GlueLogix Technical Services

Posted on Feb 7, 2014

A wireless interface for your next project Got some wire With a coil, a cap and a transistor, you can make your next project emulate a Radio Frequency Identification Device (RFID), commonly called a `tag` or an `RFID tag. ` Here`s how. A device usually called a `reader` creates a field. One or more tags communicate with the reader by varying the amount

GlueLogix Technical Services
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of energy reflected back to the reader by the tag. This process is called "backscatter, " and it`s the really neat thing about RFID technology, The general mechanism for creating backscatter is to detune a tuned element. The tuned element can be a resonant circuit or a dipole antenna, depending on the tag`s frequency range - more on that later. The point is this - your tag can be tuned, or it can be detuned, without creating much of a stir. But when the tag changes from one state to the other, it creates a disturbance in the field. A well timed series of such disturbances starts to look like a datastream. An RFID tag contains the minimum possible circuitry needed to produce that datastream: the antenna itself, a diode and capacitor to scavenge power from the field, another diode or transistor to detune the antenna, and a little intelligence. There are many types of RFID tags. Some fill unique market niches, some embody really cool technology. And some are just there because somebody thinks they can make a buck on them. The different tag types can be divided in a few ways. The most useful ways are Passive vs. Active, Tag Talk First vs. Reader Talk First, and by Frequency Range. Most of the time, when people talk about passive tags, they mean tags that get their power entirely from the RF field generated by the reader. The same people use the term "active tag" to mean tags that get their power from a battery and use the...

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