Drive an Old PC Fan with Arduino

#include <RotaryEncoder.h>
#include <U8glib.h>

// ----- Rotary settings here ----
#define ROTARYSTEPS 1
#define ROTARYMIN 80
#define ROTARYMAX 255

#define FANPIN 3

// Setup a RoraryEncoder for pins A2 and A3:
RotaryEncoder encoder(A2, A3);

U8GLIB_SSD1306_128X32 u8g(U8G_I2C_OPT_NONE);  // I2C / TWI

int pos=0;
char Potenza[5];

 
void setup() {
  // put your setup code here, to run once:
  
  Serial.begin(115200);
  Serial.println("Fan test with Encoder:");

  encoder.setPosition(0 / ROTARYSTEPS); // start with the value of 0
  analogWrite(FANPIN, 0);
  u8g.setColorIndex(1);         // pixel on for Display 


}

void loop() {
  // put your main code here, to run repeatedly:

 encoder.tick();

  int newPos = encoder.getPosition();
  if (pos != newPos) {

    if (newPos < ROTARYMIN) {
    encoder.setPosition(ROTARYMIN / ROTARYSTEPS);
    newPos = ROTARYMIN;
    } else if (newPos > ROTARYMAX) {
      encoder.setPosition(ROTARYMAX / ROTARYSTEPS);
      newPos = ROTARYMAX;
    }
    sprintf(Potenza, "%d", newPos);
    u8g.firstPage();  
    do {
      draw("Power:", 0, 12);
      draw(Potenza, 90, 12);
    } while( u8g.nextPage() );
    
   analogWrite(FANPIN, newPos);
   Serial.println(newPos);
   pos=newPos;  
 }
}


void draw(char* parola, int posx, int posy) {
  // graphic commands to redraw the complete screen should be placed here  
  u8g.setFont(u8g_font_unifont);
  //u8g.setFont(u8g_font_osb21);
  u8g.drawStr( posx, posy, parola);
}