Napr.

int stav = 0;

void loop() {
buttonState = digitalRead(start);
if(stav != buttonState)
{
CAKAJ_10ms(); // najjednoduchsie debounce :)
buttonState = digitalRead(start);
if(stav != buttonState) // po debouncovani stale uroven udrzana
{
stav = buttonState;
if (buttonState == HIGH)
invertuj_stav_rele();
}
}