Technological Studies
Systems and Control
Teacher/Lecturer Notes
and Solutions to Assignments
Higher
4559
Spring 1999
HIGHER STILL
DET: Technological
Studies
Systems and Control
Teacher/Lecturer Notes
and Solutions to Assignments
Higher
Support Materials
q
rs
TECHNOLOGICAL STUDIES
HIGHER
SYSTEMS AND CONTROL
TEACHER/LECTURER NOTES
AND SOLUTIONS TO ASSIGNMENTS
INTRODUCTION
Technological Studies: Systems and Control Teachers Notes (H) Introduction
1
Technological Studies: Systems and Control Teachers Notes (H) Introduction
2
The 'Systems and Control' teaching materials are split into four Outcomes. The
performance criteria for each Outcome is covered within the whole unit.
Due to the large size of Outcomes 3 and 4 the outcomes have been sub-divided into
smaller sections.
Outcome 1 - Control Systems
The purpose of this unit is to introduce the operation of control systems.
When students have completed this unit they should be able to:
• recognise and identify common control systems
• describe the operation of open and closed loop control systems
• make use of systems diagrams and systems technology.
Outcome 2 - Analogue Control Systems
The purpose of this unit is to introduce the operation of analogue control systems.
When students have completed this unit they should be able to:
• correctly identify common applications of analogue control
• represent analogue control systems using control diagrams and circuit diagrams
• select the appropriate configuration of op-amp in the design of analogue closed loop
control systems
• select appropriate output drive subsystems for control applications.
Technological Studies: Systems and Control Teachers Notes (H) Introduction
3
Outcome 3 - Microcontroller Controlled Mechatronic Systems
Section 1 - Introduction
The purpose of this section is to introduce the microcontroller and it's architecture.
When students have completed this unit they should be able to:
• describe the operation and architecture of microcontrollers
• understand the terms ALU, RAM, ROM, EEPROM, bus
• understand how the Basic Stamp system operates.
Section 2 - Number Systems
The purpose of this section is to introduce the main number systems used within
programmable systems for the processing of information.
When students have completed this unit they should be able to:
• Use the following terms correctly: decimal, binary, hexadecimal.
• Describe contexts when it is appropriate to use the three different number systems.
• Convert between decimal, binary and hexadecimal number systems.
Section 3 - Simple Control Routines
The purpose of this section is to introduce the PBASIC commands used in developing
control program listings.
When students have completed this unit they should be able to:
• understand the use of flowcharts
• develop flowcharts from a brief
• understand the most common PBASIC commands
• write PBASIC programs that involve loops, if statements and sub-procedures.
Section 4 - Mechatronic System Interfacing Circuits
The purpose of this section is to understand the need for interfacing input and output
devices when building mechatronic systems that are controlled by a microcontroller.
When students have completed this unit they should be able to:
• explain why interfacing circuits are required within mechatronic systems
• select appropriate interfacing techniques for common output devices
• understand the different operation of common switch types
• understand how unipolar stepper motors are controlled
• understand the need for D-A conversion
• understand how push-pull drivers are used to control dc motors
• understand pulse-width modulated control of dc motors
• understand the term 'soft-start' when applied to dc motors
• write PBASIC programs to control stepper motors
• write PBASIC programs to control the speed and direction of dc motors.
Technological Studies: Systems and Control Teachers Notes (H) Introduction
4
Outcome 4 - Microcontroller Controlled Monitoring Systems
Section 1 - Analogue to Digital Conversion
The purpose of this section is to introduce the application of A-D converters. The
section explains the function and operation of A-D converters in the context of a
programmable system.
When students have completed this unit they should be able to:
• understand the need for A-D conversion
• understand the use of an A-D converter with a microcontroller
• understand the term multiplexing and appreciate the reasons for it
• understand the term signal conditioning
• write PBASIC programs that include ADC routines.
Section 2 - Data-Logging
The purpose of this section is to introduce the concept of data-logging. The section
also involves the use of a host computer for analysing data recorded with a spreadsheet
application.
When students have completed this unit they should be able to:
• understand the term data-logging
• understand the term sampling frequency
• appreciate the use of data-logging in a practical application
• understand how data can be analysed with a spread-sheet applications
• write PBASIC programs to control data-logging experiments.
Technological Studies: Systems and Control Teachers Notes (H) Introduction
5
Assignments and Activities
Written Assignments
Each Outcome involves a number of written assignments. The first assignments in each
section are simpler questions which cover important teaching points, and the latter
assignments build up to examination style questions. It is therefore important that
students complete all the assignments.
Practical Assignments
Practical assignments involve the use of electronic circuits (discrete components or
modular systems such as EET Connect or Alpha) or microcontroller circuits (using the
modular Basic Stamp and MFA boards). Many of the microcontroller circuits also
involve interfacing to three dimensional models. Students are expected to complete all
practical assignments.
Practical Activities
Practical activities differ slightly from practical assignments in that there is no
assessment requirement for the activity. Practical activities are mainly used as 'tutorials'
in Outcomes 3 and 4 to demonstrate different software techniques. It is expected that
the student should complete each activity.
Students should not be allowed to simply open and download 'pre-saved' files when
completing activities. It is through the process of keying in the program that an
understanding of the program operation will be gained. Each activity program is kept
deliberately short so that this keying in time is not too great.
Technological Studies: Systems and Control Teachers Notes (H) Introduction
6
General notes on using the Basic Stamp
Hardware
• The Stamp controller has 8 input/output pins. Each pin can be configured as an
input or output. There are no separate input or output ports.
• The Stamp Controller provides digital (logic-level) outputs. To drive high current
loads such as motors and interfacing circuit (e.g. the Outputs Driver module) must
be used.
• The Basic Stamp modules are coloured red. All red boards can be directly
connected together. MFA modules are coloured blue. MFA input modules can be
directly connected to the Stamp Controller. However most MFA output modules
must be connected to the Stamp Controller via the small red adapter, which maps
pins 4-7 from the Stamp Controller to pins 0-3 on the MFA module.
Software
• The student assignments do not explain how to perform software features such as
saving programs, downloading, editing etc. This is because these techniques vary
according to the computer platform being used. It will therefore be necessary to
teach the students how to achieve these functions for your computer platform.
These functions are fully explained in the photocopiable prompt sheets provided
with the software.
• Students are expected to add comments, and correctly use 'white-space', within each
of their PBASIC programs.
• PBASIC programs use labels (rather than line numbers) for addressing purposes.
• The 'Serial ADC' and 'Datalogging' modules use standard sub-procedures, which are
provided in the file ‘template.bas’. Students do not need to learn these subprocedures, as they will always be provided with them if required. However they
must understand what task the sub-procedures achieve, and must know how to link
these sub-procedures into their PBASIC programs.
• Schools may distribute the Basic Stamp software to students for home use. There is
no charge for the software when distributed in this manner.
Technological Studies: Systems and Control Teachers Notes (H) Introduction
7
BASIC Stamp Equipment List
Stamp modules required:
• BAS-110
Stamp Controller (with output adapter)
• BAS-115
Datalogger Module
• BAS-117
Serial A to D Converter
• BAS-118
Serial LCD Module
• BAS-119
Output Driver
• BAS-120
Serial Printer Module
MFA modules also required:
• D540-312
MFA Sensor Module (with digital sensors)
• D540-314
MFA Stepper Motor and Driver
• D540-306
MFA Power D to A Converter
• D540-313
MFA Analogue Multiplexer
• D540-341
MFA Analogue Light Probe
• D540-340
MFA Analogue Temperature Probe
The following MFA modules are NOT required, but may optionally be used if
you already possess them:
• D540-303
MFA 8-Switch Input
• D540-005
MFA Movement Module
• D540-342
MFA Analogue Rotary Sensor
• D540-325
MFA Pneumatics Interface
• D540-310
MFA 4-Relay Unit
• D540-308
MFA 2-Digit Display
• D540-323
MFA 8-Bit Driver
• D540-304
MFA 8-LED Output
MFA Modules are produced & distributed by:
Unilab, Lynn Lane, Shenstone, Lichfield, Staffordshire, WS14 0EE
Tel: (01543) 483064 Fax: (01543) 483056
All other modules are produced by Revolution Education and distributed by:
Teaching Resources, Middlesex University, Trent Park,
Bramley Road, London, N14 4YZ
Tel: (0181) 447 0342 Fax: (0181) 447 0340
Technological Studies: Systems and Control Teachers Notes (H) Introduction
8
Control Assignment Models
A very important aspect of Outcome 3 is the control of 'real' mechatronic systems. It is
therefore expected that students have access to three dimensional models for control
exercises. These models may be fabricated from constructional sets (such as Lego or
Fishertechnic) or from discrete materials. Many schools will already possess a number
of these types of model.
The apparatus listed below provides brief outlines as to how sample models may be
constructed and interfaced to the Stamp Controller.
Buggy Apparatus
This piece of apparatus is a simple buggy that can be used to demonstrate simple
programming techniques. Many schools will already possess 'Lego' buggies which are
ideal. If building a new buggy Middlesex Teaching Resources stock a low-cost wormdrive gearbox which is very useful (order code TG1-010, wheels CW3-027)
This apparatus should consist of a small buggy with two motors driving a wheel on
each side. Two microswitches should be mounted to the front of the buggy to act as
'collision bumpers'.
Input Connection
switch 1
switch 0
Pin
7
6
5
4
3
2
1
0
Output Connection
motor B reverse
motor B forwards
motor A reverse
motor A forwards
The motors can be controlled from the Output Driver Module or the MFA Movement
Module. The microswitches can be directly wired to the screw terminals on the Stamp
Controller as explained in the student text.
Technological Studies: Systems and Control Teachers Notes (H) Introduction
9
Washing Machine Apparatus
This piece of apparatus should represent a washing machine. Many schools will already
possess 'Lego' models.
Input Connection
door microswitch
start switch
Pin
7
6
5
4
3
2
1
0
Output Connection
motor reverse
motor forward
The motor can be controlled from the Output Driver Module or the MFA Movement
Module. The microswitches can be directly wired to the screw terminals on the Stamp
Controller as explained in the student text.
Lock Apparatus
This piece of apparatus should be designed to simulate a simple time-lock. Three input
switches are required. The MFA Switch board could be used directly, or three simple
push switches could be mounted on a piece of strip-board.
