Electronic Control Systems

Gary Plimer 2005

Electronic Control Systems




Electronic devices have

been developed to make life

more enjoyable, easier,

safer or more productive.






Some examples:




Microwave oven.



Traffic lights.



Computers.



Games consoles.


Gary Plimer 2006

There are 2 types of Electronic device,


1)

Purely electronic devices such as Digital Watches


2)

Mechatronic devices such as a Video Recorders


Question:

Why do you think a Video Recorder comes


under Mechatronic devices?


Gary Plimer 2006

Pupil Assignment


1.
List three electronic devices.


2.
List three mechatronic devices.


3.
Explain the ‘mechanism’ in each of the three
mechatronic devices listed.


Some possible answers:

1)
Gameboy, Television remote control, Calculator

2)
Computer CD
-
ROM drive, Microwave oven, Remote
door lock in a car


Gary Plimer 2006

System Diagram

Both Electronic and Mechatronic devices have one thing in
common, they both have a control unit.

The system diagram for a warning
device for a freezer in a restaurant
would be drawn as below.

Gary Plimer 2006

Transducers

Input transducers are electronic devices that detect
changes in the ‘real world’ and send signals into the
process block of the electronic system.

Output transducers are electronic devices that can be
switched on and off by the process block of the electronic
system.

A popular electronic
toy is shown. Try to
identify as many input
and output
transducers as you
can.

Gary Plimer 2006

Pupil Assignment

List the Input and Output transducers for the following
products

Washing machine

Vending Machine

Personal Music Player

Hairdryer

Gary Plimer 2006

Microcontrollers





A

microcontroller

is often described as ‘a computer on a chip’






It has a memory and the ability to receive inputs and control



outputs






It is a small & inexpensive device





Often built into products to make them more
intelligent

and




easier to use





Usually programmed for a specific purpose/ product


Gary Plimer 2006

Advantages of Microcontrollers





A microcontroller can often replace several parts or

even a complete circuit.





The main advantages to using one are:



Increased reliability



Simplified product assembly (less parts)



Greater product flexibility (can be re
-
programmed)


Gary Plimer 2006

Pupil Assignment

List three devices that may contain a microcontroller.


Explain why you think it would be useful to have a
microcontroller in these devices.

Gary Plimer 2006

Inside a Microcontroller



ROM


Read only memory (permanent)


Contains STAMP operating instructions


Retains this program even when without power



EEPROM


Electronically erasable programmable read only memory


Your program is stored here


The ROM will read this and carry out the instructions



RAM


Random access memory (temporary)


Stores information from calculations whilst running


Is wiped when the power is cut



Gary Plimer 2006

Inside a Microcontroller



ALU


Arithmetic and Logic Unit


The control centre of the Microcontroller


Runs the instructions stored in the ROM


I.e. it can only READ from this memory and not write or send
information to it!



Clock


The clock synchronises all of the internal blocks


It sets the operating speed of the system



Buses


Information is carried between the various blocks on buses


These are groups of wires


Data Bus carries data between the ALU and RAM


Program Bus carries data from ROM to the ALU



Gary Plimer 2006

Inside a Microcontroller

IMPORTANT
–

Input
Output port,
connects to “Real
World”

Gary Plimer 2006

Stamp Controller

Programming Procedure:



Draw a flowchart for
the

control

task.


Write the program on
the

computer using
the Stamp

software.


Connect the download
cable from the
computer to

the stamp
controller.


Connect the power
supply

to the
stamp controller.


Use the Stamp software
to

download the
program.

Gary Plimer 2006

Getting Started
-

Programming

Start up the Stamp software
and key in the program.

Save the program and then
download it to the stamp
controller by clicking ‘Run’.


Your teacher will give you
help with the software, if
you need it.


In your own words explain
what the program does.

main:




high 7




pause 1000


low 7



pause 1000


end



Gary Plimer 2006

Pupil Assignment

red

10 s

red and

amber


2 s

green

10 s

amber


2 s

Using the times shown in the table for each stage of a Traffic
Light sequence, write a P
-
Basic Program for the lights then run
and test your program.

Gary Plimer 2006

Flow Charts

Start / Stop
Symbol

Input / Output
Symbol

Wait Symbol

There are other symbols you will
need to learn, but we will discuss
those when we need to use them.

Gary Plimer 2006

Pupil Assignment


A microwave oven operates with the following
sequence. Draw a flowchart and write a P
-
Basic
program for this sequence.


