描述

在這個項目中，我們將使用適用于 Windows 10 IoT Core on Raspberry Pi 2套件組件的 Adafruit 入門包來創建一個使用氣壓傳感器讀取溫度、壓力和高度的項目。?

注意：該套件有兩個版本，一個包含 BMP280 傳感器，另一個包含 BME280。如果你有 BME280，

硬件

根據下面“原理圖”部分中的 Fritzing 圖，將 Raspberry Pi2 連接到面包板和其他組件。

軟件?

您可以從https://github.com/ms-iot/adafruitsample下載代碼啟動項目，我們將引導您完成添加與 Web 服務對話并在地圖上獲取您的 pin 所需的代碼。什么地圖？

打開“Lesson_203\StartSolution\lesson_203.sln ”并打開 mainpage.xaml.cs 文件。

我們已經填寫了一些方法作為您在此解決方案中的起點。如果你想跳到前面，你可以在以下位置找到所有代碼已完成的解決方案：“Lesson_203\FullSolution\lesson_203.sln”

MainPage.xaml.cs

打開 MainPage.xaml.cs 文件。

添加對氣壓傳感器 (BMP280) 類的引用。

 public sealed partial class MainPage : Page
    {
        //A class which wraps the barometric sensor
        BMP280 BMP280;

現在我們在 OnNavigatedTo 方法中添加代碼，該方法將為氣壓傳感器創建一個新的 BMP280 對象并初始化該對象。

如果您不想在地圖上添加圖釘，請刪除?MakePinWebAPICall();

 //This method will be called by the application framework when the page is first loaded
        protected override async void OnNavigatedTo(NavigationEventArgs navArgs)
        {            
Debug.WriteLine("MainPage::OnNavigatedTo");
            MakePinWebAPICall();
            try
            {
                //Create a new object for our barometric sensor class                BMP280 = new BMP280();
                //Initialize the sensor
                await BMP280.Initialize();

接下來我們添加代碼來執行以下操作：

• 創建變量來存儲溫度、壓力和高度。將它們設置為 0。

• 為海平面壓力創建一個變量。默認值為 1013.25 hPa。

• 讀取溫度、壓力和高度 10 次并將值輸出到調試控制臺。

 //Create variables to store the sensor data: temperature, pressure and altitude.                 
                //Initialize them to 0.
                float temp = 0;
                float pressure = 0;
                float altitude = 0;
                //Create a constant for pressure at sea level.
                //This is based on your local sea level pressure (Unit: Hectopascal)
                const float seaLevelPressure = 1013.25f;
                //Read 10 samples of the data
                for(int i = 0; i < 10; i++)
                {
                    temp = await BMP280.ReadTemperature();
                    pressure = await BMP280.ReadPreasure();
                    altitude = await BMP280.ReadAltitude(seaLevelPressure);
                    //Write the values to your debug console
                    Debug.WriteLine("Temperature: " + temp.ToString() + " deg C");
                    Debug.WriteLine("Pressure: " + pressure.ToString() + " Pa");
                    Debug.WriteLine("Altitude: " + altitude.ToString() + " m");
                }
                          }
            catch (Exception ex)
            {
                Debug.WriteLine(ex.Message);
            }

BMP280.cs

打開 BMP280.cs 文件。??

代碼的第一部分是列出 BMP280 中不同寄存器的地址。這些值可以在BMP280 數據表中找到。

在 BMP280 類中，在寄存器地址枚舉之后添加以下內容。

 //String for the friendly name of the I2C bus
         const string I2CControllerName = "I2C1";
        //Create an I2C device
        private I2cDevice bmp280 = null;
        //Create new calibration data for the sensor
        BMP280_CalibrationData CalibrationData;
        //Variable to check if device is initialized
        bool init = false;

接下來在Initialize函數中添加如下代碼：

 //Method to initialize the BMP280 sensor
        public async Task Initialize()
        {
            Debug.WriteLine("BMP280::Initialize");
            try
            {
                //Instantiate the I2CConnectionSettings using the device address of the BMP280
                I2cConnectionSettings settings = new I2cConnectionSettings(BMP280_Address);
                //Set the I2C bus speed of connection to fast mode                settings.BusSpeed = I2cBusSpeed.FastMode;
                //Use the I2CBus device selector to create an advanced query syntax string
                string aqs = I2cDevice.GetDeviceSelector(I2CControllerName);                //Use the Windows.Devices.Enumeration.DeviceInformation class to create a collection using the advanced query syntax string
                DeviceInformationCollection dis = await DeviceInformation.FindAllAsync(aqs);
                //Instantiate the the BMP280 I2C device using the device id of the I2CBus and the I2CConnectionSettings
                bmp280 = await I2cDevice.FromIdAsync(dis[0].Id, settings);
                //Check if device was found
                if (bmp280 == null)
                {
                    Debug.WriteLine("Device not found");
                }
            }
            catch (Exception e)
            {
                Debug.WriteLine("Exception: " + e.Message + "\n" + e.StackTrace);
                throw;
            }
        }

在Begin函數中添加如下代碼：??

 private async Task Begin()
        {
            Debug.WriteLine("BMP280::Begin");
            byte[] WriteBuffer = new byte[] { (byte)eRegisters.BMP280_REGISTER_CHIPID };
            byte[] ReadBuffer = new byte[] { 0xFF };
            //Read the device signature
            bmp280.WriteRead(WriteBuffer, ReadBuffer);
            Debug.WriteLine("BMP280 Signature: " + ReadBuffer[0].ToString());            //Verify the device signature
            if (ReadBuffer[0] != BMP280_Signature)
            {
                Debug.WriteLine("BMP280::Begin Signature Mismatch.");
                return;
            }
            //Set the initalize variable to true
            init = true;
            //Read the coefficients table
            CalibrationData = await ReadCoefficeints();
            //Write control register
            await WriteControlRegister();
            //Write humidity control register
            await WriteControlRegisterHumidity();
        }

