RFID Radio Frequency Identification Tag

RFID

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 electronically.

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 (Wiki) I'd call a transponders (Wiki) because they have a battery inside. Car keyring remotes are just transmitters (Wiki). 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 Bands) 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: Wireless power) 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 cliffordjamesc2006 (and probably others).

Savi Technology Echo Point ST-654-001

This is not a passive RF ID tag, but rather an active transponder, similar in concept to the FasTrak tool bridge unit. It's designed to be used in situations where there are many similar transponders nearby, i.e. in a network of transponders, like a warehouse.
There is a user replaceable LS 17500 3.6V battery.
Tx: 433.92 MHz, FSK dev +/- 50 kHz, 27.8 kbps, 300 meter range
Rx: 123 kHz, ASK On-Off Keying, 1.6 Kbps 50% duty cycle, Range: 4' or 12' depending on the Savi reader being used

5640151 Communication system for communicating with tags, Texas Instruments Incorporated, Jun 17, 1997
5686902 Communication system for communicating with tags, Texas Instruments Incorporated, Nov 11, 1997

The FCC has: Photos, Installation Guide,

Fig 1

Fig 2
FCC ID: KL7-654T-V2
IC: 2404A-654T1

Fig 3 Serial port to allow programing the internal memory

Operation

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 2 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.

RFID Radio Frequency Identification

Near Field Communications

Background

RFID

Savi Technology Echo Point ST-654-001

Operation

Near Filed Communications (Wiki: NFC)

Patents

YouTube

Related

Links