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  AVR Applications
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작성자 leeky        
작성일 2006/12/27
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  ATmega16 RFID #2 하드웨어
3. RFID 장치의 하드웨어 설계
3.1 Hardware assumptions
This device is assumed to be capable of reading most popular and most frequently
appearing on the market types of tags. Additionally it must have a possibility to write some
information back to tag.
.
This implies following assumptions. All tags assumed to be read/write must be of type
Low Frequency, working at data carrier frequency of 125kHz, as this type is the cheapest and
most frequently used nowadays. Data transmitted from tag to interrogator (reader device) can
be modulated using FSK or PSK. Most often used type of coding is Manchester, which will
be implemented in our device.
.
Supported types of tags:
• Sokymat UNIQUE – Read Only, One Time Programmable by manufacturer, 64 bits tag
• Sokymat Q5 – Read/Write, 264 bits, with Answer-On-Request feature
• Other manufactures tags (ex. MicroChip, Marin) ISO11784/785 compliant, (keeping
memory organisation of 64 or 128 bits) or other with well defined header information
.
Hardware parts presented in project:
• Sokymat Tag Reader IC
• Atmel ATmega 16L AVR microprocessor
• TTL-RS232 converter MAX232
• Antenna 1.08mH, 65Ω at 125kHz
• Double sided printed board
• Possibility of adding 3.5V to 5V DC-DC converter
.
3.2 Working principle
The most important part is Sokymat Tag Reader IC, responsible for proper excitation
of tags (driving antenna), sending and receiving electromagnetic waves (choosing proper
modulation type), decoding and finally presenting raw data bit stream to microprocessor.
Detailed description how to set proper behaviour of this IC is shown in section 3.7.4.
Microprocessor is used as a bridge between Reader IC and host like computer or
cellular phone. A three-wire bus stands as an internal interface.
.
Gathering, translation and formatting of data before sending it to mobile phone is also
done by microprocessor. It is up to microprocessor program to correctly interpret received
data, to carry out process of writing or reading tag correctly, to buffer data before sending
them back and forth the phone and if necessary to perform some low level operations on data
stream received form tag, like Manchester decoding.
.
Keeping in mind that device can be battery operated, what's more, it can sink energy
from cellular phone battery or any other, the power consumption considerations are very
important. Microprocessor can also govern power consumption level, depending on
application. The possibility of using DC-DC converter, while demand for current is negligible
(in sleep mode), charges capacitor buffers. The maximum current consumption is at the
reading or writing time and then additional energy is taken form buffers, not only from
battery.
.
TTL levels from output of AVR are translated into RS-232 standard by MAX232
converter. Connection with mobile phone is done by serial interface, but if such solution won't
be possible because of phone software limitations, AVR will communicate with phone using
set of AT commands, which in turn are recognisable and supported by all kinds of phones.
Device size should be as small as possible, doubly sided printed board with SMD elements
used.
.
3.2.1 Device Working principle block diagram
 

3.2.2 Device parts block diagram
 
 
3.2.3 Explanation to block diagrams
Device is connected and powered from cellular phone. Java application at phone side
governs the behaviour of reader and manipulates obtained data. Collected information can be
stored in phone memory, send somewhere via SMS for further recognition (verification) or
presented to user in human readable form. Figure 3.2.1 illustrates the routine of reading a tag.
.
Device by sending interrogation signal in form of ASK modulated frequency, excites tags that
are in proximity to reader. If there is no response in certain time interval, proper message for
the user is generated that no tags are visible. If there is at least one tag in interrogation field, it
is charged with energy transmitted by electromagnetic wave. Energy stored by tag is enough
for it to start process of sending data bits into air. (In reality, excitation made by reader is
repeated until whole data is transmitted from tag, as tags can be of different bit capacity)
.
Reader must be prepared to collect data send by tag. Obtained bit stream, demodulated form
FSK signal, is sent to microprocessor where proper decoding is done (Manchester). In case
when many tags try to send their data simultaneously received information may be corrupted,
implementation of anticollision is considered
.
3.3 Schematic diagram
3.4 PCB Design and special considerations (antenna and routes)
PCB planning considerations concerns mainly routing of few important paths. These
are the power and RF (antenna) paths.
As the buffer capacitors, in case of using mobile energy source, should be located
close between the DVDD and DVSS pins of Sokymat Reader, power and ground paths are
thickened, to maintain possible lowest losses due to copper resistance.
.
Note that maximum current flowing throughout these paths can be about 1A depending on configuration.
The signal DEMOD_IN pin of Sokymat Reader IC is very susceptible against
capacitive coupling of noisy traces. The capacitive voltage divider should be located close to
the input pin (Sokymat pin 7).
.
The CDEC capacitor, which connects the sampler with the filter, is susceptible against
capacitive coupling of noise. The capacitor should be located close to the chip and the traces
should be short and not close to other traces with fast changing voltage levels.
The antenna connection is bypassed with two small ceramic capacitors (100pF each)
to ground close to the connector. This suppresses high frequency voltages to ground, which
are picked up by the wiring harness and reduces the radiation out of the circuit into the wiring.
.
3.5 Possible upgrade
3.5.1 Use of Philips HTRC1100 family Tag Reader IC
Sokymat is not the only producer of RF Tag Reader IC's. In case it is not available
PCB board is designed in such way, to allow use of Philips HTRC1100 Tag Readers IC's
family. Functionally these two are the same. They differ a little by pin topology, as shown on
figure 3.5.1.a, and taking it into consideration, two additional routes and two special jumpers
were added to PCB board.
.
Looking at schematic diagram on Figure 3.3.a. added jumpers are zw11 and zw3.
Jumper zw11 cuts the clock signal from crystal if not necessary. Philips chip needs this signal,
Sokymat not. Jumper zw3 also cuts incoming external clock input signal if someone don't
want to use such because two possible communication solutions between Tag Reader chip
and Atmel microcontroller are possible. Additionally, to allow Philips chip working properly
a special kind of plug-in in form of small piece of PCB with few paths crossed must be
mounted between main PCB board and Philips HTRC1100. This small PCB translates the pin
topology difference between Sokymat and Philips products. Such solution was taken for the
sake of PCB clarity. If not additional twelve jumpers would have to be added, what would
spoil dramatically neat look of PCB and it's size.
.
Microchip and Texas Instruments produce their own Tag readers Chips, these two
solutions wasn't take under considerations and can't be used with this PCB version.
.
Figure 3.5.1.a, Picture of pin assignments of Philips
 