Input Connection
switch 3
switch 2
switch 1
Pin
7
6
5
4
3
2
1
0
Output Connection
solenoid
buzzer
green LED
red LED
A 6V solenoid (e.g. Rapid 60-3205) and 6V buzzer (e.g. Rapid 35-0100) can be driven
directly from the Output Driver Module, or could be built more permanently on a piece
of strip-board.
Technological Studies: Systems and Control Teachers Notes (H) Introduction
10
Light Seeker Apparatus
This piece of apparatus uses two LDR sensors to detect light level, and a stepper
motor to turn the sensors towards the brightest light. Therefore the LDRs should be
mounted on a piece of board that is secured on to the stepper motor spindle. Naturally
the LDRs need to be at 90 degrees to the spindle, and separated with a piece of card,
so that when a light is shone from the side one LDR receives more light than the other.
The LDRs are used as digital sensors in this application, and so should be arranged in a
potential divider arrangement (with a 100K potentiometer for calibration purposes).
Input Connection
LDR 2
LDR 1
Pin
7
6
5
4
3
2
1
0
Output Connection
stepper coil
stepper coil
stepper coil
stepper coil
The LDRs can be connected to the MFA sensor module, or wired directly to the
Stamp Controller screw terminals. The stepper motor should be connected directly to
the Output Driver Module.
Conveyer Belt and/or Lift Apparatus
This piece of apparatus should consist of a conveyer belt, which has a microswitch
sensor at each end.
The apparatus can be configured vertically to represent a lift, or horizontally to
represent a conveyer belt.
Input Connection
switch 2
switch 1
Pin
7
6
5
4
3
2
1
0
Output Connection
Motor reverse
Motor forward
The motor can be controlled from the Output Driver Module or the MFA Movement
Module. The microswitches can be directly wired to the screw terminals on the Stamp
Controller as explained in the student text.
Technological Studies: Systems and Control Teachers Notes (H) Introduction
11
Other Physical Resources
Outcome 1 and 2 involve building electronic circuits using op-amps. These can be built
using discrete components, or via a modular system such as E&L 'EET Connect' or
Unilab 'Alpha'. Due to the physical feedback signals required in these control circuits
the circuits cannot be fully simulated using software such as 'Crocodile Clips'.
For Outcome 2 a disassembled radio-control style servo is useful for demonstration
purposes. This can be reclaimed from a broken radio-controlled toy, or purchased new
from a model shop.
For assignment 4.14 in Outcome 3 a small DC motor is required to demonstrate PWM
control. It is strongly recommended that a solar motor (e.g. Middlesex Teaching
Resources EW2-011 or JPR 450-030) is used, as this can be run at much slower
speeds than standard 'toy' DC motors. A propeller mounted on the shaft makes the
movement much more visible.
Technological Studies: Systems and Control Teachers Notes (H) Introduction
12
Software and Minimum Computer Specifications:
The Stamp Controller is programmed via a computer. Five versions of the Stamp
software are available for different computer platforms / operating system
combinations. The following information provides the minimum system requirements
to run each version of the software.
PC - DOS
stamp.exe
8086 or 286 processor, DOS 2.0, printer port
PC - 16 Bit Windows
winstamp.exe
386, 4MB, Windows 3.x, serial port
PC - 32 Bit Windows
winstamp32.exe
486, 8MB, Windows 9x or NT 3.51, serial port
Note that the DOS application stamp.exe will run on very old PCs including those
that are often considered 'obsolete' as they do not run 'Windows'. Many departments
have gathered these 'old' computers for dedicated Stamp use. The Windows
applications are fully compatible with all network types.
Acorn
!AStamp
RISC-OS 3.0, 1MB, mouse, serial port
Note that some older Archimedes machines (e.g. A3000) may require an operating
system upgrade and/or serial port upgrade.
Chips required for serial port upgrade
65C51 (28 pin) and LT1133 (24 pin).
These chips are available from Farnell Electronics.
The DOS software (stamp.exe) does NOT operate via the Archimedes PC Emulator
!PCEm.
Mac
stampx.exe
68020, 4MB, System 6.0, SoftPC
stampx.exe
PowerMac, 16MB, System 7.1, RealPC
winstamp.exe
PowerMac, 16MB, System 7.1, SoftWindows 3.0
winstamp32.exe
PowerMac, 16MB, System 7.1, SoftWindows 95
There is no 'native' Mac version of the software so one of the following PC emulators
is required - SoftPC, RealPC, SoftWindows 3.0 or 9x. The emulator 'Virtual PC'
cannot be used. Note that if you are using SoftPC or RealPC you must use the special
DOS application stampx.exe (supplied on the DOS disk in \mac,) so that downloading
is mapped to the Mac modem port rather than the PC printer port.
Due to the relatively high purchase cost of the PC emulator software some schools
have collected old '286/386' PCs for dedicated Stamp use. This may be a cheaper
alternative as second hand computers are available at very low cost as they are now
often considered obsolete as they do not run 'Windows'.
Upgrading Computer Systems
The same Stamp Controller module is used for all computer platforms. The same
programming 'language' syntax is also used for all systems. Therefore changing
computer systems at a later date simply involves buying new cables (if required) and
obtaining the alternative software. This software can be downloaded free of charge via
the Internet or can be provided on disk.
Technological Studies: Systems and Control Teachers Notes (H) Introduction
13
Stamp Controller Power Supply
The Stamp Controller has two power supply options:
2.1mm DC Power Socket
This socket is the preferred power option, and is used with the industry standard
2.1mm (tip positive) style DC power plug. This style of plug is supplied with most
'wall-plug' style DC battery eliminators. A 2.1mm to 4mm 'banana' plug power (order
code CAB-030) lead is also available for those wishing to use traditional bench-top
power supplies.
The power supply must be capable of supplying regulated 7.5 - 9V DC at 300mA. The
Stamp Controller is protected against reverse polarity and short-circuits conditions
when this type of power supply is used.
MFA Power Header.
This header is provided for users who wish to use traditional MFA battery connectors
from 6V lantern batteries or Unilab Beaver DC power supplies.
The power supplied via this connection must not exceed 6V. Exceeding this value
could permanently damage the integrated circuits on the board.
Note that the MFA power socket is 'disabled' by the 2.1mm socket, ensuring that no
damage occurs if two power supplies are accidentally connected simultaneously.
Important Note - 'Flat' 6V Lantern Batteries.
The Stamp Controller operates (runs programs from memory) down to 3V, but DOES
NOT download correctly at voltages less than approx. 4.5V. This characteristic is
particularly noticeable when using the DOS software via a PC printer port cable.
Therefore if you are receiving repeat download errors, but the module otherwise
appears to 'run' programs correctly, the most common problem is a flat battery. Test
with a new battery before reporting a fault.
Technological Studies: Systems and Control Teachers Notes (H) Introduction
14
Customising the Stamp Controller
The Stamp Controller is an extremely versatile board, and can be configured in a
number of ways. It has been designed to allow for future modifications and 'upgrades'
for other courses, and so contains a number of 'unpopulated' pcb holes for additional
components.
The following suggestions of how the board can be customised may be useful:
Perspex Cover
A pre-drilled clear perspex cover that mounts above the components on the Stamp
Controller is available separately. This covers all the integrated circuits and prevents
inquisitive and/or mischievous fingers removing components. Supplied with
instructions and a full kit of support posts and nuts/bolts.
2mm Sockets.
It is possible to add 2mm input/output sockets by enlarging the hole in the pad beside
the LED and soldering in a 2mm socket (as on the serial ADC board). A kit of 2mm
sockets (drill-bit included) is available.
Self-adhesive feet.
The self-adhesive feet on the underside of the board can be super-glued in place rather
than use the self-adhesive tape supplied on the feet.
I/O Header
The i/o pin header is found to be very useful by many for connection of voltmeter or
oscilloscope probes for demonstration purposes. However it is not strictly necessary
and so, if the perspex cover is not used to protect the components, it could be removed
by cutting off the pins with a pair of side cutters. This would prevent the possibility of
students deliberately 'shorting' the pins together with metal devices such as scissors.
Clock Resonator
If the perspex cover is not used, the 4MHz clock resonator on the Controller could be
flexed back and forth by inquisitive fingers, which would eventually cause it to shear
off. To prevent this we strongly recommend that it is glued in place with epoxy resin
(e.g. Araldite). If desired the resonator can also be totally replaced by a surface mount
type resonator, mounted on the underside of the board (pads provided). A suitable
device is Farnell code 574-605.
Technological Studies: Systems and Control Teachers Notes (H) Introduction
15
Contact Addresses:
Revolution Education Ltd
81 Cleave Road, Gillingham, Kent, ME7 4AX
Tel: (01634) 856712 Fax: (01634) 856712
Middlesex University Teaching Resources
Teaching Resources, Middlesex University, Trent Park,
Bramley Road, London, N14 4YZ
Tel: (0181) 447 0342 Fax: (0181) 447 0340
Higher Still Development Programme
PO Box 12754, Ladywell House, Ladywell Road
Edinburgh, EH12 7YH
Tel: (0171) 314 4620 Fax: (0131) 314 4621
Unilab
Unilab, Lynn Lane, Shenstone, Lichfield,
Staffordshire, WS14 0EE
Tel: (01543) 483064 Fax: (01543) 483056
E & L Instruments Ltd
E & L Instruments Ltd , Aerial Road,
Wrexham LL12 0TU
Tel: (01978) 853920 Fax: (01978) 854564
Rapid Electronics Ltd
Rapid Electronics Ltd, Heckworth Close,
Colchester, Essex, CO4 4TB
Tel: (01206) 751166 Fax: (01206) 751188
Technology Enhancement Programme
4-7 Red Lion Court, London, EC4B 4AB
Tel: (0171) 583 0900 Fax: (0171) 583 0909
Technological Studies: Systems and Control Teachers Notes (H) Introduction
16
TECHNOLOGICAL STUDIES
HIGHER
SYSTEMS AND CONTROL
TEACHER/LECTURER NOTES
AND SOLUTIONS TO ASSIGNMENTS
OUTCOME 1
Technological Studies: Systems and Control Teachers Notes (H) Outcome 1
1
Technological Studies: Systems and Control Teachers Notes (H) Outcome 1
2
Assignment 1.
Explain what is meant by the term 'systems diagram'.
When applied to control systems, a Systems Diagram is a useful way of visually
representing the desired function of the system. The systems diagram is a form of
block diagram than contains all the subsystems within a dashed box, called the
systems boundary. The systems boundary indicates the extend of the control system.
