ADC bei Attiny25 geht nicht

/*

 * ATtiny25

 * File: main.c

 */

#define F_CPU 8000000UL

#include <avr/io.h>

#include <stdlib.h>

#include <inttypes.h>

#include <util/delay.h>

uint16_t adc_value;            //Variable used to store the value read from the ADC

void adc_init(void);            //Function to initialize/configure the ADC

uint16_t read_adc(uint8_t channel);    //Function to read an arbitrary analogic channel/pin

void Motor_Stop()

{

  PORTB &= ~(1 << PB0);

  PORTB &= ~(1 << PB1);

  PORTB &= ~(1 << PB3);

  PORTB &= ~(1 << PB4);

}

void Motor_Forward()

{

  /* Vorwärts */

  PORTB ^= 1<<PB3;

  PORTB &= ~(1 << PB4);

  PORTB ^= 1<<PB0;

  PORTB &= ~(1 << PB1);

  return;

}

void Motor_Backward()

{

  /* Rückwärts*/

  PORTB &= ~(1 << PB3);

  PORTB ^= 1<<PB4;

  PORTB &= ~(1 << PB0);

  PORTB ^= 1<<PB1;

  return;

}

int main(void)

{

  uint16_t result;

    // Set up Ports to output

  DDRB = (1 << DDB0) | (1 << DDB1) | (1 << DDB3) | (1 << DDB4);

  _delay_ms (1000);

    // Set up Port B data to be all low

   // PORTB = 0; 

  while (1)

  {

    adc_value = read_adc(1);

    if (adc_value > 1023)

    {

      Motor_Stop();

    }

    else

    {

      Motor_Forward();

    }

    _delay_ms (250);

  }

  return 0;

}

void adc_init(void)

{

 ADCSRA |= ((0<<ADPS2)|(1<<ADPS1)|(1<<ADPS1));    //8Mhz/8 = 1Mhz the ADC reference clock

 ADMUX |= (1<<REFS0);                //Voltage reference from Avcc -> VCC (3v)

 ADCSRA |= (1<<ADEN);                //Turn on ADC

 ADCSRA |= (1<<ADSC);                //Do an initial conversion because this one is the slowest and to ensure that everything is up and running

}

uint16_t read_adc(uint8_t channel){

 ADMUX &= 0xF0;                    //Clear the older channel that was read

 ADMUX |= channel;                //Defines the new ADC channel to be read

 ADCSRA |= (1<<ADSC);                //Starts a new conversion

 while(ADCSRA & (1<<ADSC));            //Wait until the conversion is done

 return ADCW;                    //Returns the ADC value of the chosen channel

}