Interrupt Service Routine (continued)

//------------------------------------------------
// do on last sample of a 60hz cycle ...
//------------------------------------------------
if (tick20Count >= 40)
{
//------------------------------------------------
// compute & save filtered Vp-p value
// lowpass filter Vp-p (average with prior average)
// in an int array for current breaker number
//
// expect inputs centered upon ~512
// 40 samples of 512 make an input metric of 20,480
// metric must be at least HALF this or assume
// there is no transducer board on this input
//------------------------------------------------
if (metric > 10000)
AdcValues[breakerNumber] = (AdcValues[breakerNumber] + max_sample - min_sample)/2;
else
AdcValues[breakerNumber] = 0;
//------------------------------------------------
// toggle a digital output at end of 60hz cycle pair
//------------------------------------------------
LATB0 ^= 1;

We already used tick20Count to determine if we’re in the 2nd 60Hz cycle for min/max determination.
Here, we’ll test tick20Count again … when it’s reached 40 we’re done with this measurement. Everything within this conditional branch is to be performed on a completed sample.

We accumulate A/D samples of an input in a variable named “metric”. If we’re selecting an interface address that doesn’t enable a physical interface module, then “metric” won’t have accumulated to an expected value of at least 20,480.
If we don’t see at least 10,000, then zero out the value.

Presuming “metric” is above minimum, AVERAGE the new measurement (max_sample – min_sample) with the prior AdcValue. Averaging is simply a low pass filter to smooth out measurement fluctuation.

LATB0 is toggled merely to observe the 60Hz interrupt service cycles on an unused PIC output for diagnostic purposes.