RFID Radio Frequency Identification
Near Field Communications
© Brooke Clarke 2010 - 2013
MG236B RFID Controller Front Panel
MG236B RFID Controller Back Panel
MG236B RFID Tag
Radio Frequency IDentification (Wiki: RFID
) is different
than anti shoplifting tags (Wiki: Security Tag
The idea with a security tag is to be able to detect it
electronically if it is active. When you purchase a product
as part of the check out process the clerk disables the tag so
that you do not set off the alarm as you leave the store.
These tags have no power supply and in some way can be sensed
I've heard that Wallmart is working on using RFID tags on all
products both to do the security tag job but also to eliminate
scanning each product one at a time. Instead you would wheel
you shopping cart into a reader which would read all the RFID tags
and print up an itemized bill and change the tag so it would not
sound the alarm.
An RFID tag is different from anti shoplifting in that when
queried it will reply with some message. I think of RFID tags as
being non-powered. So, for example, the FasTrak
device and modern car keys
I'd call a transponders (Wiki
because they have a battery inside. Car keyring remotes are just
RFID tags get their power from a transmitter that sends out a CW
carrier. The RFID tag rectifies that power into DC which it
uses to power the logic and a transmitter at a much higher
frequency where the antenna is more efficient. The CW signal
is typically 125 kHz or 13.56 MHz (Wiki: ISM
) and the output from the tag is at UHF or higher
frequency so that the antenna can be efficient (i.e. the transmit
antenna size is on the order of 1/4 wavelength). Note: The
receiving antenna in the card is typically a resonant loop (Wiki:
) that's much much smaller than a 1/4 wavelength.
This is an interesting technology that's been around for a number
of years, but now is very affordable. The controller and a
half dozen tags are under $40 including shipping from eBay seller
(and probably others).
To use this system the controller
needs to be trained about which tags it should respond to.
The steps for this training are:
1. press "*" and the PIN for the controller.
2. press "5" and some made up three digit code while the tag to be
learned is touching the front panel (hear two beeps),
2a. hold other cards to the front panel (hear two beeps), go to
step 2 if more cards.
3. press "*" (hear two beeps).
The controller emits a signal at 125 kHz by means of a loop
antenna wound just inside the plastic box, see Fig
above for the red enameled wire. The controller
draws about 50 ma when idle.
When the tag gets within about two inches of the panel there is a
beep, the current draw increases to 80 ma (mechanical relay
activated) and the "OK" green LED turns on. A couple
of seconds after the tag is removed the controller reverts back to
the waiting state.
If the tag is kept close there are a number of beeps and after a
few seconds the controller ignores the tag and goes back to the
wait mode. When the tag is removed the controller beeps once
and the green LED turns on for a couple of seconds (same as when
tag first encountered).
If the 12 volt prime power is removed from the controller then
restored it still recognizes the tag(s) that have been programmed.
If the controller is mounted to a metal surface it will not work.
If the supply voltage falls below 8 when a tag is present the
controller beeps once but the relay does not pull in.
Although the tags have a ten digit serial number marked on
them. It does not seem to have any purpose for the
user. Maybe there is a test mode where the controller
reports the tag ID number?
Near Filed Communications (Wiki: NFC)
NFC is another name for an RFID that can be activated using a
13.56 MHz CW signal. There is a problem in that every time
the NFC gets enough power it will send it's message.
This means someone can have a transmitter in a backpack, briefcase
or in their clothes and if they can get close to you read your NFC
data. If you're using your NFC like a credit card then they
are capturing your credit card information. There are
"Wallets" that block the CW signal and/or the signal from the
credit card to prevent this abuse, but they are not a solution for
a cell phone since blocking it's NFC capability probably also
would keep it from receiving incoming calls.
I learned about this in relation to Google Cardboard (Official web page,
YouTube Intro) where they use an NFC tag to configure the phone
for virtual reality in landscape, turn off the information bars
and maybe start a VR app.
Electrify 2 (XT881) does not have NFC.
FasTrak Vehicle ID Transponder
- is an active transponder, not an RF ID tag.
Key, Object & Pet Location
Spying on Cell (Mobil) Phones
Orion Electronics Ltd. Cellular Base
RFIDIOt - hacking
DEF CON 21
(2013) - RFID Hacking: Live Free or RFID Hard - how
to read someone's card without them knowing and making a clone
card to gain access to their building.
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