Building an Mbed Application¶

This will guide you through creating an Mbed application. We first will cover Mbed OS to read/write to peripherals like potentiometers, LEDs and LCD screens on the Mbed Application Shield.

Prerequisites¶

An Mbed account - sign up here

Required Hardware¶

• Mbed board (NUCLEO-F429ZI)
• Potentiometer or LM35DZ/LFT1

Setup¶

1. Attach the potentiometer to your mbed board.
2. Connect the board to your computer via the *OpenSDA* port.
3. The board mounts as a mass-storage device (like a USB drive). Verify that you can see it (the drive name will be DAPLINK).

Making an mbed application¶

Import Blinky

[Repository '/teams/mbed-os-examples/code/mbed-os-example-blinky/' not found]

Printing on the Serial Console¶

We will add some code to print a message to a serial terminal on the host.

Open main.cpp

#include "mbed.h"
 
DigitalOut led1(LED1);
 
// main() runs in its own thread in the OS
int main() {
    printf("Hello World!\r\n");
    while (true) {
        led1 = !led1;
        wait(0.5);
    }
}

Using terminal applications¶

Terminal applications run on your host PC. They provide a window where your Mbed board can print and where you can type characters back to your board.

Serial configuration: The standard setup for the USB serial port is 9600 baud, 8 bits, 1 stop bit, no parity (9600-8-N-1)

Installing an application for Windows¶

There are many terminal applications for Windows, including:

• CoolTerm - this is the application we use in this example. We use it often because it usually "just works".
• Tera Term.
• PuTTY.
• Some Windows PCs come with Hyperterminal installed.

Configuring the connection¶

1. Plug in your Mbed board.
2. Open CoolTerm.
3. Click Connect. This opens up an 8-n-1 9600 baud connection to the first available serial port. If you have more than one board plugged in, you may need to change the port under Options > Serial Port > Port.

Check your connection parameters:

1. Select Options > Serial Port.
2. You should see 9600 baud, 8 bits, 1 stop bit, no parity (9600-8-N-1).
3. If you do not see your board, click Re-Scan Peripherals.

Your terminal program is now configured and connected.

Using terminal applications on Linux¶

CoolTerm should work under Linux. If for some reason it doesn't, you can try one of the following:

• Minicom
• GNU Screen

Compile and run¶

1. Select a target board in the upper right hand corner
2. Press "Compile"
3. Wait for a binary to be downloaded
4. Drag the binary to the DAPLINK disk
5. Press the board's reset button
6. "Hello World!" should show on the LCD screen

Reading the potentiometer¶

We will add some code to read the value of the potentiometer every 100 ms and, if the measured value is not equal to the last one recorded, print the value to the LCD screen on the shield.

Open 1_app_shield\main.h

Instansiate an AnalogIn object to read the potentiometer and an EventQueue to schedule reading the potentiometer. Under 'GLOBAL VARIABLES HERE' add the following code:

AnalogIn pot1(A0);
EventQueue queue;

Add a function that reads the potentiometer and prints the value to the LCD screen. Under 'FUNCTION DEFINITIONS HERE' add the following code:

void read_potentiometer() {
    static float potentiometer_val = 0;
    if ((float)pot1 != potentiometer_val) {
        potentiometer_val = (float)pot1;
        char val[13];
        sprintf(val, "%.2f", potentiometer_val);
        lcd_print(val);
    }
 }

Use the event queue to schedule reading the potentiometer every 100 ms. Under 'MAIN CODE HERE' add the following code:

queue.call_every(100, read_potentiometer);
while(1){
    wait_ms(100);
    queue.dispatch(0);
}

Compile and run¶

1. Select a target board in the upper right hand corner
2. Press "Compile"
3. Wait for a binary to be downloaded
4. Drag the binary to the DAPLINK disk
5. Press the board's reset button
6. The value of the leftmost potentiometer should be shown on the LCD screen. - Twist the potentiometer back and forth to see the value update

Blinking the LED¶

We will add some code to start blinking the LED when we push the button (SW0 on Odin and SW2 on K64F) down. If we release the button, it will stop blinking.

Open 1_app_shield\main.h

Instansiate a DigitalOut object to write to the LED and a DigitalIn object to read the button input. Under 'GLOBAL VARIABLES HERE' add the following code:

DigitalOut led(D9, 1);
DigitalIn button(BUTTON, PullUp);

Add two functions. blink_led that will switch the state of the LED. And set_blink_led that will read the joystick. If the joystick is pressed left, set_blink_led will add an event to the queue that will invoke blink_led every 500 ms. If the joystick is unpressed, set_blink_led will remove blink_led from the queue. Under 'FUNCTION DEFINITIONS HERE' add the following code:

void blink_led() {
    led = !led;
}

void set_blink_led() {
    static int blink_id = NULL;
    // Read the button
    int blink = !button.read();
    // If the button is pressed and the light is not currently blinking
    if (blink == 1 && blink_id == NULL) {
        // Add blinking the LED to event queue
        blink_id = queue.call_every(500, blink_led);
    }
    else if (blink == 0) {
        // Cancel the blinking event
        queue.cancel(blink_id);
        blink_id = NULL;
        led = 1;
    }
}

Add set_blink_led to the queue, so we can read the state of the button every 100 ms. Under 'MAIN CODE HERE' add the following code:

    queue.call_every(100, set_blink_led);

NOTE: Make sure to add this line above the while loop from the previous step.

Compile and run¶

1. Select a target board in the upper right hand corner
2. Press "Compile"
3. Wait for a binary to be downloaded
4. Drag the binary to the DAPLINK disk
5. Press the board's reset button
6. The LED will blink if you push the button down.
   1. SW2 on K64F, SW0 on Odin

Publishing changes¶

1. Right click the project folder
2. Select "Publish"
3. Write a commit message in the "Revision Commit" menu
4. Press OK
5. Select "Fork..." in the "Publish Repository" menu
6. Write a Description
7. Press OK
8. Make a note of the URL for your fork. We will use it to locally clone this repository.