Fixing DHT issues, adding and adjusting documentation

src/devices/Dhtxx/Devices/Dht21.cs

@@ -31,7 +31,7 @@ internal override Ratio GetHumidity(byte[] readBuff)
 
         internal override Temperature GetTemperature(byte[] readBuff)
         {
-            var temp = (readBuff[2] & 0x7F) + readBuff[3] * 0.1;
+            var temp = ((readBuff[2] & 0x7F) << 8 | readBuff[3]) * 0.1;
             // if MSB = 1 we have negative temperature
             temp = ((readBuff[2] & 0x80) == 0 ? temp : -temp);
 

src/devices/Dhtxx/Devices/Dht22.cs

@@ -31,7 +31,7 @@ internal override Ratio GetHumidity(byte[] readBuff)
 
         internal override Temperature GetTemperature(byte[] readBuff)
         {
-            var temp = ((readBuff[2] & 0x7F) * 256 + readBuff[3]) * 0.1;
+            var temp = ((readBuff[2] & 0x7F) << 8 | readBuff[3]) * 0.1;
             // if MSB = 1 we have negative temperature
             temp = ((readBuff[2] & 0x80) == 0 ? temp : -temp);
 

src/devices/Dhtxx/DhtBase.cs

@@ -30,19 +30,19 @@ public abstract class DhtBase : IDisposable
         protected readonly int _pin;
 
         /// <summary>
-        /// I2C device used to communicate with the device
+        /// True to dispose the Gpio Controller
         /// </summary>
-        protected readonly I2cDevice _i2cDevice;
+        protected readonly bool _shouldDispose;
 
         /// <summary>
-        /// <see cref="GpioController"/> related with the <see cref="_pin"/>.
+        /// I2C device used to communicate with the device
         /// </summary>
-        protected readonly GpioController _controller;
+        protected I2cDevice _i2cDevice;
 
         /// <summary>
-        /// True to dispose the Gpio Controller
+        /// <see cref="GpioController"/> related with the <see cref="_pin"/>.
         /// </summary>
-        protected readonly bool _shouldDispose;
+        protected GpioController _controller;
 
         // wait about 1 ms
         private readonly uint _loopCount = 10000;
@@ -58,7 +58,7 @@ public abstract class DhtBase : IDisposable
         /// Get the last read temperature
         /// </summary>
         /// <remarks>
-        /// If last read was not successfull, it returns <code>default(Temperature)</code>
+        /// If last read was not successful, it returns <code>default(Temperature)</code>
         /// </remarks>
         public virtual Temperature Temperature
         {
@@ -73,7 +73,7 @@ public virtual Temperature Temperature
         /// Get the last read of relative humidity in percentage
         /// </summary>
         /// <remarks>
-        /// If last read was not successfull, it returns <code>default(Ratio)</code>
+        /// If last read was not successful, it returns <code>default(Ratio)</code>
         /// </remarks>
         public virtual Ratio Humidity
         {
@@ -280,9 +280,21 @@ public void Dispose()
             if (_shouldDispose)
             {
                 _controller?.Dispose();
+                _controller = null;
+            }
+            else
+            {
+                if (_controller != null)
+                {
+                    if (_controller.IsPinOpen(_pin))
+                    {
+                        _controller.ClosePin(_pin);
+                    }
+                }
             }
 
