7661004-basics-ele-01

8/8/2019 7661004-Basics-Ele-01

1/488

Electronics Index Page

CLICK HERE FOR INDEX PAGE

V. Ryan 2002-2007

The section is aimed at introducing pupils to basic concepts of electronics. You will find that a rang

of basic electronics is covered including; component symbols, power sources, diodes, capacitors,

ransistors, LEDs and many more. Click on the aspect of electronics outlined below to view the

nformation sheets.

COMPONENTS / SYMBOLS

1. Electronic Components and Symbols - 1

2. Electronic Components and Symbols - 2

3.Electronic Components and Symbols - 3

4. Symbols Summary Sheet

5. Lesson Starter - Electronic Components6. Lesson Starter - Electronic Tools and Equipment

7. Basic Electronics - Wordsearch Exercise

COMPONENT AND CIRCUIT DETAILS

1. Batteries and LEDs

2. Button Batteries / Coin Cells - Simple Circuits

3. Switches -1

4. Switches - 2

5. Switches - 3

6. Incandescent Lamps (Bulbs) 1

7. Incandescent Lamps (Bulbs) 2

8. Series Circuits

9. Circuits in Parallel

ttp://www.technologystudent.com/elec1/elecex.htm (1 of 6)18/02/08 11:00 AM

8/8/2019 7661004-Basics-Ele-01

2/488


10. A Series / Parallel Circuit

11. Basic Circuit using Crocodile Technology

Circuit Simulation Software

12. The Diode

13. Capacitors

14. Resistors

15. Using Crocodile Technology to Test theRelationship between Resistors and Capacitors

16. Test Instruments

17. Light Dependent Resistors

18. The Preset Resistor

19.Making a Light / Dark Sensor

20. Sequence Drawing - Light/Dark Sensor

21. LDR Examination Question - 1

22. LDR Examination Question - 223 LDR Examination Question - 3

24. Sensor Question - LDR

25. Switches, Diode, Transistor and General Circuit Questions

26. The Thermistor

27. Information Regarding Thermistor Circuits and Darlington Pairs

28. A Typical Temperature Sensor

29. Potential Dividers

30. SI Units and OHM's Law

31. Resistors - Questions

32. Relays and Practical Circuits

33. The Basics on Transistors

34. Transistors - Darlington Pairs

35. Transistor Exam Question

36. Transistor Breadboard Project

37. Transistor Darlington Pair Breadboard Project

38. Transistor Formulas and Calculations

39. Dual Transistor Multivibrator Circuit

40. Lesson Starter - Astable Transistor Circuit (Multivibrator)

41. Examination Questions : Dual Transistor Multivibrator Circuits

42. The Thyristor

43. Steady Hand Game - Thyristor Circuit

44. Breadboards

45. Examination Questions - Jigs


8/8/2019 7661004-Basics-Ele-01

3/488


CONTROL SYSTEMS

1. Analogue / Digital Systems

2. Control Systems

3. Control Systems - An Example

MODULAR ELECTRONICS

1. Modular Electronics

2. Modular Electronics - Control Studio -13. Modular Electronics - Control Studio -2

4. Modular Electronics - Control Studio -3

DIGITAL ELECTRONICS AND LOGIC GATES1. Digital Electronics and Logic Circuits - 1

2. Digital Electronics and Logic Gates - 2 (Role of Transistors)

3. Basic Logic Gates and Logic Tables

4. Alternative representations of Logic Tables

5. Example Logic Circuit - 1

6. Example Logic Circuit - 2

7. The 4081B Integrated Circuit (AND gate) - a Practical Example.

8. The 4081B - Circuit Design

9. Digital Logic Circuit Exam Question 1



12. AND Gate Sample Question

13. AND Gate Sample Answer

12. The Binary System

13. Integrated Circuits - 1



8/8/2019 7661004-Basics-Ele-01

4/488



THE 555 INTEGRATED CIRCUIT1. The 555 Integrated Circuit (Timer) - a Simple Explanation

2. The 555 IC as an ASTABLE Circuit

3. The 555 IC as a MONOSTABLE Circuit

4. 555 MONOSTABLE Examples5. The MONOSTABLE Circuit in more detail

6. Animation 1 - 555 Timer Circuit - Frames Created by Crocodile Technology 3D

7. Animation 2 - 555 Timer Circuit - Frames Created by Crocodile Technology 3D

8. Monostable Timer Examination Questions - 1

9. Monostable Timer Examination Questions - 2

10. ASTABLE 555 Breadboard Project11. 555 ASTABLE Examples

12. The ASTABLE Circuit in more detail

THE 741 OPERATIONAL AMPLIFIER1. The Operation Amplifier used as an Amplifier - a Simple Explanation

2. The 741 Operational Amplifier used as an Amplifier with Sensors

3. The 741 Operational Amplifier - an introduction4. Inverting and Non-inverting 741 Amplifiers

5. The 741 Operational Amplifier as a Comparator

6. 741 Operational Amplifier Comparator Examination Questions and Information

THE 4017B DECADE COUNTER1. How the 4017B decade Counter Works

2. Adding a Motor and a Solenoid to the 4017B Decade Counter

(UNDER CONSTRUCTION)


8/8/2019 7661004-Basics-Ele-01

5/488


1. INDIVIDUAL RESEARCH THEME and EXAMINATION QUESTIONS

THEME: RAILWAY TRANSPORT

CONTEXT: OPERATING SYSTEMS

Pupils research the theme as they work through the resources/questions below. They should draw o

all the skills and techniques developed through the Systems and Control course.

*PLEASE NOTE: You may need to use the search facility on the index pageof this site to findnformation when answering some of the questions*

1. Systems Preparation Questions 2007 - 1

2.Systems Preparation Questions 2007 - 2


4. Systems Preparation Questions 2007 - 45. Systems Preparation Questions 2007 - 5














Web

www.technologystudent.

com


Search
http://www.google.com/

8/8/2019 7661004-Basics-Ele-01

6/488



8/8/2019 7661004-Basics-Ele-01

7/488

A Design and Technology Site

A DESIGN AND TECHNOLOGY SITE

This website contains numerous information sheets and exercises to enhance the study, understandi

and teaching of DESIGN and TECHNOLOGY.

( CLICK HERE FOR THE WORLD ASSOCIATION OF TECHNOLOGY TEACHERS)

ttp://www.technologystudent.com/index.htm (1 of 3)18/02/08 11:00 AM

8/8/2019 7661004-Basics-Ele-01

8/488


TECHNOLOGYSTUDENT.COM - SITE SEARCH

Search for:

The information sheets cover a wide range and include, the design process, gear systems, electronics, cams,rinted circuit boards, PIC microcontrollers / computer control, key words/phrases, structures, vocational wo

chnology and cultures, basic CNC work. They are intended to provide a valuable resource for teachers and

upils AND they are free. By using this website you are agreeing to abide by the copyright outlined below.

V. Ryan 2002-2005

CONTACT THE AUTHOR ? - [email protected]


Start Search Reset
mailto:[email protected]:[email protected]

8/8/2019 7661004-Basics-Ele-01

9/488


JOIN W.A.T.T - CLICK ABOVE

his work is protected by copyright law and international copyright treaties as well as other intellectual propws and treaties.

opyright law and other intellectual property laws in many countries protect the rights of the owner/author b

ranting to the owner/author a number of exclusive rights. Copying, changing, editing or publishing software

rintouts without the permission of the owner is "copyright infringement," and the law imposes penalties on

fringers. These information sheets can be used by teachers and pupils. They can be printed and used for

ducational purposes but must not be edited in any form or placed on other Websites.

