1. INTRODUCTION

Robotics nowadays is of great importance and interest for hobbyists and design engineers.

Robot in general is defined as a system that contains sensors, control systems, manipulators,

power supplies and software all working together to perform a task. It has many application

in auto, medical, manufacturing and space industries. Various types of robots are in a wide

use among which automated line-following robot is in a huge practice.

Automated line-following robot is a self-operating machine that detect and follows a line

pattern drawn on a floor. Generally, the paths are visible like a black line on a white surface

(or vice versa) or it can be invisible like a magnetic field. Actually, a fairly good and

advanced, robot could be easily adapted to maze solving, obstacle avoiding, etc. However, at

this point, it only follows a white line and independently self accommodates the turnings.

The robot consists mainly four parts two sensors, two comparators, one decision making

device and a motor driver (with two gear head dc motors). Phototransistor sensors detect the

white strip on the black background whose output is fed to microcontroller which takes the

decision and gives appropriate command to motor driver IC so as to move the motor

accordingly.

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2. OBJECTIVES

To study and implement simple embedded electronic system

To use microcontroller as a versatile component to implement logical functions

To implement simple feedback mechanism for automation

To correlate the automated line following robots in practical and real world application

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3. PROJECT OVERVIEW

Electronics systems and machines are seldom developed with a single component, rather they

are combination of different electronics parts and units. Each single components are

embedded to form different identical functional units which at once functions together to

comprise an electronic system. Automated Line- Following Robot is not an exception. It

comprises of various parts which can be described in major functional blocks.

3.1. Block Diagram Description of ALFR

The basic organization of ALFR can be divided into 4 major functional blocks.

Figure 1: Block diagram of ALFR

Sensor: The sensor sense the light reflected from the surface and feeds the output to the

comparator. When the sensor is above the white background the light falling on it from the

source reflects to the sensors, and when the sensor is above the black background the light

from the source doesn’t reflect to it. The sensor senses the reflected light to give output,

which is fed to the comparator.

Comparator: The comparator compares the analogue inputs from sensors with a fixed

reference voltage. If this voltage is greater than the reference voltage the comparator outputs

a low voltage, and if it is smaller the comparator generates a high voltage the acts as input for

the decision-making device (microcontroller).

Decision making and controlling circuit: The microcontroller is programmed to make the

robot move forward, turn right or turn left based on the input coming from the comparator.

The outputs of the microcontroller are fed to the motor driver.

Sensor 1

Sensor 2

Comparator 1

Comparator 2

Decision making and controlling circuit

Motor driving circuit

Motor 2

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Motor 1

Motor driving circuit: The current supplied by microcontroller to drive the motor is small

therefore a motor driver IC is used. It provides sufficient current to drive the motors.

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4. GANTT CHART

The Project is started from July 15, 2010 and will be ended in September 14, 2010. We have

total 70 working days.

No. Task Start End

Duration Ju

ly

Augu

st

September

3rd

week

4th

week

1st

week

2nd

week

3rd

week

4th

week

1st

week

2nd

week

1 Project discussion and topic selection

7/15/2010 7/23/2010 8

2 Proposal writing 7/23/2010 7/30/2010 73 Detail analysis on

circuit component7/31/2010 8/6/2010 7

4 Microcontroller programming

8/6/2010 8/18/2010 11

5 Block implementation and debugging

8/11/2010 9/5/2010 21

6 PCB design 8/28/2010 9/9/2010 97 Report writing 9/7/2010 9/14/2010 7

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5. METHODOLOGY

5.1. Hardware Block Diagram Implementation

The basic block building for automatic line following robot is shown below (figure 2).

Sensor Block Comparator Block Control Block Output Block

Figure 2: Circuit diagram for ALFR

5.1.1. Sensor Block

Automatic system must use some physical parameters as an input to get aware of its

surrounding. ALFR uses the reflected light rays emitted from led. The intensity of reflected

light will distinguish the path to take the further decisions

When light falls on the phototransistor (say, T1), it goes into saturation and starts conducting.