 
Table 3.5.1.b. Pin assignment for Philips HTRC
 
 
3.5.2 Other possibility of PCB usage
Project is made as an evaluation board, there are many facilities that are not essential
for fully functional working of Tag Reader/Write.
Presented PCB is a perfect base for other computer (or mobile phone) to Atmel
Atmega16L applications. There is a place for MAX232 or MAX3232 TTL to RS-232
converter, what makes this board useful in variety of applications.
.
Additionally there is a place for DC-DC 3.5V to 5V converter based on chip MAX856
that works with buffering capacitors, in case when 5V source won't be available. These are
twice 220mF giving 0.44F of energy that satisfies power demanding mobile applications.
To attract the functionality of PCB future use, and more precisely, the use of installed
Atmega16L chip, special pin-outs were established at borders of PCB. To facilitate
programming of SMD Atmel chip, SPI interface connector is placed on board as PROG.
Programming by Serial Programming Interface is described deeply in section 3.7.1 of Atmel
Functional Description.
.
If usage of TWI [7] (Two Wire Interface used for Atmel chips communication)
interface of ATmega is needed in application or JTAG functionality, TWI/INT and JTAG
connectors onboard can be used in future applications. Also external interrupts inputs are
easily available as well as A/D converter input port pins on EXT1 connector.
Battery power probing can also be easily implemented using special voltage divider
pads and PB4 port pin on ATmega.
All these additional pin-outs make a little mess in size and clarity of PCB but they
make this board functional as an evaluation base in future projects.
.
3.6 Functional description of elements
3.6.1 ATmega16L
Decision about AVR ATmega16 microcontroller as a base for application was done
basing on functions it offers. Firstly, power consumption. ATmega is a low-power chip. It
operates in voltage ranges of 2.7 - 5.5V and offers power consumption of following values,
depending on working mode:
.
Table 3.6.1.a. Sleep modes of AVR
 

Figure 3.6.1.a. Pinouts ATmega16L
 
 
By SPI Serial Downloading Both the Flash and EEPROM memory arrays can be very
easily programmed while RESET is pulled to GND. The serial interface consists of pins SCK,
MOSI (input), and MISO (output).
.
SPI Serial Programming Pin Mapping
Symbol Pins I/O Description
MOSI PB5 I Serial Data in
MISO PB6 O Serial Data out
SCK PB7 I Serial Clock
.
3.6.2 MAX3232 and electronic key switching circuit
MAX3232 is a 3.0V to 5.5V, true RS-232 transceiver which uses four 0.1μF external
capacitors. It keeps pin, package and functional compatibility with industry-standard
MAX232, so this two can be used interchangeably (assuming the same package, narrow
SO-16, is used) depending on availability. It is a low-power IC with supply current ranging
from 0.3mA to 1mA. Chosen integrated circuit is capable to work in temperatures from 0 °C
to 70 °C.
.
Idea to use this particular IC was very obvious. Firstly, we have few pieces of
MAX3232 and it's a world known standard, so why no use it. Secondly, it covers almost all
criteria for the project. Diagram of MAX3232 is depicted on figure 3.6.2.a
.
Figure 3.6.2.a. MAX3232 functional diagram
 

