synthesis of navigation system

8/9/2019 Synthesis of Navigation System

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CHAPTER 1

INTRODUCTION

1.1Introduction.Navigational systems are having lot of importance as far as modern industrial

applications are concerned. Hence any attempt towards the design of such navigational

system will definitely give deep insight into the practical problems of such challenging

projects. Different problems such as;

a) Selection of drives,

b) Physical size of the moving system,

c) Development of electronic control circuit,

d) Development of software packages etc.

which are likely to arise are presented in a detailed manner. After the

development of a model physical system their performance evaluation is carried out

experimentally and the evaluation details are presented.

Practically the moving system with manual mode and auto mode is fabricated

along with the associated hardware modules. With the help of indigenously developed

control software, the above prototypes are tested for their operational evaluation and test

results are monitored and recorded.

1.2 Problem Definition:

Objective of this project is to design and development of a driving system for

controlling the position, direction and speed of a navigational system using DC series

motor.

Key factors are mentioned below:-

i) Selecting the suitable components for the electronic circuitry based on therequirement.

ii) Design and selection of the DC series motors for the application.iii) Construct a perfect micro controller program and feedback strategy for

controlling the motors.


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iv) Interfacing serial port communication and Visual Basic interface for to getthe required performance.

1.3 Methodology:

The complete controlling of the moving system is through a central console or a

software interface from where the commands are given to the microcontroller for

performs the specified tasks. The moving system using DC series motors where the

controlling is made through serial port communication, through a sufficiently long RS232

communication channel.

i) PIC16F877A microcontroller is the heart of this project.ii) Serial communication (RS 232) along with Visual Basic interface

implemented for the navigational system with DC motors.

iii) Combination of TIP127, TIP 122 power transistors and ULN 2803 driver IC isused to drive two DC motors.

iv) Encoders and IR sensors are used for position control and obstacle detectionrespectively

1.4 Modules of the Hardware:

The components used in the development of moving system using DC motors are

7805 voltage regulator, RS232 channel and MAX232 IC, ULN 2803 driver IC, power

transistors TIP122 and TIP 127, 16F877A PIC Microcontroller IC, Infrared sensors,

optical encoder and metallic disc, Two DC series Motors, Battery source of 12 V or

variable DC power supply and Serial communication port.

1.5 Outline of the Report:

The report is organized into four chapters including that of the introduction. The

chapter 2 includes the review of the existing literature. Chapter 3 deals with the

development of PVD navigational system. Chapter 4 including experimental work and

results. The conclusion and suggestions for future work is presented in the last chapter 5,

followed by reference.


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CHAPTER 2

REVIEW OF THE EXISTING LITERATURE

2.1 Introduction:

Having given a brief introduction, a detailed review of the existing work in this

area is mentioned here. The references are includes papers, reports, books, data sheets

and other articles downloaded from webs links and a brief description about their work is

mentioned in this chapter.

2.2 Literature Review:

Mr. Firmansyah and his friends B. Hermanto and L.T. Handoko developed a

methodology to control the navigational devices using micro controller based hardware in

[1]. They considered the system with three major modules consisting of a main

navigational unit, one data acquisition unit and a data processing module. The principle

of controlling a wireless robot is neatly described in reference [1].

In [2], the authors described controlling procedures of a robot for monitoring the

temperatures at different locations. The control system is based on a wireless telemetry

mechanism and wireless communication principles. One RF receiver, RF transmitter, IR

transmitter and one IR receiver are the major hardware modules used by the authors.

In [3], the authors described about the wheeled mobile robots. Wheeled Mobile

Robots (WMRs) are built with their Wheels drive machine, Motors. Depend on their

desire design of WMR, Technicians made used of DC series Motors for motion control.

In this paper, the author would like to analyze how to choose DC series motor to be

balance with their applications of especially for WMR. Specification of DC series Motor

that can be used with desire WMR is to be determined by using MATLAB Simulink

model. Therefore, this paper is mainly focus on software application of MATLAB andControl Technology. As the driving system of DC series motor, a Peripheral Interface

Controller (PIC) based control system is designed including the assembly software

technology and H-bridge control circuit. This Driving system is used to drive two DC

series motors which are used to control the motion of WMR. In this analyzing process,

the author mainly focuses the drive system on driving two DC series motors that will


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control with Differential Drive technique to the Wheeled Mobile Robot. For the design

analysis of Motor Driving System, PIC16F84A is used and five inputs of sensors detected

data are tested with five ON/OFF switches. The outputs of PIC are the commands to

drive two DC series motors, inputs of H-bridge circuit .In this paper, Control techniques

of PIC microcontroller and H-bridge circuit, Mechanism assignments of WMR are

combined and analyzed by mainly focusing with the Modeling and Simulink of DC

Motor using MATLAB

We are mainly concentrating on how the system responds to the commands we

give and we analyze the system performance. Even though, the experimental setup is

same as suggested by the authors, they implemented the hardware by serial

communication using RS232 channel taking servo motors as the actuators. But in this

work, we will implement the hardware module, moving system with DC series motors as

the actuators using serial communication.

Details about the software part of control programming, the data logging software

is well described in [4] and [5]. The data logging refers to the command inputs to the

moving system that displays on the computer screen and this page is called hyper

terminal. There are steps to enter this hyper terminal link,

Start => Programs => Accessories => Communications => HyperTerminal

In this we have to make the settings of the suitable communication port, baud rate and

other port settings. The hyper terminal port is more accessible for the serial

communication modes. In this project, we used Visual Basic software a graphical user

interface, which is very simple to operate aged as well as normal people for the moving

system using DC series motors.

In [6], the author described about electronic navigation system with both DC

motors and stepper motors. The controller he used is Atmel AT89C52 and L293D and

ULN 2803 ICs used as drivers for DC motors and stepper motors respectively. Serial port

communication with HyperTerminal is implemented for DC motors and RF

communication is used for the stepper motors. The detailed analysis and performance

evaluation is also reported. In his work he found that the stepper motor provides better

results than the DC motors with both three and four wheel systems.


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2.3 Summary:

The principles and details regarding the control of such devices mentioned in the

above references are found much useful in the present work. Having given a detailed

review about the similar work carried out, through the above literatures, a similar work is

done here and its further explanation is presented in the coming chapters.


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CHAPTER 3

DEVELOPMENT OF NAVIGATIONAL SYSTEM

3.1 Introduction:

Having given a brief survey about the work done in the navigational problem of

moving bodies, a detailed description about the problems faced currently is the content of

this chapter. The moving body with DC series motors is considered. The navigation is

done with the help of serial port communication facility implemented by RS232 cable

and Visual Basic graphical user interface.

The objective is to navigate the moving system through a predetermined path. Adetailed description about different subsystems involved in the project is given as under.

3.2 Moving System:

As mentioned above, the moving system with DC series motors and the driving

systems are fabricated. Each motor is having separate driving and control circuits.

Elaborate description of the system is as given under.

3.2.1 Schematic block diagram

Block schematics of the walking support system with DC series motor and

associated subsystems are shown in Fig 3.2.1 below. The various subsystems are,

DC power supply

7805 Voltage regulator

Power Transistor Bridge circuit

DC series motor set

ULN2803 Driver IC

Infrared sensors

Optical encoders

Keypads

MAX232 IC and serial port communication


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Visual Basic graphical user interface

PIC 16F877A Microcontroller

Fig 3.2.1. Block diagram of navigational system with DC series motors

3.2.1(a) Power supply unit:

First and foremost part of the system is the power supply unit. A regulated power

supply of (0-15)V DC have been used for the hardware. Input is 230 V AC and output is

(0-15)V DC. A batter of 12V,2A can also be used instead of a regulated power supply.

Regulated

power supply

RS 232

Power

Supply unit

7805 Voltage

regulator

Motor 2

Motor 1 Bridge

circuit

Bridge

circuit

ULN

2803

PIC

16F877A

IR sensor 1

IR sensor 2

Optical

Encoder 1

OpticalEncoder 2

Keypad

(Direction)

Keypad

(Speed andmode

selection)

MAX 232

IC

Serial port

communication

Mouse

125

12

12

5

5

0

0


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3.2.1(b) 7805 voltage regulator:

The power requirement for the developed hardware is 12V DC for the DC motors

which is directly taken from the regulated power supply unit and 5V DC for the control

circuit is limited by using 7805 voltage regulator. The input is 12V from a regulated

power supply and the output is 5V DC to the control circuit. The schematic of the 7805

pins and circuit diagram is as shown below.

Fig 3.2.2 Pin diagram of 7805 voltage regulator

Fig 3.2.3 Circuit diagram of 7805

The input pin is given to the 12V supply either from a battery source or aregulated power Supply, ground to 0 and output i.e., 5V DC pin is given common to the

microcontroller and the control circuit.

The circuit diagram of 7805 is also shown in the figure 3.2.3. The diode D1 is the

purpose of secure connection from the external power supply. If the supply polarity is

correct the diode conducts and current flows through the circuit. If the supply polarity is


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wrong then the diode D1 will be in the reverse biased and it opposes the current flow

through the circuit. Thus it helps the circuit as well as the components.