INPUT
CONTROL
OUTPUT
DRIVER
OUTPUT
The "real world" input and output conditions of the system are shown as arrows
entering, and leaving, the systems diagram.
Technological Studies: Systems and Control Teachers Notes (H) Outcome 1
3
Assignment 2.
Describe the differences between an open loop and closed loop control system.
An Open Loop Control system represents the simplest and cheapest form of control,
where an input is processed to produce an output. With open loop control systems
there is no capability to adjust the output to suit the changing output requirements.
Closed loop control systems are capable of making decisions and adjusting their
performance to suit changing output conditions.
All closed loop control systems include a feedback sensing subsystem within the
systems diagram. The control subsystem will process the feedback signal by making a
'decision' on whether the state of the output should change.
FEEDBACK
SENSING
INPUT
CONTROL
OUTPUT
DRIVER
Technological Studies: Systems and Control Teachers Notes (H) Outcome 1
OUTPUT
4
Assignment 3.
Describe the purpose of the feedback sensing subsystem in a closed loop control
system.
All closed loop control systems include a feedback sensing subsystem within the
systems diagram. The control subsystem will process the feedback signal by making a
'decision' on whether the state of the output should change. Therefore the feedback
sensing system feeds the control subsystem with the condition of the output.
FEEDBACK
SENSING
INPUT
CONTROL
OUTPUT
DRIVER
Technological Studies: Systems and Control Teachers Notes (H) Outcome 1
OUTPUT
5
Assignment 4.
The figures above show two types of electric fire. The second electric fire is a
more modern device fitted with a thermostat.
a)
Name the type of control system used in each type of electric fire
Bar heater is an open loop control system.
Thermostat controlled heater is a closed loop control system.
b)
Draw a system diagram for each type of electric fire.
Bar heater
SWITCH
HELD
DOWN
CONTROL
OUTPUT
DRIVER
FAN & HEATER
SWITCHED ON
Thermostat controlled heater
THERMOSTAT
CONTROL
c)
HEATING
SYSTEM
Name a type of electronic sensor that may used for measuring
temperature.
Thermistor (or thermocouple)
Technological Studies: Systems and Control Teachers Notes (H) Outcome 1
6
Assignment 5.
LIMIT
SWITCH
SWITCH
UNIT
INVERTER
TRANSDUCER
DRIVER
LATCH
INPUT/OUTPUT
UNIT
MOTOR/
GEARBOX
LIFT PLATFORM
The systems diagram for a simple lift control system is shown below.
PLATFORM POSITION
SENSOR
START
LIFT
CONTROL
OUTPUT
DRIVER
RAISE LIFT
PLATFORM
A limit switch at the top of the lift detects when the lift platform has reached the
top of the run. The block diagram below shows the system diagram sub-systems
broken down into smaller blocks.
LIMIT
SWITCH
START
LIFT
SWITCH
UNIT
INVERTER
LATCH
TRANSDUCER
DRIVER
MOTOR
GEARBOX
RAISE LIFT
PLATFORM
Technological Studies: Systems and Control Teachers Notes (H) Outcome 1
7
A circuit diagram of the system is shown below.
+V
S
Q
R
Q
0V
Build the circuit shown, using discrete components, circuit simulation or a
modular electronics system.
a)
Clearly explain how the system operates.
When the start switch is momentarily pressed the system is set. The latch keeps the
system set even if the start switch is then released. The transducer driver circuit
switches the relay on, which powers the motor. The motor drives the lift cage, which
moves up until it hits the microswitch.
The microswitch resets the system. This switches the transducer driver off, which
switches the motor off and hence stops the lift cage moving.
Technological Studies: Systems and Control Teachers Notes (H) Outcome 1
8
The 'transducer driver' circuit used in this instance is a relay driver circuit.
RELAY
b)
Explain the purpose of the relay, transistor and diode within the relay
driver circuit.
The relay is used to switch the motor on and off. The relay isolates the motor from the
control circuit, as the motor is a high current load which uses a separate power
supply.
The transistor is used to switch the relay on and off.
The diode protects the transistor from the back EMF generated when the relay
switches off.
Technological Studies: Systems and Control Teachers Notes (H) Outcome 1
9
Assignment 6
The output condition using this type of control does not have to be limited to on
or off but can be applied to any two desired output states.
LIMIT
SWITCH 1
INPUT/OUTPUT
UNIT
INVERTER
LATCH
TRANSDUCER
DRIVER
INPUT/OUTPUT
UNIT
LIFT PLATFORM
MOTOR/
GEARBOX
+V
LIMIT
SWITCH 2
OV
Build the circuit shown, using discrete components or a modular electronics
system.
a)
Draw a system diagram of the control system.
LIMIT
SWITCH
SWITCH
UNIT
INVERTER
LATCH
TRANSDUCER
DRIVER
MOTOR
LIMIT
SWITCH
GEARBOX
RAISE/LOWER
LIFT PLATFORM
Technological Studies: Systems and Control Teachers Notes (H) Outcome 1
10
b)
Draw a circuit diagram of the control system.
+V
S
Q
R
Q
0V
c)
Explain the operation (function and effect) of the DPDT relay.
The DPDT relay contacts are connected to the motor. The normally closed contacts
are wired to make the motor turn in one direction, the normally open contacts are
wired to make the motor turn in the other direction.
Therefore when the relay is not energised the motor turns in one direction. When the
relay is energised the motor turns in the other direction. In this example this causes
the lift cage to move up and down.
Technological Studies: Systems and Control Teachers Notes (H) Outcome 1
11
TECHNOLOGICAL STUDIES
HIGHER
SYSTEMS AND CONTROL
TEACHER/LECTURER NOTES
AND SOLUTIONS TO ASSIGNMENTS
OUTCOME 2
Technological Studies: Systems and Control Teachers Notes (H) Outcome 2
1
Technological Studies: Systems and Control Teachers Notes (H) Outcome 2
2
Assignment 1.
The block diagram below simulates an automatic heating system. When the bulb
heats up the temperature rise is detected by the bead thermistor, which sends a
feedback signal back to the comparator.
BEAD THERMISTOR
INPUT/OUTPUT
UNIT
COMPARATOR
TRANSDUCER
DRIVER
BULB UNIT
A circuit diagram of the system is shown below.
TEMPERATURE FEEDBACK SIGNAL
+VCC
R
RT
RV
R
RV
OV
-VCC
The variable resistor, RV1 (connecting to the non-inverting input of the op-amp)
is used to set the reference level (or threshold). This sets the desired temperature
of the bulb.
Build the circuit shown, using discrete components or a modular electronics
system. Calibrate the system to the following performance criteria:
• When the bulb heats above the reference level the thermistor should sense the
temperature and send a signal to the comparator which will switch the bulb
off.
• When the bulb cools below the reference level the bulb should switch on again.
• The system should operate continuously.
Technological Studies: Systems and Control Teachers Notes (H) Outcome 2
3
a)
Describe how the circuit operates.
The op-amp is operating as a comparator, which compares two voltage levels. The
first reference voltage level is set by the potential divider circuit that contains RV1. If
the second voltage level, set by the thermistor potential divider, is less than the
reference value the op-amp switches the transistor on, which cause the bulb to light.
As the bulb lights it heats the thermistor, so the thermistor resistance decreases. This
causes the voltage level at the centre of the thermistor potential divider to increase.
When the voltage level increases above the reference voltage the op-amp switches the
transistor off, so the bulb goes out.
The thermistor then cools, the thermistor potential divider voltage drops below the
reference level, and the whole cycle repeats.
b)
Explain clearly how you calibrated the system.
Answer involving adjusting RV2 to calibrate the thermistor potential divider.
Technological Studies: Systems and Control Teachers Notes (H) Outcome 2
4
Assignment 2
Explain the following terms when applied to control systems:
open loop, closed loop
An Open Loop Control system represents the simplest and cheapest form of control,
where an input is processed to produce an output. With open loop control systems
there is no capability to adjust the output to suit the changing output requirements.
Closed loop control systems are capable of making decisions and adjusting their
performance to suit changing output conditions. They include a feedback signal from
the output back to the control subsystem.
negative feedback, positive feedback
The purpose of closed loop control is to ensure that the output is maintained, as
closely as possible, to the desired output level. To achieve this a feedback signal is fed
back from the output to the control subsystem. This enables the system to react to the
condition of the output.
Negative feedback reduces the output error (e.g. in a central heating system).
Positive feedback reinforces the error (e.g. high pitch sound generated when a
microphone is held close to a speaker).
error detector
The error-detection symbol is used within a control diagram to indicate that the
control involves two signals. The feedback signal is connected to the negative symbol
to indicate the use of negative feedback.
TEMPERATURE
SENSOR
SET
TEMPERATURE
LEVEL
OPERATIONAL
AMPLIFIER
OUTPUT
DRIVER
Technological Studies: Systems and Control Teachers Notes (H) Outcome 2
CONSTANT
OUTPUT
TEMPERATURE
5
Assignment 3
The block diagram below simulates the automatic water heating system within a
washing machine.
REMOTE
INPUT
UNIT
DIFFERENCE
AMPLIFIER
NON-INVERTING
AMPLIFIER
POWER
DRIVER
INPUT
VOLTAGE
UNIT
12V HEATER
THERMISTOR
BEAKER OF
WATER
A circuit diagram of the system is shown below.
+Vcc
THERMISTOR
100K
10K
10K
POWER
DRIVER
HEATER
10K
1K
22K
10K
10K
0V
-Vcc
Build the circuit shown, using discrete components or a modular electronics
system.
Observe the response of the system when the desired temperature is altered (by
adjusting the variable resistor). Use a digital thermometer to measure the
temperature of the fluid, and a voltmeter to measure the voltage across the
heater.
Technological Studies: Systems and Control Teachers Notes (H) Outcome 2
6
a)
Describe how the circuit operates. Clearly explain the purpose of the noninverting amplifier after the difference amplifier?
The reference voltage signal to the difference amplifier is provided by the variable
resistor in the first potential divider. The second voltage signal is provided by the
thermistor potential divider.
When there is a large difference between these voltages the difference amplifier
provides a large signal to the non-inverting amplifier. Although in signal terms this
error signal is quite large, it is not directly large enough to drive the high power
driver, and so the signal is amplified by the non-inverting amplifier to produce a
larger signal.
