Count, measure peak values and average them for finite duration ~ sinusoidal pulse?

[jellis00]

I have an application in which I have to use an ADC for input of an analog signal on which an almost sinusoidal pulse of finite duration needs to be measured. Typical pulsed signal is 7-8 cycles (up to 500 Hz) where the peak values are not always equal, so it is close to a sinusoid, but not exactly sinusoidal. I need to use PICBASIC code to sample the analog input at Nyquist (1200 Hz?) with an ADC input to my PIC 12F676 and then count the number of peaks in the waveform, measure each of the peaks, and average the counted peak values. Can anyone give me tips on how to do this...or better yet some example PICBASIC PRO code?

[HenrikOlsson]

Hi,
I'd probably sample at atleast 10 times the input frequency dependning on what else the PIC has to do while doing this thing.

Here's one idea, from the top of my head, untested....

Sample     VAR WORD
LastSample VAR WORD
Average    VAR WORD
Peaks      VAR WORD [8]
i          VAR BYTE
j          VAR BYTE
 
' You might want to insert some form of "trigger" mechanism here.
' Perhaps sample the input in a loop and wait until there's a 
' positive going trend or something - then move on the following:
 
For i = 0 to 7                    ' Get 8 peaks
 
  LastSample = 0                  ' Set up
  Average = 0                     ' Set up
  Sample = 0                      ' Set up
 
  DO 
     LastSample = Average         ' Save previous sample
     Average = 0                  ' Reset accumulator  
 
     For j = 0 to 3               ' Take 4 samples quickly    
       ADCIN 1, Sample            ' Get current input
       Average = Average + Sample ' Add to accumulator
     Next                         ' Next sample
 
     Average = Average >> 2       ' Divide by 4
  UNTIL Average < LastSample      ' Stop if this sample is lower than the last one.
 
  Peaks[i] = LastSample           ' Current sample is lower than last one, we've found the peak.
 
NEXT
 
For i = 0 to 7
  HSEROUT ["Peak number", DEC (i+1), ": ", DEC Peaks[i], " ADC counts", 13]
Next

/Henrik.