Download Electronics - Deans Community High School

Electronics
Input, process, output
All electronics systems consist of three parts, the input, process
and output. We can show these as a block diagram.
Input
Process
Output
It is possible to draw up a block diagram for any electronics
system. Some are shown below.
keypad
aerial
tuner,
decoder,
amp.
speaker
chip
display
Input devices
Input devices detect some form of energy and cause a change in
the electrical signal going to the process device.
Microphone
Changes sound energy into electrical
energy.
Thermistor
The resistance of the thermistor
changes with change in temperature.
This changes the input signal to the
process.
LDR
The resistance of the thermistor
changes with change in light level. The
brighter the light the smaller the
resistance. This changes the input
signal to the process.
Switch
The switch sends a signal to the
process device when it is opened or
closed.
Examples: Input devices required
Baby monitor: needs to pick up sound so microphone.
Automatic night light: needs to detect light and dark so LDR.
Electronic thermometer: needs to detect temperature differences so
thermistor.
Output Devices
Output devices in electronics systems change electrical energy
from the process device into some other form of energy.
Loudspeaker: changes electrical energy into
sound energy
Buzzer [alarm]: changes electrical energy into
sound energy
Lamp: changes electrical energy into light energy
LED: changes electrical energy into light energy
Motor [in mixer]: changes electrical energy into
kinetic energy
Examples: Possible uses of output devices
Loudspeaker: any situation where you want voice or
music sounds
Tannoy, public address system at
railway station, Hi-Fi
Buzzer
: any situation where you just want to
produce a noise
Clock alarm, burglar alarm, warning
buzzer
Lamp
: any situation where you want to light up an
area
Automatic night light, lighthouse
LED
: any situation where you want to indicate
something is on
Hi-Fi display, on/off indicator on a
computer
Motor
: any situation you want to produce
movement
Food mixer, fan, vacuum cleaner
Digital Logic Gates
Logic gates are the basic components in many different electronics
systems. It is important that you learn the names and shapes of
three of the basic gates. These are shown below.
AND
OR
NOT
Digital signals can only have two values:
High voltage which is usually called logic 1
Low voltage which is usually called logic 0
Logic gates are a bit like the advert for Ronseal on telly. The only
difference is that they do exactly as their name says [instead of
what it says on the tin]
What
goes in
is NOT what
comes out
So if a logic 1 goes in a logic 1 can NOT come out, this means
that a logic 0 comes out.
input A
input B
output
To get a logic 1 out, input A must be logic 1 AND input B must
be logic 1.
input A
input B
output
To get a logic 1 out, input A must be logic 1 OR input B must be
logic 1.
Examples of logic gate systems
A light that comes on automatically at night:
light
sensor
lamp
The light sensor gives a logic 0 when it gets dark. The lamp needs
a logic 1 to light. The NOT gate changes the logic 0 into a logic 1
and the lamp comes on when it gets dark.
An alarm for a drawer that can be switched off when
required.
light
sensor
buzzer
on/off
switch
If the switch is on [logic 1], then opening the drawer will give
another logic 1 into the AND gate. Two logic 1 inputs will give a
logic 1 out and the buzzer will sound.
If the switch is off [logic 0] it does not matter what the input from
the light sensor is, the output cannot be logic 1 and the buzzer will
not sound.
A warning system if it is hot or dark:
light
sensor
buzzer
temp.
sensor
If it is dark the light sensor will give out a logic 0. The NOT gate
will change this to a logic 1. If it is hot the temp. sensor will give
out a logic 1. If either input to the OR gate is logic 1 the output
will go to logic 1 and the buzzer will sound.
Learning Outcomes
 An electronic system has 3 parts
 InputProcessOutput
 Draw and recognise block diagrams of electronic systems.
keypad





chip
display
Calculator
Input devices change a form of energy into electrical energy
 microphone
Input devices can change the size of the input voltage.
 Thermistor, LDR, Switch
The resistance of a thermistor changes with changes in
temperature
The resistance of an LDR reduces as the light level increases
You should be able to choose an appropriate input device for a
given situation
 An output device changes electrical energy into another useful
energy
 A loudspeaker, buzzer, lamp, LED and electric motor are all
output devices.
 Know the energy changes: electrical 
 loudspeaker  sound
 buzzer  sound
 lamp  light
 LED  light
 electric motor  kinetic
 You should be able to choose an appropriate output device for a
given situation
Digital Logic Gates
 You should be able to draw the symbol for a NOT, an AND
and an OR gate.
 There are only two possible values for logic gate input and
output
 High voltage is the same as a logic 1
 Low voltage is the same as a logic 0
 The output from a NOT gate is the opposite of the input
 The output from an AND gate is only logic 1 when both inputs
are logic 1
 The output from an OR gate is logic 1 if either input is logic 1
 You should be able to explain how simple logic gate circuits
work.
 You should be able to design simple logic gate circuits for given
situations.
Questions
1. Draw a block diagram showing the three parts of an electronics
system.
2. The list below gives three input devices. Copy and complete the
sentences.
(a) A microphone is affected by changes in ___________ level.
(b) A thermistor is affected by changes in ___________ level.
(c) An LDR is affected by changes in ___________ level.
3. The list below gives three output devices. Copy and complete
the sentences.
(a) A ____________ changes electrical energy to kinetic energy.
(b) A ____________ changes electrical energy to light energy.
(c) A ____________ changes electrical energy to sound energy.
4. Which input device would be used for the following
applications:
(a) A frost warning device for a gardener.
(b) An early morning sunrise alarm for a keen angler.
(c) A mobile phone.
5. Which output device would be used for the following
applications:
(a) A frost warning device for a gardener.
(b) An on/off indicator for a computer.
(c) Automatic curtain closer.
(d) A security light for a driveway
6. Draw the symbols for a NOT, an AND and an OR gate
7. Copy the diagrams below and state the missing signal for each
one.
logic 0
logic 1
logic 1
logic 1
logic 1
logic 1
logic 0
logic 0
logic 0
logic 1
8. A keen angler who wanted to know when it was light in the
morning and warm enough to go fishing set up the following
system.
light
sensor
buzzer
gate A
temperature
sensor
The light sensor gives a logic 1[‘high’] when light and a logic 0
[‘low’] when dark.
The temp. sensor gives a logic 1[‘high’] when warm and a logic 0
[‘low’] when cold.
(a) What gate would have to be used for this circuit to work?
(b) Explain why did you chose this gate.
(c) What change would have to be made to the circuit if the angler
wanted to fish when it was light and cold?