COPYRIGHT AND DISCLAIMER


8/8/2019 7661004-Basics-Ele-01

10/488

lectronic Components and Symbols - 1


ELECTRONIC COMPONENTS AND SYMBOLS - 1

V. Ryan 2005

Web


com

here are a large number of symbols which represent an equally large range of electronic componentsimportant that you can recognise the more common components and understand what they actually

number of these components are drawn below and it is interesting to note that often there is more th

ne symbol representing the same type of component. (Check all your information sheets in the

ectronics section for more symbols).

ttp://www.technologystudent.com/elec1/compn1.htm (1 of 4)18/02/08 11:00 AM

Search

8/8/2019 7661004-Basics-Ele-01

11/488



8/8/2019 7661004-Basics-Ele-01

12/488



8/8/2019 7661004-Basics-Ele-01

13/488


CLICK HERE FOR MORE COMPONENTS AND SYMBOLS

CLICK HERE FOR ELECTRONICS INDEX PAGE


8/8/2019 7661004-Basics-Ele-01

14/488




V. Ryan 2005

Web


com






Search

8/8/2019 7661004-Basics-Ele-01

15/488



8/8/2019 7661004-Basics-Ele-01

16/488


CLICK HERE FOR MORE COMPONENTS AND SYMBOLS


8/8/2019 7661004-Basics-Ele-01

17/488




8/8/2019 7661004-Basics-Ele-01

18/488




V. Ryan 2005

Web


com






Search

8/8/2019 7661004-Basics-Ele-01

19/488



8/8/2019 7661004-Basics-Ele-01

20/488




8/8/2019 7661004-Basics-Ele-01

21/488

Electronic Components


COMPONENT SYMBOLS

V. Ryan 2002

Web


com

There are a large number of symbols which represent an equally large range of electroniccomponents. It is important that you can recognise the more common components and

understand what they actually do. A number of these components are drawn below and it is

interesting to note that often there is more than one symbol representing the same type of

component. (Check all your information sheets in the electronics section for more symbols).

ttp://www.technologystudent.com/elec1/comps1.htm (1 of 3)18/02/08 11:01 AM

Search

8/8/2019 7661004-Basics-Ele-01

22/488



8/8/2019 7661004-Basics-Ele-01

23/488




8/8/2019 7661004-Basics-Ele-01

24/488

esson Starter - Electronics


LESSON STARTER - ELECTRONICS

V. Ryan 2005

Web


com

IDENTIFYING ELECTRONIC COMPONENTS

elow are a number of common electronic components you are likely to use when making circuits.

nderneath each component write the correct name.

ttp://www.technologystudent.com/elec1/stelec1.htm (1 of 3)18/02/08 11:01 AM

Search

8/8/2019 7661004-Basics-Ele-01

25/488



8/8/2019 7661004-Basics-Ele-01

26/488


CLICK HERE FOR ANSWERS



8/8/2019 7661004-Basics-Ele-01

27/488

esson starter - Equipment and Components


LESSON STARTER

EQUIPMENT AND TOOLS FOR CIRCUIT WORK

V. Ryan 2005

Web


com

me basic tools / equipment / components you may use when working with circuits are shown below. Nam

ch tool / piece of equipment / component and explain what they are for.

ttp://www.technologystudent.com/elec1/stcomp1.htm (1 of 2)18/02/08 11:01 AM

Search

8/8/2019 7661004-Basics-Ele-01

28/488

esson starter - Equipment and Components

CLICK HERE FOR ANSWERS


ttp://www.technologystudent.com/elec1/stcomp1.htm (2 of 2)18/02/08 11:01 AM

8/8/2019 7661004-Basics-Ele-01

29/488

Basic Electronics - Word Exercise


BASIC ELECTRONICS - WORD EXERCISE

V. Ryan 2006

Create your own wordsearch to help promote a basic understanding of

electronics - using the following words or your own relevant words.

WIRE

SOLDER

PCB

PLIERSGOGGLES

BATTERY

BUZZER

APRON

ELECTRICITY

COMPONENTSTHYRISTOR

CUTTERS

POSITIVE

DIODE

FAULT

SAFETYNEGATIVE

TRANSISTOR

CELL

SAFETY

SWITCHCIRCUIT

You will need two colours for this exercise. Write the words seen above in one

colour and add extra letters in another.

ttp://www.technologystudent.com/elec1/elecgm1.htm (1 of 4)18/02/08 11:02 AM

8/8/2019 7661004-Basics-Ele-01

30/488


SAMPLE ANSWER

Below is the start of a sample answer to the wordsearch. As a word placed in the

grid is crossed off the list below.

WIRESOLDER

PCB

PLIERS

GOGGLES

BATTERY

BUZZERAPRON

ELECTRICITY

COMPONENTS

THYRISTOR

CUTTERS

POSITIVEDIODE

FAULT

SAFETY

NEGATIVE

RESISTOR

TRANSISTORCELL

SAFETY

SWITCH

CIRCUIT


8/8/2019 7661004-Basics-Ele-01

31/488


Try completing the word search started above.


Web


com


Search

8/8/2019 7661004-Basics-Ele-01

32/488



8/8/2019 7661004-Basics-Ele-01

33/488

Batteries and LEDs

Web


com


V. Ryan 2002-05

BATTERIES and LEDs

Many pupils are scared of electronics as they look at the books in the library. These are

often very complex as very few have been written for beginners. This can put off people

from learning about electronics and circuits. Everywhere we look there are examples of

electronics, ranging from a simple radio to a hi-tech digital television. However complex

looking an electronic device may be, they are all based on simple components gathered

together in circuits.

Batteries come in all shapes and sizes.

They store electrical charge and as we all

know when they are put into an electronic

device such as a portable radio, they

provide the power. The usual battery sizes

are seen opposite. These are the type used

in school projects and range from 1.5 volts

to 9 volts.

School projects are powered by batteries

because they are safe, easily bought and

safe.

ttp://www.technologystudent.com/elec1/battery1.htm (1 of 3)18/02/08 11:02 AM

Search

8/8/2019 7661004-Basics-Ele-01

34/488

Batteries and LEDs

QUESTION

This shows one of the most simple

circuits. When the switch is pressed, the

LED (further information below) lights.

Resistors are used in circuits because

LEDs can be destroyed by voltages over

3 volts. Why do you think the circuit

opposite does not have a resistor to

protect the LED ?

ANSWER

Each battery is 1.5 volts. The two

batteries are connected in series, they

are both linked positive to negative and

this gives us a total of 3 volts. Therefore,the LED is safe from damage.

THE LED

Light Emitting Diodes (LED) are very

rugged, they last a very long time and they

are an optical source. (A LIGHT

SOURCE)

LEDs produce red, green, yellow, or

orange light. They are used in a range of

products. Can you name any ?

Infrared LEDs are also available althoughlight from this type cannot be seen by the

human eye. These are used in security

devices.

LEDs are part of the diode family,

consequently they must be connected the

right way round or current will not pass

through. They are usually protected by a

resistor. (See DIODE information sheet).


8/8/2019 7661004-Basics-Ele-01

35/488

Batteries and LEDs

A SELECTION OF THE MOST POPULAR

COLOURS

ENLARGED LED - NOTICE THE LONG

AND SHORT LEG



8/8/2019 7661004-Basics-Ele-01

36/488

Button Batteries/ Coin Cells and Simple Circuits


BUTTON BATTERIES /COIN CELLS AND SIMPLE CIRCUITS

V. Ryan 2008

A button cell is a very small battery. A good example is the type found in most modern watches.

This type of battery is often used in camcorders as backup batteries. They ensure that the date

and time are held in memory even when the rechargeable batteries are removed. Button batteries

are usually rated at 1.5 volts or 3 volts and consequently they are used in devices that need very

little power. Watches are ideal for this type of battery as well as low power calculators andhearing aids. Large button batteries are used as backup batteries for the CMOS of computer

systems and ensure that the basic settings in the setup of the computer are held in memory, even

when the computer is switched off.

TYPICAL BUTTON CELL

ttp://www.technologystudent.com/elec_flsh/button1.html (1 of 5)18/02/08 11:02 AM

8/8/2019 7661004-Basics-Ele-01

37/488


The diagram opposite

shows an LED and two

button batteries. When the

legs of the LED are

pressed against the positive

and negative sides of the

batteries the LED lights. If

an ultra bright LED is usedthe light is quite intense.

