Transcript Document

Standard Grade
Technological Studies
Summary Notes
Compiled By
Mr. A. Cunningham
May ‘04
An acknowledgement must go to the authors of the LT Scotland Support Notes for the
Technological Studies course, as some of the diagrams and text has been used from
these notes in this document.
Contents
Systems
Page 3
Pneumatics
Page 5
Modular Electronics
Page 9
Component Electronics
Page 10
Logic Electronics
Page 14
Mechanical Systems
Page 18
Energy
Page 30
Programmable control
Page 32
Standard Grade Technological Studies
Systems Summary Notes
Types of Control
The Universal System
All systems can be analysed
in terms of input, process
and output. A diagram called
the universal system
diagram consists of these
three basic elements.
Universal system
diagram
input
process
•Manual control is performed by the
actions of humans.
•Automatic control is performed by
technological devices (often
electronic).
output
Sub-Systems
The sub-system diagram shows the internal
detail of the system. Each box, called a subsystem, can be thought of as a system within a
system and has its own input and output. The
dashed line around the sub-system is called a
system boundary and this marks the area of
interest to us. The ‘real world’ input and output
are shown as arrows entering and leaving the
sub-system diagram.
Input
input subsystem
process (control)
sub-system
•Closed Loop Manual, e.g. A person
filling a bath. The feedback is
provided by the persons eyes
watching the level of the bath.
•Closed Loop Automatic. System
controlled by a machine usually
automatic. Electronic transducers are
used as sensors and provide
feedback for electronics/computer to
make decisions.
Positional control – used to control the
exact position of an object/machine. Used
in robotic arms to ensure arm rotates to the
correct place.
Sequential Control Systems
Sequential control is used where the
outputs are required to follow a fixed cycle
of events; that is to switch on or off in a
particular sequence
output subsystem
Output
System boundary
Open & Closed Loop Control Systems
Open loop systems are the simplest of systems. They take in an input, process it and
produce an output. They do not use sensors or feedback to try and alter what the
system is doing.
Closed-loop control is a more accurate system of control and at the same time more
expensive. It employs self-monitoring, where a sensor is used to read the condition
being controlled and adjust the output if necessary. This monitoring takes place through
a feedback loop. Here an input sensor checks the output and adjusts it when it does not
meet the requirements.
More On Open & Closed Loop Control Systems
In closed-loop control the value of the output is constantly monitored as the system
operates and this value is compared with the set (or reference) value. If there is any
difference between the actual value and the set value (an error), then the input to the
system is varied in order to reduce the output error to zero.
A closed-loop system can always be identified by the presence of a feedback
loop.
An open-loop system never has a feedback loop.
temperature sensor
Darkness sensor
Switch on
cold
Set level
Electrical
energy
+
control
sub-system
output
driver
heater
Room heated
automatically
Error detector
symbol
Feedback
signal
TEMPERATURE
The diagram shows a control diagram for a typical closed loop system. The error
detector takes in two signals – one form the temperature sensor (feedback sensor) and
one from the set level. It subtracts one from the other. If there is any difference and
error signal is produced. This is passed to the control sub-system which will decide how
much to turn the heater on. This is called negative feedback and is typical in closed loop
systems. The graph below shows how the Set Level and Actual level compare in the
system above.
ACTUAL TEMPERATURE
SET TEMPERATURE
Set level
signal
TIME
Standard Grade Technological Studies
Pneumatic Systems – Summary Sheets
Safety
Advantages of Pneumatic System
Learn all the safety rules, e.g.
Clean
•
Wear safety goggles
•
•
Don’t blow air at anyone, not
ever yourself
•
Don’t let compressed air come
in contact with your skin
•
Check all connections are
secure before turning on the air
•
Don’t leave pipes trailing along
the floor
Pneumatic systems are clean
because they use compressed
air. If a pneumatic system
develops a leak, it will be air that
escapes and not oil.
Safe
•
Pneumatic systems are very
safe compared to other
systems. We cannot, for
example, use electronics for
paint spraying because many
electronic components produce
sparks.
Reliable
•
Pneumatic systems are very
reliable and can keep working
for a long time.
Economical
•
If we compare pneumatic
systems to other systems, we
find that they are cheaper to run.