Light on

Turntable on

Magnetron on

Wait 30 seconds

Magnetron off

Wait 10 seconds

Turntable off

Buzzer on

Wait 0.5 second

Buzzer off

Light off



You can decide for
yourself which pins to
allocate to the outputs
transducers

Gary Plimer 2006

Adding Comments

Comments are always added to program listings to help
explain the program operation. An example is shown
below.

Main:


high 7


‘switch pin 7 high


pause 1000

‘wait 1 second


low 7


‘switch pin 7 off


pause 1000

‘wait 1 second


goto main

‘jump to label main

Note the apostrophe which tells the program that
what follows is a comment, not a line of code.

Gary Plimer 2006

White Space

Main:


high 7


‘switch pin 7 high


pause 1000

‘wait 1 second


low 7


‘switch pin 7 off


pause 1000

‘wait 1 second


goto main

‘jump to label main

Lets have a look at the layout of the previous code. Note how the code
is indented, (tabbed in). This is known as leaving “WHITE SPACE”.
White space makes the layout and reading of programs much clearer.

The start of the program is indicated by the “LABEL” main, note the
colon after the label. Labels can have any name as long as it is not a
P
-

Basic command.

Copy down the program below and label each part as shown.


Label

Code

White Space

Comments

Gary Plimer 2006

Symbols

Sometimes it can be hard to remember which pins are connected to
which devices. The ‘symbol’ command can then be used at the start
of a program to rename the inputs and outputs.

symbol red = 7



' rename 7 ‘red’

symbol green = 5



' rename 5 ‘green’


main:




' make a label called ‘main’


high red



' red LED on


low green


' green LED off


pause 1000


' wait 1 second


low red



' red LED off


high green


' green LED on


pause 1000


' wait 1 second


goto main


' jump back to the start

Key in the program, then run and test.

Gary Plimer 2006

LOOPS

Sometimes it is
necessary to
create programs
that loop
‘forever’, as is the
case in this
flowchart. There
is no ‘Stop’
symbol because
the program
never ends!


What command
makes the
program loop?

main:




high 7




pause 2000


high 6


pause 1000


high 4


high 5


pause 3000


low 4


low 5


low 6


low 7


pause 1000


goto main



Gary Plimer 2006

Pupil Assignment

red

10 s

red and

amber


2 s

green

10 s

amber


2 s

1.
Draw a flow chart for the
control of the traffic lights


2.
Write a P
-
Basic program
using the symbol command
to give names to pins


3.
The program should loop


4.
Run and test your program

Gary Plimer 2006

Pupil Assignment

A fountain in a garden centre is to be used to attract visitors to a new range of
plastic ponds. The garden centre owner wishes to develop a microcontroller
-
based system that can be programmed to switch the fountain pump and an
external lighting system on and off at regular intervals.



Draw a flowchart for the control sequence and add the missing comments to the
program listing.


main:

high 7



' switch the pump on


pause 10000


' wait 10 seconds


high 6



' switch the lights on


pause 40000



' …


low 6




' …


pause 10000



' …


low 7




' …


pause 60000



' …


goto main



' …



Gary Plimer 2006

Pupil Assignment

Input

connection

Pin

Output

connection

7

train motor

6

points

5

green signal

4

red signal

3

2

1

0

1.

Switch the green signal on

2.

Switch the train on for 30 seconds

3.

Stop the train

4.

Switch the green signal off and the


red signal on

5.

Switch the points on

6.

Switch the train on for 30 seconds

7.

Stop the train

8.

Switch the points off

9.

Switch the red signal off

10.

Jump back to step 1

A toy shop has a train set in the window. The train set has an electric train,
a set of red/green signals and a set of moving track points that allow the
train to move around two different loops of track. Draw a flow chart and
write a P
-
Basic program to control the train set.

Gary Plimer 2006

Output Module




Allows output transducers to be

connected to the stamp controller





Typical output transducers are

Motors, Buzzers and Bulbs





To use the output module, the

output device should be connected

between the screw
-
terminal

numbered output (4
–
7) and a V+

connection.

Gary Plimer 2006

Pupil Activity

main:



' make a label called ‘main’


high 5


' motor A forward


high 7


' motor B forward


pause 1000

' wait 1 second


low 5


' motor A halt


low 7


' motor B halt


pause 1000

' wait 1 second


high 4


' motor A backward


high 6


' motor B backward


pause 1000

' wait 1 second


low 4


' motor A halt


low 6


' motor B halt


goto main

' jump back to the start

Connect 2 dc motors to the output module, enter the following code
then run and test your program.