The two coin cells shown

are each 1.5 volts. A

typical LED needs 3 volts

to emit light effectively.

The circuit diagram is shown below. The battery, switch and LED symbols have been included.

Although no switch is used in reality, the switch mimics the two fingers pressing the legs of the

LED together against the batteries.

If each button battery is rated as 1.5 volts, when two are arranged in series as shown in the

diagram below, together they are rated as 3 volts. Putting batteries together in series simply

means adding the voltages together. In this way button batteries can be used to provide higher

voltage outputs.


8/8/2019 7661004-Basics-Ele-01

38/488


A simple LED torch can be made by using two sides of compressed polystyrene (high density

polystyrene), two button batteries, an LED and a piece of foam. The polystyrene sides are held

together by double sided tape.

The foam keeps the legs of the LED from touching the terminals of the button batteries. When

the torch is pressed the legs of the LED make contact with the batteries and the LED lights.

The small hand held torch seen below has 4 button batteries each rated at 1.5 volts. This means

that the sum of the batteries is equal to 6 volts. This is enough to allow the bulb to light. Bulbs

were once common in torches but they have been replaced by ultra bright LEDs. LEDs are more

efficient than bulbs, requiring less power and they can last for thousands of hours when in use.

Bulbs on the other hand tend to blow/fail after a relatively short time.


8/8/2019 7661004-Basics-Ele-01

39/488


SIMPLE DESIGN SHEET LAYOUT



8/8/2019 7661004-Basics-Ele-01

40/488


Web


com


Search

8/8/2019 7661004-Basics-Ele-01

41/488

witches


SWITCHES - 1

V. Ryan 2002-04

Web


com

Some common switches are shown on this information sheet. Basically switches bring contacts

together in different ways but they do the same switching job.

Typical Switch Symbols

KEY SWITCH

This switch is available in different

forms. They provide limited security as

key is required to switch them on and

off.

PUSH SWITCH

ttp://www.technologystudent.com/elec1/switch2.htm (1 of 2)18/02/08 11:03 AM

Search

8/8/2019 7661004-Basics-Ele-01

42/488

witches

These can be push to make (push the

switch to allow the circuit to work) or

push to break (push the switch to turn

off the circuit).

ROCKER SWITCH

This switch is common on many

electrical devices. For example they are

found on computer units for turning them

on and off.

CLICK HERE FOR NEXT SWITCHES PAGE



8/8/2019 7661004-Basics-Ele-01

43/488

witches


SWITCHES - 2

V. Ryan 2002-04

Web


com




TOGGLE SWITCH

These are available in miniature and

standard sizes. The advantage of the

toggle switch is that they can be

extended and operated by a lever.

SLIDE SWITCH


Search

8/8/2019 7661004-Basics-Ele-01

44/488

8/8/2019 7661004-Basics-Ele-01

45/488

witches


8/8/2019 7661004-Basics-Ele-01

46/488

witches


SWITCHES - 3

V. Ryan 2002

Web


com




MICRO-SWITCH

Micro-switches can be very small.Usually they include a small arm

which when pressed clicks. They are

very useful and can be found on man

machines - used a safety switches. Fo

example, if the 'lid' of a drilling

machine is opened to change the

pulley speeds, a micro-switch is

released ensuring that all power is

turned off. These switches can be veruseful in school projects

TILT SWITCH


Search

8/8/2019 7661004-Basics-Ele-01

47/488

witches

One of the most common types of tilt

switch uses a blob of mercury in a

small tube. When the tube is tilted thmercury runs down and forms a

bridge across the two contacts turnin

the switch on. This type of switch is

used in warning systems that alert

people to an excessive angle of tilt, e

g. for drivers of farm vehicles.

PRESSURE PAD / SWITCH

This is a soft flexible switch availabl

in many sizes. It consists of two

flexible conductive foil sheets

separated by a thin felt, paper or foam

layer. If pressure is applied the

conductive surfaces touch and the

switch is on



8/8/2019 7661004-Basics-Ele-01

48/488

8/8/2019 7661004-Basics-Ele-01

49/488

ncandescent Lamps (Bulbs) - 1

The conductor at the botto

of this example bulb carries

the current, allowing it to pa

through the filament.

A number of symbols can b

used to represent a bulb. Th

typical symbols are shown

opposite. These are often sein examinations and

consequently it is important

know them.

Two versions of the same circuit are shown below. The conventional circuit diagram (on the left)

hows the filament bulb lighting brightly when the switch is turned on. The current flows through th

ilament, causing light to be emitted.n the pictorial circuit diagram on the right the components are shown as pictures rather than symbo

This basic circuit has a battery as the electrical source and a filament bulb. The bulb is called the

load as it does all the work in the circuit (ie. it lights).

Crocodile Technology software is very useful when simulating this type of circuit diagram.


ttp://www.technologystudent.com/elec1/bulb1.htm (2 of 3)18/02/08 11:06 AM

8/8/2019 7661004-Basics-Ele-01

50/488

ncandescent Lamps (Bulbs) - 1


8/8/2019 7661004-Basics-Ele-01

51/488

ncandescent Lamps (bulbs) 2


INCANDESCENT LAMPS (BULBS) - 2

V. Ryan 2005

Filament bulbs are used in many applications in and around the home. Name and sketch

four examples that you have seen. Add a description of each example.

XAMPLE ANSWER

SKETCH


8/8/2019 7661004-Basics-Ele-01

52/488


SKETCH

SKETCH


8/8/2019 7661004-Basics-Ele-01

53/488


SKETCH

he two bulbs below look very different. However, they are both composed of a filament, placed

nside an envelope of glass. The glass envelope of each bulb contains a gas. However, one of the bu

used in the house for producing standard light and the other is used in a car head light and is very

right.

Web


com


Search

8/8/2019 7661004-Basics-Ele-01

54/488


1. The household bulb is:______________2. The car headlight bulb is:____________

Explain the differences between bulb A and bulb B. You may wish to search the internet

for scientific / technical information on both bulbs



8/8/2019 7661004-Basics-Ele-01

55/488

eries Circuits


SERIES CIRCUITS

V. Ryan 2005

The circuit opposite

shows three bulbs

placed in series. This is

a called a series circuit.

Current flows through

each of the bulbs in

sequence. Currentflows through bulb A,

then bulb B and finally

bulb C. The more bulbs

that are added, the less

bright they shine. It is

possible to added so

many bulbs that they

do not light at all. This

is due to the resistancein each bulb. If any of

the bulbs fail, current

cannot flow through

the circuit and the

other components will

not work.

ANOTHER SERIES CIRCUIT DIAGRAM

ttp://www.technologystudent.com/elec1/srcirc1.htm (1 of 3)18/02/08 11:06 AM

8/8/2019 7661004-Basics-Ele-01

56/488

8/8/2019 7661004-Basics-Ele-01

57/488

eries Circuits

Web


com

ttp://www.technologystudent.com/elec1/srcirc1.htm (3 of 3)18/02/08 11:06 AM

Search

8/8/2019 7661004-Basics-Ele-01

58/488

arallel Circuits


PARALLEL CIRCUITS

V. Ryan 2005

Web


com

he circuit below shows three bulbs placed in parallel. This is a parallel circuit. Current can flow throuch of the bulbs without first having to flow through any others. If any of the bulbs fail the others wil

ll work as current can still flow through the rest of the circuit.

ttp://www.technologystudent.com/elec1/prcir1.htm (1 of 3)18/02/08 11:06 AM

Search

8/8/2019 7661004-Basics-Ele-01

59/488

arallel Circuits

ANOTHER PARALLEL CIRCUIT

he circuit below is another example of a parallel circuit. When the switch is turned on current flows

rough the bulb, solenoid and motor simultaneously. This causes the bulb to light, the solenoid to the

tivated and the motors spindle to rotate, all at the same time.

