Tutorial: mbed - Part 2

Preparation

MCU board: Nucleo-F401RE

Refer to HUINS mbed experiment kit: Pin Map

GPIO Digital In/Out

We are going to create a simple program that turns LED(LD2) on and off by pressing the user button(BT1).

mbed class

• DigitalOut

• Digital In

Look up for DigitalOut and DigitalIn in mbed documentation for the fulll list of methods

Create a **** new program named as ‘TU_mbed_GPIO_LED_button’.

Write the following source code on ‘main.cpp’

#include "mbed.h"

DigitalIn  button(USER_BUTTON);
DigitalOut led(LED1);

int main() {
    while(1) {
        if(!button) led = 1;
        else led = 0;
    }
}

Click on Compile button. Then, the binary files will be created and downloaded. Copy the binary file to MCU board via USB cable.

Push the reset button(black) and check the performance. The LED(LD2) should be turned on when the button is pressed.

External Interrupt

We are going to create a simple program that turns LED(LD2) on triggered by External Interrupt of user button(BT1).

mbed class

• InterruptIn

Create new program as ‘TU_mbed_ExtIn’.

Write the following code on ‘mbed’ complier.

We have created user defined functions of void pressed() and void released().

#include "mbed.h"

InterruptIn button(USER_BUTTON); 
DigitalOut  led(LED1);

void pressed()
{
    led = 1; 
}

void released(){
    led = 0;
}

int main()
{
    button.fall(&pressed);
    button.rise(&released);
    while (1);
}

Click on Compile button. Then, the binary files will be created and downloaded. Copy the binary file to MCU board via USB cable.

Whenever the user button(BT1) is pressed (at fall), then the LED should be ON. When the button is released then the LED should be off.

Exercise

The experiment kit has IR motion sensor(HD-SEN0018) that detects a motion of an object nearby. It is often used in automatic lighting system at the front door. It is connected to PinName D5 as DigitalIn

• Use External interrupt to get the digital in data from the motion sensor

• When the userbutton is pressed, it should turn-off the LED.

• Hint:

InterruptIn motion(D5)
// InterruptIN for button input

void motionDetected(void)
{
    // code to light up the LED
}

//  Interrupt handler function for Button to turn off LED
// Refer to void pressed(void)

int main(void)
{
    // other codes
    while(1){
    // other codes
    motion.rise(&motionDetected);
    // other codes
}

Ticker (SysTick interrupt)

We are going to create a simple program that uses System Timer Tick Interrupt that occurs periodically. Lets turn LED on and off at 1 sec of period.

mbed class

• Ticker

Use the Ticker interface to set up a recurring interrupt; it calls a function repeatedly and at a specified rate.

Create new program as ‘TU_mbed_SysTick’.

tick.attach( ) makes periodic interrupt of second unit.

You can make LED blink every second, even though there is no infinite loop in main(). This is also called as the ‘ SysTIck interrupt’.

#include "mbed.h"

Ticker     tick;
DigitalOut led(LED1);

void INT(){
    led = !led;      
}
int main(void){
    tick.attach(&INT, 1); // 1초마다 LED blink

    while(1);
}

Click on Compile button. Then, the binary files will be created and downloaded. Copy the binary file to MCU board via USB cable.

LED(LD2) should blink every second.

Exercise

This experiment kit has a digital buzzer (MCKPI-G1410).

It is connected at DigitalOut PinName PA_13

• Buzz the sound for about 1second that repeats for every 3 seconds.

You can also may use wait(sec)

To use the buzzer, square digital signals such as

while(1){
    buzzer=1;
    wait(0.01);
    buzzer=0;
    wait(0.01);
}

****