Microchip Technology MA160014 Data Sheet

DS41412F-page 326

 2010-2012 Microchip Technology Inc.

#include "p18cxxx.h"

#define COUNT 500                           //@ 8MHz = 125uS.

#define DELAY for(i=0;i<COUNT;i++)

#define RCAL .027                           //R value is 4200000 (4.2M) 

                                            //scaled so that result is in

                                            //1/100th of uA

#define ADSCALE 1023                        //for unsigned conversion 10 sig bits

#define ADREF 3.3                           //Vdd connected to A/D Vr+

int main(void)

{

    int i;

    int j = 0;                              //index for loop

    unsigned int Vread = 0;

    double VTot = 0;

    float Vavg=0, Vcal=0, CTMUISrc = 0;     //float values stored for calcs

//assume CTMU and A/D have been set up correctly

//see Example 25-1 for CTMU & A/D setup

setup();

CTMUCONHbits.CTMUEN = 1;                    //Enable the CTMU

CTMUCONLbits.EDG1STAT = 0;                  // Set Edge status bits to zero

CTMUCONLbits.EDG2STAT = 0;    

    for(j=0;j<10;j++)

    {

        CTMUCONHbits.IDISSEN = 1;           //drain charge on the circuit

        DELAY;                              //wait 125us

        CTMUCONHbits.IDISSEN = 0;           //end drain of circuit

      

        CTMUCONLbits.EDG1STAT = 1;          //Begin charging the circuit

                                            //using CTMU current source

        DELAY;                              //wait for 125us

        CTMUCONLbits.EDG1STAT = 0;          //Stop charging circuit

        

        PIR1bits.ADIF = 0;                  //make sure A/D Int not set

        ADCON0bits.GO=1;                    //and begin A/D conv.

        while(!PIR1bits.ADIF);              //Wait for A/D convert complete

              

        Vread = ADRES;                      //Get the value from the A/D

        PIR1bits.ADIF = 0;                  //Clear A/D Interrupt Flag

        VTot += Vread;                      //Add the reading to the total

    }

    

    Vavg = (float)(VTot/10.000);            //Average of 10 readings

    Vcal = (float)(Vavg/ADSCALE*ADREF);

    CTMUISrc = Vcal/RCAL;                   //CTMUISrc is in 1/100ths of uA

}