1. Systems Approach Burglar Alarm Project PROBLEM SITUATION DESIGN
BRIEF
DATA SHEETS
SYSTEM
ANALYSIS
Evaluation
Build & Test
SPECIFICATION
SOLUTION
Computer
Simulation
Resource
Selection

2. 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.

3. 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

4. Systems Approach Burglar Alarm Project PROBLEM SITUATION DESIGN
BRIEF
DATA SHEETS
SYSTEM
ANALYSIS
Evaluation
Build & Test
SPECIFICATION
SOLUTION
Computer
Simulation
Resource
Selection

5. The universal System Diagram
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

6. The universal System Diagram
Burglar Alarm Project
The universal System Diagram
Burglar Alarm
INPUT
OUTPUT
A) Arm Key Activated
Z) SCARY SOUND ENERGY
B) Burglar Through Door
C) Burglar Through Window

7. Burglar Alarm Project
The system diagram can be broken down into a sub system diagram:

8. Burglar Alarm Project Sub System Diagram
System INPUTS
Subsystem Inputs
Process Subsystems
Subsystem Outputs
System OUTPUTS D
Push Button N/O
Manual Reset
Micro Switch N/O
AND A
LATCH
DRIVER
Arm Key Activated
Reed Switch N/C OR B
Inverter
BUZZER
Burglar Thru Door Z
SCARY SOUND ENERGY
Pressure Switch N/O C
Burglar Thru Window
System Boundary
Sub System Diagram

9. Systems Approach Burglar Alarm Project PROBLEM SITUATION DESIGN
BRIEF
DATA SHEETS
SYSTEM
ANALYSIS
Evaluation
Build & Test
SPECIFICATION
SOLUTION
Computer
Simulation
Resource
Selection

10. Burglar Alarm Project The System Must:
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

11. Systems Approach Burglar Alarm Project PROBLEM SITUATION DESIGN
BRIEF
DATA SHEETS
SYSTEM
ANALYSIS
Evaluation
Build & Test
SPECIFICATION
SOLUTION
Computer
Simulation
Resource
Selection

12. Burglar Alarm Project Solution
SIMULATION LINK
Solution

13. Burglar Alarm Project Solution
SIMULATION LINK
Solution

14. Burglar Alarm Project Solution
SIMULATION LINK
Solution

15. Burglar Alarm Project Solution
SIMULATION LINK
Solution

16. Burglar Alarm Project Solution
(Arm Key) B
(Reed Switch) C
(Pressure Mat)
Buzzer 1
SIMULATION LINK
Solution

17. Systems Approach Burglar Alarm Project PROBLEM SITUATION DESIGN
BRIEF
DATA SHEETS
SYSTEM
ANALYSIS
Evaluation
Build & Test
SPECIFICATION
SOLUTION
Computer
Simulation
Resource
Selection

18. Burglar Alarm Project Selection of Resources Subsystem INPUT Devices
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

19. Selection of Resources Subsystem PROCESS 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

20. Burglar Alarm Project Subsystem PROCESS Devices
AND (TTL 7408)
INVERTER (TTL 7408)
Used to detect when the arm key is activated AND a burglar is in the system
Inverts out put from N/C reeds switch to detect when Door is open
OR (TTL 7432)
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
Used to detect when a burglar comes through the Door OR through the window
Subsystem PROCESS Devices

21. Burglar Alarm Project Subsystem OUTPUT Devices
BUZZER 6v, 30mA
For producing Scary Noise Energy at a noise level of 85 db
BC 108 NPN Transistor
Used for switching and driving the buzzer
10K Ohm Resistor
This is a protective resistor used at the transistor base
Protective Diode
This will protect the the transistor from back emf generated by the buzzer when the Buzzer is reset
Subsystem OUTPUT Devices

22. Systems Approach Burglar Alarm Project PROBLEM SITUATION DESIGN
BRIEF
DATA SHEETS
SYSTEM
ANALYSIS
Evaluation
Build & Test
SPECIFICATION
SOLUTION
Computer
Simulation
Resource
Selection

23. DATA ON TTL 74HC04 ‘INVERTER’ CHIP
Burglar Alarm Project
DATA ON TTL 74HC04 ‘INVERTER’ CHIP

24. Burglar Alarm Project
DATA ON TTL 74HC32 ‘OR’ CHIP

25. DATA ON TTL 74HC08 ‘AND’ CHIP
Burglar Alarm Project
DATA ON TTL 74HC08 ‘AND’ CHIP

26. DATA ON TTL 74HC02 ‘NOR’ CHIP
Burglar Alarm Project
DATA ON TTL 74HC02 ‘NOR’ CHIP

27. Systems Approach Burglar Alarm Project PROBLEM SITUATION DESIGN
BRIEF
DATA SHEETS
SYSTEM
ANALYSIS
Evaluation
Build & Test
SPECIFICATION
SOLUTION
Computer
Simulation
Resource
Selection

28. Burglar Alarm Project
BREAD BOARD

29. Burglar Alarm Project
BREAD BOARD

30. Burglar Alarm Project
BREAD BOARD

31. Burglar Alarm Project
BREAD BOARD

32. RESET

33. Systems Approach Burglar Alarm Project PROBLEM SITUATION DESIGN
BRIEF
DATA SHEETS
SYSTEM
ANALYSIS
Evaluation
Build & Test
SPECIFICATION
SOLUTION
Computer
Simulation
Resource
Selection