Different ics:-

L293

Description

The L293 and L293D are quadruple high- current half H- current half -H

drivers.

The L293 is designed to provide bidirectional drive current of up to 1 A

at voltage from 4.5V to 36V.

The L293D is designed to provide bidirectional drive current of up to

600-mA at voltage from 4.5V to 36V.

Both devices are designed to drive inductive loads such as relays,

solenoids, dc and bipolar stepping motors, as well as other high-current/high-

voltage loads in positive- supply applications.

All inputs are TTL compatible

Each output is a complete totem-pole drive circuit, with a Darlington

transistor sink and as pseudo-Darlington source.

Drivers are enabled in pairs, with driver 1 and 2 enabled by 1,2EN and

driver 3 and 4 enabled by 3,4EN.

When an enabled input is high, the associated drivers are enabled and

their outputs are active and in phase with their inputs.

When the enable input is low, those drivers are disabling and their

outputs are off and in the high-impedance state.

With the proper data inputs, each pair of drivers forms a full-H (or

bridge) reversible drive suitable for solenoid or motor application.

On the L293, external high –speed output clamp

ACKNOWLEDGEMENT

We take this opportuni ty to humbly express our thankfulness to a l l those

concerned with our project ent i t led l ine fol lowing robot using microcontrol ler .

We express very s incere thanks to Mr.D.M.MODI for providing us an opportuni ty

to works on such an interest ing project , wi thout whose help we could not have

completed pt sat isfactor i ly his invaluable guidance has proved to be a key tour

success pin overcoming chal lenges.

We faced during the course of the project work. We are a lso obl iged to

Mr.R.J .PATEL, HOD Electronics & Communicat ion department , for a l lowing us

to do project in this par t icular organizat ion. We are special thanks Mr.D.M.MODI

lecturer of the EC department for guide this project and good suggest ion.

Introduction

What is a line follower?

Line follower is a machine that can follow a path. The path can be visible like a black line on a white

surface (or vice-versa) or it can be invisible like a magnetic field.

Why build a line follower?

Sensing a line and maneuvering the robot to stay on course, while constantly correcting wrong moves

using feedback mechanism forms a simple yet effective closed loop system. As a programmer you get

an opportunity to ‘teach’ the robot how to follow the line thus giving it a human-like property of

responding to stimuli. Practical applications of a line follower: Automated cars running on roads with

embedded magnets; guidance system for industrial robots moving on shop floor etc.

Background:

I started with building a parallel port based robot which could be controlled manually by a keyboard.

On the robot side was an arrangement of relays connected to parallel port pins via opto-couplers.

The next version was a true computer controlled line follower. It had sensors connected to the status

pins of the parallel port. A program running on the computer polled the status register of the parallel

port hundreds of times every second and sent control signals accordingly through the data pins.

It’s difficult to control speed of motors. As cable length increases signal strength decreases and

latency increases. A long multi core cable for parallel data transfer is expensive. The robot is not

portable if you use a desktop PC. The obvious next step was to build an onboard control circuit; the

options a hardwired logic circuit or a uC. Since I had no knowledge of uC at that time, I implemented

a hardwired logic circuit using multiplexers. It basically mapped input from four sensors to four

outputs for the motor driver according to a truth table. Though it worked fine, it could show no

intelligence – like coming back on line after losing it, or doing something special when say the line

ended. To get around this problem and add some cool features, using a microcontroller was the best

option.

Algorithm:

1. L= leftmost sensor which reads 0; R= rightmost sensor which reads 0.

If no sensor on Left (or Right) is 0 then L (or R) equals 0;

Ex:

L4 L3 L2 L1 R1 R2 R3 R4

1 0 0 1 1 1 1 1

Left Center Right

Here L=3 R=0

L4 L3 L2 L1 R1 R2 R3 R4

1 1 0 0 0 0 0 0

Left Center Right

Here L=2 R=4

2. If all sensors read 1 go to step 3,

else,

If L>R Move Left

If L<R Move Right

If L=R Move Forward

Goto step 4

3. Move Clockwise if line was last seen on Right

Move Counter Clockwise if line was last seen on Left

Repeat step 3 till line is found.