This is because the components
last for a long time.
Flexible
•
Once you have bought the basic
components, you can set them
up to carry out different tasks.
Describing How A Circuit Works
You will be asked to name components in circuits and describe how the circuits
operate. In the General paper, you will only be given either AND control or OR
control style circuits. At Credit level you will usually be given a sequential circuit
(one which follows a particular sequence). A few examples are shown below:
Valve B
In order to get
the single acting
cylinder to
outstroke, you
need to actuate
valve A AND
valve B.
Shuttle valve
Valve A
Valve B
The cylinder will outstroke if valve A OR
valve B is actuated.
Could you describe how this
circuit works?
ANSWER
Valve A
OR CONTROL
When the push button is
pressed, the 5/2 valve changes
state and the cylinder
outstrokes. As it outstrokes, it
pushes the former together and
the hot plastic sheet is pressed
into shape. As this happens it
also actuates the roller. Air now
flows through the restrictor and
starts to fill up the reservoir.
Once the reservoir is full, the
5/2 valve changes state and
the cylinder instrokes, ready for
the process to begin again.
AND
CONTROL
Completing Circuits
You can be given a pneumatic circuit and be asked to finish the piping to a given
specification. If you want to do well in these questions, start by learning where
the pipes go to basic valves. Try adding the piping to the circuits below.
Exam Questions
Air Bleed Circuits
You must practise
answering lots of
Pneumatics questions with
circuits to get a feel for the
level of difficulty and the
types of question you
could be asked. There is
no substitute for hard work
I’m afraid!
They use a
diaphragm valve.
When the air tube is
blocked the air can
no longer escape
and is forced into the
diaphragm valve
which changes state
and causes the
cylinder to outstroke.
Answers
Calculations
All the formulas you need for pneumatics are given in the data booklet.
(An extract is shown below)
Force in a single acting cylinder on Outstroke (Easiest calculation)
You will get the air pressure, P and the piston diameter, d.
or use a=r2 and ½ d to
Use d to get the area, a. You can either use
get r. Then you just use F=P x a to find the force.
Try these questions:
Find the force for the pressures and diameters given
1.P=0.3N/mm2, d=12mm
2.P=0.5N/mm2, d=23mm
Force in a double acting cylinder on Outstroke & Instroke
The outstroke calculation is the same as for the single acting cylinder.
To find the instroke force you need to work out effective area of the cylinder. (
remember there is less surface area on the instroking side of the piston because
of the space taken up by the piston rod & so the force is always less than the
outstroke force.)
Effective area = piston area – piston rod area
Once you work this out simply use it with the F=P x a formula to find the force.
Try these questions:
Find the instroke force for the pressures and diameters given
1.P=0.4N/mm2, piston diameter = 15mm, piston rod diameter = 4mm
2.P=0.8N/mm2, piston diameter = 20mm, piston rod diameter = 3mm
Answers: Single acting 1) 33.9N
2) 208N
Double acting 1) 65.8N
2) 246N
Standard Grade Technological Studies
Modular Electronics Summary Notes
Analogue and digital signals
Output transducers
All components in electrical and electronic
circuits are either receiving or transmitting
electrical signals. These signals can be either
analogue or digital.
Output transducers take an electrical signal
and change it into a physical output. They
include the output boards in modular
systems or output components in any
electronic system.
Analogue devices
An analogue signal varies according to the
physical surroundings. For example, the E&L
light-sensing unit will send out a voltage that is
proportional to the amount of light falling on the
LDR.
Typical analogue input transducers are:
•input voltage units
Examples
Bulb Unit, Motor Unit, Solenoid, Relay &
Buzzer
Sub-Systems Boards
You need to know what the following boards
can be used for and how they can be linked
together to produce a system.
Transducer Driver, Switch unit, light sensor,
temperature sensor, moisture sensor, latch,
comparator, transducer driver, buzzer, lamp,
d.c. motor and solenoid (including actuating
3/2 valve). AND, OR, INVERTER(NOT),
NAND & NOR
•light-sensing units
•temperate-sensing units
•moisture/rain sensor units
•sound-sensing units.
Remember all systems will start with an
input sensor board (light, temperature,etc)
and end with a transducer driver followed by
an output transducer, e.g. a Motor, Buzzer,
etc.
