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RFID Basics
Introduction
A few months ago I checked out a stack of books at our local library by
placing the books on a kiosk. All 5 books magically appeared on the
computer screen. Around the same time my father ran in the Bolder
Boulder, a foot race of over 50,000 people. An electronic system kept track
of his time and thousands of others by only having the runners wear paper
race bibs. Pets that are found wandering can be identified and returned to
their owners with a basic scan of the neck. How is all of this possible?
Source: icons8
The answer is RFID or Radio Frequency IDentification. This tutorial will
cover the basics of how RFID works, and will help guide you towards
getting started with RFID.
Suggested Reading
If you aren’t familiar with the following concepts, check out these tutorials
before continuing. They will help with the basic understanding of RFID.
• The Basics of Binary
• What is a Battery?
• Electric Power
Basics
Basic Functionality
It may be tempting to believe that RFID functions thanks to the reader
module containing a very small hamster with x-ray eyes, but in actuality, the
system is a bit simpler than that.
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How RFID doesn’t work
RFID uses radio waves produced by a reader to detect the presence of
(then read the data stored on) an RFID tag. Tags are embedded in small
items like cards, buttons, or tiny capsules.
Image courtesy of EPC RFID
These readers also use radio waves in some systems to write new
information to the tags.
Types of RFID Systems
There are two types of RFID systems: passive or active. The tag power
system defines which type of system it is.
Passive
In a passive RFID system, the tags do not use a battery; instead, they
receive their energy to run from the reader. The reader emits an energy
field of a few feet, providing the energy for any tag in the vicinity. The tag
gathers the electromagnetic energy from the card reader, powers up, and
responds with ‘hello world’ and its identification information.
Passive tags have the benefit of being able to be read at a fast rate (10 or
more times a second). They are extremely thin (allowing them to be placed
between layers of paper) and are extremely cheap (less than $0.05 in
10,000+pcs volumes).
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In general, the smaller the tag the much shorter the read range
Active
Active RFID systems include tags that have their own internal power supply
for increased range. Active tags possess a battery and usually have larger
SMD components. After a preset amount of time the tag emits an RF
‘chirp’. A reader in the vicinity can listen and hear for this chirp. Because an
active tag is they can be read over much larger distances than passive tags
(tens of feet).
Downsides to active tags include greater bulk (because of the battery),
limited life span (tag is dead when the battery is exhausted), increased cost
per tag, and varying report rates.
m130 Active RFID asset tag from RF Code
RFID Frequencies
As well as active and passive systems, RFID systems can also be broken
out into different frequencies.
Some frequencies and systems are designed to only read one tag at a time,
while others can read multiple. Cost of readers can also vary wildly based
the frequency rating of the modules. In prior years a reader capable of
reading multiple tags was in the thousands of dollars, sometimes tens of
thousands. These systems were unattainable for most hobbyists and
prototypers. However, this is finally beginning to change, and multi-read
capable readers are becoming much more affordable.
Check out the following chart for a basic break down of the frequencies,
and their associated properties.
A Few Common RFID Reader Types
Frequency
AKA
Range
Read/Write
Read Multiple
Tags
Simultaneously
Average
Tag
Cost
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Low
Frequency
(120-150
kHz)
"Chips/microchips" (in
veterinary
applications), prox
cards, HID cards
(both trade names)
Up to
20 cm/
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