the door or shooting > through a hole in the side wall. > Easy enough to have it snap an image when the door opens (with a 1 sec delay), > which presumably happens only at the final destination. > > Autowinding is fairly easy too. Rubber hobby tire and small gear head motor > timed to wind many minutes AFTER the door closes. > > R > > Pedro Drummond wrote: > > > > Yes, but the problem here is someone that, when opening the gate, > > immediately recomposes the sensor (for example, puting a second magnet close > > to the reed switch). If he takes, say, 2-3 secs to do it, it will be > > analyzed afterwards as a glitch, probably caused by truck movement. The > > ideal would be some kind of sensor not easily or quickly "recomposed" when > > opening the gate. > > > > ----- Original Message ----- > > From: "James Nick Sears" > > To: > > Sent: Friday, January 30, 2004 2:50 PM > > Subject: Re: [EE]: Challenge for keen minds > > > > > In this case couldn't you just use a switch mounted inside the door > > > somewhere where it can't be feasibly reached from the outside until the > > door > > > has already opened and the time of intrusion has already been logged? > > > > > > > > > ----- Original Message ----- > > > From: "Pedro Drummond" > > > To: > > > Sent: Friday, January 30, 2004 12:12 PM > > > Subject: Re: [PICLIST] [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#nomail Going offline? Don't AutoReply us! > > > > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body > > > > > > > > > > -- > > > 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#nomail Going offline? Don't AutoReply us! > > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body > > -- > 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#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body .