Building an Mbed Application¶

This will guide you through creating an Mbed application. We first will cover Mbed OS to read/write to sensors and peripherals on the Mbed Connect Cloud board.

Prerequisites¶

• An Mbed account - sign up here
• Install the Mbed serial driver (for Windows PCs)

Required Hardware¶

• Mbed Connect Cloud board
• Active WiFi network

Setup¶

1. Connect the board to your computer via the micro USB port.
2. The board mounts as a mass-storage device (like a USB drive). Verify that you can see it (the drive name will be DAPLINK).
3. Add the Mbed Connect Cloud board to your online Mbed Compiler here

Making an Mbed application¶

Import the example program.

Printing to the LCD screen¶

We will add some code to print a message to the LCD screen on the board.

Open main.cpp

Declare an object to instantiate the driver for the LCD screen. Under 'GLOBAL VARIABLES HERE' add the following code:

C12832  lcd(PE_14, PE_12, PD_12, PD_11, PE_9);

Add a function that prints a message to the LCD screen. Under 'FUNCTION DEFINITIONS HERE' add the following code:

void lcd_print(const char* message) {
    lcd.cls();
    lcd.locate(0, 3);
    lcd.printf(message);
}

Invoke the previous function to print "Hello World!" to the LCD screen. Under 'MAIN CODE HERE' add the following code:

lcd_print("Hello World!");

Compile and run¶

1. Select the Mbed Connect Cloud 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

Toggling the LED¶

We will add some code to toggle the LED when we push the button (SW1) down.

Open main.cpp

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

DigitalOut  led(PB_8, 1);
InterruptIn button(PF_2);

Add a toggle_led function to switch the state of the LED. Under 'FUNCTION DEFINITIONS HERE' add the following code:

void toggle_led() {
    led = !led;
}

Whenever the button is pressed, the toggle_led function will be called (interrupting the main program then returning). Under 'MAIN CODE HERE' add the following code:

button.rise(&toggle_led);

Compile and run¶

1. Select the Mbed Connect Cloud 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 now toggle it's state (on/off) if you push the button (SW1) down

Reading the temperature/humidity sensor¶

We will add some code to read the values from the temperature/humidity sensor and print the values to the LCD screen.

Open main.cpp

Instantiate a Sht31 object to read from the temperature/humidity sensor. Under 'GLOBAL VARIABLES HERE' add the following code:

Sht31   temp_sensor(PF_0, PF_1);

Add a function that reads the temperature/humidity sensor and prints the values to the LCD screen. Under 'FUNCTION DEFINITIONS HERE' add the following code:

void read_temp() {
    float t = temp_sensor.readTemperature();
    float h = temp_sensor.readHumidity();
    char val[32];
    sprintf(val, "TEMP: %3.2fC, HUM: %3.2f%%", t, h);
    lcd_print(val);
}

Call read_temp every 2 seconds from a while loop in the main function. Under 'MAIN CODE HERE' add the following code:

while(1) {
    // WHILE LOOP CODE HERE
    read_temp();
    wait_ms(2000);
}

Compile and run¶

1. Select the Mbed Connect Cloud 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 humidity and temperature values should now be displayed and updating on the LCD screen

Reading the air quality sensor¶

We will add some code to read the values from the air quality sensor and print the values to the LCD screen.

Open main.cpp

Instantiate a CCS811 object to read from the air quality sensor. Under 'GLOBAL VARIABLES HERE' add the following code:

CCS811  air_sensor(PF_0, PF_1);

Add a function that reads the air quality sensor and prints the values to the LCD screen. Under 'FUNCTION DEFINITIONS HERE' add the following code:

void read_air() {
    air_sensor.init();
    uint16_t eco2, tvoc;
    air_sensor.readData(&eco2, &tvoc);
    char val[32];
    sprintf(val, "eCO2: %dppm, TVOC : %dppb", eco2, tvoc);
    lcd_print(val);
}

Call read_air every 2 seconds from the while loop we created previously for the temperature/humidity sensor. Under 'WHILE LOOP CODE HERE' add the following code:

read_air();
wait_ms(2000);

Compile and run¶

1. Select the Mbed Connect Cloud 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 air quality and temperature/humidity values should now be displayed and updating on the LCD screen (every 2 seconds)

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.