3.2.1(c) PIC 16F877A Microcontroller:

Microcontroller PIC16F877A is one of the PIC Micro Family microcontroller

which is popular at this moment. Because of very easy using PIC16F877A and use

FLASH memory technology so that can be write-erase until thousand times. The

superiority this Risc Microcontroller compared to with other microcontroller 8-bit

especially at a speed of and his code compression. PIC16F877A have 40 pin by 33 path

of I/O. EEPROM memory makes it easier to apply microcontrollers to devices wherepermanent storage of various parameters is needed (codes for transmitters, motor speed,

receiver frequencies, etc.). Low cost, low consumption, easy handling and flexibility

make PIC16F877A applicable even in areas where microcontrollers had not previously

been considered (example: timer functions, interface replacement in larger systems,

coprocessor applications, etc.)[8].

3.2.1(c)i Features of PIC 16F877A Microcontroller:

Operating Frequency: DC 20 MHz

Resets (and Delays): POR, BOR

Flash Program Memory (14-bit words): 8K

Data Memory (bytes): 368

EEPROM Data Memory (bytes): 256

Interrupts: 15

I/O Ports: Ports A, B, C, D, E

Timers: 3

Capture/Compare/PWM modules: 2

Serial Communications: MSSP, USART

Parallel Communications: PSP

10-bit Analog-to-Digital Module: 8 input channels

Analog Comparators: 2

Instruction Set: 35 Instructions


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3.2.1(c)iiPin Description of PIC 16F877A Microcontroller:

Fig 3.2.4 Pin diagram of PIC 16F877A

3.2.1(c)iii PORTA and the TRISA Register:

PORTA is a 6-bit wide, bidirectional port. The corresponding data direction

register is TRISA. Setting a TRISA bit (= 1) will make the corresponding PORTA pin an

input (i.e., put the corresponding output driver in a High-Impedance mode). Clearing a

TRISA bit (= 0) will make the corresponding PORTA pin an output (i.e., put the contents

of the output latch on the selected pin).

Reading the PORTA register reads the status of the pins, whereas writing to it will

write to the port latch. All write operations are read-modify-write operations. Therefore, a

write to a port implies that the port pins are read, the value is modified and then written to

the port data latch.

Pin RA4 is multiplexed with the Timer0 module clock input to become the

RA4/T0CKI pin. The RA4/T0CKI pin is a Schmitt Trigger input and an open-drain

output. All other PORTA pins have TTL input levels and full CMOS output drivers.

Other PORTA pins are multiplexed with analog inputs and the analog VREF input for


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both the A/D converters and the comparators. The operation of each pin is selected by

clearing/setting the appropriate control bits in the ADCON1 and/or CMCON registers.

Name Bit# Buffer Function

RA0/AN0 Bit 0 TTL Right shaft encoder sensor

RA1/AN1 Bit 1 TTL Left shaft encoder sensor

RA2/AN2/VREF-/CVREF Bit 2 TTL No connection

RA3/AN3/VREF+ Bit 3 TTL No connection

RA4/T0CKI/C1OUT Bit 4 ST No connection

RA5/AN4/SS/C2OUT Bit 5 TTL No connection

Table 3.2.1 Pin Description of Port A

3.2.1(c)iv PORTB and the TRISB Register:

PORTB is an 8-bit wide, bidirectional port. The corresponding data direction

register is TRISB. Setting a TRISB bit (= 1) will make the corresponding PORTB pin an


TRISB bit (= 0) will make the corresponding PORTB pin an output (i.e., put the contents

of the output latch on the selected pin). Three pins of PORTB are multiplexed with the

In-Circuit Debugger and Low-Voltage Programming function: RB3/PGM, RB6/PGC and

RB7/PGD.

Each of the PORTB pins has a weak internal pull-up. A single control bit can turn

on all the pull-ups. This is performed by clearing bit RBPU (OPTION_REG). The

weak pull-up is automatically turned off when the port pin is configured as an output. The

pull-ups are disabled on a Power-on Reset.

Name Bit# Buffer Function

RB0/INT Bit 0 TTL/ST(1) No connection

RB1 Bit 1 TTL No connection


RB3/PGM(3) Bit 3 TTL No connection


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RB6/PGC Bit 6 TTL/ST(2) No connection

RB7/PGD Bit 7 TTL/ST(2) No connection

Table 3.2.2 Pin Description of Port B

3.2.1(c)v PORTC and the TRISC Register:

PORTC is an 8-bit wide, bidirectional port. The corresponding data direction

register is TRISC. Setting a TRISC bit (= 1) will make the corresponding PORTC pin an


TRISC bit (= 0) will make the corresponding PORTC pin an output (i.e., put the contents

of the output latch on the selected pin). PORTC is multiplexed with several peripheral

functions. PORTC pins have Schmitt Trigger input buffers.

When the I2C module is enabled, the PORTC pins can be configured with

normal I2C levels, or with SMBus levels, by using the CKE bit (SSPSTAT). When

enabling peripheral functions, care should be taken in defining TRIS bits for each

PORTC pin. Some peripherals override the TRIS bit to make a pin an output, while other

peripherals override the TRIS bit to make a pin an input. Since the TRIS bit override is in

effect while the peripheral is enabled, read-modify write instructions (BSF, BCF, andXORWF) with TRISC as the destination, should be avoided. The user should refer to the

corresponding peripheral section for the correct TRIS bit settings.

Name Bit# Buffer

Type

Function

RC0/T1OSO/T1CKI Bit 0 ST Left IR Sensor

RC1/T1OSI/CCP2 Bit 1 ST Right IR sensor

RC2/CCP1 Bit 2 ST Manual/Auto mode

RC3/SCK/SCL Bit 3 ST Speed Down

RC4/SDI/SDA Bit 4 ST Speed Up

RC5/SDO Bit 5 ST No connection


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RC6/TX/CK Bit 6 ST No connection

RC7/RX/DT Bit 7 ST No connection

Table 3.2.3 Pin Description of Port C

3.2.1(c)vi PORTD and the TRISD Register:

PORTD is an 8-bit port with Schmitt Trigger input buffers. Each pin is

individually configurable as an input or output. PORTD can be configured as an 8-bit

wide microprocessor port (Parallel Slave Port) by setting control bit, PSPMODE

(TRISE). In this mode, the input buffers are TTL.

Name Bit# Buffer Type Function

RD0/PSP0 Bit 0 ST/TTL(1) Forward Key

RD1/PSP1 Bit 1 ST/TTL(1) Right Key

RD2/PSP2 Bit 2 ST/TTL(1) Reverse Key

RD3/PSP3 Bit 3 ST/TTL(1) Left Key

RD4/PSP4 Bit 4 ST/TTL(1) Left motor clockwise direction

RD5/PSP5 Bit 5 ST/TTL(1) Left motor anticlockwise direction

RD6/PSP6 Bit 6 ST/TTL(1) Right motor clockwise direction

RD7/PSP7 Bit 7 ST/TTL(1) Right motor anticlockwise direction

Table 3.2.4 Pin Description of Port D

3.2.1(c)vii PORTE and the TRISE Register:

PORTE has three pins (RE0/RD/AN5, RE1/WR/AN6 and RE2/CS/AN7) which

are individually configurable as inputs or outputs. These pins have Schmitt Trigger input

buffers.

The PORTE pins become the I/O control inputs for the microprocessor port when

bit PSPMODE (TRISE) is set. In this mode, the user must make certain that the

TRISE bits are set and that the pins are configured as digital inputs. Also, ensure

that ADCON1 is configured for digital I/O. In this mode, the input buffers are TTL.

PORTE pins are multiplexed with analog inputs. When selected for analog

input, these pins will read as 0s. TRISE controls the direction of the RE pins, even


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when they are being used as analog inputs. The user must make sure to keep the pins

configured as inputs when using them as analog inputs.

Name Bit# Buffer

Type

Function

RE0/RD/AN5 Bit 0 ST/TTL(1) No connection

RE1/WR/AN6 Bit 1 ST/TTL(1) No connection

RE2/CS/AN7 Bit 2 ST/TTL(1) No connection

Table 3.2.5 Pin Description of Port E

3.2.1(c)viii Capture/Compare/PWM modules

Each Capture/Compare/PWM (CCP) module contains a 16-bit register which can

operate as a:

16-bit Capture register

16-bit Compare register

PWM Master/Slave Duty Cycle register

Both the CCP1 and CCP2 modules are identical in operation, with the exception being

the operation of the special event trigger. Table 3.2.6 and Table 3.2.7 show the resources

and interactions of the CCP module(s).CCP Mode Timer Resource

Capture Timer1

Compare Timer1

PWM Timer2

Table 3.2.6 CCP mode Timer resources required

CCP1 Module:

Capture/Compare/PWM Register 1 (CCPR1) is comprised of two 8-bit registers:

CCPR1L (low byte) and CCPR1H (high byte). The CCP1CON register controls the

operation of CCP1. The special event trigger is generated by a compare match and will

reset Timer1.


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CCP2 Module:

Capture/Compare/PWM Register 2 (CCPR2) is comprised of two 8-bit registers:

CCPR2L (low byte) and CCPR2H (high byte). The CCP2CON register controls the

operation of CCP2. The special event trigger is generated by a compare match and will

reset Timer1 and start an A/D conversion (if the A/D module is enabled).

CCPx

Mode

CCPy

Mode

Interaction

Capture Capture Same TMR1 time base

Capture Compare The compare should be configured for the special event

trigger which clears TMR1

Compare Compare The compare(s) should be configured for the special event

trigger which clears TMR1

PWM PWM The PWMs will have the same frequency and update rate

(TMR2 interrupt)

PWM Capture None

PWM Compare None

Table 3.2.7 Interaction of two CCP modules

The speed control of the navigational system is done by the help of CCPR1

register of PIC 16F877A microcontroller. The value of CCPR1 register will change from

0 to 255 that is the pulse width of the will be changed. By default the value 128 is stored

in this register. And the speed increasing and decreasing is done by giving interrupts to

the register. If we pressing the pin RC4 or RC3, its for increasing or decreasing the

speed respectively, it will produce an interrupt and according to that the speed will

change.

3.2.1(d) IR Sensors:

Two infrared sensors are used in the navigational system. These are placed either

sides of the moving system that is right and left sides. The infrared LED transmits the IR

rays and a photo diode is there for receiving this rays. Main parts of the circuit are


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Infrared led and LM 358 operational amplifier. The LM 358 is used in the comparator

mode. The IR led is used as a potential divider in a reverse bias mode. A threshold

voltage is set at the inverting terminal of the op-amp using potentiometer. So when

infrared light reflects from a surface, the resistance of the photodiode would decrease and

this in turn on when exceeds the threshold voltage will make the output of the Op-amp go

high. The reverence distance can set depending upon the threshold voltage by adjusting

the potentiometer. Whenever an obstacle in the path, either at right side or at left side the

corresponding receiver cant get any signals from the transmitter. This will produce a

potential difference between the inverting and non inverting terminals of the op amp

and produces an output according to that. The output of left side sensor is connects to

RC0 (15th) pin and the output of the right side sensor connects to RC1 (16th) pin of the

microcontroller. If any obstacle is there then the corresponding op-amps output will

produce a 5V pulse and it goes to the corresponding pin of the microcontroller and

changes the direction of the moving system. The circuit diagram is shown in the figure

3.2.5 below.

Fig 3.2.5 Circuit diagram of Infrared sensor

Pin diagram of LM 358 Operational amplifier is shown in the figure 3.2.6 below.

LM 358 has two op-amps in its 8 pin package, thus two IR sensors could be built out ofone IC. These circuits consist of two independent, high gain, internally frequency

compensated which were designed specifically to operate from a single power supply

over a wide range of voltages. The low power supply drain is independent of the

magnitude of the power supply voltage. It is internally frequency compensated, large DC


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voltage gain around 100bB, wide bandwidth (unity gain) 1.1MHz and essentially

independent of supply voltage.

Fig 3.2.6 Pin diagram of LM 358

3.2.1(e) Optical Encoders:

Two optical encoders are using with two DC series motors for controlling the

position of the motor. Main parts of the optical encoder are one encoder disc with

required number of holes and a slotted optical switch. The encoder disc rotates between

the slotted part of optical disc. The optical signal from the sender, basically it is an

infrared LED, reaches the receiver, which is usually a photo transistorthrough the holesof the disc and cuts the signal otherwise. The figure 3.2.7 below shows the encoder discand the pin diagram of optical switch MOC7811 [9].

Fig 3.2.7 Encoder Disc and Pin Diagram of MOC 7811

Since the circumference of the wheel used for the moving system is 22cm. so here

the designed disc having 21 holes. Between two holes the system will move 1cm or the

displacement between 160. The circuit diagram of optical encoder is shown in the figure

3.2.8 below. When working with DC series motors, a shaft encoder is the most common

and accurate way of providing feed-back to the controller. Shaft encoder comes in many


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shapes and sizes, but they all rely of the same principle. Figure 3.2.7 shows a classic

encoder disk (which is one of the main parts of a shaft encoder mechanism). The optical

diode is always conducting when this optical signal passes through the encoder disc the

photo transistor in the receiving circuit gets the sufficient light source to turning on. Then

microcontroller pin gets a logic low signal from emitter of photo transistor.

Fig 3.2.8 Circuit diagram of optical encoder

3.2.1(f) Keypads:

In navigational system, two keypads are using. The first key pad is using for mode

selection, that is to select either manual mode or auto mode and to increase or decrease

the speed of the moving system. Keyboard contains one push button switch for mode

selection and two micro switches for adjusting the speed of the moving system. The

circuit diagram is shown figure below.

Fig 3.2.9 Circuit diagram for mode selection keypad


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If no key is pressed then 5V flows to the microcontroller pins RC2, RC3 and RC4

through the pull up resistors. When any key is pressed then a low signal appeared to the

corresponding micro controller pin

The second keypad is for changing the direction of the moving system. Four

micro switches are arranged in this for moving four directions like forward, reverse, right

and left. One end of each switch connected to common ground and another end is

connected to 5V through pull-up resistor and microcontroller pins. When a switch is

closed, 5v bypasses through the pull-up resistor and switch and a low signal is passing to

microcontroller. The circuit diagram of keypad for direction control is shown in figure

3.2.10 below.

Fig 3.2.10 Circuit diagram for direction control keypad

3.2.1(g) Power transistor Bridge circuit:

The basic elements used in this bridge circuit are TIP127 and TIP122 powertransistors. The pin diagrams of these transistors are given figure 3.2.11 below


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Fig 3.2.11 Pin diagram of power transistors TIP 127 and TIP 122

The TIP122 are silicon Epitaxial-Base NPN power transistor in monolithic

Darlington configuration mounted in Jedec TO-220 plastic package. They are intented for

use in power linear and switching applications. The complementary PNP types are

TIP125, TIP126 and TIP127, respectively. Here in this circuit we are using two pairs of

both transistors to make a single bridge, which can capable upto 5A current. The current

rating of the motor used in this circuit is 2A. So these bridges will help the circuit to

avoid the heating due to the overheating [10,11].

Fig 3.2.12 Power amplifier Bridge circuit.


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S1 S2 S3 S4

Current

Direction Effect

1 0 0 1 1 to 2

Motor spins

Forward

0 1 1 0 2 to 1

Motor spins

Forward

1 1 0 0

-- Breaking

occurs

0 0 0 0

-- --

Fig 3.2.13 H - Bridge representation for DC series motor direction control

Two H Bridge circuit is used in the system ie; for each motor separate H

Bridge circuits are using. Here in this system the H Bridge consist a pair of power

transistors TIP 127 and TIP122 and four BC 547 transistors. In first case when control

inputs are 1 and 0, the Q5 transistor is turned ON and the power transistors Q1 and Q4

gets sufficient voltage to turning ON. This will cause the motor to rotate in one direction.

The current flow direction will be Vcc Q1 motor Q4 Ground. At this time the

power transistors Q2 and Q3 are in OFF state and no conduction. Second case when the

control inputs are 0 and 1, the Q7 transistor is ON and power transistor Q2 and Q3

Power Transistor Switc

1 2


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gets sufficient voltage to turning ON. This will cause the motor to rotate in the opposite

direction. The same time the power transistors Q1 and Q4 are in OFF state. The current

flow direction will be Vcc Q2 motor Q3 Ground.

3.2.1(h) DC series motors:

For the development of the navigational system two DC series motors of 12V had

been used. DC series motor is a kind of DC motor in which field windings (few numbers

of thick turns) are connected in series with the armature. As field coil has to carry high

current (armature current), area of cross section of wire has to fairly large and its number

of turns has to be very small. The circuit diagram of DC series motor is shown in the

figure below [12].

Fig 3.2.14 circuit diagram of DC series motor

Here armature current, Ia = series field current, Ise = line current, IL

i.e.; Ia = Ise = IL

Back emf (Eb) = V- I (Ra - Rse)

Power drawn from supply mains = VI

Mechanical power developed Pm = Power input losses in armature and field

= VI I2 (Ra + Rse)

3.2.1h (I) Operating Characteristics of DC series motor:

1) Speed current characteristics2) Torque current characteristics3) Speed torque characteristic

Supply

(V)

Series Field

Ra(Armature)

Rse

+

-


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3.2.1h (Ia) Speed current characteristics:

From the speed equation it is obvious that speed is directly proportional to back

emf, Eb and inversely proportional to flux per pole . Flux per pole is depending on field

current which in turn depends on armature current (Ise = Ia). So as armature current is

increases, speed decreases and vice versa. From the speed current characteristic, it is

obvious that series motor is variable speed motor. With the decrease in load on DC series

motor speed increases, and become dangerously high at no load (light loads). So far this

reason series motors are never started at no load as the machine may get damaged due

heavy centrifugal forces set up in the rotating parts at dangerously high speed at no load.

The minimum load on DC series motor is not below 15% of full load.

3.2.1h (Ib) Torque current characteristics (Electrical characteristics):

From the expansion of mechanical torque T it is obvious that torque is directly

proportional to the product of flux per pole and armature current Ia. Up to saturation

point flux is proportional to field current and hence to the armature current, because Ia =

Speed

Current

Torque

Current

Fig 3.2.15 Speed Current Characteristics

Fig 3.2.16 Torque Current Characteristics


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If. Therefore on light load mechanical torque T is proportional to the square of the

armature current i.e, T Ia2 and hence curve drawn between torque and armature current

up to saturation point is a parabola, as shown in the figure above.

After saturation point flux is almost independent of excitation current and so

the torque is proportional to the armature current i.e. T Ia. Hence the characteristics

become a straight line. The useful torque is, of course, less than the total torque

developed. This is due to torque lost in iron and friction and windage loss. From this we

can infer that starting torque for DC series motor is high.

3.2.1h (Ic) Speed torque characteristics (Mechanical characteristics):

The Speed Torque characteristics is shown in the figure below. Speed Torque

characteristics, is also known as mechanical characteristics.

Speed sharply falls with the increase in torque for smaller values of load. But at

higher loads, the speed drops linearly but slowly with increasing torque. Hence series

motors are best suited for services where the motor is directly coupled to the load such as

fans whose speed falls with the increase in load torque(11).

3.2.1h (II) Performance characteristics of DC series motors

In the below figure, four important characteristics of a dc series motor, namely

torque, speed, current and efficiency, each plotted against useful output power, are

shown. From the performance curves for a DC series motor it is noted that;

Speed

Torque

Fig 3.2.17 Speed Torque Characteristics


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i) The speed of series motor falls rapidly with the increase in load, so aseries motor is not suitable for services requiring a substantially constantspeed.

ii) The efficiency increases rapidly in the beginning, reaches its maximumvalue and then decreases. This is due to the fact that at light loads the friction

and iron losses are large compared with the load and effect to these losses

becomes less with the increase in load. The armature and field copper loss

varies as the square of the current, so these losses increase rapidly with the

increase in load. The efficiency become maximum when friction and iron

losses are practically equal to the copper loss.

iii) Series motor develops a starting torque comparatively greater than thatdeveloped by a shunt motor for a given current. Hence series motors are best

suited where huge starting torque is required i.e. street cars, cranes, hoists and

locomotives.

3.2.1h (III) 22N28 210E DC series motor with K38 Gear box:

Speed

Efficiency

Armature current

Torque

Fig 3.2.18 Performance Characteristics of DC series

Fig 3.2.19 DC series Motor with gear


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The DC series motor with the gear box assembly is shown in the figure 3.2.19

above. The two DC series motors used here are 22N28 210E which having a no-load

speed of 5900 rpm. In this high speed the controlling will be difficult and torque is less.

For improving the control of speed and getting high torque geared motor is one of the

best choice. The gear used here is K38 and it will reduce the speed by 100:1 ratio. Thus

the system works with the speed of nearly 60 rpm. The maximum continuous torque and

maximum continuous power of the motor is 7.3mNm and 3.8 watts respectively.

3.2.1(i) ULN 2803 Driver IC:

The ULN2803 contains eight darlington transistors with common emitters and

integral suppression diodes for inductive loads. The eight NPN Darlington connected

transistors in this family of arrays are ideally suited for interfacing between low logic

level digital circuitry and the higher current/voltage requirements of lamps, relays, printer

hammers or other similar loads for a broad range of computer, industrial, and consumer

applications Each darlington features a peak load current rating of 600mA (500mA

continuous) and can withstand at least 50V in the off state. Outputs may be paralleled for

higher current capability. TheULN2803 is designed to be compatible with standard TTLfamilies. The main features are as follows [13]:

Eight Darlingtons with common emitters

Output current up to 500 mA

Output voltage up to 50V

Integral Suppression diodes

Versions for all popular logic families

Output can be paralleled

Fig 3.2.20 Pin diagram of ULN2803


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Fig 3.2.21 Circuit Diagram of ULN2803 Driver IC

The above figure 3.2.21 shows the diagram of driver circuit part of the main

system. The four input signals form the microcontroller is coming to the pins 1, 2, 3 and

4; the corresponding output is generated from 18, 17, 16 and 15. The input signal

amplitude is either 0V or 5V depending on the application. In the output pins the

signals will be inverted form from the input. In figure the resistors R1 to R4 will limit the

voltage to the driver IC and R5 to R8 are pull up resistors. The diodes D1 to D4 are for

the protection purpose that is to avoid the reverse current flow from the bridge circuit.

