1. NAME: LEONARD KIBET NG’ENO
INDEX: 2011P04100
COLLEGE: ELDORET POLYTECHNIC
COURSE: DIPLOMA IN ELECTRICAL AND ELECTRONICS ENGINEERING
PROJECT TITLE: SIMPLE DIGITAL SECURITY SYSTEM
DATE PRESENTED: SEMPTEMBER 2013
EXAM SERIES: NOV/DEC2013
PROJECT SUPERVISED BY: MR. STEPHEN ROP
SUBMITED TO KENYA NATIONAL EXAMINATION COUNCIL IN PARTIAL
FULFILMENT FOR THE AWARD OF DIPLOMA IN ELECTRICAL AND
ELECTRONICS ENGINEERING
6. CHAPTER ONE
INTRODUCTION
This is a simple and reliable electronic security system. It’s a watchdog Which allows the
users to detect intruders in you premises .you can use this simple security system by
installing the sensing loops around your premises. The loops are to be stretched two feet
above the ground to sense the unauthorized entry into your premises. The loops are not
connected to a3-input NOR gate and inverter to activate the alarm.
The circuit works off a 9v regulated power supply. However, battery backup is
recommended. A common cathode, 7-segment display is used to display wetter the loops
are broken or still intact. If loop 1 is broken the display will show the sum of the broken
loops. When all loops are intact the display will show 0.
1.0 AIMS AND OBJECTIVES
The main objective of the project is to make sure that the user of this systemis
alerted whenever there is an intruder or unauthorized person in their premises.
This is achieved through triggering of the alarm system.
BLOCK DIAGRAM
SIGNALINPUT SIGNAL DECORDER
DIGITAL
DISPLAY UNIT
SIGNAL ENGODERSAUDIO BLOCK
SIGNAL
AMPLIFICATION
7. DESRIPTION OF BLOCK DIAGRAM
Signal input block
This block consist of the 3 loop wires acting as input signal connected to NOR gate and inverter
CD4000.
Signal decoders block
In this section the 3 input signals fromthe input signal block is decoded in 7 output signals. The
block contains a 7 segment decoder 4511.it is a 3 input decoder and is connected to the input
signal lines and is energized by 9v power supply. This block will drive input signals to the seven
segment display.
Visual output block
This block is responsible for archiving the aimof the project and that is to provide visual output of
the position of interference. This block contains the seven segment display which provides the
numerical display 0-to 9.
Signal encoders block
This block is responsible for encoding the variable inputs to a single output signal (variable signal)
from the block. The block contains a CD4000 IC 3 dual input NOR-NOT gates. These logic gates
perform of providing a single input drive to the signal amplification block.
Signal amplification block
This block is responsible for increasing the magnitude of the encoded signal. This block contains
BJT transistor which acts as an amplifier.it is a common emitter amplifier.
Audio output block
This block achieves the main objective of the project by providing an output. This output alarms
the user that a certain position has been compromised or interfered. This block contains the
piezobuzzer. The piezobuzzer gives out a high pitched sound which is reliable in notifying the user.
Specifications required
Supply voltage--- 9V
Frequency ---50HZ
8. Current (normal conditions) ---2.25mA
CIRCUIT DESCRIPTION
The wire loops 1, 2 & 4 are connected to A, B, C inputs of 7 segment decoder 4511 IC1,
while D input is grounded permanently.
The 3 inputs are not connected to a dual 3 input NOR gate and inverter CD4000 IC2. The
circuits on a regulated power supply of 9v.
A common cathode 7 segment display (LTS543) is used to display whether the loops are
intact or not.
If a loop is broken the display will show 1.if two or more are broken let’s say 2 and 1 the
display will show 3(2+1).
When all loops are intact the display will show 0. All the 3 inputs of the gate N1 remains
low to give a high output. This high output is further given to gate N2 and as a result its
output remains low. This keeps transistor T1 keeps transistor T1 in cut off position and the
piezobuzzer does not sound.
In case of a broken loop the output of a NOR gate goes low due to high input. While output
of N2 goes high. The transistor T1 conducts and the buzzer can be muted by switching off
power to the circuit through switch S2.
CHAPTER TWO
9. THEORY OF COMPONENTS
THE 7 –SEGMENTDECORDER DRIVER [4511 IC]
Is a BCD (Binary Code Decimal) to 7—segment decoder driver. I5ts function is to convert the logic
states at the outputs of a BCD into signals which will drive a 7 –segment display. The display shows
the decimal numbers 0—9.
10. PIN
NUMBER NAME PURPOSE
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
2S
4S
LT
BI
LE
8S
1S
0V,VDD
E
D
C
B
A
G
F
+9V
VCC
Input for the 2s digit from the binary counter
Input for the 4sdigit from the binary counter.
