ADC 10-bit false results
You have incorrect multiplexer setting. To select channel 1, it should be

ADMUX  |= 1&lt;&lt;MUX0 ;  // ADC-Channel 1


Edit: Another thing is incorrect clock prescaler. To get \$f_{clk}/128\$:

ADCSRA |= 7&lt;&lt;ADPS0;  // Assign ADC-prescaler 128