PICTORIAL DRAWING OF THE SAME PARALLEL CIRCUIT DIAGRAM

Crocodile Technology software is very useful when simulating this type of circuit diagram.

UESTIONS:

Draw a simple parallel circuit and explain how it works.

Draw the same components but this time arranged as a series circuit. How do the two circuits diffe

What will happen if one of the components fails in a parallel circuit?


8/8/2019 7661004-Basics-Ele-01

60/488

arallel Circuits



8/8/2019 7661004-Basics-Ele-01

61/488

eries and Parallel Circuit


A SERIES / PARALLEL CIRCUIT

V. Ryan 2005

Web


com

he circuit below is both series and parallel. If you look closely you will see that the two bulbs are inries with each other whilst the motors are an parallel. All the components provide a clear path for the

rrent.

ttp://www.technologystudent.com/elec1/spcirc1.htm (1 of 2)18/02/08 11:06 AM

Search

8/8/2019 7661004-Basics-Ele-01

62/488

eries and Parallel Circuit

UESTIONS:

What will happen if one of the motors fails to function? Will the entire circuit fail?

Draw another example of a circuit that is both series and parallel.


ttp://www.technologystudent.com/elec1/spcirc1.htm (2 of 2)18/02/08 11:06 AM

8/8/2019 7661004-Basics-Ele-01

63/488



SIMPLE CIRCUIT EXERCISE USING CROCODILE

TECHNOLOGY SIMULATION SOFTWARE

- BATTERY, LED AND SWITCH

V. Ryan 2004

Web


com

The circuit seen below can be built using Crocodile Technology electronics simulation

software. The software allows the circuit designer to build a circuit on the screen of a

computer rather than building a real circuit out of expensive components. It can then be

tested on screen. Furthermore, the software allows pictorial representations of the

components to be used rather than circuit symbols. This makes the circuit look more

realistic.

By now you should have a good

understanding of LEDs and a

limited knowledge of resistors.

Build the circuit seen opposite using

simulation software.

When the switch is closed the LEDlights.

1. If the battery is 9 volts, what role has the resistor?

ttp://www.technologystudent.com/elec1/batcirc.htm (1 of 3)18/02/08 11:07 AM

Search

8/8/2019 7661004-Basics-Ele-01

64/488


2. Using simulation software, build the circuit seen

opposite. This time do not use the pictorial setting,

use actual electronic symbols.

When the switch is closed the LED should light.

3. Build the same circuit but this time remove the

resistor. When the switch is closed the LED and the

switch will explode. Why is the LED destroyed?

FURTHER EXERCISES:

1. Build a circuit using simulation software - composed of a 9 volt supply, a switch, a 380

ohm resistor and two LEDs, arrange in series (one after the other). What do you notice

about the brightness of the LEDS, compared to the same circuit with only one LED?

explain your answer.


8/8/2019 7661004-Basics-Ele-01

65/488




8/8/2019 7661004-Basics-Ele-01

66/488

The Diode

Web


com


THE DIODE

V. Ryan 2002-04

A diode allows electricity to flow in one direction only and blocks the flow in the opposite

direction. They may be regarded as one-way valves and they are used in various circuits,

usually as a form of protection. There are different types of diode but their basic functions are

the same. These are noted below along with examples of diodes in use.

The most common type of diode is a

silicon diode. It is enclosed in a glass

cylinder with the dark band marking thecathode terminal. This line points

towards the positive of a circuit. The

opposite terminal is called the anode.

Generally, diodes do not conduct until the

voltage reaches approximately .6 volts,

this is called the threshold point. If the

current becomes too high the diode may

crack or melt.

TYPICAL USES OF DIODES

REVERSE POLARITY PROTECTOR

ttp://www.technologystudent.com/elec1/diode1.htm (1 of 2)18/02/08 11:07 AM

Search

8/8/2019 7661004-Basics-Ele-01

67/488

The Diode

The diode in this circuit protects a radio

or a recorder etc... In the event that the

battery or power source is connected the

wrong way round, the diode does not

allow current to flow. Electronic devices

can be damaged or even destroyed if thepolarity is reversed (positive and negative

are connected to the wrong terminals).

TRANSIENT PROTECTOR

When an inductor device such as a relayis turned off a high voltage can be

generated for a short time (Dia 1). This

voltage spike can damage the relay and

other components. However, the diode

does not allow current to pass through it

in the wrong direction and short circuits

this spike.

The diode can also be used to protect a

meter from a reverse current (Dia 2).

ZENER DIODES

Normally a current does not flow through a diode in the reverse direction. The Zener Diode is

specifically designed to begin conducting in the opposite direction when the reverse voltage

reaches a voltage threshold. Zener diodes are sometimes used as a voltage sensitive switch.

Can you think of any other devices that may benefit from the use of diodes ? What aboutsolenoids ?


ttp://www.technologystudent.com/elec1/diode1.htm (2 of 2)18/02/08 11:07 AM

8/8/2019 7661004-Basics-Ele-01

68/488

Capacitors

Web


com


CAPACITORS

V. Ryan 2002-05

Capacitors are components that are used to store an electrical charge and are used in timer circuits

A capacitor may be used with a resistor to produce a timer. Sometimes capacitors are used to

smooth a current in a circuit as they can prevent false triggering of other components such as

relays.

A capacitor is composed of two conductor

separated by an insulating material called a

DIELECTRIC. The dielectric can be paper

plastic film, ceramic, air or a vacuum. The

plates can be aluminium discs, aluminium

foil or a thin film of metal applied to

opposite sides of a solid dielectric. The

CONDUCTOR - DIELECTRIC -

CONDUCTOR sandwich can be rolled into

a cylinder or left flat

HOW A CAPACITOR WORKS

ttp://www.technologystudent.com/elec1/capac1.htm (1 of 3)18/02/08 11:07 AM

Search

8/8/2019 7661004-Basics-Ele-01

69/488

Capacitors

When the circuit is switched on, the light

dependent resistor emits light and the

capacitor charges up. When the switch is

turned off the LED stills emits a light for a

few seconds because the electricity stored

in the capacitor is slowly discharged. Whe

it has fully discharged it's electricity the

LED no longer emits light. If a resistor is

introduced to the circuit the capacitor

charges up more slowly but also discharge

more slowly. What will happen to the

light ?

Electrolytic capacitors are polarised

which means they have a positive and

negative lead and must be positioned in acircuit the right way round (the positive

lead must go to the positive side of the

circuit).

They also have a much higher capacitance

than non-electrolytic capacitors.

Non-electrolytic capacitors usually have a

lower capacitance.

They are notpolarised(do not have a

positive and negative lead) and can be

placed anyway round in a circuit.

They are normally used to smooth a curren

in a circuit.

CAPACITANCE- means the value of a

capacitor.

Notice theelectrolytic capacitors

above. They all have

two polarised leads,

in other words they

have a positive and

negative leg. This

type of capacitor is

used with ICs such as

the 555 timer chip

and it is the

capacitors and

resistors that

determine the timing

sequence.


8/8/2019 7661004-Basics-Ele-01

70/488

Capacitors

Look carefully at the photographs of the

two types of capacitors. Can you work out

which one is electrolytic and which is non-

electrolytic ?

The simple circuit below is basically a

switch which is connected to a computer.

When the switch is pressed the computer

detects that the relay is closed and then

turns on a motor.

However, there is a problem. When the

switch is pressed it only closes the relay fo

a split second and this is not enough timefor the computer program to detect that it

has been pressed in the first place. A time

delay is the obvious answer and this can be

achieved by adding a capacitor in parallel

to the switch. If the relay is held closed for

3/4 seconds then the computer program

will have time to detect it - A capacitor

provides the time delay.

REMEMBER - there

are polarised and non-

polarised capacitors.

Look for a positive

and negative sign.

