A simple Arduino piezo knock sensor that cycles through a series of RGB LED patterns

knock_knock.ino

// define pins for the RGB LED
byte led_red_pin = 3;
byte led_green_pin = 5;
byte led_blue_pin =  6;

int piezo_pin = A0;
int piezo_threshold = 250; // This may have to be tuned for your piezo

int wait = 10000; // the time before the last night and the cycle resets
int debounce = 200; // the number of milliseconds we'll wait to reject bad input 

// used to handle the picking the pattern/behavior to respond to a knock
long knock_count = 0;

void config_rgb_led() {
  pinMode(led_red_pin, OUTPUT);
  pinMode(led_green_pin, OUTPUT);
  pinMode(led_blue_pin, OUTPUT);  
}


byte invert_color(byte color) {
  // uncomment this if LOW == ON for your LED
  return 255 - color;
  // uncomment this if HIGH == ON for your LED
  // return color;
}

void set_led_color(byte red, byte green, byte blue) {
  analogWrite(led_red_pin, invert_color(red));
  analogWrite(led_green_pin, invert_color(green));
  analogWrite(led_blue_pin, invert_color(blue));     
}

void setup() {
  config_rgb_led();
  set_led_color(0,0,0);
}

int read_piezo() {
  return analogRead(piezo_pin);
}

void loop() {
  // detect a knock
  if (read_piezo() >= piezo_threshold) {
    // figure out which pattern we should use
    int pattern = (knock_count + 1) % 3;
    switch (pattern) {
      case 1: // this is the first pattern
        set_led_color(255, 0, 0); // set the LED to green
        delay(debounce);
        break;
      case 2: // this is the second pattern
        set_led_color(0, 255, 0); // set the LED to green
        delay(debounce);
        break;
      case 0: // this is the third pattern
        set_led_color(0, 0, 255); // set the LED to blue
        delay(debounce);
        delay(wait - debounce);
        set_led_color(0,0,0);
        break;
      default:
        break;
    }
    knock_count += 1;
  }
}