mechatronics project kit - getting started manual …mechatronics project kit getting started manual...

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Mechatronics Project Kit

Getting Started Manual

40-100-1

FeedbackFeedback Instruments Ltd, Park Road, Crowborough, E. Sussex, TN6 2QR, UK.

Telephone: +44 (0) 1892 653322, Fax: +44 (0) 1892 663719.email: [email protected] website: http://www.fbk.com

Manual: 40-100-1 Ed03 072001 Printed in England by Fl Ltd, CrowboroughFeedback Part No. 1160–401001

MECHATRONICS PROJECT KIT Preface

40-100-1 i

THE HEALTH AND SAFETY AT WORK ACT 1974

We are required under the Health and Safety at Work Act 1974, to make available to users of this equipment certain informationregarding its safe use.

The equipment, when used in normal or prescribed applications within the parameters set for its mechanical and electrical performance,should not cause any danger or hazard to health or safety if normal engineering practices are observed and they are used inaccordance with the instructions supplied.

If, in specific cases, circumstances exist in which a potential hazard may be brought about by careless or improper use, these will bepointed out and the necessary precautions emphasised.

While we provide the fullest possible user information relating to the proper use of this equipment, if there is any doubt whatsoeverabout any aspect, the user should contact the Product Safety Officer at Feedback Instruments Limited, Crowborough.

This equipment should not be used by inexperienced users unless they are under supervision.

We are required by European Directives to indicate on our equipment panels certain areas and warnings that require attention by theuser. These have been indicated in the specified way by yellow labels with black printing, the meaning of any labels that may be fixed tothe instrument are shown below:

CAUTION -RISK OFDANGER

CAUTION -RISK OF

ELECTRIC SHOCK

CAUTION -ELECTROSTATIC

SENSITIVE DEVICE

Refer to accompanying documents

PRODUCT IMPROVEMENTS

We maintain a policy of continuous product improvement by incorporating the latest developments and components into our equipment,even up to the time of dispatch.

All major changes are incorporated into up-dated editions of our manuals and this manual was believed to be correct at the time ofprinting. However, some product changes which do not affect the instructional capability of the equipment, may not be included until it isnecessary to incorporate other significant changes.

COMPONENT REPLACEMENT

Where components are of a ‘Safety Critical’ nature, i.e. all components involved with the supply or carrying of voltages at supplypotential or higher, these must be replaced with components of equal international safety approval in order to maintain full equipmentsafety.

In order to maintain compliance with international directives, all replacement components should be identical to those originallysupplied.

Any component may be ordered direct from Feedback or its agents by quoting the following information:

1. Equipment type

3. Component reference

2. Component value

4. Equipment serial number

Components can often be replaced by alternatives available locally, however we cannot therefore guarantee continued performanceeither to published specification or compliance with international standards.

MECHATRONICS PROJECT KIT Preface

ii 40-100-1

DECLARATION CONCERNING ELECTROMAGNETIC COMPATIBILITY

Should this equipment be used outside the classroom, laboratory study area or similar such place for which it is designed and sold thenFeedback Instruments Ltd hereby states that conformity with the protection requirements of the European Community ElectromagneticCompatibility Directive (89/336/EEC) may be invalidated and could lead to prosecution.

This equipment, when operated in accordance with the supplied documentation, does not cause electromagnetic disturbance outside itsimmediate electromagnetic environment.

COPYRIGHT NOTICE

© Feedback Instruments Limited

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by anymeans, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of Feedback Instruments Limited.

ACKNOWLEDGEMENTS

Feedback Instruments Ltd acknowledge all trademarks.

IBM, IBM - PC are registered trademarks of International Business Machines.

MICROSOFT, WINDOWS 95, WINDOWS 3.1 are registered trademarks of Microsoft Corporation.

MPLAB and PIC are registered trademarks of Microchip Technologies Inc.

Meccano is a registered trademark of Meccano SA.

MECHATRONICS PROJECT KIT Contents

40-100-1 TOC 1

TABLE OF CONTENTS

1 Introduction 1-1

1.1 Modules 1-2

1.2 Equipment Required to Complete Project 1-4

1.3 Battery Charging 1-5

2 Microchip Resources 2-1

3 Mechanical Components 3-1

3.1 Chassis 3-1

3.2 Steering 3-1

3.2.1 Ackermann Steering 3-1

3.2.2 Controlled Single Wheel 3-2

3.2.3 Castor Wheel 3-2

3.3 Drive Motor 3-3

3.3.1 Single Motor 3-3

3.3.2 Dual motor 3-4

4 Description of the Electronic Circuitry 4-1

4.1 Motor Drive 4-1

4.2 Optical Wheel Rotation Sensors 4-2

4.3 Magnetic Speed Sensors 4-3

4.4 Temperature Sensor 4-4

4.5 Back EMF Sensing 4-5

4.6 Stepper Motor Drive Board 4-6


TOC 2 40-100-1

4.7 Optical Sensors 4-6

5 Programming Guidelines 5-1

5.1 Registers 5-2

5.2 Timers 5-2

5.3 Interrupts and the ISR 5-2

5.4 Stepper Motor Configuration 5-3

5.5 PIC Microprocessor Pin-out 5-4

5.6 Downloading and Running a Program 5-5

6 Sample Programs for each Module 6-1

6.1 Pulse Width Modulation (PWM) 6-2

6.1.1 Wiring Required 6-2

6.1.2 Program 6-2

6.2 Stepper Control 6-5


6.2.2 Program 6-5

6.3 Line Sensors 6-11


6.3.2 Program 6-11

6.4 Optical/Magnetic Speed Sensing 6-17


6.4.2 Program 6-17

6.5 Temperature Sensing 6-21

6.5.1 Wiring Requirements 6-21

6.5.2 Program 6-21

6.6 Back EMF Sensing 6-24

6.6.1 Wiring Requirements 6-24

6.6.2 Program 6-24


40-100-1 TOC 3

7 Solutions 7-1

7.1 3D Models/Photos 7-1

7.2 Assembly 7-2

7.3 Trouble-Shooting 7-3

7.4 The Track 7-3

7.5 Program 7-4


TOC 4 40-100-1

Notes

Chapter 1MECHATRONICS PROJECT KIT Introduction

40-100-1 1-1

1 Introduction

Mechatronics allows the integration of mechanics, electronics and computer technologiesto enhance the performance of products, systems and processes. Typical products thatuse the principles of mechatronics are camcorders, computer disk drives, industrial robotsand automobiles.

The Mechatronics Project Kit, shown in Figure 1-1, provides the means for students todesign and build a self-guided vehicle (buggy) from a set of modules, including two drivemodules, two steering and one jockey wheel solutions and a microcontroller (PIC). Whencompleted, the autonomous buggy is able to follow a track using infra red sensors. Thereare a number of different constructions possible with the components supplied in the kitbut, if required, the hole pitch and all spacing is Meccano compatible so the kit can beexpanded with any Meccano kit.

Figure 1-1: Mechatronics Kit

CHAPTER 1MECHATRONICS PROJECT KIT Introduction

1-2 40-100-1

This project has been designed to combine all aspects of engineering, includingmechanical, electrical, electronic, communications and software programming, into onedevelopment product. The buggy will be able to follow a track of insulation tape that hasbeen laid on the floor; the type of tape that is required depends on the type of floorcovering. The floor needs to be of a single colour, which is either infrared reflective ornon-reflective; with a reflective floor, a non-reflective tape is required and vice-versa for anon-reflective floor.

This is a fundamental guide to getting started on the mechatronics buggy project anddoes not cover every aspect of the design that is needed to complete the project as thereis many different outcomes possible.

