An Introduction to
Electronics
Key Stage 3
RA Moffatt
Live Wire / PCB Wizard / Control Studio / Crocodile Technology
"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
Automatic Switching:-
Light Sensing - Transistor
Projects.
R.A. Moffatt.
PCB
Wizard
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.
WALT
We
Are
Learning
To
Electronics
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
WILF:
What
I am
Looking
For
Electronics
• 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
A Child’s Comfort Light
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’.
‘Bulb - off’ when Light is ‘on’ LED
‘Bulb - on’ when Dark
The Transistor
Large Voltage
C
9V
B
PNP Transistor
0.6V
C
Small Voltage in
E
B
symbol
c
Saturated = ‘fully on’
E
b
http://www.satcure-focus.com/tutor/page4.htm
Underside view
e
The Transistor
c
e
b
b
c
b
e
c
Underside View
Top View
e
Casing Design & Manufacturers Key
BC108
Transistor
TIC106D
Thyristor
How Transistors Differ:
(max)
Transistors
Ic
Vceo
hFE
BC108
0.1A
20V
110-800
BFY 51
1.0A
30V
40
ZTX 300
0.5A
25V
50-300
hFE = refers to the gain of a Transistor
Vceo = Voltage across / safe working voltage
Ic = Collector Current
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
Automatic Switching:-
Hot & Cold Sensing Transistor Projects.
R.A. Moffatt.
PCB
Wizard
A Room Temperature Warning System
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
‘LED - on’ when Cold
LED
Light Emitting
Diode
R1
Alternative –
Flashing LED
Explain in your own words how this circuit works?
‘LED - off’ when Warm
LED
Light Emitting
Diode
Variable Resistor
Transistor
Thermistor
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.
V
IR
7
R1 =
= 350ohms
0.020
Resistor selected
470 ohms
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?
‘LED - on’ when Warm
Explain in your own words how this circuit works?
Play the AVI file to help understand how this circuit works?
Electronics - Modelling in
Live Wire / PCB Wizard
Automatic Switching:-
Timing - Transistor Projects.
R.A. Moffatt.
PCB
Wizard
The Electrolytic Capacitor
Capacitor casing design
+
symbol
Copy and simplify the sketch above and also explain using
brief notes the function of the 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
Axial electrolytic
capacitor
+
Radial
electrolytic
capacitor
Polyester film
capacitor
to be measured in microfarads
Ceramic
disc
capacitor
(F) and nanofarads (nF).
Non-electrolytic
Ex 11: Time Delay
Voltmeter
Voltage Out
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’
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 = 1K
b) R1 = 10K
c) R1 = 100K
Time constant (sec) = C (farads) X R (ohms)
Volts
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.
10 SupplyVoltage
8
6
4
2
t
Time (seconds)
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:
A Timing Circuit: (39)
A Timing Circuit: (39)
Build / Model this circuit using a Bread Board and test!
A Timing Circuit: (39)
Model the circuit using Live Wire test and explain how it works?
A Timing Circuit: (39)
Play the AVI file to help understand how this circuit works?
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 Design
TIC106D
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)
Using a Capacitor to sound an Alarm for a set-time
112 (Circuits 72)
A Steady Hand Game: (72)
Using a Capacitor to sound an Alarm for a set-time
112 (Circuits 72)
A Steady Hand Game: (72)
112 (Circuits 72)
Fault Finding / Testing:
Testing a Battery
Switch Testing
Soldering Test
Testing + /- Rails
Modelling / Testing
using Bread Boards:
Useful Electronic Web-Sites:
http://ourworld.compuserve.com/homepages/g_knott/index1.htm
http://www.williamson-labs.com/schematicreading.htm
http://www.williamson-labs.com/home.htm
http://www.electronics-lab.com
http://www.discovercircuits.com/list.htm
Acknowledgement:
Thanks, to Maurice Lynch (WELB) for use of his excellent and invaluable
112, Circuits / electronics resource in this presentation.
Raymond Moffatt.