Index


Card Technology Technology Page

    Contactless smartcards and RFID

    In contact smartcard systems, such as reading the data from a serial EEPROM over a two-wire (I2 C) or three-wire SPI or Microwire bus, the power, clock, and data lines are connected separately. Some wired smartcards use RS-232 type asyncronous communications, and in this case supply power and communication through different wires. In contactless smartcards all this communication and usually also the power for the smartcard needs to be transferred wirelessly using RF signals and/or inductive coupling methods.

    Radio Frequency Identification (RFID) systems use radio frequency to identify, locate and track people, assets, and animals. Charles Walton pioneered the RFID technology in the 1970s and 1980s. RFID is a catchall term for a broad array of technologies that includes everything from battery-powered "active" tags, such as those used in highway toll booths, to "passive" RFID tags that measure a fraction of a millimeter in each dimension, not counting the antenna in the device.

    RFID (Radio Frequency Identification) is a technology where information can be read from and/or written to a microchip without contact using High Frequency (HF) magnetic induction or Ultra High Frequency (UHF) transmission and reflection. Both HF and UHF techniques have the same function, interfacing between a reader and an information storage device by means of antennas, but they are quite different in operation.

    There are several types of RFID technologies:

    • Active unpowered RFID tag absorbs RF from interrogate signal, rectifies carrier, uses to power low-power circuitry. Circuit encodes response and transmits code back to interrogator.
    • Active self powered RFID tags carry battery or some other power, which provides a smarter function- can send more information than simple ID code, or has a longer range than interrogator-powered versions.
    • Third version is just a passive reflector with a binary function. It either passively reflects, triggering response, or just sits there and does not respond at all. Since these devices do not actually send an ID number, some do not consider them RFID (maybe in some applications you could use tags tuned to different operating frequencies for simple identification). These are types found in anti-theft devices.

    Passive RFID systems are composed of three components: an interrogator (reader), a passive tag, and a host computer. The tag is composed of an antenna coil and a silicon chip that includes basic modulation circuitry and non-volatile memory. The tag is energized by a time-varying electromagnetic radio frequency (RF) wave that is transmitted by the reader. This RF signal is called a carrier signal. When the RF field passes through an antenna coil, there is an AC voltage generated across the coil. This voltage is rectified to supply power to the tag. The information stored in the tag is transmitted back to the reader. This is often called backscattering. By detecting the backscattering signal, the information stored in the tag can be fully identified. Passive RFID devices also use a serial bus, but the power, clock, and data are all in the same signal. Instead of wires, this signal is carried through wireless means.

    Typical RFID system use inductive coupling between the card and the reader. Both of them have coils whick interactig with each other (magnetic coupling). This interaction makes it possible to transfer power to the card (through alternating magnetic field or pulses) and transfer information (modulating the magnetic field). Typical this kind of inductively coupled systems operate at 125-kHz to 13.56-MHz frequency range. ISO frequencies of 125 kHz and 13.56 MHz are generally used. 125 kHz and 13.56 MHz, utilize transformer-type electromagnetic coupling. The typical operating distance is usually few centimeter or tens of centimeters.

    Sometimes higher frequencies are used for RFID tagging, but the communicationmethods are somewhat different. 2.45 GHz, for example, uses a true RF link. There are also systems that operate at UHF frequencies (902-928 MHz in USA and 866-868 MHz in Europe). The radio systems can operate typically from few meters to 10 meters.

    Systems incorporating passive RFID tags operate inways that may seem unusual to anyone who already understands RF or microwave systems. There is only one transmitter: the passive tag is not a transmitter or transponder in the purest definition of the term, yet bidirectional communication is taking place.

    The RF field generated by a tag reader (the energy transmitter) has three purposes:

    • Induce enough power into the tag coil to energize the tag. Passive RFID tags utilize an induced antenna coil voltage for operation. This induced AC voltage is rectified to provide a voltage source for the device. As the DC voltage reaches a certain level, the device starts operating.
    • Provide a synchronized clock source to the tag. Many RFID tags divide the carrier frequency down to generate an on-board clock for state machines, counters, etc., and to derive the data transmission bit rate for data returned to the reader.
    • Act as a carrier for return data from the tag. Backscatter modulation requires the reader to peak-detect the tag's modulation of the reader's own carrier. Backscatter modulation works by repeatedly shunting the tag coil through a transistor, the tag can cause slight fluctuations in the reader's RF carrier amplitude.
    The RF link behaves essentially as a transformer; as the secondary winding(tag coil) is momentarily shunted, the primary winding(reader coil) experiences a momentary voltage drop. This amplitude-modulation loading of the reader's transmitted field provides a communication path back to the reader. It is important that the device must be equipped with a proper antenna circuit for successful RFID applications. The complexity of RFID tags can vary, typically the ICs are quite simple small memory storage holding for example 128 bits of memory that can be read, but there are also more complicated devices with similar functionality as normal smartcards.