1.1 Modules

The kit comprises of a number of different modules that can be used to construct awheeled vehicle that will be capable of following a predetermined circuit on the laboratoryfloor. These parts are supplied unassembled in order for the students to define theirparticular requirements and assemble the necessary components. The modules are:

1.1.1 Microprocessor Control Board

All inputs and outputs are available via screw terminal blocks and the board includes:

• Powerful Microchip PIC16F877 controller running at 10 MHz, with 368´8 bytesof data memory, 256´8 bytes of EEPROM data memory and 8K´14 bytes ofFLASH program memory. Programming of the PIC is achieved through theMicrochips own programming environment called MPLAB (see MicrochipResources).

• High performance RISC CPU with a 35 single-word instruction set and aninterrupt capability of up to 14 sources.

• On-board low dropout voltage regulation allows the unit to be powered from anunregulated 5.5V to 18V dc, via a 2.1 mm power inlet.

• Regulated +5V dc can be sourced from several screw terminal connectors.

• RS-232C serial port for downloading program to the on-board PIC, via a 9-wayD-type connector, which can also be used as a stand-alone serialcommunications port.

• Synchronous serial port (SSP) with I2C (master/slave).

• Up to 8 analogue input channels with a 10-bit analogue-to-digital converter.

• All inputs and outputs are available via plug-able screw terminal blocks.

• Digital I/O ports are also available via 26-way and 40-way IDC.


40-100-1 1-3

1.1.2 DC Motor Drive Circuitry

This circuitry is capable of driving an interchangeable single or dual motor arrangementand has the following sensors:

• Wheel speed via optical or magnetic sensors.

• Temperature.

• Motor speed through back emf.

1.1.3 Stepper Motor Drive Board

This board controls either the:

• Ackermann steering module.

• Single wheel steering module.

The board also has circuitry for an optical sensor to detect when the stepper motor ispointing the steering in a straight line.

1.1.4 Trolley Wheel

The trolley wheel uses the same mechanism as the single wheel but with no motor.

1.1.5 Optical Sensor Boards

There are six individual infrared reflective sensor boards that the students need toexperiment with to find the optimum sensing configuration for following a 19 mm tape.

1.1.6 Three Types of Chassis

There are three types of chassis available as follows:

• Short rectangle

• Long rectangle

• Long rectangle chassis tapered at one end.

1.1.7 Ni-Cd 7.2V 1800mAh battery.

1.1.8 A selection of brackets


1-4 40-100-1

1.2 Equipment Required to Complete Project

• Small flat blade screwdriver

• Small Philips screwdriver

• 4 mm, 5.5 mm and 7 mm spanner or nutdriver

• Multiple coloured wire

• Wire cutter

• Wire stripper

The Figure 1-2 shows the main configurations that are possible with the kit. The finaloption can be either front or rear wheel drive.

Figure 1-2: Mechatronics Kit Main Choices

Choice of twosteering systems

Choice of twodrive systems

Choice of three baseplates with the PICmicro controller on µµµµ Processor

Single DC Motorwith Differential

Dual DC MotorDirect Steering

AckermannSteering

Stepper motorcontrolled pivot

Wheel

JockeyWheel

Base1 Base2 Base3

Stepper motorcontrolled pivot

Wheel

AckermannSteering

Choice of threesteering systems

Sensor feedbackfrom each module


40-100-1 1-5

1.3 Battery Charging

The battery supplied in the kit is a rechargeable nickel-cadmium battery which can becharged up using the 12 V dc power supply and charge cable provided as shown inFigure 1-3.

The method of charging used in this application is that of a constant current sourcedelivering 1 A until the battery is nearly charged then the charging current starts toreduce.

The charge-time that the battery requires depends on the amount of discharge duringuse; when discharged to a level that will not power the motors, the battery takes between1.5 and 2 hours to charge.

Note:

The charge-time should not be exceeded, as permanentdamage to the battery will occur.

Figure 1-3: Battery Charging Connections

12 V dc powersupply connected

to the mains supplyBatteryIn-line

currentlimiter


1-6 40-100-1

Notes

Chapter 2MECHATRONICS PROJECT KIT Microchip Resources

40-100-1 2-1

2 Microchip Resources

The PIC assembler used is Microchip’s own MPLAB with the latest versions freelydownloadable from their website (www.microchip.com). Also at this site are the latestrevisions of the MPlab User Guide, PIC REFERENCE MANUAL and the PIC 16F87XDatabook, all free to download in pdf format. Another area of the site is the KnowledgeBase/Frequently Asked Questions page that can provide helpful information on variousproblems encountered. Microchip also offer a wide range of application notes for manydifferent tasks that the PIC can be programmed to do.


2-2 40-100-1

Notes

Chapter 3Construction of the

MECHATRONICS PROJECT KIT Mardave Components

40-100-1 3-1

3 Mechanical Components

3.1 Chassis

There are three different chassis to choose from and each gives the system a differentcharacteristic; the alternatives are shown in Figure 3-1.

Figure 3-1: Chassis

3.2 Steering

There are three standard options for the steering, which are described below. However, ifyou can design any other method of steering from the parts provided which give a betterperformance, this will show good initiative and design skills.

3.2.1 Ackermann Steering

This is a system that uses two wheels to steer with, linked together by two arms that areconnected to a plate attached to a stepper shaft as shown in Figure 3-2. The wayAckermann steering works is that the inside wheel has a greater turning angle for a tighterradius of the corner, thus allowing the wheels to have a differential cornering speed. Thisarrangement allows for a lot of grip whilst cornering but the turning circle is the smallest.

To assemble the Ackermann steering mechanism to the stepper motor, proceed asfollows:

1. Bolt the base plate to the Z bracket.

2. Using an M2.5 screw, attach the brass boss to the steering link and then attach thetwo track rods to the steering link plate.

3. Bolt the stepper motor to the Z bracket and slide on the brass boss, then tighten thegrub screw so that the steering linkage plate is vertical

4. If the wheels are not correctly aligned, remove track rod and either tighten or loosen to



3-2 40-100-1

suit your requirements. For correct operation of the Ackermann steering, the shaft ofthe stepper motor needs to be facing backwards so that the inner wheel has a greaterturning angle.

Figure 3-2:: Ackermann Steering Assembly

3.2.2 Controlled Single Wheel

As shown in Figure 3-3, this set up uses a single wheel that is mounted on a bracket,which can be fastened to the shaft of the stepper motor via a grub screw. Thisarrangement has a full 360° controllable rotation, which gives a fast accurate responsewith a smaller turning circle, but at the cost of some speed.

Figure 3-3: Single Wheel Kit

3.2.3 Castor Wheel

This utilises the same wheel and bracket arrangement as the controlled single wheel, but

Triangular arms

King pin

Steering arm

Ball screw

Base plate

Brass boss

Steering link

Track rod

Plastic ballsocket

Z plateStub axle



40-100-1 3-3

replaces the stepper motor with a caster block that allows the shaft to freely rotate. Thisarrangement is used when there is a different method of steering, e.g. twin motor drivingthe two driving wheels independently.

3.3 Drive Motor

There are two options for driving the buggy, both using the same control board, which hasthe capability of driving two dc motors independently with Pulse Width Modulation (PWM)signals. Both options attach motors onto the underside of the control board.

The tyres are fitted to the wheels by first turning the them inside out then rolling the tyreover the rest of the wheel.

3.3.1 Single Motor

This system uses a single motor and a mechanical slip differential as shown in Figure 3-4.The method of constructing this arrangement is described below:

1. Join the two motor mount halves together using a 16 mm self-tap screw. Hold the twohalves down on a flat surface when tightening to ensure correct alignment.

2. Press fit the two plastic rear axle bushes into the motor mounts.

3. Slide the rear axle with differential through the bushes so that the motor will be at therear, and slide the drive spacer onto the other end.

