>> Continuing on with the above idea..
>> If you need to convert your ADC value to engineering units, and are
>> oversampling to do the low pass filtering, you can make the
>> oversampling do the multiply portion of the scaling calculation.
>>
>> ie: suppose, Humidity = ADC_VALUE * 1.73  ( or whatever) then
>> just accumulate 173 samples, saves doing the scaling calculation.
>
>    Ray:
>
>    Maybe I'm missing something, but it seems to me that summing 173
>    samples and discarding the low byte will give you
>
>        ADC_VALUE * 173/256,   NOT   ADC_VALUE * 1.73.
>
>    If you really want to scale your input by 1.73, you'll need to
>    sum 443 samples (i.e., 256 * 1.73 samples) before discarding the
>    low byte.
>
>    -Andy

Correct, however, depending on signal characteristics it's
probably not nessessary to discard all of the low byte.
However much you right-shift by needs to be included in the scaling.


A simple filter algorithm that provides "RC type" low pass filtering
that is easy to implement.

               Totalizer + Input - Previous_Output
  Output =   ------------------------------------
                            N

Notes:
1. Choose a value for N = 2^X ( ie 128,256,512 etc) makes the
   division fast and simple.

2. Sample input at equal time intervals. (probably not critical)
3. Initialize Totalizer to Input*N, or Zero ( application dependant)


Ray Gardiner (DSP Systems) ray@dsp-systems.com http://www.dsp-systems.com
private email to:- ray@netspace.net.au