    Most modern RFID systems operate at 13.56 MHz frequency range. There are several standards on this field: I-Code, ISO-14443, TagSys ja TagIt. From those I-Code and ISO-14443 look most promising. The reading of those tags is possible up to distance of a few meters with a correct antenna. There are many companies that make RFID tages (for example Philips and Texas Instruments) and many companies that make readers to them (for example 3M and Nordic ID).

    It is well known that a limiting factor in the adoption of RFID technology is the inability to read RFID tags on metallic or liquid objects. The usual solution has been to use some sort of spacer to lift the tag off the metal.

    • Charles Walton, the Father of RFID - Walton got his first patent about it in 1973. There are 32 patents granted to Walton, the first to be associated with the acronym RFID dates from May 17, 1983.    Rate this link
    • The father of RFID - The next time you wave a key card to unlock the door to your office building, think of Charles Walton. One of Silicon Valley's unsung inventors, Walton's patents on radio frequency identification, or RFID, spawned those electronic door keys. Now the technology Walton pioneered in the 1970s and 1980s is poised to change the way billions of products are tracked.    Rate this link
    • Antenna Circuit Design for RFID - Since the energizing and communication between the reader and tag is accomplished through antenna coils, it is important that the device must be equipped with a proper antenna circuit for successful RFID applications.    Rate this link
    • Optimizing read range in RFID systems - Determining and improving the read range of RFID tags is especially important as these tags become more commonplace.    Rate this link
    • Passive RFID Basics - Radio Frequency Identification (RFID) systems use radio frequency to identify, locate and track people, assets, and animals. Passive RFID systems are composed of three components . an interrogator (reader), a passive tag, and a host computer. This application note discusses on those devices.    Rate this link
    • RFID tags connect smart cars to smart highways - small RF identification (RFID) tags are part of the critical communication link between automobiles and electronically directed "smart" highways and there are also many other uses for them    Rate this link
    • RFID Fundamental Operating Principles - This chapter from RFID Handbook describes the basic interaction between transponder and reader, in particular the power supply to the transponder and the data transfer between transponder and reader.    Rate this link
    • RFID Handbook - book home page with some interresting material to download    Rate this link

    Magnetic cards

    Card with magnetic stripes are not smartcard techniques, but because they are quite often used in same applications where smartcards are also used to coming to use, they are also worth to mention on the same page with smartcard technologies. Chances are you many cards that have magnetic stripes on the back on your wallet: ATM cards, credit cards, calling cards, frequent flyer cards, ID cards, passcards, etc. ANSI/ISO standards define 3 Tracks for magnetic card, each of which is used fordifferent purposes. These Tracks are defined only by their location on themagstripe, since the magstripe as a whole is magnetically homogeneous.Track 2 is most commonly used. Track 2 is used by ATMs and credit card checkers.Track 1 usually holds the cardholder's name as well as account and other discretionary data.Most card readers read either Track 1 or Track 2.Track 3 was intended to have data read and written on it, butis nowadays pretty much an orphaned standard. The data in magnetis stripes is in digital format.The most commonly used code is a 5-bit Binary Coded Decimal coded ANSI/ISO format. It uses a 16-character set, which uses 4 of the 5 available bits (plus parity).Alphanumeric data can also be encoded on magstripes. The second ANSI/ISO dataformat is ALPHA (alphanumeric) and involves a 7-bit character set with 64characters. Not all magstripe cards operate on a digital encoding method. Some cardsencode audio tones, as opposed to digital data. These cards are usuallyused with old, outdated, industrial-strength equipment where security is not anissue and not a great deal of data need be encoded on the card. Some subwaypasses with magnetic strips in them are like this.

