adc averaging readings

[amgen]

hello,
for a alternator regulator using 12f683 pwm, i want to smooth a/d readings by taking 3 readings and discard the high and low reading to make next pwm calc. I'm trying to keep math calculations from slowing down process too much. any fast way to check 3 readings and discard high and low reading?

also working on a self tuning PID. seems like the micro and program could tune itself to simply reduce/increase P,I or D to stop or set overshoot .am i missing too many brain cells?

don
american generator

[paul borgmeier]

any fast way to check 3 readings and discard high and low reading?

X1 VAR word  ;1st data point
X2 VAR word  ; 2nd data point
X3 VAR word  ; 3rd data point
Xtemp VAR word  ; temp variable

;******************
Gosub X2X1Compare

If X3 < X2 THEN ; swap if true
     Xtemp = X2
     X2 = X3
     X3 = Xtemp
ENDIF

Gosub X2X1Compare

X2 is now your keep value ; <- here is your answer

END
;******************
X2X1Compare:
     If X2 < X1 THEN ; swap if true
          Xtemp = X1
          X1 = X2
          X2 = Xtemp 
     ENDIF
Return
;******************

However, it is would be much easier and computationally faster to sample 4 values, add them together, and divide by 4 (using shift right)

Xtemp = X1+X2+X3+X4
Xtemp = Xtemp >> 2 ; <- here is your answer

Paul Borgmeier
Salt Lake City, Utah
USA

[amgen]

Paul,
Thankyou for your suggestion to take 4 readings etc. I will use that routine. Its always better the simpler.
don
american generator