Lösung: 4 Sekunden Schätzer

#define F_CPU 16000000UL

#include <avr/io.h>
#include <stdint.h>

int main(void)
{
	DDRD |= 0b11111111;
	DDRB &= ~0b00000100;
	PORTB |= 0b00000100;
	TCCR1B = 0b00000101;
	
	uint16_t zaehler = 0;
	uint8_t LEDout;
	
	while (1)
	{
		while (PINB & 0b00000100)
		{
		}
		PORTD = 0b00000000;
		LEDout = 0b11111111;
		for (uint8_t i = 0; i<=8; i++)
		{
			PORTD=LEDout;
			TCNT1 = 0;
			while (TCNT1 < 15625)
			{
			}
			LEDout = LEDout/2;
		}
		TCNT1 = 0;
		while (PINB & 0b00000100)
		{
		}
		zaehler = TCNT1;
		if (zaehler < 43750)
		{
			PORTD = 0b00000011;
		}
		else
		{
			if (zaehler > 50000)
			{
				PORTD = 0b11000000;
			} 
			else
			{
				PORTD = 0b00011000;
			}
		}
		while (TCNT1 < 65000)
		{
		}
	}
}