Re: [avr-chat] PWM, to fast!

[Alan Kilian]

> I've just got the hang of PWM (i think) but it turns out that its just
> to fast! I need about 30Hz frequency and to vary the duty cycle from
> full(ish) to about 1/3. The idea is to control the speed of a fan by
> the PWM.
> 
> Am i right in thinking:    8MHz / 128prescalar = 62500kHz is the
> slowest PWM I can make?

    What AVR processor are you using?
        I see the ATMEGA8 has a divide-by 1024 prescaler.

    The 8 MHz / prescaler is the counter frequency INTO the PWM 
        function, so I believe you will get another divide-by 256 for an
        8-bit PWM, and a divide-by 1024 for a 10-bit PWM. (I would need
        to read the data sheet for the processor you are using to be 
        sure.)

    What's wrong with a faster-than 30 HZ PWM period?

                                        -Alan

-- 
- Alan Kilian <kilian(at)bobodyne.com>