Building a side-kick display for your PC with .NET 5


I used to have a little 8" tablet next to my PC that would run a little simple app, and show calendar for today, weather and various other info. It was a neat little thing to have to glance at, and I rarely missed a meeting etc. because I would often glance and get reminded of what's on my to-do list today. However tablets don't like to be plugged in 24/7, so ultimately it died, and I've been missing having something like this for a while.

That's where I got the idea to just plug in a little external display to my PC and have a little app run on that. However, when you plug in another display, it becomes part of your desktop, and I didn't want it to be an area where other apps could go to, or where the app that is meant to launch on it, would go somewhere else, which got me wondering: Can I plug in one of those little IoT displays I had laying around into my PC and drive it with a little bit of code?


These little 1.5" OLED displays are great, and could do the job. The only problem was, this was an SPI display, and my PC doesn't have an SPI port. A bit of searching and I found Adafruit has an FT232H USB-to-SPI board that can do the trick. A quick bit of soldering, and you're good to go (see diagram wiring below): If you want to create a 3D printed case for it, you can download my models from here: (it's a tight fit so keep those wires short and tight)


Now I wanted to use .NET IoT since this was the easiest for me to write against, but unfortunately it turned out this specific Adafruit SPI device isn't supported. However the IoT team is awesome, and after reaching out, they couldn't help themselves adding this support (Thank you Laurent Ellerbach who did this on his vacation!). The display module is already supported by .NET IoT, so it was mostly a matter of figuring out what code to write to hook it up correctly. Luckily there are samples there that only needed slight tweaking. So let's get to the code.

Setting up the project

First open a command prompt / terminal, and start by creating the application worker process and add some dependencies we need:

> dotnet new worker
> dotnet add package Iot.Device.Bindings
> dotnet add package Microsoft.Extensions.Hosting.WindowsServices

You'll also want to change the target framework to 'net5.0-windows10.0.19041.0' since we'll be using the Windows APIs further down.

At the time of writing this, the FT232H PR hasn't been merged yet, so download that project from here and add it as a project reference. Hopefully by the time you read this, it'll already be part of the bindings package.

Initializing the display

The thing we'll do is to create the display driver that we need, so let's add a method for that to the Worker.cs file:

private static Iot.Device.Ssd1351.Ssd1351 CreateDisplay()
    var devices = Iot.Device.Ft232H.Ft232HDevice.GetFt232H();
    var device = new Iot.Device.Ft232H.Ft232HDevice(devices[0]);
    var driver = device.CreateGpioDriver();            
    var ftSpi = device.CreateSpiDevice(new System.Device.Spi.SpiConnectionSettings(0, 4) { Mode = System.Device.Spi.SpiMode.Mode3, DataBitLength = 8, ClockFrequency = 16_000_000 /* 16MHz */ });
    var controller = new System.Device.Gpio.GpioController(System.Device.Gpio.PinNumberingScheme.Logical, driver);
    Iot.Device.Ssd1351.Ssd1351 display = new(ftSpi, dataCommandPin: 5, resetPin: 6, gpioController: controller);
    return display;


Next we need to set a range of commands to the display to get it configured and "ready". We'll add another method for that here:

private static async Task InitDisplayAsync(Iot.Device.Ssd1351.Ssd1351 display)
    await display.ResetDisplayAsync();
    display.MakeAccessible(); // Command A2,B1,B3,BB,BE,C1 accessible if in unlock state
    display.SetDisplayOff(); // Turn on sleep mode
    display.SetDisplayClockDivideRatioOscillatorFrequency(0x00, 0x0F); // 7:4 = Oscillator Frequency, 3:0 = CLK Div Ratio (A[3:0]+1 = 1..16)
    display.SetMultiplexRatio(); // Use all 128 common lines by default....
        Iot.Device.Ssd1351.CommonSplit.OddEven, Iot.Device.Ssd1351.Seg0Common.Column0,
        Iot.Device.Ssd1351.ColorSequence.RGB); // 0x74 Color Depth = 64K, Enable COM Split Odd Even, Scan from COM[N-1] to COM0. Where N is the Multiplex ratio., Color sequence is normal: B -> G -> R
    display.SetColumnAddress(); // Columns = 0 -> 127
    display.SetRowAddress(); // Rows = 0 -> 127
    display.SetDisplayStartLine(); // set startline to to 0
    display.SetDisplayOffset(0); // Set vertical scroll by Row to 0-127.
    display.SetGpio(Iot.Device.Ssd1351.GpioMode.Disabled, Iot.Device.Ssd1351.GpioMode.Disabled); // Set all GPIO to Input disabled
    display.SetVDDSource(); // Enable internal VDD regulator
    display.SetPreChargePeriods(2, 3); // Phase 1 period of 5 DCLKS,  Phase 2 period of 3 DCLKS
    display.SetVcomhDeselectLevel(); // 0.82 x VCC
    display.SetNormalDisplay(); // Reset to Normal Display
    display.SetContrastABC(0xC8, 0x80, 0xC8); // Contrast A = 200, B = 128, C = 200
    display.SetMasterContrast(0x0a); // No Change = 15
    display.SetVSL(); // External VSL
    display.Set3rdPreChargePeriod(0x01); // Set Second Pre-charge Period = 1 DCLKS
    display.SetDisplayOn(); //--turn on oled panel