             _i2cDevice?.Dispose();
+            _i2cDevice = null;
         }
     }
 }

src/devices/Dhtxx/README.md

@@ -7,8 +7,8 @@ The DHT temperature and humidity sensors are very popular. This projects support
 |  | DHT10 | DHT11 | DHT12 | DHT21 | DHT22 |
 | :------: | :------: | :------: | :------: | :------: | :------: |
 | Image | <img src="imgs/dht10.jpg" height="60"/> | <img src="imgs/dht11.jpg" height="60"/> | <img src="imgs/dht12.jpg" height="60"/> | <img src="imgs/dht21.jpg" height="60"/> | <img src="imgs/dht22.jpg" height="60"/> |
-| Temperature Range | -40 ~ 80 ℃ | -20 ~ 60 ℃ | -20 ~ 60 ℃ | -40 ~ 80 ℃ | -40 ~ 80 ℃ |
-| Humidity Range | 0 ~ 99.9 % | 5 ~ 95 % | 20 ~ 95 % | 0 ~ 99.9 % | 0 ~ 99.9 % |
+| Temperature Range | -40 ~ 80 ℃ | 0 ~ 60 ℃ | -20 ~ 60 ℃ | -40 ~ 80 ℃ | -40 ~ 80 ℃ |
+| Humidity Range | 0 ~ 99.9 % | 2 ~ 95 % | 20 ~ 95 % | 0 ~ 99.9 % | 0 ~ 99.9 % |
 | Temperature Accuracy | ±0.5 ℃ | ±2 ℃ | ±0.5 ℃ | ±0.5 ℃ | ±0.5 ℃ |
 | Humidity Accuracy | ±3 % | ±5 % | ±4 % | ±3 % | ±2 % |
 | Protocol | I2C | 1-Wire | I2C, 1-Wire | 1-Wire | 1-Wire |
@@ -21,13 +21,29 @@ The DHT temperature and humidity sensors are very popular. This projects support
 // GPIO Pin
 using (Dht11 dht = new Dht11(26))
 {
-    Temperature temperature = dht.Temperature;
-    double humidity = dht.Humidity;
+    var temperature = dht.Temperature;
+    var humidity = dht.Humidity;
+    // You can only display temperature and humidity if the read is successful otherwise, this will raise an exception as
+    // both temperature and humidity are NAN
+    if (dht.IsLastReadSuccessful)
+    {
+        Console.WriteLine($"Temperature: {temperature.DegreesCelsius} \u00B0C, Humidity: {humidity.Percent} %");
+
+        // WeatherHelper supports more calculations, such as saturated vapor pressure, actual vapor pressure and absolute humidity.
+        Console.WriteLine(
+            $"Heat index: {WeatherHelper.CalculateHeatIndex(temperature, humidity).Celsius:0.#}\u00B0C");
+        Console.WriteLine(
+            $"Dew point: {WeatherHelper.CalculateDewPoint(temperature, humidity).Celsius:0.#}\u00B0C");
+    }
+    else
+    {
+        Console.WriteLine("Error reading DHT sensor");
+    }
 }
 ```
-**Note:** _Specifically on the RPi with the DHT22, 1-Wire works using Raspian but not with IoT-Core. The device has to switch the 1-wire pin between input and output and vice versa. It seems that Windows IoT-Core OS can't switch the pin direction quick enough. There have been suggestions for using two pins; one for input and one for output. This solution has not been implemented here, but these are some handy links that may help setting that up:_
+**Note:** _On the RPi with any of the DHT sensor, 1-Wire works using Raspian but not with Windows 10 IoT Core. The device has to switch the 1-wire pin between input and output and vice versa. It seems that Windows IoT Core OS can't switch the pin direction quick enough. There have been suggestions for using two pins; one for input and one for output. This solution has not been implemented here, but these are some handy links that may help setting that up:_
 - https://github.com/ms-iot/samples/tree/develop/GpioOneWire
-- And on Hackster.io (https://www.hackster.io/porrey/go-native-c-with-the-dht22-a8e8eb
+- And on Hackster.io: https://www.hackster.io/porrey/go-native-c-with-the-dht22-a8e8eb
 
 ### I2C Protocol
 
@@ -41,18 +57,82 @@ using (Dht12 dht = new Dht12(device))
 {
     var tempValue = dht.Temperature;
     var humValue = dht.Humidity;
+    if (dht.IsLastReadSuccessful)
+    {
+        Console.WriteLine($"Temperature: {tempValue.Celsius:0.#}\u00B0C");
+        Console.WriteLine($"Relative humidity: {humValue:0.#}%");
+
+        // WeatherHelper supports more calculations, such as saturated vapor pressure, actual vapor pressure and absolute humidity.
+        Console.WriteLine(
+            $"Heat index: {WeatherHelper.CalculateHeatIndex(tempValue, humValue).Celsius:0.#}\u00B0C");
+        Console.WriteLine(
+            $"Dew point: {WeatherHelper.CalculateDewPoint(tempValue, humValue).Celsius:0.#}\u00B0C");
+    }
+    else
+    {
+        Console.WriteLine("Error reading DHT sensor");
+    }
+}
+```
+
+## Reading frequency and quality measurement
+
+In the case of I2C or GPIO, any type of DHT needs a bit of time between 2 readings. DHT22 documentation refer to a sensing period of 2 seconds and a collecting period higher than 1.7 seconds. 
+Measuring with higher frequency won't give you more accurate numbers. As you can see from the specifications, the accuracy depends on the sensor type, it goes from ±2 ℃ for the DHT11 to ±0.5 ℃ for the others. 
+Even if the parity check can come clear, we do recommend to check that the data are in a normal range. For example of humidity is higher than 100%, then it means that measurement is wrong. 
+This check has not been done in the binding itself, so you may consider adding a check on your application side.
+
+The DHT sensors are very sensitive, avoid too long cables, electromagnetic perturbations and compile the code as release not debug to increase the quality of measurement.
+
+## FAQ
+
+**I always get wrong measurements, what's happening?**
+
+Please check that the sensor is plugged correctly, make sure you are using the correct pin. 
+
+Please check you are using the correct sensor, only DHT10 and DHT12 supports I2C. All others support only GPIO with 1 wire protocol. DHT12 supports both.
+
+**The data I measure are not correct, humidity seems ok but temperature is always weird, what's the problem?**
+
+Please check you are using the correct sensor. Refer to the top part of this page to check which sensor you have. Using a DHT11 instead of a DHT22 will give you a wrong temperature.
+
+**I am trying to get a temperature and humidity 5 times per seconds but I mainly get wrong measurements, why?**
+
+This is absolutely normal, you should check the measurements once every 2 seconds approximately. Don't try to get more measures than once every 2 seconds.
 
+**When reading the temperature and humidity and trying to write the data in the console, I get an exception, why?**
+
+You need to check first if the measurement has been successful. If the measurement hasn't been successful, the default values will be NaN and so you won't be able to convert the temperature or humidity and you'll get an exception. This is the correct way of first reading the sensor and then checking the reading was correct and finally using the temperature and humidity data:
+
+```csharp
+var tempValue = dht.Temperature;
+var humValue = dht.Humidity;
+if (dht.IsLastReadSuccessful)
+{
     Console.WriteLine($"Temperature: {tempValue.Celsius:0.#}\u00B0C");
     Console.WriteLine($"Relative humidity: {humValue:0.#}%");
-
-    // WeatherHelper supports more calculations, such as saturated vapor pressure, actual vapor pressure and absolute humidity.
-    Console.WriteLine(
-        $"Heat index: {WeatherHelper.CalculateHeatIndex(tempValue, humValue).Celsius:0.#}\u00B0C");
-    Console.WriteLine(
-        $"Dew point: {WeatherHelper.CalculateDewPoint(tempValue, humValue).Celsius:0.#}\u00B0C");
 }
 ```
 
