Debouncing

gistfile1.ino

//arbitrary number to signal that a
//key is not bouncing
const uint8_t NOT_BOUNCING = 20;
//how many ms a key is expected to bounce
const uint8_t BOUNCE_TIME = 10;
//how many bouncing keys can be handled
//in parallel
const uint8_t MAX_BOUNCING = 5;

//the index where the last bouncing key
//is stored in the below array
uint8_t bounceIndex = 0;
//an array to store the bounce times
unsigned long bounceTimers[MAX_BOUNCING];

struct Key {
  byte id;
  boolean pressed;
  uint8_t bounceKey;
  Key(byte id) : id(id), pressed(false), bounceKey(NOT_BOUNCING) {};
};

boolean toggleKey(struct Key *key) {
  key->bounceKey = checkStillBouncing(key->bounceKey);
  if(key->bounceKey == NOT_BOUNCING){
    key->bounceKey = debounceKey();
    key->pressed ? key->pressed = false : key->pressed = true;
    return true;
  }
  return false;
}

uint8_t checkStillBouncing(uint8_t bounceKey){
  //check if the key is actually bouncing
  if(bounceKey == NOT_BOUNCING) return NOT_BOUNCING;
  //check if the bounce time is over
  if(millis() - bounceTimers[bounceKey] > BOUNCE_TIME) return NOT_BOUNCING;
  //else return the index of the bouncing counter
  return bounceKey;  
}

uint8_t debounceKey(){
  //get the next available index 
  //in the bounceTimers array
  //or wrap around
  (bounceIndex + 1) == MAX_BOUNCING ? bounceIndex = 0 : bounceIndex++;
  //store the current time stamp
  bounceTimers[bounceIndex] = millis();
  return bounceIndex;
}