To make 10bit A/d into 8-bit, just shift right twice. That's it.

--Bob


At 11:33 PM 7/16/2003 -0500, you wrote:
>Andy, just one question.  How would you change the code to handle a 10-bit
>a/d sample?  Probably not necessary in the case where I'm determining fuel
>level (1/256 is plenty of resolution), but I'm curious if it can be done
>yet kept simple.  I suppose I could really make the fuel gauge rock-steady
>by using this algorithm along with sampling around 250ms or so...
>
>Regards, Bob
>
>Andrew Warren <aiw@CYPRESS.COM> wrote ..
> > Bob Japundza <PICLIST@mitvma.mit.edu> wrote:
> >
> > > I have been thinking about the tanks sloshing around as being
> > > noisy signal, and that is one of the reasons why I've been
> > > contemplating the median filter.  Do you have a better suggestion?
> >
> >     Seems to me that a straight low-pass filter would work well.
> >
> > > I tried an analog low-pass RC filter, and didn't have good luck
> > > with it, because of the low resistance of the senders (30-240 ohm
> > > Stewart-Warner float types) and not to mention it made me nervous
> > > to have large caps tied to the fuel senders, in an airplane, no
> > > less.
> >
> >     Try a digital low-pass filter.  Given a series of input samples
> >     in the range 0-255, this code (all 7 words of it) should perform
> >     a 256-sample moving-window average and give you the filtered
> >     result in AVEHI.
> >
> >     ; Run this on every input sample.  Enter with the new input
> >     ; sample in NEW.  Exits with filtered result in AVEHI, and
> >     ; NEW unchanged.
> >     ;
> >     ; Might want to initialize AVEHI to something reasonable at
> >     ; program start; if it were me, I'd probably just initialize
> >     ; AVEHI to the first input sample.
> >     ;
> >     ;          (WIDTH-1)*AVE + NEW
> >     ;    AVE = -------------------
> >     ;                 WIDTH
> >
> >     AVEHI   EQU     [ANY FILE REGISTER]   ;Holds the average [0-255].
> >     AVELO   EQU     [ANY FILE REGISTER]   ;Holds the fractional part
> >                                           ;of the average.
> >     NEW     EQU     [ANY FILE REGISTER]   ;Holds the new sample.
> >
> >     FILTER256:
> >
> >         MOVF    AVEHI,W
> >         SUBWF   NEW,W
> >         SKPC
> >         DECF    AVEHI
> >         ADDWF   AVELO
> >         SKPNC
> >         INCF    AVEHI
> >
> >     -Andy
> >
> > === Andrew Warren -- aiw@cypress.com
> > === Principal Design Engineer
> > === Cypress Semiconductor Corporation
> > ===
> > === Opinions expressed above do not
> > === necessarily represent those of
> > === Cypress Semiconductor Corporation
> >
> > --
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