(The conclusion has yet to be done but thought I’d give
you a draft in case any drastic changes have to be done
below. I will go into more detail in the construction of
the circuit if needed. Many thanks. )
Introduction:
• Aims
To create a secure system of receiving data from a chaotic transmitter over
a link.
• Objectives
1. To create and simulate a receiver using Orcad design program.
2. To create a prototype on a breadboard.
3. To create a P.C.B (printed circuit board) of the circuit using
Orcad layout design program.
• Specifications
• Summary of the approach taken
The approach to this was simple in theory, basically my partner in this
project (David Mitchell) took on the job of using orcad to create a receiver,
and using his circuit diagrams he created, I would physically create the
prototype and get simulation results. Then we could compare simulation
results etc, and see how the theoretical simulations reflected the actual
simulations
1
• Block diagram
Figure 1 block diagram
Above is an overall block diagram of the project. On the left hand side of the
am carrier box is clearly the transmitted data, and on the right is the receiver.
This part on the right is what are project is about i.e. receiving encrypted data
over a secure link. This will be covered in detail in latter sections.
• Information and materials provided at the start of the
project.
Information and materials were readily available to us. All components that
were used were free from the stores in the college. And all the information
2
on the project could be gotten from the library, web or resources given by
our supervisor.
Project background
• Background theory
This system uses chaos to encrypt the signal that is to be transmitted. It also
needs chaos to decrypt the signal received from the transmitter. So what is
chaos? Chaos is a typical behavior of nonlinear dynamic systems (i.e. a random
change in time or motion, which is complex to predict). Chaos is created from a
circuit known as chua’s circuit. Chua's circuit is a simple electronic circuit
that exhibits classic chaos theory behavior. It was introduced in 1983 by Leon
Chua. Made from standard components (resistors, capacitors, inductors), this
circuit must satisfy three criteria before it can display chaotic behaviour which
are:
1. one or more locally active resistors
2. one or more nonlinear elements
3. three or more energy-storage elements.
Chua's circuit is the simplest electronic circuit meeting these criteria.
• Initial investigations used to determine the best solution
• References to previous work by other areas
3
Before the physical building of the chua circuit, my project partner created a
basic circuit in orcad. He simulated the circuit, and when it worked he gave this
schematic to me. This was used as a plan for the building of the circuit. This
process was repeated for the majority of the project and time after time the
circuit in orcad was improved which resulted in the physical circuit to be
improved, either by removing parts and replacing parts or starting the circuit
from scratch.
• References to any sources of information used
Due to the fact all of the work done on my side of the project depended on the
simulations and schematics from orcad (done by my partner), all the
information I used to build the chua circuit came from the schematics. Some
background information was got from wikipedia on the chua, but it was not as
necessary due to the fact my roll in the project was building the schematics
given to me by my partner. It must be noted that the building of the circuit is
not as simple as building other circuits, as it is very temperamental and “is
quite delicate (sensitive to component values)” according to an article on the
building of a chua circuit. All of this was found out as the project developed, as
will be seen in latter stages of this report.
• Element of analysis; how Orcad was translated into
a physical circuit.
For the very first circuit created, a matrix board was used. (This will be covered
in detail in further sections). This requires the skill of soldering and is ideal for
4
a permanent solution but due to the temperance of the chua circuit the
breadboard was ultimately the right path to take when constructing and altering
the physical circuit. So a breadboard was used in order to translate the orcad
schematic to a physical circuit. The layout of the breadboard is obviously
completely different to the layout that would be used for a matrix board and
thus the layout of an orcad schematic. Below is a brief and simple example of
the layout of a standard breadboard and how the holes are connected :
The top and bottom rows are linked horizontally all the way across as shown
by the red and black lines in the diagram below. The power supply is
connected to these rows, + at the
top and 0V (zero volts) at the
bottom. The other holes are linked
vertically in blocks of 5 with no
link across the centre as shown by
the blue lines on the diagram.
Notice how there are separate
blocks of connections to each pin of ICs.
5
Technical description and construction
details with results:
• Description of the software developed and results.