4. Attach the motor to the mounting brackets with two M3x12 screws and lightly tighten,attach motor gear to shaft and tighten grub screw. Then adjust the motor position foralignment of the two gears, so that the wheel spins freely.

Figure 3-4: Single Motor Arrangements

5. Using the M3x25 screws, screw the drive block on to the differential block.

6. Insert the black plastic hex wheel drive onto the two locating pins on the drive blockand the wheel onto the hex drive; then loosely tighten nut. Repeat similarly on other

Optical sensing tapeon differential block

Optical sensing tapeon drive block

Differentialaxle gear

Motor mounts

Differentialspacer

Axle



3-4 40-100-1

side.

7. The motor mounts are then screwed to the motor drive board using flanged head self-tap screws and the magnetic sensor is screwed up so that there is a 1-2 mm gapbetween the gear and the sensor.

3.3.2 Dual motor

This system uses two motors running from two sets of control signals for independentdrive and direction control. The method of constructing this arrangement is describedbelow:

1. Attach the motors to the mounting brackets with two screws and lightly tighten, attachmotor gear to shaft and tighten grub screw.

2. Fit the axle bushes to the motor bracket and slide the axle through.

3. Fit two washers to each side then slide the collar on.

4. Using the M3x20 and a nut, join together the drive block and the Axle gear then slideon the axle. The wheels are fitted in the same way as for the differential drive.

5. Attach the brackets to the board (the motor position will need adjusting so that thegears mesh together evenly) and align the magnetic sensor with the centre of thegear.

Figure 3.5: Dual Motor Arrangements

Axle gear

Motor gear

Optical sensing tape on drive block

Motor mount

Axle

Axle gear Optical sensing tape on drive block

Chapter 4MECHATRONICS PROJECT KIT Description of the Electronic Circuitry

40-100-1 4-1

4 Description of the Electronic Circuitry

The pots on the motor drive board have been factory pre-set to specific values andaltering these will change the feedback characteristics and result in inaccuratemeasurements.

The pots on the optical sensor boards are for adjustment of the sensitivity of the opticalswitch for different heights.

4.1 Motor Drive

Three signals are required from the microcontroller to drive the motor circuit, PWM,direction and bi/uni. These are injected into a GAL with the following circuit programmed:

Figure 4-1: GAL Logic

Figure 4-1 controls the firing sequence of the MOSFET H-bridge for the dc motor, whichcan be seen in Figure 4-2.

Bi/Uni

Fwd/Rv

PWM

C

A

B

D


4-2 40-100-1

Figure 4-2: Motor Drive Circuit

4.2 Optical Wheel Rotation Sensors

As shown in Figure 4-3, this is a simple circuit that switches the transistor on when theoptical sensor output passes the transistor threshold. Adjusting the variable resistormoves this threshold so that the transistor switches and therefore tweaks the sensitivity.

Figure 4-3: Optical Wheel Rotation Sensor Circuit

AK

CE

IC11OPTOREFLECTOR

C22100n

RV5100K

R50220R R51

2K2

R521K0

0V

+5V

[ ISTS708 ]

TR9ZTX108C

D10

BAX13

B

TR2IRLZ24N

TR12SJ174

M1

MOTOR

R21

4K7

D3UF4002

R204K7

D2UF4002

+ C9470u

TR4IRLZ24N

TR32SJ174

D4UF4002

D5UF4002

R22

4K7

R25

4K7

7.2V

7.2V

0V

35V

3 21

IC3A

4049

7 61

IC3C

4049

5 41

IC3B

4049

14 151

IC3F

4049

9 101

IC3D

4049

11 121

IC3E

40490V

C

A

B

D


40-100-1 4-3

4.3 Magnetic Speed Sensors

The magnetic sensor circuit (Figure 4-4) has a filter on the input to reduce the affect ofany noise that might be picked up from the motor; this is then ac coupled and biased up to2.5 V (half the supply) and amplified with a gain of 52. The signal is then passed into acomparator with the other input being 2.5 V. The output of this circuit will either be high orlow.

Figure 4-4: Magnet Sensor Circuit

R510K

R6

510K

3

21

411

IC1ALMC660CN5

67

IC1BLMC660CN

AV1

AV2

R110K

R41M0

0V

R710K

R3100K

MAGNETICSENSOR

R810K

R2100K

C3100n

C2100n

C110n

C410n0V

0V

+5V

+5V

0V

0V

+5V

0V


4-4 40-100-1

4.4 Temperature Sensor

The temperature sensor circuit is shown in Figure 4-5. The maximum voltage out of thetemperature sensor is 1.75 V with a temperature of 125°C, the motor will not reach thistemperature as the output signal is amplified by a factor of four. This means that at thelimit of the analogue signal (5 V), the temperature of the case of the motor would be 75°C,which is higher than the case of the motor will go.

The formula for calculating the temperature from the 10-bit conversion is:

500mVC)TempC(10mV/Vout

sensortheofoutevoltaggainamp

XVout

PICtheintoltagevo1024

5convertionbinaryofnumberdecimalX

oo +×=

=

×=

Figure 4-5: Temperature Sensor Circuit

3

21

411

IC4ALMC660CNR30

3K3

R31

3K3

+5V

0V

0V

+VS

1

VO 2

GN

D3

IC6LM50BIM3

0V

+5V

TEMPERATURESENSOR

RV220K


40-100-1 4-5

4.5 Back EMF Sensing

The back EMF is only available under certain conditions, these being that the bi/uni signalneeds to be set to bi and the back EMF available signal is low.

Figure 4-6: Back EMF Sensing Circuit

The circuit above samples the back EMF signal during the pwm off period via ananalogue switch, which is controlled by the back EMF available signal. The capacitor thenholds the average value, which is amplified to give a range between 0 and 5 volts for thePIC to read during pwm on period. The back emf signal has a dc offset to take intoaccount when the PIC converts the analogue signal. This motor offset is 0.5 volts.

10

98

IC4CLMC660CN

12

1314

IC4DLMC660CN

C10100n

R2610K 0V

R272K2

0V

R2310K

R24

10K

RV120K

0V

2 1

7SW2ASW MAX323


4-6 40-100-1

4.6 Stepper Motor Drive Board

As shown in Figure 4-7, the driving signals for the stepper motor are buffered intoMOSFETS that provide the switching for the coils in the motor. The inputs to this circuitneed to have 100k ohms pull-down resistors otherwise they float high and cause anincorrect stepping sequence.

Figure 4-7: Stepper Motor Drive Circuit

4.7 Optical Sensors

The individual reflective sensor boards use the same basic circuit as the optical wheelrotation sensor. The two changes are the addition of an LED to have a visualrepresentation of which sensor the tape is underneath, and resistor R50 has beenreduced to 68 ohms, this will increase the drive current to the infra red LED.

There is also a board that contains a slotted sensor, as this type of optical switch has abetter coupling and therefore only two other components are needed to operate thedevice. This can be used for the detection of the steering pointing straight ahead on theAckermann steering.

R4100K

R3100K

R1100K

R2100K

TR1IRLD014

TR2IRLD014

TR3IRLD014

TR4IRLD014

7 6IC1C 4050

9 10IC1D 4050

11 12IC1E 4050

14 15IC1F 4050

0V

0V

Signals toStepper MotorSignals from

microprocessor

5V on board

Chapter 5MECHATRONICS PROJECT KIT Programming Guidelines

40-100-1 5-1

5 Programming Guidelines

A manual is provided by Abitec on the PIC board layout and pic877 software fordownloading your program, which includes a full explanation and an example.

