RFID Reader documentation v2.1

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 (known as "parasitic

power"). The tag is then able to send back any information stored on the tag by reflecting the

electromagnetic waves as described above. "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. The RFID Card Reader is designed

specifically for low-frequency (125 kHz) passive tags.

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 must 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 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).

There really is no such thing as a "typical" RFID tag. The read range of a tag ultimately depends on many

factors: the frequency of RFID system operation, the power of the reader, environmental conditions,

physical size of the tags antenna and interference from other RF devices. Balancing a number of

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

RFID Card Reader's antenna was designed with a specific inductance and "Q" factor for 125 kHz RFID

operation at a tag read distance of around 4 inches.

BASIC Stamp

1 Program

The following code examples read tags from a RFID Card Reader and compare the values to known tags

(stored in an EEPROM table).

' =========================================================================

' File....... RFID.BS1

' Purpose.... RFID Tag Reader / Simple Security System

' E-mail..... support@parallax.com

' Started....

' Updated.... 07 FEB 2005

' {$STAMP BS1}

' {$PBASIC 1.0}

' =========================================================================

' -----[ Program Description ]---------------------------------------------

' Reads tags from a Parallax RFID reader and compares to known tags (stored

' in EEPROM table). If tag is found, the program will disable a lock.

' -----[ Revision History ]------------------------------------------------