This section will give the steps in which were taken by my partner to develop
the receiver. As this was not directly associated with my input it will be brief
due to the fact many steps have to be taken to simulate and construct such a
complex system (i.e a receiver using chaos):
Figure 2
6
Figure 3
Figure 3 above shows the output observed from the PRBS generator
R9
R1
100
220
R4
I
22k
OUT
Vsweep
13
12Vdc
- 11
TL084
+
14
OUT
2
V--15V
V+
U7A
3
V+
+
+15V
4
4
+15V
U6D
12
TL084
- 11
V--15V
R5
R2
20k
220
R6
3.3k
1
R3
2.2k
0
Figure 4
Figure 4 above shows the circuit used to demonstrate the nonlinear resistance
7
Figure 5
Figure 5 above shows the nonlinear negative resistance obtained from the circuit.
Table of value from nonlinear negative resistance circuit of breadboard
8
8.0V
-4.67mA
7.5V
-4.27mA
-0.5V
0.2mA
7.0V
-3.95mA
-1.0V
0.34mA
6.5V
-3.61mA
-1.5V
0.55mA
6.0V
-3.30mA
-2.0V
0.7mA
5.5V
-2.96mA
-2.5V
0.9mA
5.0V
-2.67mA
-3.0V
1.3mA
4.5V
-2.31mA
-3.5V
1.6mA
4.0V
-1.97mA
-4.0V
2.0mA
3.5V
-1.60mA
-4.5V
2.2mA
3.0V
-1.30mA
-5.0V
2.55mA
2.5V
-0.95mA
-5.5V
2.9mA
2.0V
-0.70mA
-6.0V
3.23mA
1.5V
-0.55mA
-6.5V
3.6mA
1.0V
-0.36mA
-7.0V
3.92mA
0.5V
-0.16mA
-7.5V
4.25mA
0V
0mA
-8.0V
4.6mA
9
Nonlinear Negative Resistance Graph
10
8
6
Voltage (V)
4
2
0
-2
-4
-6
-8
-10
-6
-4
-2
0
2
4
6
Current (mA)
Graph Using table values
10
Out
V
{Res}
100
XaxisC22
R1
XaxisC12
RL
20
R
C1
100n
C2
4.7n
NLR
2
L1
10mH
1
0
Figure 6
Figure 6 above shows the conventional linear oscillator used in the Chua circuit
TL084
13
RL
Zin
11 -15V
V-
20
OUT
C
12
0.1u
14
+ 4 +15V
U1D V+
R
5k
0
Figure 7
Above is circuit diagram of the gyrator, used instead of inductor for variable inductance.
11
Figure 8
Shown in figure 8 looks at the spectrum of the oscillator of the Chua circuit, oscillates at 4
kHz
Chua_Out
V
R6
220
22k
11
-15V
V-
20
OUT
C4
3
0.1u
C2
100n
-
+ 4
U1A
OUT
OUT
6
- 11
TL084
+15V
V+
R17
5k
7
9
TL084
V-
R7
PARAMETERS:
Res = 1.74K
0
- 11
8
V-
R8
20k
R9
3.3k
V+
+
+
C3
4.7n
1
4
U1C
10
V+
-15V
TL084
2
5
+15V
U1B4
R13
+15V
R5
-15V
100
XaxisC2
R15
{Res}
XaxisC1
R14
220
R12
2.2k
Figure 9
Figure 9 above shows the circuit diagram for the Chua circuit used in the simulation.
12
Figure 10
Shown in figure 10 above is the voltage across variable resistor in the oscillator.
Figure 11
Figure 11 above shows the chaotic output from the circuit known as a Lorenz Attractor
13
Figure 12
Shown above in figure is a block diagram of the transmitter circuit.
Figure 13
Figure 13, signal of PRBS + chaos + DC offset
14
Figure 14
Figure 14 is the carrier, freq = 50 kHz, amplitude = 5
Figure 15
Figure 15 above shows the modulated carrier signal
15
Chaotic Receiver
Figure 16
Figure 16 above show the block diagram of the chaotic receiver.
D1
Input
Rectif ied
D1N4148
R9
1k
0
Figure 17
Figure 17 above shows the rectifier
16
Figure 18
Shown above in Figure 18 is the rectified
Figure 19
Shown above in Figure 19 is the rectified signal and the chaos to be subtracted
17
0
R4
40k
+15V
R2
rectif ied_in
U12A
4
3
V+
+
100k
OUT
R1
chaos_in
2
100k
- 11
TL084
1
Dif f out
V- -15V
R3
40k
Figure 20
Figure 20 above shows the diagram of the difference amplifier used to subtract the chaos
Figure 21
Figure 21 is chaos subtracted from the rectified signal
18
0
5Vdc
V23
U4B4
5
V+
+
OUT
6
V22
- 11
TL084
7
V-
2Vdc
0
Figure 22
A voltage comparator, shown in Figure 22
Figure 23
Figure 23 above shows the output of comparator
19
R33
1k
R30
-15V
TL084
2
1k
R31
11
V-
OUT
1k
3
1
+ 4
U12A V+ +15V
0.5Vdc
V8
0
0
Figure 24
Figure 24 above shows summing amp to add DC to shift the signal
Figure 25
Figure 25 is the shifted signal but the waveform is negative because of the summing amp.
