Movie. Result of project

Arduino will store position of motor. Returning to original position as soon as signal "start" received (from Visual Studio)

motor_position (main function)

void loop() {
  if (stringComplete) {
    // clear the string when COM receiving is completed
    mySt = "";  //note: in code below, mySt will not become blank, mySt is blank until '\n' is received
    stringComplete = false;
  }

  //receive command from Visual Studio
  if (mySt.substring(0,8) == "vs_start"){
    motor_start = true;
  }
  if (mySt.substring(0,7) == "vs_stop"){
    motor_start = false;
  }

  //find position
  if(motor_start){
    //start finding position since receive "vs_start" from Visual Studio
    analogWrite(pin_pwm,40); //set motor speed = 40/255 = 15.6%
    if(encoder_r+encoder_f < -1){
      digitalWrite(pin_fwd,1);
      digitalWrite(pin_bwd,0);
    }
    else{
      if(encoder_r+encoder_f > 1){
        digitalWrite(pin_fwd,0);
        digitalWrite(pin_bwd,1);
      }
      else{
        //stop motor if position between +1 ~ -1
        analogWrite(pin_pwm,0);   //stop motor
        digitalWrite(pin_fwd,0);  //stop motor
        digitalWrite(pin_bwd,0);  //stop motor
      }
    }
  }
  else{
    //stop finding position since receive "vs_stop" from Visual Studio
    analogWrite(pin_pwm,0);   //stop motor
    digitalWrite(pin_fwd,0);  //stop motor
    digitalWrite(pin_bwd,0);  //stop motor
  }
}

void detect_a_r() {
  m_direction = digitalRead(pin_b); //read direction of motor
  if(!m_direction){
    encoder_r += 1;   //increasing encoder at forward run
  }
  else{
    encoder_r += -1;  //decreasing encoder at backward run
  }

  attachInterrupt(digitalPinToInterrupt(pin_a), detect_a_f, FALLING); //change interrupt to Falling edge
}
void detect_a_f() {
  m_direction = digitalRead(pin_b); //read direction of motor
  if(m_direction){
    encoder_f += 1; //increasing encoder at forward run
  }
  else{
    encoder_f += -1; //decreasing encoder at backward run
  }

  attachInterrupt(digitalPinToInterrupt(pin_a), detect_a_r, RISING);  //change interrupt to Rising edge
}

Visual Studio (main function)

#pragma endregion
private: System::Void Form1_Load(System::Object^  sender, System::EventArgs^  e) {
serialPort1->Open();
timer1->Start();
i=300;
}
private: System::Void button1_Click(System::Object^  sender, System::EventArgs^  e) {
serialPort1->WriteLine("vs_start"); //start finding position
}
private: System::Void button2_Click(System::Object^  sender, System::EventArgs^  e) {
serialPort1->WriteLine("vs_stop"); //stop finding position
}
private: System::Void timer1_Tick(System::Object^  sender, System::EventArgs^  e) {
int len=mStr->Length;
if(mStr->Substring(0,7)=="encoder"){
position=mStr->Substring(7,len-7);
label1->Text=position;
//print motor speed into Chart
this->chart1->Series["Series1"]->Points->AddXY(i,System::Convert::ToDouble(position));
i++;
this->chart1->ChartAreas["ChartArea1"]->AxisX->Minimum=i-300; //shift x-axis
}
}
private: System::Void serialPort1_DataReceived(System::Object^  sender, System::IO::Ports::SerialDataReceivedEventArgs^  e) {
mStr=serialPort1->ReadLine();
}