Lamp test – when low, the chip takes the entire segment on the display
high (to test connection).
Blanking input – when low, the chip doesn’t output to the display to
conserve battery life for instance.
Latch enable- latches on the current output when high (i.e. the input
change the output when LE is low)
Input for the 8s digit from the binary counter.
Input for the IS digit from the binary counter.
The connection to 0V rail.
Output for the seven segment E input.
Output to the seven segment D input.
Output to seven segment s C input.
Output to the seven segment B input.
Output of the seven segments A input.
Output of the seven segments G input.
Output to the seven segment F input.
The connection to +9V rail
12. The 4511 is the driver IC of the seven segment cathode display.
Its operating principle is to input a four bit BCD (binary coded decimal value) and energize
the proper output lines to form the corresponding decimal digital on the 7- seven segment
display.
The 4511 display driver IC requires a common cathode 7 segment display unit.
When operating on 4 switches in a binary counting sequence (0000 to 1111). A(0000) input
should result in decimal 0 displaying , a 0001 input should result in decimal 1 and so on
through 1001 e.g.(1010,1011,1100,1101,1110 or 1111) are above single decimal digit and
so have no function on the 4511 IC.
The and BI that is lamp test and blanking input are active low and so they are connected to
VDD for normal operation. When the lamp test low all the display segment should light
(showing number 8) when the blank input is low the display will be blank.
The LE input should be low for normal operation. When LE is high the displayed number is
stored internally to give a constant display regardless of any changes which may occur to
the input A-D.
The outputs of the G can source up to 25mA. Thus we must use seven resistors placed in
series between the 4511 output terminals and the corresponding terminal of display unit.
13. RESISTOR
Is a component showing a known resistance. It opposes the flow of current through it.
Uses of resistors
i. Used to limit current flowing.
ii. Used to establish proper values of circuit voltages due to IR drops.
iii. It has no polarity thus can be connected in either direction.
Resistor specification
They are normally specified in terms of
o Power rating
o Resistance value
o Thermal stability
Classification of resistors
It can be classified into two types.
i. Fixed resistors
14. ii. Variable resistors
Fixed resistors
Their values of resistance cant be changed
Variable resistors
Their values of resistance can be varied.
This project requires fixed resistors
Resistor designation
Resistors are always marked with color code and indicate the value. The color code consists four
color band pointed around the resistor body. This is used because the printed label could be hard
to read as components crowded on the band.
Project resistor values
i. 47kΩ resistor
ii. 470kΩ resistor
iii. 1kΩ resistor
FIXED
RESISTOR VARIABLE
RESISTOR
15. The 47kΩresistor are connected in series with the logic gates and decoder to limit current flowing
into them.
470kΩ resistor is connected in the cathode of the seven segment display to the ground.
1kΩ resistor in series with the logic gate and the transistor to limit the base current flowing into
the transistor.
THE TRANSISTOR
It consist of a junction formed by sandwiching either p-type or n-type semiconductor between
pairs of opposite types. There two types of transistors
P-N-P Transistor
N-P-N Transistor
p PN
N P N
16. A transistor has two P_N junction .one forward biased and the other is reversed biased. The
forward path has a low resistance and the reversed biased has a high resistance. The weak signal is
taken from the low resistance circuit and output is taken from a high resistance circuit. This means
that a transistor transfers a signal from low resistance to high resistance thus increasing voltage
(amplifying).
Transistor action
The emitter base junction of a transistor is forward biased while collector base junction is reversed
biased. If we ignore the presence of emitter base junction then practically no current would flow
in the circuit collector because of the reversed biased present then forward biased is on , it causes
the emitter circuit almost entirely flow I the collector circuit.
BC548 is the transistor used in this project as an amplifier. It’s a common emitter amplifier
transistor.
TRANSISTOR AS AN AMPLIFIER.
Common emitter CE(amplifier)
17. Circuit operation
When positive half circle of the signal is applied
i. IB
ii. Is energized
iii. IC is increased by times the increase of IB=IC=𝛽IB
iv. VBE is increased because it is already positive with respect to the ground.
v. VCE is decreased as in the formula VcE =VCC-ICRC.
vi. Drop ICRC is increased considerably and consequently.
STATIC CHARACTERISTICS OF COMMON EMMITTER CIRCUIT
Current amplificationfactor
This is the ratio of change of IB of the base current for a given collector emitter voltage. It is
represented by the symbol β
𝛽 = ⧍𝐼𝐶/⧍𝐼𝐵 For a given value of Vce
18. Figure above shows relationship between collector and base current for a given collector emitter
voltage.