The heater switches on and the temperature of the water rises. This causes the signal
from the thermistor potential divider circuit to approach the reference signal, and so
the error difference decreases. When the two signals are quite near the amplified
error signal is not enough to drive the output driver, and so the heater switches off.
Therefore, unlike a comparator based system, the heater switches off before the
desired temperature is reached, not after the desired temperature has been passed.
b)
Explain clearly how the system responds when the desired temperature
level is altered.
When the reference signal is altered the difference between the two signals is
increased and so a large error results. If this is a large negative error the heater
switches on to heat the water. If this is a large negative error the system waits for the
water to cool in the surrounding air.
Technological Studies: Systems and Control Teachers Notes (H) Outcome 2
7
Assignment 4.
A proportional control system is used to regulate the flow rate of coal onto a
conveyer belt. The system should sense the weight of coal on the conveyer belt
and automatically adjust the gate height to ensure that a constant flow of coal is
supplied.
POWER
SUPPLY
RACK
AND
PINION
CONTROL
UNIT
VARIABLE HEIGHT
GATE
P
CONVEYOR
FRAME PIVOTED
HERE
CONSTANT SPEED
DRIVE MOTOR
LOAD SENSOR
Technological Studies: Systems and Control Teachers Notes (H) Outcome 2
8
a)
Draw a systems diagram of the flow rate control system.
LOAD
SENSOR
OPERATIONAL
AMPLIFIER
b)
OUTPUT
DRIVER
RACK &
PINION
MOTOR
Explain the term 'proportional control'.
In proportional closed loop control systems the output signal is directly related to the
error signal. Therefore if there is a large error there will be a larger output signal
than with a small error. This helps reduce 'overshoot' errors within the system.
c i)
Name the configuration of op-amp used in proportional control systems.
Difference amplifier
c ii)
Draw a circuit diagram of the op-amp.
Rf
+Vcc
R1
R1
V1
-Vcc
V2
Rf
Technological Studies: Systems and Control Teachers Notes (H) Outcome 2
Vo
9
d i)
Name a suitable output driver circuit which could be used with the
control system.
Push-pull follower analogue driver
d ii)
Draw a circuit diagram of the driver circuit.
+Vcc
NPN
OP-AMP
SIGNAL
LOAD
PNP
0V
-Vcc
Technological Studies: Systems and Control Teachers Notes (H) Outcome 2
10
Assignment 5.
The figure shows the layout of an audio mixing desk.
TACHOGENERATOR
AUDIO MIXING
HEAD
RECORDING REEL DRIVEN BY DC MOTOR
The tape is fed through the audio mixing head by being pulled on to a recording
reel driven by a dc motor. As the tape builds up on the recording reel, the tape
speed through the audio mixing head will increase.
To prevent this from happening, the dc motor is fitted to a closed loop control
system.
A tachogenerator connected to a pulley senses the tape feed rate and sends an
error signal to the control system.
a)
Name the type of closed loop control used in this application.
Proportional closed loop control.
b)
Name the amplifier used in this type of closed loop control.
Difference amplifier.
Technological Studies: Systems and Control Teachers Notes (H) Outcome 2
11
c)
Draw a control diagram of the system.
TACHOGENERATOR
OUTPUT
DRIVER
OPERATIONAL
AMPLIFIER
d)
MOTOR
SPEED
MOTOR
Draw a circuit diagram of the control system and explain the function of
each part of the circuit.
Rf
+Vcc
R1
R1
V1
-Vcc
V2
Rf
Technological Studies: Systems and Control Teachers Notes (H) Outcome 2
Vo
12
Assignment 6.
The figure illustrates a system for controlling the wing mirrors on a car by
adjusting remote dials on the dash.
DIALS
A control diagram of the system for rotational movement in the X-axis (one
mirror) is shown in the figure below. Similar systems are used for the Y-axis and
for the other mirror.
FEEDBACK
SENSOR
REMOTE
DIAL
OPERATIONAL
AMPLIFIER
OUTPUT
DRIVER
MOTOR
WING MIRROR
POSITION
a) With reference to the control diagram, explain clearly how the system
operates.
When the car driver adjusts the dial the op-amp subsystem switches on the output
driver, which cause the motor to move. As the motor moves the negative feedback
signal from the mirror is fed back to the operational amplifier. When the mirror is in
the correct new position the error detection is zero, so the op-amp switches off the
output driver (so the motor switches off).
b) Name the type of control used in this system.
Proportional closed loop control.
Technological Studies: Systems and Control Teachers Notes (H) Outcome 2
13
c) Name the configuration of op-amp required.
Difference amplifier.
d) State two reasons why the op-amp cannot be used to drive the motor directly.
Op amp cannot source a high current for the motor.
The back EMF of the motor could damage the op-amp.
It is necessary to be able to reverse the direction of the motor.
e) Name a suitable output driver which could be used with this system.
Analogue push-pull follower
f) Draw a circuit diagram of the output driver.
+Vcc
NPN
OP-AMP
SIGNAL
LOAD
PNP
0V
-Vcc
Technological Studies: Systems and Control Teachers Notes (H) Outcome 2
14
TECHNOLOGICAL STUDIES
HIGHER
SYSTEMS AND CONTROL
TEACHER/LECTURER NOTES
AND SOLUTIONS TO ASSIGNMENTS
OUTCOME 3
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
1
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
2
Assignment 1.1
List the advantages of using a microcontroller within a product design.
One microcontroller can often replace a number of separate parts, or even a complete
electronic circuit. Some of the advantages of using microcontrollers in a product
design are:
• increased reliability and reduced stock inventory (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
Assignment 1.2
Describe the input sensors and output transducers that may be linked to a
microcontroller in the following common household appliances:
- microwave oven
- washing machine
- electronic bicycle speedometer
Device
Microwave Oven
Input Sensors
Keypad
Door Microswitch
Temperature Sensor
Washing Machine
Control Dial
Door Microswitch
Temperature Sensor
Bicycle Speedometer
Press Switches
Reed Switch or
Hall Effect Sensor
Output Transducers
Seven Segment Display
Internal Light
Turntable Motor
Bell
Magnetron
Door Lock Solenoid
Solenoid Valves
Heater
Motor
LCD Display
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
3
Assignment 1.3
Explain the following microcontroller terms: ALU, bus, clock
Arithmetic/Logic Unit (ALU) and Clock
The processing unit (full name arithmetic and logic unit (ALU)) is the 'brain' of the
microcontroller. It operates by reading instructions from the read only memory ROM
(permanent program memory) and then carrying out the mathematical operations for
each instruction. The speed at which these operations occur is controlled by the clock
circuit.
The clock circuit within the microcontroller 'synchronises' all the internal blocks
(ALU, ROM, RAM etc.) so that the system remains stable. The clock circuit is built
into the microcontroller, but an external crystal or resonator is required to set the
clock frequency. A typical clock frequency for use with a microcontroller is 4MHz,
but speeds as high as 20MHz can also be achieved. With a clock frequency of 4MHz
the microcontroller completes one million instructions a second!
Buses
Information is carried between the various blocks of the microcontroller along
'groups' of wires called buses. The 'data bus' carries the 8-bit data between the ALU
and RAM / Input-Output registers, and the 'program bus' carries the 13-bit program
instructions from the ROM.
The size of the data bus provides a description for the microcontroller. Therefore an
'8 bit microcontroller' has a data bus '8-bits' wide. Microcontrollers with 16-bit and
32-bit data buses are also available.
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
4
Assignment 1.4
Explain the differences between the following types of memory:
- RAM, ROM, EEPROM
RAM
ROM
EEPROM
- Random Access Memory
- Read Only Memory
- Electrically Erasable Programmable Read Only Memory
The ROM contains the operating instructions (i.e. 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. Most microcontrollers are one-time-programmable types, which means the
ROM can only be programmed once. If you make a mistake, and have to change the
program, the chip has to be thrown away and a new chip programmed with the
revised program. To overcome this problem some microcontrollers now use FLASH
EEPROM memory instead. This type of 'erasable-permanent' memory allows the
ROM to be re-programmed if a mistake is made.
The RAM is 'temporary' memory used for storing information whilst the program is
running. This memory is 'volatile', which means that as soon as the power is
disconnected the contents of the memory is lost.
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
5
Assignment 1.5
Describe the similarities and differences between programming, and constructing
interfacing circuits for a 'true' microcontroller and the 'Basic Stamp' system.
Microcontrollers are normally programmed in assembler code or 'C', while the Basic
Stamp is programmed in the 'user friendly' language BASIC (Beginners' All Purpose
Symbolic Instruction Code). When using the Basic Stamp the program is stored in an
external EEPROM chip, rather than the usual method of embedding the program in
the microcontroller itself.
Therefore the primary difference between programming standard microcontrollers
and programming the Basic Stamp is that, when you 'download' a program to the
Basic Stamp, you are actually programming the external EEPROM, rather than the
microcontroller ROM.
When you build electronic systems you are still connecting directly to the
'microcontroller' input/output pins, and so the electronic connections are identical to
those made to standard microcontrollers.
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
6
Assignment (Section 2)
Convert each of the following binary numbers into decimal:
2.1) 11110000
240
2.2) 11000011
195
2.3) 01010101
85
2.4) 10101010
170
Convert each of these decimal numbers into binary:
2.5) 17
00010001
2.6) 23
00010111
2.7) 11
00001011
2.8) 38
00100110
2.9) 33
00100001
Convert the following binary numbers to hexadecimal:
2.10) %11011101
&DD
2.11) %11111001
&F9
2.12) %01010101
&55
2.13) %10101010
&AA
2.14) %11001010
&CA
Convert the following hexadecimal numbers to binary:
2.15) &4E
%01001110
2.16) &0D
%00001101
2.17) &FD
%11111101
2.18) &5A
%01011010
2.19) &B2
%10110010
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
7
Assignment 3.3
What is the function of the Data Direction Register (DDR)?
Each pin can be configured to be an output (to send digital signals) or an input (to
receive digital signals). The Data Direction Register (DDR) is used to configure the
port, and in the PBASIC language the DDR is allocated the label 'dirs'.
If all the bits in the DDR are set high then all the pins will be set as outputs. If all the
bits are set low each pin will be set as an input.
Assignment 3.4
What is meant by the term "white-space"? Why is it important to use whitespace and comments when writing programs?
The term 'white-space' is used by programmers to define tabs, spaces and blank lines,
and the correct use of white-space can make the program listing much easier to read
and understand.