The MAX3232 have 2 receivers and 2 drivers, and they both are connected to male
DB9 type connector, situated on the edge of printed board for possible future use, maybe in
other applications. Only one pair of driver is used in RFID project.
.
The capacitor type used for C1–C4 is not critical for proper operation. Polarized or
non-polarized capacitors can be used. The charge pump (inside IC) requires 0.1μF capacitors
for 3.3V operation. For other supply voltages, do use values as follows: 0.1 μF as C1 and
0.47μF as C2, C3, C4 for supply voltage range from 3.0V to 5.5V.
.
In most circumstances, a 0.1μF bypass capacitor is adequate to fix power supply
decoupling. In applications, that are sensitive to power supply noise, decouple VCC to ground
with a capacitor of the same value as charge-pump capacitor C1. Connect bypass capacitors as
close to the IC as possible.
.
The DB9 connector, from schematic diagram, is used not only for data transmission.
The 4-th pin can be used as input to drive electronic key circuit. This on-off power switching
circuit for MAX3232 is added on purpose, to maintain low power consumption, when device
in not operating. MAX3232 doesn't contain any built-in shutdown circuit. Instead pads for
two MOSFET transistors of type P and N can added to circuit board. These pads of type SOT-
23 are marked as QP and QN respectively. The end user can decide which of two transistors
to use. One of them or both can be used, depending what kind of triggering we'd like to use, to
switch on or off the power for MAX3232 [8].
.
Figure 3.6.2.b. MAX3232 Pin topology and packages
 
 
Table 3.6.2.c. MAX3232 pin description
 
 
3.6.3 DS1813 Reset Integrated Circuit [9]
The DS1813 monitors the status of the power supply (VCC). When an out-of-tolerance
condition is detected, (power failure) an internal power-fail signal is generated, which forces
reset to the active state. When VCC returns to an in-tolerance condition, the reset signal is kept
in the active state for approximately 150 ms to allow the power supply and processor to
stabilise. The reset active time according to data sheet is form 100ms to 300ms, typically
150ms.
.
The DS1813 also monitors a pushbutton on the reset output. If the reset line is pulled
low, a reset is generated upon release and will be held in reset output low for typically 150
ms. This time guarantee a reliable reset for ATmega16L microprocessor which needs in worst
case 65ms.
.
The DS1813 current consumption at VCC less than 5.5V is in range of 30÷40 μA.
Operating temperature range is from -40 °C to +85 °C.
As the cost of DS1813 element is relatively big (quarter the price of ATmega16L) it's
possible not to mount it on printed board. The reset pushbutton still works despite the absence
of DS1813. Choosing TO-92 package instead of surface mount SOT-23 package was a matter
of availability on the market. It's very hard to obtain DS1813, especially surface mount, in
quantities less than 100pcs.
.
Figure 3.6.3.a. DS1813 TO-92 package pin
 

Figure 3.6.3.b. Pushbutton reset circuit
 
 
3.6.4 Sokymat TagReader IC
Sokymat TagReader IC [10] is a Read/Write analog front-end with serial μC interface
for usage in 125kHz RFID applications. Pin descriptions and meaning are depicted on Figure
3.6.4.a and in Table 3.6.4.b respectively.
.
TagReader IC is designed to work at the carrier frequency range from 100kHz to
150kHz with an attached antenna circuit and a microcontroller. It also contains bridge driver
used for direct antenna driving without necessity of adding additional power transistors. The
clock for the antenna driver is either generated using the integrated PLL or it is connected
from outside through the EC pin. The phase of this signal is compared with the signal, which
is driving the antenna driver. Therefore the PLL is able to lock the carrier frequency to the
resonant frequency of the antenna.
.
Data transmission is done by OOK (On-Off Keying, 100% Amplitude Modulation).
Sokymat provides simultaneous send/receive mode, FDX type (Full Duplex Transmission)
where interrogation signal and returned data appears at the time.
Sleep mode with 1μA current draw is ideal in portable applications. Provided μC
Interface to communicate with a microprocessor gives a full control over a chip and it's
features precisely described on following pages.
.
Figure 3.6.4.a. Pin Assigment
 
 
Table 3.6.4.b. Pin Descriptions
 
 
3.6.4.2 Serial Interface operation
Device operation is controlled by 8 bit Configuration Register. This register is written
via serial interface. Serial Interface is controlled by signal CLK and is set in Initial State when
power is applied (Power on Reset, beginning of timing on Figure 3.6.4.2.a). Power Down bit
of Configuration Register is set to 0 (power down mode) so TagReader is in inactive sleep
mode with low current consumption.
.
Figure 3.6.4.2.a. Serial interface I/O timing
 
