Systems
Approach
Burglar Alarm
Project
PROBLEM
SITUATION
DESIGN
BRIEF
DATA SHEETS
SYSTEM
ANALYSIS
Evaluation
Build & Test
SPECIFICATION
Computer
Simulation
SOLUTION
Resource
Selection
Problem
Situation
Burglar
Alarm
Project
PROBLEM
SITUATION
An Alarm company is developing a simple low cost security system for use in a new block
of small flats
The electronic control sub-system is based on a combinational logic circuit which
operates the alarm via a transistor
The alarm “arm switch” is incorporated into the the front door key lock. Locking the door
will set the alarm giving signal high (1).
A Reed switch and magnet are mounted on the door and frame and gives a low(0)
signal when the door is opened
The pressure mat gives a high (1) output when stood on.
Design
Brief
Burglar
Alarm
Project
DESIGN
BRIEF
Design an electronic logic control sub-system to process the signal from the
Inputs in order to operate the Alarm buzzer as described above
Systems
Approach
Burglar Alarm
Project
PROBLEM
SITUATION
DESIGN
BRIEF
DATA SHEETS
SYSTEM
ANALYSIS
Evaluation
Build & Test
SPECIFICATION
Computer
Simulation
SOLUTION
Resource
Selection
Systems
Approach
Burglar Alarm
Project
The universal System Diagram
INPUT
PROCESS
OUTPUT
Any device or system can be analysed in
terms of INPUT, PROCESS & OUTPUT
Burglar Alarm Project
The universal System Diagram
INPUT
Burglar
Alarm
A) Arm Key Activated
B) Burglar Through Door
C) Burglar Through Window
OUTPUT
Z) SCARY SOUND ENERGY
Burglar Alarm Project
The system diagram can be broken down into a sub
system diagram:
Burglar Alarm Project
System
INPUTS
D
Subsystem
Inputs
Process
Subsystems
Subsystem
Outputs
System
OUTPUTS
Push Button
N/O
Manual Reset
AND
Micro
Switch N/O
A
LATCH
DRIVER
Arm Key Activated
Reed
Switch N/C
B
Inverter
OR
BUZZER
Burglar Thru Door
Z
Pressure
Switch N/O
C
SCARY
SOUND
ENERGY
Burglar Thru
Window
System Boundary
Sub System Diagram
Systems
Approach
Burglar Alarm
Project
PROBLEM
SITUATION
DESIGN
BRIEF
DATA SHEETS
SYSTEM
ANALYSIS
Evaluation
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SPECIFICATION
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Simulation
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Burglar Alarm Project
SPECIFICATION
The System Must:
1) Detect a Burglar entering through the door or the window
2) Enable owner to disable it to go about their business
without setting it off
3) It must give a continuous audible warning to deter
burglars, and should be reset by owner
4) It should be low cost, reliable and durable
5) Sensor should be unobtrusive
Systems
Approach
Burglar Alarm
Project
PROBLEM
SITUATION
DESIGN
BRIEF
DATA SHEETS
SYSTEM
ANALYSIS
Evaluation
Build & Test
SPECIFICATION
Computer
Simulation
SOLUTION
Resource
Selection
Burglar Alarm Project
SIMULATION LINK
Solution
Burglar Alarm Project
SIMULATION LINK
Solution
Burglar Alarm Project
SIMULATION LINK
Solution
Burglar Alarm Project
SIMULATION LINK
Solution
Burglar Alarm Project
A
(Arm Key)
B
(Reed Switch)
C
(Pressure Mat)
Buzzer
0
0
0
0
0
0
1
0
0
1
0
0
0
1
1
0
1
0
0
1
1
0
1
1
1
1
0
0
1
1
1
1
Solution
SIMULATION LINK
Systems
Approach
Burglar Alarm
Project
PROBLEM
SITUATION
DESIGN
BRIEF
DATA SHEETS
SYSTEM
ANALYSIS
Evaluation
Build & Test
SPECIFICATION
Computer
Simulation
SOLUTION
Resource
Selection
Burglar Alarm Project
Selection of Resources
Pressure
Switch N/O
For detecting pressure under mat when
burglar comes through window
Micro
Switch N/O
For detecting when door is locked
“Arming” the alarm
Reed
Switch N/C
For detecting when the door is open.
(This switch is high when the door is closed)
Subsystem INPUT Devices
Burglar Alarm Project
Selection of Resources
Integrated circuits consist of plastic cases filled with electronic circuitry.
There are many resistors, transistors and other components packed into
the chips. There are literally thousands of ICs on the market, all designed
to do different jobs – logic gates, amplifiers, timers, etc.
In this work we will be using the TTL (transistortransistor logic) range of
chips.
TTL chips require a stable 5V supply to work properly. (Great difficulties
will be met if any other voltage is used.) Any unconnected pins
automatically go to logic 1. In other words, if a wire connected to a pin
is connected to the 0-volt rail (logic 0), it will go to logic 0. If the wire is
disconnected from the 0-volt rail it will go to logic 1. However, it is good
practice to connect pins to ‘high’ or ‘low’ as needed.
All TTL chips have a four-digit code number, which always starts with 74.
For example, a 7400 is a quad two-input NAND chip.
Although the chip contains complex circuitry, the internal wiring can be
shown as simple logic circuits with the inputs and outputs of each logic
gate shown. This is called a pin-out diagram.
Subsystem PROCESS Devices
Burglar Alarm Project
AND (TTL 7408)
Used to detect when the arm key is activated
AND a burglar is in the system
OR (TTL 7432)
Used to detect when a burglar comes
through the Door OR through the window
INVERTER (TTL 7408)
Inverts out put from N/C reeds switch to
detect when Door is open
NOR (TTL 7402)
2 cross coupled Nor Gates make an SR
FLIP-FLOP Keeping the output high if a
burglar closes the door or steps off the mat
Subsystem PROCESS Devices
Burglar Alarm Project
BUZZER
6v, 30mA
BC 108 NPN
Transistor
10K Ohm
Resistor
Protective
Diode
For producing Scary Noise Energy at a
noise level of 85 db
Used for switching and driving the
buzzer
This is a protective resistor used at the
transistor base
This will protect the the transistor from back
emf generated by the buzzer when the
Buzzer is reset
Subsystem OUTPUT Devices
Systems
Approach
Burglar Alarm
Project
PROBLEM
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DESIGN
BRIEF
DATA SHEETS
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ANALYSIS
Evaluation
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SPECIFICATION
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Simulation
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Selection
Burglar Alarm Project
DATA ON TTL 74HC04 ‘INVERTER’ CHIP
Burglar Alarm Project
DATA ON TTL 74HC32 ‘OR’ CHIP
Burglar Alarm Project
DATA ON TTL 74HC08 ‘AND’ CHIP
Burglar Alarm Project
DATA ON TTL 74HC02 ‘NOR’ CHIP
Systems
Approach
Burglar Alarm
Project
PROBLEM
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DESIGN
BRIEF
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ANALYSIS
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Burglar Alarm Project
BREAD BOARD
Burglar Alarm Project
BREAD BOARD
Burglar Alarm Project
BREAD BOARD
Burglar Alarm Project
BREAD BOARD
RESET
Systems
Approach
Burglar Alarm
Project
PROBLEM
SITUATION
DESIGN
BRIEF
DATA SHEETS
SYSTEM
ANALYSIS
Evaluation
Build & Test
SPECIFICATION
Computer
Simulation
SOLUTION
Resource
Selection