Final Report on Line Follower Robot

TABLE OF CONTENTS

Chapter No

Chapter 11. Introduction .31.1. Line follower ................................................................................41.2. Importance of line follower51.3. Background6Chapter 22. The ATMEGA 16 microcontroller72.1 IC L 293...102.2 LED..132.3 Component used..142.4 Block diagram..21Chapter 33.Overview.223.1. The Algorithm ...24Chapter 44.1 Implement sensor circuit264 Constructions284.1 Working.304.4 Motor Interface and Control Circuit..31

Chapter 55. Possible Improvements41References and Resources ..42Books and Links

Chapter 1

Introduction

A line following robot is a mobile machine employed to sense and follow the black lines that are drawn on the white surface. As this robot is developed using a breadboard, it will be very simple to construct. This technique can be incorporated into the Automated Guided Vehicles (AGV) for providing the easy way of operation. Generally, the AGV is integrated with the microprocessor and computers for controlling its system. It also uses a position feedback system for traveling in the desired path. In addition, the electric signals and RF communication are needed for communicating with the vehicle and system controller. Such awkward functions are completely not required in this line following robot, and it just uses the IR sensors to travel on the black lines

1.1 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. It is a machine that follows a line, either a black line on white surface or vise-versa. For Beginners it is usually their first robot to play with. In this tutorial, we will teach you to make the line follower robot move on the line with a type of feedback mechanism. Its the most basic example of adding small intelligence to a robot, but its actually the designers intelligence!!After reading this section completely you will be playing with the one shown below. Moreover we will make it modular so that it can be easily modified in future.The main electronics/mechanical components that will be used in making this line follower robot are two sensors made using LDRs, transistors as motor driver circuit, acrylic sheet, General purpose board, Two DC motors and battery. Line-following robots with pick-and-placement capabilitiesare commonly used in manufacturing plants. These move on a specified path to pick thecomponentsfrom specified locationsand place them on desired locations.

Basically, a line-following robot is a self-operating robot thatdetects and follows a line drawn on the floor. The path to be taken isindicated by a white line on a black surface. The control system usedmust sense the line and maneuver the robot to stay on course whileconstantly correcting the wrong moves using feedback mechanism,thus forming a simple yet effective closed-loop system.

1.2Importance of line follower

Sensing a line and manoeuvring the robot to stay on course, while constantly correcting Wrongmoves 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 embeddedmagnetsguidance system for industrial robots moving on shop floor etc.

1.3Background:

We started with building a parallel port based robot which could be controlled manually. 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. The drawbacks of using a personal computer were soon clear Its 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 was hardwired logic circuit or an uC. Since I had no knowledge of uC at that time, I implementeda 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. Line Follower

Chapter 2

The ATMEGA 16microcontroller:

VCC: Digital supply voltage. (+5V) GND: Ground. (0 V) Note there are 2 ground Pins. Port A (PA7 - PA0) Port A serves as the analog inputs to the A/D Converter. Port A also serves as an 8-bit bi-directional I/O port, if the A/D Converter is not used. When pins PA0 to PA7 are used as inputs and are externally pulled low, they will source current if the internal pull-up resistors are activated. The Port apins are tri-stated when a reset condition becomes active, even if the clock is not running. Port B (PB7 - PB0) Port B is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). Port B also serves the functions of various special features of the ATmega16 as listed on page 58 of datasheet. Port C (PC7 - PC0) Port C is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). Port C also serves the functions of the JTAG interface and other special features of the ATmega16 as listed on page 61 of datasheet. If the JTAG interface is enabled, the pull-up resistors on pins PC5 (TDI), PC3 (TMS) and PC2 (TCK) will be activated even if a reset occursPort D (PD7 - PD0) Port D is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). Port D also serves the functions of various special features of the ATmega16 as listed on page 63 of datasheet. RESET: Reset Input. A low level on this pin for longer than the minimum pulse length will generate a reset, even if the clock is not running XTAL1: External oscillator pin 1 XTAL2: External oscillator pin 2 AVCC: AVCC is the supply voltage pin for Port A and the A/D Converter. It should be externally connected to VCC, even if the ADC is not used. If the ADC is used, it should be connected to VCC through a low-pass filter. AREF: AREF is the analog reference pin for the A/D Converter.

All 40 pin are output pins all pins are taking input as well as output. port a has special use it can be use as analog to digital convertor. ADC work by taking a reference value in between 0-5v any value above the reference is considered 1 as high and 0 as low .Pin 10.30= 5vcc (input voltage)Pin 11.31= ground

Pin 12.13= crystal oscillator use for controlling frequency.Pin 32= it gives the reference voltage for ADC it isinternally set as 2.65v

Fig 1 At mega 16 pin diagramIC L293

L293D is a dualmotor H bridge driver integrated circuit (IC). Motor drivers act signal. This higher current signal is used to drive the motors.

L293D contains two inbuilt H-bridge driver circuits. In its common mode of operation, two DC motors can be driven simultaneously, both in forward and reverse direction. The motor operations of two motors can be controlled by input logic at pins 2 & 7 and 10 & 15. Input logic 00 or 11 will stop the corresponding motor. Logic 01 and 10 will rotate it in clockwise and anticlockwise directions, respectively.

Enable pins 1 and 9 (corresponding to the two motors) must be high for motors to start operating. When an enable input is high, the associated driver gets enabled. As a result, the outputs become active and work in phase with their inputs. Similarly, when the enable input is low, that driver is disabled, and their outputs are off and in the high-impedance state.

