Simplest Line Follower Using PIC24

// ****************************************************************
// line_follower.c - For line follower robot 
// Author: Ajaya Dahal - ad2323@msstate.edu
// ****************************************************************

#include "pic24_all.h"

// Define the time, in us, between Timer2 and Timer3 interrupts to generate PWM of 1KHz.
#define ISR_PERIOD  (1000)

//MOTOR Enable
#define CONFIG_MOTOR1_EN() CONFIG_RB3_AS_DIG_OUTPUT()   
#define CONFIG_MOTOR2_EN() CONFIG_RB4_AS_DIG_OUTPUT()   
#define MOTOR_1_EN (_LATB3)
#define MOTOR_2_EN (_LATB4)


//left motor
#define CONFIG_MOTOR1_A()  CONFIG_RB5_AS_DIG_OUTPUT()  
#define CONFIG_MOTOR1_B()  CONFIG_RB6_AS_DIG_OUTPUT()  
#define MOTOR_1_A (_LATB5)                             
#define MOTOR_1_B (_LATB6)                             

//right_motor
#define CONFIG_MOTOR2_A()  CONFIG_RB13_AS_DIG_OUTPUT()   
#define CONFIG_MOTOR2_B()  CONFIG_RB14_AS_DIG_OUTPUT()   
#define MOTOR_2_A (_LATB13)                              
#define MOTOR_2_B (_LATB14)                              


//setup sensors
#define CONFIG_SENSOR_A()  CONFIG_RB0_AS_DIG_INPUT()  
#define CONFIG_SENSOR_B()  CONFIG_RB1_AS_DIG_INPUT()  
#define ENABLE_SENSOR_A()  ENABLE_RB0_PULLDOWN()  
#define ENABLE_SENSOR_B()  ENABLE_RB1_PULLDOWN()  

#define SENSOR_A (_RB0)
#define SENSOR_B (_RB1)


//function to move forward
void move_forward(void){
    MOTOR_1_A = 1;
    MOTOR_1_B = 0;
    MOTOR_2_A = 1;
    MOTOR_2_B = 0;
}

//function to stop motor
void stop_motors(void){
   //disable the enable pin will stop motor
    MOTOR_1_EN = 0; 
   MOTOR_2_EN = 0;
}

//function to turn left
void move_left(void){
    MOTOR_1_A = 0;
    MOTOR_1_B = 0;
    MOTOR_2_A = 1;
    MOTOR_2_B = 0;
}

//function to turn right
void move_right(void){
    MOTOR_1_A = 1;
    MOTOR_1_B = 0;
    MOTOR_2_A = 0;
    MOTOR_2_B = 0;
}

//function to move reverse  NOT IMPLEMENTED but for future use
void move_reverse(void){
    MOTOR_1_A = 1;
    MOTOR_1_B = 0;
    MOTOR_2_A = 1;
    MOTOR_2_B = 0;
}

//config motor pins
void configMotors(void){
    CONFIG_MOTOR1_EN();
    CONFIG_MOTOR2_EN();

    CONFIG_MOTOR1_A();
    CONFIG_MOTOR1_B();
    CONFIG_MOTOR2_A();
    CONFIG_MOTOR2_B();
}

//config sensor pins
void configSensors(void){
    CONFIG_SENSOR_A();
    CONFIG_SENSOR_B();
    ENABLE_SENSOR_A();
    ENABLE_SENSOR_B();
}

//create PWM for left motor
void createPWM_Left(void){
    //700+300 = 1000us = 1ms results in 1KHz PWM with 30% duty cycle. 
    if (MOTOR_1_EN == 1) {
        PR2 = usToU16Ticks(700, getTimerPrescale(T2CONbits)) - 1;  
        MOTOR_1_EN = 0;
        
    } else {
        PR2 = usToU16Ticks(300, getTimerPrescale(T2CONbits)) - 1;
        MOTOR_1_EN = 1;
    }
}

//create PWM for right motor
void createPWM_Right(void){
    //700+300 = 1000us = 1ms results in 1KHz PWM with 30% duty cycle. 
    if (MOTOR_2_EN == 1) {
        PR3 = usToU16Ticks(700, getTimerPrescale(T3CONbits)) - 1;
        MOTOR_2_EN = 0;
        
    } else {
        PR3 = usToU16Ticks(300, getTimerPrescale(T3CONbits)) - 1;
        MOTOR_2_EN = 1;
    }
}


// Interrupt Service Routine for Timer2 which is for LEFT motor
void _ISR _T2Interrupt(void) {
   createPWM_Left();
  // Clear the timer interrupt bit, signaling the PIC that this interrupt has been serviced.
  _T2IF = 0;
}

// Interrupt Service Routine for Timer3 which is for RIGHT motor
void _ISR _T3Interrupt(void) {
   createPWM_Right();
  // Clear the timer interrupt bit, signaling the PIC that this interrupt has been serviced.
  _T3IF = 0;
}

void  configTimer2(void) {
  T2CON = T2_OFF | T2_IDLE_CON | T2_GATE_OFF
          | T2_32BIT_MODE_OFF
          | T2_SOURCE_INT
          | T2_PS_1_8;
  // Subtract 1 from ticks value assigned to PR2 because period is PRx + 1.
  PR2 = usToU16Ticks(ISR_PERIOD, getTimerPrescale(T2CONbits)) - 1;
  // Start with a cleared timer2 value.
  TMR2  = 0;
  // Enable Timer2 interrupts.
  _T2IF = 0;
  _T2IP = 1;
  _T2IE = 1;
  // Start the timer only after all timer-related configuration is complete.
  T2CONbits.TON = 1;
}

void  configTimer3(void) {
  T3CON = T3_OFF | T3_IDLE_CON | T3_GATE_OFF
          | T3_SOURCE_INT
          | T3_PS_1_8;
  // Subtract 1 from ticks value assigned to PR2 because period is PRx + 1.
  PR3 = usToU16Ticks(ISR_PERIOD, getTimerPrescale(T3CONbits)) - 1;
  // Start with a cleared timer2 value.
  TMR3  = 0;
  // Enable Timer3 interrupts.
  _T3IF = 0;
  _T3IP = 1;
  _T3IE = 1;
  // Start the timer only after all timer-related configuration is complete.
  T3CONbits.TON = 1;
}

//function that compares the sensors status and control the motor driver accordingly
void start_following(void){
    if(!SENSOR_A && !SENSOR_B){
        move_reverse();
    }
    else if(SENSOR_A && !SENSOR_B){
        move_left();
    }
    else if(!SENSOR_A && SENSOR_B){
        move_right();
    }
    else{
        move_forward();
    }
}


int main (void) {
  configBasic(HELLO_MSG);
  configMotors();
  configSensors();
  configTimer2();
  configTimer3();
  stop_motors();
  
  while (1) {
    start_following();
    DELAY_MS(20);
    stop_motors();
     // Blink the heartbeat LED to show that the PIC is running.
    doHeartbeat();
    DELAY_MS(10);
  }
}