PIC16F688 based Digital Voltmeter

Actually this is the another version of my older DVM project that was based on PIC12F683. The older version displays the measured voltage on a LCD that is driven serially by PIC12F683 using 3 I/O pins. The new one uses PIC16F688 microcontroller that doesn't require the serial driver as it has got enough pins to drive a LCD directly in 4-bit mode. The theory and math is just the same. You can read my PIC12F683 version of this project here.

Circuit Diagram

Circuit on breadboard

Important: You need a regulated +5V supply for accuracy of the output. The ADC uses Vdd as the reference for conversion, and all computations are done with Vdd = 5V. You can get a regulated +5V using a LM7805 linear regulator IC.

 My source for a regulated +5V using LM7805

My variable power supply source for testing the DVM

Read the detail theory and math involved in this project here.

Software
Use mikroC compiler to compile this code. Use options Internal Clock @ 4 MHz, MCLR Enabled, and Power-Up Timer Enabled.

/*
  Digital Voltmeter based on PIC16F688
  Rajendra Bhatt, Oct 12, 2010
*/

// LCD module connections
sbit LCD_RS at RC4_bit;
sbit LCD_EN at RC5_bit;
sbit LCD_D4 at RC0_bit;
sbit LCD_D5 at RC1_bit;
sbit LCD_D6 at RC2_bit;
sbit LCD_D7 at RC3_bit;
sbit LCD_RS_Direction at TRISC4_bit;
sbit LCD_EN_Direction at TRISC5_bit;
sbit LCD_D4_Direction at TRISC0_bit;
sbit LCD_D5_Direction at TRISC1_bit;
sbit LCD_D6_Direction at TRISC2_bit;
sbit LCD_D7_Direction at TRISC3_bit;
// End LCD module connections

char Message1[] = "DVM Project";
unsigned int ADC_Value, DisplayVolt;
char *volt = "00.0";

void main() {
  ANSEL = 0b00000100; // RA2/AN2 is analog input
  ADCON0 = 0b00001000; // Analog channel select @ AN2
  ADCON1 = 0x00;
  CMCON0 = 0x07 ; // Disbale comparators
  TRISC = 0b00000000; // PORTC All Outputs
  TRISA = 0b00001100; // PORTA All Outputs, Except RA3 and RA2
  Lcd_Init();        // Initialize LCD
  Lcd_Cmd(_LCD_CLEAR);             // CLEAR display
  Lcd_Cmd(_LCD_CURSOR_OFF);        // Cursor off
  Lcd_Out(1,1,Message1);
  Lcd_Chr(2,10,'V');

do {

   ADC_Value = ADC_Read(2);
   DisplayVolt = ADC_Value * 2;
   volt[0] = DisplayVolt/1000 + 48;
   volt[1] = (DisplayVolt/100)%10 + 48;
   volt[3] = (DisplayVolt/10)%10 + 48;
   Lcd_Out(2,5,volt);
   delay_ms(100);
  } while(1);

 }


Output
The DVM has been tested with various input voltages ranging from 0-20 V and found to be very accurate. Here are some of the pictures of testing.