1. An Introduction to Electronics Key Stage 3
RA Moffatt
Live Wire / PCB Wizard / Control Studio / Crocodile Technology

2. "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.

3. 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

4. Electronics - Modelling in Live Wire / PCB Wizard
Automatic Switching:-
Light Sensing - Transistor Projects.
R.A. Moffatt.

5. 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!

6. 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!
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!

7. 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

8. 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.

9. WALT Electronics 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

10. What I am Looking For WILF: 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

11. 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’.

12. ‘Bulb - off’ when Light is ‘on’ LED

13. ‘Bulb - on’ when Dark

15. The Transistor Large Voltage c b e C 9V B 0.6V E
PNP Transistor B C E
Small Voltage in e b c
symbol
Saturated = ‘fully on’
Underside view

16. c b e
The Transistor e b c e c b
Underside View
Top View

17. Casing Design & Manufacturers Key
BC108
Transistor
Casing Design & Manufacturers Key
TIC106D
Thyristor

19. hFE = refers to the gain of a Transistor Ic = Collector Current
How Transistors Differ:
Transistors Ic
(max)
Vceo
hFE
BC108
0.1A
20V
BFY 51
1.0A
30V 40
ZTX 300
0.5A
25V
50-300
hFE = refers to the gain of a Transistor
Ic = Collector Current
Vceo = Voltage across / safe working voltage

20. Dark Sensor – ‘Dark – Light on’

21. Dark Sensor – ‘Dark – Light on’

22. Dark Sensor – ‘Dark – Light on’

23. Draw and complete the circuit diagram to make the bulb ‘switch on’
automatically when light shines on the sensor?
Inform the students the mark allocation for this question:-
Two correct symbols 4 marks
Position in correct order 2 marks
Named correctly 2 marks
Name the type of electronic components required to make this circuit work?

24. Electronics - Modelling in Live Wire / PCB Wizard
Automatic Switching:-
Hot & Cold Sensing - Transistor Projects.
R.A. Moffatt.

25. 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

26. ‘LED - on’ when Cold LED Light Emitting DiodeR1
Alternative –
Flashing LED
Explain in your own words how this circuit works?

27. ‘LED - off’ when Warm
LED
Light Emitting
Diode
Variable Resistor
Transistor
Thermistor

28. 7 R1 = = 350ohms 0.020 V I R 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.
= 350ohms
R1 = 7
0.020 V
I R
Resistor selected 470 ohms

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

30. ‘LED - on’ when Warm Heat Sensor ( Fire Alarm )
How could this circuit be modified to latch or ‘stay on’ if the
temperature increases?

31. ‘LED - on’ when Warm
Explain in your own words how this circuit works?

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

33. Timing - Transistor Projects.
Electronics - Modelling in Live Wire / PCB Wizard
PCB
Wizard
Automatic Switching:-
Timing - Transistor Projects.
R.A. Moffatt.

34. The Electrolytic Capacitor
Capacitor casing design +
symbol
Copy and simplify the sketch above and also explain using
brief notes the function of the Capacitor?

35. + 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).
Axial electrolytic capacitor +
Radial electrolytic capacitor
Polyester film capacitor
Ceramic disc capacitor
Non-electrolytic

36. Build the circuit as shown and time how long it takes the capacitor
Voltage Out
Ex 11: Time Delay
Voltmeter
Build the circuit as shown and time how long it takes the capacitor
to fully charge?
Check how long it takes Vo to reach two thirds the supply voltage =
‘time constant’

37. 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.

38. 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:-
R1 = 1K
R1 = 10K
R1 = 100K
EX 9:
Time constant (sec) = C (farads) X R (ohms)

39. 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.
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:
Time constant (sec) = C (farads) X R (ohms)

40. A Timing Circuit: (39)

41. A Timing Circuit: (39)
Build / Model this circuit using a Bread Board and test!

42. A Timing Circuit: (39)
Model the circuit using Live Wire test and explain how it works?

43. A Timing Circuit: (39)
Play the AVI file to help understand how this circuit works?

44. A Timing Circuit: (41)
Play the AVI file to help understand how this circuit works?

45. A Timing Circuit using a Thyristor (41)

46. Micro-Switch Alarm: (80)

47. A thyristor is a semiconductor device which acts as a switch
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

48. 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

49. 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.

50. A Steady Hand Game: (72)
Using a Capacitor to sound an Alarm for a set-time
112 (Circuits 72)

51. A Steady Hand Game: (72)
Using a Capacitor to sound an Alarm for a set-time
112 (Circuits 72)

52. A Steady Hand Game: (72)
112 (Circuits 72)

53. Fault Finding / Testing:
Testing a Battery
Soldering Test
Switch Testing
Testing + /- Rails

54. Modelling / Testing
using Bread Boards:

55. 112, Circuits / electronics resource in this presentation.
Useful Electronic Web-Sites:
Acknowledgement:
Thanks, to Maurice Lynch (WELB) for use of his excellent and invaluable
112, Circuits / electronics resource in this presentation.
Raymond Moffatt.