The programming environment has its own simulator and for this a project needs to be setup. To set up the environment mode; open MPlab, select project and new project, entername and select OK, under project files select the file and then select node properties(needs to be set up first by selecting options and development mode). A window will openand, in that window, make sure that MPLAB-SIM simulator is selected and the processorselected is the PIC16F877.

The Figure 5-1 shows a typical workstation for programming the buggy.

Figure 5-1: Mechatronics Kit Programming Environment

The beginning of any program needs a directive statement so that the compiler can linkthe necessary source files for the particular processor used.

All the instruction set and detailed methods of programming are contained in the PICmanual. In this chapter, the main considerations that need to be known are highlighted.

Register bits can be accessed through their bit number (e.g. STATUS,2) or through theirbit name (e.g. STATUS,Z), both these instructions look at the zero flag, z. When adestination field is required after the operand, the codes zero or one used to determineaccumulator or file can be replaced with the letters w (accumulator) or f (file).


5-2 40-100-1

5.1 Registers

The STATUS register holds key information about which memory bank the program islooking at and what happened to the accumulator in the previous instruction, (carry andzero flags). The INTCON register contains various interrupt and enable bits and flag bitsfor the external interrupts and portb interrupt on change. The PIE1 register contains theenable bits for the peripheral interrupts, with the corresponding flag bits in the PIR1register.

Other useful registers include ADCONO, ADCON1 – for analogue to digital conversioncontrol and analogue pin select. ADRESH, ADRESL for the ADC result.

The CCP registers are used for the control of the pulse width modulation and interrupts,with timer 2 being used for the PWM frequency and associated registers being PR2 andTCON2.

Other useful registers include TRIS* (* = A, B, C, D or E) data direction and some controlfor the ports.

A list of all registers and their memory locations can be found in the PIC Manual, Chapter2. Specific control bits for each individual register can also be found in the relevantchapter of the PIC manual.

5.2 Timers

Timer 2, which is used for the PWM timing, needs to be set up with the maximum amountof prescale and a maximum value in the timer register in order to scale down the controlfrequency to the motors, as the motor has a low optimum control frequency. The prescaleis set in the T2CON register bits 1 and 2 and the period is set in PR2 register. The controlof the mark to space ratio is achieved by a 10 bit binary number that can vary from0-100%, the lower two bits can be found in CCP1CON bits 5 and 4 and the upper 8 bitsare stored in the CCPR1L register.

Full explanations of each timer can be found in the PIC Manual, Chapters 5, 6 and 7.

5.3 Interrupts and the ISR

The use of interrupts is a personal choice as they are not necessary but useful in longprograms with different tasks running sequentially (some tasks could miss a vital piece ofinput data required). Because interrupts can occur at any time, the program might be inthe middle of a calculation. Therefore, the w register and the STATUS register need to besaved first so that when the ISR is finished, the program registers can be returned to theiroriginal state. More details can be found in Chapter 12.10 of the PIC16F87X ReferenceManual.


40-100-1 5-3

5.4 Stepper Motor Configuration

Stepper motor colour code for the wires to each phase should be:

A B C D E F

440-420 White Brown Red Yellow Brown Blue

Step Sequence

Step A B A| B|

1 b a

2 a a

3 a a

4 a a

This step sequence is required for continuous rotation of the shaft.

Note:When using the Ackermann steering at its maximum angle,

no further steps should be made as this could cause damage toeither the steering mechanism or to the motor.

F E D

C

B

AM A

A|

B

B|


5-4 40-100-1

5.5 PIC Microprocessor Pin-out

The PIC microprocessor pin-out is shown in Figure 5-2.

Figure 5-2: PIC Microprocessor Pin-out


40-100-1 5-5

5.6 Downloading and Running a Program

Proceed as follows:

1. Connect the cable to a free serial port on the PC and the port on the PIC board.

2. Set the Prg/Run switch to the Prg position.

3. Apply power to the board; the yellow LED is lit.

4. Start the software. This should automatically detect the PIC board on the serial port itwas connected to. The status bar at the bottom of the window details the state of theconnection.

5. If a program is in the PIC, select ‘Program’ menu and ‘Erase All’.

6. Select the ‘file’ menu and ‘load’.

7. Locate and select the .HEX file you wish to program.

8. Select ‘Prog. and Configure’ radio button. The ‘Program Selected Range’ radio buttonshould be selected, the amount of memory is automatically set for the required size ofprogram.

9. Select the ‘Program’ menu and the ‘Program’ command; the red and green LED’s arelit. The bar along the bottom of the screen shows the progress of the download.

10.When the download is complete, switch the Prg/Run switch to Run.

11.Press the Start/Stop button to start the program; the green LED is lit.

12.Press the Start/Stop button to stop the program.

13.For reprogramming, set the Prg/Run switch to the Prg position and return to step 5.


5-6 40-100-1

Notes.

Chapter 6MECHATRONICS PROJECT KIT Sample Programs for each Module

40-100-1 6-1

6 Sample Programs for each Module

The following programmes were written for a buggy with the single-motor mechanicaldifferential drive, Ackermann steering and the three reflective sensors mounted from thefront at a distance of 14 mm apart and 8 mm off the floor.

Student Tips

1. For some of these programs you will need to construct a bank of 8 and a bank of 2LED’s, the basic circuit for these that can be built on is

2. Another useful board to make would be an 8-pin DIL switch package to simulate inputsof 0 V and 5 V, for debugging purposes.

O/P from330R


6-2 40-100-1

6.1 Pulse Width Modulation (PWM)

The PWM frequency that is required for optimal motor response is very low, and with thissystem the lowest pwm frequency possible is 600 Hz.

6.1.1 Wiring Required

PIC board RC2 → motor board PWM 1

PIC board RC3 → motor board FD/RV 1

PIC board RC4 → motor board BI/UNI 1

6.1.2 Program

; Mechatronics project

; PIC used 16f877

; this program turns the wheels at a constant speed in one direction for about4 ; seconds and then in the other direction for about 4 seconds using the PWM; timer

;

;

; file name pwm.asm

; date last modified 04/02/2000

; written by Martyn Langfield

;

;***************************************

; directive statement

;***************************************

list p = 16f877

include <p16f877.inc>

;***************************************

; allocate memory locations

;***************************************

delay_hi equ H'31'

delay_lo equ H'32'

TMP2 equ H'33'

count equ H'34'

count2 equ H'35'


40-100-1 6-3

;***************************************

;vector settings

;***************************************

ORG H'00'

goto start

ORG H'23'

;****************************************

;initialisation

;****************************************

start

movlw H'FF'

BSF STATUS,RP0 ; select bank1

movwf PR2 ; pwm period = FF

movlw H'20' ; value for duty cycle

BCF STATUS,RP0 ; bank 0

movwf CCPR1L ; duty cycle location

bsf CCP1CON,5

bcf CCP1CON,4 ; lsb of the 10bit duty cycle


bcf INTCON,7 ; disable global interrupts

movlw H'00'

movwf TRISC ; portc output

bsf PIE1,1 ; TMR2 to PR2 Match Interrupt Enable bit


bsf T2CON,1 ; timer 2 prescale to 16

bsf T2CON,2 ; TIMER 2 ON

bsf CCP1CON,3

bsf CCP1CON,2 ; SETS BITS FOR PWM MODE

movlw H'FF'

movwf count ; set up count with value FF hex

movlw H'05'

movwf count2 ; set up hi count with value 05 hex


6-4 40-100-1

;**************************************

;main program

;**************************************

main

bcf PORTC,4 ; set control method bi/uni

movf TMR2,0 ; READ TIMER2

movwf TMP2

btfsc PIR1,1 ; CHECK IF INTERRUPT FLAG SET

call increment ; yes call subroutine

goto main ; no

;************************************

;subroutines

;************************************

increment

bcf PIR1,1 ; clear interrupt flag

decfsz count,1 ; decrement count and skip when zero is reached

return

decfsz count2,1 ; decrement count2 and skip when zero is reached

return

goto toggle

return

toggle

movlw H'FF'

movwf count ; load the value of ff to the register count

movlw H'05'

movwf count2 ; load the value of 05 to the register count 2

btfsc PORTC,3 ; test bit 3 portc

goto clear ; if clear goto clear

bsf PORTC,3 ; set bit 3 portc

movlw H'20'

movwf CCPR1L ; set pwm period

return

clear

bcf PORTC,3 ; clear it 3 portc

movlw H'20'

movwf CCPR1L ; set pwm period


40-100-1 6-5

return

END

6.2 Stepper Control


PIC board RD0 → stepper board B′

PIC board RD1 → stepper board A′

PIC board RD2 → stepper board B

PIC board RD3 → stepper board A

PIC board RB0 → slotted sensor board

6.2.2 Program

;Mechatronics project

;PIC 16f877

;this program moves the steering to one limit then finds the centre

;then moves to either extreme and back to centre position and checks if centre;position reached

