debounce.c

/* The cord switch is attached to CORD_IN, and we're using internal pullups.
   so normally the value reads HIGH. when cord is pulled and connects to ground, reads LOW. */
/* In so many words, we're using the debounce protocol
   described at university of utah "debouncing.pdf" section "software debouncers" */
/* return 1 if cord pull is detected, else 0 */
/* If 1 is returned, it will only be returned once (until cord is released and cycled). */
#define DEBOUNCE_TIME 100
int debounceState = HIGH;
int debounceTimer = DEBOUNCE_TIME;
int checkCordIn() {
  int cord = digitalRead(CORD_IN);
  if (cord == LOW) { // cord might be being pulled
    if (debounceState == HIGH) { // we care, we're waiting to detect a real pull
      debounceTimer--;
      if (debounceTimer == 0) { // it's been down for DEBOUNCE_TIME, release the hounds
        debounceState = LOW;  // we don't care anymore (until release)
        return 1;
      }
    }
  }
  else { // cord not fully pulled, reset the detector
    debounceState = HIGH;
    debounceTimer = DEBOUNCE_TIME;
  }
  return 0;
}