At 08:49 17/08/99 +1000, you wrote:
>> Chris Eddy wrote:
>
>> I need good snappy response, but I need the needle to move
>> smoothly.  Are there any filter gurus out there that can identify my
>> problem?
>>
>
>Maybe you need to work out the amount of steps needed for a given move
>and then step in a linear  mode to that point. If the input value
>changes, then recalculate to the new position. I guess you could get
>fancier and do a logarithmic move so that the needle moves fast
>initially and slows down as it approaches the end point.
>
>
>--
>Best regards
>
>Tony
>
>http://www.picnpoke.com
>Email sales@picnpoke.com
>
>


Yep this is the sort of thing one needs to do if it is to look like an
analogue counterpart.
You say in chunks, sounds like the time constant of the IIR is too short
(Not enough taps) And that you are reponding at a rate that may be way too
fast.
We all need to know a little more before we attempt to look at the problems
(Yes I think that there is more than one and I don't think that it is the
filter as yet, although it may be fixable in this area). Firstly how well
does it work when it has to move from a large value to a small value and
vice versa, secondly how does it move when subjected to small veraiations
ie. 3 or so bits worth (The IIR filter should do its job here) Then how
often do you sample, do you leave the ADC in continuios sample mode while
the IIR is active, or do you use a sample and hold type thing?

Please tell us more. I don't know much, but may be able to help.

Dennis