This is something that I would do:
unsigned long _timer1_period=0; //timer period, in seconds
unsigned long _timer1_counter=0; //timer1 counter
//timer1 isr
ISR(TIMER1_OVF_vect) {
_timer1_counter+=0x10000ul; //increment timer_counter
if (_timer1_counter >=F_CPU) {
_timer1_counter -= F_CPU; //reset timer_counter
_timer1_period -= 1; //decrement duration_sec
if (!_timer1_period) { //elapsed time has been reached
//turn off the led
digitalWrite(LEDPin, LOW);
TIMSK1 &=~(1<<TOIE1); //turn off timer1 interrupt
}
}
}
//initialize the timer
//to expire in user-specified period of time
void tmr1_init(unsigned long duration_sec) {
_timer1_counter = 0; //reset timer1 counter
_timer1_period=duration_sec; //set timer period
TCCR1B = 0x00; //turn off the timer
TCCR1A = 0x00; //normal portion operation
TCNT1 = 0; //reset the timer
TIFR1 |= (1<<TOV1); //clear the timer flag
TCCR1B = 0x01; //turn on the timer, 1:1 prescaler
TIMSK1 |= (1<<TOIE1); //enable the timer interrupt
sei(); //enable global interrupt
}
The isr keeps track of time elapsed and at the end, turns itself off. The other routine just initialize the timer. Once it is set, it goes on by itself.
Here would be your user code:
if (buttonState==HIGH) {
digitalWrite(LEDPin, HIGH); //turn on the led pin
tmr1_init(5); //initialize the timer to elapse in 5 seconds
}
As the routines are set-and-forget type, your user code is greatly simplified: all it does is to set up the timer and then it moves on.