RFID Radio Frequency Identification

Near Field Communications

Brooke Clarke 2010 - 2013


Fig 1 MG236B RFID Controller Front Panel
Fig 2 MG236B RFID Controller Back Panel
              Controller Back Panel
Fig 3 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 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). 


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.

My Motorola Electrify 2 (XT881) does not have NFC.
Motorola Electrify 2
          (XT881) does not have NFC


FasTrak Vehicle ID Transponder - is an active transponder, not an RF ID tag.
Key, Object & Pet Location Tags -
Spying on Cell (Mobil) Phones
Orion Electronics Ltd. Cellular Base Station ST616-CBS
Cell Phones


RFIDIOt - hacking tools

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.

Back to Brooke's List of all web pages in alphabetical orderProducts for Sale, Electronics, Home page

[an error occurred while processing this directive] page created 13 May 2010.