File content as of revision 4:0507835a3dce:

// The following file implements all the functions necessary 
// for the robot.
// Please don't modify any of these functions!

#include "mbed.h"
#include "Motor.h"
#include "hcsr04.h"
#include "functions.h"

// Two sensors are used to detect a line, line_sens1 and line_sens2
// if there is a difference between the readings of these sensors 
// the robot has detected a line.
// Setting pins for line sensor
DigitalInOut line1(p20);
DigitalInOut line2(p19);

// Setting pins for motor, as follows:
// Example: Motor____(PWM, Forward, Reverse)
Motor MotorLeft(p23, p28, p27);
Motor MotorRight(p22, p29, p30);

// Setting pins for ultrasonic sensor, as follows:
// Example: usensor(Trigger, Echo)
HCSR04 usensor(p25,p26);

// Returns value from the QRE1113
// lower numbers mean more refleacive
// more than 3000 means nothing was reflected.
int read_line1()
{
    // Time to record how long input is active
    Timer temp_t;
    
    // Activate the line sensor and then read
    line1.output();
    line1 = 1;
    wait_us(15);
    line1.input();
    
    // Start timer
    temp_t.start();

    // Time how long the input is HIGH, but quit
    // after 1ms as nothing happens after that
    while (line1 == 1 && temp_t.read_us() < 1000);
    return temp_t.read_us();
}

int read_line2()
{
    // Time to record how long input is active
    Timer temp_t;
    
    // Activate the line sensor and then read
    line2.output();
    line2 = 1;
    wait_us(15);
    line2.input();
    
    // Start timer
    temp_t.start();

    // Time how long the input is HIGH, but quit
    // after 1ms as nothing happens after that
    while (line2 == 1 && temp_t.read_us() < 1000);
    return temp_t.read_us();
}

int detect_line()
{
    int line1val = read_line1();
    int line2val = read_line2();
    
    if ((line1val-line2val) > 50) {
        printf("Line detected from front");
        return 1;
    } else if ((line1val-line2val) < -50) {
        printf("Line detected from back");
        return -1;
    } else {
        printf("Line not detected");
        return 0;
    }
}

void reverse(float speed)
{
    printf("Reverse\n");
    MotorLeft.speed((speed));
    MotorRight.speed(-(speed));
    wait_ms(1000);
    return;
}

void reverseandturn(float speed)
{
    printf("Reverse and turn\n");
    MotorLeft.speed((speed-0.3));
    MotorRight.speed(-(speed-0.1));
    wait_ms(2000);
    return;
}

void charge(float speed)
{
    MotorLeft.speed(speed);
    MotorRight.speed(speed);
    return;
}

void stop()
{
    MotorLeft.speed(0.0);
    MotorRight.speed(0.0);
    return;
}

int detect_object(int range, float speed)
{
    // Start a timer - finds an object for 10 seconds
    // if it doesn't find anything returns 0
    Timer usensor_t;
    usensor_t.start();
    
    // Variable to store sensed value
    int sense, dist;
    sense = 0;
    dist = 0;
        
    while (usensor_t.read_ms() < 10000)
    {
        // Start the ultrasonic sensor
        usensor.start();
        dist = usensor.get_dist_cm();
        
        // If an object is detected based on out set range return 1
        if (dist <= range && dist >= 1) {
            sense = 1;
            break;
        } else {
            sense = 0;
            MotorLeft.speed(speed);
            MotorRight.speed(-(speed));
        }
    }
    return sense;
}