Digital devices
A digital signal is one which has only two
settings, on or off. In electronic terms it has
only two levels, high or low.
Relays
You must be able to complete a
diagram showing a system with a
relay, a motor and a separate power
+ 6V supply.
The push switch unit is a typical simple digital
transducer.
Remember relays are used to
switch on higher powered circuits
using low power control circuits.
+V
O/P
IND
POS
SIG
+
+
+
S
0V
S
0V
S
0V
-
0V
TP
-
-
NEG
TP
+
+
+
S
0V
S
0V
S
0V
-
-
-
0v
0v
RANGE
+5V DC TO +8V DC
ACTIVE
HIGH
E & L INSTRUMENTS Ltd
0v
E & L INSTRUMENTS Ltd
E & L INSTRUMENTS Ltd
Standard Grade Technological Studies
Logic Electronics Summary Notes
Logic Gates & Truth Tables
You must learn the symbols, truth tables and Boolean expressions for the
logic gates shown
NOT
Z=A
Z = A.B
AND
Z = A+B
OR
Z = A.B
NAND
Z = A+B
NOR
Z  AB
A
B
Z
XOR
A
Z
0
1
1
0
A
0
0
1
1
B
0
1
0
1
Z
0
0
0
1
A
0
0
1
1
B
0
1
0
1
Z
0
1
1
1
A
0
0
1
1
B
0
1
0
1
Z
1
1
1
0
A
0
0
1
1
B
0
1
0
1
Z
1
0
0
0
A
B
Z
0
0
0
0
1
1
1
0
1
1
1
0
Boolean Expressions from truth tables
A
B
C
Z
0
0
0
0
Steps to follow:
0
0
1
0
•Find the 1s in the Z column
0
1
0
0
•Write the Boolean expression for each 1, e.g. Z
= A.B.C
0
1
1
0
1
0
0
0
•Write the expressions out in words, e.g. Z = ( A
AND NOT B AND C) OR (A AND B AND C)
1
0
1
1
1
1
0
0
1
1
1
1
You must be able to take a truth table and
produce Boolean expressions from it.
•Write out the inputs, e.g. A , B C
•Draw in any NOT gates
•Draw in the AND gates
Z=A . B . C
Z=A . B . C
Z = (A AND NOT B AND C) OR (A AND B AND C)
•Finally draw in the OR gates if required
A
B
Z
C
NAND Equivalents
NOT
NOR
AND
XOR
OR
Pin-out Diagrams & Drawing Circuits
You must be able to select suitable logic ICs (chips) and draw in the
connections for a given logic system. An example is given below. Don’t
forget to draw in the connections for +Vcc ( the positive supply voltage)
and 0v.
INPUT A
OUTPUT
INPUT B
+Vcc
+Vcc
14
+Vcc
13
12
11
10
9
8
14
13
12
2
Input A
Input B
3
4
10
9
5
6
8
7432
7408
1
11
5
6
7
1
2
3
Gnd
(0V)
4
OUTPUT
7
Gnd
(0V)
0v
Remember you don’t need to use all the logic gates in a chip – if
you only need one, you only use one!
Drawing Logic Diagrams form Written Descriptions
You have two choices here to solve this type of problem:
1.
Try to draw a diagram out straight away from what you have been told, or
2.
Draw a truth table out for the problem and then go through the process
outlined on the previous page for turning a truth table into a logic diagram.
The choice you make depends on the difficulty of the system. See over for an
example.
Logic Diagram from a Written Description – Example
A machine (M) is to start under the following conditions
•The guard is down ( Guard Down: G=1, Guard Up: G=0)
•The operator is sitting on the seat ( On seat: S=1, Not on seat: S=0)
•Either the fast button or the slow button is pressed ( FST – Fast, SL – Slow)
•The machine temperature is low ( Temp Low: T=0, Temp High: T=1)
The logic diagram can be produced by simply reading the specification. We
know that all the 4 conditions must be true before the machine will start – so
we will need a 4 input AND gate. There are 5 inputs in total – G, S, FST, SL
& T. The FST & SL inputs need to go through an OR gate because we are
told that only one needs to be pressed and the temperature input must go
through a NOT gate so that we will get a 1 out from it when it is low.
