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9289B–RFID–03/13
Description
This document outlines the procedure for evaluating an active RFID tag system consisting
of 1) a base station configured as an LF transmitter 2) a base station configured as an RF
receiver and 3) an active RFID tag.
The base station is used to transmit LF (100kHz-150kHz) ASK-modulated data and receive
RF (434MHz) ASK/FSK-modulated data from the RFID tag. The RFID tag is an active por-
table ultra-low-power RFID device powered by a 3.3V coin cell battery. It is used to receive
LF signals generated by the base station from up to 2m away (depending on the LF trigger
antenna size) from the transmitting LF antenna. The tag also transmits an RF message to
the base station reporting fob ID, measured RSSI, and other sensor data.
The fob, once powered, continuously monitors the LF frequency in ultra-low-power mode.
Once a valid signal is detected containing the correct device ID, the fob wakes up, pro-
cesses LF input data, and responds to the base station by sending the RF message with
application payload. Once the transmission is complete it returns to its ultra-low-power
sleep state and resumes monitoring the LF channel for a new message.
The LF and RF signal transmission uses a custom signaling protocol. Each of the protocols
is unique and includes its specific preamble, header, payload, and CRC (data integrity)
fields.
This RFID system allows the use of multiple tags in field operation by incorporating anticol-
lision protocol support. A slotted ALOHA anticollision protocol has been implemented for
these applications. In case of a reception error on the RF channel (more than one device
transmitting at a time), the error is sent from the RF receiver module via the UART cable to
the LF module. The LF module must then re-transmit the LF message which allows individ-
ual tags to choose a new arbitrary slot (one of any other seven slots) when sending the RF
message response. Anticollision RF message return time slots are chosen randomly by the
tag.
This active 125kHz RFID system can be easily used in areas such as inventory and item
monitoring applications.
APPLICATION NOTE
Atmel ATA6286-EK3 Active RFID Evaluation Kit
Atmel ATAN0057