YOUR TEACHER WILL EXPLAIN THE MODULE CONNECTIONS

Gary Plimer 2006

Pupil Assignment




Copy the flow chart into your

work book




Write a P
-
Basic program to

control the movement of the

buggy as indicated by the


Flowchart

Gary Plimer 2006

Pupil Assignment




Build a maze on the table out of

books.




Write a PBASIC program to steer

the buggy through the maze.




Add comments to each line in

your program to explain how it

works.

Gary Plimer 2006

Speed Control



There are two ways to control the speed of a d.c. motor.




Vary the voltage applied to the motor. Unfortunately the

‘turning power’ (torque) of the motor will also drop, which

means the whole motor system will be less powerful
.





The second way to control the motor is to always apply the

full voltage but then to switch the power supply on and off

rapidly. The advantage of this system is that the torque

remains quite high.





This method is known as
PULSE WIDTH MODULATION

Gary Plimer 2006

Pulse Width Modulation




Motor off is known as
SPACE

–

Larger Space to Mark Ratio

= slow speed




Motor on is known as

MARK

–

Larger Mark to Space Ratio

= fast speed





Gary Plimer 2006

Pupil Activity

Connect a d.c. solar motor across the ‘V+’ and ‘7’ terminals on the
output driver module.


Key in, download and run the program listed below. This program drives
the motor at approximately half speed, as the space (off time) is twice
the length of the mark (on time).


main:

high 7




' output high


pause 5




' pause for 5 ms


low 7




' output low


pause 10



' pause for 10 ms


goto main



' loop



Try out different speeds (by experiment) by altering the length of the
pause delays.

Gary Plimer 2006

Pupil Assignment


1)


Explain the terms ‘mark’ and ‘space’ in relation to

PWM speed control of a d.c. motor.


2)


Describe the advantages and disadvantages of

using PWM speed control.


3)


Sketch 2 PWM graphs, one for a fast speed and

one for a slow speed.

Gary Plimer 2006

Pupil Assignment


The motor on the washing machine is
controlled by outputs 6 and 7 (motor B).
Switching output 6 on will make the motor
turn one way; switching output 7 on will
make the motor turn the other way.



Draw a flowchart and write a PBASIC
program that will make the motor rotate at
full speed in each direction for five seconds.



Write a second PBASIC program that will
make the motor rotate at half speed in each
direction for five seconds. Use PWM speed
control for the motor.



Gary Plimer 2006

For Next Loops

It is often useful to repeat the same part of a program
a number of times, for instance when flashing an LED.
In these cases a
‘for … next’

loop can be used.

START

SET COUNTER = 5

SWITCH PIN 7

HIGH

WAIT 1 s

SWITCH PIN 7

LOW

HAVE WE

LOOPED 5

TIMES?

STOP

WAIT 1 s

YES

NO

?

Note the new flowchart
symbol. This is the
decision symbol

Gary Plimer 2006

For Next Loops
–

Pupil Activity

Key in, download and run the following program.


symbol counter = b0

' define the variable ‘counter’

symbol red = 7


' define pin 7 with the name ‘red’


main:


for counter = 1 to 5


' start a for … next loop






high red


' switch pin 7 high






pause 1000


' wait for 1 second







low red


' switch pin 7 low






pause 1000


' wait for 1 second



next counter



' end of for … next loop



end




' end program

Gary Plimer 2006

Pupil Assignment

Connect the buggy to the output
module.


The buggy should follow the path
shown in the diagram, moving in each
direction for three seconds.


Draw a flowchart for the movement of
the buggy, making use of a ‘for … next’
command structure.


Write a high
-
level program in PBASIC
to control the movement of the buggy
as shown by your flowchart.


Gary Plimer 2006

Sub
-

Procedures




A sub
-
procedure is a separate ‘mini
-
program’ that

can be called from the main program.





Once the sub
-
procedure has been carried out, the

main program continues.





Sub
-
procedures are often used to separate the

program into small sections to make it easier to

understand.





Sub
-
procedures that complete common tasks can

also be copied from program to program to save

time.

