Running Windows on Raspberry Pi 5: A C# GPIO Relay Control Guide

If you are attempting to run Windows on Raspberry Pi for embedded hardware interfacing in 2026, you must navigate a major architectural shift: the Pi 5 no longer uses the Broadcom BCM2711 SoC for peripheral management. It uses the custom RP1 southbridge chip. Because of this, standard desktop Windows 11 ARM64 (flashed via the community 'WoR' project) lacks stable ACPI GPIO mappings, leaving your pins dead. The direct answer for reliable hardware control is to use Windows 11 IoT Enterprise LTSC (ARM64) on a Raspberry Pi 5 (8GB) equipped with an NVMe drive, targeting the .NET 8 System.Device.Gpio library.

This guide provides the exact hardware bill of materials, the RP1 pin mapping, compilable C# code with hardware-safe error handling, and the debugging decision tree for the inevitable driver exceptions you will encounter.

The Decision Path: Which Windows Variant to Choose?

Not all Windows installations on ARM silicon are created equal. Use this decision matrix to select the correct OS for your embedded project. We terminate this path with the only viable choice for production C# GPIO control.

2026 Hardware Spec Sheet: Pi 5, RP1, and NVMe Requirements

Windows 11 is aggressively chatty. It writes registry hives, telemetry, and page files constantly. Running Windows on a microSD card will result in SD controller lockups and boot loops within weeks. You must use an NVMe drive via the Pi 5's PCIe 2.0 interface.

Pin Mapping: Navigating the RP1 Southbridge

The physical 40-pin header on the Pi 5 is identical to the Pi 4, but the internal memory-mapped IO addresses have completely changed due to the RP1 chip. The .NET System.Device.Gpio library (v3.0+) abstracts this, but you must use standard BCM (Broadcom) logical numbering, not physical pin numbers.

C# .NET 8 Implementation: Relay Control Code

This code targets the Raspberry Pi 5 (8GB) running Windows 11 IoT Enterprise LTSC. It requires .NET 8 and the System.Device.Gpio NuGet package (version 3.0.0 or higher to support the RP1 chip).

using System;
using System.Device.Gpio;
using System.Threading;

namespace Pi5WindowsRelay
{
    class Program
    {
        // Explicit BCM pin definitions for Pi 5 RP1
        const int RelayPin1 = 17; // Physical Pin 11
        const int RelayPin2 = 27; // Physical Pin 13
        const int RelayPin3 = 22; // Physical Pin 15

        static void Main(string[] args)
        {
            Console.WriteLine("Initializing GPIO on Windows 11 IoT (Pi 5 RP1)...");
            
            // Initialize controller using Logical (BCM) numbering scheme
            using GpioController controller = new GpioController(PinNumberingScheme.LogicalBoard);
            
            try 
            {
                // Open pins and set to Output (High state = Relay OFF for active-low modules)
                controller.OpenPin(RelayPin1, PinMode.Output, PinValue.High);
                controller.OpenPin(RelayPin2, PinMode.Output, PinValue.High);
                controller.OpenPin(RelayPin3, PinMode.Output, PinValue.High);

                Console.WriteLine("Pins opened. Cycling relays for 10 seconds...");

                DateTime endTime = DateTime.Now.AddSeconds(10);
                bool state = false;

                while (DateTime.Now < endTime)
                {
                    state = !state;
                    PinValue writeValue = state ? PinValue.Low : PinValue.High; // Active LOW relay
                    
                    controller.Write(RelayPin1, writeValue);
                    controller.Write(RelayPin2, writeValue);
                    controller.Write(RelayPin3, writeValue);
                    
                    Console.WriteLine($"Relays set to: {writeValue}");
                    Thread.Sleep(1000);
                }
            }
            catch (PlatformNotSupportedException ex)
            {
                Console.ForegroundColor = ConsoleColor.Red;
                Console.WriteLine($"FATAL: {ex.Message}");
                Console.WriteLine("Action: Ensure you are using System.Device.Gpio v3.0+ and running on IoT Enterprise, not WoR Desktop.");
                Console.ResetColor();
            }
            catch (UnauthorizedAccessException ex)
            {
                Console.ForegroundColor = ConsoleColor.Yellow;
                Console.WriteLine($"PERMISSION ERROR: {ex.Message}");
                Console.WriteLine("Action: Run the compiled .exe as Administrator or configure Windows IoT Device Portal permissions.");
                Console.ResetColor();
            }
            finally
            {
                // Ensure pins are safely closed to prevent floating states on reboot
                if (controller.IsPinOpen(RelayPin1)) controller.ClosePin(RelayPin1);
                if (controller.IsPinOpen(RelayPin2)) controller.ClosePin(RelayPin2);
                if (controller.IsPinOpen(RelayPin3)) controller.ClosePin(RelayPin3);
                Console.WriteLine("GPIO pins safely closed.");
            }
        }
    }
}

Debugging: Fixing the 'No GPIO Driver' Exception

When deploying to Windows on ARM, the most common failure mode is the application crashing immediately upon attempting to instantiate the GpioController.

The Exact Error String:
System.PlatformNotSupportedException: The board is not supported by any of the default GPIO drivers.

This exception is thrown by the .NET IoT library when it iterates through its internal list of board drivers (BCM2835, BCM2711, RP1) and fails to map the ACPI hardware addresses exposed by the Windows kernel. Here are the ranked causes and fixes:

1. Cause 1: Outdated NuGet Package (Most Likely). The RP1 chip requires the RaspberryPi5Driver introduced in late 2024. If your System.Device.Gpio package is version 2.x or older, it only knows how to talk to the Pi 4's BCM2711. Fix: Run dotnet add package System.Device.Gpio --version 3.0.0 (or latest).
2. Cause 2: Running WoR Desktop instead of IoT Enterprise. The community Windows-on-Raspberry UEFI bootloader does not inject the necessary ACPI DSDT tables for the RP1 GPIO controller into standard Windows 11 Desktop. The OS literally cannot see the hardware. Fix: Re-flash using the official Microsoft Windows 11 IoT Enterprise FFU.
3. Cause 3: User-Mode Access Restrictions. Unlike Linux, Windows restricts raw memory-mapped IO access. If the driver is present but the app lacks rights, it fails to initialize the driver handle. Fix: Right-click your compiled .exe and select 'Run as Administrator'.

The First 3 Things to Check When It Fails

Before rewriting code, perform this physical and OS-level verification sequence:

1. Check Device Manager: Open Device Manager -> System Devices. Look for 'RP1 GPIO Controller'. If it is missing or has a yellow triangle, your Windows IoT FFU is outdated or the PCIe/NVMe HAT is causing an IRQ conflict.
2. Verify Package Version: Open your terminal and run dotnet list package. Confirm System.Device.Gpio is ≥ 3.0.0.
3. Check Execution Context: Ensure your PowerShell/CMD session was launched with elevated (Admin) privileges before executing the dotnet run command.

Extending and Simplifying the Build

Once the basic relay toggling is stable, you have two distinct paths for project evolution:

How to Extend (Enterprise Integration):
Add the MQTTnet NuGet package to turn this Pi 5 into an Azure IoT Hub or AWS IoT Core edge node. Because you are running Windows 11 IoT Enterprise, you can leverage native Windows Defender Application Control (WDAC) to lock down the OS, preventing unauthorized executables from running, while using Windows Update for Business to manage OTA security patches for the fleet.

How to Simplify (The Concrete Pivot):
If your project does not strictly require C# or Windows-specific enterprise management, the RP1 Windows driver stack adds unnecessary overhead and boot-time latency. Default Recommendation: If you are fighting ACPI tables and just need the relays to work today, simplify the build by switching to a Raspberry Pi 4 Model B (4GB) running Raspberry Pi OS Lite (64-bit) with Python. The Pi 4's BCM2711 chip has a decade of mature Linux GPIO documentation, eliminating the Windows ARM driver translation layer entirely.