Electronic Control Systems

1
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.

2

• There are 2 types of Electronic device,
• Purely electronic devices such as Digital
  Watches
• Mechatronic devices such as a Video Recorders
• Question Why do you think a Video Recorder
  comes under Mechatronic devices?

3
Pupil Assignment

• List three electronic devices.
• List three mechatronic devices.
• Explain the mechanism in each of the three
  mechatronic devices listed.

• Some possible answers
• Gameboy, Television remote control, Calculator
• Computer CD-ROM drive, Microwave oven, Remote
  door lock in a car

4
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.
5
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.
6
Pupil Assignment
List the Input and Output transducers for the
following products
Personal Music Player
Vending Machine
Washing machine
Hairdryer
7
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

8
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)

9
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.
10
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

11
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

12
Inside a Microcontroller
IMPORTANT Input Output port, connects to Real
World
13
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.

14
Getting Started - Programming
main high 7 pause 1000 low 7 pause
1000 end
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.
15
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.
16
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.
17
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
18
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.
19
White Space
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.
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
Label
Comments
Code
20
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.
21
LOOPS
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
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?
22
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

23
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 '
24
Pupil Assignment
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.
Input connection Pin Output connection
7 train motor
6 points
5 green signal
4 red signal
3
2
1
0

• Switch the green signal on
• Switch the train on for 30 seconds
• Stop the train
• Switch the green signal off and the
• red signal on
• Switch the points on
• Switch the train on for 30 seconds
• Stop the train
• Switch the points off
• Switch the red signal off
• Jump back to step 1

25
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 (47) and a V connection.

26
Pupil Activity
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
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
27
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

28
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.

29
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

30
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

31
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.
32
Pupil Assignment

• Explain the terms mark and space in
  relation to PWM speed control of a d.c. motor.
• Describe the advantages and disadvantages of
  using PWM speed control.
• Sketch 2 PWM graphs, one for a fast speed and
  one for a slow speed.

33
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.
34
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.
Note the new flowchart symbol. This is the
decision symbol
NO
?
YES
35
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
36
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.
37
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.

38
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
39
Flowchart Symbol
Sub-Procedure symbol
Your teacher will show you the correct way to
draw a flowchart which includes a sub-procedure
40
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

41
Input Module

• 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

42
Digital Signals and Input Transducers
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
43
Analogue Signals
Volts (V)
Time (s)
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.
44
More Symbols
Microswitch (Single pole, single throw).
Light Dependent Resistor, LDR
Push Switch
-t
Push to make
Thermistor
Variable Resistor
Reed Switch
Magnet
45
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
46
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
47
Pupil Assignment
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.
Input connection Pin Output connection
7 red light
6 yellow light
5 green light
4
3
2
1
pressure mat 0
48
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
49
Pupil Assignment
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.
Input connection Pin Output connection
7 motor reverse
6 motor forward
5 solenoid bolt
4 LED
3
2
door Microswitch 1
start switch 0
50
Analogue Sensing
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
main ' make a label called main if
sensorA gt 50 then red ' jump to red if the value
gt 50 goto green ' value is lt 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
51
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.
52
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.
53
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.
54
Pupil Assignment

• Convert each of the following binary numbers into
  decimal.
• 11110000
• 11000011
• 01010101
• 10101010

• Convert each of these decimal numbers into
  binary.
• 17
• 23
• 11
• 38
• 33

55
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
56
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
57
Stepper Motors
Stepper motors are very accurate motors that are
commonly used in computer disc- drives, printers,
XY 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).
58
Stepper Motors
The table below shows the four different steps
required to make the motor turn. Copy the table
into your workbook
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
59
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.
60
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).
61
End of unit Assignment

• When a train is 1 mile from the crossing, a
  signal is sent, warning of the trains
  approach.
• When the warning signal is received, the
  crossings 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..