    Barcode

    Barcode technique, but because they are quite often used in similar applications, barcodes are also worth to mention on the same page with smartcard technologies. Bar codes are used in many applications to encode numeric or ASCII informationto stripes which are easilily readable by electronic device called bar code scanner.UPC or EAN symbol are found on most retail products around the world. Many electronics products have barcodes on their circuit board foridentification purposes and many packages have bar codes.Genrally in barcodes the information is coded to the width ofthe bars and their distance from each other.When reading barcodes there is generally one optosensor which gives 1 or 0 signaldepending of sensor is over the black bar or white background.(for example 1 on background and 0 on black bar or other way).Bar code systems can use several symbologies. A symbology is equivalent to a language. Each symbology has strengths and weaknesses. Many symbologies are around for historical or political reasons, while others have definite technical advantages. For general-purpose use, Code 128 is usually the best choice. It provides use of the full (128-character) ASCII set as well as the best readability and reliability available. If you are making a general-purpose system that needs to read only numbers and uppercase letters, you can use Code 39. If you need numbers only, you should use Interleaved 2 of 5 or Code 128. In any case, avoid symbologies that require reconfiguration of the reader, and your life will be easier.Checksums are additional characters appended to bar codes to guarantee good reads. Checksums are necessary on some bar codes that are prone to errors.Printing barcodes is nowadays done usually with a normal PC and normal laser printer. You just need a suitable software and a normal printer and you can print your own bar codes.Reading of bar code information can be done in many ways. If you use ready made reader units, you do not usually need to worryabout the decoding process yourself. You just need to make sure that the bar code reader you have supports the bar code you use. The commercial barcode readersusually can output the code contents in ASCII format throughserial port or PC keyboard interface. Readers are available from simple pen linke devices to complicated laser based bar cide scanners as used in many shops at counter.If you need to do the barcode decoding yourself, you need to know thedetails of the code. The general process in decoding is tobegin by waiting for a black bar. When we see the beginning ofthe first black bar, we reset our clock to zero. Then we wait the signal to toggle to the white level, so we canclock and write down the reading as the measured width of the first black bar. When we get the white-to-black transition we read the clock and write down that reading as the width of the first white bar. We continue to time the width of the bars in this way for thewhole length of the code. After this we can start decoding of the codeby using the facts that there is a known ratio between thick andthin bars. And the code suaully starts with a known start code (knownbar and white space lengths).

    • Altek Pages - premier Barcode site, barcode specifications    Rate this link
    • Barcode 1 - A Web Of    Rate this link
    • BarCode 1 - a web of information about bar code    Rate this link
    • Barcodes: Color & Contrast - Many barcode problems which turn out to be caused by low contrast barcodes. The human eye is many times more sensitive than the best barcode scanner - what appears to be a good barcode by eye may be barely perceptible by the scanner. The best contrast is obtained when the background reflects all the light and the bars reflect none. This is never fully achieved in practice but there must be a significant difference between the bars and background if the code is to be read reliably.    Rate this link
    • Barcodes FAQ - introduction on printing bar codes, many popular barcodes listed    Rate this link
    • Barcode Information & Specifications    Rate this link
    • Barcode Server - form that generates 12 digit UPC bas codes    Rate this link
    • Bar Code Symbologies - Bar code systems can use several symbologies. A symbology is equivalent to a language. Each symbology has strengths and weaknesses. Many symbologies are around for historical or political reasons, while others have definite technical advantages. This document has information about many different bar codes.    Rate this link
    • Code 128 Specification - very high density alphanumeric bar code    Rate this link
    • Linux Reads Bar Codes - A hardware and device driver project for Linux    Rate this link
    • Pankkiviivakoodistandardi - Information on bar coding used in bills in Finland to make payin gof them with ATM easier. This document is in Finnish.    Rate this link
    • Uniform Code Council - bar code organization for coordinating bar codes used in products    Rate this link
    • What is a Keyboard Wedge? - A keyboard wedge is a system whereby it becomes possible to enter data into a computer in a way not anticipated by the programmer who wrote the application. It is based on the idea that all applications programs allow data to be entered via the keyboard. If the computer can be fooled into accepting 'dummy' keyboard data then that data will be processed and handled correctly by the application. Wedge systems are typically used to enter small packets of machine collected data into applications written for keyed data. This data may come from a barcode reader or similar device.    Rate this link
    • Barcodes - This web page has introductions to 4 State BPO Code (British Post Office, Royal Mail Code), AZTEC Code, Codabar, Code 128, Code 49, Code 93, EAN (EAN-13, EAN-8 EAN-99), Interleaved 2 of 5 Code (also referred to as USS ITF 2/5, ITF and I-2/5), Maxi Code, MSI/Plessey Code, PDF417 Code and UPC (UPC-A & UPC-E)    Rate this link


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