presence circuit

Posted on Feb 6, 2014

However effective a domestic alarm system may be, it`s invariably better if it never goes off, and the best way to ensure this is to make potential burglars think the premises are occupied. Indeed, unless you own old masters or objects of great value likely to attract professional` burglars, it has to be acknowledged that the majority of burglarie

presence circuit
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s are committed by petty` thieves who are going to be looking more than anything else for simplicity and will prefer to break into homes whose occupants are away. Rather than simply not going on holiday which is also one solution to the problem (!) we`re going to suggest building this intelligent presence simulator which ought to put potential burglars off, even if your home is subjected to close scrutiny. Like all its counterparts, the proposed circuit turns one or more lights on and off when the ambient light falls, but while many devices are content to generate fixed timings, this one works using randomly variable durations. So while other devices are very soon caught out simply by daily observation (often from a car) because of their too-perfect regularity, this one is much more credible due to the fact that its operating times are irregular. The circuit is very simple, as we have employed a microcontroller a little` 12C508 from Microchip, which is more than adequate for such an application. It is mains powered and uses rudimentary voltage regulation by a zener diode. A relay is used to control the light(s) though this is less elegant than a triac solution, it does avoid any interference from the mains reaching the microcontroller, for example, during thunderstorms. We mustn`t forget this project needs to work very reliably during our absence, whatever happens. The ambient light level is measured by a conventional LDR (...

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