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"Hello, blinky!" background service

We'll create a simple Blinky app and connect a LED to your Windows IoT Core device (Raspberry Pi 2 or 3, Up Squared or DragonBoard). Be aware that the GPIO APIs are only available on Windows IoT Core, so this sample cannot run on your desktop.

Headless mode

This application is designed for a headless device. To better understand what Headless mode is and how to configure your device to be headless, follow the instructions here.

Load the project in Visual Studio

You can find the source code for this sample by downloading a zip of all of our samples here and navigating to the samples-develop\HelloBlinkyBackground. The sample code is available in either C++ or C#, however the documentation here only details the C# variant. Make a copy of the folder on your disk and open the project from Visual Studio.

Make sure you connect the LED to your board. Go back to the basic 'Blinky' sample if you need guidance.

Note that the app will not run successfully if it cannot find any available GPIO ports.

Once the project is open and builds, the next step is to deploy the application to your device.

When everything is set up, you should be able to press F5 from Visual Studio. The Blinky app will deploy and start on the Windows IoT device, and you should see the attached LED blink.

Let's look at the code

The code for this sample is pretty simple. We use a timer, and each time the 'Tick' event is called, we flip the state of the LED.

Timer code

Here is how you set up the timer in C#:

using Windows.System.Threading;

BackgroundTaskDeferral _deferral;
public void Run(IBackgroundTaskInstance taskInstance)
{
    _deferral = taskInstance.GetDeferral();

    this.timer = ThreadPoolTimer.CreatePeriodicTimer(Timer_Tick, TimeSpan.FromMilliseconds(500));
    . . .
}

private void Timer_Tick(ThreadPoolTimer timer)
{
    . . .
}

Initialize the GPIO pin

To drive the GPIO pin, first we need to initialize it. Here is the C# code (notice how we leverage the new WinRT classes in the Windows.Devices.Gpio namespace):

using Windows.Devices.Gpio;

private void InitGPIO()
{
    var gpio = GpioController.GetDefault();

    if (gpio == null)
    {
        pin = null;
        return;
    }

    pin = gpio.OpenPin(LED_PIN);

    if (pin == null)
    {
        return;
    }

    pin.Write(GpioPinValue.High);
    pin.SetDriveMode(GpioPinDriveMode.Output);
}

Let's break this down a little:

  • First, we use GpioController.GetDefault() to get the GPIO controller.

  • If the device does not have a GPIO controller, this function will return null.

  • Then we attempt to open the pin by calling GpioController.OpenPin() with the LED_PIN value.

  • Once we have the pin, we set it to be off (High) by default using the GpioPin.Write() function.

  • We also set the pin to run in output mode using the GpioPin.SetDriveMode() function.

Modify the state of the GPIO pin

Once we have access to the GpioOutputPin instance, it's trivial to change the state of the pin to turn the LED on or off. You can modify 'Timer_Tick' to do this.

To turn the LED on, simply write the value GpioPinValue.Low to the pin:

this.pin.Write(GpioPinValue.Low);

and of course, write GpioPinValue.High to turn the LED off:

this.pin.Write(GpioPinValue.High);

Remember that we connected the other end of the LED to the 3.3 Volts power supply, so we need to drive the pin to low to have current flow into the LED.