int sensorPin = A0;    // select the input pin for the potentiometer
int sensorValue = 0;  // variable to store the value coming from the sensor
int timer = 50;
int lowPin = 6;
int highPin = 13;

void setup() {
  // declare the ledPin as an OUTPUT:
  for (int thisPin = 6; thisPin < 14; thisPin++)  {
    pinMode(thisPin, OUTPUT);      
  }
}

void loop() {
  // read the value from the sensor:
  sensorValue = analogRead(sensorPin);    

  if (sensorValue < 700){
    chaserUp();
  }
  else {
    chaserDown();
  }
}

void chaserUp(){
  for (int thisPin = lowPin; thisPin <= highPin; thisPin++) { 
    // turn the pin on:
    digitalWrite(thisPin, HIGH);   
    delay(timer);                  
    // turn the pin off:
    digitalWrite(thisPin, LOW);
  }
}

void chaserDown(){
  for (int thisPin = highPin; thisPin >= lowPin; thisPin--) { 
    // turn the pin on:
    digitalWrite(thisPin, HIGH);
    delay(timer);
    // turn the pin off:
    digitalWrite(thisPin, LOW);
  }
}