Example 1

1. The program blinks the onboard LED 1 at 1/0.2 = 5 Hz.
2. DigitalOut is a C++ class. myled is declared as an object of DigitalOut using pin LED.
3. wait(0.2) cause the microcontroller busy-waiting for next statement to be executed.
4. while ( ) means "while the statement within the bracket is true'". In C/C++, anything but 0 is true. So the statement while (1) is always evaluated to be true and hence it runs non-stop. You may like to substitute -1, 100, 0, '0', "0", "Hi" to test out.

#include "mbed.h"

DigitalOut myled(LED1);

int main() {
    while (1) {
        myled = 1;
        wait(0.2);
        myled = 0;
        wait(0.2);
    }
}

#include "mbed.h"

DigitalOut myled(LED1);

int main() {
    myled = 1;
    while (1) {
        myled = !myled;
        wait(0.2);
    }
}

Example 2

1. The program blinks the onboard LED 1 and LED 2 at 1/0.2 = 5 Hz, alternatively.
2. As we need to distinguish the LEDs from each other, we have to name them differently. In C/C++, no two variables share the same name. Name is case sensitive and may consist of letters, digits, and underscores, but they must not begin with a digit.

#include "mbed.h"

DigitalOut myled1(LED1);
DigitalOut myled2(LED2);

int main() {
    myled1 = 1;
    myled2 = 0;
    while (1) {
        myled1 = !myled1;
        myled2 = !myled2;
        wait(0.2);
    }
}

#include "mbed.h"

DigitalOut myled1(LED1);
DigitalOut myled2(LED2);

int main() {
    myled1.write(1);
    myled2.write(0);
    while (1) {
        myled1.write( !myled1.read());
        myled2.write( !myled2.read());
        wait(0.2);
    }
}

Example 3

1. The program passes a light from LED 1 to LED4, cyclically.
2. An array of DigitalOut objects was declared and initialized at same time. The definition of DigitalOut requires us to define the pin during its variable declaration. Look at the constructor for DigitalOut.
3. To access individual object in the array, we use a numerical index, starting from 0. The index is expressed with square brackets [].
4. for (i = 0; i < 4; i++) setups a looping mechanism which initially setup the value of i to 0. Before the body of the for loop is executed, the statement i < 4 is evaluated. If it is true, the loop body is executed. After each iteration, i is increment by 1.

#include "mbed.h"

DigitalOut myleds[] = {(LED1), (LED2), (LED3), (LED4)};

int main() {
    int i;
    int previous;

    while (1) {
        for (i = 0; i < 4; i++) {
            if (i == 0) 
                previous = 3;
            else 
                previous = i - 1;
            
            myleds[i] = 1;
            myleds[previous] = 0;

            wait(0.2);
        }
    }
}

#include "mbed.h"

DigitalOut myleds[] = {(LED1), (LED2), (LED3), (LED4)};

int main() {
    int i = 0;
    int previous = 3;

    while (1) {
        myleds[i] = 1;
        myleds[previous] = 0;
        previous = i;
        i = ++i % 4;
        wait(0.2);
    }
}

Example 4

1. The program below blinks 3 external LEDs which are red, green and blue.

#include "mbed.h"

DigitalOut red  (p5);
DigitalOut green(p6);
DigitalOut blue (p7);

int main() {
    red = 1;
    green = blue = 0;
    wait(0.2);
    
    green = 1;
    red = blue = 0;
    wait(0.2);

    blue = 1;
    red = green = 0;
    wait(0.2);
}

Discovery

1. Use digital multimeter to measure the voltage
   1. between each DigitalOut pin (p5 or p6 or p7) and the ground.
   2. between the 220 Ω resistor.
   3. between each LED.
2. Compare your results with the information from http://www.oksolar.com/led/led_color_chart.htm

Questions

1. Determine the voltage across each of the LED.
2. Determine the current passes through each of the LED.

Example 5

1. The program below blinks 3 external LEDs which are red, green and blue. The connection is different from Example 4.

#include "mbed.h"

DigitalOut red  (p5);
DigitalOut green(p6);
DigitalOut blue (p7);

int main() {
    red = 0;
    green = blue = 1;
    wait(0.2);
    
    green = 0;
    red = blue = 1;
    wait(0.2);

    blue = 0;
    red = green = 1;
    wait(0.2);
}