When no light falls on the phototransistor, it is cut-off. A white LEDs has been used to

illuminate the white path on a black background. Phototransistors T1 and T2 are used for

detecting the white path on the black background.

5.1.2. Comparator Block

Collectors of phototransistors T1 and T2 are connected to the inverting inputs of operational

amplifiers A2 and A1. The signal voltage at the inverting input of the operational amplifiers

is compared with the fixed reference voltage, which is formed by a potential divider circuit of

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5.6-kilo-ohm resistor and 10-kilo-ohm preset. This reference voltage can be adjusted by

changing the value of the 10-kilo-ohm preset.

When sensor T2 is above the black surface, it remains cut-off as the black surface absorbs

virtually all the light falling from LED2 and no light is reflected back. The voltage at the

inverting input (pin2) of operational amplifiers A1 is higher than the references voltage as its

non-inverting (pin3) and therefore the amplifier output at pin1 becomes zero.

When sensor T2 is above the white line, the light gets reflected from the white surface to fall

on phototransistor T2. Phototransistor T2 goes into saturation and conducts. The inverting

input (pin 2) of operational amplifier A1 goes below the reference voltage at its non-inverting

input (pin 3) of operational amplifier A1 and therefore output pin 1 goes high. This way, the

comparator outputs logic ‘0’ for black surface and logic ‘1’ for white surface.

Similarly, comparator A2 compares the input voltage from phototransistor T1 with a fixed

reference voltage.

5.1.3. Control Block

The outputs of operational amplifiers A1 and A2 are fed to microcontroller. An 8-bit

microcontroller having 4 KB of Flash, 128 bytes of RAM, 32 I/O lines, two 16-bit

timers/counters, on-chip oscillator and clock is used. Also 12MHz crystal is used for

providing the basic clock frequency. All I/O pins are reset to ‘1’ as soon as RST pin goes

high. Holding RST pin high for two machine cycles while the oscillator is running resets the

device. Power-on reset is derived from resistor R5 and capacitor C1. Switch S2 is used for

manual reset. The microcontroller, based on the inputs from sensor T1 (say, left) and sensor

T2 (say, right), controls the motor to make the robot turn left, turn right or move forward.

Table for action corresponding to the microcontroller inputs and outputs can be summed in a

table.

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Inputs Outputs ActionP3.0 P3.1 P2.3 P2.2 P2.1 P2.00 0 1 0 1 0 Forward0 1 0 0 1 0 Left1 0 1 0 0 0 Right1 1 0 0 0 0 Stop

Table1. Action corresponding to Microcontroller I/Os.

5.1.4. Output Block

Port pins P2.0, P2.1, P2.2 and P2.3 are connected to pins 15, 10, 7 and 2 of motor

driverL293D. Port pins P2.0 and P2.1 are used for controlling the right motor, while port

pins P2.2 and P2.3 are used for controlling the left motor. Three wheels can be used for this

robot-one on the front and two at the rear. Front wheel can rotate in any direction as

specified by the rear wheel. To make the robot turn left, the left-side motor should stop and

the right-side motor should rotate in the clockwise direction. Similarly, to make the robot

turn right, the right-side motor should stop and the left-side motor should rotate in clockwise

direction. For forward motion, both the motors should rotate in clockwise direction.

5.2. Software Implementation

Microcontroller used in decision making and controlling circuit is solely responsible to drive

the motors in logical way. This microcontroller needs to be programmed for being capable of

making such decisions. The flow chart and algorithm which can be helpful to program the

microcontroller are discussed below.

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5.2.1. Flow Chart

Figure 3: Program flow-chart of ALFR.

5.2.2. Algorithm

Step 1. Start.

Step 2. Move both wheels forward.

Step 3. Get both sensors output.

If (over white line; high)

Stop left wheel & move right wheel;

Go to step 3.

Otherwise;

Go to step 4.

Step 4. Get right sensors output.

