Sound box

Description:

A box that detects when it is knocked and responds back, using piezo sensors for input and output.

Video:

http://www.youtube.com/watch?v=WSD6PbzcTnE (turn up the sound!)

Materials:

• Metal peppermint creams box, found in the abandoned TUI box
• One bare peizo element
• One housed piezo element 

Arduino code:

int analogInPin = A5;
int sensorValue;
int speakerPin = 10;
int scale = 0;
int buffer[50];

void setup() {
  memset(buffer,0,50);
  Serial.begin(9600);
  pinMode(speakerPin, OUTPUT); 
}

void loop() {
  // read sensor value into a 20 item buffer, store a 0 as 1 (helps later when comparing values)
  // 
  sensorValue = analogRead(analogInPin);
  if(sensorValue == 0) { 
    sensorValue++; 
  }

  for(int g = 49; g>0; g--) {
    int f = g - 1;
    buffer[g] = buffer[f];
  }
  buffer[0] = sensorValue;

  // buffer output debug, throws so much data at the serial that it slows down the program.  
  /*  
   for(int z=0; z<20; z++) {
   Serial.print(buffer[z]);
   Serial.print(" ");
   }
   Serial.println(" ");
   
   */

  delay(20);

  // look at what happened 1.9 and 2.0 seconds ago
  int diff48_49 = buffer[48] - buffer[49];

  // sound if it is a significant thump
  // needed because the piezo sensor gradually changes its reading, steadily
  // approaching 1023 (~1 or 2 per .1 sec) after being struck
  if( abs(diff48_49) > 5) {

    // a larger difference means a harder hit, scale it to a PWM value to control volume
    scale = map(abs(diff48_49),5,200,1,255);
    if(scale>255) { 
      scale = 255; 
    }
    // debugosity 
    Serial.print("buffer[48_49]:");
    Serial.print(abs(diff48_49));
    Serial.print(" scale:");
    Serial.println(scale);


    analogWrite(speakerPin, 0);
    for( int i=0; i<5; i++ ) {   // play it for .1 second

      analogWrite(speakerPin, scale);
      delayMicroseconds(10000);
      analogWrite(speakerPin, 0);
      delayMicroseconds(10000);
    }

  }

}