A comment starts after an apostrophe (') and continues to the end of the line.
Although the comments are not needed to make the program work, they are an
essential part of the program as they explain in 'plain language' what the program is
doing. Comments are particularly important if the program is to be studied by
someone else at a later date.
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
8
Assignment 3.5
A set of temporary traffic lights are required for a system of road-works.
red
red and amber
green
amber
10 sec
2 sec
10 sec
2 sec
Draw a flowchart for the lights sequence shown by one set of the traffic lights.
Use the times shown in the table for each stage.
START
RED ON
WAIT 10 Sec.
AMBER ON
WAIT 2 Sec.
RED & AMBER OFF
GREEN ON
WAIT 10 Sec.
GREEN OFF
AMBER ON
WAIT 2 Sec.
AMBER OFF
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
9
Write a PBASIC program to achieve this operation. Use the following pin
configuration - red (7), amber (6) and green (5).
init: let dirs = %11100000
' set pins 5-7 as outputs
main: high 7
pause 10000
high 6
pause 2000
let pins = %00100000
pause 10000
let pins = %01000000
pause 2000
low 6
goto main
'
'
'
'
'
'
'
'
'
'
set pin 7 high
wait for 10 seconds
set pin 6 high
wait for 2 seconds
set pin 5 high
wait for 10 seconds
switch pin 6 high
wait for 2 second
pin 6 low
loop forever
(Note this example shows a mixture of high / low and let pins = commands for
illustration purposes).
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
10
Assignment 3.6
OUTPUT
DRIVER
MODULE
STAMP
CONTROLLER
Connect a buggy to the output driver module (or MFA movement module) as
shown in the diagram.
START
MOVE FORWARD
WAIT 3 SEC.
TURN LEFT
WAIT 1 SEC.
MOVE FORWARD
WAIT 3 SEC.
STOP
Write a high level program in PBASIC to control the movement of the buggy as
shown by the flowchart above.
init: let dirs = %11110000
' set pins 4-7 as outputs
main: let pins = %01010000
pause 3000
let pins = %10010000
pause 1000
let pins = %01010000
pause 3000
end
'
'
'
'
'
'
'
forward
wait for 3 seconds
left
wait for 1 second
forward
wait for 3 seconds
stop
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
11
Assignment 3.8
OUTPUT
DRIVER
MODULE
STAMP
CONTROLLER
Connect a buggy to the output driver module (or MFA movement module) as
shown in the diagram.
3
3
3
3
The buggy should follow the movement path as shown in the diagram above.
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
12
Draw a flowchart for the movement of the buggy, making use of a for...next
command structure.
START
SET COUNTER = 4
MOTORS
FORWARD
WAIT 3
MOTORS
LEFT
WAIT 1
LOOPED
4 TIMES ?
NO
YES
STOP
Write a high level program in PBASIC to control the movement of the buggy as
shown by your flowchart. (It will be necessary to experiment with time delays to
establish how quickly your buggy moves and turns).
symbol counter = b0
' define the variable "counter"
init: let dirs = %11110000
' set pins 4-7 as outputs
main: for counter = 1 to 4
let pins = %01010000
pause 3000
let pins = %10010000
pause 1000
next counter
'
'
'
'
'
'
end
start a for...next loop
forward
wait for 3 seconds
left
wait for 1 second
end of for...next loop
' end program
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
13
Assignment 3.9
As part of a Christmas decoration, a lighting sequence is to be controlled by a
microcontroller. The output connections are shown below.
Input Connection
Pin
7
6
5
4
3
2
1
0
Output Connection
Yellow Light
Purple Light
Blue Light
Green Light
Red Light
The red and green lights should come on together and stay on for 5 seconds.
Then they both go off and the yellow and blue lights should come on together for
8 seconds. They then go off and the purple light flashes on and off 6 times (the
'on' and 'off' times being 0.5 seconds each). The sequence then repeats itself.
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
14
Draw a flowchart and write a PBASIC program for this sequence.
START
RED & GREEN ON
WAIT 5 Sec.
RED & GREEN OFF
YELLOW & BLUE ON
WAIT 8 Sec.
YELLOW & BLUE
OFF
SET COUNTER = 6
PURPLE ON
WAIT 0.5 Sec.
PURPLE OFF
WAIT 0.5 Sec.
NO
LOOPED
6 TIMES ?
YES
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
15
symbol counter = b0
' define the variable "counter"
init: let dirs = %11111111
' set all pins as outputs
main: let pins = %00000101
pause 5000
let pins = %01001000
pause 8000
'
'
'
'
red and green on
wait 5 seconds
yellow and blue on
wait 8 seconds
for counter = 1 to 6
let pins = %00100000
pause 500
let pins = %00000000
pause 500
next counter
'
'
'
'
'
'
start a for...next loop
purple on
wait 0.5 second
purple off
wait 0.5 second
end of for...next loop
goto main
' loop forever
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
16
Assignment 3.11
START
SWITCH ALL
PINS HIGH
WAIT5 SECONDS
SWITCH ALL
PINS LOW
WAIT0.5 SECONDS
SWITCH ALL
PINS HIGH
WAIT0.5 SECONDS
HAS THIS BEEN
DONE 10 TIMES?
N
Y
SWITCH ALL
PINS LOW
STOP
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
17
Develop a PBASIC program that will carry out the instructions shown in the
flowchart above.
symbol counter = b0
' define the variable "counter"
init: let dirs = %11111111
' set all pins as outputs
main: let pins = %11111111
pause 5000
' all pins high
' wait 5 seconds
for counter = 1 to 10
let pins = %00000000
pause 500
let pins = %11111111
pause 500
next counter
'
'
'
'
'
'
start a for...next loop
all pins low
wait 0.5 second
all pins high
wait 0.5 second
end of for...next loop
let pins = %00000000
end
' all pins low
' stop the program
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
18
Assignment 3.12
A motor, connected to pin 7, is to run when a 'start' switch (connected to pin 2)
is momentarily pressed. The motor continues to run until another 'stop' switch
(connected to pin 3) is pressed - at which point the motor switches off. The
system should then reset to wait for another 'start' signal.
Draw a flowchart and write a PBASIC program for this sequence.
START
NO
IS PIN 2
HIGH ?
YES
SWITCH MOTOR
ON
NO
IS PIN 3
HIGH ?
YES
SWITCH MOTOR
OFF
init: let dirs = %10000000
' set pin 7 as output
main: if pin2 = 1 then mon
goto main
' continue when start switch
' else loop
mon:
' motor on
high 7
loop: if pin3 = 1 then moff
goto loop
' continue when stop switch
' else loop
moff: low 7
goto main
' motor off
' back to start
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
19
Assignment 3.13
STAMP
CONTROLLER
OUTPUT
DRIVER
MODULE
Connect a buggy to the output driver module (or MFA movement module) as
shown in the diagram. Connect the micro-switch 'bumpers' to pins 0 and 1 on
the Stamp Controller via the screw terminals as shown below.
V+
0
1
2
3
0V
SHOWS HOW WIRE 2 SWITCHES TO
THE SCREW TERMINALS ON THE
STAMP CONTROLLER
The buggy should continue in a forward direction until either of the two microswitch bumpers is activated. At this point the buggy should reverse for 3 seconds,
rotate 90 degrees clockwise, and then continue in a forwards direction.
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
20
Draw a flowchart and write a PBASIC program to control the movement of the
buggy as described above.
START
MOTOR
FORWARD
YES
IS PIN 0
HIGH ?
NO
YES
IS PIN 1
HIGH ?
MOTOR
REVERSE
NO
WAIT 3 Sec.
MOTOR
TURN
WAIT 2 Sec..
init: let dirs = %11110000
' set pins 4-7 as outputs
main: let pins = %01010000
' forward
loop: if pin0 = 1 then bump
if pin1 = 1 then bump
goto loop
' test switch 0
' test switch 1
' else loop
bump: let pins = %10100000
pause 3000
let pins = %10010000
pause 2000
goto main
'
'
'
'
'
reverse
wait for 3 seconds
left
turn for 2 seconds
back to start
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
21
Assignment 3.14
START
GREEN LED ON
SWITCH
PUSHED?
NO
YES
GREEN LED OFF
AMBER LED ON
WAIT 3 sec.
AMBER LED OFF
RED LED ON
WAIT 4 sec.
AMBER LED ON
WAIT 2 sec..
RED/AMBER LED OFF
GREEN LED ON
Develop a PBASIC program that will carry out the instructions shown in the
flowchart above.
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
22
Use the following pin configuration.
Input Connection
Start Switch
Pin
7
6
5
4
3
2
1
0
Output Connection
Red Light
Amber Light
Green Light
init: let dirs = %11110000
' set pins 4-7 as outputs
main: let pins = %00100000
' green on
loop: if pin3 = 1 then lite
goto loop
' test start switch
' else loop
lite: let pins = %01000000
pause 3000
let pins = %10000000
pause 4000
let pins = %11000000
pause 2000
goto main
'
'
'
'
'
'
'
amber on
wait for 3 seconds
red on
turn for 4 seconds
red & amber on
wait for 2 seconds
back to start
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
23
Assignment 3.16
As part of a shop display, a lighting sequence is to be controlled by a
microcontroller. The output connections are shown below.
Input Connection
switch 2
switch 1
Pin
7
6
5
4
3
2
1
0
Output Connection
Red Light
Yellow Light
Green Light
Orange Light
If switch 1 is pressed, each light should flash on and off 5 times in sequence i.e.
orange then green then yellow then red (each 'on' and 'off' time should be 0.5
seconds). the system then resets for the next switch push.
If switch 2 is pressed all lights should flash simultaneously 3 times. There should
then be a 2 second pause, before all lights should flash simultaneously 6 times
(each 'on' and 'off' time should be 0.5 seconds). The system then resets for the
next switch push.
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
24
Draw a flowchart and write a PBASIC program for this sequence (use a subprocedure for the flash routines).
START
SWITCH 1
ON ?
YES
FLASH 1
NO
SWITCH 2
ON ?
YES
FLASH 2
NO
FLASH 1
FLASH 1
LET COUNTER = 5
LET COUNTER = 10
ORANGE & YELLOW
ON
RED & GREEN
ON
WAIT 0.5 Sec.
WAIT 0.5 Sec.
ORANGE & YELLOW
OFF
RED & GREEN
OFF
WAIT 0.5 Sec.
