int ledPin=13;
int sensorPin=0;

double alpha=0.75;
int period=20;
double change=0.0;

void setup()
{
	pinMode(ledPin,OUTPUT);
}

void loop()
{
	static double oldValue=0;
	static double oldChange=0;
	int rawValue=analogRead(sensorPin);
	double value=alpha*oldValue+(1-alpha)*rawValue;
	change=value-oldValue;

	digitalWrite(ledPin,(change<0.0&&oldChange>0.0));
	
	oldValue=value;
	oldChange=change;
	delay(period);
}