Mini project Digital Volt Meter (DVM) using PIC16F877A with C code

DVM Project Overview

Digital Volt Meter is a Mini Project that I made as my project of the subject ‘Microprocessor Based Instrumentation System’. In this project I have used three major electronic components. They are PIC16F877A, LCD Display (16 X 2) and Low power Quad op-amp (LM324). PIC16F877A is used as an ADC module which converts the analog input into corresponding 10 bit digital output. It also provides enable and RS signals to the LCD display. LCD Display is used to display the converted digital binary data to decimal format so that user can easily understand the voltage. And finally Low power quad op-amp is used as buffer and as inverter. The DVM measures the voltages ranging from –50 V to +50 V

. But PIC can operate only up to +5 V. So to measure the +50 V, the voltage divider is used. This divider divides the input voltage 10 times so that +50V input voltage is now becomes +5V at the PIC input.  Inside PIC a program is written which multiplies the converted digital value by 10 before sending it to the LCD display. A screen capture of a rough design of the project in Proteus 7.0 Professional is given below.

PIC16F877A ADC Module

The A/D convertor module has eight inputs. The conversion of analog input results in a corresponding 10 bit digital output. The A/D module has four registers. They are

1. A/D Result High Register (ADRESH)
2. A/D Register Low Register (ADRESL)
3. A/D Control Register 0 (ADCON0)
4. A/D Control Register 1 (ADCON1)

The ADICON0 register controls the operation of the A/D module and the ADICON1 register configures the functions of the port pins.

The structure of ADICON0

ADCS1

ADCS0

CHS2

CHS1

CHS0

GO/DONE’

-

ADON

bits 7-6 : ADCS1:ADCS2 => Conversion channel select

bits 5-3: CHS2:CHS0 => Analog channel select [000 = Channel 1, 001 = Channel 2 and so on up to channel 7]

bit 2: GO/GONE’ => AD Conversion status bit [1 indicates conversion in progress and 0 indicates conversion not in progress]

bit1: Unimplemented

bit 0: ADON => A/D on bit [1 indicates converter module is power up and 0 indicates shut down]

The structure of ADICON1

ADFM

ADCS2

-

-

-

PCFG3

PCFG1

PCFG0

bit 7 : ADFM => A/D Result format [1 indicates Right Justified and 0 indicates Left Justified]

bit 6: ADCS2 => Conversion channel select

bits 5-4: Unimplemented

bits 3-0: A/D port configuration control bits

LDC Display (16 x 2)

Pin No.	Name	Funciton
1	Vss	Ground
2	Vdd	+Ve Supply
3	Vee	Contrast
4	RS	Register Select
5	R/W	Read/Write
6	E	Enable
7	D0	Data bit 0
8	D1	Data bit 1
9	D2	Data bit 2
10	D3	Data bit 3
11	D4	Data bit 4
12	D5	Data bit 5
13	D6	Data bit 6
14	D7	Data bit 7

C Source Code

#include <htc.h>
#define data PORTB
#define RS RD0
#define EN RD1

__CONFIG(HS & WDTDIS & PWRTEN & BORDIS & LVPDIS);

float valch0,valch1;

void delay_ms(int n )
{
    TMR1H=0xEC; 
 TMR1L=0x77;
 T1CKPS1=0;
 T1CKPS0=0;
 TMR1CS=0;
 TMR1IF=0;
 TMR1ON=1;
    while(n>0)
    {
  while(!TMR1IF);
  TMR1IF=0;
  TMR1H=0xEC; 
  TMR1L=0x77;
  n--;
 }
}

float select_adc(unsigned char chnl){    // init_adc(channel name);
    CHS2=CHS1=0;CHS0=chnl;
    delay_ms(10);
    ADON=1;
    ADGO=1;
    while(ADGO);
    return (((ADRESH*256+ADRESL)*5.0/1023)*10);
}




void LCD_Write(unsigned char values,int rs){
 data = values;
 RS = rs;    // rs=0 command and rs=1 data
 EN = 1;
 delay_ms(1);
 EN = 0;
}

void LCD_clear(void){
 LCD_Write(0x01,0);  //this clears LCD
}

void LCD_goto(unsigned char row,unsigned char column){
 if(row==1){
  LCD_Write(0x80+column,0);
 }
 else if(row==2){
  LCD_Write(0xC0+column,0);
 }
}

void LCD_num(int n){

  LCD_Write((n/100)+48,1);
  LCD_Write(((n%100)/10)+48,1);
  LCD_Write((n%10)+48,1);
}

void initLCD(void){

 TRISD=0x00;//as output
 TRISB = 0x00;
 delay_ms(100);


 LCD_Write(0x30, 0); //8 - bit display
 EN=1; EN = 0;
 LCD_Write(0x38,0);    //2 lines mode



 LCD_Write(0x0C,0);    //dispaly on , cursor blinking
 delay_ms(1);

 LCD_clear();LCD_goto(1,0);delay_ms(1);
 LCD_goto(1,7);
 LCD_Write('D',1);delay_ms(100);
 LCD_Write('V',1);delay_ms(100);
 LCD_Write('M',1);delay_ms(100);
 LCD_goto(2,12);
 LCD_Write('v',1);delay_ms(100);
 LCD_goto(2,7);
 LCD_Write('.',1);delay_ms(100);

}

void main(void){
    PCFG3=PCFG2=PCFG1=PCFG0=0;
 ADFM=1;
 ADCS1=1;
 ADCS0=0;
    TRISA=0xFF;
 initLCD();

    while(1){

        valch0=select_adc(0);
        valch1=select_adc(1);


        if(valch0 <= 0.00 && valch1!=0){
            valch0=valch1;
            LCD_goto(2,1);
            LCD_Write('-',1);
            delay_ms(5);
        }

        else{
            LCD_goto(2,1);
            LCD_Write('+',1);
            delay_ms(5);
        }


        LCD_goto(2,4);
        LCD_num(valch0);
        LCD_goto(2,8);
        LCD_num((valch0-(int)valch0)*1000);

    }
}