Moving Average and DIV32

Hello all,
I'm trying to calculate the the moving average of a word size variable. The formula I'm using is listed below and is standard as far as I can tell. New values of watts are added to the average when a counter is incremented by 1 in my program.

Code:

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  wattsAvg = (wattsAvg*counter + watts)/(counter + 1) 'moving average of watts

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The results obtained are correct as as long as the numbers stay within word size limits. However, that is not the case as my numbers can range as follows:
counter : 0 to 400
watts : up to 7500 max

I think the problem would be solved with longs, but these require an 18F part. I'm using a 16F1823 as I need very small size device. I tried DIV32 as follows;

Code:

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  dummy = wattsAvg*counter + watts
  wattsAvg = div32 (counter + 1)

---

This does not work. Apparently you cannot mix multiplication and addition on the dummy line. The result is always zero.

Grateful for any ideas.

Since you are averaging then it does not make any difference if you do your calculation on the whole number or on the difference from the average. Flag if the difference is negative, so you will know that it will be a subtraction and work with the difference, that being smaller will never overflow your word.

Cheers

Al.

With a little help from our Friend Darrel ...

Code:

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' This routine will keep a "Running Average"

' Instead of adding a bunch of values together and then dividing by the number of samples,
' it averages each sample into the final result immediately.
' This eliminates the need for 32 bit math.
' To allow it to "Catch up" to large changes, set the FAspread to an acceptable range.
' Simply place the new number in VALUE and GoSub AVERAGE
' The Average will be returned into the same variable VALUE

       
AvgCount        CON  16                ' = Number of samples to average
FAspread        CON  1000        ' = Fast Average threshold +/-
ADavg                VAR  WORD
Value                VAR  WORD

' -=-=-=-=-=-=  Average Analog values -=-=-=-=-=-=-=-=-=-=
Average:
    IF Value = ADavg Then NoChange
    IF ABS (Value - ADavg) > FAspread OR Value < AvgCount Then FastAvg
    IF ABS (Value - ADavg) < AvgCount Then RealClose
    ADavg = ADavg - (ADavg/AvgCount)
    ADavg = ADavg + (Value/AvgCount)
    GoTo AVGok
  FastAvg:
    ADavg = Value
    GoTo AVGok
  RealClose:
    ADavg = ADavg - (ADavg/(AvgCount/4))
    ADavg = ADavg + (Value/(AvgCount/4))
  AVGok:
    Value = ADavg                        ' Put Average back into Value
  NoChange:
Return

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found here: http://www.pbpgroup.com/modules/wfse...hp?articleid=7

Guys,
This seems to work per your suggestions:

Code:

---

  if watts = wattsAvg then
  wattsAvg = watts
  endif

  if watts > wattsAvg then
  wattsAvg = wattsAvg + (watts - wattsAvg)/(counter + 1)
  endif
 
  if watts < wattsAvg then
  wattsAvg = wattsAvg + (wattsAvg - watts)/(counter + 1)
  endif

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Disregard my last post. Upon retest the code shown did not work.

Please disregard this whole inquiry. I'm going down the wrong track.