CLICK HERE FOR EXAMPLES - HOW CAPACITORS CAN BE USED


8/8/2019 7661004-Basics-Ele-01

71/488

Resistors


RESISTORS

V. Ryan 2002 - 04

Web


com

esistors determine the flow of current in an electrical circuit. Where

ere is high resistance then the flow of current is small, where the

sistance is low the flow of current is large. Resistance, voltage and

rrent are connected in an electrical circuit by Ohms Law.

esistors are used for regulating current and they resist the current flow and the extent to which they do this ieasured in ohms (). Resistors are found in almost every electronic circuit.

he most common type of resistor consists of a small ceramic (clay) tube covered partially by a conducting

rbon film. The composition of the carbon determines how much current can pass through.

ttp://www.technologystudent.com/elec1/resist1.htm (1 of 4)18/02/08 11:08 AM

Search

8/8/2019 7661004-Basics-Ele-01

72/488

Resistors

Resistors are too small to have numb

printed on them and so they are mark

with a number of coloured bands. Ea

colour stands for a number. Three co

bands shows the resistors value in oh

and the fourth shows tolerance. Resis

can never be made to a precise value the tolerance band (the fourth band) t

us, using a percentage, how close the

resistor is to its coded value. The resi

on the left is 4700 ohms.

he value of a resistor can be written in a variety of ways. Some examples are given below:

47R means 47 ohms5R6 means 5.6 ohms

6k8 means 6800 ohms

1M2 means 1 200 000 ohms

common value is 'K' which means one thousand ohms. So if a resistor has a value of 7000 ohms it can also

d to have a value of7K.

RESISTORS IN SERIES AND IN PARALLEL

esistors can be connected together in two ways to give different overall values. This is especially useful if y

not have a resistor of the correct value and need to make it up from other available ones.

Resistors in SERIES - When resistors are connected in series, their

lues are added together:

R total=R1+R2

For example: 1K+1K+3K9=5K9 (total value)


8/8/2019 7661004-Basics-Ele-01

73/488

Resistors

Resistors in PARALLEL -When resistors are connected in

rallel, their total resistance is given as: 1/Rtotal = 1/R1 + 1/R2

For example: 1/Rtotal = 1/1K + 1/1K = 0.5K or 500 ohms

OR= R1 x R2

R1 +R2

= 1 x 1 = 1

1 +1 = 2 = 0.5k

Click here for more resistors in parallel questions

VARIABLE RESISTORS

Variable resistors have adjustable valu

Adjustment is normally made by turn

spindle (e.g. the volume control on aradio) or moving a slider.

SYMBOL

he rotary variable resistor is the cheapest type of variable resistor.

smaller version of this variable resistor is the pre-set resistor. The

e-set resistor is the type usually used in small electronic projects

ou will probably use this type in school based projects).

PRESET RESISTOR

CLICK HERE FOR POTENTIAL DIVIDERS SHEET (RESISTORS CONTINUED)



8/8/2019 7661004-Basics-Ele-01

74/488

Resistors


8/8/2019 7661004-Basics-Ele-01

75/488

The Relationship Between Capacitors and Resistors


THE RELATIONSHIP BETWEEN CAPACITORS

AND RESISTORS - USING CROCODILE TECHNOLOGYELECTRONICS SIMULATION SOFTWARE

V. Ryan 2004

Web


com

ectronics software such as Crocodile Technology is perfect for testing circuits without

tually building them from real components.

oth capacitors and resistors are important components in circuits, especially delay or timer

rcuits. Combining resistors and capacitors in a circuit will increase / decrease a timingquence.

simple circuit is shown shows four capacitors and resistors in parallel. On the left hand side

the circuit an LED is seen, this is protected by a 300 ohm resistor. As the switch is closed

e capacitors can be seen to charge up and the LED lights immediately. When the switch is

pened the LED stays on for a short time and then fades slowly. This happens because the

ch capacitor has a charge of electricity. This is released slowly when the +9 volts is

witched off.


Search

8/8/2019 7661004-Basics-Ele-01

76/488


The total capacitance is calculated by simply adding the values of the capacitors together.

sing electronics software such as Crocodile Technology, change the resistor values to 1K. When

witch is closed the LED lights almost immediately. When the switch is opened the LED stays alight

longer time and fades more slowly until final it emits no more light. Increasing the value of the resi

uses the capacitors to charge up more slowly. Most important of all, when the switch is opened the

pacitors discharge their electricity more slowly. The LED stays alight for a longer time

UESTIONS:

Using simulation software such as Crocodile Technology, build a capacitor and resistor circuit

corporating a relay. The relay should remain energised for a short time after the circuit switch is

pened.



8/8/2019 7661004-Basics-Ele-01

77/488



8/8/2019 7661004-Basics-Ele-01

78/488

Test Instruments

Web


com

CLICK HERE FOR INDEX

PAGE

TEST

INSTRUMENTS

V. Ryan 2002

An Analogue Multimeter

Voltage, current and resistance can easily be measured by using a multimeter. There are

two types, analogue and digital. The multimeteris the most important electronic test

instrument. Two wires are normally used along with the multimeter (called probes) and they

are colour coded - black and red.

DIGITAL METER ANALOGUE METER

ttp://www.technologystudent.com/elec1/metre1.htm (1 of 3)18/02/08 11:08 AM

Search

8/8/2019 7661004-Basics-Ele-01

79/488

8/8/2019 7661004-Basics-Ele-01

80/488

Test Instruments

In order to do this you would follow these steps:

1. Set the function selector to ohms and to the range where you expect to find a reading.

There may be a range for zero to 1K OR 1K and over etc....

2. Ensure that the probes are attached correctly and touch them across the component you

are measuring, in this case a resistor.

3. The results can be read on the scale. If there is no reading, try another range setting.

To measure DC voltage follow these steps:1. Set the function selector to one of the DCV positions.

2. Connect the test probes to the circuit and read the voltage on the scale.

EXAMPLE OF DIGITAL METER EXAMPLE OF ANALOGUE METER

QUESTIONS:

1. Draw simplified diagrams of both types of meters.

2. Explain how digital and analogue meters differ.


ttp://www.technologystudent.com/elec1/metre1.htm (3 of 3)18/02/08 11:08 AM

8/8/2019 7661004-Basics-Ele-01

81/488

Light Dependent Resistors


LIGHT DEPENDENT RESISTORS

V. Ryan 2002 - 04

Web


com

LDRs or Light Dependent Resistors are

very useful especially in light/dark

sensor circuits. Normally the resistance

of an LDR is very high, sometimes as

high as 1000 000 ohms, but when they

are illuminated with light resistance

drops dramatically.

The animation opposite shows that when

the torch is turned on, the resistance of the

LDR falls, allowing current to pass through

it.

ttp://www.technologystudent.com/elec1/ldr1.htm (1 of 3)18/02/08 11:08 AM

Search

8/8/2019 7661004-Basics-Ele-01

82/488


This is an example of a light sensor

circuit :

When the light level is low the resistanceof the LDR is high. This prevents current

from flowing to the base of the

transistors. Consequently the LED does

not light.

However, when light shines onto the

LDR its resistance falls and current

flows into the base of the first transistor

and then the second transistor. The LEDlights.

The preset resistor can be turned up or

down to increase or decrease resistance,

in this way it can make the circuit more

or less sensitive.

1. The circuit above is a light sensor. That means light must shine into the LDR forthe circuit to be activated. Draw a circuit composed of the same components that

activates when it is DARK (when the LDR is covered). This is a typical examination

question.

HINT: Simply swap the preset resistor and the LDR.

2. What is the role of the preset resistor ?



8/8/2019 7661004-Basics-Ele-01

83/488



8/8/2019 7661004-Basics-Ele-01

84/488

reset Resistors


THE PRESET RESISTOR

V. Ryan 2002-05

Web


com

Preset resistors are used in circuits when it

is necessary to alter the resistance. Dark/

light and temperature sensors usually have

these components as the preset resistor

allows the circuit to be made more or less

sensitive (they can be turned up or down -

reducing or increasing resistance).