;

;file name centre.asm

;date last amended 22/03/2000

;written by Martyn Langfield

;

;*****************************************

;directive statement

;*****************************************

list p = 16f877


;*****************************************

;allocate memory locations

;*****************************************

big equ H'30'

delay_hi equ H'31'

delay_lo equ H'32'


6-6 40-100-1

tmp equ H'33'

tmp2 equ H'34'

count equ H'35'

count2 equ H'36'

;****************************************

;vector settings

;****************************************

ORG H'00'

goto start

ORG H'23'

;****************************************

;initialisation

;****************************************

start

clrf PORTA

clrf PORTB

clrf PORTC

clrf PORTD

clrf PORTE

movlw H'00'


movwf TRISD ; setup o/p ports

movwf TRISC

movlw H'FF'

movwf TRISB ; setup i/p port


movlw H'05'

movwf count ; setup count with 05 hex

clrf count2 ; setup count2 with 00 hex

clrf tmp

clrf tmp2

;**************************************

;main program

;**************************************


40-100-1 6-7

main

btfsc PORTB,0 ; check if centre sensor is ‘1’

call find ; if not call find

drive

call delay

call step_right

movf count2,w ; move count2

movwf tmp ; to tmp register

movlw B'00100000' ; load w reg with value

subwf tmp,f ; sub value of w reg from tmp

btfss STATUS,Z ; test for zero flag

goto drive ; no then repeat

drive2

call delay

call step_left






goto drive2 ; no then repeat

call delay

btfsc PORTB,0 ; test for centre flag on input

call find ; no flag then find

bsf PORTC,5 ; centre found set bit 5 portc

call ldelay

drive3

call delay

call step_left





drive4

call delay

call step_right


6-8 40-100-1







call delay

btfsc PORTB,0 ; test for centre flag on input

call find ; no flag then find

bsf PORTC,5 ; centre found set bit 5 portc

call ldelay

goto drive

;************************************

;subroutines

;************************************

find

call ldelay

call right

step

btfsc PORTB,0 ; test if centre

goto inc ; no, then goto inc

call found ; yes, then goto found

return

inc

call step_left

call ldelay

goto step

right

movlw b'00001001' ; step steering to limit

movwf PORTD

call delay

movlw b'00001100'

movwf PORTD

call delay

movlw b'00000110'

movwf PORTD


40-100-1 6-9

call delay

movlw b'00000011'

movwf PORTD

call delay

decfsz count,1

goto right

movlw H'09'

movwf count

return

step_right

bcf PORTC,5 ; clear steering straight flag

movf PORTD,W ; reed portd to w reg

movwf tmp2 ; move w reg to tmp2

rrf tmp2,F ; rotate right tmp2

btfsc STATUS,C ; test for overflow

bsf tmp2,3 ; if yes set bit 3 in tmp2

movf tmp2,w ; move tmp2 to w reg

movwf PORTD ; move w reg to portd

incf count2,f ; increment count2

return

step_left

bcf PORTC,5 ; clear steering straight flag

bcf STATUS,C ; clear carry flag

movf PORTD,W ; reed portd to w reg

movwf tmp2 ; move w reg to tmp2

rlf tmp2,F ; rotate left tmp2

btfsc tmp2,4 ; test for overflow in tmp2

bsf tmp2,0 ; if yes set bit 0

bcf tmp2,4 ; clear bit 4

movf tmp2,w ; move tmp2 to w reg

movwf PORTD ; move w reg to portd

decf count2,f ; decrement count2

return

found

movlw B'00010000'

movwf count2 ; load count2 with centre count

bsf PORTC,5 ; output 1 on portc bit5 to signal centre located


6-10 40-100-1

call ldelay ; long delay

call ldelay

call ldelay

call ldelay

return

delay

movlw H'00'

movwf delay_lo

movlw H'70'

movwf delay_hi

outer

inner

incfsz delay_lo,1

goto inner

incfsz delay_hi,1

goto outer

return

ldelay

movlw H'00'

movwf delay_lo

movlw H'00'

movwf delay_hi

movlw H'FA'

movwf big

extra

outer2

inner2

incfsz delay_lo,1

goto inner2

incfsz delay_hi,1


40-100-1 6-11

goto outer2

incfsz big,1

goto extra

return

END

6.3 Line Sensors


PIC board RD7 → sensor board 3



PIC board RD0 → stepper board B′

PIC board RD1 → stepper board A′

PIC board RD2 → stepper board B

PIC board RD3 → stepper board A

6.3.2 Program


;PIC 16f877

;To look at a line and move the steering accordingly

;

;file name line3s.asm



;

;******************************************


;******************************************

list p = 16f877



6-12 40-100-1

;******************************************


;******************************************

delay_hi equ H'31'

delay_lo equ H'32'

TMP equ H'33'

count equ H'34'

rstcount equ H'35'

lstcount equ H'36'

;******************************************

;vector settings

;******************************************

ORG H'00'

goto start

ORG H'23'

;****************************************

;initialisation

;****************************************

start


clrf PORTA ; clear ports

clrf PORTB

clrf PORTC

clrf PORTD

clrf PORTE


movlw H'00'

movwf TRISB ; PORTB OUTPUT


movwf TRISE ; porte output

movwf TRISA ; porta output

movlw B'11110000'

movwf TRISD ; portd 0-3 O/P 4-7 I/P


40-100-1 6-13

BCF STATUS, RP0 ; bank 0

movlw B'00010100'

movwf count ; setup count for maximum steering travel

movlw H'05'

movwf rstcount ; initial steering count right

movlw H'0A'

movwf lstcount ; initial steering count left

call steer ; call subroutine to straighten steering

;**************************************

;main program

;**************************************

main

btfss PORTD,6 ; test centre line sensor

goto main ; yes repeat

btfss PORTD,7 ; test left sensor

goto left1 ; yes goto left1

btfss PORTD,5 ; test right sensor

goto right1 ; yes goto right1

goto main ; no sensor on begin test again

;************************************

;subroutines

;************************************

right1

movf count,w ; move count to w reg

btfsc STATUS,Z ; test if zero flag set

goto main ; if yes go to read sensors

decf count,f ; decrement count

rlf PORTD,w ; shift left portd and put in w reg

movwf TMP ; move w reg to tmp

btfsc TMP,4 ; test for over flow

goto under1 ; yes


6-14 40-100-1

bcf TMP,0 ; clear bit 0 of tmp

movf TMP,0 ; move tmp to w reg

movwf PORTD ; output stepper control signal

call delay

goto main

under1

bcf TMP,4 ; clear bit 4 in tmp

bsf TMP,0 ; set bit 0 in tmp

movf TMP,0 ; move tmp to w reg


call delay

goto main

left1

movf count,w

addlw B'11011000' ; add a number to the w reg so that when the; steering is at its limit a zero condition is met

btfsc STATUS,Z ; test zero flag

goto main ; yes

incf count,1 ; increment steering counter

rrf PORTD,0 ; rotate contents of portd right and place in w reg

movwf TMP

btfsc STATUS,C ; check for overflow

goto over1 ; yes


call delay

goto main

over1

bsf TMP,3 ; over flowed bit needs to be moved to other end of; the o/p nibble

movf TMP,0 ; move tmp to the w reg


call delay

goto main

steer ; routine to find the centre position by counting; half the maximum number of steps from one limit; to the other limit


