Why does this LED stay ON?

When I run the "blink" program, the LED turns on and off like it should. However, when I run the "Knock" program, it stays lit but flickers when the piezo is knocked. Why is it staying lit? Thanks!

const int led = 1; // led connected to digital pin 1 const int piezo = A0; // the piezo is connected to analog pin 0 const int threshold = 10; // threshold value to decide when the detected sound is a knock or not

// these variables will change: int sensorReading = 0; // variable to store the value read from the sensor pin

void setup() { pinMode(led, OUTPUT); // declare the ledPin as as OUTPUT Serial.begin(9600); // use the serial port }

void loop() { // read the sensor and store it in the variable sensorReading: sensorReading = analogRead(piezo);

// if the sensor reading is greater than the threshold: if (sensorReading >= threshold) { // update the LED pin itself: digitalWrite(led, HIGH); // send the string "Knock!" back to the computer, followed by newline Serial.println("Knock!"); delay(100); // delay to avoid overloading the serial port buffer }else{ digitalWrite(led, LOW); }

}

This

const int led = 1;      // led connected to digital pin 1

and this

Serial.println("Knock!");

do not get along.

Digital pin 1 is the tx pin for Serial.println().

SurferTim, thanks so much!

-jonathan