On Tuesday 14 June 2005 02:27 pm, Spehro Pefhany scribbled:
> No, you're not off track. You could take the reading (with minimal LPF) and
> compare it to the displayed variable. If the difference exceeds a threshold
> you preload the variable (essentially set K = 0). That way you can tolerate
> a very long filter time constant because it only affects the last few
> counts. You could try more levels than just two but it might not be
> necessary.
>
> As Olin points out, it's possible with any of the "non-sticky" schemes that
> the variable sits on the edge of a threshold long term and flickers back
> and forth. You can make that less likely, but it's still probably possible.

Exactamundo.  And I am still noticing this.


> If you added a smidge of stickiness you could eliminate even that, but that
> adds some complexity. For example, suppose for the moment you have the
> number y = x * 10 available and are going to display d, to approximate x
> /10; (d is the previous display variable).
>
> y += ((y-10*d)> 5) ? -2:+2;
> d = y/10;
>

Maybe it's late, I'm hungry, or both, but I can't get a clear picture of the 
result of this in my head.  I need to plot some values on paper and track 
this.... after dinner though.


> Will give you just a whisper of stickyness. Probably enough to be
> irritating if you're using pots to calibrate the old-fashioned and
> time-tested way. ;-) If you're doing calibration in EEPROM, of course, you
> just use the original value of y.

No pots here.


> Of course you'd probably prefer to do this in powers of two and maybe in
> assembly,
> the C code and base-10 is just for pedagogic piclist purposes.

Gotcha.

Cheers,
-Neil.



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