Diagram
Draw the inputs on the LHS first
AND gate
Next add in any OR or NOT gates
And finally add the
G
S
M
FST
SL
T
Standard Grade Technological Studies
Mechanical Systems – Summary Sheets
Types of Motion:
Rotary
Turning in a circle. This is the most
common type of movement, for
example wheels, clock hands,
compact discs, CD-ROMs.
Linear
Movement in a straight line, for
example movement of a paper
trimmer cutting a straight edge on
paper or a lift moving between floors.
Reciprocating
Backwards and forwards movement
in a straight line, for example the
needle in a sewing machine or the
piston in a car engine.
Oscillating
Swinging backwards and forwards in
an arc, for example the pendulum of
a clock, a playground swing or a
rocking horse.
Levers
Levers can be used as force multipliers or distance multipliers. A force
multiplier allows you to get a large force out for a small force in. A distance
multiplier allows you to get a large distance out for a small distance in.
Mechanical Advantage (MA) =
Load
Effort
Velocity Ratio (VR)=
Distance Effort is moved
Distance Load is moved
Efficiency =
=
VR
MA
X 100%
Moments
A moment is a turning effect.
Moment = Force x Distance
If a body is in equilibrium the sum of the clockwise
moments must equal the sum of the anticlockwise
moments. Or
CWM = ACWM
F1 d1 = F2  d2
This can apply to straight lever, angled levers and
beams.
Free-body diagrams
This is a diagram showing all the forces acting on a
body.
Example: draw a free-body diagram representing
the forces acting on the fork-lift truck.
2k
N
Weight
W
2m
0.7m
0.8m
R1
R1 & R2 are the reaction forces. They push up to
balance the forces pushing down due to the weight
of the truck and its load.
Another condition of equilibrium is:
upwards forces = downwards forces
This is used with the principle of moments to
calculate reaction forces in structures.
R2
R2
Free-body example
•
Draw a free-body diagram for the car
•
Calculate the reaction forces R1 and R2.
9.5kN
1.5
m
R1
1m
R2
Take the moments about R1 (just think about it as being like a pivot)
CWM = ACWM
F1 d1 = F2  d2
9.5k x 1.5 = R2 x 2.5
R2 = 14250  2.5
R2 = 5700N
Now use
upwards forces = downwards forces
R1 + R2 = 9.5kN
R1 + 5700 = 9500
R1 = 9500 – 5700
R1 = 3800N
Gears
Gears are toothed wheels designed to transmit rotary motion and power from
one part of a mechanism to another. Gears are used to increase or decrease
the output speed of a mechanism and can also be used to change the direction
of motion of the output.
Gear Ratios
Gear Ratio =
Number of teeth on driven gear
Number of teeth on driver gear
or
Gear Ratio =
Driven
Driver
In the simple gear train above the gear ratio would be:
If gear A is still rotating at 100 rpm in a clockwise direction then gear B will
now rotate at 50 rpm in an anticlockwise direction.
24 2
 or 2:1
12 1
Input speed
Output speed =
Gear ratio
Gear ratio =
Idler gears
To get the driven gear to rotate in the same
direction as the driver, a third gear is inserted
in the system. This idler gear has no effect on
the gear ratio of the system. The size of the
idler is not important and is normally a small
gear.
Ratchet and pawl
A wheel with saw-shaped teeth round its
rim is called a ratchet. The ratchet wheel WINCH DRUM
usually engages with a tooth-shaped lever RATCHET
called a pawl. The purpose of the pawl is to
allow rotation in one direction only and
prevent rotation in the opposite direction.
Ratchet and pawl gears are used in
winches to prevent slippage.
CABLE
CRANK
HANDLE
PAWL BAR
Gear Trains
When 2 or more gears are meshed together they form a simple
gear train. The overall gear ratio of the train can be worked out
using the first driver gear and the last driven gear.
The gear train shown includes
4 gears meshed together. The
number of teeth each has is:
500rpm
A = 50 teeth
+
B = 10 teeth
A
+
B
+
+
C
C = 25 teeth
D
D = 120 teeth
If A is the input driver the
overall gear ratio is:
Gear ratio =
Teeth on D 120

or 12:5 = 2.4:1
Teeth on A 50
It doesn’t matter if you have 2 or 52 gears in a simple train, the overall
gear ratio is still calculated using the first and last gear in the train.
