Simple Fan Controller for the TC74 and some 6 pin server fans. https://blog.tuckerosman.com/2019/02/building-temperature-based-fan.html

FanController.ino

//See https://blog.tuckerosman.com/2019/02/building-temperature-based-fan.html for more information.
//#include <Math.h>
//#define CURVE_FACTOR 1.03

#include <TC74_I2C.h>
#define FANSPEED_PIN 4

TC74_I2C TC74(TC74_A0);
int temperature;

void setup() {
  pinMode(FANSPEED_PIN, OUTPUT);
  digitalWrite(FANSPEED_PIN, HIGH);
  TC74.Init();
  delay(1000);
}

void loop() {
  temperature = TC74.ReadTemp();
  if (temperature != 128 && temperature != 0) { //Is this a valid temperature?
    //The exponential curve I wanted to use. Takes more cycles since the ATTiny85 has no float hardware
    //analogWrite(FANSPEED_PIN, ceil(255 * (pow(CURVE_FACTOR,temperature)/42.69)));
    analogWrite(FANSPEED_PIN, (255/127)*temperature);
  } else {
    //If we did not get a valid temperature, then blow the fans at full speed just to be safe.
    digitalWrite(FANSPEED_PIN, HIGH);
  }
  delay(1000);
}