+**I have a Raspberry Pi 4 and I get an exception when creating the DHT sensor**
+
+See this [issue 1145](https://github.com/dotnet/iot/issues/1145). We're actively trying to fix it automatically. You will have to force using either the Raspberry Pi 3 driver, either the LibGpiodDriver. This is how you can force using a specific drive, in this case the Raspberry Pi 3 one which will work:
+
+```csharp
+GpioDriver driver = new RaspberryPi3Driver();
+var controller = new GpioController(PinNumberingScheme.Logical, driver);
+// This uses pin 4 in the logical schema so pin 7 in the physical schema
+var dht = new Dht11(4, gpioController: controller);
+```
+
+**My DHT sensor using 1 wire protocol is not working on my Raspberry Pi with Windows 10 IoT Core, what can I do?**
+
+On the RPi with any of the DHT sensor, 1-Wire works using Raspian but not with Windows 10 IoT Core. The device has to switch the 1-wire pin between input and output and vice versa. It seems that Windows IoT Core OS can't switch the pin direction quick enough. There have been suggestions for using two pins; one for input and one for output. This solution has not been implemented here, but these are some handy links that may help setting that up:_
+- https://github.com/ms-iot/samples/tree/develop/GpioOneWire
+- And on Hackster.io: https://www.hackster.io/porrey/go-native-c-with-the-dht22-a8e8eb
+
+Now if your sensor is an I2C sensor, it should just work perfectly on Windows 10 IoT Core.
+
 ## References
 
