Alarm circuit

Systems ApproachBurglar Alarm Project

PROBLEM SITUATION

DESIGN BRIEF

SYSTEMANALYSIS

SPECIFICATION

SOLUTION

ResourceSelection

Build & Test

ComputerSimulation

DATA SHEETS

Evaluation

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

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


PROBLEM SITUATION

DESIGN BRIEF

SYSTEMANALYSIS

SPECIFICATION

SOLUTION

ResourceSelection

Build & Test

ComputerSimulation

DATA SHEETS

Evaluation

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


The universal System Diagram

Burglar Alarm

INPUT OUTPUT

A) Arm Key ActivatedB) Burglar Through DoorC) Burglar Through Window

Z) SCARY SOUND ENERGY

The system diagram can be broken down into a sub system diagram:


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


System OUTPUTS

System INPUTS


PROBLEM SITUATION

DESIGN BRIEF

SYSTEMANALYSIS

SPECIFICATION

SOLUTION

ResourceSelection

Build & Test

ComputerSimulation

DATA SHEETS

Evaluation


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


PROBLEM SITUATION

DESIGN BRIEF

SYSTEMANALYSIS

SPECIFICATION

SOLUTION

ResourceSelection

Build & Test

ComputerSimulation

DATA SHEETS

Evaluation

Solution


SIMULATION LINK

Solution


SIMULATION LINK

Solution


SIMULATION LINK

Solution


SIMULATION LINK

Solution


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


PROBLEM SITUATION

DESIGN BRIEF

SYSTEMANALYSIS

SPECIFICATION

SOLUTION

ResourceSelection

Build & Test

ComputerSimulation

DATA SHEETS

Evaluation

Subsystem INPUT Devices

Micro Switch

N/O

Reed Switch

N/C

Pressure Switch

N/O


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)

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.


Selection of Resources

Subsystem PROCESS Devices

OR (TTL 7432) NOR (TTL 7402)

AND (TTL 7408) INVERTER (TTL 7408)


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

Subsystem OUTPUT Devices

10K Ohm Resistor

Protective Diode

BC 108 NPN

Transistor


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


PROBLEM SITUATION

DESIGN BRIEF

SYSTEMANALYSIS

SPECIFICATION

SOLUTION

ResourceSelection

Build & Test

ComputerSimulation

DATA SHEETS

Evaluation

DATA ON TTL 74HC04 ‘INVERTER’ CHIP


DATA ON TTL 74HC32 ‘OR’ CHIP


DATA ON TTL 74HC08 ‘AND’ CHIP


DATA ON TTL 74HC02 ‘NOR’ CHIP



PROBLEM SITUATION

DESIGN BRIEF

SYSTEMANALYSIS

SPECIFICATION

SOLUTION

ResourceSelection

Build & Test

ComputerSimulation

DATA SHEETS

Evaluation

BREAD BOARD


BREAD BOARD


BREAD BOARD


BREAD BOARD


RESET


PROBLEM SITUATION

DESIGN BRIEF

SYSTEMANALYSIS

SPECIFICATION

SOLUTION

ResourceSelection

Build & Test

ComputerSimulation

DATA SHEETS

Evaluation

Alarm circuit

Engineering