Relationshipbetween
For a common emitter transistor
Characteristics of a common emitter amplifier
It should have the following characteristics.
i. Its current gain β is high {50—300}
ii. Its output is moderately large[50k]
19. iii. It has moderately low input resistance3.
iv. It has a very high voltage gain
v. It produces very high power gain
SEVEN SEGMET DISPLAY
It id composed of seven elements. Individually on and off, they can be combined to produce
simplified representation of the Arabic numerical.
Often the seven segments are arranged in an oblique (slanted) arrangement, which aids
readability. Each of the numbers 0.6,7 and 9 may be represented by 2 or more different glyphs on
seven segment displays.
20. The LED based 7- segment display showing the 16 Hex digits.
The seven segments are arranged as a rectangle of two vertical segments on each side with one
horizontal segment on the top , middle and bottom. Additionally, the seventh segment bisects the
rectangle horizontally. There are also fourteen segment display and sixteen segment displays (for
full alpha numeric); however, those have mostly been replaced by dot matrix displays.
The animation to the left cycles through the common glyphs of the ten decimal numerals and the
six hex decimal “letter digits” (A-F). It is an image sequence of a LED display which is described
technology wise.
The segments of a 7 –segments display are referred to by the letters A to G, as shown to the right,
where the optional DP decimal point (an eight segment) is used for displays of non – integer
numbers.
Implementation
Seven segment displays may use the following.
a) Liquid crystal display.
b) Arrays of light emitting diodes
c) Vacuum fluorescent
d) Cathode gas discharge.
e) Vane displays ---magnetically flipped light reflecting segment(vanes)
LED 7– SEGMENT DISPLAY IMPLEMENTATION.
In a simple LED package typically all of the cathodes (negative terminals) or the entire anode
(positive terminal) of the segment LED
21. LED (Light Emitting Diode)
A k A =Anode
K = cathode
A PN junction diode, which emits light when forward, biased is known as LED.
The LED are connected together and brought out to a common pin; this is referred to as a
common cathode or common anode device. Hence a seven segments plus decimal point package
will only require nine pins.
Integrated displays also exists, with single or multiples digits. Some of these integrated displays
incorporate their own internal decoder, though most do not –each individual LED is brought out to
connecting pin as described.
Multiple digit LED displays as used in the pocket calculators and similar devices used in
multiplexed displays to reduce the number of IC pins required to control the display. For example,
all the anodes of segment A of each digit position would be connected together and to a driver
pin, while the cathodes of all the segments for each digit would be connected. To operate any
particular segments of any digit, the controlling integrated circuit will turn on the cathode driver
for the selected digit and the anode driers for the desired segment; then after a short blanking
interval the next digit would be selected and new segment lit, in a sequential fashion.in this
manner an eight digit display with seven segment and a decimal point would only require 8
cathode drivers and 8anode drivers instead of 64 drivers and IC pins. Often in pocket calculators
the digit drive line would be used to scan the keyboard as well, providing further savings; however
pressing multiple keys at once would produce odd results the multiplexed display.
22. Limitation of LED displays over LCD displays.
Unlike LEDs, the shapes of elements in an LCD panel are arbitrary since they are formed on the
displays by a kind of printing process. In contrast the shapes of LED segments tend to be simple
rectangles, reflecting the fact that they have to be physically molded to shape, which makes it
difficult to form more complex shapes than the segments of 7—segment displays.
Seven segment display character representations
Alphabetic display
In addition to the ten numerical, seven segment display can be used to show Latin ,Cyrillic and
Greek alphabets including punctuation, but only few representations are unambiguously by using
a mixture of letter cases(AbcdEF is typical) and using a representation of 6 that has the top
segment illuminated.
Application
i. During trouble shooting
ii. Short message giving status information (e.g “no DISC” on CD player)
Numbers to seven –segment code
23. A single byte can encode the full state of a 7-segment display. The most popular bit encoding are
g,f,e,e,c,b,g and abcdefg. Both usually assumed 0 is off and1 is on.
Digit gfedcba abcdefg a b c d e f g
0 0*3F 0*7E 1 1 1 1 1 1 0
1 0*06 0*30 0 1 1 0 0 0 0
2 0*5B 0*6D 1 1 0 1 1 0 1
3 0*4F 0*79 1 1 1 1 0 0 1
4 0*66 0*33 0 1 1 0 0 1 1
5 0*6D 0*5B 1 0 1 1 0 1 1
6 0*7D 0*5F 1 0 1 1 1 1 1
7 0*07 0*70 1 1 1 0 0 0 0
8 0*7F 0*7F 1 1 1 1 1 1 1
9 0*6F 0*7B 1 1 1 1 0 1 1
26. LOGIC GATES
logic gates operate with binary numbers
types of logic gates
1) The OR gate
Circuit representation 2 input OR gate
Truth table
A B C
0 0 0
0 1 1
1 0 1
1 1 1
The OR gate has an output of 1(switch closed) when either A or B or both are closed. Denoted by +
A + B = C or A OR B = C
27. 2) ExclusiveOR gate
A C
B
Behaves like a two way switch
Truth table
A B C
0
0
1
1
0
1
0
1
0
1
1
0
The XOR gate has its output 1when its input is different and an output of 0 when its input is same.
