Re: Low pass filter on a PIC

Manfred wrote:

> I'm developing a microcontroller-based speed controller for my small
> hydroelectric plant. I'm using a PIC 16F628 for this. I'm detecting the
> zero crossings of the 50Hz signal coming from the generator, and
measuring
> the duration of each half cycle,

> The little problem I have is that a small 420Hz signal on the power
line,
> apparently coming from the generator's internal voltage regulator, is
> causing jitter in the zero crossings,
> So I would like to apply a low pass filter function to my
> signal, with a cutoff frequency of roughly 20Hz, before the P-I
function.
>   

The PI function is a lowpass filter by itself. However there is not much 
you can do when the noise is already in. Add an analog filter upfront 
the PIC comparator. That will reduce the interferrence without 
significantly degrading the performance of the loop.


Vladimir Vassilevsky

DSP and Mixed Signal Design Consultant

http://www.abvolt.com