DIGITAL VOLTMETER USING 89C51 MICROCONTROLLER

Guide,Prof. S. A. Karmude

By,Saylee S. Joshi

INTRODUCTION• Voltmeter is a voltage measuring instrument. • We can measure the potential difference between any two

points in an electrical network using voltmeter. • There are two types of voltmeter as analog voltmeter and

digital voltmeter. • Analog voltmeter moves pointer on a scale but it has some

limitations like accuracy of few percent of full scale.• Digital voltmeter can display numerical value of voltage on a

display by use of analog to digital converter (ADC). • All the data processing and manipulating is in digital form, so

it is very essential to use ADC.

Cont….

• We have used ADC0804 analog-to-digital converter IC. The range of input voltage is 0-15V. Here the input voltage should be DC voltage so as to get the steady output on the LCD display.

• If you give the AC voltage as an input, it will display continuously running numbers as the nature of AC voltage.

Block Diagram

Components Required For Digital Voltmeter Using 89c51 Microcontroller• Microcontroller, AT89C51• Analog to Digital Converter, ADC0804‐ ‐• 16×1 LCD• Oscillator circuit for the microcontroller– 12MHz Crystal Capacitor– 33pF Capacitors

• Voltage divider circuit/ Input terminals– 200k, 100k Resistors– 100nF Capacitor

• ADC Clock Circuit 100k Potentiometer (to adjust the back light of the ‐ LCD)– 10k Resistor– 150pF Capacitor

• 100k Potentiometer (to adjust the back light of the LCD)‐

Circuit Diagram Of Digital Voltmeter Using 89c51 Microcontroller

Lcd Pin DiagramPin no. Name Description1 Vss Ground

2 Vdd +5V

3 Vee Contrast  Adjustment  ‐2V  to  ‐5V

4 RS Register  Select

5 RW 1  ‐Read  ,  0‐ Write

6 E Enable  Strobe

7 D0 Data  Line

8 D1 Data  Line

9 D2 Data  Line

10 D3 Data  Line

11 D4 Data  Line

12 D5 Data  Line

13 D6 Data  Line

14 D7 Data  Line

15 LED+ Backlit  LED  +V   Vdd  (Optional  signal)

16 LED‐ Backlit  LED  –V   Vss  (Optional  signal)

Components1. 8051 Based Controller: 12. ADC0804: 13. LCD 16x1: 14. Potentiometer 10K: 15. Resistor 10K: 26. Resistor 200K: 17. Resistor 100K: 18. Capacitor 33pF: 29. Capacitor 10uF: 110. Capacitor 150pF: 111. Capacitor 100nF: 112. Crystal 12Mhz: 1

C Program For Digital Voltmeter Using 89c51 Microcontroller#include <REGX51.H>#include "lcd.h"#define adc_port P1 //ADC Port#define rd P3_7 //Read signal P3.7#define wr P3_6 //Write signal P3.6#define cs P3_5 //Chip Select P3.5#define intr P3_4 //INTR signal P3.4void conv(); //Start of conversion

functionvoid read(); //Read ADC functionunsigned int adc_avg,adc;void main(){char i;

LCD_INI();while(1)

{ //Forever loop

adc_avg = 0;for(i=0;i<10;i++){conv(); //Start conversionread(); //Read ADCadc_avg += adc;}adc_avg = adc_avg/10;wrt_cmd(0x80);wrt_string("V(DC): ");adc = adc_avg * 59;hex2lcd((unsigned char)(adc/1000));

Cont….wrt_data('.');adc = adc%1000;hex2lcd((unsigned char)(adc/10));wrt_data('V');}}void conv(){cs = 0; //Make CS lowwr = 0; //Make WR lowwr = 1; //Make WR highcs = 1; //Make CS high

while(intr); //Wait for INTR to go low

}void read(){cs = 0; //Make CS lowrd = 0; //Make RD lowadc = adc_port; //Read ADC portrd = 1; //Make RD highcs = 1; //Make CS high}

Advantages

• This system is used to measure the voltage in low voltage applications.

• Used to measure the toy batteries.• We can measure the physical quantities like

temperature, humidity, gas etc. using this system with a little modification.

 disadvantages

• The input analog voltage range should be 0 to 5V.

• Using this system we can measure only one analog input value at a time.