4. Goto step 1.

Implementation

Sensor Circuit:

Description:  These simple devices operate at 940nm and work well for generic IR systems

including remote control and touch-less object sensing. Using a simple ADC on any microcontroller

will allow variable readings to be collected from the detector. The emitter is driven up to 50mA with

a current limiting resistor as with any LED device. The detect is a NPN transistor that is biased by

incoming IR light.

Applications:

IR Schematic - Basic object detection schematic

Seattle Robotics - Infrared object detection

Robot Room - Excellent website with lots of goodies

Motor Interface and Control Circuit:

The 8 sensors are connected to PORTA.

You need not connect anything to AVCC and AREF, it is required only if ADC is used.

The L298 Motor Driver has 4 inputs to control the motion of the motors and two enable inputs which

are used for switching the motors on and off. To control the speed of the motors a PWM waveform

with variable duty cycle is applied to the enable pins. Rapidly switching the voltage between Vs and

GND gives an effective voltage between Vs and GND whose value depends on the duty cycle of

PWM. 100% duty cycle corresponds to voltage equal to Vs, 50 % corresponds to 0.5Vs and so on.

The 1N4004 diodes are used to prevent back EMF of the motors from

disturbing the remaining circuit. Many circuits use L293D for motor control, I chose L298 as it has

current capacity of 2A per channel @ 45V compared to 0.6 A @ 36 V of a L293D. L293D’s package

is not suitable for attaching a good heat sink, practically you can’t use it above 16V without frying it.

L298 on the other hand works happily at 16V without a heat sink, though it is always better to use

one.

Truth Table for controlling the direction of motion of a DC motor

COMPONENT DESCRIPTION

PREPARATION OF PCB

It is called printed circuit board consists of conducting circuit pattern applied to one or both side of an

insulating base depending upon that it is called single side P.C.B. or double side P.C.B. conductive

materials available are silver, brass Aluminum and copper. Copper is most widely used. The thickness of

conducting materials depends upon the current carrying conductor’s capacity of circuit. Thus a thicker

copper layer will have more capacity.

PRINTED CIRCUIT BOARD

Printed Circuit Board is piece of plastic insulating board on the one side of which a complete layout

diagram of an electronics circuit consisting of copper conducting paths is printed by a special photo

engraving process on other side of PCB electronics components like resistor, capacitors, transistors,

diodes etc. are mounted suitable holes are provided in the PCB for mounting the components.

These components are connected to the conducting patch by soldering. PCBs are used for assembling

electronic circuit assembly more compact uniform and stable. PCB used for transmitter and receiver.

8051-MICROCONTROLLER

A microcontroller is a small computer on a single integrated circuit consisting internally of a

relatively simple CPU, clock, timers, I/O ports and memory. As in every embedded systems we are

having controller to control or process all the activities and devices.

FEATURES OF 8051 MICROCONTROLLER

8-bit program status word.

Internal ROM.

Internal RAM of 128 bytes.

Two 16 bit timer/counter: To and T1.

32 input/output pins arranged as four 8-bit ports: P0, P1, P2, and P3.3

Serial function register’s: IE, IP, TCON, TMOD, SCON, SBUF, TH0, TH1.

8-bit arithmetic logic unit.

8-bit Accumulator register.

8-bit program status word.

16-bit program counter.

16-bit stack pointer.

Three internal intterupt: T0, T1, RI or TI.

Two external interrupt: INTO and INT1.

Clock circuit and reset circuit.

Crystal oscillator

CRYSTAL OSCILLTOR:-

A miniature 4 MHz quartz crystal enclosed in a hermetically sealed HC-49/US package, used as the

resonator in a crystal oscillator. A crystal oscillator is an electronic circuit. That uses the mechanical

resonance of a vibrating crystal of piezoelectronic material to create an electrical signal with a very

precise frequency.

