Data Sheet

RFID Technology Overview

Material in this section is based on information provided by the RFID Journal (www.rfidjournal.com).

Radio Frequency Identification (RFID) is a generic term for non-contacting technologies that use radio

waves to automatically identify people or objects. There are several methods of identification, but the

most common is to store a unique serial number that identifies a person or object on a microchip that is

attached to an antenna. The combined antenna and microchip are called an "RFID transponder" or "RFID

tag" and work in combination with an "RFID reader" (sometimes called an "RFID interrogator").

An RFID system consists of a reader and one or more tags. The reader's antenna is used to transmit

radio frequency (RF) energy. Depending on the tag type, the energy is "harvested" by the tag's antenna

and used to power up the internal circuitry of the tag. The tag will then modulate the electromagnetic

waves generated by the reader in order to transmit its data back to the reader. The reader receives the

modulated waves and converts them into digital data.

There are two major types of tag technologies. "Passive tags" are tags that do not contain their own

power source or transmitter. When radio waves from the reader reach the chip’s antenna, the energy is

converted by the antenna into electricity that can power up the microchip in the tag (typically via

inductive coupling). The tag is then able to send back any information stored on the tag by modulating

the reader’s electromagnetic waves. "Active tags" have their own power source and transmitter. The

power source, usually a battery, is used to run the microchip's circuitry and to broadcast a signal to a

reader. Due to the fact that passive tags do not have their own transmitter and must reflect their signal

to the reader, the reading distance is much shorter than with active tags. However, active tags are

typically larger, more expensive, and require occasional service.

Frequency refers to the size of the radio waves used to communicate between the RFID system

components. Just as you tune your radio to different frequencies in order to hear different radio stations,

RFID tags and readers have to be tuned to the same frequency in order to communicate effectively. RFID

systems typically use one of the following frequency ranges: low frequency (or LF, around 125 and 134.2

kHz), high frequency (or HF, around 13.56 MHz), ultra-high frequency (or UHF, around 868 and 928

MHz), or microwave (around 2.45 and 5.8 GHz).

The read range of a tag ultimately depends on many factors: the frequency of RFID system operation,

the power of the reader, and interference from other RF devices. Balancing a number of engineering

trade-offs (antenna size vs. reading distance vs. power vs. manufacturing cost), the Parallax RFID

Read/Write Module's antenna was designed specifically for use with low-frequency (125 kHz) passive

tags.

BASIC Stamp 2 Program

The example program shown below is a simple system-level test to read the tag ID and write a block of

data. This .bs2 program, along with a more comprehensive code example demonstrating the full

capabilities of the RFID Read/Write Module, is available for download on the product page; search

“28440” at www.parallax.com