MarkT:
The timer is counting 0..255, so repeats every 256 clock cycles, so its output is clock / 256 ??
Ok.. So 0x02 mean 2x256=512 and clock output would be clock/512.. True?
Anyway, i don't understand why but this line don't work. With "TCCR0B = TCCR0B & 0b11111001 | 0x01;" i should get frequency 31,25 kHz (my cpu slock is 8 MHz) but speed of fan is always on 100%. If i change last three bits to 010 (to prescaler 8, so frequency should be around 4 kHz) it works, but this is too low. I can still hear annoying sound from fan.