#include <avr/io.h>
#include <util/delay.h>

/*

Blinks an LED connected to pin B0.

Assumes the positive pin of the LED is connected to B0.
The negative pin is connected through a resistor to GND.

A 1K resistor works well for most LEDs.
Decrease if too dim.

*/

int main(void) {
    DDRB = 255U; // Make all PB* -- PORT B -- pins output
    PORTB = 0x0; // turn all PB* -- PORT B -- pins off.
    
    while (1) {
        PORTB = 0x1; // high 
        _delay_ms(250);  // 1/4 second on
        PORTB = 0X0; // low
        _delay_ms(2500); // 2.5 seconds off
    }
}