3.2.1(i) MAX232 IC:

The MAX232 was the first IC which in one package contains the necessary

drivers (two) and receivers (also two), to adapt the RS-232 signal voltage levels to TTL

logic. It became popular, because it just needs one voltage (+5V) and generates the

necessary RS-232 voltage levels (approx. -10V and +10V) internally. This greatly

simplified the design of circuitry. Circuitry designers no longer need to design and build

a power supply with three voltages (e.g. -12V, +5V, and +12V), but could just provide

one +5V power supply , e.g. with the help of a simple 7805 voltage converter.

It should be noted that the MAX232 is just a driver/receiver. It does not generate

the necessary RS-232 sequence of marks and spaces with the right timing, it does not


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decode RS-232 signal, it does not provide a serial/parallel conversion. All it does is to

convert signal voltage levels. The key features of MAX232 are as follows [14].

3.2.1 i(i) Features of MAX232

Operate from Single +5V Power Supply (+5V and +12V).

Low-Power Receive Mode in Shutdown

Multiple Drivers and Receivers

3-State Driver and Receiver Outputs

Open-Line Detection.

3.2.1 i(ii) Pin Description of MAX232

Fig 3.2.22 Pin Diagram of MAX232

Fig 3.2.23 Circuit diagram of MAX 232 IC


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The circuit diagram of MAX232 IC is shown in the figure 3.2.23 above. In order

to make two devices communicate, whether they are desktop computers,

microcontrollers, or any other form of integrated circuit, we need a method of

communication and an agreed-upon language. The most common form of communication

between electronic devices is serial communication. Communicating serially involves

sending a series of digital pulses back and forth between devices at a mutually agreed-

upon rate. The sender sends pulses representing the data to be sent at the agreed-upon

data rate, and the receiver listens for pulses at that same rate. This is whats known as

asynchronous serial communication. There isnt one common clock in asynchronous

serial communication; instead, both devices have their own clock and agree on a rate to

which to set their clocks.

Here the two devices PC and microcontroller are to exchange data at a rate of

9600 bits per second. First, we would make three connections between these devices:

a) a common ground connection, so both devices have a common reference point tomeasure voltage by;

b) one wire for the sender to send data to the receiver on (transmit line for thesender);

c) One wire for the receiver to send data to the sender on (receive line for thesender).

3.2.1(j) Visual Basic Graphical user interface.

Instead of keypad, the navigational system can be controlled by using serial port

communication. Using MAX 232 IC and RS 232 cable we can connect it to a computer.

There are many programs and tools to interface a computer with microcontroller or other

peripherals. Visual Basic tool is one of the best user friendly graphical interface which is

widely used nowadays. The aged people, who is using walking support system is not

aware of software programs or tools. Here the importance of Visual Basic tool, which is

having colorful graphical front end. Using the mouse only we can control the moving

system. The below figure 3.2.24 shows the visual basic front end for the walking support

system.


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Fig 3.2.24 Visual Basic front end

When the person presses a particular switch then the background color of the

button in the front will change from red to green. Thus the person who operates it can

easily understand the direction of the moving system. The below figure 3.2.25 shows the

system moving towards the forward direction.

Fig 3.2.25 Visual Basic front end for forward direction


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When any key is pressed then a character is sent to the microcontroller and the

microcontroller will send to the control signals to the bridge circuit according to the

character which it received. When forward key is pressed then both the motors will

rotates at clockwise direction that is the signal to bridge circuit will be 1 0 1 0. For

moving reverse direction, the both motors moves anticlockwise direction then the signal

voltage to bridge circuit will be 0 1 0 1. For moving right direction the right motor

moves anticlockwise (backward) and left motor moves clockwise (forward) direction.

The control signal to the bridge for right direction is 1 0 0 1. Like for left direction the

control signals will be 0 1 1 0.

3.3 Flow chart of the moving system:

START

X = Distance,

Y = angle

Is switch

S1 is open

Is any key

pressed

Is Forward

key pressed

Is Right key

pressed

Is Reverse

key pressed

Is Left key

pressed

Move Forward

MotorL_clk = 1;

MotorL_Acl = 0;

MotorR_clk = 1;

MotorR_Acl = 0;

Move Right

MotorL_clk = 1;

MotorL_Acl = 0;

MotorR_clk = 0;

MotorR_Acl = 1;

Move Right

MotorL_clk = 0;

MotorL_Acl = 1;

MotorR_clk = 0;

MotorR_Acl = 1;

Move Right

MotorL_clk = 0;

MotorL_Acl = 1;

MotorR_clk = 1;

MotorR_Acl = 0;

YES(Manual)

YE YE YE YE

NO

NO NO

No movement

A //Auto mode


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Fig 3.3.1 Flow chart of Navigational system

A

Distance = X

Move Forward

Is distance

synthesis of navigation system

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