This should be enough to start using our panel. Let's modify the ExecuteAsync method to initialize the display and have it start drawing something:

Iot.Device.Ssd1351.Ssd1351? display;

protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    display = CreateDisplay();
    await InitDisplayAsync(display);
        while (!stoppingToken.IsCancellationRequested)
            display.FillRect(System.Drawing.Color.Red, 0, 0, 128, 128);
            await Task.Delay(1000, stoppingToken);
            display.FillRect(System.Drawing.Color.White, 0, 0, 128, 128);
            await Task.Delay(1000, stoppingToken);
    catch (OperationCanceledException)

If you run your app now, you should see something like this:

Untitled Project

If not, check your wiring.

Note that the SetDisplayOff code is quite important. If you kill the app before that code executes, you'll notice that the display will be stuck on whatever last screen you were showing. This isn't good for OLEDs, as it can cause burn-in over time. This also happens if your PC goes into standby, so it's a good idea to turn the display off when standby occurs. It's also a good idea to ensure the display is turned off in the event of an exception, so it's good to have that code in a finally statement.
To detect standby, add a reference to the Windows SDKs by setting <UseWindowsForms>true</UseWindowsForms> in your project's PropertyGroup and it'll bring in the required reference. Then add the following code:

Microsoft.Win32.SystemEvents.PowerModeChanged += (s, e) =>
    if (e.Mode == Microsoft.Win32.PowerModes.Suspend)
    else if (e.Mode == Microsoft.Win32.PowerModes.Resume)


At this point, we're pretty much all set to make this little display more useful.

Drawing to the display

Let's create a bit of code that writes a message to the screen. We can just use its System.Drawing APIs to draw a bitmap and send it to the device. Let's create a small helper method first to do that:

private void DrawImage(Action<System.Drawing.Graphics, int, int> drawAction)
    using System.Drawing.Bitmap dotnetBM = new(128, 128);            
    using var g = System.Drawing.Graphics.FromImage(dotnetBM);
    drawAction(g, 128, 128);

Note that we flip the image before sending it, so the display gets the pixels in the right expected order. Next lets modify our little drawing loop, to draw something instead:

DrawImage((g, w, h) =>
    g.DrawString("Hello World", new System.Drawing.Font("Arial", 12), System.Drawing.Brushes.White, new System.Drawing.PointF(0, h / 2 - 6));
await Task.Delay(1000, stoppingToken);
DrawImage((g, w, h) =>
    g.DrawString(DateTime.Now.ToString("HH:mm"), new System.Drawing.Font("Arial", 12), System.Drawing.Brushes.White, new System.Drawing.PointF(0, h / 2 - 6));
await Task.Delay(1000, stoppingToken);


You should now see the display flipping between showing "Hello World" and the current time of day. You can use any of the drawing APIs to draw graphics, bitmaps etc. For instance I have the worker process monitor my doorbell and cameras, and if there's a motion or doorbell event, it'll start sending snapshots from the camera to the display, and after a short while, switch back to the normal loop of pages.

