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/* CC-BY-SA - diegoCode - 2020 */

#define outPin 4

#define ledPin 13

#define T_LED 100 // blink period (ms)

int countLed = T_LED;

void setup() {

// configure pins

pinMode(outPin, OUTPUT);

pinMode(ledPin, OUTPUT);

// set up timer interrupt

setTimerInterrupt(1500); // int @1ms (1000 us)

}

void loop() {

if (countLed == 0) {

togglePin(ledPin);

countLed = T_LED;

}

// timer compare ISR

ISR(TIMER1_COMPA_vect) {

togglePin(outPin);

if (countLed) --countLed;

}

// toggle pin

void togglePin(long pin){

digitalWrite(pin, digitalRead(pin) ^ 1);

}

// set up timer1 -

// compare interrupt @ uSecs microseconds

void setTimerInterrupt(long uSecs) {

noInterrupts(); // disable all interrupts

TCCR1A = 0;

TCCR1B = 0;

TCNT1 = 0;

// compare match register 16MHz/256 * t(s) - 1

OCR1A = (16e6 / 256L * uSecs) / 1e6 - 1;

TCCR1B |= (1 << WGM12); // CTC mode

TCCR1B |= (1 << CS12); // 256 prescaler

TIMSK1 |= (1 << OCIE1A); // enable timer compare interrupt

interrupts(); // enable all interrupts

}