Input Speed
Ratio
500
=
2.4
 208rpm
Output Speed =
Compound gears
If gears are required to produce a very large change in speed, for
example if the multiplier ratio is 100:1, then problems can arise with the
size of gear wheels if a simple gear train is used.
This problem can be overcome by mounting pairs of gears on the same
shaft, this arrangement is called a compound gear system.
Compound Gear Ratio
Calculate the gear ratio of each pair of gears and
then multiply the ratios together.
Driven 80 4


Driver 20 1
Driven 60 6
Gear ratio CD =
=

Driver 10 1
4 6 24
Overall Ratio =  
1 1 1
 If the input speed was 100rpm:
Gear ratio AB =
Output Speed =
Input Speed 100
=
= 4.17rpm
Gear Ratio
24
Worm and wheel
Another way of making large speed reductions is to use a worm gear and
wormwheel. The worm, which looks rather like a screw thread, is fixed to the
driver shaft. It meshes with a wormwheel, which is fixed to the driven shaft.
The driven shaft runs at 90 degrees to the driver shaft. When considering the
speed changes in most worm gear systems, you can think of the worm as if it
were a spur gear with one tooth. It is a single tooth wrapped around a cylinder.
Torque
Torque is the amount of turning produced by a force.
Torque  Force  radius
Nm
m
N
Example 1
How much torque is required to tighten the nut if the force required is 45
N and the radius of the tool is 200 mm.
Torque  Force  radius
= 45  0.2
= 9Nm
radius
Belt-and-chain drives
These are used when rotary motion has to be transmitted over a relatively
long distance and gear trains would be too prone to losses due to friction.
Belt & Pulley Drive
A belt is wrapped around two or more pulleys. The belt is tightened or
tensioned by pulling one of the pulleys out and locking it in place. Pulleys
are thin metal discs with a groove cut into the circumference of the disc.
DRIVEN
PULLEY
1
40 mm
2
DRIVER
PULLEY
V-belt
160 mm
The tensioned belt transmits the rotary motion from pulley 2 to pulley 1. The
belt is angled as shown in figure 2 to give better grip to prevent the belt from
slipping. A change in speed can be accomplished by varying the diameter of
the driver pulley and driven pulley. The driver pulley will turn in the same
direction as the driven pulley.
Belt & Pulley Drive (continued)
A change in direction can be achieved by crossing the belt over. See diagram below
DRIVEN
DRIVER
Multiplier Ratio
Like gears, you can vary the speed of a pulley system by using different sizes
of pulley. The multiplier ratio is very similar to the gear ratio and is calculated
as follows:
Multiplier Ratio =
Diameter of Driven Pulley
Diameter of Driver Pulley
Output Speed =
Input Speed
Multiplier Ratio
Speed & Torque
When a pulley, belt or chain system produces an increase in speed, you get
a corresponding decrease in Torque. Likewise, when a system produces a
speed decrease, you get a corresponding increase in Torque.
Belt tensioning – Jockey Wheels
One advantage of a belt system is that it can absorb shock loads by
slipping. Too much slippage is undesirable however and the inclusion of a
small pulley called a Jockey wheel can ensure that a belt remains in
tension.
DRIVER
DRIVEN
JOCKEY
PULLEY
Toothed belts
Belt drives tend to use their ability to slip to their advantage. However, where
slippage would damage a mechanism, toothed belts have been developed that
retain the advantages of normal belts but do not slip.
Chain drives
Where large forces have to be
transmitted, and there can be no
slippage allowed, chain drives are
used. Instead of a pulley, a toothed
wheel known as a sprocket is used to
drive a chain. The chain in turn drives
another toothed wheel. Once again, the
speed can be varied by making the
sprockets different sizes.
DRIVEN
DRIVER
Chain tension
Chain-drive systems must also have a
means to tension the chain. If the chain
is over-tensioned there will be excessive
wear on the chain, sprockets and
bearings in the system. In some bicycles
and even motorcycles, the chain is
tensioned by gently pulling the wheel
back until the chain is tight and then
tightening the locking wheel nuts.