A small screwdriver can be used to turn the

centre part of the preset resistor, altering the

value of the resistance.

The range of resistance varies, for example:

0 to 100 ohms

0 to 1M ohms

ttp://www.technologystudent.com/elec1/preset1.htm (1 of 3)18/02/08 11:08 AM

Search

8/8/2019 7661004-Basics-Ele-01

85/488

reset Resistors

The two circuits below are sensor circuits. The one of the left is a temperature sensor and

the one on the right is a light sensitive circuit. Increasing the value of the preset resistor by

turning the centre with a small screwdriver makes the circuit less sensitive. For instance,

the temperature sensor would require a higher temperature and the light sensitive circuit

would need more intense light before they activated.


8/8/2019 7661004-Basics-Ele-01

86/488

reset Resistors

TEMPERATURE SENSOR LIGHT SENSOR



8/8/2019 7661004-Basics-Ele-01

87/488

MakingaLight / Dark Sensor


MAKING A LIGHT / DARK SENSOR

V. Ryan 2005

Web


com

Opposite is a simplelight/ dark sensor. Th

can be connected as a

input or switch to

another circuit. The

sensors has three gre

wires (1, 2 and 3). W

2 should always be

connected to one of t

inputs. If wire 1 is alconnected then the

sensor acts as a dark

sensor. If wires 2 and

are connected to the

inputs then sensor

operates as a light sen

The preset resistor

allows the person usithe circuit to alter its

sensitivity to light/da

When are light sensors used?

CONSTRUCTING A CIRCUIT USING SIMULATION SOFTWARE

ttp://www.technologystudent.com/elec1/lgtdrk1.htm (1 of 5)18/02/08 11:09 AM

Search

8/8/2019 7661004-Basics-Ele-01

88/488


All circuits are drawn

software such as

Crocodile Clips. Usin

this software the

individual componen

can be joined togethe

the screen. Once thecircuit is drawn its

operation can be

simulated to see if it

works. If it fails it ca

corrected on the

computer screen and

tested again.

Using software to tes

circuit designs savestime as there is no ne

to physically solder

together components

also saves money as

components and

materials are not was

on failed circuits

he circuit is then made into a PCB (Printed Circuit Board). Components are added and soldered in

sition (See PCB Section of this website). Two views of the same circuit are shown below. How do t

ffer?


8/8/2019 7661004-Basics-Ele-01

89/488


Complete the table below by writing some details about the components used in the light/dark senso

rcuit.


8/8/2019 7661004-Basics-Ele-01

90/488




8/8/2019 7661004-Basics-Ele-01

91/488



8/8/2019 7661004-Basics-Ele-01

92/488

equence Drawing - Light/Dark Sensor


SEQUENCE DRAWING - LIGHT/DARK SENSOR

V. Ryan 2006

A typical light/dark sensor is shown below. It consists of a number

of components and is known to be a reliable circuit. Study the

circuit carefully and list any improvements you think would make

he circuit even more reliable, easier to make, more robust etc.....

Arrange the stages of making a light / dark sensor shown below -

nto the correct sequence. Draw your version of the sequence

drawing.


8/8/2019 7661004-Basics-Ele-01

93/488



8/8/2019 7661004-Basics-Ele-01

94/488



8/8/2019 7661004-Basics-Ele-01

95/488


CLICK HERE FOR SAMPLE ANSWER



8/8/2019 7661004-Basics-Ele-01

96/488


Web


com


Search

8/8/2019 7661004-Basics-Ele-01

97/488

LDR Examination Question


LDR EXAMINATION QUESTION

V. Ryan 2005

Web


com

A pupil has designed and manufactured a model based on the automatic control of street lights. Whehe light level drops the street light comes on automatically .The systems diagram below shows how

he pupils circuit works. The sensor detects when the day light fades and a relay circuit turns on the

treet lights.


Search

8/8/2019 7661004-Basics-Ele-01

98/488


The circuit below has been manufactured as a sensor. It has been developed to sense a drop in the li

evel.

1. Name of component A:_________________

2. Name of component B:_________________

3. Which component is the one that behaves as a sensor._____________________________________________

4. How does the resistance of this component change whe

the light fades.

_____________________________________________

5. Which component is used to adjust the sensitivity of th

circuit.

_____________________________________________

. The dark sensing circuit shown above can be altered to detect light. Complete the next circuit by

dding the light sensor.


8/8/2019 7661004-Basics-Ele-01

99/488


. What is the name of component C shown in the sensing circuit above?

Name of component C:_______________________

. What is its function ?



8/8/2019 7661004-Basics-Ele-01

100/488

Light / Dark Sensor - Animal Feeder Circuit


LIGHT / DARK SENSOR - ANIMAL FEEDER

CIRCUIT

V. Ryan 2006

he sensor below is a light/dark sensor. This is part of an automatic animal feeder. As it becomes dark

nsor activates a relay that in turn turns on a motor, rotating a fly wheel. The fly wheel operates a

echanical system that releases food to a small animal, such as a hamster. Food is release during the

ght. The circuit shown below is drawn using 'Crocodile Technology 3D' software. This is electronic

mulation software which allows the designer to draw a circuit in 3D and test it for faults.

A list of component names are seen below the diagram. Write each of the component names in the

rrect place on the diagram.


8/8/2019 7661004-Basics-Ele-01

101/488


NAP

DR

ONNECTOR

TRANSISTOR

RELAY

FLY WHEEL

BATTERY

PCB

RESISTOR

DIODE

MOTOR

Only one transistor is used in this circuit. The electronics simulation software 'Crocodile Technolog

D' has identified a possible fault - sometimes it is wise to include two transistors called a darlington

ir rather than the one transistor shown in the diagram above. Draw below a circuit diagram

presenting a darlington pair.

Why is it wise to use a darlington pair (two transistors) rather than a single transistor?


8/8/2019 7661004-Basics-Ele-01

102/488



Web


com


Search

8/8/2019 7661004-Basics-Ele-01

103/488

Light / Dark Sensor Question


LIGHT / DARK SENSOR QUESTION

V. Ryan 2006

Below is a typical chocolate bar dispenser. It includes a light sensor that detects when the

dispenser needs filling.

1. The circuit diagram below is incomplete. Add all the missing components and explain how the

circuit works. Include the following components: 1 LDR, 2 fixed resistors, 1 npn transistor and a

relay that is energised when light is sensed.


8/8/2019 7661004-Basics-Ele-01

104/488


POSSIBLE ANSWER BELOW


8/8/2019 7661004-Basics-Ele-01

105/488


2. The circuit/dispenser designer has recently improved the design of the dispenser and wants to

use to LDRs.

LDR 1 = LOW This will sense when there are five products left in the dispenser

LDR 2 = EMPTY This will sense when the dispenser is empty.

Indicate on the diagram below where LDR 1 and LDR 2 will be located.


8/8/2019 7661004-Basics-Ele-01

106/488


3. A mechanism has been added to the drawer. This moves the drawer forwards and backwards

to allow chocolate to be removed from the drawer. Add a suitable mechanism to the incomplete

drawing below. Label your diagram



8/8/2019 7661004-Basics-Ele-01

107/488


4. Add notes explaining how the mechanism works.

5. When there are only five chocolate bars left in the dispenser the low warning light should

light. This allows staff in the shop to fill up the machine. When the dispenser is empty the empty

warning light is turned on and an alarm sounds.

Complete the flowchart below with appropriate missing statements.


8/8/2019 7661004-Basics-Ele-01

108/488



8/8/2019 7661004-Basics-Ele-01

109/488




8/8/2019 7661004-Basics-Ele-01

110/488



Web


com


Search

8/8/2019 7661004-Basics-Ele-01

111/488

ensor Questiuon - LDR


SENSOR QUESTION - LDR

V. Ryan 2006

Many production lines are automated. What is an automated production line?