 
 
Figure 3.6.4.2.b. Serial Interface state transition diagram
 
 
CLK and IN are used to enter data into the serial interface and do the interface reset.
Because of this combined functionality it is important to control the rising edges of both
signals.
.
Data entering into serial interface
The CLK signal has to be low. Then, first pulse on CLK pin switches the Serial
Interface in Command State. While being in Command State the functionality of the IN and
OUT pins changes. The communication to the chip (writing into the serial shift register) is
done synchronously by using the CLK signal. Diagnosis information is transmitted at the
second half of writing into the serial shift register to the microcontroller by using the CLK
signal as well.
.
IN pin is used to enter 8 bit data, OUT pin is used as diagnostic output. During clock
cycles 2 to 9 the Serial Interface receives 8 bit information. The 8 bits are shifted in 8 bit shift
register on rising edge of CLK. On the falling edge of pulse 9 the 8 bit information is loaded
in Configuration Register. During cycles 10 to 12 the microcontroller gets status information
back from the device. The status bits are put on pin OUT after rising edge on signal CLK.
With the 13 th clock pulse Serial Interface transition in Active State, pins IN and OUT resume
their normal function. Additional pulses on pin CLK do not have any influence on TagReader
operation.
.
The figure 3.6.4.2.c shows how to enter the value “1” into the serial interface. IN has
to be high at least tS before the rising edge of CLK. The value for tS is given in table 3.6.4.1.c.
If this time is chosen to small or even negative (CLK before IN) the data might not be
accepted or the serial interface reset could be activated. The relative position of the falling
edges is uncritical.
.
Figure 3.6.4.2.c. Serial Interface Data Entering
 
 

Interface Reset:
It is necessary that every serial communication (each writing to the serial shift
register) starts with interface reset (synchronisation method) defined as on Figure 3.6.4.2.d.
By skipping the reset, TAGREADER shift register and the connected microcontroller could
not be in phase due to EMI or ESD influence. In this case the written or read information
would be wrong and it is difficult for the microcontroller to figure this out
A high Signal at the CLK pin and a rising edge at the IN pin causes transition of Serial
Interface in Initial State. Interface Reset is accepted in all states of Serial Interface and is
needed to obtain transition from Serial Interface back in Initial State.
.
Figure 3.6.4.2.d. Serial Interface Reset
 
 
By performing Interface Reset, so shifting in configuration register new 8
configuration bits, change of TagReader operation is done. Clock cycles without leading
interface reset are meaningless.
It is recommended that the rising edge on IN appears at least a settle time of tS after
the rising edge of CLK. The internal reset is active as long as both signals are high. This time
should exceed the minimum tRES given in 3.6.4.1.b table. The falling edges of both signals are
uncritical, they can have any order.
.
Figure 3.6.4.2.e. Start of communication
 
 
During the interface reset the IN pin has be low and a momentary modulation of the
antenna driver can not be avoided. The In pin should be pulled high between the 9th and the
12th clock pulse to avoid modulation at the end of data transmission.
The pause between the first 8 bits which are input for the chip and the last 3 bits,
which are the output should be made longer due to the analogue settle time, as the outputted
data might be wrong. The recommended pause length depends on the written data and is
described in the Timing Characteristics Table 3.6.4.1.b. Violating this pause may cause wrong
status bit information. Writing the same data in the shift register after the recommended pause
duration again without a delay between the 9th and 10th clock cycle results in a correct status
output.
.
Transponder data reception
After chip command execution, data from the transponder are transmitted through the
chip asynchronously, without using the CLK signal. Depending on the used transponder, for
example a UNIQUE standard, information is Manchester coded with bit rate of RF/64. Bit
stream in such standard appears at microcontroller where all work with proper information
decoding starts. This is a quite easy task assuming that some kind of synchronisation is sent
by transponder and it's parameters are known in advance. After this process, extracted data in
form of hexadecimal values is sent via RS-232 to computer or and other device.
In this configuration the EC pin can be left unconnected as it is pulled internally to
VSS. This configuration uses the PLL for the antenna clock generation.
.
Bits meaning in Structure of Serial Interface Command [10]
As mentioned earlier the Configuration Register changes its state with the falling edge
of clock 9 in the Command Mode. Changing the Power Down bit, changing the gain, the
demodulation phase or the clock source causes a delay of about 100ms until the operating
points of analog blocks are settled. This time can be reduced to about 25ms if the fast analog
start-up has been set. In order to receive a correct diagnostic output an appropriate pause has
to be inserted between CLK pulses 9 and 10.
.
Anyway the chip can be forced to return an answer immediately after sending the 8
configuration bits but the diagnostic data like PLL-Status may be incorrect since the analog
operating points are not set yet. See also figure 3.6.4.2.b, which present possible states of
Serial Interface and conditions for transitions between them.
.
Figure 3.6.4.2.f. depicts Serial Interface Command bits.
 
