Line Follower ROBOT

This Project Line Following Autonomous Robot is based on 8 bit Microcontroller AT89C2051. This Robot follows the black line which is drawn over the white surface or it follows the white line which is drawn over the black surface. The infrared sensors are used to sense the line. When the infrared signal falls on the white surface, it gets reflected and if it falls on the black surface, it is not reflected this principle is used to scan the Lines for the Robot.All the above systems are controlled by the Microcontroller. In our project we are using the popular 8 bit microcontroller AT89C2051. It is a 20 pin microcontroller.The Microcontroller AT89C2051 is used to control the motors. It gets the signals from the infrared sensors and it drives the motors according to the sensor inputs. Two stepper motors are used to drive the robot.

I designed my Robot, which use two motors control  rear wheels and the single front wheel is free. It has 4-infrared sensors on the bottom for detect black tracking tape, when the sensors detected black color, output of  comparator, LM324 is low logic and the other the output is high.

How to build a line follower Robot ?

Microcontrollor AT89C2051 and H-Bridge driver L293D were used  to control direction and speed of motor.

Fig 1. Circuit diagram of my Robot.

Fig 2. Circuit diagram of Infrared sensors and comparators.    

Fig 4.  Position of sensors,  left hand side is side view and right hand side is top view.

Software

Software for write to AT89C2051 is robot1.hex ,which was written by C-language ,the  source code is robot1.ccompiled by using MC51 in TINY model with my start up code robot.asm .

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My Line-Following Robot

Building a Line Following Robot

This is the story of how I am building a line following robot. Use the links below if you want to jump around this page.

1. Line Following Basics 2. Selecting the Sensors 3. Selecting the Software and Hardware 4. The Line Following Course 5. The Line Following Algorithm

1. Line Following Basics

There are a number of ways to set up the course for a line following robot. It can be a black line on a white background or the reverse. Either way, the robot is "trained" to use sensor readings to detect the line and follow it by adjusting the course and/or speed of the robot.

Here is a typical easy line following course:

And if there is a competition, the winner is usually the robot that can complete a lap or a set number of laps in the shortest time.

As soon as sharp turns or crossing intersections are introduced, the problem becomes more difficult. The robot now has to have more sensors and be "smarter" to detect these different situations. Here are two examples of more complex courses:

Since I want to be able to navigate more complex race courses, I have chosen to use multiple sensors to detect the lines.

Here is part 1 of a multi-part article I'm writing about "How I Built a Line Following Robot":

Part 1: Selecting the sensors, building the eight element in-line sensor array, constructing the motors and caster.

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2. Selecting the Sensors

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I've used the QRD1114 sensor before and I like it. I would recommend it to those who like building their own circuits from scratch. It looks like this:

It is cheap, accurate and fairly easy to set up. It is just the IR transmitter and a phototransistor receiver with no electronics, so the user must set up the circuitry on a printed circuit board or proto-board. Here is a typical set-up schematic:

Also, the output is analog, so you must either have a built in A/D converter in your microcontroller or add an A/D chip to your design.

Since I wanted to keep this simple and easy for students, I decided to try a new sensor, a SingleLine Detector from LynxMotion.com shown here:

Notice the blue potentiometer with the yellow receptacle for a phillips screwdriver. This pot is used to adjust the sensor sensitivity. Just above the pot, you will see a red

LED. This shows what the sensor is seeing, so is useful when setting up and testing the unit.

The advantage to this sensor is that the electronics is built in and the output is a one (5 vdc) or a zero (0 vdc) at the input pin of the microcontroller. This sensor costs about $14.00, or three or four times the cost of the QRD1114, but the ability to "plug and play" is worth the additional cost.

How Many Sensors?

Once you decide on the sensor, the next decision is to decide on how many sensors are required to do the job. With no consideration for speed, one or two sensors are sufficient. The problems with this approach become apparent when the robot speeds up. As speed increases, turns come faster and the robot reaction time must improve. But then comes the question - - How many sensors are enough???

I'm working on another project with a different microcontroller where I built an eight-in-line sensor array, so I wanted to experiment with fewer sensors. So I needed a number between three and eight. I picked five, an odd number, so that when the robot is on track, it is only over one sensor. The argument could be made that six sensors spaced close together can also be effective. Anyway, for no particular reason, I picked five over six sensors.

3. Selecting the Software and Hardware

This robot is built using the concepts and ideas of a college electronics course called "Embedded Systems". The hardware and software for that course are predetermined, therefore, the following will be the heart of the systems discussed for this robot:

Microcontroller: Basic Stamp 2 from Parallax.com Language: PBASIC Integrated Development Environment (IDE) (The software where you write,

debug and test your programs.) PBASIC 2.5 Development Board: The Board of Education, Rev D from Parallax.com

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4. The Line Following Course

I decided to start with a simple line following course and then build a more complex course. Here is my first course laid out on a white-board:

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5. The Line Following Algorithm

A line following robot with five sensors only has a limited number of possible combinations (assuming no read error). If the sensors are spaced such that only one sensor is normally over the line at one time, then the combinations are limited to these:

00000

10000

01000

00100

00010

00001

11111

The possible reading of 11111 is for the situation in some courses when the robot hits the end of the course, which is usually a black circle or square.

In the real world, these combinations will not be enough to allow for all situations. A lost robot, stumbling on to a line, might have any number of unplanned combinations, like:

00111

11110

10001

. . . or a number of other combinations. The approach will be to assume the algorithm to be workable in the simplest form, and then add any common combinations that occur.

Let's write some pseudocode to set up an arbitrary behavior.

Read sensors

00000 = Robot is lost! Continue line search procedure. 10000 = Robot off to the right. Left motor ahead slow, right motor stop 00001 = Robot off to the left. Right motor ahead slow, left motor stop 01000 = Robot drifting left. Slow down right motor. 00010 = Robot drifting right. Slow down left motor motor. 00100 = PERFECT!! Full speed ahead. 11111 = End of course. Shut down. XXXXX = any other reading = Proceed with last command.

I said arbitrary behavior because the proper speed control for the motors under these conditions is unknown. An extremely cautious procedure would stop one of the motors whenever the robot begins to drift off center. This is cautious, but very bad in a contest where a fast line follower is needed. For fast line following, the motors need to be kept at the top speed that the robot can handle without loosing control.

So, I will initially set up the motor speeds as shown below. Then adjust to the conditions that allow the fastest speed.

READING LEFT MOTOR RIGHT MOTOR00000 slow ahead medium ahead (Slow left circle, searching)10000 stop slow ahead00001 slow ahead stop01000 slow ahead fast ahead00010 fast ahead slow ahead00100 Fast ahead fast ahead11111 stop stopXXXXX last command last command

The exact speeds for "slow", "medium" and "fast" will have to be determined by experimentation and trials. The initial plan would be to be conservative and on the slow side until the algorithm is proven to work correctly and then by adding speed until control is lost, then back off slightly.