PWM Freak

This is very small library for configuring the PWM frequency for AVR based Arduinos. I didnt write it, It is taken from the playground.arduino.cc site and provided in this library for your convenience.

Why Change the Default Frequency?

If you are controlling a motor, voice coil or any sort of inductive device you are likely hearing a humming sound while using the default PWM frequency. This is simply because the switching of the inductive device is within our hearing range. By increasing the frequency to 20Khz (or higher like 31.2Khz) we'll put it well above our hearing range...but dont expect the dogs to like it!

Setting PWM base frequency

Simply add the library using the Arduino library manager and include the PWMFreak.h include file.

#include <PWMFreak.h>

Then in your setup function call the function to set the frequency for the given pin. The function will figure out what timer is backing that pin and set the PWM frequency. Other PWM pins that rely on the same timer will also be affected!

void setup()
{
    // change PWM for pin 6 to use divisor value 1
    setPwmFrequency(6, 1);

}

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: https://forum.arduino.cc/index.php?topic=16612#msg121031