Arduino PWM pin and 5V fan speed control

Forum 2005-2010 (read only) Hardware Interfacing
1

Hi,

Despite a lot of readings in this forum, I didn't find anything (?) about the speed control of a 5V fan...so I'm posting.
I made a first try, with a 2N2222 on the pin 11, with a 2.2k resistor between base and pin 11 and a 12V fan. It works and I can control the fan speed through a very simple program.
But when I replace my 12V fan by a 5V fan, it works only when the value on the PWM pin equals 255 (i.e full out). When it goes below this value, the fan stops and nothing more happens except from a very low "bzzzzzzzzzzzzzz"... I tried both with an external power supply and with the 5V pin from the arduino.
My question is: why this happens ?
Do the load drived by the transistor have to be greater than the voltage of the "command" circuit ?

Thanks for your answers !

2

Are you trying to drive the 5v fan directly from pin 11 instead of using the 2N2222 sinking driver?

3

No. I've only replaced the fan and kept the same other components and schematic.

4

Really? Huh! That really should work.

What is your PWM period? Have you tried shorter or longer periods?

5

Here is my code:

int ventiloPin = 11;
int incomingByte = 0;      
int val = 255;

void setup()
{
  Serial.begin(9600);      
  pinMode(ventiloPin, OUTPUT);   
}

void loop(){
  if (Serial.available() > 0) {
    incomingByte = Serial.read();
    if(incomingByte == '+' && val<245) {
      val += 10;
    }
    if(incomingByte == '-' && val>10){
      val -= 10;
    }
  }
analogWrite(ventiloPin, val); 
}

All the values below 255, passed to analogWrite, give the same result, described in my first message...

6

up :-/