> -----Original Message-----
> From: Tim ODriscoll [SMTP:tim@STOKEPOGESWAY.NET]
> Sent: Monday, June 23, 2003 10:19 AM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Re: [PIC]: 16F628 and analog inputs
>
> On Sun, 22 Jun 2003, Gaston Gagnon wrote:
> > The low pass filter output will average the pwm value. A simple RC
> > network should do.
> > The idea is to have the pwm output average to match your analog signal.
> > You watch the comparator output to determine if the pwm value should be
> > increased or decreased.
> > The pwm value is the digital image of your analog signal.
> >
> Aaah, I see now... I think I need to add 'low pass filters' to my list of
> things to read up on :)
>
> Although I've never tried it, I'm not sure it would work for my
> application... My analog input is a video signal, so it's changing quite
> quickly and the low pass filter sounds like it will take some time to
> settle. So, by the time I've read back the last voltage to compare to the
> current one, I've lost the rest of the scanline.
>
For video applications, even the inbuilt ADC is probably not going to be
fast enough.  Typicaly a complete conversion cycle on a PIC will take
between 30 and 40 us which means you will get one, maybe two samples per
line.  You generaly need a high speed/flash converter for video work.

Regards

Mike


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