What Is Wall Follower Engineering Essay

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Wall follower is an autonomous robot which follows wall either to its left or right by maintaining constant distance from it. Robot must be able to detect particular wall, estimate distance from it and keep following it.

In the following section, we will discuss the robot which follows wall to its left side.

However with some minor suitable changes, users can make robot for other possibilities also.

BLOCK DIAGRAM

Let us see how the wall follower robot works. First see the block diagrams.

Sensor array for wall detection

Decision making circuit or controller to decide direction of motion

Motor driver circuit

Motors to provide controlled motion

EXPLANATION OF BLOCK DIAGRAM

An array of sensor is used to estimate distance of the wall which is than compared with fixed distance. Based on the status of sensors, special circuit or controller decides the required direction of motion required to maintain the required distance. Motor driver circuit is used to ON/OFF the LEFT/RIGHT motors of the robot to provide desired motion.

SENSORS

Sensors are required to estimate distance of the wall to be followed with respect to the robot's position. Most widely used sensors for the wall follower robot are PHOTOSENSERS. The basic principle is the intensity of reflected light decreases with increase in distance between emitter and detector.

Sensor circuit contains emitter, detector and comparator assembly.

PHOTOSENSORS

IR or VISIBLE light is emitted from the emitter (IR light is mostly preferred to avoid interference from the visible light which is generally around the robot. However IR light is also present in atmosphere but its intensity is much less than that of visible light, so IR light can give much reliable output. For better accuracy of the sensors, they must be covered properly for the isolation from the surrounding.)

This emitted light strikes the surface and gets reflected back. Photo detector is used to detect the intensity of light reflected. The corresponding analog voltage is induced based on the intensity of reflected light which is proportional to distance between wall and robot. This voltage is compared with the fixed reference voltage in comparator circuit and hence it is converted into logic 0 or logic 1 which can be used by the controller.

The comparator circuit may be designed in two ways.

Case-1

Distance > Fix distance=1

Distance < Fix distance=0

Case-2

Distance > Fix distance=0

Distance < Fix distance=1

In the following section, case-1 is used.

EMITTER CIRCUIT

Sample circuit for the sensor is as shown in fig.

R1=390 ohms D2=IR LED

OP-AMP PIN OUT

Vcc is 5V power supply

Input+ is non-inverting input terminal of an op-amp =V+

Input- is inverting input terminal of an op-amp=V-

Output is either logic1 or logic 0 depending upon both input terminals.

Output is Logic 1 if V+ > V- and Logic 0 if V+ < V-

DETECTOR CIRCUIT

A

C

B

D

GND

5V

5V

A= centre point of voltage divider circuit (always 2.5V)

B= Non-inverting terminal of OP-AMP

C= Inverting terminal of OP-AMP

D=Output terminal of OP-AMP

WORKING OF DETECTOR CIRCUIT

When robot is at fixed desired distance, the induced analog output is Vin . Reference voltage at point B is fixed at this value.

When robot is far from the wall, voltage decreases at C. As V+ > V- , output is logic 1.

When robot is close to the wall, voltage increases at C. As V+ < V- , output is logic 0.

SPECIAL SENSORS FOR DISTANCE MEASUREMENT

Some special sensors are made for accurate distance measurement such as GP2D12. Pin out and characteristic graph of the sensor is as shown in fig.

This sensor can be used in the same way as explained earlier for normal IR sensors. These types of sensors provide high reliable and accurate measurements which is almost independent of surrounding atmosphere.

MOTOR DRIVER IC

L293 is one of the most widely used IC for motor driving. One IC can drive two different motors independently.

Pin-out for the L293 is as shown in fig.

E1 & E2- logic 1 (5V) to enable M1 or M2 respectively. Both the pins can be controlled either from controller or by directly connecting 5V power supply.

Pin 8- Voltage required to drive motors-It can be 9V or 12V.

Vcc- 5V power supply

M1-B-=to drive M1 in forward direction

M1-A =to drive M1 in reverse direction

M2-A=to drive M2 in reverse direction

M2-B=to drive M2 in forward direction

These pins must be driven by controller.

We do not need reverse motion here. So M1-A and M1-B will be set at logic 0.

Hence for various motions of robot, see the following truth table.

M1-A

M1-B

Motion

0

0

Stop

0

1

Left turn

1

0

Right turn

1

1

Forward

COMPLETE CIRCUIT DIAGRAM

CIRCUIT CONNECTIONS

There are three sensors. They are connecter with microcontroller P89V51RD2BN as

Side Sensor1-Front= Pin P0.1

Side Sensor2-Back=Pin P0.2

Front Wall Detector=Pin P0.0

Motor driver IC L293 gets four inputs from P89V51RD2BN as

M1-A=P2.0

M1-B=P2.1

M2-A=P2.2

M2-B=P2.3

Left side motor is M1 and right side motor is M2.

HARDWARE REQUIREMENTS

In this robot, very few hardware elements are required. You need following things.

Body of PLY/PLASTIC/METAL etc.

It is required to enclose the entire robot within it. You can make robot in which circuitry is visible. In such case, you need a base only.

Many types of materials are available which can fulfil the requirements, but thin sheet of PLY is the best choice as drilling and fitting of assemblies on ply is very easy.

PVC/PLASTIC pipe

It is required for proper alignment of motors. You can fit motor at each end of the pipe so that any misalignment between motor's axis is avoided which will improve performance of robot on track while moving.

Clamps, screws & screw driver

Combine assembly of motors and pipe can be fitted on base of robot using clamps and screws.

Drilling Machine

It is required to drill holes on base of robot for screws.

STEP BY STEP HARDWARE PREPARATION

First prepare GPBs/PCBs of sensors, controller's working environment and motor driver assembly and provide interconnections between them also.

Select base material (we assume it as a PLY) and shape of it.

Calculate approx. space required for individual circuits and prepare a plan how they will be placed.

Draw the plan on ply. Provide some margins.

Cut ply as per the plan.

Drill holes at corners of circuits and at their respective position on base.

Fit the circuit with base with the help of screws.

Now your robot is ready.

If you want, you can cover the entire robot in suitable body.

Isolate sensors from atmosphere so that their performance is not affected by atmospheric light, camera flashing etc. (This is very much essential when you are using IR sensors/ LDR etc.)

LOGICAL OPERATION

SR NO

SENSOR'S STATUS

CORRECTIVE ACTION

I/P VALUE TO L293

FRONT WALL

P0.2

SIDE SENSOR- FRONT

P0.1

SIDE SENSOR- BACK

P0.0

 

 

 

 

 

 

 

1

On

X

X

Turn Left

0x08

2

Off

On

On

Turn Right

0x01

3

Off

Off

On

Turn Left

0x08

4

Off

On

Off

Turn Right

0x01

5

Off

Off

Off

Turn Left

0x08

 

 

 

 

 

 

ON= DISTANCE< FIX DISTANCE

OFF= DISTANCE> FIX DISTANCE

 

 

 

 

 

 

CODE

(This code is written in Keil µvision4 and tested with 11.0592MHz crystal frequency,12V 200rpm motors.)

#include<reg51.h>

//forward=0x09;value to be put on P2 for forward motion

//left turn=0x08; value to be put on P2 for left turn

//right turn=0x01; value to be put on P2 for right turn

//P0 as input port-connected to sensors

//P2 as output port-connected to L293-motor driver IC

void delay(unsigned char di) //delay subroutine

{

unsigned char dii;

unsigned int d;

for(dii=0;dii<di;dii++)

for(d=0;d<1275;d++);

}

void main()

{

unsigned arr[4]={0x08,0x01,0x08,0x01} , i;

while (P0.2==1)

{

P2=0x08; //when wall is at front, take right turn

delay (10);

}

i= P0 & 0x03;

P2=arr[i];

delay (10);

}

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