Gary Plimer 2006

Pupil Activity

symbol red = 7




' rename pin 7 ‘red’

symbol buzzer = 6



' rename pin 6 ‘buzzer’

symbol counter = b0


' define a counter using variable b0


main:




' make a label called ‘main’


gosub flash


' call the sub
-
procedure flash


gosub noise


' call the sub
-
procedure noise


goto main



' loop back


end




' end of the main program

flash:




' make a sub
-
procedure called ‘flash’


for counter = 1 to 25

' start a for … next loop





high red


' red LED on





pause 50


' wait 0.05 second





low red


' red LED off





pause 50


' wait 0.05 second


next counter


' next loop


return



' return from the sub
-
procedure

noise:


high buzzer


' buzzer on


pause 2000


' wait 2 seconds


low buzzer


' buzzer off


return



' return from the sub
-
procedure

Gary Plimer 2006

Flowchart Symbol

Sub
-
Procedure symbol

Your teacher will show you
the correct way to draw a
flowchart which includes a
sub
-
procedure

Gary Plimer 2006

Pupil Assignment

A washing machine motor should rotate
15 seconds in one direction before
reversing and rotating 15 seconds in
the opposite direction. This should
repeat 10 times.




Draw a flowchart




Write a P
-
Basic program making

use of sub
-
procedures




Run and test your program

Gary Plimer 2006


Allows sensors to be connected to the stamp
controller


There are 4 digital and 2 analogue inputs


Pins 0 and 1 have a test button, they can be pressed
instead of adding switches



Input Module

Gary Plimer 2006

Digital Sensors act like switches


They are either


ON or OFF





HIGH or LOW





1 or 0






Some common switches you will meet are the ,

Microswitch

Push and Rocker switch

Reed switch


Digital Signals and Input Transducers

Gary Plimer 2006

Analogue Signals

Time (s)

Volts
(V)

Analogue signals can vary between a maximum and minimum value
and depend on the conditions being monitored, for example light or
temperature.


Common analogue input transducers are the Light Dependent
Resistor, thermistor, (temperature sensor) and variable resistor.

Gary Plimer 2006

More Symbols

Microswitch (Single
pole, single throw).

Push Switch

Reed Switch

Thermistor

-
t

Light Dependent
Resistor, LDR

Magnet

Variable
Resistor

Push to make

Gary Plimer 2006

if
-
then Command

To enable the Stamp Controller to accept inputs, we need
to learn a new command, the
IF
–

THEN

command

Connect a switch to pin 0, key in, download and run the program
listed below. This program makes output pin 7 flash every time the
push
-
switch on input pin 0 is pushed.


main:





' make a label called ‘main’


if pin0 =1 then flash


' jump if the input is on


goto main



' else loop back around


flash:





' make a label called ‘flash’


high 7




' switch output 7 on


pause 2000



' wait 2 seconds


low 7




' switch output 7 off


goto main



' jump back to start

Gary Plimer 2006

Pupil Assignment

A burglar alarm must sound a
buzzer and light a warning signal
for 20 seconds when any of the 2
windows in a room are opened.
Each window contains a reed
switch that is connected to the
alarm.


Draw a flowchart and write a
PBASIC program that will operate
the burglar alarm correctly. Use the
following input and output
connections.

Input

connection

Pin

Output

connection

7

red light

6

buzzer

5

4

3

2

switch 1

1

switch 0

0

Gary Plimer 2006

Pupil Assignment

Input

connection

Pin

Output

connection

7

red light

6

yellow light

5

green light

4

3

2

1

pressure
mat

0

As part of a Christmas
decoration in a shop, a
lighting sequence is to be
controlled by a
microcontroller. The output
connections are shown below.


When a visitor treads on a
pressure mat under the
carpet, the lights should flash
on and off in sequence three
times.

Gary Plimer 2006

Pupil Assignment

Develop a PBASIC program that will carry out the
instructions shown in the flowchart. Use the
following pin configuration.

Input

connection

Pin

Output

connection

7

red light

6

amber light

5

green light

4

3

2

1

start switch

0

Gary Plimer 2006

Pupil Assignment

Input

connection

Pin

Output

connection

7

motor reverse

6

motor
forward

5

solenoid bolt

4

LED

3

2

door

Microswitch

1

start switch

0

A washing machine operates as
follows.

Wait until the start switch is on.

Wait until the door switch is on.

Switch on the LED.

Switch on the solenoid bolt.

Wash cycle: repeated 20 times
–

motor forwards for five seconds,
motor backwards for five
seconds.

Spin cycle: repeated 10 times
–

motor forwards for two seconds,
motor backwards for two
seconds.

Switch off the solenoid bolt.

Switch off the LED.


Draw a flowchart and write a
PBASIC program to control the
movement of the washing
machine as described above.