However, to give better control, a springloaded jockey wheel such as that used in
Derailleur gears on racing bikes and
mountain bikes is used
Spring loaded jockey wheels
to maintain the tension as
different sized gear wheels
are chosen.
Converting Motion
Cams
FOLLOWER
RECIPROCATING
MOTION
Changes rotary motion into
reciprocating motion.
ROTARY
CAM
ROTARY
MOTION
Crank & Slider
Changes rotary motion into
reciprocating motion.
CRANK
SLIDER
PINION
Rack & Pinion
Changes rotary motion into linear
motion.
RACK
Worm & Nut
Changes rotary motion into linear
motion.
Worm
Every full rotation of the worm results in
the nut moving a distance equal to the
pitch of the worm.
Example: A worm has a pitch of
2.5mm. If the worm is rotating at
Number
revolutions
1000for
 2.5
100rpmof
how
long will =it take
the nut
= 400
to move 1m?
 The time taken will be 400  100 = 4 minutes
Efficiency & Friction
No machine is ever 100% efficient. This is
because there are always losses in a system,
e.g. energy is lost due to friction causing heat,
or sound or light.
Uses of friction
Friction can be useful in some circumstance,
e.g. in car brakes, car tyres or in belt drive
systems where the belt needs to grip the pulley
in order to make it turn.
Disadvantages of Friction and ways to reduce it
Friction causes unwanted wear on components and results in energy
losses in machines as energy is converted into heat & sound. There are a
number of ways of reducing friction, examples of which are given below.
We can reduce friction by oiling ("lubricating") the surfaces. This means
that the surfaces no longer rub directly on each other, but slide past on a
layer of oil. It's now much easier to move them. Other methods include:
•using "ball bearings" or "roller bearings", where balls or rollers allow the
surface to move easily without actually touching each other
•using special materials, for example, Teflon, which have a very low
coefficient of friction and thus slide easily (Teflon is used in "non-stick"
frying pans for this reason)
OUTER RACE
CAGE
BALL BEARING
INNER RACE
Compound Levers
When you require a large force multiplication or mechanical advantage, levers
can be linked together (A bit like compound gears) to produce a compound
mechanical advantage. The example below illustrates this and shows how to
calculate the output force.
Fin
0.6m
The compound lever
system shown is used to
control a manual brake on
a trolley. If an input force
of 12N is applied what is
the output force at the
wheel?
0.25m
LINK
0.15m
Fulcrum
0.08m
Fout
Cons idethe
r firs tle ve r(thehandle )and us e
the principleof m om e nts
to findthe forceout
w hichgoe sto the link .
 CWM   ACWM
12 0.85  F 0.25
12 0.85
F
0.25
F  40.8N
So w e now k nowthat the forcepus hingdow non the
be llcrankis 40.8N. Allyoune e dto do now is w orkout
the outputforcefromthe be llcrankus ingthe principleof
m om e nts
again.
 CWM   ACWM
40.8  0.15  Fout  0.08
40.8  0.15
0.08
Fout  76.5N
Fout 
Eas y!
MechanicalAdvantage
76.5
12
M.A. 6.38
M.A.
ForceOut
ForceIn
Standard Grade Technological Studies
Energy Summary Notes
Forms of energy
Forms of energy
Non-renewable - finite
Oil, Coal, Natural Gas & Nuclear
Kinetic – energy a body has when
moving
Renewable – infinite
Solar, Wind, Wave, Tidal & Hydro electric
Potential – energy stored in a body
when it is raised up a height, or energy
stored when, for example, a spring is
compressed.
Advantages of renewable sources
Wind – no pollution caused, can be built in
remote locations.
Solar – again no pollution, allow the
trapping and concentration of the Sun’s
energy
Wave - Wave power systems use kinetic
energy in the waves to turn turbines. No
pollution generated
Disadvantages of renewable sources
Wind – turbines are noisy and unsightly.
Winds vary and so continual generation of
electricity is not guaranteed.
Solar – relies on long periods of sun light to
be most effective. Not so good in Scotland
in the winter
Wave – expensive to install and prone to a
lot of wear as they have to be out at sea.
