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2/17/2011
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Electronic and Electricity
Electronics and Electricity
– Sources of Energy
– The terminology and basic principles of Electricity
– Ohm’s Law
– Series and Parallel circuits
– The functions/ limitations /symbols of electrical
components
– Design/Experimenting/ Building and
Troubleshooting Electrical circuits
Overview/ Introduction Video Main Points from the Video• Electricity - is the movement of charged
atomic particles called electrons
• The Battery – Creates the force that
moves the electrons
• Electrons – have a negative (-) charge and
for this reason they travel from the
negative terminal to the positive terminal
of the battery
Main Points from the Video
• A Conductor – provides the path for the electrons to travels on
• Flowing Electrons = Current (measured in Amperes)
• The force moving electrons = Voltage (Potential Difference)
• A circuit is the path that current flows in
• A Light bulb will reduce the current in the circuit
Energy
• Energy is the ability to do work
• Electrical energy is one of many types of energy
• Others include:
•Wind
•Wave
•Solar
•Mechanical
•Nuclear
•Heat
•Sound
•Chemical
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Sources of Energy
• Energy sources are divided up into two types:– Renewable
– Non Renewable.
• Non renewable sources or fossil fuels as they are often known include peat, coal and oil will run out as there is only a limited supply.
• Renewable sources like hydro electric power, wind and wave power will not run out.
Sources of Energy
Principle of the Conservation of
Energy• Energy cannot be created or destroyed
but can only be transferred from one
form to another.
Conductors and Insulators
• Conductor – a material that conducts
electricity. Examples include copper, steel
and water.
• Insulator – a material that does not or is
a poor conductor of electricity. Examples
include plastic, rubber or wood.
Current• Current – is the
movement of electrons through a conductor
• Current - is measured in Amps (I)
• An Ampere or Amp –is the measure of the
amount of electric charge(electrons) passing a point in a circuit
Current will only
flow when the
circuit is
complete
Voltage or Potential Difference
• Voltage or Potential Difference – is the power to drive electrons around a circuit, and it is measured in volts.
• Voltage is created by the battery
• Electrons leave the negative side and they are then attracted to the positive side
• The higher the voltage the more electrons that will flow (higher current)
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Resistance
• Resistance = opposition to the flow of current in a circuit
– Wayne Rooney (current) vs. Richard Dunne (resistance)
• All electrical components have a certain amount of resistance
• High Resistance = Low Current
• Low Resistance = High Current
• Resistance is measure in Ohm’s Ω
Ohm’s Law
• V = voltage (volts)
• I = Current (amps)
• R = Resistance (Ω)
V = I x R
I = V/R
R = V/I Cover they quantity
in which you want to
calculate
Series and Parallel Circuits
Main Points from the Video
• When the light bulbs are in series the
current must flow through all of the
light bulbs
• When connected in series the bulbs
barely glow as the voltage is shared
across the four light bulbs
• In series if one bulb is disconnected it
will break the circuit
Main Points from the Video
• When the four bulbs are connected in
parallel all light bulbs shine brightly
• If one bulb is disconnected the others
will shine brightly
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Series and Parallel Circuits
• In a Series circuit, components are
connected one after the other and
there is only one path for the current
to flow around the circuit.
• In a Parallel circuit the components
are connected side by side and this
forces the current to take more than
one path.
Series and Parallel Circuits
Series Circuits• The voltage in a Series circuit is shared
by each of the components and how it is
shared depends on the resistance of
each of the component.
• If two components have equal
resistance the voltage will be shared
evenly.
Parallel Circuits
• In a parallel circuit the current is shared between the different paths.
• The amount of current in each path is dependent on the total resistance of the path.
• The current in each path will add up to the total current of the circuit.
• It is important to remember that there will be a greater flow of current in the path of least resistance.
Parallel Circuits Parallel Circuits
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Parallel Circuits Parallel Circuits
• Whilst current is divided up in each
path on the circuit voltage is not, the
voltage in each path will remain the
equal to the voltage that is applied to
the circuit (i.e. the battery voltage).
• The number of components or the
amount of resistance will make no
difference to the voltage
Resistors
Resistors
• Although all compounds have some resistance to the flow of current, resistors are electrical components designed specifically to reduce the flow of current in a circuit.
• Resistors are used of a number of reasons:– To protect components from being damaged
by too much current
– To create a potential divider circuit i.e. to direct current normal in to a transistor.
– To create a time delay with capacitors
Resistor - Potential Divider CircuitFixed Resistors
• The most common type of resistor is the
fixed resistor.
• Fixed Resistors have coloured band printed
on to them to show the resistance
• Each colour represents a number
• When calculating the resistance the
coloured bands are read from left to right
with the tolerance band on the right hand
side.
