1. ELECTRONIC SYSTEMS AND CONTROL

2. CURRENT
 Current is the continuous
movement of free
electrons through the
conductors of a circuit.
 Ammeter - Measures the
flow of electrons in a
circuit, which is known as
current - connected in
series.
 Symbol of current (I).
 The (I) unit of
measurement of electric
current, the ampere, is
named after André-Marie
Ampère.

3. VOLTAGE
+ The ability of a cell to
produce current is
called voltage.
+ Voltage is the
electrical
potential energy.
+ Is measured in Volts.
+ Voltmeter
 Measures the voltage
produced by a power
supply – always
connected in parallel.
+ Symbol for Volt (V) or

4. OHM’S LAW & RESISTANCE
 Resistance - Free
electrons move through
conductors with some
degree of friction.
 Resistance is
measured in Ohm (Ω).
 Symbol of resistance
(R).
 A Resistor - Slows
down the flow of
electrons in a circuit.

5. EQUATIONS
 Resistance = voltage/current R= V/I
 Voltage = current x resistance V= I x R
 Current = voltage/resistance I=V/R
 Resistance in Serie:
 When resistors are connected in Series, the effect is to add more
resistance to the circuit.
 E.g. The value of resistors in series: RT(Total) =
R1+R2+R3[Resistor Values]
 *A resistor is a series circuit is called a voltage divider.
 Resistance in Parallel:
 When resistors are connected in parallel, the effect is to reduce the
resistance in the circuit.
 E.g. The value of resistors in parallel: 1/Rt = 1/R1 + 1/R2 + 1/R3
 *Resistors in a parallel circuit is called a current divider.

6. Measured
in Volts (V).
V = I x R
V
I = V R
R = V I
A
Ω
Measured in Amps (A). Measured in Ohms(Ω).

7. RESISTOR COLOUR CODES
The First three bands give the
value of the resistor in ohm(Ω).
The fourth band indicates how
accurate the given value is.
Resistor value: 2% - RED
5% - GOLD
10% - SILVER
E.g.:

8. RESISTIVE COMPONENTS
 Variable Resistor  Light Dependent
 Can be used to adjust resistor (LDR)
the flow of current in a  It’s a component whose
circuit. resistance depends upon
the amount of light falling
on it – it reacts to light.
 When the LDR in the
circuit is covered up, the
 Thermistor bulb gets dimmer and
 Is a component whose finally goes out.
resistance varies with
temperature.

9. CONTROL ELECTRICS
 The switch  Single pole double
 It’s the simplest throw switch (SPDT).
control unit form in an  Double Pole single
electrical circuit. The throw switch (DPST).
simplest type of
switch is the single  Double pole single
pole single throw throw switch(DPDT).
switch (SPST).
 It has 2 parts: a pole
& a contact.  Push to Make & Push to
break switches:

10. MORE COMMON TYPE OF SWITCHES:
Toggle switch Push
Switch
Slide switch Reed Switch
A Rotary Switch

11. RELAYS
 The Relay - is a switch turned on and off by an
electromagnet.
 Relay Latch - Fixes a circuit in “On” position.
- A latch is like a lock.
 Relay Buzzer -The relay switches “on” and
“off” very rapidly, producing a
buzzing sound.
-A relay can therefore be used to
make a crude buzzer.

12. CONTROL ELECTRONICS
THE DIODE LIGHT EMITTING DIODES (LED)
 Is a semiconductor device.  A LED is a special form of diode
 It’s a component which allows that gives out light when
current to flow in one direction connected the correct way
only. around.
 A Semiconductor diode consists  LED’s normally need to be
of a PN junction and has two connected in series with a
terminals: resistor to prevent them drawing
 [P] - Anode(+) too much current and burning
 [N] – Cathode(-) out.
 Current flows from the anode to  LED’s are used mainly as visual
the cathode within the diode.
indicators that a circuit is working
 When a forward voltage is
applied, the diode conducts. or an appliance is “On”.
 When a reverse voltage is  An LED converts electrical
applied, their is no conduction. energy to light.

13. TRANSISTORS
 A Transistor is a semiconductor device.
 Made of three layers of N-Type & P-Type semiconductor material, Geranium
and Silicone.
 The three layers are called - Emitter, Base & Collector.
 There are three types of transistors:
 NPN PNP
 The NPN Transistor has a small current flowing to the base of the
transistor enables a large current to flow between the collector and emitter.
 The PNP Transistor uses a small base current and negative base voltage
to control a much larger emitter-collector current.
 The FET transistor – Field Effect Transistor only needs a small field of
current.

14. TIMING CIRCUITS
CAPACITORS - A CAPACITOR IS A COMPONENT WHICH CAN STORE AND RELEASE
ELECTRICAL ENERGY.
- CAPACITANCE IS MEASURED IN FARAD.
1. POLARIZED - CAPACITOR 2. NON – POLARIZED CAPACITOR
 Polarized capacitors tend to  Non-polarized capacitors
be higher value types. which are low value types.
 These have a positive(+)  These can be connected
and negative(-) lead which either way round in a
must be connected the circuit.
correct way round in a  Do not have a (+) or (-)
circuit (+ to + and - to -) . lead.
 Normally used to smooth a
current in a circuit.

15. THREE FACTORS THAT INFLUENCE THE CAPACITY
OF A CAPACITOR:
 1.) Lowering the surface area of plates.
 2.) Increase distance between plates.
 3.)The kind of material used for dielectric.

16. REFERENCES:
 Download.pptx. (n.d.). Retrieved from
http://www.tes.co.uk/Download.aspx?storycode=6071059&type=X&id=6269844
 explaining how Resistors work.ppt. (n.d.). Retrieved from
http://teachersunderground.co.uk/Electronics/explaining%20how%20Resistors%
20work.ppt
 Garratt,J. (1996). Design and Technology. Cape Town: Cambridge University
Press.
 Ohm’s Law - Resources - TES. (n.d.). Retrieved April 30, 2012, from
http://www.tes.co.uk/teaching-resource/Ohm-s-Law-
6071059/addtofavourite/addtofavourite/
 Resistor colour code wheel.ppt. (n.d.). Retrieved from
http://teachersunderground.co.uk/Electronics/Resistor%20colour%20code%20w
heel.ppt