near field communicatin
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Near-Field CommunicationGroup #31
Keshav Bansal
Dan HvalaTyler Rossi
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Introduction NFC is a short-range wireless
technology.
NFC provides unique advantages overother available wireless technologies.
The design includes a near-field
transmitter and receiver to send datafrom one computer to another
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Benefits & Features Not restricted to 1-to-1 communication
Multiple devices in a small area can
communicate with each other using thesame frequency.
Maximum transfer bit rate of 800kbps.
No special software is required. Operation at a frequency of 13.5 MHz
No ethical concerns due to range
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Modulation/Demodulation
Scheme Frequency Shift Keying (FSK)
VCO produces a frequency-modulated
signal at the transmitter
Phase lock loop demodulates the signal atthe receiver.
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System Overview Hardware
Transmitter
PC interface (MAX232A) Voltage-Controlled Oscillator (POS+25)
Power Amplifier (LM6181)
Loop Antenna
Receiver Loop Antenna
Amplifier (LM6181)
Phase Lock Loop (NE564)
PC interface (MAX232A)
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System Overview
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Pictures
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System Overview(Schematic)
5
4
3
2
1
9
7
6
8
Serial Port
VCC
0.1uF
0.1uF
0.1uF
0.1uF
0.1uF
1
2
3
4
8
7
6
5
16
15
14
13
9
10
11
12
MAX232A
T1 Out
C2+
C1+
T1 InV-
C2-
V+ Gnd
VCC
R1 In
T2 InT2 Out
C1-
R2 OutR2 In
R1 Out
Antenna
50
50
50
820820
V+
V-
LM6181
8
7
6
5
1
2
3
4
POS
-25VCO
VTune
GND
RFOut
VCC
GND
GND
GND
GND
2K
220
180
180
180180
V-
V+
HA17741
3.7V
Antenna
VCC
0.1uF
0.1uF
0.1uF
0.1uF
0.1uF
1
2
3
4
8
7
6
5
1
61514
13
9
10
11
12
MAX232A
T1 Out
C2+
C1+
T1 InV-
C2-
V+ Gnd
VCC
R1 In
T2 InT2 Out
C1-
R2 OutR2 In
R1 Out
1
2
3
4
8
7
6
5
161514
13
9
10
11
12
NE564
AnalogueOut
Loop Filter
V+
VCOOutFM/RF Input
Loop Filter
LoopGain
Control
Hysteresis
set
TTLOutput
Set Cap
V+Bias Filter
Input
VCOOutTTL
Ground
Set Cap
5
4
3
2
1
9
7
6
8
Serial Port
50
50
50
820820
V+
V-
1K
1K
2K
1.2K
10K
5V
5V
300pF
300pF
0.1uF
0.1uF
510
510
33pF
10uF
0.22uF0.22uF
10K
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PC Interface Connects through serial cable
Received by MAX232A
0 to 5V square wave
Voltage divider
Non-inverting voltage adder
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PC Interface
(Schematic)
5
4
3
2
1
9
7
6
8
Serial Port
VCC
0.1uF
0.1uF
0.1uF
0.1uF
0.1uF
1
2
3
4
8
7
6
5
16
15
14
13
9
10
11
12
MAX232A
T1 Out
C2+
C1+
T1 InV-
C2-
V+ Gnd
VCC
R1 In
T2 InT2 Out
C1-
R2 OutR2 In
R1 Out
2K
220
180
180
180180
V-
V+
HA17741
3.7V
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MAX232A Input/Output
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Voltage Controlled Oscillator Operates on a 12-V power supply
Accepts an input from 3.7V to 4.2V
from the PC interface. Outputs a signal whose frequency
varies according to the input voltage
level
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VCO Output
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Power AmplifierAccepts an input from the VCO
Outputs the signal to the loop antenna
Power gain of approximately 11dB
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Power Amplifier
(Schematic)
50
50
50
820820
V+
V-
Vin
Vout
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Amplifier Input/Output
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Loop Antenna
Loop Diameter = 6.5 cm
Inductance = 3 uH
Capacitor used to resonate the antennaat 13.5 MHz = 45 pF
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Loop Antenna
Very directional
Larger loop = more gain
Picks up less noise
Small, multi-loop turn does not radiatemuch
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Frequency Comparisons
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Phase Lock Loop
Tracks the frequency and phase of theinput
Frequency of an FSK signal changesaccording to the data bits; therefore,PLL can demodulate an FSK signal.
Output is the VCO control voltage.
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Phase Lock Loop(Block Diagram)
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Phase Lock Loop Tracking
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Band-Pass Filters(Eliminated)
Tuned to 10MHz and 13.5MHz
Pass-band of 2-3MHz
Signal did not decay fast enough outside ofthe pass-band
Vin
-
+Vout
+Supply
-Supply
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Difficulties
Small antenna bandwidth made us torevise our original design.
Drift in the frequency of VCO.
Amplifier oscillation
Most significant bit flipping
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Future Hardware Development
Less power consumption
More efficient loop antenna for larger
range.
Smaller setup
Two-way communication
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Analysis
Strengths
No interference due to decaying fields
Within FCC regulation FCC requires max E-field of 334uV/m at 30m
Our max E-field at 30m is 180uV/m
Weaknesses
Very small range Sensitive to distance and alignment
653mW
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Results
Maximum bit rate of 800kbps
Text communication between two PCs
Transmission range of 30cm
Ability to send a text file between PCs
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Credits
Ethan Miller
Dr. Ada Y. Poon
Dr. Christopher Schmitz
Dr. Steven Franke
Workers in the ECE Parts Shop
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