20
R35
1k
-15V
TL084
6
R34
11
V-
-
1k
OUT
5
lev elled
7
V
+ 4
U12B V+ +15V
0
Figure 26
Figure 26 is an Inverting op amp used to invert the signal back to positive.
R28
lev elled
cr_out
15k
C10
500p
0
Figure 27
Figure 27 is a low pass CR filter.
21
Figure 28
The graph above, Figure 28, shows the output from the CR filter
0
4
V24
5Vdc
12
+
V+
U11D
cr_out
0.5Vdc
0
-
TL084
comp2_out
V-
13
V25
14
11
OUT
0
Figure 29
Figure 29 is another comparator
22
5.0V
2.5V
0V
0s
1.00ms
2.00ms
3.00ms
4.00ms
4.46ms
V(COMP2_OUT)
Time
Figure 30
Figure 30 above shows the output of the comparator
Figure 31
Figure 31 is the filtered output from the second comparator
23
+15V
4
U12D
R40
cr_out2
12
V+
+
1k
OUT
13
TL084
- 11
14
gain
V
V- -15V
R38
450
R39
1k
0
Figure 32
Figure 32 is the non-inverting op amp to adjust gain
Figure 33
Figure 33 is the signal with adjusted gain
24
Figure 34
Figure 34 above is another summing amp and inverting amp to shift the signal down again.
Figure 35
•
Finally our recovered PRBS signal
It must be noted that my partner carried out this work.
25
•
Description of the hardware developed
Figure 36 the first attempt
Above is the first attempt at building the chua, it was a very basic circuit and used
basic resistors with normal tolerances. The chip in the centre is a TL084 chip, this
contains 4 op-amps, and in this case only two were used. This was de-soldered and
new parts were placed but it was not successful. Below it the out put diagram of the
particular circuit. It is nothing more than noise.
Figure 37 failed simulation
26
Figure 38. Second attempt.
Above we can see the second attempt at building the chua circuit. It is evident to see
that this time a breadboard was used. But again only two out of four of the chips opamps were used. The layout was quite disarranged due to the fact it was the first
attempt at building such a circuit. The output was identical to the output of the
previous circuit. Basically it didn’t work. So going back to orcad a new schematic was
developed that contained an inductor as the previous schematics but this time another
op-amp was used to create this inductance, before one component was used. Now
resisters and op-amps were used instead. Also a buffer and one more op amp for the
gyrider were used. This can be seen in figure 39.
27
Figure 39. Attempt number three.
Here it is evident to see two tl084 chips, all pins were used in one chip and 1 op amp
in the other chip. This was briefly tested (the output below can be seen in figure 40)
but just before it was fully checked for the problem a new schematic came into the
equation. This was a much simpler chua and it was very similar to the second
attempted circuit. It had three op-amps which means only one chip was needed. This
was due to the fact the buffer was removed and one out of two op-amp’s from the
inductor was also removed. This circuit is illustrated in figure 41.
Figure 40 Output for above circuit.
28
Figure 41 Successful Circuit.
Above is the circuit in which the chaotic signal was achieved. Three op-amps were
used. And due to the sensitivity of the circuit a pot had to be used in order to slowly
change the resistance until the desired signal was achieved. It also needed very low
tolerance resisters again due to the sensitivity of the chua circuit. In figure 42 we see
the output signal that is identical to the simulated output signal in orcad. This just
reflects the accuracy of the software. This signal will be deducted from the encrypted
signal that comes in from the receiver, which will reveal the desired message from the
PBRS.
Figure 42 chaotic signal
29
Conclusion
• Significant observations and conclusions clearly
stated
• Summery of critical results
• Highlight possible improvements and make
suggestions for future development or investigation.
(This has yet to be done but thought I’d give you a draft
in case any drastic changes have to be done above. I will
go into more detail in the construction of the circuit if
needed. Many thanks. )
30