An automated production line is shown below. Parts / components move along the production linehere they are sensed, clamped down, drilled and then released, moving down the production line agai

he whole process is controlled by a PIC Microcontroller. The conveyor belts rotates continually until nsor detects a component.

rite the sequence of instructions for the entire process on the following instruction sheet. Basic

structions you are to use are described below.

ttp://www.technologystudent.com/elec1/senq1.htm (1 of 5)18/02/08 11:10 AM

8/8/2019 7661004-Basics-Ele-01

112/488


ou are to write your answer as a set of instructions and as a flowchart.


8/8/2019 7661004-Basics-Ele-01

113/488


CLICK HERE FOR POSSIBLE ANSWER

The sensor being used on the production line is shown below. Complete the circuit diagram of the sa

rcuit. Label the components.

http://www.technologystudent.com/elec1/senq2.htmhttp://www.technologystudent.com/elec1/senq2.htm

8/8/2019 7661004-Basics-Ele-01

114/488


CLICK HERE FOR POSSIBLE ANSWER

Each component being drilled is identical. Each has a central hole and is rectangular in shape. It has

en decided that each component must be checked for the presence of the hole after drilling. This is pa

quality control.

. What is the meaning of quality control?

b. Using sketches and notes explain how the circuit shown at the top of the page could be used to chec

r the presence of the hole in each component.


8/8/2019 7661004-Basics-Ele-01

115/488


SKETCH(S)

NOTES


Web


com


Search

8/8/2019 7661004-Basics-Ele-01

116/488

Circuit Question - Switches and Other Components


CIRCUIT QUESTION - SWITCHES AND

OTHER COMPONENTS

V. Ryan 2007

he circuit below has a motor that can only be operated when both of the push to make switches are

essed.

The component names are listed below. Clearly label each of the components in the circuit.

ANSWER

ttp://www.technologystudent.com/elec_flsh/switch1.html (1 of 7)18/02/08 11:10 AM

8/8/2019 7661004-Basics-Ele-01

117/488


The component symbols that make up the circuit are shown below. Arrange them to form the circuit

agram.

ANSWER


8/8/2019 7661004-Basics-Ele-01

118/488


What is the function of the toggle switch?

POSSIBLE ANSWER

he toggle switch is the main switch to the circuit. It must be in the on position for the circuit to work

olates the circuit if it is in the off position.

What is the function of the relay?

POSSIBLE ANSWER

he relay is a type of switch. It is the physical link between two circuits. The first circuit on the left han

de is the one with the two push to make switches. The second circuit is on the right and has the motor


8/8/2019 7661004-Basics-Ele-01

119/488


The component shown

posite is to be added to the

rcuit. What is it called?

AME:

ANSWER

DIODE

What is the function of the new component?

ANSWER

he diode will be placed in parallel to the relay and the opposite way round. When the circuit is turned

e diode will protect the other components from back emf.

Draw the symbol for this

w component in the box .

ANSWER


8/8/2019 7661004-Basics-Ele-01

120/488


The npn transistor shown

posite is also to be added toe circuit. Draw its symbol in

e space below

ANSWER

In the space below complete the new circuit that incorporates the new and original components plus

sistor to protect the transistor.


8/8/2019 7661004-Basics-Ele-01

121/488


POSSIBLE ANSWER



Search

8/8/2019 7661004-Basics-Ele-01

122/488

8/8/2019 7661004-Basics-Ele-01

123/488

Thermistors


THE THERMISTOR

V. Ryan 2002

Web


com

An example of a thermistor is seen tothe left. They are made up of a mixture

of sulphides or oxides or sometimes

metals such as copper, iron or cobalt.

They tend to be formed into a disc or a

bead sealed with plastic or glass.

They have great resistance at low

temperatures but when they warm up

their resistance decreases rapidly.Current can then flow through them.

This makes them ideal as one of the

components for a temperature sensor.

Build the simple thermistor circuit below.

When the thermistor is cool or cold the LED

should not light because of the high

resistance.

However, warm up the thermistor by blowing

warm air from a hair drier across it. This

should warm it sufficiently that in a few

seconds the resistance will drop and the LED

will light.

ttp://www.technologystudent.com/elec1/therm1.htm (1 of 2)18/02/08 11:11 AM

Search

8/8/2019 7661004-Basics-Ele-01

124/488

Thermistors

WHEN THE THERMISTOR IS COLD

RESISTANCE IS HIGH AND CURRENT

CANNOT PASS THROUGH. WHEN WARMED,

RESISTANCE FALLS AND CURRENT PASSES

THROUGH.

Circuit explanation in detail:

When the thermistor is warmed up by

the hair drier its resistance drops, this

will take a few seconds. As its

resistance drops current begins to flow

from positive 9 volts to negative 0

volts. Current flows into the base of the

transistors allowing the LED to light.

The preset resistor can be turned up or

down to increase or decrease resistance,

in this way it can make the circuit more

or less sensitive.

1. Explain how this circuit could be used in the home.

2. What is the role of the preset resistor ?


ttp://www.technologystudent.com/elec1/therm1.htm (2 of 2)18/02/08 11:11 AM

8/8/2019 7661004-Basics-Ele-01

125/488

nformation Regarding Thermistor Circuits and Darlington Pairs


INFORMATION REGARDING THERMISTOR CIRCUITS

AND DARLINGTON PAIRS

V. Ryan 2007

nsors such as the thermistor based circuit shown below are not always reliable. This is usually due to

e circuit relying on one transistor. The circuit below has two transistors, called a Darlington Pair. T

rangement of transistors amplifies current flowing from the thermistor and ensures that the LED ligh

hen the temperature is LOW. Resistance of thermistor high and current flows through the transistors

owing the LED to light

ttp://www.technologystudent.com/elec_flsh/therm1.html (1 of 2)18/02/08 11:13 AM

8/8/2019 7661004-Basics-Ele-01

126/488

nformation Regarding Thermistor Circuits and Darlington Pairs

gh temperature. Resistance of thermistor reduces significantly and current flows from positive straig

negative. The LED does not light.

UESTION:

The LED in the circuit above lights when the temperature is low (icy). However, it would be useful i

e LED would light when it is warm/hot. This circuit could be used for a warning device when

mperatures are too high.. Draw an updated version of the circuit that would allow this to happen.


Web


com

ttp://www.technologystudent.com/elec_flsh/therm1.html (2 of 2)18/02/08 11:13 AM

Search

8/8/2019 7661004-Basics-Ele-01

127/488

A Temperature Sensor


A TYPICAL TEMPERATURE SENSOR

V. Ryan 2005

Web


com

Opposite is a simple temperaturesensor. It operates in exactly the

same way as a light/dark sensor

except that it has a component

called a thermistor rather than a

LDR (Light Dependent Resistor).

The thermistor's resistance value

changes when the temperature rises

or falls. This triggers the relay.

The preset resistor allows the

person using the circuit to alter its

sensitivity to changes in

temperature..

When are temperature sensors used?


ttp://www.technologystudent.com/elec1/tmpsen1.htm (1 of 2)18/02/08 11:13 AM

Search

8/8/2019 7661004-Basics-Ele-01

128/488

A Temperature Sensor

ttp://www.technologystudent.com/elec1/tmpsen1.htm (2 of 2)18/02/08 11:13 AM

8/8/2019 7661004-Basics-Ele-01

129/488

otential Dividers


POTENTIAL DIVIDERS

V. Ryan 2002

Web


com

What are they - they can be used to split the voltage of a circuit. They are widely used in electronic circuits for

setting and adjusting voltages - e.g. in radios, games and toys. You may find that you need a supply of 6 volts an

you have a 9 volt battery, your only option may be to make a potential divider.

When two resistors of equal value (e.g. 1K) are

connected across a supply, current will flow through

them. If a meter is placed across the supply shown in

the diagram it will register 9v. If the meter is then

placed between the 0v and the middle of the tworesistors it will read 4.5v. The battery voltage has bee

divided in half.

