Arduino controlled PWM PC Fan

Question

I am looking at getting 2 Evercool EC8015HH12BP 80x10mm (4-wire) PWM fans. However, I am looking at controlling the fan speed with the arduino via the PWM pins.

I found the following diagram that seems to be what I am looking for in order to hook the fan up to the Arduino:

The code that I think I can use is this:

int pwmPin = 9;      // digital pin 9
int pwmVal = 10;

void setup()
{
  pinMode(pwmPin, OUTPUT);   // sets the pin as output
  Serial.begin(9600);
}

void loop()
{
  if (pwmVal != 255) {
         analogWrite(pwmPin, pwmVal);
         //pwmVal += 10;
         Serial.print(pwmVal);  // Print red value
         Serial.print("\n");    // Print a tab
  } else {
         Serial.print('at max high');  // Print red value
         Serial.print("\n");    // Print a tab
  }
  delay(1000);
}

I gather that the PWM would be in the range of 0-255 when writing out to it from the ardunio? I will be using the DS18B20 Thermometer Temperature Sensor in order to see how fast I need to spin the fan.

However, the fan speed (max 12V right now) never slows down one bit.

I'm using D9 on the Arduino Nano ATmega 328.

The reference is here for the board (in case i have the board pin wrong): enter link description here

Any helpful feedback would be great!

Answer 1

One thing to note is that

if (pwmVal != 255) {
    pwmVal += 10;
    ...

is not going to stop at 255, since pwmVal will be 250, then 260, e.t.c. One way to fix this would be write

if(pwmVal < 255)
{
   pwmVal += 10;
}
else
{
   pwmVal = 255;
}

By the way your code is written, if DEBUG is set to 0, nothing will happen (pwmVal will be set to 0). If DEBUG is set to 1, the fan speed will increase at a rate set by "wait" (which isn't defined in this code), until it gets to it's maximum. The value will also be printed to the serial port.

Answer 2

PWM frequency needs to be between 21kHz and 28kHz according to formfactors.org/developer/specs/4_Wire_PWM_Spec.pdf . I don't know how to set PWM frequency on an Arduino, but I suspect it needs to be set.

The same doc suggests that you may have reversed your sense and PWM pins (though your diagram and photo show two different things!). I can't verify this or take responsibility for your fan if its wrong.

Answer 3

Sorry for adding this as another answers, but I wasn't allowed to add a comment to Scott Seidman's answer and further add information to gbmhunters comment.

The PWN frequency can be controlled using the PWM registers, something which is also required if you want to use the Arduino as an IR transmitter, like a programmable remote control.

More information on the PWN registers can be found in this post, initially written by Ken Shirriff: https://www.arduino.cc/en/Tutorial/SecretsOfArduinoPWM