40-100-1 6-15

right_ST

movlw H'00'

movwf CCPR1L ; set 0 pwm signal (pwm off)

movlw b'00000011' ; stepper motor sequence to right limit

movwf PORTD

call delay

movlw b'00000110'

movwf PORTD

call delay

movlw b'00001100'

movwf PORTD

call delay

movlw b'00001001'

movwf PORTD

call delay

decfsz rstcount,1 ; reduce loop count by one

goto right_ST

movlw H'05'

movwf rstcount ; re-setup loop count

left_ST

movlw b'00001001' ; stepper sequence to left limit

movwf PORTD

call delay

movlw b'00001100'

movwf PORTD

call delay

movlw b'00000110'

movwf PORTD

call delay

movlw b'00000011'

movwf PORTD

call delay

decfsz lstcount,1

goto left_ST

movlw H'0A'

movwf lstcount ; re-setup loop count


6-16 40-100-1

right_ST2

movlw b'00000011' ; step 5 loop counts to centre the steering

movwf PORTD

call delay

movlw b'00000110'

movwf PORTD

call delay

movlw b'00001100'

movwf PORTD

call delay

movlw b'00001001'

movwf PORTD

call delay

decfsz rstcount,1

goto right_ST2

movlw H'05'

movwf rstcount re- setup loop count

return

delay

movlw H'00'

movwf delay_lo

movlw H'00'

movwf delay_hi

outer

inner

incfsz delay_lo,1

goto inner

incfsz delay_hi,1

goto outer

return

END


40-100-1 6-17

6.4 Optical/Magnetic Speed Sensing


PIC board RB5 → Motor board Opt/Mag1




LED’s were connected to port d to indicate the counted pulses from the motor board.

6.4.2 Program


;PIC used 16f877

;this program uses the PWM timer to turn the wheels at a constant speed in one

;direction for a count of 256 and then reverses the direction for a count of256

;

;file name pwm&opt.asm

;date last modified 04/02/2000


;

;***************************************


;***************************************

list p = 16f877


;***************************************


;***************************************

delay_hi equ H'31'

delay_lo equ H'32'

TMP2 equ H'33'

pulse equ H'36'

w_temp equ H'37'


6-18 40-100-1

status_temp equ H'38'

;***************************************

;vector settings

;***************************************

ORG H'00'

goto start

ORG H'23'

;*****************************************

;isr

;*****************************************

ORG 0x004 ; interrupt vector location

Movwf w_temp ; save off current W register contents

Movf STATUS,w ; move status register into W register

movwf status_temp ; save off contents of STATUS register

btfsc PIR1,1 ; is interrupt tmr2

goto per ; yes

btfsc INTCON,RBIF ; is interrupt portb

goto port_t ; yes

per

bcf PIR1,1 ; clear tmr2 interrupt

goto Restore

port_t

btfss PORTB,4 ; test if positive edge

goto Restore ; no

incf pulse,1 ; add 1 to register

btfsc STATUS,Z ; is zero flag set

call toggle ; yes

bcf INTCON,RBIF ; clear portb interrupt

Restore

movf status_temp,w ; retrieve copy of STATUS register

movwf STATUS ; restore pre-isr STATUS register contents


40-100-1 6-19

swapf w_temp,f

swapf w_temp,w ; restore pre-isr W register contents

retfie ; return from interrupt

;****************************************

;initialisation

;****************************************

start

movlw H'FF' ; value for pwm period


movwf PR2

movlw H'0E' ; value for duty cycle


movwf CCPR1L ; duty cycle location upper 8 bits

bcf CCP1CON,5 ; bit 1 of duty cycle


clrf PORTC ; clear data registers

clrf PORTD


bcf INTCON,T0IF

bcf INTCON,RBIF ; clear portb interrupt flag


movlw H'00'


movwf TRISD


movlw H'FF'

movwf TRISA ; porta i/p

movwf TRISB




bsf CCP1CON,3 ; set for pwm mode



6-20 40-100-1

clrf pulse ; clear pulse

bcf PORTC,4 ; bi/uni set to bi

bsf INTCON,PEIE ; ENABLE peripheral interrupts

bsf INTCON,RBIE ; enable port b interrupt on change

bsf INTCON,GIE ; enable global interrupts

;**************************************

;main program

;**************************************

main

movf pulse,w

movwf PORTD ; display counted pulses

goto main

;************************************

;subroutines

;************************************

toggle

btfsc PORTC,3 ; test direction bit

goto clear

bsf PORTC,3 ; set direction bit

movlw H'11' ; set speed for direction

movwf CCPR1L

return

clear

bcf PORTC,3 ; clear direction bit

movlw H'11' ; set speed for direction

movwf CCPR1L

return

END


40-100-1 6-21

6.5 Temperature Sensing

6.5.1 Wiring Requirements

PIC board RE2 → Temp1

LED’s connected to ports D and C4 and C5 to display the 10-bit conversion.

6.5.2 Program


;PIC 16f877

;an analogue input with binary value displayed on LED's

;

;file name analo.asm



;

;********************************************


;********************************************

list p = 16f877


;********************************************


;********************************************

delay_hi equ H'31'

delay_lo equ H'32'

;********************************************

;vector settings

;********************************************

ORG H'00'

goto start

ORG H'23'


6-22 40-100-1

;****************************************

;initialisation

;****************************************

start


clrf PORTA ; clear port o/p buffers

clrf PORTB

clrf PORTC

clrf PORTD

clrf PORTE


movlw H'00'

movwf TRISB ; PORTB o/p


movwf TRISD ; portd o/p

movlw H'07'

movwf TRISE ; Porte i/p

movlw H'FF'


;**************************************

; main program

;**************************************

main


movlw B'10000000'

movwf ADCON1 ; SETUP PORT A & E FOR analogue AND RIGHT JUSTIFIED

bcf STATUS,RP0 ; select bank0

movlw B'10111001'

movwf ADCON0 ; SET TO CONVERT AN7 (PORTE,2), clocked at 32Tosc; and select AD on

call sdelay ; delay for acquisition time

bsf ADCON0,2 ; set conversion go


40-100-1 6-23

done

btfss ADCON0,2 ; poll for done bit

goto display

goto done

display

bsf STATUS,RP0 ; BANK 1

movf ADRESL,w

bcf STATUS,RP0 ; BANK 0

movwf PORTD ; output value of conversion

swapf ADRESH,w ; swap nibbles to w reg so that the two high bits; are in locations 4 and 5

movwf PORTC ; output higher 2 bits of result on portc bits 4&5

call delay

call delay

call delay

goto main

;************************************

; subroutines

;************************************

delay movlw H'00'

movwf delay_hi

movlw H'00'

movwf delay_lo

outer

inner

incfsz delay_lo,1

goto inner

incfsz delay_hi,1

goto outer

return

sdelay


6-24 40-100-1

movlw H'64'

movwf delay_lo

lo

incfsz delay_lo,1

goto lo

return

END

6.6 Back EMF Sensing

6.6.1 Wiring Requirements

PIC board RE2 → back emf1

PIC board RB7 → emf av.1




LED’s connected to port D and port B0&1 to display the conversion.

