int ledc = 13;  
int sensorPin = 0;
int period = 20;
int change, oldvalue, value;
int time = 0;

void setup ()
{
  pinMode(ledc, OUTPUT);
  Serial.begin (9600);
}
void loop ()
{
  value = analogRead (sensorPin);
  Serial.print ("  ");
  Serial.println(value);
  change = abs(oldvalue - value);
  if(change > 1 )
  {
    Serial.println (change);
    time +=1;
  }
  else
  {
     time -=1;
     if (time < 0)
       time = 0;
  }
  
  if (time > 0)
    analogWrite(ledc, 255);
  else
    analogWrite(ledc,0);
    
  oldvalue = value;
  delay (period);
}