alarm circuit
DESCRIPTION
Alarm circuitTRANSCRIPT
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Systems ApproachBurglar Alarm Project
PROBLEM SITUATION
DESIGN BRIEF
SYSTEMANALYSIS
SPECIFICATION
SOLUTION
ResourceSelection
Build & Test
ComputerSimulation
DATA SHEETS
Evaluation
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Problem SituationBurglar 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 pressure mat gives a high (1) output when stood on.
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 electronic control sub-system is based on a combinational logic circuit which operates the alarm via a transistor
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Design BriefBurglar Alarm Project
Design an electronic logic control sub-system to process the signal from the Inputs in order to operate the Alarm buzzer as described
above
DESIGN BRIEF
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Systems ApproachBurglar Alarm Project
PROBLEM SITUATION
DESIGN BRIEF
SYSTEMANALYSIS
SPECIFICATION
SOLUTION
ResourceSelection
Build & Test
ComputerSimulation
DATA SHEETS
Evaluation
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Systems Approach
PROCESS
INPUT OUTPUT
Any device or system can be analysed in terms of INPUT,
PROCESS & OUTPUT
The universal System Diagram
Burglar Alarm Project
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Burglar Alarm Project
The universal System Diagram
Burglar Alarm
INPUT OUTPUT
A) Arm Key ActivatedB) Burglar Through DoorC) Burglar Through Window
Z) SCARY SOUND ENERGY
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The system diagram can be broken down into a sub system diagram:
Burglar Alarm Project
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A
B
C
Z SCARY SOUND ENERGY
Arm Key Activated
Burglar Thru Door
Burglar Thru Window
System Boundary
Subsystem Inputs
Subsystem Outputs
Process Subsystems
Reed Switch
N/C
Micro Switch
N/O
Pressure Switch
N/O
Inverter OR
AND LATCH
DRIVER
BUZZER
Sub System Diagram
Manual Reset
D
Push Button
N/O
Burglar Alarm Project
System OUTPUTS
System INPUTS
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Systems ApproachBurglar Alarm Project
PROBLEM SITUATION
DESIGN BRIEF
SYSTEMANALYSIS
SPECIFICATION
SOLUTION
ResourceSelection
Build & Test
ComputerSimulation
DATA SHEETS
Evaluation
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Burglar Alarm Project
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
SPECIFICATION
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Systems ApproachBurglar Alarm Project
PROBLEM SITUATION
DESIGN BRIEF
SYSTEMANALYSIS
SPECIFICATION
SOLUTION
ResourceSelection
Build & Test
ComputerSimulation
DATA SHEETS
Evaluation
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Solution
Burglar Alarm Project
SIMULATION LINK
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Solution
Burglar Alarm Project
SIMULATION LINK
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Solution
Burglar Alarm Project
SIMULATION LINK
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Solution
Burglar Alarm Project
SIMULATION LINK
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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 SIMULATION LINK
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Systems ApproachBurglar Alarm Project
PROBLEM SITUATION
DESIGN BRIEF
SYSTEMANALYSIS
SPECIFICATION
SOLUTION
ResourceSelection
Build & Test
ComputerSimulation
DATA SHEETS
Evaluation
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Subsystem INPUT Devices
Micro Switch
N/O
Reed Switch
N/C
Pressure Switch
N/O
Burglar Alarm Project
Selection of Resources
For detecting pressure under mat when burglar comes through
window
For detecting when door is locked “Arming” the alarm
For detecting when the door is open. (This switch is high when the door is
closed)
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Subsystem PROCESS Devices
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 (transistortransistor 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.
Burglar Alarm Project
Selection of Resources
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Subsystem PROCESS Devices
OR (TTL 7432) NOR (TTL 7402)
AND (TTL 7408) INVERTER (TTL 7408)
Burglar Alarm Project
Used to detect when the arm key is activated AND a burglar is in the
system
Used to detect when a burglar comes through the Door OR through the
window
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
Inverts out put from N/C reeds switch to detect when Door is
open
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Subsystem OUTPUT Devices
10K Ohm Resistor
Protective Diode
BC 108 NPN
Transistor
Burglar Alarm Project
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
For producing Scary Noise Energy at a noise level of 85 db
BUZZER 6v, 30mA
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Systems ApproachBurglar Alarm Project
PROBLEM SITUATION
DESIGN BRIEF
SYSTEMANALYSIS
SPECIFICATION
SOLUTION
ResourceSelection
Build & Test
ComputerSimulation
DATA SHEETS
Evaluation
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DATA ON TTL 74HC04 ‘INVERTER’ CHIP
Burglar Alarm Project
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DATA ON TTL 74HC32 ‘OR’ CHIP
Burglar Alarm Project
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DATA ON TTL 74HC08 ‘AND’ CHIP
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DATA ON TTL 74HC02 ‘NOR’ CHIP
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Systems ApproachBurglar Alarm Project
PROBLEM SITUATION
DESIGN BRIEF
SYSTEMANALYSIS
SPECIFICATION
SOLUTION
ResourceSelection
Build & Test
ComputerSimulation
DATA SHEETS
Evaluation
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BREAD BOARD
Burglar Alarm Project
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BREAD BOARD
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BREAD BOARD
Burglar Alarm Project
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BREAD BOARD
Burglar Alarm Project
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RESET
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Systems ApproachBurglar Alarm Project
PROBLEM SITUATION
DESIGN BRIEF
SYSTEMANALYSIS
SPECIFICATION
SOLUTION
ResourceSelection
Build & Test
ComputerSimulation
DATA SHEETS
Evaluation