Digital Voltmeter project Using Microcontroller

Digital Voltmeter measure voltage between two point in circuit . Now we are going to make a digital voltmeter which can measure 50 volt maximum . We will use pic18f2550 microcontroller and it's ADC pin . Remember that an ADC channel of pic18f2550 can count from 0 to 1023 . Because it's ADC channel register is 10bits. As we like to  measure 50 volt , we need to apply a simple technique . So we have to convert 50 volt to 5 volt  and we get reading 1023 at adc channel  for 50 volt .

For converting we will connect 68k ohm, 22k ohm and 10k ohm resistors in serial so that during applying 50 volt it makes 5 volt drop at 10k ohm resistor . It's the main theme .

ADC(Analog to Digital Converter ) :

We need a basic knowledge about ADC . Let's  take a look at here :

ADCON1 Register

Basically ADC is like as voltage divider . According to voltage It produce output .

bit 5 : VCFG0: Voltage Reference Configuration bit (VREF- source)
1 = VREF- (AN2)
0 = VSS or 0 volt

bit 4 :VCFG0: Voltage Reference Configuration bit (VREF+ source)
1 = VREF+ (AN3)
0 = VDD or 5volt

We will set  VCFG0[bit 5]=0and VCFG0[bit4]=0 . So we will get highest value 5volt[1023] and lowest value 0volt[0].The ADCON1 is a 10 bit register that means  2 to the power 10  is it's highest counting capacity and result is 1024 . So this register can count from 0 to 1023 . When 0 volt , we get reading at RA0 pin  0 .When 5 volt , we get reading at RA0 pin 1023. It means 5volt equivalent to 1023 .

 If  1023 reading value    equal   to 50 volt.
So 1      reading value    equal   to  50/1023 volt
So 'read_val'  reading  value   equal  to (50/1023)*read_val .

 Source Code :

sbit LCD_RS at LATB7_bit;
sbit LCD_EN at LATB6_bit;
sbit LCD_D4 at LATB5_bit;
sbit LCD_D5 at LATB4_bit;
sbit LCD_D6 at LATB3_bit;
sbit LCD_D7 at LATB2_bit;

sbit LCD_RS_Direction at TRISB7_bit;
sbit LCD_EN_Direction at TRISB6_bit;
sbit LCD_D4_Direction at TRISB5_bit;
sbit LCD_D5_Direction at TRISB4_bit;
sbit LCD_D6_Direction at TRISB3_bit;
sbit LCD_D7_Direction at TRISB2_bit;
      char volt[]="        ";
        char mv[]="v";
void main() {
 double source=0;
 float calv=0;
 float sum=0;
 float mult=0;
  ADCON1=0x0E;                 // Configure RA) pin as input
  CMCON=7;
  ADC_Init();                        // Initialize ADC
  Lcd_Init();                        // Initialize LCD
  Lcd_Cmd(_LCD_CLEAR);               // Clear display
  Lcd_Cmd(_LCD_CURSOR_OFF);
  Lcd_Out(2,15,mv);
 while(1){
  source=ADC_Read(0);
  calv=(source*50.50)/1023;
  floattostr(calv,volt);
  Lcd_Out(1,1,"Volt Meter");
   Lcd_Out(2,1,"V=");
   Lcd_Out(2,4,volt);
 }
} 

Circuit :

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