Back to Arduino Interrupts

#include <TimerOne.h>
  
const byte LED = 13;

void handleOtherStuff() {
    delay(100);
    //Serial.println(Timer1.read());
}

unsigned int led = LOW;
void timerISR()
{
    digitalWrite(LED, led);
    led ^= (HIGH^LOW);
}

void setup() {
    //Start up the serial port
    Serial.begin(9600);
    while (!Serial); // for Leonardo
    Serial.println(F("Initialized example7"));
  
    // configure the pins
    pinMode(LED, OUTPUT);
    
    Timer1.initialize();         // breaks analogWrite() for digital pins 9 and 10 
    Timer1.attachInterrupt(timerISR, 500000);  // attaches timerISR() as a timer overflow interrupt -- blinks at 1 Hz
    //Timer1.attachInterrupt(timerISR, 13);  // attaches timerISR() as a timer overflow interrupt -- blinks at 38 kHz
}

void loop() {
    handleOtherStuff();
} 

This example uses a timer overflow interrupt.  You will have do download the TimerOne library and install it in your Arduino directory. See this page for instructions.