Subsystem: P4

Task Title:
Theft Alarm
Latch

 

Introduction and Aims

To create an alarm system that is triggered by a wire or contact being broken. This is similar to the type of alarm used in shops to protect valuable electrical items - such as computers. Once triggered, this system will remain activated and not turn off until it has been manually reset by pressing a button.


Subsystem Circuit and Block Diagram

 

IP1
Push to Break Switch
P4
Latch
OP1
Sinked
L.E.D. and Buzzer
   


Investigating the System

Using the "Library of Subsystems" here and the circuit and block diagrams above, complete the following:

1, The SCR has three connections to it: G,A and C.These stand for G- , A- and C- . (See P4 Thyristor Latch).

2, Using the LED Resistor link at the top, calculate the value of resistor R1 if: (Vs = 9 volts, If = 30mA and Vf = 2.1 volts)

so R1 = ohms.

3, To turn the SCR off you need to .

 

Modelling the System/Circuit

There are different ways to model and test circuits before components are soldered to a P.C.B.. Modelling is an important stage as it helps you spot any problems and make modifications more easily.

Method 1: Breadboard

Using this method, components are pushed into the interconnected holes as shown in the diagram below. The lines shown, indicate which holes are internally connected.

Print this page and by using the circuit diagram above, design the breadboard layout for this system.

Method 2: Computer Simulation

To begin, ask your supervisor if circuit simulation software is available on your PC. This method allows you to build up your circuits quickly and cheaply in a virtual environment but will not give you hands-on experience of the components you will be using when finally soldering your P.C.B..

Method 3: Using OnTrack modelling hardware

See P4 project guide.