/*

Knock Sensor

This sketch reads a piezo element to detect a knocking sound.

It reads an analog pin and compares the result to a set threshold.

If the result is greater than the threshold, it writes "knock" to the serial

port, and toggles the LED on pin 13.

The circuit:

- positive connection of the piezo attached to analog in 0

- negative connection of the piezo attached to ground

- 1 megohm resistor attached from analog in 0 to ground

created 25 Mar 2007

by David Cuartielles <http://www.0j0.org>

modified 30 Aug 2011

by Tom Igoe

This example code is in the public domain.

http://www.arduino.cc/en/Tutorial/Knock

*/

// these constants won't change:

const int ledPin = 13; // LED connected to digital pin 13

const int knockSensor = A0; // the piezo is connected to analog pin 0

const int threshold = 100; // 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

int ledState = LOW; // variable used to store the last LED status, to toggle the light

void setup() {

pinMode(ledPin, 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(knockSensor);

// if the sensor reading is greater than the threshold:

if (sensorReading >= threshold) {

// toggle the status of the ledPin:

ledState = !ledState;

// update the LED pin itself:

digitalWrite(ledPin, ledState);

// send the string "Knock!" back to the computer, followed by newline

Serial.println("Knock!");

}

delay(100); // delay to avoid overloading the serial port buffer

}