On 5/15/05, Kenneth Lumia <klumia@adelphia.net> wrote:
> Interesting idea.
> 
> The MPX sensor output has a large amount of noise.  You
> will need to filter it extensively before applying it to your circuitry.
> I seem to recall the app notes specifying a 750 Hz or so low
> pass filter.  You will probably want an even lower cutoff frequency
> than suggested.  A single pole RC is probably not sufficient for what
> you are after - a multiple pole op-amp filter may be better.
> Similarly, the PWM will probably need more filtering as well.
> Extremely clean power to the circuit is a must.  Also, choose your
> sampling frequency carefully to avoid harmonics.  Watch out for
> non-linear regions of the op-amp near ground and 5V rails.
> Finally, once you've treated it as best as is reasonable in
> hardware, remember that software filtering is your friend.
> 
> > Is this a solution that is worth trying?  I can take away any static error
> > during calibration but is there any sources for temperature or other
> > dynamic errors that I need to take care of.
> 
> I'd try it, with additional filtering of course.  Temperature will
> effect the results, you will need to determine the temperature
> range and the accuracy required over that range to see if you
> exceed the expected results (a rather complicated calculation,
> considering all the "analog" parts and their tolerances).
> 
> klumia@adelphia.net
> 

This seems a good application for an old fashioned dual-slope A-D
converter.  They can have pretty good resolution and they naturally
integrate the signal.

Has anyone built one with a PIC?

Regards,
Mark
markrages@gmail
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