Drawing a calendar

Let's make the display a little more useful. Since we can access the WinRT Calendar APIs from our .NET 5 Windows app, we can get the calendar appointments from the system. So let's create a little helper method to get, monitor and draw the calendar:

private Windows.ApplicationModel.Appointments.AppointmentStore? store;
private System.Collections.Generic.IList<Windows.ApplicationModel.Appointments.Appointment> events =
    new System.Collections.Generic.List<Windows.ApplicationModel.Appointments.Appointment>();

private async Task LoadCalendar()
    store = await Windows.ApplicationModel.Appointments.AppointmentManager.RequestStoreAsync(Windows.ApplicationModel.Appointments.AppointmentStoreAccessType.AllCalendarsReadOnly);
    await LoadAppointments();
    store.StoreChanged += (s, e) => LoadAppointments();
private async Task LoadAppointments()
    if (store is null)
    var ap = await store.FindAppointmentsAsync(DateTime.Now.Date, TimeSpan.FromDays(90));
    events = ap.Where(a => !a.IsCanceledMeeting).OrderBy(a => a.StartTime).ToList();

private void DrawCalendar(System.Drawing.Graphics g, int width, int height)
    float y = 0;
    var titleFont = new System.Drawing.Font("Arial", 12);
    var subtitleFont = new System.Drawing.Font("Arial", 10);
    float lineSpacing = 5;
    foreach (var a in events)
        var time = a.StartTime.ToLocalTime();
        if (time + a.Duration < DateTimeOffset.Now)
            _ = LoadAppointments();
        string timeString = a.AllDay ? time.ToString("d") : time.ToString();
        if (time < DateTimeOffset.Now.Date.AddDays(1)) //Within 24 hours
            if (a.AllDay) timeString = time.Date <= DateTimeOffset.Now.Date ? "Today" : "Tomorrow";
            else timeString = time.ToString("HH:mm");
        else if (time < DateTimeOffset.Now.AddDays(7)) // Add day of week
            if (a.AllDay) timeString = time.ToString("ddd");
            else timeString = time.ToString("ddd HH:mm");
        if (!a.AllDay && a.Duration.TotalMinutes >= 2) // End time
            timeString += " - " + time.Add(a.Duration).ToString("HH:mm");
        var color = System.Drawing.Brushes.White;
        if (!a.AllDay && a.StartTime <= DateTimeOffset.UtcNow && a.StartTime + a.Duration > DateTimeOffset.UtcNow)
            color = System.Drawing.Brushes.Green; // Active meetings are green
        g.DrawString(a.Subject, titleFont, color, new System.Drawing.PointF(0, y));
        y += titleFont.Size + lineSpacing;
        g.DrawString(timeString, subtitleFont, System.Drawing.Brushes.Gray, new System.Drawing.PointF(2, y));
        y += subtitleFont.Size + lineSpacing;
        if (y > height)

Most of the code should be pretty self-explanatory, and most of just deals with writing a pretty time stamp for each appointment. Replace the bit of code that draws "Hello World" with this single one line:


And you should now see your display alternating between time of day, and you upcoming calendar appointments.


As you can tell, once the display and code is hooked up, it's pretty easy to start adding various cycling screens to your display, and you can add anything you'd like that fits your needs.

I'm using my Unifi client library to listen for camera and doorbell events and display camera motions, I connect to home assistant's REST API to get current temperature outside and draw a graph, so I know if weather is still heating up, or cooling down, and whether I should close or open the windows to save on AC. I have a smart meter, so I show current power consumption, which helps me be more aware of trying to save energy, and when a meeting is about to start, I start flashing the display with a count down (I'm WAY better now at joining meetings on time). There are lots and lots more options you could do, and I'd love to hear your ideas what this could be used for. I do hope in the long run, this could evolve into a configurable application with lots of customization and plugins, as well as varying display size.
On my list next is to use a 2.4" LED touch screen instead, to add a bit more space for stuff, as well as the ability to interact with the display directly.

Parts List

- WaveShare 1.5" OLED
- Adafruit has an FT232H USB-to-SPI board

Source code

Just want all the source code for this? Download it here

Using the C#/Win32 code generator to enhance your WinUI 3 app

With the new C#/WIn32 code generator it has become super easy to generate interop code for Windows APIs. Previously we had to go read the doc and figure out the proper C# signature, or browse and hope it is covered there. We could also reference an external package like PInvoke.Kernel32, PInvoke.User32 etc. etc. but it would also pull in a lot more dependencies and APIs than you probably need.

