## arduino 更改pwm频率的方法

arduino, 硬件相关 |
1月 06 2016

// Set pin 9’s PWM frequency to 3906 Hz (31250/8 = 3906)
// Note that the base frequency for pins 3, 9, 10, and 11 is 31250 Hz
setPwmFrequency(9, 8);

// Set pin 6’s PWM frequency to 62500 Hz (62500/1 = 62500)
// Note that the base frequency for pins 5 and 6 is 62500 Hz
setPwmFrequency(6, 1);

// Set pin 10’s PWM frequency to 31 Hz (31250/1024 = 31)
setPwmFrequency(10, 1024);

Please keep in mind that changing the PWM frequency changes the Atmega’s timers and disrupts the normal operation of many functions that rely on time (delay(), millis(), Servo library).

/**
* Divides a given PWM pin frequency by a divisor.
*
* The resulting frequency is equal to the base frequency divided by
* the given divisor:
*   – Base frequencies:
*      o The base frequency for pins 3, 9, 10, and 11 is 31250 Hz.
*      o The base frequency for pins 5 and 6 is 62500 Hz.
*   – Divisors:
*      o The divisors available on pins 5, 6, 9 and 10 are: 1, 8, 64,
*        256, and 1024.
*      o The divisors available on pins 3 and 11 are: 1, 8, 32, 64,
*        128, 256, and 1024.
*
* PWM frequencies are tied together in pairs of pins. If one in a
* pair is changed, the other is also changed to match:
*   – Pins 5 and 6 are paired on timer0
*   – Pins 9 and 10 are paired on timer1
*   – Pins 3 and 11 are paired on timer2
*
* Note that this function will have side effects on anything else
* that uses timers:
*   – Changes on pins 3, 5, 6, or 11 may cause the delay() and
*     millis() functions to stop working. Other timing-related
*     functions may also be affected.
*   – Changes on pins 9 or 10 will cause the Servo library to function
*     incorrectly.
*
* Thanks to macegr of the Arduino forums for his documentation of the
* PWM frequency divisors. His post can be viewed at:
*   http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1235060559/0#4
*/
void setPwmFrequency(int pin, int divisor) {
byte mode;
if(pin == 5 || pin == 6 || pin == 9 || pin == 10) {
switch(divisor) {
case 1: mode = 0x01; break;
case 8: mode = 0x02; break;
case 64: mode = 0x03; break;
case 256: mode = 0x04; break;
case 1024: mode = 0x05; break;
default: return;
}
if(pin == 5 || pin == 6) {
TCCR0B = TCCR0B & 0b11111000 | mode;
} else {
TCCR1B = TCCR1B & 0b11111000 | mode;
}
} else if(pin == 3 || pin == 11) {
switch(divisor) {
case 1: mode = 0x01; break;
case 8: mode = 0x02; break;
case 32: mode = 0x03; break;
case 64: mode = 0x04; break;
case 128: mode = 0x05; break;
case 256: mode = 0x06; break;
case 1024: mode = 0x7; break;
default: return;
}
TCCR2B = TCCR2B & 0b11111000 | mode;
}
}