[sdiy] ADC filtering (was A/D converter ...)

[Matthew Smith]

Quoth dan snazelle at 08/05/11 08:58...
> could anyone point me to a (maybe in C) code example of how this would work?
> or just some more info?
> 
> would it be sort of like putting using a FOR statement to let it read 4 values, then average them?
> (do you use the un-averaged AND averaged readings? or do you throw out the first four?

I'm a bit curious how chopping the oldest value would be achieved 
without using an array or circular buffer.

Below is a 'desktop C' stab at how I'd do it. (The volatile declarations 
are there so I don't forget them when in an embedded context - we may be 
calling avg4() from an ISR, thus volatile required.)

Still wonder if there isn't a more efficient way than using the array.

Cheers

M


#include <stdio.h>

volatile unsigned int avgreg[4]={0, 0, 0, 0};
volatile unsigned int avg_counter=0;

unsigned int avg4(unsigned int);

int main(void)
{
   unsigned int x, result;

   result=avg4(10);
   result=avg4(12);
   result=avg4(8);

   /*
    ...etcetera.

    Obviously, you'd actually do somethign
    with the value of result.

   */

   return(0);
}

unsigned int avg4(unsigned int i)
{
   unsigned int avgtmp;

   avgreg[3]=avgreg[2];
   avgreg[2]=avgreg[1];
   avgreg[1]=avgreg[0];
   avgreg[0]=i;

   /* Insufficient to make average, return input. */
   if (avg_counter<3)
   {
     avg_counter++;
     return(i);
   }

   avgtmp=avgreg[0]+avgreg[1]+avgreg[2]+avgreg[3];
   avgtmp>>=2;

   return(avgtmp);
}