Create Your Own Line Tracker Robot

 Application Note
Line Tracker Robot using AVR Microcontroller
Created by Hendawan Soebhakti on Desember 2007


Line Tracker Robot
In this project we will discuss how to create a robot line tracker that can be
move to follow the tracks of 3 cm thick black line. Black lines are arranged to form a number of intersections. The robot is programmed to be able to count the number of intersections that have been through, then turned in the direction desired. To read the lines, the robot is equipped with proximity sensors that can distinguish between black lines with white floor. This proximity sensor can be calibrated to match the sensor readings to the room lighting conditions. So that the sensor readings are always accurate.

 In order for the movement of the robot becomes more refined, then the speed of the robot is set in accordance with the conditions of proximity sensor readings. If the position of the robot deviates from the line, then the robot will slow down. But if the robot directly above the line, then the robot will move quickly. Robots can also return to the line at the time of the robot apart altogether from the line. This can be done since the robot always remember the last condition sensor readings. If the last condition is to the left of the line, then the robot will move to the right, and vice versa.

Sensor Proximity
Sensor proximity can be our own making. The principle works is simple, utilizing only the nature of light to be reflected when the light-colored objects and will be absorbed if the dark matter. As light sources we use LED (Light Emiting Diode) which will emit red light. And to catch the reflection of light LED, we use a photodiode. If the sensor is above the black line then photodioda will receive very little light reflection. But if the sensor is above the white line then photodioda will receive a lot of reflected light. Here is the illustration:

 The nature of photodioda is that the more light received, then the smaller the value of diode resistance. By doing a little modification, then the amount of resistance can be converted into a voltage. So if the sensor is above the black line, then the sensor output voltage will be small, and vice versa. Here is a picture series of proximity sensors are used on this robot:

 In order to be read by the microcontroller, then the voltage sensor must be adjusted by TTL voltage level that is 0-1 volts for logic 0 and 3-5 volts for logic 1. This can be done by installing a functioned as an operational amplifier comparator. The output of the photodiode that go into the inverting input of op-amp will be compared with the specific voltage of the variable resistor VR. Voltage of VR is what we set it to a proximity sensor can adjust the room lighting conditions.

 Proximity sensor consists of 6 pairs of LED and photodiode are arranged such that the distance between the sensor and another one smaller than the width of the black line. Consider the following picture:

 Mechanical design of robot

 Robot Movement Algorithm
 Before creating the program, then we need to define all possible proximity sensor readings. Thus we can determine the movement of a robot whose goal is to keep the robot is always located right above the line. Here are some possible lines by proximity sensor readings:

 After knowing the possibilities of the position sensor, we then have
defined action of each condition.