Formulae
Ep = mgh
potential energy
2
Ek = ½mv kinetic energy
Ee = ItV
electrical energy
Eh = CmT heat energy
P = E/t
Power
Work Done = F x d
Work done
Note: you don’t have to learn these as
they will be given in the data booklet.
Electrical - the most versatile form of
energy, it can be converted into many
other forms of energy easily.
Heat - the energy transferred to a body
which causes an increase in its
temperature.
The Law of Conservation of
Energy
The law of conservation of energy
asserts that for a closed system, where
no energy goes in or out, the total
energy within the system must always
be the same, although its form may
change.
Conserving (Saving energy)
Most of the energy we use comes from
non-renewable sources like fossil fuels.
These energy sources will run out
eventually and so it is important that we
make them last as long as possible by
limiting their use. You can save energy
by: insulating homes and buildings,
using energy saving light bulbs, driving
fuel efficient cars, walking/cycling rather
than driving,etc.
Energy transformations
You must be able to examine a diagram of
a system (usually a power generating
systems like hydro electric or wind power)
and write down the energy transformations
which take place, e.g. Kinetic  Potential
 Kinetic Electrical
Kinetic
A
D
Potential
Kinetic
E
F
The diagram shown is a typical example of
the type of question you could be asked.
Kinetic
C
Calculating efficiency
The efficiency of an energy transformation
is a measure of how much of the input
energy appears as useful output energy.
The efficiency of any system can be
calculated using the equation:
Useful Energy Out
Efficiency =  =
Useful Energy In
Energy Out

Energy In
Note:  is the ratio of output to input
energy. This can never be greater than
one. In order to convert  to a percentage,
the efficiency, , is multiplied by 100.
No machine is 100% Efficient
No machine is ever 100% efficient, there
are always losses due to friction, heat loss
and a fundamental principle of physics:
some energy is always "lost" or wasted
when one form of energy is converted to
another. The "lost" energy is usually in the
form of heat.)
Electrical
B
Electrical
Identify the forms of energy at points A
(wind vane), B (generator), C (pump), D
(water tank), E (water wheel) and F
(generator).
Energy Audits
An energy audit is a list of all the energies
coming IN and going OUT of a system. The
total for the energies IN must be the same as
the totals for the energies OUT.
Once you have calculated all of the energies
in and out you should construct a systems
diagram like the one shown below.
Standard Grade Technological Studies
Programmable Control – Summary Sheets
Uses of Microcontrollers
Microcontrollers are single-chip
‘computers’ designed to control
specific processes or products. They
are found in a variety of products,
e.g. household appliances (for
example a microwave), alarm
systems (for example a fire alarm),
medical equipment (for example an
incubator for premature babies)
and electronic equipment (for
example a computer mouse).
Advantages of Microcontrollers
•One microcontroller can often
replace a number of separate parts,
or even a complete electronic circuit.
•increased reliability and reduced
quantity of stock (as one
microcontroller replaces several
parts)
•simplified product assembly and
smaller end products
•greater product flexibility and
adaptability since features are
programmed into the microcontroller
and not built into the electronic
hardware
•rapid product changes or
development by changing the
program and not the electronic
hardware.
Disadvantages of
Microcontrollers
To program a microcontroller you
need a computer. This can make it
more expensive than building an
electronic circuit.
Parts of the Microcontroller
RAM
ALU
I/O
Port
ROM
BUS
Clock
Microcontrollers contain both ROM (permanent
memory) and RAM (temporary memory).
The ROM (Read Only Memory) contains the
operating instructions (that is, the ‘program’) for the
microcontroller. The ROM is ‘programmed’ before
the microcontroller is installed in the target system,
and the memory retains the information even when
the power is removed.
The RAM (Random Access Memory) is ‘temporary’
memory used for storing information whilst the
program is running.
The ALU (Arithmetic and Logic unit) is used to
perform calculation and to make logical decisions
within the microcontroller.
The clock circuit within the microcontroller
‘synchronises’ all the internal blocks (ALU, ROM,
RAM, etc.) so that the whole system works correctly.
Buses: Information is carried between the various
blocks of the microcontroller along ‘groups’ of wires
called buses. The ‘data bus’ carries data between
the ALU and RAM, and the ‘program bus’ carries the
program instructions from the ROM to the ALU.