OPERATION

A crystal is a solid in which the constituent atoms, molecules, or ions are packed in a regularly

ordered, repeating pattern extending in all three spatial dimensions.

Almost any object made of an elastic material could be used like a crystal, with appropriate

transducers, since all objects have natural resonant frequencies of vibrations. The resonant frequency

depends on size, shape, elasticity, and the speed of sound in the material. High frequency crystals are

typically cut in the shape of a simple, rectangular plate

When a crystal of quartz is properly cut and mounted, it can be made to distort in an electric field by

applying a voltage to an electrode near or on the crystal. This property is known as piezoelectricity.

When the field is removed, the quartz will generate an electric field as it returns to its previous shape,

and this can generate a voltageThe result is that a quartz crystal behaves like a circuit composed of an

inductor, capacitor and resistor, with a precise resonant frequency.

CAPACITOR

Capacitors are electronic components used for storing charge and energy. In their simplest form,

Capacitors consist of two conducting plates separated by an insulating material called the dielectric

Applications

Automotive

Diesel ECU and Fuel Injector Drivers

EPS Electric Power Steering

HID Headlight AFL

HVAC Climate Control

Capacitance

Capacitance is the ability of a capacitor to store energy in an electric field. Capacitance is also a

measure of the amount of electric potential energy stored (or separated) for a given electric potential.

A common form of energy storage device is a parallel-plate capacitor. In a parallel plate capacitor,

capacitance is directly proportional to the surface area of the conductor plates and inversely

proportional to the separation distance between the plates. The SI unit of capacitance is the farad; 1

farad is 1 coulomb per volt. The energy (measured in joules) stored in a capacitor is \capacitor of

capacitance C, holding a charge +q on one plate and −q on the other. Moving a small element of

charge dq from one plate to the other against the potential difference V = q/C requires the work dW:

WhereW is the work measured in joules, q is the charge measured in coulombs and C is the

capacitance, measured in farads. A capacitor is a passive electrical component that can store energy in

the electric field between a pair of conductors. The process of storing energy in the capacitor is

known as “charging”, and involves electric charges of equal magnetic, but opposite polarity, building

up on each plate. A capacitors ability to store charge is measured by its capacitance, in units of farads.

Capacitors are occasionally referred to as condensers. This term is considered archaic in English, but

most other languages use a cognate of condenser to refer to a capacitor. A wide variety of capacitors

have been invented, including small electrolytic capacitors used in electronic circuits, basic parallel

plate capacitors, mechanical variable capacitors, and the early Leyden jars, among numerous other

types of capacitors.

RESISTOR

Resistors consist of a resistance track with connections at both ends and a wiper which moves along

the track as you turn the spindle. The track may be made from carbon, ceramic and metal mixture or a

coil of wire.

Resistors may be used as a rheostat with a two connections (the wiper and the track) or as a

potentiometer with all three connections in use. Some resistors are designed to be mounted directly

on the circuit board.

Resistance is a property of a resistor. Resistance is a property of conductor that depends upon of it in

dimension, material, temperature and which determine the current resolution from given potential

difference across resistance. Resistor is used to reduce a voltage or reduce power.

The two limits or value in which the resistance value can fall or increased due to temperature, time

moisture and heat dissipation, resistor are available in many types, but in our case we use a carbon

cracked film resistor.

This resistor in different voltage ranges of 1/10, 1/3, 1/4 or 2 watts. The value normally ranges

between 1017 to 20MH.

LIGHT EMITTING DIODE

A light emitting diode is a semiconductor diode that emits light when an electric current is applied in

the forward direction of the device, as in the simple LED circuit. The effect is a form of electronic,

where incoherent and narrow spectrum light is emitted from the p-n junction. The color of the emitted

light depends on the composition and condition of the semiconducting material used.

LEDs are widely used as inductor lights on electronic devices and increasingly in higher power

applications such as flashlights and area lighting. An LED is usually a small area light source, often

with optics added to the chip to shape its radiation pattern and assist in reflection.

The refractive index of most LED semiconductor materials is quite high, so in almost all cases the

light from the LED is coupled in to a much lower-index medium. The large index difference makes

the reflected back in to the semiconductor, where it may be absorbed and turned in to additional heat;

this is usually one of the dominant causes of LED inefficiency. Often more then half of the emitted

light is reflected back at the LED package and package air interfaces.

The reflection is most commonly reduced by using a half sphere package with the diode in the center,

so that the outgoing light rays strike the surface perpendicularly, at which angle the reflection is

minimized.

RESET CIRCUIT

The PIC 16F84A differentiates between various kin Ds of RESET:

Power on reset

MCLR during normal operation

MCLR during SLEEP

WDT Reset

WDT Wake-up

The MCLR Reset path has a noise filter to ignore small pulses Some registers are not affected in any

RESET condition, their status is unknown on a POR and unchanged in any other RESET. Most other

registers are reset to a “RESET state” on POR, MCLR or WDT Reset during normal operation.

RELAY

It closes the voltage less point of contact while the door lock works to control the electromagnetic

door lock or equipment outside. A relay is an electrically operated switch. Current flowing through

the coil of the relay creates a magnetic field which attracts a lever and changes the switch contacts.

The coil current can be on or off, so relay have two switch positions and most have double throw

switch contacts.

Relays allow one circuit to switch a second circuit which can be completely separate from the first.

For example a low voltage battery circuit can use a relay to switch a 230v AC mains circuit. There is

no electrical connection inside the relay between the two circuits; the link is magnetic and

mechanical.

Most relays are designed for PCB mounting but you can solder wires directly to the pins providing

you take care to avoid melting the plastic case of the relay. The relay’s switch connections are

usually labeled COM, NC and NO.

Advantages of relays:

1. Relays can switch AC and DC, transistors can only switch DC.

2. Relays can switch higher voltages than standard transistors.

3. Relays are often a better choice for switching large currents.

4. Relays can switch many contacts at once.

Disadvantages of relays:

1. Relays are bulkier than transistors for switching small currents.

2. Relays cannot switch rapidly; transistors can switch many times per second.

3. Relays use more power due to the current flowing through their coil.

DC motor driver

Basic circuit of using L293 forms an H- bridge driver is shown in figure.

As shown for such inductive load as DC motor, external dioodes for suppressing back EMF must be

connected.

The inboard uses L293D instead, the L293Dhas internal diodes, however providing a bit less driving

capacity,i.e,600Ma@4.5v-36V. From the truth table, we see that direction of the motor cn control by

pin C and D.

VINH enable/ disable power to the motor, thus for speed regulation, we than use this pin for PWM

singling. External diode must be connecting for L 293.

Motors and wheels

They fit nicely and provide enoromes torque at low speed exatly matching the needs for the meticules

floor examination. A brass tube couples the d shape motor shaft to a LEGO wheel. Because the

LEGO BAR connects with friction to all standard compatible LEGO wheels a wide selection of high

quality production prescion tires are available and quickly interchangeable.

A screw hole is drilled and tapped to lock the brass to the gear head shaft. Since the shaft is off center

on the motor, the moter bodies are purposely misaligned with each other so other, so that the wheels

actual line up. Be sure to center punch holes before drilling a center punch looks like a solid metal

pencil with a hardnededtip. Aim the tip against the location for the hole slightly with a hammer.

LINE TRACKING SENSOR

Since there is no ADC for 89c51 chip, each competitor may build their own Line tracking sensor,

some may use LM Quad comparator with ir transmitter and receiver, some may use LDR as described

in LINE FOLLOWER ROBOT.

APPLICATIONS

BIBLIOGRAPHY

The 8051/8052 Microcontroller: Architecture, Assembly Language