Line Follower Robot

Robotics Workshop Currents 15th march 2008 EEE Department NIT Trichy

Developed By: Mayur Agarwal Prashant Agrawal Krishna Nand Gupta Hitesh Meghani

To Our Readers

We are glad to have had an opportunity to share our knowledge with interested robotics enthusiasts. In this book we have attempted to provide a brief compilation of our experiences in robotics (participating and winning in Technical Festivals all over the country), extending over last three years.

The prospect of practically implementing engineering concepts is the hallmark of robotics. By reading the basics in this book you will gain a significant insight into various tools employed in shaping a robot. However to participate in technical festivals with ever changing problem statements you will be required to apply these basics concepts and come up with innovative algorithms and superior designs.

Do not expect this book to be a panacea for all robotic problems, rather you will have to sit and work for hours to get a functioning robot. Transform each failure into a stepping stone instead of stumbling over it. We appreciate the beauty of diamond but little do we wonder how it became so bright? Its perseverance extending thousands of years transformed it into its present sparkling state.

We encourage you to plunge further into the field of robotics with dedicated perseverance, make your own mistakes and gain valuable experience from them.

ALL THE BEST

Your valuable suggestions and inquisitive doubts are welcome. You can contact us at

Mayur Agarwal (mayurmagic.nitt@gmail.com )

Krishna Nand Gupta (kng_sweet94@yahoo.com)

Prashant Agarwal (pras_nitt@yahoo.co.in )

Hitesh Meghani (h.nittian@gmail.com )

~ 1 ~

Introduction The line follower is a self operating robot that detects and follows a line that is

drawn on the floor. The path consists of a black line on a white surface (or vice versa). The control system used must sense a line and maneuver the robot to stay on course, while constantly correcting the wrong moves using feedback mechanism, thus forming a simple yet effective closed loop System. The robot is designed to follow very tight curves.

Sample Paths The path is a black line on a white background with width of 3 cm (except at

bends where a little variation may be present). It may contain paths laterally displaced by around 3 cm and also gap of at most 5 cm. (All these specifications may vary from one competition to another).

Figure 1: Basic Sample Arena

Figure 2: Sample Arena of Kurukshetra’08 (Anna University)

Figure3: Sample Arena of Pragyan’07 (NIT Trichy)

Figure4: Sample Arena of Robo‐Relay of Kishitij’08 (IIT KGP)

From above images we can conclude that in most of line follower competitions, some additional task has to be performed apart from following the line.

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Sample Calculation: Say Receiver has resistance- Rs=150kΩ without light (on black surface) Rs=10kΩ with light (on white surface) The voltage that goes to comparator Without light: (on black surface) Vp= *5 V=4.6875 V With light: (on white surface) Vp= *5 V=2.500 V

Thus we get the variation in voltage, which is sensed by the comparator IC (LM324). The comparator then, gives logical high or low according to input. Comparator Comparator is a device which compares two input voltages and gives output as high or low. In a circuit diagram it is normally represented by a triangle having-Inverting (negative) Input (-), Non-Inverting (positive) Input(+), Vcc, Ground, Output.

Properties of comparator:

If V+ > V- then Vo=Vcc (Digital High 1 output)

If V+ < V- then Vo=0 (Digital Low 0 output)

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Let’s see some examples

Use of comparator in IR sensor As above we see that two inputs are required for comparator. One input is from photo-receiver (like photo-diode), other is generated by us using potentiometer (preset). The second voltage is also called as reference voltage for that sensor. Setting of reference voltage (Vref) We can vary reference voltage by using potentiometer, such that it can vary from 0V to Vcc. We set the reference voltage as mean value of the sensor outputs measured with and without light.

From above example Vref = . . = 3.5875 V

Lets connect Inverting Input of Comparator to photo- receiver, Non-Inverting Input to potentiometer (as shown in figure) and output to micro controller.

Sample Calculation: Let V+ = 3.5875 V With light :(on white surface) V- = 0.9090 V Thus V+>V- and Vo= Vcc = 5 V Thus we get digital HIGH output. Without light:(on black surface) V- = 3.333 V Thus V+<V- and Vo = 0 V Thus we get digital LOW output.

