When robot is placed on the fixed path, it follows the path by detecting the line. The robot direction of motion depends on the two sensors outputs. When the two sensors are on the line of path, robot moves forward. If the left sensor moves away from the line, robot moves towards right. Similarly, if right sensor moves away from the path, robot moves towards its left. Whenever robot moves away from its path it is detected by the IR sensor.
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IR sensor consists of IR transmitter and IR receiver on a board. When the vehicle is moving on a black line, IR rays are continuously absorbed by the black surface and there is no reflected ray making output high. Whenever, the robot moves out to the white surface, it starts reflecting the IR rays and making the output low. Thus depending on the output of IR sensor microcontroller indicates the motors to change their direction.
Components in the circuit:
- ATmega8 microcontroller
- Motor driver IC (L293D)
- Motors
- Resistors-R1 to R4.
- IR transmitters – IR TX1,IR TX2
- IR Receivers -IR RX1,IR RX2
How to Design a Line Following Robot?
The circuit consists of Atmega8 microcontroller, IR transmitters, IR Receivers, motor driver, Motors.
ATmega8 microcontroller is a AVR family microcontroller. It is an 8 bit microcontroller with 23 programmable pins. This has many peripheral features like programmable USART, two 8-bit timer/counter, one 16-bit timer/counter, three PWM channels, 10bit resolution six channel analog to digital counter, analog comparator etc. It has 8KB flash memory, 512 bytes of EEPROM and 1KB SRAM.
The DC motors of the robot are connected to the controller using a motor driver IC. As the output of the controller is maximum 5v, it cannot drive the motors. So, to amplify this voltage motor driver, IC is used. L293D can amplify up to 36v.The driver IC has 16 pins. 2, 7, 10, 15 are input pins and are connected to the PD0-PD3 pins of microcontroller.16 pin is connected to 12v.This voltage drives the motors. 8th pin is connected to 5v. This is required for internal operations of the IC.
The two IR sensors are connected to PB0 and PB1 pins of the microcontroller. The IR transmitter and IR receiver are connected as shown in the circuit diagram.
Arrange the chassis and connect the two wheels of the robotic vehicle to the motors which are in turn connected to the microcontroller.
Design of IR Sensors
IR sensor circuit consists of mainly IR transmitter and IR receiver. IR transmitter is similar to an LED. Its operating voltage is around 1.4V. So to protect it, a 150Ω resistor is placed in series with it and is connected in forward biased. IR receiver is connected in reverse bias and a 10KΩ resistor is placed between VCC and the receiver. Output is taken between resistor and IR receiver.
Since this is an analog output, we can convert it to a digital HIGH and LOW with the help of a simple comparator IC like LM358, for example. The IR Sensor Module used in this project uses the same configuration and the circuit diagram is shown below.
Working of IR Sensors
The IR transmitter continuously transmits the IR rays. When IR transmitter is on the black surface these rays were absorbed by the surface and when it is on white surface these rays were reflected. The IR receiver has maximum resistance when no IR rays are received and voltage from VCC flows through the resistor. At the output pin, voltage is approximately 5V.
As the intensity IR rays received by the receiver increases, resistance value decreases and reverse break down occurs. Thus voltage through the resistor is grounded. So, at the output pin, it will produce 0V.
Line Following Robotic Vehicle Circuit Working
- Initially draw the path on a light colored surface with black color tape.
- Place the robot on the floor.
- Now power on the circuit.
- Robot moves in the specified path.
- When it moves out of path, sensors check it and automatically adjust the robot.
Code
#include<reg51.h>
sbit mot1=P2^0;
sbit mot2=P2^1;
sbit mot3=P2^2;
sbit mot4=P2^3;
sbit s_left=P2^6;
sbit s_right=P2^7;
void forward (void);
void backward (void);
void left (void);
void right (void);
void forward (void)
{
mot1=0;
mot2=1;
mot3=1;
mot4=0;
}
void backward (void)
{
mot1=0;
mot2=1;
mot3=0;
mot4=1;
}
void left (void)
{
mot1=0;
mot2=1;
mot3=0;
mot4=0;
}
void right (void)
{
mot1=0;
mot2=0;
mot3=1;
mot4=0;
}
void stop (void)
{
mot1=0;
mot2=0;
mot3=0;
mot4=0;
}
void main()
{
s_left=1;
s_right=1;
while(1)
{
if(s_left==0 && s_right==0)
{
forward();
}
else if(s_left==1 && s_right==1)
{
stop();
}
else if(s_left==0 && s_right==1)
{
left();
}
else if(s_left==1 && s_right==0)
{
right();
}
}
}
Line Following Robot Circuit Applications
- This can be used in driver less car system with some added features like obstacle detection.
- This can also be used in industrial and defense applications.
Limitations of Line Follower Robot
- Line follower robot requires 2-3 inches broad line.
- It may not move properly if the black line drawn is of low intensity.
- The IR sensors may sometimes absorb IR rays from surroundings also. As a result, robots may move in improper way.
Note: If anybody interested on more robotics projects, visit the page: Robotics Projects
Read more: Line Follower Robot using Microcontroller