Denoted by
A B = C or A XOR B = C
3) The AND gate
A
C
B circuit representation
28. Truth table
A B C
0
0
1
1
0
1
0
1
0
0
0
1
Given an output 1 when both switches are 1.
Denoted by X, ₀
A × B = C
A.B = c
AB = C
4) The NOT gate
A B
Truth table
Inverts the input or A = Ā
A B
0
1
1
0
29. 5) The NOR gate
A
C
B
Will have an output 1 only when all its inputs are 0
Truth table
A B C
0
0
1
1
0
1
0
1
1
0
0
0
A
B C
30. The logic gates used in this project is an CD400 IC which is the combination of
NOR gate and NOT gate giving an output equivalent to an OR gate.
6) The exclusiveNOR gate XNOR
A
C
B
Truth table
A B C
0
0
1
1
0
1
0
1
1
0
0
1
XNOR has an output 1 when the inputs are all the same and output 0 when inputs are different.
7) The NAND gate
A
C
B
31. Truth table
A B C
0
0
1
1
0
1
0
1
1
1
1
0
The NAND has an output 0 when the inputs are all 1 or switch closed and output 1 when each of
the inputs are closed differently are open.
LAWS OF BOOLEAN ALGEBRA
1. OR laws
A + 0 = A A + Ā = A when A = 0, Ā = 1
A + 1 = 1 A + A = 1 A + A = 0 + 1 = 1
When A = 1, Ā = 0
A + Ā = 1 + 0 = 1
32. 2. AND laws
A – 0 = 0 A.A = A when A = 0, Ā = 1
A – 1 = A A.Ā = 0 A.A = 0 * 1
= 0
When A = 1, Ā = 0
A.Ā = 1.0 = 0
3. NOT LAWS
Ō = 1 Ā = A
Ī = 0
33. 4000 dual 3- input NOR and NOT gate
The 3 input NOR gates and a single NOT gate is one package
1
2 13
General characteristics
Supply; 3 to 15V, small fluctuations are tolerated.
Inputs; have very high impedance (resistance). This is a good because it means they will
not affect the part of the circuit where they are connected. However it also means that the
unconnected inputs can easily pick up electrical noise and rapidly change between high
and low states in an unpredictable way. This is likely to make the IC behave erratically and
it will significantly increase the supply current. To prevent problems all un used inputs
must be connected to the supply (either +Vs. or 0V). This applies even if that part of the IC
is not being used in the circuit.
Outputs; can sink and source only about 1mA if you wish to maintain the correct output
voltage to drive the CMOS input. If there is no need to drive any inputs the maximum
current is about 5mA with a 6V supply (just enough to light an LED). To switch larger
currents you can connect a transistor.
Fan –out; one output can drive up to 50 inputs.
Gate propagation time; typically 30ns for a signal to travel through a gate with a 9v supply,
it takes a longer time at a lower supply voltages.
40000
1
34. Power consumption; is very low, a few ųW. It is much great at high frequencies.
Circuit representationof the CD 4000 3 input NOR NOTIC
14
3
4 6 8 9
5
7
N1 = NOR gate representation
N2 NOT gate representation
3,4,5 are input NOR 1 of the IC
6 is the output NOR1 of the IC
8 Is the input NOT of the IC
9 is the output NOT of the IC
14 is the connection to the VCC or supply voltage
7 is the connection to the 0V or ground voltage.
35. Truth table of the gates
NOR gate
3 4 5 6
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
1
0
0
0
0
0
0
0
Boolean algebra
NOR gate
A + B + C = D or 3+4+5 = 6
NOT gate
8 9
1
0
0
1
NOT gate
D = D not the output of the NOR gate is complimented by NOT gate
36. Piezo transducers
These are output transducers which convert an electrical signal to sound.
They require a driver circuit (such as 555 timers or a stable) to provide a signal and if the signal is
near their natural frequencies of about 3KHZ they will produce a particular loud sound.
Requirements
Piezo transducers requiresmall currentusually less than 10mA so they can be
connected directly to the outputs such ICs.
They are ideal for buzzes and beeps, but are not suitable for speech or music
because they distortthe sound.
They are sometimes supplied with red and black leads but they may be connected
either way round. PCBmounting are also available.
Piezo transducers can also be used as input transducers for deting sudden loud
noises or impacts, effectively behaving like crude microphone.
Circuit symbol
