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d00a014 Jun 4, 2014
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#include <TimerOne.h>
// This example creates a PWM signal with 25 kHz carrier.
//
// Arduino's analogWrite() gives you PWM output, but no control over the
// carrier frequency. The default frequency is low, typically 490 or
// 3920 Hz. Sometimes you may need a faster carrier frequency.
//
// The specification for 4-wire PWM fans recommends a 25 kHz frequency
// and allows 21 to 28 kHz. The default from analogWrite() might work
// with some fans, but to follow the specification we need 25 kHz.
//
// http://www.formfactors.org/developer/specs/REV1_2_Public.pdf
//
// Connect the PWM pin to the fan's control wire (usually blue). The
// board's ground must be connected to the fan's ground, and the fan
// needs +12 volt power from the computer or a separate power supply.
const int fanPin = 4;
void setup(void)
{
Timer1.initialize(40); // 40 us = 25 kHz
Serial.begin(9600);
}
void loop(void)
{
// slowly increase the PWM fan speed
//
for (float dutyCycle = 30.0; dutyCycle < 100.0; dutyCycle++) {
Serial.print("PWM Fan, Duty Cycle = ");
Serial.println(dutyCycle);
Timer1.pwm(fanPin, (dutyCycle / 100) * 1023);
delay(500);
}
}