Multiple PWM Outputs with Unique Frequencies

Hardware Arduino Due
7

Okay, I finally came up with a clean alternate approach for setting up PWM frequencies from within a sketch, for up to two unique frequencies. The trick is to utilize the two PWM clocks (CLKA & CLKB) provided by the SAM3X8E chip.

I wrote and enclosed a library (pwm01.h). It includes 4 user functions to: 1) setup PWM resolution, 2) setup PWM pin, frequency & pick clock, 3) write duty cycle, and 4) stop PWM. See example code for usage:

#include "C:\Programs\arduino-1.5.1r2\hardware\arduino\sam\libraries\Pwm01\pwm01.h"

void setup() 
{
    uint32_t  pwm_duty = 32767;
    uint32_t  pwm_freq1 = 2;  
    uint32_t  pwm_freq2 = 5000;

    // Set PWM Resolution
    pwm_set_resolution(16);  

    // Setup PWM Once (Up to two unique frequencies allowed
    //-----------------------------------------------------    
    pwm_setup( 6, pwm_freq1, 1);  // Pin 6 freq set to "pwm_freq1" on clock A
    pwm_setup( 7, pwm_freq2, 2);  // Pin 7 freq set to "pwm_freq2" on clock B
    pwm_setup( 8, pwm_freq2, 2);  // Pin 8 freq set to "pwm_freq2" on clock B
    pwm_setup( 9, pwm_freq2, 2);  // Pin 9 freq set to "pwm_freq2" on clock B
      
    // Write PWM Duty Cycle Anytime After PWM Setup
    //-----------------------------------------------------    
    pwm_write_duty( 6, pwm_duty );  // 50% duty cycle on Pin 6
    pwm_write_duty( 7, pwm_duty );  // 50% duty cycle on Pin 7
    pwm_write_duty( 8, pwm_duty );  // 50% duty cycle on Pin 8
    pwm_write_duty( 9, pwm_duty );  // 50% duty cycle on Pin 9

    delay(30000);  // 30sec Delay; PWM signal will still stream
        
    // Force PWM Stop On All Pins
    //-----------------------------    
    pwm_stop( 6 );
    pwm_stop( 7 );
    pwm_stop( 8 );
    pwm_stop( 9 );
}

void loop() 
{  
}

The pwm01.h library and example code were tested in IDE 1.5.1r2. Additional notes on this library:

  • Applies to Arduino-Due board, PWM pins 6, 7, 8 & 9.
  • Libary Does not operate on the TIO pins.
  • Unique frequencies set via PWM Clock-A ("CLKA") and Clock-B ("CLKB")
    Therefore, up to two unique frequencies allowed.
  • Set max duty cycle counts (pwm_max_duty_Ncount) equal to 255 per Arduino approach.
    This value is best SUITED for low frequency applications (2hz to 40,000hz) such as
    PWM motor drivers, 38khz infrared transmitters, etc.
  • Future library versions will address high frequency applications.
  • Arduino's "wiring_analog.c" function was very helpful in this effort.

pwm01.h (3.96 KB)