#include "pindefs.h"
byte state = HIGH;
volatile int counter = 0;

void timerSetup () {
   TIMSK2 = (TIMSK2 & B11111110) | 0x01;
   TCCR2B = (TCCR2B & B11111000) | 0x07;
}

void setup() {
   pinMode(LED1, OUTPUT); digitalWrite(LED1, state);
   pinMode(LED2, OUTPUT); digitalWrite(LED2, state);
   pinMode(LED3, OUTPUT); digitalWrite(LED3, state);
   pinMode(LED4, OUTPUT); digitalWrite(LED4, state);
   timerSetup();
}
 
void loop() {
  if (counter>50) {
    state = !state;
    digitalWrite(LED1, state);
    counter = 0;
  }
}
 
ISR(TIMER2_OVF_vect){
   counter++;
}