NO
ALL
DONE ?
WAIT 0.5 Sec.
NO
ALL
DONE ?
YES
RETURN
YES
RETURN
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
25
symbol counter = b0
' define the variable "counter"
init: let dirs = %11110000
' set pins 4-7 as outputs
main: if pin1 = 1 then do1
if pin2 = 1 then do2
goto main
' test switch 1
' test switch 2
' else loop
do1:
for counter =
let pins =
pause 500
let pins =
pause 500
let pins =
pause 500
let pins =
pause 500
next counter
goto main
do2:
let b1 = 3
gosub flash
pause 2000
let b1 = 6
gosub flash
goto main
1 to 10
' start a for...next loop
%00010000 ' light on
' wait 0.5 second
%00100000 ' light on
' wait 0.5 second
%01000000 ' light on
' wait 0.5 second
%10000000 ' light on
' wait 0.5 second
' end of for...next loop
' loop to start
' sub-procedures
flash:
for counter = 1 to b1
let pins = %11110000
pause 500
let pins = %00000000
pause 500
next counter
return
'
'
'
'
'
'
3 flashes
do sub
wait 2 seconds
6 flashes
do sub
loop to start
'
'
'
'
'
'
'
start a for...next loop
lights on
wait 0.5 second
lights off
wait 0.5 second
end of for...next loop
return from sub
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
26
Assignment 3.17
Connect the washing machine model to the Stamp Controller.
A sequence of events for the operation of the washing machine is given in the
table below:
Step 1
Step 2
Step 3
Step 4
Step 5
Step 6
Wait until the door switch is closed.
Wait until the start switch is pushed.
Rotate the drum clockwise for 10 seconds.
Rotate the drum anti-clockwise for 10 seconds
Repeat steps 3 and 4 10 times
Rotate the drum clockwise for 5 seconds.
Rotate the drum anti-clockwise for 5 seconds
Repeat steps 5 and 6 5 times
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
27
Draw a flowchart for the control sequence described above.
START
NO
DOOR
CLOSED ?
YES
NO
START
PUSHED?
SET COUNTER = 5
YES
SET COUNTER = 10
DRUM
CLOCKWISE
DRUM
CLOCKWISE
WAIT 5 Sec.
WAIT 10 Sec.
DRUM
ANTICLOCKWISE
DRUM
ANTICLOCKWISE
WAIT 5 Sec.
WAIT 10 Sec.
NO
NO
ALL
DONE ?
ALL
DONE ?
YES
YES
STOP
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
28
Write, and test, a PBASIC program for the control sequence described above.
symbol counter = b0
symbol time = b1
symbol cycle = b2
' define the variable "counter"
' define the variable "time"
' define the variable "cycle"
init: let dirs = %11000000
' set pins 6-7 as outputs
step1:
if pin0 = 1 then step2
goto step1
' test start switch
' else loop
step2:
if pin1 = 1 then step3
goto step2
' test door switch
' else loop
step3:
let time = 10000
let cycle = 10
gosub wash
' set time to 10 secs
' set cycles to 10
' do sub
let time = 5000
let cycle = 5
gosub wash
' set time to 5 secs
' set cycles to 5
' do sub
end
' sub-procedures
wash:
for counter = 1 to cycle
let pins = %01000000
pause time
let pins = %10000000
pause time
next counter
return
'
'
'
'
'
'
'
start a for...next loop
clockwise
wait time
anticlockwise
wait time
end of for...next loop
return from sub
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
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Assignment 3.18
MAINS WATER
INLET VALVE
HEAD STORAGETANK
AGITATOR
MOTOR
DUMP PUMP MOTOR
CONVEYOR
MOTOR
The diagram shows the layout of a pulper machine used in a paper mill.
A batch of pulp and fillers, i.e. 5 x 20 kg bales of pulp and 2 x 50 kg bags of
fillers, is mixed during the pulping process with 1600 litres of water.
The operation of the pulping process is controlled by a microcontroller. The
microcontroller connections are as follows:
Input Connection
Start switch
Pin
7
6
5
4
3
2
1
0
Event Operator Action
1
Load conveyer with batch
2
Press start button
3
4
5
6
7
Output Connection
Agitator motor
Dump Pump
Conveyer
Inlet valve
Control Activity
Sequence commences.
Open inlet valve. Close valve after 10 minutes.
1 minute after inlet valve opens, start agitator
motor. run agitator motor for 11 minutes.
Start conveyer 2 minutes after inlet valve
opens. Run conveyer for 3 minutes.
1 minute after agitator motor stops, start dump
pump. run dump pump for 3 minutes.
Reset and wait for next start command.
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
30
(a) Based on the instructions given in the table, draw up a flow chart which
shows the control sequence for the pulping sequence.
START
NO
START
BUTTON ?
YES
OPEN VALVE
CLOSE VALVE
WAIT 1 Min
WAIT 2 Min
START MOTOR
STOP MOTOR
WAIT 2 Min
WAIT 1 Min
START
CONVEYOR
START PUMP
WAIT 3 Min
WAIT 3 Min
STOP
CONVEYOR
STOP PUMP
WAIT 4Min
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
31
(b) With reference to your flow chart, write a high level program in PBASIC to
control the operation of the pulper.
Assume use of a pre-written time delay sub-procedure called 'delay' which will
produce a time delay in multiples of one minute, according to the value set in the
variable 'mins' before the sub-procedure is called.
Example - To wait five minutes:
init: let dirs = %11110000
let mins = 5
call delay
' set pins 4-7 as outputs
symbol mins = b0
main: if pin0 = 1 then doit
goto main
' test start switch
' else loop
doit: high 4
let mins = 1
gosub delay
' open inlet
' set time
' do delay
high 7
let mins = 2
gosub delay
' start motor
' set time
' do delay
high 5
let mins = 3
gosub delay
' start conveyer
' set time
' do delay
low 5
let mins = 4
gosub delay
' stop conveyer
' set time
' do delay
low 4
let mins = 2
gosub delay
' close inlet
' set time
' do delay
low 7
let mins = 1
gosub delay
' stop motor
' set time
' do delay
high 6
let mins = 3
gosub delay
' start pump
' set time
' do delay
low 6
goto main
' stop pump
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
32
Assignment 3.21
SWITCH 1
SWITCH 2
SENSOR
MODULE
STAMP
CONTROLLER
SERIAL LED
Connect two switches to the sensors module, and the serial LCD module, to the
Stamp Controller as shown.
When the switch connected to pin '0' is pressed the Stamp Controller should add
1 to the current total, and then display the new value on the LCD. When the
switch connected to pin '1' is pressed the Stamp Controller should subtract 1
from the current total, and then display the new value on the LCD.
Draw a flowchart and write a PBASIC program to control the operation
described above.
START
WAIT 1 Sec.
PIN 0
HIGH ?
LET b0 = b0 + 1
PIN 1
HIGH /
LET b0 = b0 - 1
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
UPDATE LCD
33
symbol counter = b0
' define the variable
init: let dirs = %10000000
let pins = %10000000
' make pin 7 an output
' switch pin 7 high
pause 5
serout 7,T2400,(254,1)
pause 30
' short pause
' send 'clear LCD' command
' wait 30 ms
main: serout 7,T2400,(254,128)
serout 7,T2400,("Value = ")
serout 7,T2400,(#counter," ")
pause 1000
'
'
'
'
send
send
send
wait
'line 1' command
message
counter value
1 sec
loop: if pin0 = 1 then add1
if pin1 = 1 then take1
goto loop
' test switch 0
' test switch 1
add1: let counter = counter + 1
goto main
' add 1
' refresh display
take1:
let counter = counter - 1
goto main
' take 1
' refresh display
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
34
Assignment 4.1
Draw appropriate interfacing circuit diagrams for the following output devices.
Clearly explain your choice of circuit in each case.
a)
LED
0V
b,c) Buzzer, 6V DC Motor
(Same circuit - motor shown)
Vt
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
35
d,e) 12V DC solenoid, 24V pneumatic solenoid valve
(Same circuit - solenoid shown)
+ 5V
+ 12V
RELAY
SOLENOID
0V
0V
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
36
Assignment 4.2
Connect the electronic lock model to the Stamp Controller.
START
BUZZER OFF
RED LED ON
BOLT OUT
WAIT 2s
SWITCH 1
PRESSED?
NO
BUZZER ON
YES
SWITCH 2
PRESSED?
NO
YES
SWITCH 3
PRESSED?
NO
YES
RED LED OFF
GREEN LED ON
BOLT IN
WAIT 3s
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
37
Write, and test, a PBASIC program for the control sequence shown in the
diagram above.
Input Connection
Switch 3
Switch 2
Switch 1
Pin
7
6
5
4
3
2
1
0
Output Connection
Bolt
Buzzer
Green LED
Red LED
init: let dirs = %11110000
' make pins 4-7 outputs
main: let pins = %10010000
' red LED & bolt
if pin1 = 0 then beep
if pin2 = 0 then beep
if pin3 = 0 then beep
' test switch 1
' test switch 2
' test switch 3
open: let pins = %00100000
pause 3000
goto main
' green LED
' wait 3 seconds
' back to start
beep: let pins = %11010000
pause 2000
goto main
' red LED, bolt & buzzer
' wait 2 seconds
' back to start
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
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Assignment 4.4
Describe three products which may contain stepper motors. Describe how the
motor is used in each case.
Printer
XY Plotter
Clock
One-arm bandit
etc.
- to move the printing head back and forth
- to move the pen back and forth
- to move the second hand
- to rotate the wheels so they land on particular symbols
Assignment 4.5
A toy manufacturer is designing a new programmable robot toy. Describe the
advantages and disadvantages of using stepper motors (rather than dc motors) to
manoeuvre the robot.
Stepper motors will allow the toy to move in an exact straight line, whilst dc motors
will tend to veer off course (as one motor spins slightly faster than the other). Stepper
motors will turn corners more accurately. Stepper motors will provide more torque
than equivalent sized dc motors. Stepper motors are more expensive than dc motors.
Stepper motors draw current when stationary and so will drain batteries quickly. DC
motors can achieve higher speeds than stepper motors.
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
39
Assignment 4.6
12V DC
SUPPLY
STAMP
CONTROLLER
OUTPUT
DRIVER
STEPPER
MOTOR
Connect a stepper motor to the output driver module as shown.
Develop a PBASIC program that will rotate the stepper motor 48 steps in one
direction, and then 48 steps in the other direction.
The table below show the four different steps required to make the motor turn
Step
1
2
3
4
1
Coil 4
1
1
0
0
1
Coil 3
0
0
1
1
0
Coil 2
1
0
0
1
1
symbol counter = b0
' define the variable
init: let dirs = %11110000
' make pins 4-7 outputs
main: for counter =
let pins =
pause 50
let pins =
pause 50
let pins =
pause 50
let pins =
pause 50
next counter
for counter =
let pins =
pause 50
let pins =
pause 50
let pins =
pause 50
let pins =
pause 50
next counter
end
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
1 to 12
%10100000
%10010000
%01010000
%01100000
1 to 48
%01100000
%01010000
%10010000
%10100000
Coil 1
0
1
1
0
0
start a for...next loop
step 1
wait 0.05 second
step 2
wait 0.05 second
step 3
wait 0.05 second
step 4
wait 0.05 second
next loop
start a for...next loop
step 4
wait 0.05 second
step 3
wait 0.05 second
step 2
wait 0.05 second
step 1
wait 0.05 second
next loop
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
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Assignment 4.7
Connect the stepper motor light seeker apparatus to the Stamp Controller.
Input Connection
LDR1
LDR0
Pin
7
6
5
4
3
2
1
0
Output Connection
Coil 4
Coil 3
Coil 2
Coil 1
The two LDRs are connected to input pins 0 and 1, and the two potentiometers
may require adjustment for sensitivity (depending on light conditions).
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
41
Draw a flowchart and write a PBASIC program that will cause the apparatus to
'follow' a light source that is moved around the apparatus.
START
BOTH
INPUTS
ON ?
YES
NO
BOTH
INPUTS
OFF ?
YES
NO
INPUT 1
ON ?
YES
MOVE I STEP
CLOCKWISE
YES
MOVE 1 STEP
ANTICLOCKWISE
NO
INPUT 2
ON ?
NO
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
42
symbol counter = b0
' define the variable
init: let dirs = %11110000
' make pins 4-7 outputs
main: if pin0 = 1 then both
if pin1 = 1 then just2
goto main
' test LDR on pin0
' test LDR on pin1
' else loop
both: if pin1 = 1 then main
' both on so loop
just1:
let pins =
pause 50
let pins =
pause 50
let pins =
pause 50
let pins =
pause 50
goto main
'
'
'
'
'
'
'
'
'
move
step
wait
step
wait
step
wait
step
wait
4 steps left
4
0.05 second
3
0.05 second
2
0.05 second
1
0.05 second
'
'
'
'
'
'
'
'
'
move
step
wait
step
wait
step
wait
step
wait
4 steps right
1
0.05 second
2
0.05 second
3
0.05 second
4
0.05 second
just2:
let pins =
pause 50
let pins =
pause 50
let pins =
pause 50
let pins =
pause 50
goto main
%01100000
%01010000
%10010000
%10100000
%10100000
%10010000
%01010000
%01100000
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
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Assignment 4. 9
Crystal glassware is decorated by cutting grooves on to the outside surface. The
process leaves the untouched parts of the glass clear and reflective, whereas the
cut grooves are dull and rough and require to be polished.
The diagram shows the layout of a prototype system, developed by a student, to
polish crystal glasses with eight parallel grooves cut along the length of the glass.
GROOVE SENSOR
4-PHASE
STEPPER MOTOR
CRYSTAL
GLASS
GROOVES
POLISHING BRUSH
DRIVEN BY DC MOTOR
PNEUMATIC CYLINDERS
MOVE BRUSH MOTOR
INTO/OUT FROM THE GLASS
The system is to be controlled by a microcontroller. With a glass in place, the
start button is pressed to cause the cutting disk to switch on and move into the
cutting position. The first groove is cut for five seconds. The cutter is then
withdrawn. The stepper motor rotates the glass through 90 degrees into position
for the next groove. The process continues until all four grooves have been cut.
The stepper motor used by the student has a step angle of 7.5 degrees. It is
controlled by means of an SAA1027 driver IC signalled from the microcontroller.
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
44
Input Connection
Pin
7
6
5
4
Output Connection
Pneumatic Cylinder
(1 = instroke, 0 = outstroke)
DC Motor
(1 = on, 0 = off)
Stepper Direction
(0 to 1 pulse = 1 step)
Stepper Pulse
(1 = clockwise, 0 = anticlockwise)
3
2
1
Start button
(logic 1 when pressed)
0
(a) Calculate the number of steps the stepper motor must rotate to rotate the
glass through 90 degrees.
90 degrees ÷ 7.5 degrees = 12 steps
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
45
(b) Draw up a flow chart which shows the control sequence for the polishing
process.
START
NO
START
BUTTON ?
YES
SWITCH MOTOR
ON
SET COUNTER = 4
CYLINDER IN
WAIT 5 Sec.
CYLINDER OUT
ROTATE 90O
NO
ALL
DONE ?
YES
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
46
(c) With reference to your flow chart, write a high level program in PBASIC to
control the polishing process.
init: let dirs = %11110000
' make pins 4-7 outputs
main: if pin0 = 1 then loop
goto main
' test start switch
' else loop
loop: high 6
low 5
' motor on
' stepper direction clockwise
for b1 = 1 to 4
high 7
pause 5000
low 7
for b2 = 1 to 12
high 4
low 4
next b2
next b1
'
'
'
'
'
'
start a for...next loop
cylinder in
wait 5 seconds
cylinder out
start a for...next loop
12 pulsed steps
low 6
goto main
' motor off
' loop to start
' next stepper pulse
' next cut
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
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Assignment 4.12
Connect the conveyer belt model to the Stamp Controller.
A single block is to be moved continuously back and forth along the conveyer
belt without falling off either end.
Draw a flowchart that will control the movement as described.
START
MOTOR
FORWARD
NO
SWITCH 1
ON ?
YES
MOTOR
REVERSE
NO
SWITCH 2
ON ?
YES
Write, and test, a PBASIC program for the control sequence as drawn in your
flowchart.
init: let dirs = %11000000
' make pins 6-7 outputs
main: let pins = %01000000
' forward
loop: if pin1 = 1 then loop2
goto loop
' wait for switch
' else loop
loop2:
let pins = %10000000
' backward
loop3:
if pin2 = 1 then main
goto loop3
' wait for switch
' else loop
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
48
Assignment 4.16
Details of a speed control unit for a dc motor are shown below.
10K
10K
2
22K
1
+5V
39K
0
-5V
0V
a) Name the configuration of operational amplifier being used.
Summing amplifier.
b) Name the method of dc motor speed control being used.
Digital to analogue conversion
c) Explain clearly how the system operates.
The summing amplifier adds the total of the three input signals. The three input
signals can only be 5V or 0V in this example. As the input resistors are weighted the
output voltage is a ratio of the digital inputs..
In this example the output voltage is equal to
Vo
= -5 (Pin 2 x (10K/10K) + Pin 1 x (10K/22K) + Pin 0 x (10K/39K))
= -5 (Pin 2 + 0.5 (Pin 1) + 0.25 (Pin0))
where the pin value is 0 or 1. Note this example will not operate correctly at high
values as the op-amp cannot source an output greater than V+ (5V in this case)
d) State what the output voltage supplied to the motor will be when the following
values are applied to the input pins.
i) 1
Vo = -5(0.25) = -1.25V
ii) 3
Vo = -5(0.5+0.25) = -3.75V
iii) 4
Vo = -5(1) = -5V
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
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Assignment 4.17
A small dc motor, which is used to drive a model conveyer belt, is to be
controlled by a microcontroller. The microcontroller gives out a 6V signal when
an output bit is switched to logic 1. The speed of the motor must be varied
according to the loads which are being carried. for convenience, the speed is to
be reduced using pulse-width modulated control.
Output connections to the microcontroller are as follows.
Input Connection
Pin
7
6
5
4
3
2
1
0
Output Connection
Motor Anticlockwise
Motor Clockwise
Develop a short PBASIC procedure which could be used to drive the motor is a
clockwise direction with a mark-to-space ratio of 2:1.
symbol mark = 2
symbol space = 1
' define mark = 2
' define space = 1
init: let dirs = %00110000
' make pins 4-5 outputs
main: high 5
pause mark
low 5
pause space
goto main
'
'
'
'
'
motor on
wait mark time
motor off
wait space time
loop
Explain how you could alter the procedure to make the motor rotate in an anticlockwise direction, with the same mark-to-space ratio.
Replace the high/low 4 commands with high/low 5
Technological Studies: Systems and Control Teachers Notes (H) Outcome 3
50
TECHNOLOGICAL STUDIES
HIGHER
SYSTEMS AND CONTROL
TEACHER/LECTURER NOTES
AND SOLUTIONS TO ASSIGNMENTS
OUTCOME 4
Technological Studies: Systems and Control Teachers Notes (H) Outcome 4
1
Technological Studies: Systems and Control Teachers Notes (H) Outcome 4
2
Assignment 1.1
A microcontroller based monitoring system is used to monitor sound signals over
a period of time. It is found that the maximum voltage generated from the sound
signals is 6V. However the maximum voltage that may be fed into the
microcontroller system is 1.8V.
a) Draw a circuit diagram of a suitable signal conditioning system, based on
operational amplifiers, which will allow the signals to be monitored without
damaging the microcontroller system. Indicate the values of any components
used in your circuit.
Input Signal = 6V
Required output signal = 1.8V
Therefore Gain = output / input = 1.8 / 6 = 0.3
R2
6K6
Vout
Vin
R1
10K
0V
b) If the sound signal is fed into the microcontroller through an ADC which has a
voltage reference of 1.8V, write down the 8-bit binary pattern you would expect
from the ADC when the sound signal generates a voltage of 4.8V.
Clearly identify the least significant bit (LSB).
4.8V x 0.3 = 1.44V
1.8V gives a reading of 255
1.44V gives a reading of 1.44/1.8 * 255 = 204
204 = %11001100 (<LSB)
Technological Studies: Systems and Control Teachers Notes (H) Outcome 4
3
Assignment 1.2
The signal from a temperature sensing sub-system is processed by an ADC before
being read by a microcontroller. The ADC has a voltage reference of 1.8 volts
which produces a binary word of %11111111
a) What is an ADC and why is it required before processing by the
microcontroller?
