'+--------------------------------------------------------------+
'|                     RMS convertor for MX170                  |
'+--------------------------------------------------------------+
' The RMS value of a signal is the R(oot)M(ean)S(quare) value.
' It is calculated by adding up the squares of the input signal
' The mean of these squares is rooted. This process is explained
' in the steps below.
' This example uses the ADC in the PIC32MX170 to measure the
' AC input signal. Output is displayed at a 16x2 LCD.

'----------------------  Defines -------------------------------
ADCpin = 23         ' ADC input pin
Total = 800         ' array size for measuring 220mSec @ 48MHz
Offset = 1.650      ' numeric offset at 3.300V
CalValue = 24.85    ' gain factor attenuator and AC coupling @ 50Hz

Option explicit
'------------------------- Dim Variables --------------------
Dim Sample!(Total)
Dim SumSQ!, Value!
Dim i%,j%,a%

'---------------------- Initialize hardware -------------------
SetPin ADCpin, AIN  ' initialize ADC
CPU 48              ' maximum speed for the MX170

'LCD
LCD init 4,5,6,7,2,26
LCD 1,1,"Samples =       "
LCD 2,1,"RMS =          V"


'--------------------------- Measuring ----------------------

Do
  'sample input signal
  For i%=1 To Total
    Sample(i%)=Pin(ADCpin)-Offset
  Next i%

  'find zero crossings
  i%=0:j%=Total-1
  'first zero crossing in array
  Do
    i%=i%+1
  Loop Until(Sample(i%)>0 And Sample(i%+1)<0)

  'last zero crossing in array
  Do
    j%=j%-1
  Loop Until (Sample(j%)>0 And Sample(j%+1)<0)

  'calculate SQUARES
  SumSQ!=0
  For a%=i% To j%
    SumSQ! = SumSQ! + (Sample!(a%)*Sample!(a%))
  Next a%

  'calculate MEAN
  SumSQ! = SumSQ!/(j%-i%)

  'calculate ROOT
  Value! = Sqr(SumSQ!)

  'display values on 16x2 LCD
  LCD 1,11,Str$(j%-i%)
  LCD 2,7,Left$(Str$(Value!*CalValue!),5)

Loop