Control the frequency in SDR# with a rotary encoder. From the tutorial http://eartoearoak.com/tutorials-and-examples/sdrsharp-physical-controls

SDRSharp Frequency Control.ino

/*
  Basic example demonstrating the how to control SDR# frequency
  with SDRSharp Net Remote, an Arduino and rotary encoder.
  
  Copyright 2015 Al Brown
 
  Requires:
      http://eartoearoak.com/software/sdrsharp-net-remote
      http://www.pjrc.com/teensy/td_libs_Encoder.html
 
  Connections:
      Encoder    Arduino
      A          D3
      B          D2
      C          GND
 
  This program is free software: you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation, or (at your option)
  any later version.

  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <Encoder.h>

// Initialise the encoder on digital pins 2 & 3
Encoder encoder(2, 3);
long oldPos  = -999;

// Initial frequency
long frequency = 100000000;


void setup() {
  Serial.begin(115200);
}

void loop() {
  // Get the encoder position
  long newPos = encoder.read();
  if (newPos != oldPos) {
    oldPos = newPos;
	
    // Send the command to change the frequency via the serial port
    Serial.print("{\"Command\": \"Set\", \"Method\": \"Frequency\", \"Value\": ");
    Serial.print(frequency + (newPos * 1000));
    Serial.println("}");
  }
}