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Basic hardware connections of ATmega8L Pin 1 (Reset):

The use of reset pin is to reset the ATmega8L microcontroller. This can be done by connecting this pin to ground. In normal mode of execution it should have at least 2.7V. Thus it is connected to +5 V through 10k ohm resistance .We should make sure that its potential be above 2.7 for proper execution of code. Pin 7 and 20 (Vcc):

Pin 7 and 20 should be connected to Power supply. (2.7 to 5.5 volt for ATmega8L) Pin 8 and 22 (Ground):

Pin 8 and 22 should be connected to Ground. This ground should be common to for the entire circuit.

Input and Output Ports

• In ATmega8L we have three I/O (input/output) ports viz. Port B, Port C and Port D.

• One can configure any pin of each of these ports as input or output pin by appropriate programming.

Pin PORT Connection PWM 14 PB0 Negative of right NO 15 PB1 Positive of right YES 16 PB2 Positive of Left YES 17 PB3 Negative of Left NO

Thus we can use Port C or Port D or remaining Pins of Port B as input. But for the sake of simplifying hardware connections we choose Port D pins as input pins.

Make sure Ground and Vcc do not get interchanged and Vcc should not exceed 5.5 V. If you connect supply wrongly, ATmega8L will suffer permanent damage.

We will be using Port B pins (PB0 to PB3) as output pins because at pinPB1 and PB2 we have on-chip PWM output that can control the speed of motors.

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B) Software Details: Programming and Simulating The program code acts as the decision-maker embedded in the micro-

controller i.e. it decides what will be the outputs for particular set of input combination.

Programs for the AVR series of microcontrollers can be written in assembly (AVR ASM), C and BASIC. AVR Studio, WinAVR, etc. are some free development softwares for programming the AVR Microcontrollers. We will be using winAVR for programming and AVR Studio for simulating (Simulation means debugging the code on software, one can virtually give the input and check the output for that code).

In winAVR programmers Notepad we write our C code, after compilation it generates ‘.hex’ file which is a hardware level code.

Sample Code: To blink a LED connected at pin 6 (PD4) of ATmega8L. #include <avr/io.h> //header file to include input output port #include <util/delay.h>//header file to include delay function #define LED PD4 int main(void) DDRD = (1 << LED); /* DDR=Data Direction register... its to define PD4 OUTPUT pin rest bits of DDRD can be 0 or 1 does not make any significance */ while (1) PORTD = (1 << LED); // switch on _delay_ms(200); PORTD = (0 << LED); // switch off _delay_ms(200); return 0;

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The tableLeft MotStraight Stop Reverse Straight Straight Reverse

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Electrical Characteristics of L293D

Symbols

Parameter Testing Condition

Min. Max. Units

Vss Logic Supply Voltage Pin 16 4.5 36 V Vs Supply Voltage Pin 8 Vss 36 V Ven L Enable Low Voltage Pin 1 and 9 ‐0.3 1.5 V Ven H Enable High Voltage Pin 1 and 9 Vss<=7

Vss>7 2.3 2.3

Vss 7

V

VIL Input Low Voltage Pin 2, 7, 10 and 15 ‐0.3 1.5 V VIH Input High Voltage Pin 2, 7, 10 and 15 Vss<=7

Vss>7 2.3 2.3

Vss 7

V

Points regarding L293D

Supply voltage (Vss) is the Voltage at which we wish to drive the motor. Generally we prefer 6V for dc motor and 6 to 12V for gear motor, depending upon the rating of the motor.

Logical Supply Voltage will decide what value of input voltage should be considered as high or low .So if we set Logical Supply Voltage equal to +5V, then -0.3V to 1.5V will be considered as Input Low Voltage and 2.3 V to 5V will be considered as Input High Voltage.

L293D has 2 Channels .One channel is used for one motor. • Channel 1 - Pin 1 to 8 • Channel 2 - Pin 9 to 16

Enable Pin is used to enable or to make a channel active. Enable pin is also called as Chip Inhibit Pin.

All Inputs (Pin No. 2, 7,10and 15) to L293D IC are the respective outputs from microcontroller (ATmega8L).

E.g.-We connected Pin No. 2, 7, 10 and 15 of L293D IC to Pin No. 14, 15,16and 17 of ATmega8L respectively in our robots, because on pin 15 and 16 of ATmega8L we can generate PWM.

All Outputs (Pin No. 3, 6,11and 14) of L293D IC goes to the inputs of Right and Left motors.

