You can control the counter TOP by setting the OCRxA register to the value you desire. See the datasheet for information on how this register affects the timer prescaler. You can control the prescaler by using the TCCRxB register (x is the number of the timer you are using, and will be either 0 or 2 for an 8-bit timer or 1 for a 16-bit timer). Timer frequency = system clock / prescaler Timer frequency is determined by the selected prescaler, where: If I have a timer being clocked at 1 MHz and the timer counts from 0 to 99 before overflowing, my generated PWM will be equal to:

If 249 = 1kHz, I can also see that 62 = 12 kHz from another post.įast PWM frequency is given by the following equation: OCR2B = 125 // set the PWM to 50% duty cycle PinMode(3, OUTPUT) // enable the PWM output (you now have a PWM signal on digital pin 3) OCR2A = 249 // top/overflow value is 249 => produces a 1000 Hz PWM TCCR2B = 0x0C // select timer2 clock as 16 MHz I/O clock / 64 = 250 kHz

set pin high on overflow, clear on compare match with OCR2B configure hardware timer2 to generate a fast PWM on OC2B (Arduino digital pin 3) I must admit this is on the edge of my comprehension, I can see that in the following code I need to change the OCR2A and TCCR2B values so set the prescaler and TOP value in order to get 25Mhz, however, I can't follow the calculation in order to work out what I should be putting into the register/variable. Hmm, well I found 'bens' posts, of which this one seems to be the most relevant: It has been discussed in the forum before, so try to serach the forum for 'PWM frequency' I'm quite sure you can change the PWM frequency on Arduino.

4 pin fan controller