Specifications

5.4. HARDWARE
Error Type Errors Detected
Single bit errors 100%
Double bit errors 100%
Odd-numbered errors 100%
Burst errors (<16bits) 100%
Burst errors of exactly 17bits 99.9969%
All other burst errors 99.9984%
Table 5.3: CRC-16: Probabilities of e rrors occurring and being detected.
Data from [12].
5.4 Hardware
Various designs were considered for the RFID readers, with details provided
in the sections below. All designs were constructed on “bread-board” type
prototyping platforms for evaluation. After finalising the designs, prototype
printed circuit boards (PCBs) were laid-out and the boards cut to evaluate
the readers’ performance.
5.4.1 Initial Considerations and Design Options
Many manufacturers provide low-cost application specific (ASIC) RFID reader
ICs
2
, however, devices which operate at the required frequencies were not
locally available for evaluation at the time of this proj ect. Furthermore,
an article in the October 2005 edition of Elektor Electronics by Martin
Ossmann provided a base design for a microprocessor-based RFID reader[13].
Unfortunately, it was designed around an Atmel AT90S1200 microprocessor
which did not have local support. The ideas were well explained in the
article, however, and a similar system based on Microchip’s PIC 18F series
of processors was successfully constructed.
The RFID readers need to force as much power into the antenna as
possible during the charging phase. Thus, it is desirable to have a high
drive voltage. 12V Sealed Lead Acid (SLA) batteries are popular choices for
battery backup, and this has been chosen as the primary system voltage to
2
Including Texas Instruments, Philips, Atmel, Microchip and ID MOS.
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