An Introduction to Electronics

Key Stage 3

Live Wire / PCB Wizard / Control Studio / Crocodile Technology

RA Moffatt

"To Teach" is a somewhat meaningless term.  I cannot teach anyone anything; I can only HELP them to Learn something--maybe.   I can try to be an Enabler. To really Learn requires full participation by the Learner:

"One can lead a horse to water, but can't make him do the backstroke."

Also, and more importantly, Learning is NOT a linear process. No one learns in a straight line, logically or sequentially. I have only met one person who claimed to learn in a linear fashion; "he is feeling much better now," and will be released next September.

Assessment for Learning

“Of the good teacher pupils speak respectfully saying ‘he taught me this’ or ‘she taught me that’. Of the very good teacher, they do not say this, instead, they say ‘we learned it all by ourselves.’”

Lao Tse 600AD

Electronics - Modelling in Live Wire / PCB Wizard

R.A. Moffatt.

Automatic Switching:-

Light Sensing - Transistor Projects.

PCBWizard

Electronic Tasks Day II:

1) Conditions: Dark - Circuit ‘Light-on’. (Circuit 3)

• Construct the Potential Divider circuit and Populate using a Bread Board • Populate using a PCB Board • Record how this circuit works Use a Multi-meter to test!

2) Conditions: Cold – Flashing ‘LED on’. (Circuit 13)

• Model the Potential Divider Circuit using Live Wire circuit.• Design your own PCB artwork using PCB Wizard• Make-up your own PCB Board• Populate and test!

3) Task: Using a potential divider circuit to show how a capacitor can be used to provide a time delay. • Listen to the AVI file; - explain briefly how this circuit works? (Circuit 39)• Model this circuit and test using the Bread Board• Make a PCB and populate• Test!

4) Timer – using a Thyristor as a Latch (Circuit 41)

• Model the timing circuit (41) using Live Wire and test!• Simplify this circuit design using PCB Wizard for ease of

soldering• Listen to the AVI file to help understand how this circuit

works?• Construct a PCB of your design and test!

5) Micro-Switch Alarm – using a Thyristor as a Latch (Circuit 80)

• Model the timing circuit (80) using Live Wire and test!• Build / model this circuit using a bread Board and Test!• Simplify this circuit design using PCB Wizard for ease of

soldering• Listen to the AVI file to help understand how this circuit

works?• Construct a PCB of your design and test!

6) A Steady Hand Game – Using a Capacitor (Circuit 72)

• Model this circuit using Live Wire and test!• Explain how this circuit works?• Change the size of C1 to provide a longer output

Automatic Switching: Transistor Project

You will have an opportunity to:-

Design/Model a Light /Temperature sensing circuit using Live Wire.

Design a PCB using PCB Wizard Manufacture a printed circuit board.

Two of these circuits respond to a changes in light levels and the other two respond to a changes in temperature levels.

We

Are

Learning

To

To understand the concept of a potential divider which provides automatic switching of electronic circuits

This is because .. We can learn how to design electronic circuits and systems using automatic switching for our project work

Remember to: • refer to the water analogy to help understand how the Potential Divider works

ElectronicsWALT

WILF:

What

I am

Looking

For

• an understanding of the potential divider as

a sensor / automatic switch• the ability to sketch a circuit diagram of an

automatic temperature / light sensing

sensor circuit• to be able to model and test an automatic

switching circuit• to make a PCB and build a sensing circuit as

an example of a transistor-based control

system

Electronics

Design Opportunity:

A young child may have trouble sleeping at night if the bedroom room is too dark or if the mains light when left ‘on’ is too bright!

Design Brief:

To design a child's bedside light which will act as a comfort light and switch ‘on’ automatically when the mains light is switched ‘off’.

A Child’s Comfort Light

‘Bulb - off’ when Light is ‘on’ LED

‘Bulb - on’ when Dark

The Transistor

Small Voltage in

Large Voltage

http://www.satcure-focus.com/tutor/page4.htm

PNP Transistor

B

C

E

symbol Saturated = ‘fully on’

B

C

E

0.6V

9V

e

b

c

Underside view

e

b

c

Underside View

cb

e

The Transistor

ec

b

Top View

Casing Design & Manufacturers Key BC108Transistor

TIC106DThyristor

Transistors Ic (max)

Vceo hFE

BC108 0.1A 20V 110-800

BFY 51 1.0A 30V 40

ZTX 300 0.5A 25V 50-300

How Transistors Differ:

hFE = refers to the gain of a Transistor

Ic = Collector Current Vceo = Voltage across / safe working voltage

Dark Sensor – ‘Dark – Light on’

Dark Sensor – ‘Dark – Light on’

Dark Sensor – ‘Dark – Light on’

Draw and complete the circuit diagram to make the bulb ‘switch on’automatically when light shines on the sensor?

Name the type of electronic components required to make this circuit work?

Electronics - Modelling in Live Wire / PCB Wizard

R.A. Moffatt.

Automatic Switching:-

Hot & Cold Sensing - Transistor Projects.

PCBWizard

Design Opportunity:

An elderly person living alone in a flat requires some type

of electronic warning system to indicate the fall in temperature

hence preventing hypterthema.

Design Brief:

Design an electronic system that will include a warning

indicator when the temperature level of a room drops below

25 degrees

A Room Temperature Warning System

‘LED - on’ when Cold

R1

Alternative – Flashing LED

LEDLight EmittingDiode

Explain in your own words how this circuit works?

