PIC Microcontoller DSP Math Method

8bit 16 step Averageing filter by Andrew Warren

    ; Written by Andrew Warren [fastfwd at ix.netcom.com].
    A couple days ago, I wrote that an averaging filter of the form:

          (WIDTH-1)*AVE + NEW
    AVE = -------------------
                 WIDTH

was "absurdly simple" if WIDTH = 256.  A couple of people have asked
in private email for the code; here it is:

    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

7 words, 7 instruction cycles, "NEW" is unchanged.

See also:

• David A Cary refers to

  http://www.htsoft.com/cgi-bin/agnes?PicforumAgnes+PicforumAgnesHTMLArticle+2775.2 Frank Everest mentions very similar idea:

    temp = (average - new) >> time_value
    average = average - t
  

  is a quick implementation of

  average = ( (2^time_value - 1)*average + (1)*new ) / 2^time_value.

Questions:

• Looking for a 16bit word from externel adc any sample may be 10 times and average it to get a stable value. Then display the final results on the character LCD. I know how to control the LCD, I have routines for that. Only need the code to average a 16 bit word 10 times.
  Thanks