从 DLPIO20 设备上的 DS18B20+ 传感器读取实时温度数据时出现问题。我在 Windows 平台上使用 FTD2XX.DLL .NET 包装器（版本 1.0.14）（根据链接： http: //www.ftdichip.com/Support/SoftwareExamples/CodeExamples/CSharp/FTD2XX_NET_v1.0.14.zip） .
演示该问题的测试应用程序如下。
这就是我所说的实时。
2.1 在相当恒定的环境温度（假设为 20°C）下，在调试模式下读取的温度很少，可以看到一致的结果（第 55 行温度读取周期结束时的断点）。
2.2.然后，在断点时，只需在传感器上呼吸或使用其他方式将其加热到高于环境温度几度。
2.3. 运行两个或三个以上的温度读数循环。
传感器加热后我得到的第一个读数是 20° C 的“旧”温度。只有在第二个或第三个读取循环中，我才能得到 28° C 左右的实际结果。
有趣的是，使用测试应用程序 IO20Demo（购买 DLP-IO20 板时提供）如果我在读取之前发出 Convert 命令，我立即得到 28°C 的实时结果。有了这个程序和托管的 .NET 包装类，我还在 Read 之前发送了 Convert 命令，但无济于事。最大的不同是 IO20Demo 不使用托管包装类，而是直接使用 FTD2XX.lib。
你能帮我理解我在这里做错了什么吗？如何使用托管的 .NET 包装类获取实时温度数据？
非常感谢您的帮助！
/// <summary>
/// Program for DLPIO20 device to read temperature data from DS18B20+
/// digital temperature sensor attached to one of its channels.
/// </summary>
class Program
{
static void Main(string[] args)
{
FTDI FtdiWrapper = null;
// DLPIO20 channel where the DS18B20+ sensor is attached
byte sensorChannel = 0x06;
try
{
// create new instance of the FTDI device class
FtdiWrapper = ConnectToFirstFtdiDevice();
if (FtdiWrapper == null || !FtdiWrapper.IsOpen)
{
throw new Exception("Error connection to FTDI device.");
}
// didn't helped at all for 85dC issue
//PurgeRxBuffer(FtdiWrapper);
// helped avoid 85dC issue at first read
ConvertSensorData(FtdiWrapper, sensorChannel);
// send read sensor command
float? degreesC = null;
for (int i = 0; i < 100; i++)
{
// calling Convert just before ReadTemperatureSensor causes
// IO20Demo (using FTD2XX.lib) to return real temperature
// but it doesn't help when using .NET wrapper
ConvertSensorData(FtdiWrapper, sensorChannel);
// other failed attempts to get real time sensor data
// previous value returned:
//PurgeRxBuffer(FtdiWrapper);
// read but only initiate conversion on success
degreesC = ReadTemperatureSensor(FtdiWrapper, sensorChannel);
if (degreesC == null)
{
throw new Exception("Error converting raw data to Celsius");
}
var message = string.Format("Success! {0}° Celsius.", degreesC);
Console.WriteLine(message);
}
Console.WriteLine("Press any key to exit ...");
Console.ReadKey();
}
catch (Exception ex)
{
Console.WriteLine(ex);
Console.WriteLine("Press any key to exit ...");
Console.ReadKey();
}
finally
{
if (FtdiWrapper != null && FtdiWrapper.IsOpen)
{
FtdiWrapper.Close();
}
}
}
这是用于连接到第一个 FTDI 设备的代码
static private FTDI ConnectToFirstFtdiDevice()
{
FTDI FtdiWrapper = new FTDI();
UInt32 ftdiDeviceCount = 0;
FTDI.FT_STATUS ftStatus = FTDI.FT_STATUS.FT_OTHER_ERROR;
// Determine the number of FTDI devices connected to the machine
ftStatus = FtdiWrapper.GetNumberOfDevices(ref ftdiDeviceCount);
// Check status
if (ftStatus != FTDI.FT_STATUS.FT_OK)
throw new Exception(string.Format("Error after GetNumberOfDevices(), ftStatus: {0}", ftStatus));
if (ftdiDeviceCount == 0)
throw new Exception("No FTDI device found");
// Allocate storage for device info list
var ftdiDeviceList = new FTDI.FT_DEVICE_INFO_NODE[ftdiDeviceCount];
// Populate our device list
ftStatus = FtdiWrapper.GetDeviceList(ftdiDeviceList);
if (ftStatus == FTDI.FT_STATUS.FT_OK)
{
// Open first device in our list by serial number
ftStatus = FtdiWrapper.OpenBySerialNumber(ftdiDeviceList[0].SerialNumber);
if (ftStatus != FTDI.FT_STATUS.FT_OK)
throw new Exception(string.Format("Error opening first device, ftStatus: {0}", ftStatus));
ftStatus = FtdiWrapper.SetBaudRate(9600);
if (ftStatus != FTDI.FT_STATUS.FT_OK)
throw new Exception(string.Format("Error to set Baud rate, ftStatus: {0}", ftStatus));
// Set data characteristics - Data bits, Stop bits, Parity
ftStatus = FtdiWrapper.SetDataCharacteristics(FTDI.FT_DATA_BITS.FT_BITS_8, FTDI.FT_STOP_BITS.FT_STOP_BITS_1, FTDI.FT_PARITY.FT_PARITY_NONE);
if (ftStatus != FTDI.FT_STATUS.FT_OK)
throw new Exception(string.Format("Error to set data characteristics , ftStatus: {0}", ftStatus));
// Set flow control - set RTS/CTS flow control
ftStatus = FtdiWrapper.SetFlowControl(FTDI.FT_FLOW_CONTROL.FT_FLOW_RTS_CTS, 0x11, 0x13);
if (ftStatus != FTDI.FT_STATUS.FT_OK)
throw new Exception(string.Format("Error to set flow control , ftStatus: {0}", ftStatus));
// Set read timeout to 5 seconds, write timeout to infinite
ftStatus = FtdiWrapper.SetTimeouts(5000, 0);
if (ftStatus != FTDI.FT_STATUS.FT_OK)
throw new Exception(string.Format("Error to set timeouts, ftStatus: {0}", ftStatus));
}
return FtdiWrapper;
}
转换原始传感器数据的方法
static private void ConvertSensorData(FTDI FtdiWrapper, byte sensorChannel)
{
FTDI.FT_STATUS ftStatus = FTDI.FT_STATUS.FT_OTHER_ERROR;
UInt32 numBytesWritten = 0;
byte[] convertCommand = new byte[] { 0x03, 0x40, sensorChannel };
ftStatus = FtdiWrapper.Write(convertCommand, convertCommand.Length, ref numBytesWritten);
bool isAllBytesWritten = numBytesWritten == convertCommand.Length;
if (ftStatus != FTDI.FT_STATUS.FT_OK && isAllBytesWritten)
throw new Exception(string.Format("Failed to write Convert command to device; Status: {0}, isAllBytesWritten: {1}", ftStatus.ToString(), isAllBytesWritten));
}
读取传感器温度的方法
static private float? ReadTemperatureSensor(FTDI FtdiWrapper, byte sensorChannel)
{
float? degreesC = null;
FTDI.FT_STATUS ftStatus = FTDI.FT_STATUS.FT_OTHER_ERROR;
UInt32 numBytesWritten = 0;
byte[] readSensorCommand = new byte[] { 0x03, 0x41, sensorChannel };
ftStatus = FtdiWrapper.Write(readSensorCommand, readSensorCommand.Length, ref numBytesWritten);
bool isAllBytesWritten = numBytesWritten == readSensorCommand.Length;
if (ftStatus != FTDI.FT_STATUS.FT_OK && isAllBytesWritten)
throw new Exception(string.Format("Failed to write readSensorCommand to device; Status: {0}, isAllBytesWritten: {1}", ftStatus.ToString(), isAllBytesWritten));
// Read back response
UInt32 numBytesAvailable = 0;
UInt32 numBytesExpected = 2; // read sensor command expected to return 2 bytes
while (numBytesAvailable == 0)
{
Thread.Sleep(40); // value of 40 taken from DLP IO20 demo solution
ftStatus = FtdiWrapper.GetRxBytesAvailable(ref numBytesAvailable);
if (ftStatus != FTDI.FT_STATUS.FT_OK)
throw new Exception("Failed to get number of bytes available to read; error: " + ftStatus);
} //while (numBytesAvailable < numBytesExpected);
if (numBytesAvailable != numBytesExpected)
throw new Exception("Error: Invalid data in buffer. (1350)");
UInt32 numBytesRead = 0;
byte[] rawData = new byte[numBytesExpected];
ftStatus = FtdiWrapper.Read(rawData, numBytesAvailable, ref numBytesRead);
if (ftStatus != FTDI.FT_STATUS.FT_OK)
throw new Exception("Failed to read data from device after command has been sent; error: " + ftStatus);
//convert raw response data to degrees Celsius
degreesC = ConvertTemperature(rawData);
return degreesC;
}
清除发送缓冲区的方法
static private void PurgeRxBuffer(FTDI FtdiWrapper)
{
UInt32 numBytesAvailable = 0;
UInt32 numBytesRead = 0;
FTDI.FT_STATUS ftStatus = FTDI.FT_STATUS.FT_OTHER_ERROR;
byte[] rx = new byte[1001]; //allocate large enough space to read from device
Thread.Sleep(5);
ftStatus = FtdiWrapper.GetRxBytesAvailable(ref numBytesAvailable);
if (ftStatus != FTDI.FT_STATUS.FT_OK)
throw new Exception("Failed to get number of bytes available to read; error: " + ftStatus);
if (numBytesAvailable > 1000)
numBytesAvailable = 1000;
while (numBytesAvailable > 0)
{
//read the data from the buffer
numBytesRead = 0;
ftStatus = FtdiWrapper.Read(rx, numBytesAvailable, ref numBytesRead);
ftStatus = FtdiWrapper.GetRxBytesAvailable(ref numBytesAvailable);
if (ftStatus != FTDI.FT_STATUS.FT_OK)
throw new Exception("Failed to get number of bytes available to read; error: " + ftStatus);
if (numBytesAvailable > 1000)
numBytesAvailable = 1000;
Thread.Sleep(5);
}
}
将温度从原始数据转换为摄氏度的方法
static private float? ConvertTemperature(byte[] rawData)
{
float? tempCelsius = null;
bool isnegative = false;
//check input
if (rawData.Length < 2)
throw new Exception(string.Format("Input parameter rawData for temperature conversion must be 2 bytes, actual length is: {0}", rawData.Length));
int temp = rawData[0] | (rawData[1] << 8);
if ((temp & 0x8000) == 0x8000)//if MSBit is set then negative temperature
{
temp &= 0x07ff;
isnegative = true;
temp = 0x800 - temp;
}
temp &= 0x07ff;
tempCelsius = (float)((float)temp / 16.0);
if (isnegative) tempCelsius *= -1;
return tempCelsius;
}
}