An Analogue-to-Digital Converter (ADC) is a device which can convert analogue
quantities into digital signals. Temperature is an analogue quantity, but the
microcontroller only operates with digital signals. Therefore the ADC is require to
process the analogue temperature reading into a digital signal.
b) Calculate the binary word produced by the ADC at 200ºC, if the voltage signal
from the temperature sensing sub-system at this temperature is 1.2V.
Clearly identify the least significant bit (LSB).
1.8V gives a reading of 255
1.2V gives a reading of 1.2/1.8 * 255 = 170
204 = %10101010 (<LSB)
Technological Studies: Systems and Control Teachers Notes (H) Outcome 4
4
Assignment 1.5
TEMPERATURE
PROBE
SERIAL
ADC
MODULE
STAMP
CONTROLLER
DATALOGGER
MODULE
SERIAL
LCD MODULE
Build the circuit as shown in the diagram above.
a) Write a high level program in PBASIC that will continually monitor and
display the temperature of the water on the LCD.
main: gosub adcread
'Get the ADC reading
serout S_OUT,T2400,(254,128) 'Print on LCD line 1
serout S_OUT,T2400,("Temp = ",#data," ")
pause 1000
'Wait 1 second
goto main
'Loop
b)The temperature of the water should not be allowed to drop below 45 degrees
Celsius. Modify your PBASIC program so that the immersion heater (connected
to pin3) is automatically switched on when the water cools below the critical
temperature.
main: gosub adcread
'Get the ADC reading
serout S_OUT,T2400,(254,128) 'Print on LCD line 1
serout S_OUT,T2400,("Temp = ",#data," ")
if data < 45 then doon
low 3
goto main
doon: high 3
goto main
'Jump if temp low
'Heater off
'Loop
'Heater on
'Loop
Technological Studies: Systems and Control Teachers Notes (H) Outcome 4
5
Assignment 1.6
A local council has issued standard size "wheely bins" to all households so that
the dust carts can empty them automatically. The dustman simply clamps the
wheely bin onto a platform and then presses a switch. the platform then rotates
through 130 degrees as shown in the diagram. The platform stays in the
emptying position for 5 seconds and then returns to its original position, where it
triggers a micro switch on the rear of the dustcart. Platform movement is
controlled by a dc motor and gearbox.
130
0
STARTSWITCH
WHEELY
BIN
PLATFORM
MICRO-SWITCH
The process is controlled by a microcontroller. the angle of rotation of the
platform is sensed by a rotary potentiometer. The potentiometer is capable of
rotating 360 degrees from the starting position, and rotation between 0 and 360
degrees sends a proportional reading of between 0 and 255 via an ADC module
connected to the microcontroller.
Technological Studies: Systems and Control Teachers Notes (H) Outcome 4
6
Input Connection
Micro-switch
Start switch
Pin
7
6
5
4
3
2
1
0
Output Connection
Motor anti-clockwise (Lowers bin)
Motor clockwise (Raises bin)
(a) Calculate the analogue reading when the platform is 130 degrees from the
original position.
360 degrees gives a reading of 255
Therefore 130 degrees gives a reading of 130/360 * 255 = 92
Technological Studies: Systems and Control Teachers Notes (H) Outcome 4
7
(b) Draw up a flow chart which shows the control sequence for the emptying of
the wheely bin.
START
NO
START
SWITCH
YES
MOTOR
CLOCKWISE
NO
ANGLE
O
=130
YES
MOTOR
OFF
WAIT 5 Sec.
MOTOR
ANTICLOCKWISE
NO
ANGLE
=0O
YES
MOTOR
OFF
Technological Studies: Systems and Control Teachers Notes (H) Outcome 4
8
(c) With reference to your flow chart, write a high level program in PBASIC to
control sequence for the emptying of the wheely bin.
Assume use of a pre-written time delay sub-procedure called 'adcread' which will
return the analogue reading in a variable called 'data'.
main: if pin0 = 1 then loop
goto main
'Test start switch
'Else loop
loop: high 4
call adread
if data > 92 then up
goto loop
'Lift
'Read
'Test
'Else
up:
low 4
wait 4000
high 5
'Motor off
'wait for seconds
'Lower bin
lp2:
call adread
if data = 0 then main
goto lp2
'Read analogue value
'Test for down
'Else continue
bin
analogue value
for top
continue
(Note that the microswitch could also be used to detect the lower position)
Technological Studies: Systems and Control Teachers Notes (H) Outcome 4
9
Assignment 2.1
Suggest a suitable sampling frequency for each of the following monitoring
systems. In each case clearly explain why your sample frequency is appropriate.
a) Monitoring the temperature in a greenhouse.
Once every 10 minutes
Temperature will not change rapidly in this environment and so a slow sample rate
will do.
b) Monitoring the speed of an aeroplane.
Once every second
The speed could change rapidly. but the pilot would not check he instruments any
quicker than once per second.
c) Monitoring the heart rate of a premature baby in an incubator.
Ten times per second
A baby’s heart rate can beat up to 200 times per minute and so a high sample rate is
required.
d) Monitoring the temperature in a restaurant cold store.
Once every 10 minutes
Temperature will not change rapidly in this environment and so a slow sample rate
will do.
Technological Studies: Systems and Control Teachers Notes (H) Outcome 4
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Assignment 2.6
A datalogging system is to be used to record the temperature and light level in a
greenhouse over a period of 1 day.
TEMPERATURE
PROBE
MULTIPLEXER
SERIAL
ADC
MODULE
STAMP
CONTROLLER
DATALOGGER
MODULE
LIGHT
SENSOR
Build the apparatus as shown in the diagram above.
a) Explain why it is necessary to use a multiplexer in this situation.
Two analogue sensors are being used, and as there is only one ADC it is necessary to
use the multiplexer to 'switch' the ADC between the two analogue sensors.
b) Write a 'test' program in PBASIC that will record the temperature and light
levels over a 5 minute period.
Select a sampling frequency e.g. 5 seconds
Therefore number of readings = 5 mins * 12 readings = 60
main: for b10 = 1 to 60
' Start a for...next loop
low ADC_MPX
let page = 0
let address = b10
gosub adcread
gosub eewrite
'
'
'
'
'
select sensor 1
set EEPROM page
set EEPROM address
get analogue reading
write to EEPROM
high ADC_MPX
let page = 1
let address = b10
gosub adcread
gosub eewrite
'
'
'
'
'
select sensor 2
set EEPROM page
set EEPROM address
get analogue reading
write to EEPROM
pause 5000
next b10
' wait 5 seconds
' next loop
end
Technological Studies: Systems and Control Teachers Notes (H) Outcome 4
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c) Use the datalink program to retrieve the data from the datalogger module.
Using a spreadsheet draw a line graph to show the data recorded.
Datalogging Experiment
200
Value
150
Series1
100
Series2
50
46
41
36
31
26
21
16
11
6
1
0
Reading
Technological Studies: Systems and Control Teachers Notes (H) Outcome 4
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Assignment 2.7
A pet shop owner requires a data logging system that will allow him to monitor
the temperature of one of the large display aquariums in the shop.
The datalogger should record the temperature every ten minutes over a 24 hour
period. At the end of the period the owner wants to be able to print out a table of
results from the datalogger without having to use a host computer to analyse the
data.
(a) Draw a block diagram of the system.
TEMPERATURE
PROBE
SERIAL
ADC
MODULE
STAMP
CONTROLLER
DATALOGGER
MODULE
SERIAL
PRINTER
MODULE
Technological Studies: Systems and Control Teachers Notes (H) Outcome 4
PRINTER
13
(b) Draw up a flow chart which shows the control sequence for the datalogging
experiment.
START
SET COUNTER=144
STORE TEMP.
WAIT 10 Min.
ALL
DONE?
NO
YES
SWITCH
PUSHED?
NO
YES
PRINT
DATA
Technological Studies: Systems and Control Teachers Notes (H) Outcome 4
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(c) With reference to your flow chart, write a high level program in PBASIC to
perform the experiment.
24 hours with 10 minute sample rate = 24 * 6 = 144 readings
main: for b10 = 1 to 144
let page = 0
let address = b10
gosub adcread
gosub eewrite
for b11 = 1 to 10
pause 60000
next b11
next b10
loop: if pin3 = 1 then print
goto loop
'
'
'
'
'
Start a for...next loop
set EEPROM page
set EEPROM address
get analogue reading
write to EEPROM
' 10 loops of 1 minute
' wait 1 minute
' next loop
' next loop
' wait for switch
' else loop
print:
serout S_OUT,T2400,(STX)
' Start printing command
serout S_OUT,T2400,(TAB,"Reading",TAB,TAB,"Temp")
serout S_OUT,T2400,(CR,LF,LF) 'Next line.
for b10 = 1 to 144
'Start a for..next loop.
let page = 0
'Set page
let address = b10
'Set address
gosub eeread
'Read data from EEPROM.
serout S_OUT,T2400,(TAB,#address,TAB,TAB,#data)
serout S_OUT,T2400,(CR,LF) 'Next line
next b10
'Next loop.
serout S_OUT,T2400,(FF)
serout S_OUT,T2400,(ETX)
goto loop
'Print form-feed
'Send printer module to sleep
Technological Studies: Systems and Control Teachers Notes (H) Outcome 4
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Assignment 2.8
In a maternity hospital premature babies are cared for in incubators. The
temperature inside each incubator is continuously monitored.
A microcontroller based datalogging system is used to monitor the temperature
from four separate incubators by means of a 4-bit multiplexer.
a) With the aid of sketches, explain the function of a 4-bit multiplexer and
suggest why it is useful in this application.
CHANNEL 0
00
CHANNEL 1
01
CHANNEL 2
10
CHANNEL 3
11
ADC
A 4-bit multiplexer can be used to switch between 16 analogue sensors. In this
situation only four temperature sensors are used, so a 2-bit multiplexer (as shown in
the diagram) would be sufficient. However a 4-bit multiplexer allows space in the
system to add more sensors at a later date if required. The multiplexer allows all the
incubators to be monitored from a single ADC at one central position.
b) Suggest a suitable way of presenting the output from the datalogging system
for use by the nursing staff. Explain your answer.
A suitable method of presenting the output would be on an LCD display. This
situation does not to record the temperatures, but does need to set off an alarm if the
temperature goes too high or too low in any of the incubators. An LCD would be a
simple visual way that the nursing staff could monitor the temperature.
Technological Studies: Systems and Control Teachers Notes (H) Outcome 4
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