‘LED - off’ when Warm

Thermistor

Variable Resistor

LEDLight EmittingDiode

Transistor

Calculation of the value of R1

It is most important that an LED has no more than 2V dropped across it.

Also the current flowing through the LED should not exceed 20 mA.

When the transistor switches on, the voltage at the collector is

approximately 0V, between the top rail and the collector is 9V, so 7V must be dropped across R1.

With 7V dropped across and the maximum permissible current of 20 mA

flowing through the LED, the size of resistor can be calculated using

Ohms Law.

= 350ohmsR1 = 70.020

Resistor selected 470 ohmsV

I R

Play the AVI file to help understand how this circuit works?

‘LED - on’ when Warm Heat Sensor ( Fire Alarm )

How could this circuit be modified to latch or ‘stay on’ if the temperature increases?

Explain in your own words how this circuit works?

‘LED - on’ when Warm

Play the AVI file to help understand how this circuit works?

Electronics - Modelling in Live Wire / PCB Wizard

R.A. Moffatt.

Automatic Switching:-

Timing - Transistor Projects.

PCBWizard

The Electrolytic Capacitor

+

Copy and simplify the sketch above and also explain using brief notes the function of the Capacitor?

symbol

Capacitor casing design

Radial electrolytic capacitor

Capacitors: What do they Do?

A Capacitor stores electric

charge. It consists of two plates

separated by an insulator called

the dielectric. The charge stored

depends on the size of the

capacitor and the voltage applied

to it. The unit of capacitance, the

farad, is very large and most

capacitors you will use are likely

to be measured in microfarads

(F) and nanofarads (nF).

Polyester film capacitor

Ceramic disc capacitor

Axial electrolytic capacitor

+

Non-electrolytic

a) Build the circuit as shown and time how long it takes the capacitor to fully charge?b) Check how long it takes Vo to reach two thirds the supply voltage =

‘time constant’

Voltage Out

Ex 11: Time Delay

Voltmeter

When the switch is

closed, a current flows

into the capacitor until it is

full. If R is a resistor with a

high resistance the

current flows slowly,

and if it is a resistor of

low value the current

flows quickly. Compare

this with water from a tap

filling a basin. The amount

of water flowing into the

basin is altered depending

on whether the tap is fully

open or almost closed.

Ex 11 (b): Capacitors

Build the circuit as shown press and hold SW1 and test how long it takes for the voltage meter to reach 9V using:-

a) R1 = 1Kb) R1 = 10Kc) R1 = 100K

Time constant (sec) = C (farads) X R (ohms)

Time Constant

When the switch is

closed and the capacitor

starts to charge, the

voltage output can be

monitored using a

voltmeter. To start with

the voltmeter will show

0V, increasing to 9V

when the capacitor is

fully charged. A graph

can be plotted of the

voltage output against

the time taken.

Time constant (sec) = C (farads) X R (ohms)

The first part of

the graph is

almost a straight

line, which then

curves and tails

off as it takes

longer and longer

to fill the

capacitor. The

time taken to

reach two thirds of

the supply voltage

is called the time

constant and can

be calculated

using the formula:

Vo

lts

Time (seconds)

S upply V oltage

2

4

6

8

10

t

A Timing Circuit: (39)

Build / Model this circuit using a Bread Board and test!

A Timing Circuit: (39)

A Timing Circuit: (39)

Model the circuit using Live Wire test and explain how it works?

Play the AVI file to help understand how this circuit works?

A Timing Circuit: (39)

A Timing Circuit: (41)

Play the AVI file to help understand how this circuit works?

A Timing Circuit using a Thyristor (41)

Micro-Switch Alarm: (80)

A thyristor is a semiconductor device which acts as a

switch. However, when switched on it can only pass

current in one direction. It is in fact a switchable diode

sometimes known as a silicon controlled rectifier (SCR).

Casing DesignTIC106D

IH = Holding Current - minimum

current required to maintain the thyristor in the on-state

GVT = gate trigger voltage

required to produce the gate trigger current

A Thyristor (silicon controlled rectifier or SCR) is a little like a transistor.

When a small current flows into the GATE (G), this allows a larger current

to flow from the ANODE (A) to the CATHODE (C). Even when the current

into the gate stops the thyristor continues to allow current to flow from

anode to cathode. It latches on.

A Steady Hand Game: (72)

112 (Circuits 72)Using a Capacitor to sound an Alarm for a set-time

A Steady Hand Game: (72)

112 (Circuits 72)Using a Capacitor to sound an Alarm for a set-time

112 (Circuits 72)

A Steady Hand Game: (72)

Fault Finding / Testing:

Testing a Battery Soldering Test

Switch Testing Testing + /- Rails

Modelling / Testing using Bread Boards:

Useful Electronic Web-Sites:

http://ourworld.compuserve.com/homepages/g_knott/index1.htmhttp://www.williamson-labs.com/schematicreading.htmhttp://www.williamson-labs.com/home.htmhttp://www.electronics-lab.comhttp://www.discovercircuits.com/list.htm

Acknowledgement:

Thanks, to Maurice Lynch (WELB) for use of his excellent and invaluable112, Circuits / electronics resource in this presentation.

Raymond Moffatt.