How to use output PWM in AVR
Modulate the LED "on" time.

Something like this.

for(int i=0; ; i++,i%=8)
{
    for(int k=0; k&lt;26; k++)
    {
        PORTC |=(1&lt;&lt;i);
        delay_ms(10);
        PORTC &amp;= ~(1 &lt;&lt; i);
        delay_ms(10);
    }
    delay_ms(dela);
}