6.6.2 Program


;PIC 16f877

;PWM and the 10 bit digital conversion of the motor back emf displayed on LED's

;this program is solely interrupt driven, so will do nothing until an interrupt;occurs

;

;file name pwm&bemf.asm



;

;*******************************************



40-100-1 6-25

;*******************************************

list p = 16f877


;*************************************


;*************************************

delay_hi equ H'31'

delay_lo equ H'32'

TMP2 equ H'33'

count equ H'34'

count2 equ H'35'

tmp equ H'36'

status_temp equ H'37'

w_temp equ H'38'

display_av equ H'39'

average_lo equ H'40'

average_hi equ H'41'

;**************************************

;vector settings

;**************************************

ORG H'00'

goto start

ORG H'23'

;*****************************************

;isr

;*****************************************

ORG 0x004 ; interrupt vector location

Movwf w_temp ; save off current W register contents

Movf STATUS,w ; move status register into W register

movwf status_temp ; save off contents of STATUS register

btfsc PIR1,1 ; test if pwm interrupt

goto per ; yes


6-26 40-100-1

btfsc INTCON,RBIF ; test if portb interrupt

goto port_t

goto restore

per

call increment


goto restore

port_t

btfsc PORTB,7 ; test if zero on pin 7

goto clr ; yes

call adc ; call analogue to digital conversion

clr bcf INTCON,RBIF ; clear portb interrupt

restore

movf status_temp,w ; retrieve copy of STATUS register

movwf STATUS ; restore pre-isr STATUS register contents

swapf w_temp,f

swapf w_temp,w ; restore pre-isr W register contents

retfie ; return from interrupt

;****************************************

; initialisation

;****************************************

start


clrf PORTA ; clear port o/p buffers

clrf PORTB

clrf PORTC

clrf PORTD

clrf PORTE


movlw H'00'

movwf TRISD ; portd o/p



40-100-1 6-27

movlw H'07'

movwf TRISE ; Porte i/p

movlw B'00000010'

movwf TRISC ; portc output except pin 1 i/p

movlw B'10000000'

movwf TRISB ; PORTB o/p except pin 7

movlw H'FF'

movwf PR2 ; value for pwm period 'FF'




bcf CCP1CON,5


bcf INTCON,RBIF ; clear portb interrupt flag



movlw B'10000000'

movwf ADCON1 ; SET-UP PORT A & E FOR analogue and right; justified


bsf CCP1CON,3


movlw H'FF'

movwf count ; set up count with value 10

movlw H'02'

movwf count2 ; set up hi count2 with value 01

bsf PORTC,4 ; bi/uni

movlw H'FF'

movwf display_av ; set number of conversions to average


6-28 40-100-1

clrf average_lo ; clear average registers

clrf average_hi



bsf INTCON,PEIE ; ENABLE peripheral interrupts

bsf INTCON,RBIE ; enable port b interrupt on change

bsf INTCON,7 ; enable global interrupts

;**************************************

;main program

;**************************************

main

nop

goto main

;************************************

; subroutines

;************************************

increment

decfsz count,1 ; counts a set number of pwm frequency cycles

return

decfsz count2,1

return

call toggle

return

toggle

movlw H'FF' ; then resets the count

movwf count

movlw H'02'

movwf count2

incf CCPR1L,1 ; and increments the mark to space ratio

return

adc


40-100-1 6-29

call sdelay

movlw B'10111001'

movwf ADCON0 ; SET TO CONVERT AN7 (PORTE,2), clocked at 32Tosc; and select AD on

call sdelay ; delay to allow the holding capacitor on the PIC

call sdelay ; to charge

bsf ADCON0,2 ; set conversion go

done

btfsc ADCON0,2 ; poll for done bit

goto done

bsf STATUS,RP0 ; BANK 1

movf ADRESL,w ; read lower 8 bits

bcf STATUS,RP0 ; BANK 0

addwf average_lo,f ; add to low average

btfss STATUS,C ; test for carry

goto upper ; no

incf average_hi,f ; yes

upper

movf ADRESH,w ; read upper 2 bits

addwf average_hi,f ; add to hi average

rrf average_hi,f ; divide by 2

rrf average_lo,f ; divide by 2

decfsz display_av,f ; average 255 conversions

return

movlw H'FF'

movwf discount

display

movf average_lo,w

movwf PORTD ; output value of conversion

movf average_hi,w


6-30 40-100-1

movwf PORTB ; output higher 2 bits of result

return

sdelay

movlw H'96'

movwf delay_lo

lo

incfsz delay_lo,1

goto lo

return

END

Chapter 7MECHATRONICS PROJECT KIT Solutions

40-100-1 7-1

7 Solutions

7.1 3D Models/Photos

The following are three typical examples of the major components of the buggy kit.

Single motor mechanicaldifferential with single-wheelcontrolled steering.

Single-motormechanical differentialwith Ackermannsteering.

Dual-motor drive, giving thedriving wheels independentcontrol capable of steering,with caster wheel at otherend.


7-2 40-100-1

7.2 Assembly

Using the single-motor solution and Ackermann steering on the long rectangular chassiswith the tapered end, the sensor boards were hung at the front at a height of 8 mm fromthe floor and at a distance of 14 mm apart from centre of sensor to centre of sensor. ThePIC board was mounted across the back with the battery in front with its terminals facingto the right .

This solution controls the speed of a dc motor, varying the speed in discrete steps withthe amount of turning angle on the stepper motor. The system also reads the line via fiveoptical sensors and adjusts the angle on the Ackermann steering according to how muchthe buggy is off the centre of the line.

Figure 7-1: Wiring for Five Sensor Line Following Solution

6 wayconnecto

Sensor Boards

Stepper Boardµprocessor Board

Steppermotor

Motor Board

+5VGNDRA0

+5V0VO/p

+5VGNDRC2RC3RC4

+5V0VPWM 1FD/RVBI/UNI

Power from battery

Power to PIC board

PIC board Power

+5VGNDRA1

+5V0VO/p

+5V

RA2

+5V0VO/p

+5VGNDRA3

+5V0VO/p

+5VGNDRA4

+5V0VO/p

+7.2V unreg+5VGNDRD0RD1RD2RD3

+5V0VB′A′BA

UNREG


40-100-1 7-3

4.5m 2m

3.25m2.5m

1.5m

2.4m

The wiring is best started on the peripheral boards when they are off the chassis with longwires, which can be cut to the required length later. Then the boards can be fixed to thechassis and the wires tied to the chassis or tied together in suitable places. The wires canbe cut to the required length and connected to the terminal blocks on the PIC board. Thepower plug from the motor board needs to be plugged in to the power in on the PIC boardand the battery needs to be connected to the flying lead on motor board.

7.3 Trouble-Shooting

If the progpic program does not automatically set up the communications link with the PICboard, check that all connectors are fully engaged, the power is connected and the run/prog switch is in the prog position; then select the “Comms” menu and “detect”.

Whilst running the program the motors hum but do not turn, first check that the battery isfully charged. If it is then increase the PWM on period until the motors turn.

If the steering wheel(s) turn the opposite way to the line, check the wiring is the correctorientation from the sensor boards and to the stepper board.

The LED’s on the sensor board will light when the when there is no reflected signal.

7.4 The Track

The track that was used for testing was set out as follows:

Figure 7-2: Diagram of Test Track


7-4 40-100-1

Using the program listed below, the following results were obtained for the test trackshown in Figure 7-2. The circuit was completed in about 20 seconds with a full batterypack, and the buggy kept going for 12.5 circuits, each circuit was slower then the previousone until there was not enough power left in the battery to drive the motor. The conditionof the floor can make a considerable amount of difference to the overall performance ofthe buggy. If the floor has ridges, the buggy will tend to jump at the front end. Addingweight to the front end can improve the stability.