If the resistor values are changed to 2K and 1K the

voltage will be 6v. The voltage at the centre is determined

by the ratio of the two resistor values and is given by the

formula:

V = supply voltage x R2/R1+R2

V= 9v x 2000


Search

8/8/2019 7661004-Basics-Ele-01

130/488

otential Dividers

1000+2000

v = 9v x (2000/3000 ohms)

V = 9v x 0.6666666 ohms

V = 6v

An alternative way to work out the answer is to:

1. Add both resistors together.

2. Divide the voltage by the sum of both resistors.

3. Take the largest resistor and multiply it by the

answer found in stage two.

1K + 2K = 3K

9v/3k (is the same as 9/3) = 3

2k x 3 = 6v

CLICK HERE FOR MORE POTENTIAL DIVIDER QUESTIONS

http://www.technologystudent.com/elec1/potdiv1.htmhttp://www.technologystudent.com/elec1/potdiv1.htm

8/8/2019 7661004-Basics-Ele-01

131/488

I Units and OHMs Law


SI UNITS and OHM's LAW

V. Ryan 2002

Web


com

SI UNITS

The system of units used inTechnology and Science is

the Systeme Internationale

dunites (International

system of units). Usually

abbreviated to SI units and

is based on the metric

system. This was introduced

in 1960 and is now adopted

by the majority of countriesas the official system of

measurement. The basic

units in the SI system are

listed in the table to the right

with their symbols.

PREFIX NAME MEANING

T tera multiply by 1 000 000 000 000

(i.e. X 1012)

G giga multiply by 1 000 000 000

(i.e. X 109)

M mega multiply by 1000 000 (i.e. X 106)

k kilo multiply by 1 000 (i.e. X 103)

m milli divide by 1000 (i.e. X 10-3)

micro divide by 1 000 000 (i.e. X 10-6)

n nano divide by 1 000 000 000

(i.e. X10-9)

p pico divide by 1 000 000 000 000

(i.e. X 10-12)

ttp://www.technologystudent.com/elec1/ohm1.htm (1 of 3)18/02/08 11:13 AM

Search

8/8/2019 7661004-Basics-Ele-01

132/488


Ohms Law

Provides us with a very important formula for working out current, resistance and voltage

(Potential Difference). In order to use this formula properly you must understand SI Units.

Voltage = V Resistance = R Current = I

Problem 1.If the currentthrough a resistor is 0.8A and

the voltage is 20v - what is the

resistance ?

Problem 2.Determine the p.d. (voltage) which must be

applied to a 2kW resistor in

order that a current of 10mA

may flow.

Resistance R = 2k= 2X 103 = 2000 .

Current I = 10mA = 10 X 10-3 A or 0.01 A.

From Ohms law, potential difference,

V = IR = (0.01)(2000) = 20V

Problem 3.A coil has acurrent of 50 mA flowing

through it when the voltage is

12 V. What is the resistance of

the coil?


8/8/2019 7661004-Basics-Ele-01

133/488


Have a go at answering the following questions:

Problem 4.A 100 V batteryis connected across a resistor

and causes a current of 5mA to

flow. Determine the resistance

of the resistor. If the voltage is

reduced to 25 V, what will be

the new value of the current

flowing?

Problem 5.What is theresistance of a coil which

draws a current of (a) 50 mAand (b) 200mA from a 120 V

supply.

What is an INSULATOR ?

An insulator is a material that does not allow current to flow through it. Materials such as rubber

and plastic are good insulators and this is why they are used in the electrical industry to insulateparts.

Consider electric drills. Why do they have a plastic case ? The plastic insulates the person using

the drill from all the electrical parts so that they are protected from electrocution.

CLICK HERE ELECTRONICS INDEX PAGE


8/8/2019 7661004-Basics-Ele-01

134/488

Resistors - Questions


RESISTORS - QUESTIONS

V. Ryan 2005

Web


com

esistors determine the flow ofrrent in an electrical circuit.

here there is high resistance

en the flow of current is small,

here the resistance is low the

ow of current is large.

esistance, voltage and current

e connected in an electrical

rcuit by Ohms Law.

ead the passage regarding resistors. Fill the gaps using correct the words listed below.

esistors _____________ the flow of current through a ____________. Resistance is measured in ___

hen resistance is high the flow of current is _______ . When resistance is low the flow of current is

______Resistance, voltage and current are connected in an electrical circuit by ______________.

TYPES OF RESISTOR

number of resistors are shown below. They include a VARIABLE RESISTOR, PRESET RESISTO

XED RESISTOR, LIGHT DEPENDENT RESISTOR and a THERMISTOR. Using the guidelines

ove each drawing, print each correct name in BLOCK CAPITALS.

ttp://www.technologystudent.com/elec1/restr1.htm (1 of 3)18/02/08 11:14 AM

Search

8/8/2019 7661004-Basics-Ele-01

135/488

Resistors - Questions

raw an arrow from each resistor to its symbol. Please note, one of the resistors has two symbols.

xplain / describe the use of each of resistors listed below:

XED RESISTOR:

ARIABLE RESISTOR:

GHT DEPENDENT RESISTOR:

HERMISTOR:

RESET RESISTOR:

he circuit diagram and 3D drawing below show the same light / dark sensor circuit. Add labels to bot

awings, clearly identifying each component.

ttp://www.technologystudent.com/elec1/restr1.htm (2 of 3)18/02/08 11:14 AM

8/8/2019 7661004-Basics-Ele-01

136/488

8/8/2019 7661004-Basics-Ele-01

137/488

Relays and Practical Circuits


THE RELAY

V. Ryan 2002

Web


com

A relay is an electromagnetic switch. In other words it is activated when a current is

applied to it. Normally a relay is used in a circuit as a type of switch (as you will see

below). There are different types of relays and they operate at different voltages. Whenyou build your circuit you need to consider the voltage that will trigger it.

RELAY SYMBOLS

ttp://www.technologystudent.com/elec1/relay1.htm (1 of 3)18/02/08 11:14 AM

Search

8/8/2019 7661004-Basics-Ele-01

138/488


The main part of a relay is the coil at the centre. A small current flowing through the

coil in the relay creates a magnetic field that pulls one switch contact against or away

from another. Putting it simply, when current is applied to the contacts at one side of

the relay the coil allows the contacts at the other side to work.

Usually relays are used to turn on a second circuit. The first circuit activates the relay

which then turns on the second circuit.

EXAMPLE CIRCUIT

This simple circuit activates the relay only when the LDR is dark (covered). This could

be used as part of an automatic animal feeder. For instance, if the animal was fed at

night the circuit above would activate the relay. A second circuit, connected to the other

side of the relay releases food into a dish.

CLICK HERE FOR PRACTICAL EXAMPLES OF RELAYS


http://www.technologystudent.com/elec1/relay2.htmhttp://www.technologystudent.com/elec1/relay2.htm

8/8/2019 7661004-Basics-Ele-01

139/488



8/8/2019 7661004-Basics-Ele-01

140/488

Transistor Basics


TRANSISTORS

V. Ryan 2002 - 04

Web


com

ransistors can be regarded as a type of switch, as can many electronic components. They are used i

ariety of circuits and you will find that it is rare that a circuit built in a school Technology Departm

oes not contain at least one transistor. They are central to electronics and there are two main types;NPN and PNP. Most circuits tend to use NPN. There are hundreds of transistors which work at

ifferent voltages but all of them fall into these two categories.

TWO EXAMPLES OF DIFFERENT SHAPES OF

TRANSISTOR

ransistors are manufactured in different

hapes but they have three leads (legs).

heBASE- which is the lead responsible for

ctivating the transistor.he COLLECTOR - which is the positive lead.

heEMITTER - which is the negative lead.

he diagram below shows the symbol of an

NPNtransistor. They are not always set out as

hown in the diagrams to the left a

7661004-basics-ele-01

Documents