將以下代碼添加到接下來的 2 個函數中以寫入控制寄存器。

 //Method to write 0x03 to the humidity control register
        private async Task WriteControlRegisterHumidity()
        {
            byte[] WriteBuffer = new byte[] { (byte)eRegisters.BMP280_REGISTER_CONTROLHUMID, 0x03 };
            bmp280.Write(WriteBuffer);
            await Task.Delay(1);
            return;
        }
        //Method to write 0x3F to the control register
        private async Task WriteControlRegister()
        {
            byte[] WriteBuffer = new byte[] { (byte)eRegisters.BMP280_REGISTER_CONTROL, 0x3F };
            bmp280.Write(WriteBuffer);
            await Task.Delay(1);
            return;
        }

將以下代碼添加到 ReadUInt16_LittleEndian 函數中即可：

 //Method to read a 16-bit value from a register and return it in little endian format
        private UInt16 ReadUInt16_LittleEndian(byte register)
        {
            UInt16 value = 0;
            byte[] writeBuffer = new byte[] { 0x00 };
            byte[] readBuffer = new byte[] { 0x00, 0x00 };
            writeBuffer[0] = register;
            bmp280.WriteRead(writeBuffer, readBuffer);
            int h = readBuffer[1] << 8;
            int l = readBuffer[0];
            value = (UInt16)(h + l);
            return value;
        }

將以下代碼添加到 ReadByte 函數以從寄存器中讀取 8 位數據。

 //Method to read an 8-bit value from a register
        private byte ReadByte(byte register)
        {
            byte value = 0;
            byte[] writeBuffer = new byte[] { 0x00 };
            byte[] readBuffer = new byte[] { 0x00 };
            writeBuffer[0] = register;
            bmp280.WriteRead(writeBuffer, readBuffer);
            value = readBuffer[0];
            return value;
        }

接下來的 3 個功能已為您完成。可以在數據表中找到編寫這些函數所需的信息。

• ReadCoefficeints：這是從寄存器地址讀取所有校準數據的函數。

• BMP280_compensate_T_double：在此函數中，使用 BMP280 數據表中的補償公式計算以 oC 為單位的溫度。

• BMP280_compensate_P_Int64：在此函數中，使用 BMP280 數據表中的補償公式計算以 Pa 為單位的壓力。

添加如下代碼完成ReadTemperature功能。

 public async Task<float> ReadTemperature()
        {
            //Make sure the I2C device is initialized
            if (!init) await Begin();
            //Read the MSB, LSB and bits 7:4 (XLSB) of the temperature from the BMP280 registers
            byte tmsb = ReadByte((byte)eRegisters.BMP280_REGISTER_TEMPDATA_MSB);
            byte tlsb = ReadByte((byte)eRegisters.BMP280_REGISTER_TEMPDATA_LSB);
            byte txlsb = ReadByte((byte)eRegisters.BMP280_REGISTER_TEMPDATA_XLSB); // bits 7:4
            //Combine the values into a 32-bit integer
            Int32 t = (tmsb << 12) + (tlsb << 4) + (txlsb >> 4);
            //Convert the raw value to the temperature in degC
            double temp = BMP280_compensate_T_double(t);
            //Return the temperature as a float value
            return (float)temp;
        }

重復相同的步驟以完成 ReadPressure 函數。?

 public async Task<float> ReadPreasure()
        {
            //Make sure the I2C device is initialized
            if (!init) await Begin();
            //Read the temperature first to load the t_fine value for compensation
            if (t_fine == Int32.MinValue)
            {
                               await ReadTemperature();
            }
            //Read the MSB, LSB and bits 7:4 (XLSB) of the pressure from the BMP280 registers
            byte tmsb = ReadByte((byte)eRegisters.BMP280_REGISTER_PRESSUREDATA_MSB);
            byte tlsb = ReadByte((byte)eRegisters.BMP280_REGISTER_PRESSUREDATA_LSB);
            byte txlsb = ReadByte((byte)eRegisters.BMP280_REGISTER_PRESSUREDATA_XLSB); // bits 7:4
            //Combine the values into a 32-bit integer
            Int32 t = (tmsb << 12) + (tlsb << 4) + (txlsb >> 4);
            //Convert the raw value to the pressure in Pa
            Int64 pres = BMP280_compensate_P_Int64(t);
            //Return the temperature as a float value
            return ((float)pres) / 256;
        }

最后完成ReadAltitude函數：

 //Method to take the sea level pressure in Hectopascals(hPa) as a parameter and calculate the altitude using current pressure.
        public async Task<float> ReadAltitude(float seaLevel)
        {
            //Make sure the I2C device is initialized
            if (!init) await Begin();
            //Read the pressure first
            float pressure = await ReadPreasure();
            //Convert the pressure to Hectopascals(hPa)
            pressure /= 100;
            //Calculate and return the altitude using the international barometric formula
            return 44330.0f * (1.0f - (float)Math.Pow((pressure / seaLevel), 0.1903f));
        }

您的項目現在可以部署了！

預期產出

?

部署代碼后，您應該會在 Visual Studio 輸出窗口中看到 10 個氣壓數據樣本。??

?

在這里查看下一課。