int sininen = 2;
int keltainen = 3;
int vihrea = 4;
int ledOn1=false;
int ledOn2=false;
int ledOn3=false;

void setup()
{
  Serial.begin(9600);
  pinMode(sininen, OUTPUT);
  pinMode(keltainen, OUTPUT);
  pinMode(vihrea, OUTPUT);
}

void loop()
{
  if ( Serial.available()) {
    char ch = Serial.read();
    if ('s'==ch) {
      ledOn1=!ledOn1;
      digitalWrite(sininen, ledOn1);
    }
    if ('k'==ch) {
       ledOn2=!ledOn2;
       digitalWrite(keltainen, ledOn2);
    }
    if ('v'==ch){
       ledOn3=!ledOn3;
       digitalWrite(vihrea, ledOn3);
    }
  }
  delay(100);
}