I/O Port: This is the INPUT/OUTPUT port which
connects the microcontroller to ‘real world’ inputs
and outputs, e.g. from switches and sensors, motors
and lights. The Basic Stamp has eight I/O ports
which can be configured as either inputs or outputs.
EEPROM: electrically erasable programmable readonly memory. This is where Pbasic programs are
stored for use by the microcontroller. Like ROM this
memory is not lost when the power is cut and like
RAM this memory can also be erased and a new
program stored on it.
Decimal to Binary Conversion
Example:
128
64
32
16
8
4
2
1
1
0
0
1
1
1
1
0
158 =
Method: Draw up the binary place values (see the table) and put a 1 in the
largest place value which is less than the number, in this case 128.
Subtract this place value from the number, 158-128=30, and then put a 1
under the largest place value which is less than this number, I.e. 16,
subtract again to get 30-16=14, and so on.
Binary to Decimal Conversion
This is easy! Just write the binary number under the place value table and
add up the place values with a 1 under them.
128
64
32
16
8
4
2
1
1
1
1
0
0
1
1
0
128+64+32+4+2= 230 Easy!
Flowcharts: these are used to plan out how a control sequence will work.
Different symbols are used depending on whether the sequence is testing an
input, switching on an output or pausing. The symbols you have to use are
shown below:
Used for
outputs, e.g.
Switch pin 5
high
Line showing
the flow of data.
Arrows added to
show direction
Process
symbol, used to
show a pause
or a calculation,
e.g. Wait 1sec
Decision, used to test
inputs or if a loop has
been completed, e.g. Is
switch 1 on?, or have
we looped 5 times?
Entry to or exit from a
subprocedure
Terminator, either
START or STOP
Programs
It isn’t easy to summarise programming as it is something you really have to “do”.
Instead I have included example of some of the main concepts you need to know.
Switching on pins
High 5
‘ switches on pin 5
Let pins=%01100000
‘ switches on pins 6 and 5 and all the rest off
Let pins=0
‘ switches all the pins off
Time delays
‘waits fro 4 seconds before moving on
Pause 4000
If, then – testing inputs
Loop1:
if pin1=0 then loop1
‘if pin1 isn’t on then go back to loop1
Loop2:
if pin3=1 then turn
‘if pin3 is on then go to turn
Loops
If you want to repeat a section of program a set number of times you use a FOR,
NEXT loop. You must use a variable, ie b0,b1,b2 etc in the loop or use the symbol
command to set up a variable name.
Symbol counter=b0
‘sets counter to represent the variable b0
For counter = 1 to 10
‘ start of loop
high 5
‘ switch pin 5 on
pause 1000
‘ wait 1 second
low 5
‘ switch pin 5 off
pause 1000
‘ wait for 1 second
Next counter
‘ end of loop (10 times)
Continuous Loops
If you want a program to repeat over and over forever, you should include a goto
main at the end of the program, this will make the program jump back to the main
label which is usually at the start of a program.
Setting up Input and Output pins
Let dirs=%11110000
‘ sets pins 4-7 as outputs and 0-3 as inputs
Controlling the speed of motors
Pulse width modulation (PWM) is used to control the speed of d.c. motors. It
works by switching the power to the motor on and off rapidly. The ratio
between the time on and off is called the mark-space ratio and variation of this
allows control over the speed. The main advantage of this type of speed
control is that it is possible to maintain a reasonably high torque at low speeds
compared to slowing motors by simply reducing the voltage. The diagrams
below show howmark
it works.
mark
space
space
space
space
space
space
on
on
off
off
Slow speed
Faster speed
Sample program using PWM
main:
high 7
' output high (mark)
pause 5
' pause for 5 ms
low 7
' output low (space)
pause 10
' pause for 10 ms
goto main
' loop
More on programs
GOSUB is used if you want to jump to a sub-procedure in a program. Subprocedures start with a label, e.g. left: and end with a RETURN. This sends
the program back to the line just after the sub-procedure was called using
GOSUB.
Example
‘jump to sub procedure lights
Gosub lights
‘jump to sub procedure flash
Gosub flash
Flash:
let pins=%11110000
‘switch all lights on
pause 2000
‘wait 2 seconds
let pins=0
‘switch all pins off
return
‘ go back