PWM Fan Controller

hi there,

     i have 4-pin fan control using pwm on wide range of rpm's arduino use in small wind tunnel . range of speeds i'm interested ranges fan off max fan rpm. in particular, able access lower range of rpm's of fan (if possible go low of rpm such can see blades spinning rather them being blur).  have code i've pieced together  seems doing trick extent. of relevant technical specs of fan , personal notes listed in code below well. hope notes show i've been doing plenty of research subject prior asking forum.

     what i've noticed setup when run fan @ operating voltage of 12v pwm not appear change rpm @ 0% pwm duty cycle. however, when reduce source voltage lower values(i.e 1.00v) can use code turn fan on , off using 0% pwm duty cycle.

     i aware of intel pwm fan technical specification sheet http://formfactors.org/developer%5cspecs%5crev1_2_public.pdf

     of interest me 3 different types of pwm fan specifications( type a,b, , c). appears pwm fan type need type c, since able still reduce fan speed in linear fashion @ levels below minimum operating rpm , pwm.

my questions are:
1. verify whether arduino code changing rpm of fan change pwm duty cycle?
2. confirm whether hypothesis regarding fan type correct or incorrect? if correct how find fan need? i've googled around , seems manufacturers don't readily include pwm fan type.
3. third pin of fan can used tachometer understanding. can be used in conjunction arduino fan speed reading?
4. there pwm fans can achieve slow rpm's i'm after?

thank time! :]

code: [select]


/*
purpose: control pwm of noctua nf-a8 pwm fan via user input achieve low fan speeds

fan properties:
pwm fan pin specifications:
                  pin id  pin color pin purpose
                   1       black         gnd
                   2       yellow        5v
                   3       green        tachometer
                   4       blue          pwm
general pwm fan specs:
operating voltage: 12 v
current 0.08 a
rpm range: 2200 rpm (max)
           1750 rpm (max when using low noise adpater)
           450 rpm  (stall speed)
pwm frequency range: 21-28 khz
target pwm frequency: 25 khz

arduino pwm notes:
timer output  arduino output  chip pin  pin name  base frequency(hz)  divisors available
oc0a               6            12        pd6           62500           1,8,64,256,1024
oc0b               5            11        pd5           62500           1,8,64,256,1024
oc1a               9            15        pb1           31250           1,8,64,256,1024
oc1b              10            16        pb2           31250           1,8,64,256,1024
oc2a              11            17        pb3           31250         1,8,32,64,128,256,1024
oc2b               3             5        pd3           31250         1,8,32,64,128,256,1024

                   
instructions:   
                 1.power arduino via usb connection
                 2.connect fan gnd psu , arduino gnd psu(i.e. common ground)
                 3.connect fan 5v directly arduino 5v
                 4.connect fan tach directly arduino digitalpin tx->1
                 5.connect fan pwm directly arduino digitalpin 3
                 6.upload code onto arduino uno board
                 7.open serial monitor
                 8.type in "pwm" quotations onto serial monitor
                 9.enter integer value between 0-255 regulate value of pwm (0 off , 255 max)
                 10. repeat step 9 needed
*/     

// variable declarations
string command;
char werd;
int currentfan = 0;
int pwmpin = 3;
int pwmpinspeed = 0;

int commandcheck;

void setup() {

  // fans
  pinmode(3, output);//pwm pin
  tccr2a = 0x23;
  tccr2b = 0x09;  // select clock
  ocr2a = 79;  // aiming 25khz
  ocr2b = 62;
  analogwrite(3,0);
  serial.begin(9600);
  serial.println();
}

void loop(){

  ocr2b = 62;
  delay(1000);
  ocr2b = 120;
  delay(1000);
  // reads serial commands
  while ( serial.available() > 0 ) {
    // small delay because can deliver bytes quickly
    delay(5);
    // have read 1 byte (one character) @ time
    werd = serial.read();
    // append character "command" string
    command += werd;
  }
 
  // clear serial it's ready next command
  serial.flush();
  if ( command.length() > 0 ) {
    commandcheck = 0;
    if ( command == "pwm" ) {
        currentfan = 0;
    }
    else {
        commandcheck = 1;
    }
    if ( commandcheck == 1 ) {
    // ".toint()" appended command variable converts "command" string onto integer  used regulate pwm
      if ( currentfan == 0 ) {
        //front
       analogwrite(pwmpin, command.toint());
       pwmpinspeed = command.toint();
      }
      else {
        //unknown command
      }
    }
    command = "";
    serial.print(pwmpin);
    serial.print("fan speed: ");
    serial.println(pwmpinspeed);
    clear();
  }
}

void clear() {
  serial.println();
}

[\code]



you unlikely see fan goes below 30%rpm when pwm zero. in event do, find doesn't operate @ levels.

0%rpm unusual requirement. last 20% going flow unmeasurable amount of air fans.

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