25 kHz 4 Pin PWM Fan Control with Arduino Uno

1const byte OC1A_PIN = 9;
2const byte OC1B_PIN = 10;
3
4const word  PWM_FREQ_HZ = 25000; //Adjust this value to adjust the frequency (Frequency in HZ!)  (Set currently to 25kHZ)
5const word TCNT1_TOP = 16000000/(2*PWM_FREQ_HZ);
6
7void  setup() {
8  
9  pinMode(OC1A_PIN, OUTPUT);
10
11  // Clear Timer1 control  and count registers
12  TCCR1A = 0;
13  TCCR1B = 0;
14  TCNT1  = 0;
15
16  //  Set Timer1 configuration
17  // COM1A(1:0) = 0b10   (Output A clear rising/set  falling)
18  // COM1B(1:0) = 0b00   (Output B normal operation)
19  // WGM(13:10)  = 0b1010 (Phase correct PWM)
20  // ICNC1      = 0b0    (Input capture noise canceler  disabled)
21  // ICES1      = 0b0    (Input capture edge select disabled)
22  //  CS(12:10)  = 0b001  (Input clock select = clock/1)
23  
24  TCCR1A |= (1 << COM1A1)  | (1 << WGM11);
25  TCCR1B |= (1 << WGM13) | (1 << CS10);
26  ICR1 = TCNT1_TOP;
27}
28
29void  loop() {
30
31    setPwmDuty(0);
32    delay(5000);
33    setPwmDuty(25); //Change  this value 0-100 to adjust duty cycle
34    delay(5000);
35//    setPwmDuty(50);
36//    delay(20000);
37//    setPwmDuty(75);
38//    delay(20000);
39//    setPwmDuty(100);
40//    delay(20000);
41}
42
43void setPwmDuty(byte duty) {
44  OCR1A = (word) (duty*TCNT1_TOP)/100;
45}
46