 
Bit #1: The relative demodulation phase can be changed with this bit allowing higher
tolerances in the transponder to antenna matching.
.
Bit #2: This bit determines whether the chip is in sleep mode with low power consumption
or active. Active mode means the chip is using the current contents Configuration
register for operation. Note that there is no answer from the chip after sending the
power down bit. This means that on falling edge of bit 9 Serial Interface transition
in Initial State if Power Down bit is set to 0.
.
Bit #3: EC pin and bit #4 control the meaning of this bit.
If EC is pulled to VD and bit #4 is 0, the direction of data is switched with this bit,
pins IN and OUT are not used at the same time. Depending on the Data Direction
bit either the OUT pin is outputting the data sent by the Transponder or the IN pin
is modulating the Antenna Driver. When OUT pin is used, IN pin has no influence
on antenna drivers (they are always ON independent of IN pin).
.
When IN pin is used OUT pin is always driven to VSS. Such set up allows to
connect OUT and IN pin together to achieve a two wire connection in an active
antenna configuration (see also figure 3. Typical operating configuration as Active
Antenna).
.
If the EC pin is pulled to VSS or left open and bit #4 is 0, the meaning of Bit #3 is
different. Now it switches either the Data Comparator (output of the demodulation
chain) or the Clock Reference (signal driving the antenna) divided by 32 to the
OUT pin.
.
The combination of connecting EC pins to VSS (or left open) and bit #3 set to “0” is
the most convenient mode for a standard I/O communication with the transponder.
Both data directions are active at the same time, so no additional command is
required on the Serial Interface to switch the data direction between sending and
receiving of data.
.
Bit #4: The clock for driving the antenna and demodulating the received signal can be
generated by an internal PLL if this bit is set to “0” or by an external source
connected to the pin EC if Bit #4 is set to “1”. In case the Ec pin is not used it
should be left open or connected to VSS.
.
Bit #5: This decides whether the analog circuitry is doing a fast start-up or not. The settling
time can be reduced from about 100ms to about 25ms if parameters like sample
point or gain setting have been changed. If fast analog start-up is set it is active
from falling edge of pulse 9 to the rising edge of pulse 10 on pin CLK.
.
Bit #6 & Bit#7:
These bits control the gain of the amplifier. By combining both bits the gain can be
set in four steps of 6dB. Note that Bit #6 is decreasing the gain by 50% whereas Bit
#7 is increasing the gain by 100%. Default state is a gain of 480. Refer to 3.6.4.2.g.
table
.
Table 3.6.4.2.g. Gain setting
 
 
 
Bit #8: This bit switches into a test mode when set. The test mode will be left after clock
pulse 13 on pin CLK. Therefore the test mode is volatile even if it has been selected
by accident. Note that the functionality and pin assignment in this mode is different.
It should be avoided in the application and always set to 0.
.
Bit #9 – Bit#11:
These bits are the diagnostic output of the TagReader and are not logically
connected with each other. A single failure can cause one or more failure flags to
occur. The pattern can be interpreted by the microcontroller if necessary.
.
The detectable faults are an unlocked PLL (due to antenna mistuning for example),
a short circuited connection to the antenna or a signal below a certain threshold.
The short circuit detection is done by a voltage level comparison of the antenna
driver. If the driver can not pull the output close enough to VSS or VDD, a short
circuit is detected and the driver is switched off immediately. This state is steady
until the next command is sent. In the case bit #4 is 1 (external clock) the PLL is
not used, PLL-status bit is set to 0.
.
In table 3.6.4.2.h. all possible diagnostic information returned by TagReader are
present. The X’s are showing an undefined status. Depending on the safety margin of the
design, the bit could be read as “0” or “1”. Figure 3.6.4.2.i. shows most typical working
application.
.
Table 3.6.4.2.h. Diagnostic information summary
 

Typical Operating Application
Figure 3.6.4.2.i. Typical operating configuration, with direct μC interface
 
