add sample for si7021 temperature read over i2c (#86)

* add sample for si7021 temperature read over i2c

* add Si7021 device class

* remove ReadTempFromSi7021.cs

* add device sample for Si7021 and humidity read command

* remove reference to README in Si7021 csproj file

src/devices/Si7021/Si7021.cs

+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Device.I2c;
+
+namespace Iot.Device
+{
+    public class Si7021 : IDisposable
+    {
+        const byte si7021_cmd_read_temperature = 0xE3;
+        const byte si7021_cmd_read_humidity = 0xE5;
+        private I2cDevice _i2cDevice;
+
+        public Si7021(I2cDevice i2cDevice)
+        {
+            _i2cDevice = i2cDevice;
+        }
+
+        public void Dispose()
+        {
+        }
+
+        public double ReadTempFahrenheit()
+        {
+            double temp_celcius = ReadTempCelcius();
+            double temp_fahrenheit = (ReadTempCelcius() * (9 / 5)) + 32;
+            
+            return temp_fahrenheit;
+        }
+        
+        public double ReadTempCelcius()
+        {
+            byte[] buffer = new byte[2];
+
+            // Send temperature command, read back two bytes
+            _i2cDevice.WriteByte(si7021_cmd_read_temperature);
+            _i2cDevice.Read(buffer.AsSpan());
+            
+            // Calculate temperature
+            double temp_code = buffer[0] << 8 | buffer[1];
+            double temp_celcius = (((175.72 * temp_code) / 65536) - 46.85);
+            
+            return temp_celcius;
+        }
+        
+        public double ReadHumidity()
+        {
+            byte[] buffer = new byte[2];
+            
+            // Send humidity read command, read back two bytes
+            _i2cDevice.WriteByte(si7021_cmd_read_humidity);
+            _i2cDevice.Read(buffer.AsSpan());
+            
+            // Calculate humidity
+            double rh_code = buffer[0] << 8 | buffer[1];
+            double humidity = ((125 * rh_code) / 65536) - 6;
+            
+            return humidity;
+        }
+    }
+}

src/devices/Si7021/Si7021.csproj

+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>netcoreapp2.1</TargetFramework>
+    <EnableDefaultItems>false</EnableDefaultItems> <!--Disabling default items so samples source won't get build by the main library-->
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="System.Device.Gpio" Version="0.1.0-prerelease*" />
+    <Compile Include="Si7021.cs" />
+  </ItemGroup>
+
+</Project>

src/devices/Si7021/samples/Si7021.sample.cs

+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Device.I2c;
+using System.Device.I2c.Drivers;
+
+namespace Iot.Device.Samples
+{
+    class Program
+    {
+        static void Main(string[] args)
+        {
+            Console.WriteLine("Hello Si7021!");
+
+            const int si7021Address = 0x40;
+            const int busId = 1;
+
+            var i2cSettings = new I2cConnectionSettings(busId, si7021Address);
+            var i2cDevice = new Windows10I2cDevice(i2cSettings);
+            var i2CSi7021 = new Si7021(i2cDevice);
+
+            using (i2CSi7021)
+            {
+                Console.WriteLine($"Temperature in fahrenheit: {i2CSi7021.ReadTempFahrenheit()}");
+                
+                Console.WriteLine($"Temperature in celcius: {i2CSi7021.ReadTempCelcius()}");
+                
+                Console.WriteLine($"Relative humidity is: {i2CSi7021.ReadHumidity()}%");
+            }
+        }
+    }
+}

src/devices/Si7021/samples/Si7021.sample.csproj

+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>netcoreapp2.1</TargetFramework>
+    <LangVersion>latest</LangVersion>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="System.Device.Gpio" Version="0.1.0-prerelease*" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\Si7021.csproj" />
+  </ItemGroup>
+
+</Project>

tools/DevicesApiTester/Commands/I2c/I2cCommand.cs

@@ -16,7 +16,7 @@ namespace DeviceApiTester.Commands.I2c
         [Option('b', "bus-id", HelpText = "The bus id the I2C device to connect to", Required = true)]
         public int BusId { get; set; }
 
-        [Option('a', "device-address", HelpText = "The device address for the connection to the I2C device", Required = true)]
+        [Option('a', "device-address", HelpText = "The device address (in decimal format) for the connection to the I2C device", Required = true)]
         public int DeviceAddress { get; set; }
 
         protected I2cDevice CreateI2cDevice(I2cConnectionSettings connectionSettings)

tools/DevicesApiTester/Commands/I2c/ReadBytes.cs

@@ -30,8 +30,7 @@ namespace DeviceApiTester.Commands.I2c
                 // Read bytes of data
                 var buffer = new byte[ByteCount];
                 i2c.Read(buffer.AsSpan());
-
-                Console.WriteLine($"Bytes read:{Environment.NewLine}{HexStringUtilities.FormatByteData(buffer)}");
+                Console.WriteLine($"Bytes read:{Environment.NewLine}{BitConverter.ToString(buffer)}");
             }
 
             return 0;