Electronics Design and Manufacture
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RFIDRW-E is a RFID reader writer module with an externally connected
antenna coil for allowing greater application flexibility. As well as the popular
EM4100, T5557/67, EM4205 / EM4305, and TIRIS transponders this unit
can also read animal identification tags using the FDX-B and HDX protocols
as described by ISO11784/11785.
This unit comes supplied with our standard rfidcoil-49a antenna coil which
needs to be connected for the unit to operate. Alternatively users can attach
their own antenna and tune the unit by means of attaching a suitable tuning
capacitor as described in the data sheet and further below.
These units are available with either RS232 or USB interface.
Its features are:
(*2) Reading range indicated is based on connection of our RFIDCOIL-49A antenna. Reading range may increase
or decrease depending on the specifications of the antenna attached, transponder type,and power supply conditions.
About FDX-B and HDX animal identification.The RFIDRW-E is able to read animal identification tags that are encoded using the standard FDX-B and HDX protocol as described in the ISO 11784 & 11785 standards. When animal tag reading is selected the
RFIDRW-E will first scan for FDX-B transponders and then HDX transponders in alternate fashion. For a more detailed description of FDX-B and HDX animal identification transponders see
FDX-B Animal Identification Protocol description. and HDX Animal Identification Protocol description.
RFID antenna basics.In a RFID reader the antenna is a simple inductor, typically in the form of a coil. When an inductor is
coupled to a capacitor and driven by an alternating signal the amplitude of the voltage across the inductor
varies depending on the values of the drive frequency, the inductor, and the capacitor. This tuned circuit is
illustrated in Figure 1. When the frequency reaches a critical value the voltage across the inductor reaches a
maximum value which can be many times the amplitude of the driving voltage. This is known as the
resonant frequency. RFID readers typically operate at this resonant frequency to maximize the power
transferred to the antenna.
Where LR = Inductance of the antenna.
CR = Tuning capacitor added.Rs = Series resistance of the antenna and circuit.
Figure 1. Basic tuned circuit.
The resonant frequency of a tuned circuit can be found using the following formula.
Where fo = the operating frequency
LR = is the antenna inductance.
CR = value of the tuning capacitor
Equation 1. Calculating the resonant frequency
Connecting the RFID antenna.
resonant frequency. This means that the antenna drive circuit will automatically tune the operating
frequency to the antenna and tuning capacitor being used. This maximizes the power transferred to the
antenna and increases read range. The drive circuit can operate anywhere in the range from 100 to 150 kHz
depending on the values of LR and CR.
The RFIDRW-E has a series of terminal pads for antenna connection and configuration. These connection
pads are designated A+, AR, A-, CT, VC, and VR. There is also a connection pad TP which allows the
current operating frequency to be measured by a frequency counter. Figure 2 illustrates the antenna drive
circuit with a typical antenna connection.
Figure 2. Antenna Drive Interface
This unit is designed to be connected to our standard RFIDCOIL-49A antenna but can easily be used with other
coil antennas. Internal tuning capacitors Cri and Series Resistor Ri preset the unit to operate at 134Khz when
used in conjunction with the RFIDCOIL-49A to minimize external components. When used with any other
antenna coil a tuning capacitor is required to set the units operating frequency which is typically 125kHz, or
134kHz depending on the transponder type. Examples of connecting various antennas are shown below.
134kHz reader with RFIDCOIL-49A
1254kHz reader with RFIDCOIL-49A
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