7.5 Program


;PIC 16f877

;to drive the motor and to read the 5 line sensors

;and move the steering accordingly

;

;file name: follow6.asm

;last modified 11/06/01


;


list p = 16f877


;

;project definitions

;


delay_hi equ H'31'

delay_lo equ H'32'

delay2_hi equ H'33'

delay2_lo equ H'34'

TMP equ H'35'

count equ H'36'

rstcount equ H'37'

lstcount equ H'38'

;vector settings

ORG H'00'

goto start

ORG H'23'


40-100-1 7-5

;****************************************

;initialization

;****************************************

start


clrf PORTA ; clear ports

clrf PORTB

clrf PORTC

clrf PORTD

clrf PORTE

movlw H'FF' ; load w reg with FF

BSF STATUS, RP0 ; select bank1

movwf PR2 ; load value for pwm frequency

movlw H'00'

movwf TRISB ; PORTB OUTPUT

movwf TRISE ; porte output

movlw B'0000010'

movwf TRISC ; portc pin 1 i/p rest o/p

movlw B'00000000'

movwf TRISD ; portd 0-3 O/P 4-7 I/P

movlw H'FF'

movwf TRISA ; porta INPUT

movlw H'07'

movwf ADCON1 ; SETUP PORT A FOR DIGITAL I/O




bcf CCP1CON,5


BSF STATUS, RP0 ; select bank1

bsf INTCON,7 ; enable globle interupts



7-6 40-100-1




bsf CCP1CON,3


movlw B'00010010'

movwf count ; setup count for maximum steeing traval

movlw H'05'

movwf rstcount ; initial steering count right

movlw H'0A'

movwf lstcount ; initial steering count left

call steer ; call subroutine to straighten steering

bsf PORTC,2 ; bi/uni set 1

;**************************************

;main program

;**************************************

main

btfss PORTA,4 ; and goto the relevant dirrection

goto center ; routine

btfss PORTA,3

goto left1

btfss PORTA,2

goto far_left

btfss PORTA,5

goto right1

btfss PORTC,1

goto far_right

movlw H'30' ; set speed

movwf CCPR1L

goto main


40-100-1 7-7

;************************************

;subroutines

;************************************

center


goto center_left ; routine

btfss PORTA,5

goto center_right

movf count,w

addlw B'11101110'

btfss STATUS,Z

goto test_c


movwf CCPR1L

goto main

test_c

btfss STATUS,C

goto center_left

goto center_right

center_left


movwf CCPR1L

movf count,w

addlw B'11101100' ; check if steering is at limit

btfsc STATUS,Z

goto main

btfsc STATUS,C

goto center_right

incf count,f ; increment steering counter

rrf PORTD,w ; rotate contents of portd right and place in w reg

movwf TMP



7-8 40-100-1

goto over

movwf PORTD

call delay

goto main

over

bsf TMP,3 ; bit needs to be carried to other end of the o/p; nibble

movf TMP,0

movwf PORTD

call delay

goto main

center_right


movwf CCPR1L

movf count,w

sublw B'00010000'

btfsc STATUS,Z

goto main

btfsc STATUS,C

goto center_left

decf count,f ; same as for left but shifting left

rlf PORTD,w

movwf TMP

btfsc TMP,4

goto under

bcf TMP,0

movf TMP,0

movwf PORTD

call delay

goto main


40-100-1 7-9

under

bcf TMP,4

bsf TMP,0

movf TMP,0

movwf PORTD

call delay

goto main

left1


goto left_left ; routine

left

movlw H'40' ; old 35 30, 40 A0 45

movwf CCPR1L

movf count,w


btfsc STATUS,Z

goto main

btfsc STATUS,C

goto right



movwf TMP


goto over1

movwf PORTD

call delay

goto main

over1


movf TMP,0


7-10 40-100-1

movwf PORTD

call delay

goto main

left_left

movlw H'3C' ; set speed

movwf CCPR1L

movf count,w


btfsc STATUS,Z

goto main

btfsc STATUS,C

goto right_right



movwf TMP


goto over2

movwf PORTD

call delay

goto main

over2


movf TMP,0

movwf PORTD

call delay

goto main

right1

btfss PORTC,1 ; and goto the relevant dirrection

goto right_right ; routine

right


movwf CCPR1L


40-100-1 7-11

movf count,w

sublw B'00001100'

btfsc STATUS,Z

goto main

btfsc STATUS,C

goto left


rlf PORTD,w

movwf TMP

btfsc TMP,4

goto under1

bcf TMP,0

movf TMP,0

movwf PORTD

call delay

goto main

under1

bcf TMP,4

bsf TMP,0

movf TMP,0

movwf PORTD

call delay

goto main

right_right

movlw H'3C' ; set speed

movwf CCPR1L

movf count,w

sublw B'00000110'

btfsc STATUS,Z

goto main

btfsc STATUS,C

goto left_left


rlf PORTD,w


7-12 40-100-1

movwf TMP

btfsc TMP,4

goto under2

bcf TMP,0

movf TMP,0

movwf PORTD

call delay

goto main

under2

bcf TMP,4

bsf TMP,0

movf TMP,0

movwf PORTD

call delay

goto main

far_right


movwf CCPR1L

movf count,w

btfsc STATUS,Z

goto main


rlf PORTD,w

movwf TMP

btfsc TMP,4

goto under3

bcf TMP,0

movf TMP,0

movwf PORTD

call delay

goto main

under3

bcf TMP,4

bsf TMP,0


40-100-1 7-13

movf TMP,0

movwf PORTD

call delay

goto main

far_left


movwf CCPR1L

movf count,w


btfsc STATUS,Z

goto main



movwf TMP


goto over3

movwf PORTD

call delay

goto main

over3


movf TMP,0

movwf PORTD

call delay

goto main

steer

right_ST

movlw H'00'

movwf CCPR1L

movlw b'00000011' ; stepper motor sequence

movwf PORTD

call delay2


7-14 40-100-1

movlw b'00000110'

movwf PORTD

call delay2

movlw b'00001100'

movwf PORTD

call delay2

movlw b'00001001'

movwf PORTD

call delay2

decfsz rstcount,f

goto right_ST

movlw H'05'

movwf rstcount

left_ST

movlw b'00001001'

movwf PORTD

call delay2

movlw b'00001100'

movwf PORTD

call delay2

movlw b'00000110'

movwf PORTD

call delay2

movlw b'00000011'

movwf PORTD

call delay2

decfsz lstcount,f

goto left_ST

movlw H'0A'

movwf lstcount

right_ST2

movlw b'00000011'

movwf PORTD

call delay2

movlw b'00000110'

movwf PORTD

call delay2


40-100-1 7-15

movlw b'00001100'

movwf PORTD

call delay2

movlw b'00001001'

movwf PORTD

call delay2

decfsz rstcount,f

goto right_ST2

movlw H'05'

movwf rstcount

movlw b'00001100'

movwf PORTD

call delay2

movlw H'50'

movwf CCPR1L

return

delay

movlw H'00'

movwf delay_lo

movlw H'DF'

movwf delay_hi

outer

inner

incfsz delay_lo,f

goto inner

incfsz delay_hi,f

goto outer

return

delay2


7-16 40-100-1

movlw H'00'

movwf delay2_lo

movlw H'B0'

movwf delay2_hi

outer2

inner2

incfsz delay2_lo,f

goto inner2

incfsz delay2_hi,f

goto outer2

return

END

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