Hardware Reference
In-Depth Information
You might think that because RFID is radio-based, you
could use it to do radio distance ranging as well, but that's
not the case. Neither passive nor active RFID systems are
typically designed to report the signal strength received
from the tag. Without this information, it's impossible
to use RFID systems to determine the actual location of
a tag. All the reader can tell you is that the tag is within
reading range. Although some high-end systems can
report the tag signal strength, the vast majority of readers
are not made for location as well as identification.
Figure 9-6
The field of an RFID reader, by Timo Arnall. This stop-motion
photo shows the effective range and shape of the RFID reader's
field. The reader shown is an ID Innovations ID-20, which you'll see
in the next project.
to different frequencies, there are also different protocols.
For example, in the 13.56 band alone, there are the ISO
15693 and ISO 14443 and 14443-A standards. Within the
ISO 15693 standard, there are different implementations
by different manufacturers—Philips' I-Code, Texas Instru-
ments' Tag-IT HF, Picotag—as well as implementations by
Infineon, STMicroelectronics, and others. Within the ISO
14443 standard, there's Philips' Mifare and Mifare UL, ST's
SR176, and others. So, you can't expect one reader to read
every tag. You can't even count on one reader to read all
the tags in a given frequency range. You have to match the
tag to the reader.
RFID systems vary widely in cost. Active systems can cost
tens of thousands of dollars to purchase and install. Com-
mercial passive systems can also be expensive. A typical
passive reader that can read a tag a meter away from
the antenna typically costs a few thousand dollars. At the
low end, short-range passive readers can come as cheap
as $30 or less. As of this writing, $30 to $100 gets you a
reader that can read a few inches. Anything that can read
a longer distance will be more expensive.
There are a number of cheap and simple readers on the
market now, covering the range of passive RFID frequen-
cies and protocols. ID Innovations makes a range of small,
inexpensive, and easy-to-use 125kHz readers with a serial
output. The smallest of these is less than 1.5 inches on a
side and is capable of reading the EM4001 protocol tags.
Spark Fun and CoreRFID both sell these readers and
matching tags. You'll use one of these in the next project.
There are many different RFID protocols, just as with
barcodes. Short-range passive readers come in at least
three common frequencies: two low-frequency bands
at 125 and 134.2kHz, and high-frequency readers at
13.56MHz. The higher-frequency readers allow for faster
read rates and longer-range reading distances. In addition