Gary Plimer 2006

Analogue Sensing

main:





' make a label called ‘main’


if sensorA > 50 then red

' jump to red if the value > 50


goto green



' value is < 50 so jump to green


red:





' make a label called ‘red’


high 4




' switch output 4 on


low 5




' switch output 5 off


goto main



' jump back to start


green:





' make a label called ‘green’


high 5




' switch output 5 on


low 4




' switch output 4 off


goto main



' jump back to start

Copy the program to your workbooks. Connect a LDR to the input
module, key in the program, run and test. In your own words
explain what is happening

Gary Plimer 2006

Pupil Assignment

A street lamp must turn on when the
light level is below the level ‘100’ and
turn off when the level is above ‘100’.


The lamp is connected to output 7
and the LDR light sensor is
connected to sensor A.


Draw a flowchart and write a PBASIC
program that will make the street
lamp work correctly.



Gary Plimer 2006

Pupil Assignment

State whether each of the input transducers below is an analogue or
digital sensor.


(a) LDR

(b) reed switch

(c) microswitch

(d) thermistor

(e) variable resistor

(f) tilt switch

(g) push switch

(h) rocker switch


For each of the input transducers give an example of an electronic
product that may use that transducer. Explain how the transducer would
be used within the product.



Gary Plimer 2006

Number Systems

The Stamp Microcontroller can accept decimal numbers as
well as binary numbers. However, we need to tell the
microcontroller what we are using.

Decimal values are written as usual: 10

(= 10 in decimal)


Binary values are indicated by a % symbol: %10 (= 2 in
decimal)

Your teacher will now show you how to convert
decimal to binary and binary to decimal.

Gary Plimer 2006

Pupil Assignment

Convert each of the following binary numbers into decimal.


1)
%11110000

2)
%11000011

3)
%01010101

4)
%10101010

Convert each of these decimal numbers into binary.


1)
17

2)
23

3)
11

4)
38

5)
33

Gary Plimer 2006

The “let dirs” command

Up till now, if we wanted to switch on more than one output,
we needed to switch them on one by one. However, by using
binary, we can now switch on more than one pin at a time.


To enable us to achieve this, we must first tell the
microcontroller what pins are outputs and which are inputs.


To do this we use the
dirs

command.


Let dirs = %00001111

‘let pins 0 to 3 be outputs the rest




inputs

Gary Plimer 2006

The “let pins” command

Once we have instructed the microcontroller what is outputs
and what is inputs, we use the let pins command.

Let dirs =%11111111

‘all pins outputs

Main:



let pins = %00001111

‘switch on pins 0 to 3


pause 1500


‘1.5 second delay


let pins = 0


‘switch all pins off


pause 1500


‘1.5 second delay


let pins = %11110000

‘switch on pins 4 to 7


pause 1500


‘1.5 second delay


let pins = 0


‘switch off all pins


end



‘end program



Gary Plimer 2006

Stepper Motors

Stepper motors are very accurate
motors that are commonly used in
computer disc
-

drives, printers, X
–
Y plotters and clocks. Unlike d.c.
motors, which spin round freely
when power is applied, stepper
motors require that their power
supply is continuously ‘pulsed’ in
four different patterns. For each
pulse, the stepper motor moves
around one ‘step’, typically 7.5
degrees (giving 48 steps in a full
revolution).

Gary Plimer 2006

Stepper Motors

Step

Coil 4

(output 7)

Coil 3

(output 6)

Coil 2

(output 5)

Coil 1

(output 4)

1

1

0

1

0

2

1

0

0

1

3

0

1

0

1

4

0

1

1

0

1

1

0

1

0

The table below shows the four different steps required to
make the motor turn. Copy the table into your workbook

Gary Plimer 2006

Pupil Assignment

An X
-
Y plotter movement is
controlled by stepper motors.
Write a P
-
Basic program that
will rotate the one stepper
motor 20 steps in one
direction then 20 steps in the
opposite direction.


Your teacher will show you
how to connect the stepper
motor to the stamp.

Gary Plimer 2006

End of unit Assignment

A new automatic railway
crossing is to be installed at a
local site. The operation of the
crossing should follow a set
sequence.

Design a PBASIC control program
to control the sequence described
on the next slide. The train sensors
give a logic (1) when the train is
sensed. For this simulation, you
only need to control one side of the
crossing, (one barrier and one
warning light).

Gary Plimer 2006

End of unit Assignment





When a train is 1 mile from the crossing, a signal

is sent, warning of the train’s approach.




When the warning signal is received, the

crossing’s warning lights begin to flash.




The lights should flash on and off continuously at

1 second intervals.




After 30 seconds, the crossing barriers come

down.




The barriers remain down until the train activates

a second signal 1 mile further down the track.





After 30 seconds the barriers should rise and the

lights should stop flashing..