Fixed Resistor Symbol
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Fixed ResistorsFixed Resistors
Fixed Resistor -Tolerance• Resistors are not one hundred percent
accurate.
• The tolerance band indicates the
percentage accuracy of the resistor.
Fixed Resistor –Tolerance Example
• If a 330Ω resistor has a gold tolerance band. The operating value of the resistor will be anywhere between 330 Ω ± 5%. The maximum value will be 330 + 5% and the minimum value will be 330 – 5%.
• 5% of 330 =_____________________
• Maximum value of resistor =
• Minimum value of resistor =
Variable Resistor• A variable resistor can change the
resistance between two points in a circuit
by rotating a spindle.
• By rotating the spindle the resistance can
be increased and decreased in the circuit.
• A variable resistor has three pins,
however only two pins must be
connected, the middle pin and either of
the outer pins.
Light Dependent Resistor (LDR)• The resistance of an LDR varies depend of the
level of light falling on it.
• Darkness = High Resistance
• Light = Low Resistance
• LDR are used for creating light and dark sensor
circuits.
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Thermistor
• The resistance of a thermistor increases and decreases with temperature change.
• A wide range of themistor are avaiable but the most common is the NTC (Negative temperature coefficient) in which the resistance decreases with temperature
increases, which make them suitable for fire alarms.
• Thermistors are generally used in hot and cold sensor circuits.
Thermistor
Diodes and LED’s
Diode
• A diode allows electricity to flow in one direction only and blocks the flow in the opposite direction
• Silicon Diode are the most common type and they have a band marking the positive terminal
+
-
LED – Light Emitting Diode
• LED’s give off light when current flows through them
• LED’s must always be connected in series with a resistor as they are damaged by high voltage
• The anode(+) is recognisable by the longer leg
Bulb
• Give off light
when current
flows through it
• Bulbs have no
polarity thus they
can be connected
anyway around
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Motor
• Motors translate
current into circular
motion
• Motors can be
connect either way
around, but the way
they are connected
will determine if the
rotate clockwise or
anti clockwise
Buzzer
• A buzzer gives off
continuous sound
when current flows
through it
• They have polarity
which is indicated by
the colour of the
wires
+
-
Capacitors and Capacitance
Capacitors and Capacitance
• Capacitors are used to store an electrical charge.
• When power is supplied to a circuit that includes a capacitor, the capacitor charges up.
• When power is turned off the capacitor discharges its electrical charge slowly.
• Capacitance refers to how much charge a capacitor can hold, and it is measured in Farads (F).
• One farad is a very large amount of capacitance therefore capacitors are found in µF (µ = 10^-6).
Capacitors
• The amount of time that a capacitor takes
to charge up and discharge can be used for
timing circuits
• Capacitors are also used to smoothen out
current
Capacitors and Capacitance
There are two types of capacitors
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Switches
Switches
Switches Switches
• There are many different types and
classifications of switch available
• Switches are used to control the flow of
electricity to a circuit
• A switch allows you to turn a circuit/s on
or off
Common Switch Symbols Poles and Throws
• A Pole is the moving contact in a switch
• A Throw is the stationary contact in a switch
Pole
Throw
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Single Pole Single Throw Switch
• An SPST switch has one single moving contact
and one stationary contact
1 Pole
1 Throw
SPST Symbol
Double Pole Single Throw
Double
Pole
1 Contact Position
= 1 Throw
DPST• A DPST switch is used to turn on/off two
different circuits at the same time
• Example: The Hair Drier
– A hair drier has two circuit
• The Heating Element
• The Fan
– Both circuits must work together
DPST symbol
Single Pole Double Throw Switch
SPDT
1 Pole
2 Throws
Single Pole Double Throw Switch
SPDT
• This type of switch can be used to control
two different circuits. When one circuit is
on the other is off.
• The two circuits can never be on or off at
the same time.
SPDT Applications
• High and Low beam Head lights in a car
• When the high beams are on the low beams
are off and when visa versa
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Double Pole Double Throw (DPDT)
• A DPDT switch consists of two SPDT
switches connected together
mechanically.
• It could be used to control four devices,
turning two circuits on and off at the
same time.
x
Double Pole Double Throw (DPDT)
• A much more common use for the DPDT
switch is to control the forward and reverse
motion of a motor
DPDT Motor Circuit
DPDT Motor Circuit
Slide Switch this
direction for
clockwise
motion
Slide Switch
this direction
for Anti-
clockwise
motion
DPDT
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Limit or Micro Switches
• This type of switch is turned on and off by small amounts of movement.
• These are generally used to control motor circuits.
