Arduino piezo code

/* Piezo Knock
* -----------
* Turn a standard piezo buzzer into a force sensor
*
* Created 24 October 2006
* copyleft 2006 Tod E. Kurt * http://todbot.com/
*/


int ledPin = 13;
int piezoPin = 0;

int THRESHOLD = 100; // set minimum value that indicates a knock

int val = 0; // variable to store the value coming from the sensor
int t = 0; // the "time" measured for how long the knock lasts

void setup() {
pinMode(ledPin, OUTPUT);
Serial.begin(9600);
Serial.println("ready"); // indicate we're waiting
}


void loop() {
digitalWrite(ledPin,LOW); // indicate we're waiting

val = analogRead(piezoPin); // read piezo
if( val >= THRESHOLD ) { // is it bigger than our minimum?
digitalWrite(ledPin, HIGH); // tell the world
t = 0;
while(analogRead(piezoPin) >= (THRESHOLD/2)) {
t++;
} // wait for it to go LOW (with a little hysteresis)
if(t!=0)
Serial.println(t);
}
}