// Call this function to start a timer. Interval is in milliseconds.
// The timer number will be passed to the callback. If you want the
// timer to run only when triggered, use an interval of 0.
int startTimer(unsigned long interval, void (*action)(int));

// Call this function to stop a timer. Can be used in the callback
// function for a "one shot" timer.
void stopTimer(int index);

// Use this function to trigger a timer. Useful in interrupt handlers when
// you have a lot of work to do also when you want to do something
// periodically or when an event happens.
void triggerTimer(int index);

// Call this function in loop to run all your timers.
void runTimers();