• They have 3 terminals or pins:– COM –this terminal is always connected to the
terminal
– NO – this is connected when you want the switch to be a push to make switch, in which the switch is off but when pressed it goes on.
– NC- this is connected when you want the switch to act as a push to break switch, in which the circuit is always connected to the power but when the switch is pressed it is disconnected from the power.`
The Transistor
• The transistor has two functions:
1. To act as an electronic switch
2. To amplify current
• A transistor has 3 pins:– Base – which activates the
transistor
– Collector – which is the positive lead
– Emitter – Which is the negative lead
Potential Dividers
Potential Dividers• Potential Dividers are used to split the
voltage of a circuit.
• They are widely used in technology to get
the right voltage at the base of a transistor
Potential Dividers• A voltage divider consists of two resistors in
series so that the applied voltage is divided
between the two resistors to produce the
required base voltage.
How a Potential Divider Works• A Potential Divider
works on the principle
that current will
always follow the path
of least resistance:
High resistance =
Higher voltage
between the base
and emitter
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Circuits and Designing Circuits
Circuits
• Circuits are explained using circuit diagram
• Each component has a unique symbol that is
used all round the world
Designing Circuits1. Task
2.Input (sensor)
3.Processes
4.Output
Designing Circuit
• Task – this is what you want your circuit to do or achieve
• Input or Sensor - responds to a change in the surrounding (light, motion, temperature etc)
• Processes – reacts to a change and triggers an output
• Output Devices – signal or react to a change that has been picked up in the input stage (light/LED, buzzer, motor etc...)
Task Input/
Sensor
Process Output
Heat
Sensor with a
Fan
Potential Divider
(1 variable
resistor and a
Thermistor)
Transistor Relay and Motor
Dark
Sensor with a
light
Potential Divider
(1 variable
resistor and a
LDR)
Transistor LED / Light Bulb
Moisture
Sensor with a
Heating element
Potential Divider
(1 variable
resistor and
moisture probes)
Transistor Heating Element
Automatic Light Sensing Circuit
• Using an LDR as part of the voltage divider will
allow the output to be controlled by changing
light levels.
• Remember the resistance of an LDR varies
from 400Ω in light to about 10MΩ in darkness.
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Automatic Light Sensing Circuit
Input
Potential Divider
(LDR and Variable
Resistor)
Output
LED
Process
Transistor
Automatic Light Sensing Circuit• The LDR has low resistance
when bright which allows current to flow
• The other resistor is a variable resistor (set to high resistance)
• Current follows the path of least resistance i.e.. through the transistor
• In darkness no current will flow in the potential divider due to high resistance, this means there is no voltage between the base and the collector and no output
Automatic Dark Sensing CircuitAutomatic Dark Sensing Circuit
• By switching the LDR and the Variable resistor you will create a Dark Sensing Circuit
• When Bright , LDR has low resistance
• When dark, the LDR has high resistance
• This means current will flow through the transistor when it is dark only as this will be the path of least resistance
Variable Resistor V.s Fixed Resistor
• A variable resistor is used as opposed to the a fixed resistor as this allow the sensitivity of the light/ dark sensor to be controlled
• In other words it allows you to set what level of brightness or darkness the out put will be triggered
Hot/ Cold & Wet Dry Sensor Circuit
• The hot / cold or wet/dry sensor circuit are
almost identical in appearance and operation
to the light / dark sensor, the only difference
is the LDR is replaced thermistor a set of
moisture probes.
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Automatic Temperature Sensing
Circuit
• Replacing the LDR with a thermistor will
give a temperature sensing circuit.
• The resistance of NTC thermistors
decreases as the temperature rises.
• The circuit below sound an alarm at low
temperatures(output).
Low Temperature Sensing Circuit
Thermistor
High Temperature Sensing Circuit
Changing the position of the variable resistor
and thermistor will sound an alarm at high
temperatures.
Automatic Moisture/Dry Sensing
Circuit
• Replacing the LDR with a set of moisture probes will create a moisture/dry sensing circuit.
• Moisture probes use the liquid as a conductor
• This mean when liquid is present there is low resistance and when there is no liquid present their is high resistance between the probes
Automatic Moisture/ Dry Sensing
Circuit
Moisture
Probes
Changing the position of the moisture
probes and the variable resistor will
change it from a moisture to a dry sensor
Darlington Pair• A Darlington pair consists of two
transistor connected together.
• In this configuration the emitter of the
first transistor is connected to the base
of the second transistor.
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Darlington Pair
• This configuration give a much greater gain
then a single transistor and it id used when
the base voltage is very small.
• In addition due to the amplification this
configuration is very sensitive to change and
even the smallest change in light levels for
example will give an output.