Now with the code generator, it's as simple as adding the nuget package, and then add the method name you want to a "NativeMethods.txt" file, and you instantly have access to the method and any structs and enums you need. It also uses all the latest C#9 features for improved interop code.

You can read the full blogpost on this here:


Using the C# Win32 Interop Generator with WinUI 3

The latest WinUI 3 Preview 4 release does have several improvements around improving your window, but there is also a lot still missing. However most of those features can be added by obtaining the window's HWND handle and calling the native Win32 methods directly.

So let's set out to try and control our window using CsWin32.


First, we'll create a new WinUI Desktop project:



Next we'll add the Microsoft.Windows.CsWin32 NuGet package the project (not the package project!) to get the Win32 code generator. However, note that the current v0.1.319-beta version has some bugs that you'll see when WinUI is referenced. So instead we'll use the daily build which has been fixed (you can skip this if you're reading this and a new version has been published). Go edit the project file, and add the following to get the latest daily from the nuget server that hosts these builds: (also shout-out to Andrew Arnott for quickly fixing bugs as they were discovered)

    <PackageReference Include="Microsoft.Windows.CsWin32" Version="0.1.370-beta">
      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>


Next we'll add a new text file to the root of the project named NativeMethods.txt.

Screenshot 2021-02-19 100955

We're now set up to generate the required methods.

The first Win32 method we need is the ShowWindow method in User32.dll, so add the text ShowWindow to its own line in the NativeMethods.txt file.

Note that you should now be able to get auto completion and full intellisense documentation on the method Microsoft.Windows.Sdk.PInvoke.ShowWindow. Pretty cool huh?

Screenshot 2021-02-19 094339

If you use VS16.9+, you can also expand the Project Name -> Dependencies -> Analyzers -> Microsoft.Windows.CsWin32 -> Microsoft.Windows.CsWin32.SourceGenerator and see the code that gets generated.

Screenshot 2021-02-19 094156

None of this is coming from a big library. It's literally just an internal class directly compiled into your application. No external dependencies required, and if you're building a class library, no dependencies to force on your users either.


Controlling the WinUI Window

As you can see in the screenshot above, the first thing we need to do is provide an HWND handle. You can get this from the Window, but it's not obvious, as we need to cast it to an interface we define. Let's create a new static class called WindowExtensions to help us do this:

using System;
using System.Runtime.InteropServices;
using WinRT;

namespace WinUIWinEx
    public static class WindowExtensions
        internal interface IWindowNative
            IntPtr WindowHandle { get; }

        public static IntPtr GetWindowHandle(this Microsoft.UI.Xaml.Window window)
            => window is null ? throw new ArgumentNullException(nameof(window)) : window.As<IWindowNative>().WindowHandle;


Now we want to call the ShowWindow method. If you read the documentation for this method: you'll see takes a number indicating the desired window state, like 0 for hide, 3 for maximize, 5 for show, 6 for minimize and 9 for restore.

        private static bool ShowWindow(Microsoft.UI.Xaml.Window window, int nCmdShow)
            var hWnd = new Microsoft.Windows.Sdk.HWND(window.GetWindowHandle());
            return Microsoft.Windows.Sdk.PInvoke.ShowWindow(hWnd, nCmdShow);

        public static bool MinimizeWindow(this Microsoft.UI.Xaml.Window window) => ShowWindow(window, 6);
        public static bool MaximizeWindow(this Microsoft.UI.Xaml.Window window) => ShowWindow(window, 3);
        public static bool HideWindow(this Microsoft.UI.Xaml.Window window) => ShowWindow(window, 0);
        public static bool ShowWindow(this Microsoft.UI.Xaml.Window window) => ShowWindow(window, 5);
        public static bool RestoreWindow(this Microsoft.UI.Xaml.Window window) => ShowWindow(window, 9);


Because these are all extension methods, this now enables us to make simple calls inside our Window class like this:



The CsWin32 code generator just makes this really easy. I've taken all of this a few levels further and started a WinUIEx project on GitHub, where you can see the above code and much more, like setting your windows to be always-on-top or adding a tray icon to your app, so you can minimize to the tray.

You can find the repo on github here: