Running Windows on Raspberry Pi 5: A GPIO Hardware Monitor Guide

Running Windows on Raspberry Pi 5 (specifically the 8GB variant) transforms the board from a standard Linux hobbyist node into a viable edge-computing terminal. While Raspberry Pi OS dominates the maker space, installing Windows 11 ARM64 via the Windows on Raspberry (WoR) project unlocks the enterprise .NET ecosystem. This allows you to write robust, strongly-typed C# applications that interact directly with GPIO and I2C buses using the Microsoft .NET IoT Libraries.

This guide details how to build an I2C environmental monitor with a status LED under Windows 11 ARM64. We will cover exact hardware benchmarks, UEFI bus configuration, and provide complete, compilable .NET 8 code with hardware-level error handling.

Hardware Requirements and Performance Benchmarks

Before flashing an OS, you must select the correct board. The code and benchmarks in this guide target the Raspberry Pi 5 (8GB RAM) Rev 1.0. While Windows 11 ARM64 can technically boot on a Pi 4, the Pi 5's PCIe bus and Cortex-A76 cores eliminate the severe I/O bottlenecks that plague the older silicon under a heavy desktop OS.

Parts List and GPIO Pin Mapping

To replicate this build, you need components that are explicitly compatible with the Pi 5's 3.3V logic and Windows ARM64 driver stack. Do not use 5V logic sensors without a level shifter; the Pi 5 GPIO pins are not 5V tolerant and Windows will not protect you from frying the SoC.

Bill of Materials

• Board: Raspberry Pi 5 (8GB RAM)
• Cooling: Official Raspberry Pi Active Cooler (Mandatory for Windows background tasks)
• Sensor: Adafruit BME280 I2C/SPI Breakout (Product ID: 2652)
• Indicator: 5mm Green LED with 330Ω current-limiting resistor
• Wiring: 22 AWG solid core hookup wire (4 strands)
• Storage: 64GB NVMe SSD via M.2 HAT+ (Highly recommended over microSD for Windows)

GPIO Pin Mapping Table

The Raspberry Pi 5 maintains the standard 40-pin header layout. The System.Device.Gpio library uses Broadcom (BCM) numbering by default, not physical pin numbers.

UEFI Configuration and Windows Setup

Unlike Raspberry Pi OS, where you enable I2C via raspi-config or config.txt, Windows on Raspberry relies on the board's UEFI firmware to expose hardware buses to the OS. If you skip this step, the Windows I2C driver will not load, and your .NET code will throw a platform exception.

1. Flash the WoR Image: Use the Windows on Raspberry Imager to flash the Windows 11 ARM64 ISO to your NVMe drive or high-endurance microSD.
2. Access UEFI: Boot the Pi 5 and rapidly press Esc when the Raspberry Pi logo appears to enter the UEFI BIOS.
3. Navigate to Device Manager: Go to Device Manager > Raspberry Pi Configuration > Advanced Configuration.
4. Enable I2C: Locate the I2C0 and I2C1 toggles. Set I2C1 to Enabled. (I2C1 maps to BCM pins 2 and 3).
5. Disable Limit RAM: Ensure "Limit RAM to 3GB" is unchecked so Windows can utilize the full 8GB.
6. Save and Exit: Press F10 to save, then allow Windows to complete its out-of-box experience (OOBE).

C# .NET 8 Code for I2C Sensor Reading

With Windows booted and I2C enabled in UEFI, install Visual Studio 2022 (ARM64 native) or use VS Code with the .NET 8 SDK. Create a new Console Application and install the required NuGet packages:

dotnet add package System.Device.Gpio
dotnet add package Iot.Device.Bindings

The following code initializes the BME280 sensor on I2C Bus 1, reads the telemetry, and toggles an LED on BCM 17 if the temperature exceeds a threshold. It includes explicit pin definitions and hardware-level error handling.

using System;
using System.Device.Gpio;
using System.Device.I2c;
using System.Threading;
using Iot.Device.Bmxx80;
using Iot.Device.Bmxx80.ReadResult;

namespace PiWindowsHardwareMonitor
{
    class Program
    {
        // --- Pin & Bus Definitions ---
        const int LED_PIN = 17;             // BCM 17 (Physical 11)
        const int I2C_BUS_ID = 1;           // I2C Bus 1 (BCM 2/3)
        const int BME280_ADDRESS = 0x76;    // Default Adafruit BME280 I2C address
        const double TEMP_THRESHOLD_C = 28.0; // LED trigger threshold

        static void Main(string[] args)
        {
            Console.WriteLine("Initializing Windows ARM64 Hardware Monitor...");
            
            using GpioController gpio = new GpioController(PinNumberingScheme.Logical);
            gpio.OpenPin(LED_PIN, PinMode.Output);
            gpio.Write(LED_PIN, PinValue.Low);

            I2cConnectionSettings i2cSettings = new(I2C_BUS_ID, BME280_ADDRESS);
            
            try
            {
                using I2cDevice i2cDevice = I2cDevice.Create(i2cSettings);
                using Bme280 bme280 = new Bme280(i2cDevice);

                Console.WriteLine("BME280 initialized successfully. Polling every 2 seconds.");

                while (true)
                {
                    // Force a synchronous reading to avoid stale cache
                    bme280.SetSampling(Sampling.UltraLowPower, Sampling.UltraLowPower, Sampling.UltraLowPower, Mode.Forced);
                    bme280.ReadTemperature(); // Dummy read to trigger measurement
                    Thread.Sleep(100); // Wait for measurement cycle

                    Bme280ReadResult readResult = bme280.Read();
                    
                    double tempC = readResult.Temperature.DegreesCelsius;
                    double humidity = readResult.Humidity.Percent;
                    double pressure = readResult.Pressure.Hectopascal;

                    Console.WriteLine($"Temp: {tempC:F2} °C | Hum: {humidity:F2} % | Press: {pressure:F2} hPa");

                    // GPIO Logic: Turn on LED if temp exceeds threshold
                    if (tempC > TEMP_THRESHOLD_C)
                    {
                        gpio.Write(LED_PIN, PinValue.High);
                    }
                    else
                    {
                        gpio.Write(LED_PIN, PinValue.Low);
                    }

                    Thread.Sleep(2000);
                }
            }
            catch (System.IO.IOException ioEx)
            {
                Console.WriteLine($"I/O Hardware Fault: {ioEx.Message}");
                Console.WriteLine("Check I2C wiring, pull-up resistors, and UEFI settings.");
            }
            catch (UnauthorizedAccessException authEx)
            {
                Console.WriteLine($"Permission Denied: {authEx.Message}");
                Console.WriteLine("Run the compiled .exe as Administrator.");
            }
            catch (Exception ex)
            {
                Console.WriteLine($"Unhandled Exception: {ex.Message}");
            }
            finally
            {
                gpio.Write(LED_PIN, PinValue.Low);
                Console.WriteLine("GPIO pins safely reset. Exiting.");
            }
        }
    }
}

Troubleshooting: I2C Semaphore Timeout Errors

When interfacing I2C sensors under Windows 11 ARM64, the most common failure mode is a bus timeout. If your application crashes immediately upon calling bme280.Read(), you will likely see this exact error string in the console:

System.IO.IOException: Error 121. The semaphore timeout period has expired.

This error indicates that the Windows I2C master driver asserted the clock line, but the slave device (the BME280) held it low for longer than the Windows driver's hardcoded timeout limit—a phenomenon known as I2C clock stretching.

First Three Things to Check When I2C Fails

When your I2C read fails with Error 121 or a "Device Not Found" exception, execute these checks in order:

1. Verify UEFI I2C Toggle: Reboot into UEFI and confirm I2C1 is explicitly set to Enabled. Windows Device Manager should list "Raspberry Pi I2C Controller" under System Devices. If it is missing, UEFI is hiding the bus.
2. Inspect Physical Pull-Up Resistors: The Pi 5 internal pull-ups are often too weak (around 50kΩ) to pull the line high fast enough for Windows' strict timing. Solder external 4.7kΩ pull-up resistors between SDA/3.3V and SCL/3.3V on your breadboard.
3. Scan the Bus Address: Windows lacks a native i2cdetect tool. Download a third-party ARM64 I2C scanner utility (like I2CScanner.exe from GitHub) to verify the sensor is actually responding at 0x76 and not 0x77.

Extending and Simplifying the Build

This baseline monitor proves that Windows on Raspberry Pi can handle bare-metal hardware protocols reliably, provided you respect the ARM64 driver quirks. Depending on your end goal, you can scale this project up or down.

How to Simplify

If you do not strictly require the Windows desktop environment or .NET ecosystem, drop Windows entirely. Flash Raspberry Pi OS Lite (64-bit) and rewrite the logic in Python using the adafruit-circuitpython-bme280 library. Linux handles I2C clock stretching natively via kernel interrupts, entirely eliminating the "Error 121" semaphore timeout bug, and the OS RAM overhead drops from 2.2GB to under 150MB.

How to Extend

To turn this local monitor into an industrial edge node, integrate the MQTTnet NuGet package. Wrap the while(true) loop in a background worker service (IHostedService) and publish the Bme280ReadResult as a JSON payload to a local Mosquitto broker. From there, Home Assistant can ingest the MQTT topic to trigger smart home climate control routines, all running from a C# service natively on the Pi 5's Windows desktop.