Fig: 2 L293D pin diagram

PIN 1 = enable pin for motor 1PIN 2 = input 1 for motor 1PIN 3 = output 1 for motor 1PIN 4 = ground (0v)PIN 5 = ground (0v)PIN 6 = output 2 for motor 1PIN 7 = input 2 for motor 1PIN 8 = supply voltage for motors;9-12v(up to 36v)PIN 9 = enable pin for motor 2PIN 10 = input 1 for motor 1PIN 11 = output 1 for motor 1PIN 12 = ground (0v)PIN 13 = ground (0v)PIN 14 = output 2 for motor 1PIN 15 = input 2 for motor 1PIN 16 = supply voltage; 5v(up to 36)

LED

LEDs are used for the testing of the circuits and as well for debugging. In cases where the voltage changes from 0V to 5V and back to 0V, LEDs are useful because a multimeter cannot be used for such purpose and the circuits can be tested just by checking the glowing of the LEDs. The Cathode terminal of the LED is connected to the ground and anode to 5V. The cathode terminal can be identified by looking into the LED and seeing which side is thicker as can be seen in the figure.

Fig: 3 LED

2.1Component used

Chassis:

Chassis, basically the frame of the robot on which motors and wheels are mounted and all the circuitry part is also placed on it.

Fig 4

Caster wheel

A Caster wheel is an undriven, single wheel that is designed to be mounted to the bottom of a larger object so as to enable that object to be easily moved. They are available in various sizes, and are commonly made of rubber, plastic, nylon, aluminum,or stainlesssteel,etc.

Fig 6

Wheel:Wheel is a circular object that revolves on an axle and is fixed below a vehicle or other object to enable it to move over the ground.

Fig: 7

DC MOTOR

DC Motors convert electrical energy (voltage or power source) to mechanical energy (produce rotational motion). They run on direct current.

Fig 8

Source:

An ideal voltage source is a voltage source that maintains the same voltage across the source's terminals no matter what current is drawn from the terminals of the source or what current flows into the terminals.

DC source:Direct current (DC) is the unidirectional flow of electric charge. Direct current is produced by sources such as batteries, solar cells, and commutator-type electric machines of the dynamo type, etc.

Voltage Regulator

Usually the motors used in the bot require a supply voltage of 12V while most of the circuitry requires 5V. In order to avoid the usage of two separate batteries an electronic component called voltage regulator is used. Voltage regulator can be defined as a component which is used to convert certain fixed voltage levels into some other voltages. Thus in our case we will be using a voltage regulator which can convert 12V into 5V. One such voltage regulator is LM7805.

Fig 9

The top part of the figure above shows the LM7805 with the pins 1,2 and 3. In the schematic shown the input corresponds to Pin 1, GND to Pin 2 and output to Pin 3. This implies that if 12V is applied at pin 1(i.e. it is connected to the positive terminal of the battery) and the pin 2 is grounded (i.e. it is connected to negative terminal of the battery) pin 3 will give a 5V output. The regulator works even without the capacitors but it is better if capacitors are used as they cut down the voltage fluctuations.

IC7805

IC 7805 is a 5V Voltage Regulator that restricts the voltage output to 5V and draws 5V regulated power supply.

Fig 10

SENSOR:

IR reflective sensors have one emitter (IR LED) and one receiver (Phototransistor or photo diode. If we have white surface it reflects the light and it will sensed by the receiver, similarly if we have black surface it absorbs the light and receiver can not sense light. Photo diode has property that if IR light fall on it its electrical resistance comes down (i.e. it comes down from 150k to 10k if no noise present).

Fig 11

The sensors use for line detecting in a line-follower bot are IR sensors. These sensors have a pair of transmitter and receiver when the sensor is on a reflecting surface (white) the light transmitted by the transmitter is detected by the receiver and when the sensor is on black surface or a non-reflecting surface exactly opposite happens.. The figure on the right side shows the assembled sensor. These readymade sensors are directly available in the market. Making the sensor from the T-R pair will not be explained in this tutorial.

Block Diagram

Fig 12The basic principle involved in this is it captures the line position with IR sensors mounted at front end of the robot. The block diagram of the line follower robot shows that, when the sensor senses the path, output will be 0s or 1s which are then fed to the microcontroller, and then the microcontroller decides the next move according to the program. When both the sensors are indicating low (0) then robot start moving on the black path, for white if it indicates high (1) then it moves along the path.

Chapter 3

OVERVIEW

Fig 13

The robot uses IR sensors to sense the line, an array of 8 IR LEDs (Tx) and sensors (Rx), facing The ground has been used in this setup. The output of the sensors is an analog signal which Depends on the amount of light reflected back, this analog signal is given to the comparator to produce 0s and 1s which are then fed to the uC.

L4 L3 L2 L1 R1 R2 R3 R4 Left Centre Right Sensor Array

Starting from the centre, the sensors on the left are named L1, L2, L3, L4 and those on the right are named R1, R2, R3, and R4. Let us assume that when a sensor is on the line it reads 0 and when it is off the line it reads 1

The uC decides the next move according to the algorithm given below which tries to position the robot such that L1 and R1 both read 0 and the rest read 1.

L4 L3 L2 L1 R1 R2 R3 R4 1 1 1 0 0 1 1 1 Left Centre Right Desired State L1=R1=0, and Rest=1 Line Follower

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:

Left centre Right Here L=3 R=0

Left centre Right Here L=2 R=4 2. If all sensors read 1 go to step 3, else, If L>R Move Left If Lldev) move(R, 0,195+12*rdev); if(rdev