6677 4 wire fan code

//Pin 2 to PC fan "Tacho" line (pin 3 on standard connectors) with 10k pullup to 5v.
//pin 11 to PC fan PWM/Input line (pin 4 on standard connectors, absent on 3 pin fans).


unsigned int counter;
unsigned int lastCounter;

unsigned long timeToReset;
void setup() {
  counter = 0;
  lastCounter = 0;
  // put your setup code here, to run once:
  pinMode(2, INPUT);
  attachInterrupt(0, rpm, RISING);
  pinMode(13, OUTPUT);
  //attachInterrupt(0, toggleLED, RISING);
  pinMode(11, OUTPUT);
  setPwmFrequency(11, 1);
  Serial.begin(9600);
  timeToReset = 1000;
}

void loop() {
  // put your main code here, to run repeatedly:
  if (millis() > timeToReset) {
    timeToReset = millis() + 1000;
    lastCounter = counter;
    counter = 0;
    Serial.print("RPM: ");Serial.println(lastCounter * 60);
  }
  if (Serial.available()) {
    char input = Serial.read();
    switch (input) {
      case '0':
      analogWrite(11, 0);
      Serial.println("11, 0");
      break;
      case '5':
      analogWrite(11, 128);
      //Serial.println("11, 128");
      break;
      case '8':
      analogWrite(11, 204);
      //Serial.println("11, 204");
      break;
      case '9':
      analogWrite(11, 255);
      //Serial.println("11, 255");
      break;
      case 'f':
      //Serial.print("RPM: ");Serial.println(lastCounter);
      default:
      break;
    }
  }
}

void toggleLED() {
  digitalWrite(13, !digitalRead(13));
}
void rpm() {
  counter++;
}
void setPwmFrequency(int pin, int divisor) {
  byte mode;
  if(pin == 5 || pin == 6 || pin == 9 || pin == 10) {
    switch(divisor) {
      case 1: mode = 0x01; break;
      case 8: mode = 0x02; break;
      case 64: mode = 0x03; break;
      case 256: mode = 0x04; break;
      case 1024: mode = 0x05; break;
      default: return;
    }
    if(pin == 5 || pin == 6) {
      TCCR0B = TCCR0B & 0b11111000 | mode;
    } else {
      TCCR1B = TCCR1B & 0b11111000 | mode;
    }
  } else if(pin == 3 || pin == 11) {
    switch(divisor) {
      case 1: mode = 0x01; break;
      case 8: mode = 0x02; break;
      case 32: mode = 0x03; break;
      case 64: mode = 0x04; break;
      case 128: mode = 0x05; break;
      case 256: mode = 0x06; break;
      case 1024: mode = 0x7; break;
      default: return;
    }
    TCCR2B = TCCR2B & 0b11111000 | mode;
  }
}