This is a simple circuit to drive an 4-Pin PWM Fan using an ATtiny 45. With an Arduino Uno the first code was running after 30 minutes, but I would like to use a very small circuit in my gaming PC, so I tried to adopt it to some left over ATTinys. It was not as easy as I thought, because fast PWM on ATtiny needs special setup of some registers. The best description I found was on this website, which sets the PWM to 32 kHz, with 8Mhz F_CPU and no CKLDIV, which is a little bit higher than 25 kHz needed for the PWM of the Fan, but it worked with full duty cycle.
https://blog.podkalicki.com/attiny13-hardware-pwm/
The second challenge was that Arduiono analogread() did not work on the ATtiny at all. I found an alternative way on the following page:
http://www.hilltop-cottage.info/blogs/adam/avr-adc-1-basic-examples-attiny85/
The NTC conversion/correction to °C from 10bit ADC output was generated with this page: https://www.sebulli.com/ntc/index.php
The circuit and code should be self explanatory.
Example screenshots of changing pulse width on NTC with different temperatures and the frequency of about 32kHz.
