Hardware Reference
In-Depth Information
Figure 9-7
RFID tags in all shapes and sizes. All
of thes items have RFID tags in them.
Photo by Timo Arnall. For more infor-
mation on RFID design research by
Arnall and his colleagues, see
www.
nearfield.org
.
Parallax sells a 125kHz reader that can also read EM Micro-
electronic tags, such as EM4001. It has a built-in antenna,
and the whole module is about 2.5" x 3.5" on a flat circuit
board. The ID Innovations readers and the Parallax readers
can read the same tags. The EM4001 protocol isn't as
common in everyday applications as the Mifare protocol,
a variation on the ISO 14443 standard in the 13.56MHz
range. Mifare shows up in many transit systems, like the
London Tube. SonMicro makes a module that can both
read from and write to these tags, which you'll see in the
project after next.
research carefully in advance, because not all readers will
read all tags. Pet tags can be some of the trickiest—many
of them operate in the 134.2kHz range, in which there are
fewer readers to choose from.
You also have to consider how it behaves when tags are in
range. For example, even though the Parallax reader and
the ID Innovations readers can read the same tags, they
behave very differently when a tag is in range. The ID Inno-
vations reader reports the tag ID only once. The Parallax
reader reports it continually until the tag is out of range.
The behavior of the reader can affect your project design,
as you'll see later on.
As shown in Figure 9-7, RFID tags come in a number of
different forms: sticker tags, coin discs, key fobs, credit
cards, playing cards, even capsules designed for injection
under the skin. The last are used for pet tracking and
are not designed for human use, though there are some
adventurous hackers who have inserted these tags under
their own skin. Like any radio signal, RFID can be read
through a number of materials, but it is blocked by any
kind of RF shielding, such as wire mesh, conductive fabric
lamé, metal foil, or adamantium skeletons. This feature
means that you can embed it in all kinds of projects, as
long as your reader has the signal strength to penetrate
the materials.
The readers mentioned here have TTL serial interfaces, so
they can be connected to a microcontroller or a USB-to-
Serial module very easily. The ID Innovations and Parallax
readers have a similar serial behavior, so you could swap
one for the other with only a few code changes to your
program.
X
Most RFID capsules are not sterilized for internal
use in animals (humans included), and they're
definitely not designed to be inserted without qualified
medical supervision. Besides, insertion hurts. Don't
RFID-enable yourself or your friends. Don't even do it
to your pets—let your vet do it. If you're really gung-ho
to be RFID-tagged, make yourself a nice set of RFID-tag
earrings.
!
Before picking a reader, think about the environment in
which you plan to deploy it, and how that affects both the
tags and the reading. Will the environment have a lot of
RF noise? In what range? Then, consider a reader outside
that range. Will you need a relatively long-range read? If so,
look at the high-frequency readers. If you're planning to
read existing tags rather than tags you purchase yourself,
