LIMPOPO PROVINCE PAT 2 :ELECTRONIC

SYSTEM & CONTROLS

Learners’na
me name:
School:

District:

Grade: 9 2025
Term 3

Investigate
1 Date: 12
-1 Aug2025
5 5
Design
20 Date: 26
-29 Aug2025

Make
3 Date: 08
- 1 Sep2025
5 7
SCENARIO It is frightening and even dangerous, to come back to a dark
house at the end of a working day. There are many different
types of outdoor lights on the market. Nancy wants the
outdoor lights at her home to be in the evenings when
she comes from work. She does not want to leave the light
on all day as this will be a waste of electricity and
unnecessarily expensive. She needs some type of device
that detects the fading daylight. This will cause her outside
houselights to switch on automatically once the correct
level of darkness has been reached.

Design and make a

circuit that will switch
lights on automatically
when night falls and off
in sunrise.
 LET’S DO IT!
A SIMPLE AND CHEAP DARK
-DETECTING Solder the transistor on the board and
solder one wire of the LDR to the emitter
LED CIRCUIT and other to the base, solder the negative
wire of the LED to the base of the
transistor with a 330 Ohms resistor and
 "How do you make an LED turn on when it gets dark?" solder 220k resistor with the one side of
the 330 Ohms resistor. Finally, we need to
 You might call it the "nightlight problem," but the same sort of question
comes up in a lot of familiar situations
-- emergency lights, streetlights, and the add the LED. To do so, we need to know
list goes on. which side is the "positive," or anode side
of the device. Regrettably, markings of
 You will investigate how to build a very -- perhaps
simple even the simplest
- LEDs are not consistent, so the best way
darkness-activated LED circuit. To our LED and battery, using just three to be sure is to test it. The simple circuit is
components, which cost less altogether (and much less if you buy in bulk). You
can build it in less than five minutes or less (much less with practice) ready for testing now. Connect 9v battery
terminals to the circuit as shown in the
 What can you do with such an inexpensive -controlled
light LED circuit? diagram and see the output. As you block
Almost anything really. But one fun application is to make LED circuits that turn
themselves off in the daytime to save power.

 It is a simple and powerful concept, which uses transistor (BC 547 NPN) as a
switch to switch ON and OFF the street light system automatically.

 It automatically switches ON lights when the sunlight goes below the visible
region of our eyes. (e. g in the evening after Sunset). It automatically switches
OFF lights when Sunlight falls on it (e. g in the morning), by using a sensor
called LDR (Light Dependent Resistor) which senses the light just like our eyes.
RESISTANCE

Heat generated Emit light

 When electricity flows through a  When some metals get extremely

conductor, heat is generated, i.e., hot, they emit light.
nickel and chrome. Heat up when
electricity is forced to flow throughit.
A light bulb is a source of light.
Stove and kettle elements are
normally made of a mixture of nickel
and chrome.
 
RESISTANCE

 If the resistance in a circuit is very low, for example when the

terminals of a cell are connected with a piece of thick copper wire,
the current will flow very strongly. This is called a “short circuit”. It
can result in so much heat being generated that damage is caused
to the cell and other parts of the circuit, the conducting wires can
melt and a fire can start.
 By adding more resistance to a circuit, you can control how great
the current is that flows through the circuit. In this way, you can
protect the components in a circuit from too much current flowing
through them. Increasing the resistance also means the cell or
battery powering the circuit will last longer. You can add precise
amounts of resistance by using resistors with the required
resistance value.
RESISTANC
E
Resisto is anything which limits the flow of current in
circuit
r oraAre electronic components that oppose the flow
current. of
Resistance is measured
Ohms .
in (Ω) made to resist flow of
Resistors are specially
current.
When resistors are connected in series they add
resistance
more to the
circuit.
When resistors are connected in parallel they
resistance
reduce in the
circuit.
TYPES OF RESISTORS

Fixed value have series of

coloured
resistorsbands on them that tell us
value of their
resistance.
Variable are also known
as potentiometer
resistors (Pot). Their
resistance
s can vary
minimum
from to maximum.
Its symbol
Use the chart in the previous
slide to color in the resistor on
the next slide. The value rating
of the resistor should beΩ330 COLOUR CODE
CHART
NOTE: Drag the color from the
top to its position on the

resistor. Good luck

TRANSISTORS
 Transistor operates switch;
as a it

2,2 � ) this current will open

needs a base current (current that will
enter via
the transistor
� thereby allowing
collector current (current via the bulb)
to pass to another terminal of the cell.