 * **DHT10** [datasheet (Currently only Chinese)](http://www.aosong.com/userfiles/files/media/DHT10%E8%A7%84%E6%A0%BC%E4%B9%A6.pdf)

src/devices/Dhtxx/samples/DhtSensor.sample.cs

@@ -15,29 +15,109 @@ internal class Program
         public static void Main(string[] args)
         {
             Console.WriteLine("Hello DHT!");
+            Console.WriteLine("Select the DHT sensor you want to use:");
+            Console.WriteLine(" 1. DHT10 on I2C");
+            Console.WriteLine(" 2. DHT11 on GPIO");
+            Console.WriteLine(" 3. DHT12 on GPIO");
+            Console.WriteLine(" 4. DHT21 on GPIO");
+            Console.WriteLine(" 5. DHT22 on GPIO");
+            var choice = Console.ReadKey();
+            Console.WriteLine();
+            if (choice.KeyChar == '1')
+            {
+                Console.WriteLine("Press any key to stop the reading");
+                // Init DHT10 through I2C
+                I2cConnectionSettings settings = new I2cConnectionSettings(1, Dht10.DefaultI2cAddress);
+                I2cDevice device = I2cDevice.Create(settings);
 
-            // Init DHT10 through I2C
-            I2cConnectionSettings settings = new I2cConnectionSettings(1, Dht10.DefaultI2cAddress);
-            I2cDevice device = I2cDevice.Create(settings);
+                using (Dht10 dht = new Dht10(device))
+                {
+                    Dht(dht);
+                }
 
-            using (Dht10 dht = new Dht10(device))
+                return;
+            }
+
+            Console.WriteLine("Which pin do you want to use in the logical pin schema?");
+            var pinChoise = Console.ReadLine();
+            int pin;
+            try
             {
-                while (true)
-                {
-                    var tempValue = dht.Temperature;
-                    var humValue = dht.Humidity;
+                pin = Convert.ToInt32(pinChoise);
+            }
+            catch (Exception ex) when (ex is FormatException || ex is OverflowException)
+            {
+                Console.WriteLine("Can't convert pin number.");
+                return;
+            }
+
+            Console.WriteLine("Press any key to stop the reading");
+
+            switch (choice.KeyChar)
+            {
+                case '2':
+                    Console.WriteLine($"Reading temperature and humidity on DHT11, pin {pin}");
+                    using (var dht11 = new Dht11(pin))
+                    {
+                        Dht(dht11);
+                    }
+
+                    break;
+                case '3':
+                    Console.WriteLine($"Reading temperature and humidity on DHT12, pin {pin}");
+                    using (var dht12 = new Dht12(pin))
+                    {
+                        Dht(dht12);
+                    }
 
-                    Console.WriteLine($"Temperature: {tempValue.DegreesCelsius:0.#}\u00B0C");
-                    Console.WriteLine($"Relative humidity: {humValue:0.#}%");
+                    break;
+                case '4':
+                    Console.WriteLine($"Reading temperature and humidity on DHT21, pin {pin}");
+                    using (var dht21 = new Dht21(pin))
+                    {
+                        Dht(dht21);
+                    }
+
+                    break;
+                case '5':
+                    Console.WriteLine($"Reading temperature and humidity on DHT22, pin {pin}");
+                    using (var dht22 = new Dht22(pin))
+                    {
+                        Dht(dht22);
+                    }
+
+                    break;
+                default:
+                    Console.WriteLine("Please select one of the option.");
+                    break;
+            }
+        }
+
+        private static void Dht(DhtBase dht)
+        {
+            while (!Console.KeyAvailable)
+            {
+                var temp = dht.Temperature;
+                var hum = dht.Humidity;
+                // You can only display temperature and humidity if the read is successful otherwise, this will raise an exception as
+                // both temperature and humidity are NAN
+                if (dht.IsLastReadSuccessful)
+                {
+                    Console.WriteLine($"Temperature: {temp.DegreesCelsius}\u00B0C, Relative humidity: {hum.Percent}%");
 
                     // WeatherHelper supports more calculations, such as saturated vapor pressure, actual vapor pressure and absolute humidity.
                     Console.WriteLine(
-                        $"Heat index: {WeatherHelper.CalculateHeatIndex(tempValue, humValue).DegreesCelsius:0.#}\u00B0C");
+                        $"Heat index: {WeatherHelper.CalculateHeatIndex(temp, hum).DegreesCelsius:0.#}\u00B0C");
                     Console.WriteLine(
-                        $"Dew point: {WeatherHelper.CalculateDewPoint(tempValue, humValue).DegreesCelsius:0.#}\u00B0C");
-
-                    Thread.Sleep(2000);
+                        $"Dew point: {WeatherHelper.CalculateDewPoint(temp, hum).DegreesCelsius:0.#}\u00B0C");
                 }
+                else
+                {
+                    Console.WriteLine("Error reading DHT sensor");
+                }
+
+                // You must wait some time before trying to read the next value
+                Thread.Sleep(2000);
             }
         }
     }