 
3.6.4.3. Any Tag Writing Possibility
It is very easy to implement writing feature by Sokymat IC. To obtain such possibility,
TagReader must be in mode "Data to TxP" where EC pin and bit #3 are both set to high
during Command Mode.
.
All signals given to the IN pin will result in switching the antenna bridge driver (On-
Off Keying modulation to the Transponder). In other words, the signal at the IN pin is
modulating the antenna signal. A “high” signal switches the antenna driver On, whereas a
“low” signal is forcing the antenna driver into tri-state mode to achieve a fast de-energizing of
the coil.
.
By sending a proper bit stream on IN pin, any kind of transponder can be
programmed. Only thing that has to be obeyed is timing diagram for specific tag type. Refer
to section 2.3.2.2 for explanation of Q5 tag type programming procedure. For example,
keeping low state on IN pin for 60ms will result in gap (no signal at antenna) in interrogating
field of the same duration. Presented device is capable to obtain interrogating gap on-off
resolution of 150μs what is far more than expected in any king writing procedure. More about
timing values and testing results in section 4. Device Testing.
For more, type specific information refer to bibliography and electronic materials
enclosed on CD-ROM.
.
3.6.5 Antenna design considerations
Antenna parameters and performance plays a crucial role in reading process just after
the power-end driving it. RFID ToolBox antenna is 2 centimetres width giving a read range of
0.5 cm distance. At first sight it sounds poor but larger loops tend to yield wider coverage
areas for the transponder tags, but the flux strength is lower and received noise from the
environment may result in obtaining a worse "Signal-To-Noise Ratio" at the receiver.
.
A high Q antenna not only transfers maximum energy at resonance, it also has a
narrow band-pass limiting out-of-band interference. Refer to Figure 3.6.5.a to reveal the
current and quality factor dependency of antenna.
.
Figure 3.6.5.a. Antenna current vs. Quality Factor
  

To optimise the reading range the antenna current should be therefore maximised.
With a given quality factor the necessary inductivity can be found in the diagram. The
inductivity as parameter is 200μH, 500μH, 1mH, 2mH and 5mH from top to bottom.
The quality factor should be as high as possible but is limited by the susceptibility
against component value deviations and the necessary bandwidth for the communication.
Usually quality factors are in the range of 10 to 15.
Antenna used in project have following parameters: L=1070μH, R=65Ω at resonance
frequency of 125kHz.
.
3.6.5.1 EMI filter in case of noisy environment
In applications where the functionality even under the influence of strong
electromagnetic fields is required, additional filter circuitry for connecting the antenna coil
with the TAGREADER is recommended. The filter shown below is implemented in presented
device. It suppresses high frequency voltages, which could have been picked up by the
antenna cable or the antenna itself. Because of the –60dB level of the useful transponder
signal in relation to the 125kHz carrier frequency the communication is by nature susceptible
against electromagnetic interference.
.
Figure 3.6.5.1.a. EMI filter configuration
 
 
 
If the quality factor trimming resistor value is large enough it may be split equally on
both antenna connections and may replace the 10μH inductors. The susceptibility against
interference is increased compared to the inductor solution, especially for higher frequencies,
but may be still sufficient for the given application.
.
The short circuit protection is done with the capacitive decoupling of both antenna
drivers. The smaller capacitor determines the resonance frequency together with the
inductance of the coil. The larger capacitor should be in relation 10 to 100 times larger so that
a low voltage and high tolerance type can be used. The larger the capacitance, the lower is the
influence on the resonance frequency.
.
4. Device Testing
4.1 Data acquire tests
Following results are obtained from several readings of different Sokymat Unique
transponders. To be sure that readings are accurate, stopping criterion for tests was a 5 times
identical output in a row in five reading attempts. Parity bits are shown on grey background.
Returned information can be formatted in three different ways (option selected from
application menu). As hexadecimal data in human readable form (5 bytes information).
.
As whole packet of 64 bits (8 bytes, with parity and header information but header information is
omitted in following printout for clarity as it is always nine '1' one by one). Finally data can
be presented as a packet of 40 bits (5 bytes, data is presented to user without parity bits and
header information shown). For the sake of results clarity only data bits with row and column
parity bits are presented.
.
Model: Tear Shape Unique
 

Credit Card Unique no. B
 
 
4.2 Waveforms and timings measurements
After assembling process following measurements were taken to judge and check
correctness of signals on crucial communication paths.
.
Figure 4.2.a Sokymat Command
 

Figure 4.2.b. Sokymat Reset Command
  
.
Figure 4.2.c. Sokymat 8-bit Command Transmit
 
 
Figure 4.2.d. Start of Tag Response
 
 
Figure 4.2.e. Response without antenna
  

ATmega16을 사용한 RFID 읽기/쓰기 장치의 제작 #3 (소프트웨어 설계)으로 계속됩니다.

.
   
윗글 ATmega16 RFID #3 소프트웨어
아래글 ATmega16 RFID #1 태그
    N         제목    글쓴이 작성일 조회 추천
AVR 자료실 안내 avrtools™ 2008/09/02 (화) 153 0
97 AVR Basic Compiler (4K Free) avrtools™ 2008/12/03 (수) 176 0
96 코드비젼 V2.05.0 평가판 avrtools™ 2011/07/17 (일) 116 0
95 8x8 LED Audio Spectrum Display avrtools™ 2009/10/18 (일) 238 0
94 AVR 펌웨어로 만드는 USB 드라이버 avrtools™ 2009/10/07 (수) 412 0
93 AVR-CDC and V-USB avrtools™ 2009/10/06 (화) 210 0
92 AVR USB-HID-Bootloader의 제작 avrtools™ 2009/10/01 (목) 245 0
91 AT91SAM7S256 개발환경과 컴파일러 [2] avrtools™ 2008/11/03 (월) 2161 0
90 SAM7S256 USB 드라이버와 AT91-ISP avrtools™ 2008/11/01 (토) 1144 0
89 AT91SAM7S256 공부를 시작합니다. avrtools™ 2008/11/01 (토) 571 1
88 ICCAVR V7.16A AVR 컴파일러 45일판 avrtools™ 2009/03/09 (월) 122 0
87 CodeVisionAVR1248b 最新版下载 leeky 2008/11/08 (토) 287 0
86 AVR UART 소스 (ICC AVR V6) avrtools™ 2008/12/03 (수) 162 0
85 cvAVR Soft Uart Source avrtools™ 2008/12/03 (수) 135 0
84 cvAVR 직렬포트와 LCD 시험용 소스 avrtools™ 2008/12/03 (수) 132 0
83 Free SmallC for AVR avrtools™ 2008/12/03 (수) 149 0
82 AVR910-ISP용 AVR-OSP2 Ver5.43 avrtools™ 2008/12/03 (수) 159 0
81 Code Vision AVR 컴파일러 2K 데모버전 avrtools™ 2008/12/02 (화) 88 0
80 AVR delay loop generator avrtools™ 2008/12/02 (화) 140 0
79 ICC tiny C컴파일러 V6 데모버전 (30일 제한판) avrtools™ 2008/12/02 (화) 58 0
78 ICC AVR C 컴파일러 V6 (4K 제한판) avrtools™ 2008/12/02 (화) 77 0
77 DasmAVR (Windows용 AVR 역어셈블러) avrtools™ 2008/12/02 (화) 123 0
76 AVR PROG KIT avrtools™ 2008/12/02 (화) 167 0
75 AVR JTAG ICE KIT avrtools™ 2008/12/02 (화) 237 0
74 AVR 부동소수점, 지연시간 계산기 avrtools™ 2008/12/02 (화) 139 0
73 ATtiny45 USB to RS232 인터페이스 avrtools™ 2008/09/26 (금) 186 0
72 MEGA32 128x64 GLCD Scope 제작 avrtools™ 2008/09/22 (월) 298 0
71 PC송신방식 Tiny2313 50x7 LED 전광판 avrtools™ 2008/09/10 (수) 251 0
70 mega8 적외선 거리측정 레이더 leeky 2006/05/07 (일) 1366 0
69 ATmega16 RFID #3 소프트웨어 leeky 2006/12/27 (수) 879 0
68 ATmega16 RFID #2 하드웨어 leeky 2006/12/27 (수) 1126 0
67 ATmega16 RFID #1 태그 leeky 2006/12/27 (수) 857 0
66 ISO 14443A RFID 카드의 읽기/쓰기 방법 [1] leeky 2007/02/25 (일) 1488 1
65 ATmega8 PSK31 RF Modem의 제작 leeky 2006/03/07 (화) 1376 21
64 T89C51SND1C 64M USB MP3 플레이어 avrtools 2006/03/04 (토) 968 8
63 AVR 13.56MHz RFID 읽기/쓰기 장치의 제작 [7] leeky 2007/02/19 (월) 994 4
62 WhereAVR for APRS GPS/Telemetry avrtools 2006/05/05 (금) 384 2
61 ATmega8 UI-TNC 무선모뎀의 제작 avrtools 2006/03/07 (화) 391 0
60 AVR APRS(GPS) Packet 무선모뎀 avrtools 2006/03/07 (화) 374 0
59 AT90PWM3 교류모터 속도제어 leeky 2006/04/07 (금) 921 1
58 M128 MMC LED 전광판 leeky 2006/03/07 (화) 911 0
57 Charon 2 이더넷 모듈의 소개 avrtools 2006/04/04 (화) 473 0
56 S2313 LED 회전계 (TACHO METER) avrtools 2006/03/28 (화) 596 0
55 Mega8 + 128x128 LCD 스코프 avrtools 2006/03/28 (화) 1183 0
54 Mega8 + OV6630 Treva 모바일용 카메라의 화상처리 leeky 2006/03/19 (일) 774 0
53 YUKI Mega8 MP3 Player #3 avrtools 2006/03/11 (토) 835 0
52 AVR JTAG 에뮬레이터의 제작 avrtools 2006/03/07 (화) 832 0
51 USB AVR 프로그래머 AvrUsb500 avrtools 2006/03/07 (화) 724 1
50 Mega88 USB 버스 모니터 avrtools 2006/03/07 (화) 381 0
49 M16 MMC Flash Memory leeky 2006/03/07 (화) 448 1
48 M163 SD,MMC Interface leeky 2006/03/07 (화) 433 0
47 S2313 MMC to Serial leeky 2006/03/07 (화) 313 0
46 ATmega48 UDP/IP 적외선 리모콘 수신장치 avrtools 2006/03/07 (화) 410 0
45 HDD MP3 플레이어 leeky 2006/03/07 (화) 595 0
44 MP3 yampp-3/USB leeky 2006/03/07 (화) 288 0
43 MP3 Player yampp-3 leeky 2006/03/07 (화) 253 0
42 YUKI MP3 플레이어2의 제작 (ATmega8 + SD Card) avrtools 2006/03/07 (화) 369 0
41 AVR CD 플레이어 leeky 2006/03/07 (화) 530 0
40 S2313 초음파 거리계 (미터, TV 스크린, LED 표시) avrtools 2006/03/07 (화) 543 0
39 RF Spectrum Monitor avrtools 2006/03/07 (화) 372 0
38 Easy Ethernet AVR 웹서버 leeky 2006/03/07 (화) 448 0
37 90S4433 LCD표시 100Mhz 주파수 카운터 leeky 2006/03/07 (화) 245 0
36 ELM Audio Spectrum Monitor avrtools 2006/03/07 (화) 351 0
35 Mega8 Door Bell leeky 2006/03/07 (화) 276 0
34 AVR 휴대용 DVM leeky 2006/03/07 (화) 481 0
33 Minimum Mass Waveform Capture and Display leeky 2006/03/07 (화) 259 0
32 AT90S2313 디지털 용량계 avrtools 2006/03/07 (화) 363 0
31 SLO2016 Alphanumeric Intelligent Display leeky 2006/03/07 (화) 173 0
30 AT90S2313 흔드는 LED 전광판 (POV) leeky 2006/03/07 (화) 425 0
29 ATtiny2313 Scrolling LED Sign avrtools 2006/03/07 (화) 361 0
28 Tiny22,S1200 나이트 라이더 avrtools 2006/03/07 (화) 306 0
27 ATtiny26L의 AD 변환과 PWM 출력제어 leeky 2006/03/07 (화) 471 0
26 S2313을 사용한 DS1820 온도계 leeky 2006/03/07 (화) 261 0
25 ATmega8535 온도센서 leeky 2006/03/07 (화) 291 0
24 AVR2313 100MHz RF연결 주파수 측정메터 avrtools 2006/03/07 (화) 190 0
23 VHF 무선 데이터 송신기 leeky 2006/03/07 (화) 499 0
22 90S2313 1MHz 파형 포착기 leeky 2006/03/07 (화) 224 0
21 VHF 무선 데이터 수신기 avrtools 2006/03/07 (화) 361 0
20 AVR 5x7 Dotmatrix LED leeky 2006/03/07 (화) 234 0
19 Mega163 웹 LCD leeky 2006/03/07 (화) 391 0
18 AVR 이더넷 시험소프트 avrtools 2006/03/07 (화) 293 0
17 AVR 넷트웍 시계 (타임 프로토콜) avrtools 2006/03/07 (화) 371 0
16 RS-232 to 100 MHz RF desktop avrtools 2006/03/07 (화) 232 0
15 AVR 6디지트 50MHz 주파수 카운터 leeky 2006/03/07 (화) 209 0
14 AVR DS1820 온도센서 avrtools 2006/03/07 (화) 248 0
13 AVR 직접주파수 발생기 (AT90S2313 DDS) avrtools 2006/03/07 (화) 368 0
12 프로그래머블 PLL 제어 avrtools 2006/03/07 (화) 216 0
11 AVR AT90S2313 7Segment LED Display leeky 2006/03/07 (화) 210 0
10 TINY15L 무전원 4채널 온도계 avrtools 2006/03/07 (화) 313 0
9 8PIN AVR을 사용한 풀컬러 LED leeky 2006/03/07 (화) 345 0
8 DS1820 고분해능 온도계 avrtools 2006/03/07 (화) 332 0
7 S2313 디지털 전압계 avrtools 2006/03/07 (화) 448 0
6 S2313 적외선 USB 모듈 avrtools 2006/03/07 (화) 316 0
5 S2313 주파수 카운터 avrtools 2006/03/07 (화) 253 0
4 AVR90S2313과 Treva 카메라의 연결 leeky 2006/03/07 (화) 292 0
3 Mega8 PID 온도제어 leeky 2006/02/24 (금) 527 1
2 90S2333 3채널 다이오드 온도계 avrtools 2006/02/24 (금) 233 0
1 AT89S8252로 만드는 1~40MHz DDS leeky 2006/02/14 (화) 306 0
1

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