Arduino Knock Sensor Drum Kit v1.01 from Morgellon on Vimeo.

• Read how to use a piezo buzzer as a knock sensor

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

• Read how to make a piezo buzzer play various tones, instead of just one!

http://arduino.cc/en/Tutorial/PlayMelody

Here’s the sample code I used, with a few tweaks added:

int ledPin = 13;      // led connected to control pin 13
int knockSensor = 0;  // the knock sensor will be plugged at analog pin 0
byte val = 0;         // variable to store the value read from the sensor pin
int statePin = LOW;   // variable used to store the last LED status, to toggle the light
int THRESHOLD = 100;  // threshold value to decide when the detected sound is a knock or not

// TONES  ==========================================
// Start by defining the relationship between
//       note, period, &  frequency.
#define  c     3830    // 261 Hz
#define  d     3400    // 294 Hz
#define  e     3038    // 329 Hz
#define  f     2864    // 349 Hz
#define  g     2550    // 392 Hz
#define  a     2272    // 440 Hz
#define  b     2028    // 493 Hz
#define  C     1912    // 523 Hz
// Define a special note, ‘R’, to represent a rest
#define  R     0

// SETUP ============================================
// Set up speaker on a PWM pin (digital 9, 10 or 11)
int speakerOut = 9;
// Do we want debugging on serial out? 1 for yes, 0 for no
int DEBUG = 1;

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

// MELODY and TIMING  =======================================
//  melody[] is an array of notes, accompanied by beats[],
//  which sets each note’s relative length (higher #, longer note)
int melody[] = {  C,  b,  g,  C,  b,   e,   C,  c  };
int beats[]  = { 16, 16, 16,  8,  8,  16,  16, 16  };
int MAX_COUNT = sizeof(melody) / 2; // Melody length, for looping.

// Set overall tempo
long tempo = 10000;
// Set length of pause between notes
int pause = 1000;
// Loop variable to increase Rest length
int rest_count = 100; //<-BLETCHEROUS HACK; See NOTES

// Initialize core variables
int tone = 0;
int beat = 0;
long duration  = 0;

// PLAY TONE  ==============================================
// Pulse the speaker to play a tone for a particular duration
void playTone() {
long elapsed_time = 0;
if (tone > 0) { // if this isn’t a Rest beat, while the tone has
//  played less long than ‘duration’, pulse speaker HIGH and LOW
while (elapsed_time < duration) {

digitalWrite(speakerOut,HIGH);
delayMicroseconds(tone / 2);

// DOWN
digitalWrite(speakerOut, LOW);
delayMicroseconds(tone / 2);

// Keep track of how long we pulsed
elapsed_time += (tone);
}
}
else { // Rest beat; loop times delay
for (int j = 0; j < rest_count; j++) { // See NOTE on rest_count
delayMicroseconds(duration);
}
}
}

void loop() {
val = analogRead(knockSensor);    // read the sensor and store it in the variable “val”
if (val >= THRESHOLD) {
// statePin = !statePin;           // toggle the status of the ledPin (this trick doesn’t use time cycles)
digitalWrite(ledPin, HIGH); // turn the led on or off
Serial.println(“Knock!”);       // send the string “Knock!” back to the computer, followed by newline
for (int i=0; i<MAX_COUNT; i++) {
tone = melody[i];
beat = beats[i];

duration = beat * tempo; // Set up timing

playTone();
// A pause between notes…
delayMicroseconds(pause);
}
delay(10);                      // short delay to avoid overloading the serial port
}
digitalWrite(ledPin, LOW);
}

Arduino Knock Sensor Drum Kit v1 from droops on Vimeo.

When a drum is struck, a knock sensor (backwards peizo) talks to the arduino and activates an led ot change the color of the drum (blue), after a delay the blue led goes out and the drum becomes orange again.  I used a pullup resistor between the pins of the knock sensor, but i didnt get any different results with different values, so its probably dependent on the peizo that you use.

/*
droop's drum kit

dailyduino.com

droops - gmail

thanks for the idea josh!!
*/

int knockPin = 3; //pin for incoming knock sensor
int knockVal; //value from knock sensor
int knockLedPin = 10; //bue led
int normalLedPin = 4;  //orange led
int lightBlue = 2000; //counter for keeping blue light on
int limit = 1000; //how sensitive the knock sensor is, lower = higher sensitivity based on piezo and pull down resistor
int blueTime = 2000; //how long the blue led stays on

void setup(){
  pinMode(knockLedPin, OUTPUT);
  pinMode(normalLedPin, OUTPUT);
  pinMode(knockPin, INPUT);
  Serial.begin(9600);
  digitalWrite(knockLedPin, LOW);
  digitalWrite(normalLedPin, HIGH);
}

void loop(){

  knockVal = analogRead(knockPin); //read the knock sensor

  if (knockVal < limit){
    lightBlue = 0; //drop the value to activate the led
    Serial.println(knockVal);  //dump to serial for debugging
  }

  //this keeps the blue light on after a knock is registered
  if(lightBlue < blueTime){
    digitalWrite(normalLedPin, LOW);
    digitalWrite(knockLedPin, HIGH);
    lightBlue++;
  } else {
    digitalWrite(knockLedPin, LOW);
    digitalWrite(normalLedPin, HIGH);
  }  

}