---- START NEW MESSAGE --- Received: from cherry.ease.lsoft.com [209.119.0.109] by dpmail10.doteasy.com with ESMTP (SMTPD32-8.05) id A9071050021C; Thu, 29 Jan 2004 20:09:43 -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 <0.00CC4110@cherry.ease.lsoft.com>; Thu, 29 Jan 2004 23:09:28 -0500 Received: from MITVMA.MIT.EDU by MITVMA.MIT.EDU (LISTSERV-TCP/IP release 1.8e) with spool id 8831 for PICLIST@MITVMA.MIT.EDU; Thu, 29 Jan 2004 23:03:11 -0500 Received: from MITVMA (NJE origin SMTP@MITVMA) by MITVMA.MIT.EDU (LMail V1.2d/1.8d) with BSMTP id 3983; Thu, 29 Jan 2004 22:51:38 -0500 Received: from smtp1.globo.com [200.208.9.168] by mitvma.mit.edu (IBM VM SMTP Level 430) via TCP with ESMTP ; Thu, 29 Jan 2004 22:51:37 EST X-Warning: mitvma.mit.edu: Host smtp1.globo.com claimed to be mail.globo.com Received: from user88l53zxzyb (200.158.164.92) by mail.globo.com (6.0.053) id 3FD4F1170035967C for PICLIST@MITVMA.MIT.EDU; Fri, 30 Jan 2004 01:51:39 -0200 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: <001b01c3e6ec$bd319740$0301a8c0@user88l53zxzyb> Date: Fri, 30 Jan 2004 01:51:27 -0300 Reply-To: pic microcontroller discussion list Sender: pic microcontroller discussion list From: Pedro Drummond Subject: [EE]: Challenge for keen minds To: PICLIST@MITVMA.MIT.EDU Precedence: list X-RCPT-TO: Status: U X-UIDL: 371856422 Hi, all. I have to implement a gate opening detector. It will log date and time each time the gate is open and for how long. Must be battery-driven, battery must last as much as possible, must be rugged and robust, and tamper-proof. People WILL try to defeat it. What I have already thought: 1) It will be all enclosed in a box with no openings, time of day programming will be done with an IR remote, data will be collected from it the same way. Aside from these operations, battery consumption must be minimum. Any ideas to improve this number 1 ? 2) How to detect gate openings ? Well, if I use a regular reed switch, people will defeat it inserting a flexible magnet close to the sensor before opening the gate. The same applies for metal (induction) sensors, proximity (capacitive) sensors. I thought of having a second device on the moving door sending IR data to the main device, but another battery consumption here is out of the question. Last idea was to have a sequence of magnetized and non-magnetized surfaces, similar to a bargraph, only much larger, that will match the reed (or HAL) sensors in the device. Much harder to fool and easier to save battery, yet not the elegant solution we all pursue... Any ideas here ? Thanks a lot, Pedro -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details. .