(0,6 �) to
 Transistor operates as amplifier;
an it
needs a very small current

(9 �) to pass the
open the base of the transistor
� to
allow a big current
transistor. �
 Types of Transistors
 NPN transistor
 PNP transistor
CAPACITOR

Capacitor is used to store electrical charge to be used when

needed.
Capacitance is measured in
farads.
Capacitors we use are measured in Pico which is trillion of
farads
Capacitor is made up of two conductors farad.
separated by an insulating material
dielectric
called
.The dielectric can be paper, plastic, ceramic, glass, polyester, polystyrene,
vacuu
air or
m
HOW DOES THE LDR WORK

The LDR in the dark its resistance is very high. If

there is light the resistance of LDR is very low.
When light falls on the LDR, it begins to conduct up
to about 1.5 mA, which pulls down the voltage at the
lower side of the resistor by 1.5 V, turning off the
transistor, which turns off the LED. When it's dark,
the transistor can conduct about 15 mA through the
LED. So, the circuit uses only about 1/10 as
much current while the LED is off.
 PROBLEM
STATEMENT
Investigate : 15 Marks
INVESTIGATE
Formal Task Individual
 Fill in the blank spaces investigating how a LDR works:
Explain what would happen when you point the LDR
towards the light and then away from the light. (10)
In ________________ the LDR will ________________ all the ______________ current to
ground, keeping the LED _____________. In the ______________, the LDR will have a INVESTIGATE:
QUIZ
______________ allowing current to _______________ through the _______________
resistor into the transistor's _________________, causing it to __________________.
Word bank:
light, off, emitter, low resistance, shunt, potentiometer, LED, fixed, base, dark, conduct
current, collector, high resistance, flow, bright
Formal Task Individual
 Match the items with the description.
(3
Instructions: Match the items in Column A with the correct descriptions in Column B )
by writing the correct letter next to each item.
Column A Column B Match

INVESTIGATE:
Output A. The transistor switches
base current, allowing
current to flow
Input B. LDR comes to the
darkness or light falls on
it
QUIZ
Process C. LED emits light

670�Ω with ±5 % tolerance

.
 Colour or write the colour of each band on the resistor, to
show the given resistance.
� (2)
Total: 15 Marks
Design : 20 Marks
DESIGN
Formal Task Individual
I am going to design and make
(what is that you DESIGN BRIEF:
expected
are to that QUIZ
would be used purpose
design) to ( )
and how it will benefit the
community at large (mention
two things). (5)
Formal Task Group

DESIGN
SPECIFICATIONS
& CONSTRAINTS:
QUIZ
Make : 35 Marks
MAKE
MAKE: QUIZ
 Exploded view of the circuit housing
using the isometric grid. Copy or
draw the structure that would be
used as an enclosure for the
electronic circuit that will be
assembled on the strip board.
Remember to position the LDR, LED
and battery where they will be most
effective for the intended purpose.
Use the Isometric grid provided, you
may recopy or draw your own
housing using the picture as the
guide. Scale 1:1 or indicate the Scale.
Ensure that you space the parts and
keep the proportions and angles
correct. (15
)
 MAKE: QUIZ

Skill Description Marks

Mark Mark
Exploded Views drawing allocated Obtained

Correct technique/
interpretation (3D
Isometric)
3
Dimensions (height,
width & length), &
Outlines
Components placed at
the most effective and 3
intended positions
Parts labels 4

Name, scale, and title 3

Neatness 2

1
5
 MAKE: QUIZ

 Make the model

 Study the electronic circuit below and answer the questions that follow.

 Collection of components: LDR, LED, resistors and transistor. (6)

 Connect circuit diagram using the components: LDR, LED, resistors and
transistor using OctoStudio,

 Draw a Circuit diagram. Interpretation and ability to connect LDR, LED,

resistors and NPN transistor. (10)

 Explain troubleshooting a-emitting

non LED doesn’t emit light as
expected or LED burns. Mention at least four troubleshooting ways.
(evaluation and recommendations
) (4)
MAKE: QUIZ

You
An hour to do your
have:
planning.
1 hour to draw specified working
Make sure that every team member plays a part in the building
drawings.
When
process.done ensure that the grids are included for
Use the materials thriftily and
marking.
intelligently.
You are only allowed to ask for assistance from your group
moving
members.around
No coping or referring to other groups’ work. Remember
an
this is
examination.
Total:
35
Skill Criteria Yes/No

Investigation Quiz on how an LDR works × 3 (number of group members)

System diagram × 3 (number of group members)
Fixed resistor × 3 (number of group members)
Design Design brief × 3 (number of group members)
Design specifications and constraints/ initial idea
Make Exploded views × 3 (number of group members)
Circuit Diagram × 3 (number of group members)
Evaluation and modification

CHECKLIST FOR THE BOARD PREPARATION