URGENCY, PIEZOELECTRIC ERROR!!!

Hello, good evening! I’m looking to resolve this error, if anyone can help me, I thank.

Well, the thing is, I am to do a eletronic drum integrating Java with Arduino, then, capture what shade or dish I hit, I will use the Trandutor Piezoelectric (http://migre.me/gUvYL) sensor, only that here comes the problem. When making the first tests with the sensor, I say print the values ??read from the sensor, the analog port, only the Serial Monitor values ??start to regress one on one.
Here I am doing ascend an LED when it comes to 299, the LED does not stop blinking, as this regress. Someone could tell me why this regressing and what could be done to not regress more?

int piezoeletric = A0;
int led = 13;
int readedSign;

void setup() {
  Serial.begin(9600);
  pinMode(led, OUTPUT);
  pinMode(piezoeletric, INPUT); 
}
void loop() {
  
  readedSign = analogRead(piezoeletric);
  Serial.println(readedSign);
  
  if(readedSign - 200 < 100)  {
    Serial.println(readedSign);
    digitalWrite(led, HIGH);
    delay(50);
    digitalWrite(led, LOW);
    delay(50);  
  }
}

Thank you!!

Show us your wiring diagram.

That’s the diagram:

WiringDiagram.png

You need a resistor in series with the LED (220 ohm - 1 Kohm) and a resistor in parallel with the piezo element (typically 100 Kohm - 1 Megohm). http://arduino.cc/en/Tutorial/Knock

Thaks so much jremington, it's worked nice, and helped me a lot!!!