Linebot

/ / INTRODUCTION

This bot follows a black line on a white surface.

The infrared emitter sends a continuous beam of infrared light that is reflected from the ground back to the infrared detector. The detector is an infrared photo-transistor that uses infrared light to activate the transistor base. the more infrared light that gets to the detector, the more the transistor conducts. By using 5 IR sensors in a line, the arduino can determine the exact position of the non-reflective (black) line underneath the robot. The arduino continually adjusts the motors based on the sensors readings to keep the bot on the line.

Parts

Arduino
Makerbotted base
Makerbotted servo holders
Makerbotted caster wheel
Makerbotted battery clip
Makerbotted wheels
Protoshield
2 continuous rotation servo motors
5 IR emitter/detectors
perforated prototyping board
5 10k resistors
5 150Ω resistors
nuts and bolts
1/2 inch chrome ball
9 Volt battery
2 rubber bands
SPST toggle switch

IR Sensor

The infrared emitter LED is next to the infrared phototransistor detector. The small divider between them ensures that no IR light is read by the detector that is not first reflected from the surface. The sensors should be placed about 1/2 inch apart.

Each IR sensor is comprised of 2 LEDs. The blue LED is the IR emitter and the black LED is the phototransistor. Place the sensor in the protoboard with the blue LED closest to the top:
When you place the sensors in the board fold the right side leads towards each other. This will hold the sensor in the board.
Solder the sensors into place and solder the right leads of each sensor together-forming a solder-bridge between the anode of the emitter and the collector of the transistor.
Connect the anodes of each sensor to 5V (the right side that is bridged
Connect each cathode of the IR emitter to ground (top left) through 150 Ω resistor.
Connect each cathode of the IR detector (bottom left) to ground through 10KΩ resistor.
Connect both resistors together. They will ultimately be connected to GND

Add wires if needed
Make the connection to GND
Also connect each cathode of the IR detector (bottom left) to an analog pin on the Arduino
Connect the bridged right side to each other
Connect the bridged right side to 5V
Add wires to connect your board to your Arduino
Cover the exposed wires with electrical tape.
Test the sensor by connecting power and ground of your sensor to power and ground of your arduino (your arduino must also be connected to power—a battery or the computer. Point a digital camera at the sensor and in the viewfinder you should see a pale blue light.
Connect the sensors to the analog pins. If the sensors are facing down, the far left is sensor 1 and the far right is sensor 2

Servo Motors

Here is how to control continuous rotation motors with the arduino:

#include <Servo.h>

Servo left;
Servo right;

void setup(){
  left.attach(9);
 right.attach(10);
  
}
void loop(){
  left.write(0);
  right.write(179);
  
}

Power switch

Cut the red wire of the power supply. Solder each lead to a lead of the toggle switch.

Connecting to the Arduino

Connect the sensors to pins A0-A4.
Connect a potentiometer to pin A5

How it all works:

You want the 3rd sensor to be over the black line. If the value of sensor 3 is below the threshold (reading black), then you want the Arduino to move forward:

left motor is moving backwards
right motor is moving forwards

If sensor 3 rises above the threshold value, then check both sensor 2 and 4

// Linus the Line-bot
// Follows a Black line on a White surface (poster-board and electrical tape).
// Code by JDW 2010 – feel free to modify.

#include <Servo.h>  // this includes the Afmotor library for the motor-controller

Servo motor_left;  // attach motor_left to the Adafruit motorshield M1
Servo motor_right; // attach motor_right to the Adafruit motorshield M3

// Create variables for sensor readings

int sensor1 = 0;
int sensor2 = 0;
int sensor3 = 0;
int sensor4 = 0;
int sensor5 = 0;

// Create variables for adjusted readings

int adj_1 = 0;
int adj_2 = 0;
int adj_3 = 0;
int adj_4 = 0;
int adj_5 = 0;

// You can change the min/max values below to fine tune each sensor on your bot

int s1_min = 200;
int s1_max = 950;

int s2_min = 200;
int s2_max = 950;

int s3_min = 200;
int s3_max = 950;

int s4_min = 200;
int s4_max = 950;

int s5_min = 200;
int s5_max = 950;

// this threshold defines when the sensor is reading the black line
int lower_threshold = 20;

// value to define a middle threshold (half of the total 255 value range)
int threshold = 128;

// this threshold defines when the sensor is reading the white poster board
int upper_threshold = 230;

// this value sets the maximum speed of linus (255 = max). 
// using a speed potentiometer will over-ride this setting.

int speed_value = 255;  
int speed_pot;

// end of changeable variables

void setup()  
{
  Serial.begin(9600); // start serial monitor to see sensor readings

// declare left motor 
  motor_left.attach(9);

