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..
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