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I work in a school with a very tight budget, recently the security system at the library stopped working, I think is a redio frequency system (the books have a small card that is detected when you cross the door). Fixing was estimated at more than $5000 USD. Is there any way to make a system like this from scratch? We don´t want fancy features like interface to computer systems, we only need the system to make a sound when a book crosses at a certain point, it is possible?
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061
IIRC the most common tag is called an EAS (Electronic Article Surveillance) and uses a tuned circuit (the antenna with blob in the middle) The other sort uses a magnetic glass (metglas) sheet separated from a metal plate with a polymer, this relies on an imprinted magnetic pattern which is wiped using a degausser to "null" the tag. There are RFID systems as well, 13.56 MHz and 125 kHz are quite common.
For the first system a straightforward tuned coil set to the middle of the resonance range will work, it would detect the presence or absence of a tag by the drop in tuned circuit energy.
Registered Member #311
Joined: Sun Mar 12 2006, 08:28PM
Location:
Posts: 253
First thing would be to look at fixing the existing system - could just be a power supply or something simple. $5K is ridiculous - you could probably buy something new for less than that
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Question about security detectors