If (over white line; high)

Stop right wheel & move left wheel;

Go to step 4.

Otherwise;

Go to step 5.

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Step 5. Get output from both sensors.

If (both over white; high)

Go to step 6.

Otherwise;

Go to step 2.

Step 6. Stop.

5.3. Working

Figure 4: Path of ALFR

Fig. 5 shows the path of the line-follower robot, where ‘L’ is the left sensor and ‘R’ is the

right sensor.

At the start, when the robot is at point ‘A’ sensors T1 and T2 are above the black surface and

port pins P3.0 and P3.1 of the microcontroller receive logic ‘0’. As a result, the robot moves

forward in straight direction.

At point ‘B’, a left turn is encountered, and the left sensor comes above the white surface,

whereas the right sensor remains above the black surface. Port pin P3.0of the microcontroller

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receives logic ‘1’ from the left sensor and port pin P3.1 receives logic ‘0’ from the right

sensor. As a result, the left motor stops and the right motor rotate, to make the robot turn left.

This process continues until the left sensor comes above the black background.

Similarly, at point ‘C’, where a right turn is encountered, the sane procedure for right turn is

executed. When both the sensors are at the white surface, the robot should stop. The output

of the microcontroller (IC2) depends on the inputs received at its port pins P3.0 and P3.1 as

shown in table (Table1).

5.4. Components List

Semiconductors:

IC1 - LM324 quad operational amplifier

IC2 - AT89C51 microcontroller

IC3 - L293D motor driver

T1, T2 - L14F1 photo-transistor

D1 - 1N4007 diode

LED1, LED2 - 5mm LED

Resistors: (all 1/4 - watt, ±5% carbon):

R1, R2, R5 - 10-kilo-ohm

R3, R4 - 5.6-kilo-ohm

R6 - 330-ohm

R7 - 220-ohm

R8 - 1-kilo-ohm

VR1, VR2 - 10-kilo-ohm preset

Capacitors:

C1 - 10µF, 16V electrolytic

C2, C3 - 33pF ceramic disk

C4 - 47µF, 16V electrolytic

C5 - 0.1µF ceramic disk

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Miscellaneous:

S1 - On/off switch

S2 - Push-to-on switch

Xtal - 12MHz crystal

M1, M2 - 20rpm, 6V DC geared motor

Batt. - 6V, 4.5AH battery

- 2 side brackets for mounting motors

- 1 caster wheel (front wheel)

- 2 wheels for the rear

- Chassis

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6. APPLICATION

Line following robot has a great reception in automation engineering. ALFR with different

capabilities are commonly used in industry and manufacturing plants. It has many

application in auto, medical and space industries. Automation cars will have a huge

impression over current transportation system in near future.

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7. CONCLUSION

This robot is a great tool for expanding a student’s imagination and engineering expertise as

it gives a basic, yet complete introduction to robotics. This project then shows how this small

yet diverse and powerful platform can then be added upon, in this case, with line-tracking.

This allows the robot to be used to teach someone beyond even the basics.

Automated Line- Following Robot proposed is a versatile machine that has some intelligence

of tracing the specified line. Microcontroller for the decision making and logic section makes

it a powerful device. In nutshell, Automated Line- Following Robot is a simple and effective

automated system that has some very good applications in household and industries.

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REFERENCES

Automated line-following Robot. Electronics for you magazine. Retrieved from September

2009.

Intelligent line following Robot. Retrieved July 28, 2010 from http://www.wineyard

technologies.com/tools/assests/wk22.pdf

An Autonomous Line Following Robot. Retrieved July 28, 2010 from

http://www.mil.ufl.edu/imdl/papers/IMDLReport Summer05/dutka-paul/MILee.pdf

Degelman, D. (2009). APA style essentials. Retrieved from http://

www.vanguard.edu/faculty/ddegelman/detail.aspx?doc_id=796

Gantt chart Retrieved July 29, 2010 from http://www.smartdraw.com/downloads/

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