I’m working on an application where I need fine adjustment of PWM frequency. The existing PWM code that I found, such as the Arduino PWM Frequency Library, only allows integral frequencies to be selected. On pins supported by 16-bit timers, the Arduino PWM Frequency Library allows fine adjustment of duty cycle, but not frequency. After searching for a while, I found an interesting article in Udo Klein’s Blinkenlight blog: Flexible Sweep. In the article, Klein has an Arduino sketch which sweeps the LEDs of a Blinkenlight board from 0-999.9999 Hz in increments of .0001 Hz.
I hacked his sketch into PrecisionPWM, which outputs PWM to any arbitrary digital pin in increments of .0001 Hz. What’s nice is that since it doesn’t use the ATmega’s internal PWM generator, you can use it on any arbitrary digital pin, whether or not it supports hardware PWM.
Download from github: PrecisionPWM