Output Connections

• OUTPUT 1 (Pin No 3) --- Negative Terminal of Right Motor • OUTPUT 2 (Pin No 6) --- Positive Terminal of Right Motor • OUTPUT 3 (Pin No 10) --- Positive Terminal of Left Motor • OUTPUT 4 (Pin No 14) --- Negative Terminal of Left Motor

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For one motor:

Positive Terminal Negative Terminal Motor Output 0 0 No movement Vss 0 Straight 0 Vss Reverse Vss Vss No Movement

One channel can control one motor. Enable pin should be high for activating

the corresponding channel. Input 1 corresponds to Output 1.

If Enable 1=High (1) Input1 =High (1), Output1=Vss Input1 =Low (0), Output1=0 If Enable 1=Low (0) Input1 =High (1), Output1=0 Input1 =Low (0), Output1=0 if Enable pin low, the output will always be 0. If its high output depends on input

Let’s check the sample outputs for some sample inputs (when both the Enable pins are high):

Input 1

Input2

Input 3

Input 4

Output 1

Output 2

Output 3

Output 4

Motors Output Movement Right Left

Low High High Low 0 Vss Vss 0 Straight Straight Straight Low High Low Low 0 Vss 0 0 Straight No mov Left Turn Low Low High Low 0 0 Vss 0 No mov Straight Right Turn Low High Low High 0 Vss 0 Vss Straight Reverse Sharp Left High Low High Low Vss 0 Vss 0 Reverse Straight Sharp Right High Low Low High Vss 0 0 Vss Reverse Reverse Backward

You can see the datasheet of that IC for more details.

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Algorithm for Line Follower There are various line follower algorithms. The main use of the algorithm is to

move the robot on the line in a smooth fashion. Apart from the task, the algorithm also depends on hardware including number of sensors, type of motors, chassis etc. Same problem can be approached by different algorithms. Readers are encouraged to develop their own algorithms.

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Appendix: 1. Printed Circuit Board

When making the circuit with the electronic parts of the resistors, the capacitors, the transistors, the ICs and so on, it is necessary to connect the lead line of each part appropriately. Also, each part must be fixed, too. The printed circuit board is used to do the wiring among the parts and the fixation of the part.

Advantages: • Reliability and durability due to compact nature of the circuit especially needed

for mobile applications like robotics. • Easy debugging. • Large number of circuits can be made with a greater accuracy and at a cheap

cost. • Chances of loose connections get eliminated.

Disadvantages

• Once the circuit is made on a PCB its layout cannot be changed. • PCB leads can burn at higher values of current rendering it useless for further

use • PCB designing can be a tedious and time consuming process.

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Bottom

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~ 23 ~

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Top VView:

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~ 24 ~

mage of B

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Explanation of all compponents:

~ 25 ~

:

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Bottom

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PWMPulse Wivarious fr Thfrequency

DefinitioFrom abo

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he periodic y and duty

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Time pis calle

Frequ On Tim Off Ti Duty C Avera

ulation (PWs (time perisquare wa-cycle.

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~ 27 ~

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Examples

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USE of

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DC Motor Speed α δ

Now

And

Thus

Advantages of PWM:

1. Here the switch is either on or off unlike normal regulation(using variable resistance), so less power is wasted as heat and smaller heat-sinks can be used.

2. Since no resistor is used, there is no power loss. 3. Can be easily automated by programmable control.

Disadvantages: 1. We require extra circuitry to implement PWM (in AVR we have in built

PWM-circuitry on chip). 2. Some authorities claim the pulsed power puts more stress on the DC motor

bearings and windings, shortening its life.

Implementation of PWM: For developing PWM, we require two properties:

1. Time Period (T) 2. On-Time Period (Ton)

Implementation of PWM in microcontroller: In microcontroller we use clock of several Mega Hz. Thus time of one clock

E.g. In ATmega 8 clock frequency is approximately 1 Mega Hz.

Tclk=1/(1M Hz)=1 µs

Vavg α δ

DC Motor Speed α Vavg

Tclk =1/(clock frequency) Robo

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For imple Nt=

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Ni=cyc

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CR= Numb

= It is a indcle.

When i

And if

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Nt=ber of cloc

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in micrococycles for o=T/Tclk ck cycles foR= Ton/T

unter, that c

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ontroller wone time pe

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hen PWhen PWM

we require teriod of PW

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