Line Follower Robot using Arduino UNO

1/* 
2Library used: Adafruit Motor Shield library V1 version: 1.0.1
3For this code to run as expected: 
41.The centre to centre distance between the Line sensors should be 11 to 11.5 cm
52. The width of black tape should be 4.8 to 5 cm
63. The distance of the sensor LED from the flat ground surface should be 2 cm.
7*/
8#include <AFMotor.h>
9// MACROS for Debug print, while calibrating set its value to 1 else keep it 0
10#define DEBUG_PRINT 0
11// MACROS for Analog Input
12#define LEFT_IR A0
13#define RIGHT_IR A1
14// MACROS to control the Robot
15#define DETECT_LIMIT 300
16#define FORWARD_SPEED 60
17#define TURN_SHARP_SPEED 150
18#define TURN_SLIGHT_SPEED 120
19#define DELAY_AFTER_TURN 140
20#define BEFORE_TURN_DELAY 10
21// BO Motor control related data here
22// Here motors are running using M3 and M4 of the shield and Left Motor is connected to M3 and Right Motor is connected to M4 using IC2 of the shield
23AF_DCMotor motorL(3);  // Uses PWM0B pin of Arduino Pin 5 for Enable
24AF_DCMotor motorR(4);  // Uses PWM0A pin of Arduino Pin 6 for Enable
25// variables to store the analog values
26int left_value;
27int right_value;
28// Set the last direction to Stop
29char lastDirection = 'S';  
30void setup() {
31#if DEBUG_PRINT  
32  Serial.begin(9600);
33#endif  
34  // Set the current speed of Left Motor to 0
35  motorL.setSpeed(0);
36  // turn on motor
37  motorL.run(RELEASE);
38  // Set the current speed of Right Motor to 0
39  motorR.setSpeed(0);
40  // turn off motor
41  motorR.run(RELEASE);
42  // To provide starting push to Robot these values are set
43  motorR.run(FORWARD);
44  motorL.run(FORWARD);
45  motorL.setSpeed(255);
46  motorR.setSpeed(255);
47  delay(40);  // delay of 40 ms
48}
49void loop() {
50  left_value = analogRead(LEFT_IR);
51  right_value = analogRead(RIGHT_IR);
52#if DEBUG_PRINT
53  // This is for debugging. To check the analog inputs the DETECT_LIMIT MACRO value 300 is set by analysing the debug prints
54  Serial.print(left_value);
55  Serial.print(",");
56  Serial.print(right_value);
57  Serial.print(",");
58  Serial.print(lastDirection);
59  Serial.write(10);
60#endif
61  // Right Sensor detects black line and left does not detect
62  if (right_value >= DETECT_LIMIT && !(left_value >= DETECT_LIMIT)) {
63    turnRight();
64  }
65  // Left Sensor detects black line and right does not detect
66  else if ((left_value >= DETECT_LIMIT) && !(right_value >= DETECT_LIMIT)) {
67    turnLeft();
68  }
69  // both sensors doesn't detect black line
70  else if (!(left_value >= DETECT_LIMIT) && !(right_value >= DETECT_LIMIT)) {
71    moveForward();
72  }
73  // both sensors detect black line
74  else if ((left_value >= DETECT_LIMIT) && (right_value >= DETECT_LIMIT)) {
75    stop();
76  }
77}
78void moveForward() {
79  if (lastDirection != 'F') {
80    // To provide starting push to Robot when last direction was not forward
81    motorR.run(FORWARD);
82    motorL.run(FORWARD);
83    motorL.setSpeed(255);
84    motorR.setSpeed(255);
85    lastDirection = 'F';
86    delay(20);
87  } else {
88    // If the last direction was forward
89    motorR.run(FORWARD);
90    motorL.run(FORWARD);
91    motorL.setSpeed(FORWARD_SPEED);
92    motorR.setSpeed(FORWARD_SPEED);
93  }
94}
95void stop() {
96  if (lastDirection != 'S') {
97    // When stop is detected move further one time to check if its actual stop or not, needed when the robot turns
98    motorR.run(FORWARD);
99    motorL.run(FORWARD);
100    motorL.setSpeed(255);
101    motorR.setSpeed(255);
102    lastDirection = 'S';
103    delay(40);
104  } else {
105    // When stop is detected next time then stop the Robot
106    motorL.setSpeed(0);
107    motorR.setSpeed(0);
108    motorL.run(RELEASE);
109    motorR.run(RELEASE);
110    lastDirection = 'S';
111  }
112}
113void turnRight(void) {
114  // If first time Right Turn is taken
115  if (lastDirection != 'R') {
116    lastDirection = 'R';
117    // Stop the motor for some time
118    motorL.setSpeed(0);
119    motorR.setSpeed(0);
120    delay(BEFORE_TURN_DELAY);
121    // take Slight Right turn
122    motorL.run(FORWARD);
123    motorR.run(BACKWARD);
124    motorL.setSpeed(TURN_SLIGHT_SPEED);
125    motorR.setSpeed(TURN_SLIGHT_SPEED);
126  } else {
127    // take sharp Right turn
128    motorL.run(FORWARD);
129    motorR.run(BACKWARD);
130    motorL.setSpeed(TURN_SHARP_SPEED);
131    motorR.setSpeed(TURN_SHARP_SPEED);
132  }
133  delay(DELAY_AFTER_TURN);
134}
135void turnLeft() {
136  // If first time Left Turn is taken
137  if (lastDirection != 'L') {
138    lastDirection = 'L';
139    // Stop the motor for some time
140    motorL.setSpeed(0);
141    motorR.setSpeed(0);
142    delay(BEFORE_TURN_DELAY);
143    // take slight Left turn
144    motorR.run(FORWARD);
145    motorL.run(BACKWARD);
146    motorL.setSpeed(TURN_SLIGHT_SPEED);
147    motorR.setSpeed(TURN_SLIGHT_SPEED);
148  } else {
149    // take sharp Left turn
150    motorR.run(FORWARD);
151    motorL.run(BACKWARD);
152    motorL.setSpeed(TURN_SHARP_SPEED);
153    motorR.setSpeed(TURN_SHARP_SPEED);
154  }
155  delay(DELAY_AFTER_TURN);
156}