Trying to figure out how to change from inverted fast PWM to Fast PWM in the following sketch. It was written to be used with a transistor, but I am going straight from the pin to connector. The total sketch is to change the PWM freq to 25kHz. This what the fan needs per the intel spec sheet. Then vary the speed. Please take alook and see if there are anymore problem. It is for a Mega 2560 Only second week working with an Arduino.... A real Noobie.....
Thanks
Daka
/ Analog output (i.e PWM) pins. These must be chosen so that we can change the PWM frequency without affecting the millis()
// function or the MsTimer2 library. So don't use timer/counter 1 or 2. See comment in setup() function.
// THESE PIN NUMBERS MUST NOT BE CHANGED UNLESS THE CODE IN setup(), setTransistorFanSpeed() AND setDiodeFanSpeed() IS CHANGED TO MATCH!
// On the Mega we use OC1B and OC1C
const int transistorFanPin = 12; // OC1B
const int diodeFanPin = 13; // OC1C
// Definitions for PWM fan control
const unsigned char maxFanSpeed = 80; // this is calculated as 16MHz divided by 8 (prescaler), divided by 25KHz (target PWM frequency from Intel specification)
void setup()
{
// Set up the PWM pins for a PWM frequency close to the recommended 25KHz for the Intel fan spec.
// We can't get this frequency using the default TOP count of 255, so we have to use a custom TOP value.
// Only timer/counter 1 is free because TC0 is used for system timekeeping (i.e. millis() function),
// and TC2 is used for our 1-millisecond tick. TC1 controls the PWM on Arduino pins 9 and 10.
// However, we can only get PWM on pin 10 (controlled by OCR1B) because we are using OCR1A to define the TOP value.
// Using a prescaler of 8 and a TOP value of 80 gives us a frequency of 16000/(8 * 80) = 25KHz exactly.
// On the Mega we use TC1 and OCR1B, OCR1C
TCCR1A = (1 << COM1B1) | (1 << COM1B0) | (1 << COM1C1) | (1 << COM1C1) | (1 << WGM11) | (1 << WGM10); // OC1A disconnected, OC1B = OC1C fast PWM
TCCR1B = (1 << WGM13) | (1 << WGM12) | (1 << CS11); // TOP = OCR1A, prescaler = 8
TCCR1C = 0;
OCR1AH = 0;
OCR1AL = 79; // TOP = 79
OCR1BH = 0;
OCR1BL = maxFanSpeed;
OCR1CH = 0;
OCR1CL = maxFanSpeed;
TCNT1H = 0;
TCNT1L = 0;
// We have to enable the ports as outputs before PWM will work.
pinMode(transistorFanPin, OUTPUT);
pinMode(diodeFanPin, OUTPUT);
}
// Set the transistor fan speed, where 0 <= fanSpeed <= maxFanSpeed
void setTransistorFanSpeed(unsigned char fanSpeed)
{
OCR1BH = 0;
OCR1BL = fanSpeed;
}
// Set the diode fan speed, where 0 <= fanSpeed <= maxFanSpeed
void setDiodeFanSpeed(unsigned char fanSpeed)
{
OCR1CH = 0;
OCR1CL = fanSpeed;
}
void loop()
{
setTransistorFanSpeed(80);
delay(30000); // run for 30 seconds at maximum fan speed
setTransistorFanSpeed(0);
delay(30000); // run for 30 seconds at low fan speed
}