// declare right motor
  motor_right.attach(10);
   motor_left.write(179);
   motor_right.write(0);
}

void update_sensors(){

// this will read sensor 1
  sensor1 = analogRead(0); 
  adj_1 = map(sensor1, s1_min, s1_max, 0, 255);
  adj_1 = constrain(adj_1, 0, 255);

// this will read sensor 2
  sensor2 = analogRead(1);     //  sensor 2 = left-center
  adj_2 = map(sensor2, s2_min, s2_max, 0, 255);
  adj_2 = constrain(adj_2, 0, 255);

// this will read sensor 3
  sensor3 = analogRead(2);         // sensor 3 = center
  adj_3 = map(sensor3, s3_min, s3_max, 0, 255);
  adj_3 = constrain(adj_3, 0, 255);

// this will read sensor 4
  sensor4 = analogRead(3);     //  sensor 4 = right-center
  adj_4 = map(sensor4, s4_min, s4_max, 0, 255);
  adj_4 = constrain(adj_4, 0, 255);

// this will read sensor 5
  sensor5 = analogRead(4);  // sensor 5 = right
  adj_5 = map(sensor5, s5_min, s5_max, 0, 255); 
  adj_5 = constrain(adj_5, 0, 255);

}

void loop(){

update_sensors(); // update sensors

// first, check the value of the center sensor
  if (adj_3 < lower_threshold){

// if center sensor value is below threshold, check surrounding sensors
    if (adj_2 > threshold && adj_4 > threshold){

// if all sensors check out, drive forward	
       motor_left.write(179);
  motor_right.write(0);
    }
    // you want the bot to stop when it reaches the black box.

else if (adj_1 < 1){
      if (adj_2 < 1){
        if (adj_3 < 1){
          if (adj_4 < 1){
            if (adj_5 < 1){

//  if all sensors are reading black, stop Linus.
           
 motor_left.write(90);
  motor_right.write(90);
            }
          }
        }
      }
    }
  }

// otherwise, the center sensor is above the threshold
  // so we need to check what sensor is above the black line

else {

// first check sensors 1
    if (adj_1 < upper_threshold && adj_5 > upper_threshold){
  
       motor_left.write(90);
  motor_right.write(0);
    }

// then check sensor 5
    else if (adj_1 > upper_threshold && adj_5 < upper_threshold){
      
       motor_left.write(179);
  motor_right.write(90);
    }

// if not sensor 1 or 5, then check sensor 2
    else if (adj_2 < upper_threshold && adj_4 > upper_threshold){
    
       motor_left.write(90);
  motor_right.write(0);
    }

// if not sensor 2, then check sensor 4
    else if (adj_2 > upper_threshold && adj_4 < upper_threshold){
      motor_left.write(179);
  motor_right.write(90);
    }

}

///// Print values for each sensor

/////sensor 1 values
  Serial.print("sensor 1:  ");
  Serial.print(sensor1);
  Serial.print("  -  ");

Serial.print("Adj 1:  ");
  Serial.print(adj_1);
  Serial.print("  -  ");

/////sensor 2 values
  Serial.print("sensor 2:  ");
  Serial.print(sensor2);
  Serial.print("  -  ");

Serial.print("Adj 2:  ");
  Serial.print(adj_2);
  Serial.print("  -  ");

/////sensor 3 values
  Serial.print("sensor 3:  ");
  Serial.print(sensor3);
  Serial.print("  -  ");

Serial.print("Adj 3:  ");
  Serial.print(adj_3);
  Serial.print("  -  ");

/////sensor 4 values
  Serial.print("sensor 4:  ");
  Serial.print(sensor4);
  Serial.print("  -  ");

Serial.print("Adj 4:  ");
  Serial.print(adj_4);
  Serial.print("  -  ");

/////sensor 5 values
  Serial.print("sensor 5:  ");
  Serial.print(sensor5);
  Serial.print("  -  ");

Serial.print("Adj 5:  ");
  Serial.print(adj_5);
  Serial.print(" ");

}

// end of code

Test out the bot on the track. If you hold sensor 3 ver the line both wheels should move.

Experiment with these lines:

// this threshold defines when the sensor is reading the black line
int lower_threshold = 20; 

// value to define a middle threshold (half of the total 255 value range)
int threshold = 128; 

// this threshold defines when the sensor is reading the white poster board
int upper_threshold = 230;

// this value sets the maximum speed of linus (255 = max). 
// using a speed potentiometer will over-ride this setting.

Add a potentiometer to control the speed. 179 is fastest forward. 0 is fastest slower. 90 is stopped.

The center pin from the potentiometer goes to an analog pin, an outer lead goes to gnd and the other to power

Source:Arduino Robotics
By: John-David Warren; Josh Adams; Harald Molle
Publisher: Apress