On Fri, Jan 15, 2010 at 10:34:12AM +0000, Mike Harrison wrote:
>  I'm trying to get my head round how to damp a cyclic compass heading
> value without odd things happening around the transition from 0 to 359 -
> I'm sure there is a simple trick to it but can't figure out what it
> is....
> 
> What I normally do for non-cyclic values is a simple IIR filter 
> new_value=old_value*damp+last_reading*(1-damp)

This is equivalent to:
new_value = old_value + (1-damp)*(last_reading-old_value)

ie add a fraction of the difference between lastest and old to get the new
value.  This will still work if you calculate the difference so that it's
between -180 and 180, and of course wrap the final addition.

Regards,

Chris
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist