Hey cool -- some concrete math.  I've been calculating to 4 bits to the right 
of the b.p. (binary point, which is my terminology for binary equivalent of a 
decimal point), and so far it's been quite accurate.  I did some experiments 
with coming *up* to a certain value and going *down* to that value and it 
seems to settle back to the same point quite well (meaning the error is 
unnoticeable).  I'm doing a bit of rounding as well.

Cheers,
-Neil.


On Thursday 12 May 2005 12:22 pm, Spehro Pefhany scribbled:
> This simulates a single-pole RC low pass filter with time constant
> tau = Ts * (1/K - 1)  (where Ts is sample period)
>
> So, if you want tau = 0.5 seconds and you are sampling 20 times a second
> (Ts = 0.05) then you'd use K = 1/9 .
>
> The output never quite reaches the input (with infinite precision math), so
> it's an IIR filter. With a step change the error after t time is
>
> % error  = 100% * exp(-t/tau)). So with 0.5 second tau, after 5 tau (2.5
> seconds)
> you'd have an error of about 0.7%.
>
>
>
> Best regards,
>
> Spehro Pefhany --"it's the network..."            "The Journey is the
> reward" speff@interlog.com             Info for manufacturers:
> http://www.trexon.com Embedded software/hardware/analog  Info for
> designers:  http://www.speff.com Inexpensive test equipment & parts
> http://search.ebay.com/_W0QQsassZspeff


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