Make a Fan Controller with Arduino

I have a server of two Raspberry Pis and they needed to be cooled. I grabbed a fan. But it was way to loud! So I got an Arduino, wrote some Code and now I can control my fan.

Step 1: Figure out the pins of the fan connector

You need a fan with a Plus (red) pin, a Minus (black) pin and a Speed pin. Some fans with three pins have plus, minus but then a Speedometer pin. The Speedometer pin is an output of the fan saying how fast the fan is rotating. Fans with four pins have a Speedometer pin and a Speed pin.

Step 2: Connect the Arduino to the fan

Connect 12V to the Plus pin of the fan, GND to the Minus pin of the fan and a PWM pin, for example pin 3 of the Arduino to the Speed pin of the fan.

Step 3: Code

#include <EEPROM.h>
#define FAN_PIN 3;
#define FS_ADDR 0x01
int fanSpeed;
void setup() {
 // put your setup code here, to run once:
 pinMode(3, OUTPUT);
 EEPROM.get(FS_ADDR, fanSpeed);
 if(fanSpeed < 1) fanSpeed = 255;
 analogWrite(FAN_PIN, fanSpeed);
 Serial.begin(9600);
}
char rx_byte = 0;
String input = "";
void loop() {
 if (Serial.available() > 0) {    // is a character available?
   rx_byte = Serial.read();       // get the character
   // check if a number was received
   if ((rx_byte >= '0') && (rx_byte <= '9')) {
     input.concat(rx_byte);
   }
   else if (rx_byte == '\n') {
     Serial.print("Received: ");
     Serial.println(input);
     if(input.toInt() < 256) {
       fanSpeed = input.toInt();
       EEPROM.put(FS_ADDR, fanSpeed);
     } else {
       Serial.println("Invalid Number");
     }
     input = "";
   }
   else {
     Serial.println("Not a number.");
   }
 } // end: if (Serial.available() > 0)
 analogWrite(FAN_PIN, fanSpeed);
}

Step 4: Control it!

You can change the fan speed with putting in a number over serial. It saves the number also in the EEPROM (at FS_ADDR) so when it resets, the speed will be the same than before.