Digital voltmeter using pic microcontroller

In this project, a digital voltmeter using pic microcontroller is designed. Digital voltmeter using a pic can read the voltage from  0-40 volt. This voltmeter can read-only DC voltage. Digital AC voltmeter can also be designed using microcontrollers.

DC Voltmeter Introduction

Digital DC voltmeter is designed to measure DC voltage using the PIC16F877A microcontroller. A voltage divider circuit is used to divide voltage into two parts. To prevent more than 5 volts appearing across the pic microcontroller. Because the microcontroller can not read voltage more than 5 volts directly.

In this project, we used two types of displays namely 16×2 LCD and 4-digit seven-segment display. In the first first section, we will see how to display a value on LCD and in the second section, we will see how to display measured voltage value on a 4-digit seven-segment display.

DC voltmeter with LCD display

Liquid crystal display is interfaced with the microcontroller to display measured voltage value.  Built-in analog to digital converter of pic microcontroller is used to a measured analog voltage.

Recommended Reading

Before going further in this article about digital voltmeter using pic controller, you should know how to interface LCD with pic16f877A microcontroller and how to use analog to digital converter module of pic microcontroller. If you don’t know read the following articles first:

Digital Voltmeter with LCD display Circuit Diagram

Circuit diagram of digital voltmeter using pic microcontroller and 16×2 LCD is given below. A 40-volt battery is used as a voltage source whose voltage you want to measure. PIC16F877A microcontroller can not directly read 40 volts. The voltage divider circuit using a resistor is used to step down dc voltage appearing across analog to digital converter pin of PIC16F877A microcontroller.

Digital voltmeter using pic microcontroller

How to Measure Dc Voltage?

Resistor R1=18k and R2=2k are used as voltage dividers. According to voltage division formula, voltage less than 5 volts appears across pic microcontroller in the case of maximum input voltage 40 volts.

Vout = (R2 / R1+R2 ) * Vinput
Vout = ( 2 / 18+2) * 40 = 4 volt

Hence when we apply a maximum input voltage of 40 volts, only 4 volts appear across the pic microcontroller which is less than 5 volt. PIC16F877A microcontroller has seven analogs to digital converter channels. It means it can be interfaced with seven analog channels or it can measure seven analog quantities.

ADC Channel

In this project, AN0/RA0 channel of the pic16F877A microcontroller is used. ADC module of pic microcontroller converts an analog signal into binary numbers. PIC16F877A microcontroller has a 10 bit ADC. So it converts an analog signal to a 10-bit digital number which can be back converted into voltage using the following calculation in the programming of digital voltmeter.

Resolution = (Vrer+ - Vref-) / (1024 -1 ) ;

ADC resolution is an important concept to discuss here. Resolution means minimum value of the analog signal for which ADC counter increment by one. For example, pic16f877A microcontroller has 10-bit ADC and it counts binary from 0-1023 for every minimum analog value of the input signal. This minimum analog value is called resolution ADC increment by one. For example, pic16f877A microcontroller has 10-bit ADC and it counts binary from 0-1023 for every minimum analog value of the input signal. This minimum analog value is called resolution.

In this project, we are taking Verf+= 5 volts and Vref- = 0 volt. Hence by using these values in the above formula, this minimum voltage will be:

resolution = (5 - 0 )/ (1023) = 4.8876 mV;

It means for every analog signal of 4.87mV, ADC value increments by one.

Simulation Result

Liquid crystal display is used to display values of voltage. As shown in the figure below. The below diagram shows the result of the digital voltmeter using the pic microcontroller and LCD display.

pic16f877a Digital voltmeter with LCD display

Video lecture

Digital voltmeter Code MikroC

Now, let’s discuss how to write a program for digital dc voltmeter using a pic microcontroller. Above I have discussed the function of each component and its working in dc voltage measurement with pic microcontroller. The code for digital voltmeter is written using the MikroC Pro compiler. Voltage measured by the ADC module of PIC16F877A microcontroller can be calculated by following programming commands:

voltage = ADC_Read(0); // ADC channel zero stores value in variable voltage
voltage = (voltage * 5 * 10)/ (1024); // resolution factor and voltage divider factor

Statement one is used to reading ADC value and stores its value in variable “voltage” and in second statement voltage value is multiplied with resolution factor and voltage divider factor to convert it into actual input voltage value.

Digital Voltmeter Code with LCD Display

This code is written using MikroC for Pic compiler.  Create a new project with MikroC compiler by selecting PIC16F877A microcontroller and set frequency to 8MHz. If you don’t know how create new project in mikroC, we suggest you read this post:

sbit LCD_RS at RB4_bit;
sbit LCD_EN at RB5_bit;
sbit LCD_D4 at RB0_bit;
sbit LCD_D5 at RB1_bit;
sbit LCD_D6 at RB2_bit;
sbit LCD_D7 at RB3_bit;

sbit LCD_RS_Direction at TRISB4_bit;
sbit LCD_EN_Direction at TRISB5_bit;
sbit LCD_D4_Direction at TRISB0_bit;
sbit LCD_D5_Direction at TRISB1_bit;
sbit LCD_D6_Direction at TRISB2_bit;
sbit LCD_D7_Direction at TRISB3_bit;
int Adread;
float voltage;
char volt[4];
void main() {

PORTA = 0;
TRISA = 0X01;
PORTB = 0;
TRISB = 0;
LCD_Init();
ADC_Init();
LCD_Cmd(_LCD_CURSOR_OFF);
LCD_Cmd(_LCD_CLEAR);
LCD_Out(1, 1, "Digital voltmeter");
delay_ms(1000);
while (1)
{
voltage = ADC_Read(0);
voltage = (voltage * 5 * 10)/ (1024);
inttostr(voltage,volt); // it converts integer value into string
Lcd_Out(2,1,"Voltage = ");
Lcd_Out(2,11,Ltrim(volt));
Lcd_Out(2,13,"Volt");
}
}

Code Working

Now let’s understand the working of code. First, we used ‘sbit’ to define pins connection with LCD and PIC16F877A. These lines are used to define pic microcontroller pins that will be used with 16×2 LCD.

sbit LCD_RS at RB4_bit;
sbit LCD_EN at RB5_bit;
sbit LCD_D4 at RB0_bit;
sbit LCD_D5 at RB1_bit;
sbit LCD_D6 at RB2_bit;
sbit LCD_D7 at RB3_bit;

sbit LCD_RS_Direction at TRISB4_bit;
sbit LCD_EN_Direction at TRISB5_bit;
sbit LCD_D4_Direction at TRISB0_bit;
sbit LCD_D5_Direction at TRISB1_bit;
sbit LCD_D6_Direction at TRISB2_bit;
sbit LCD_D7_Direction at TRISB3_bit;

These code lines initialize built-in library of ADC module and liquid crystal dislpay.

LCD_Init(); // intialize LCD library
ADC_Init(); // initialize ADC library
LCD_Cmd(_LCD_CURSOR_OFF); // turn off LCD cursor
LCD_Cmd(_LCD_CLEAR); // Clear whatever is written on LCD
LCD_Out(1, 1, "Digital voltmeter"); // print "Digital voltmeter"on first line and first row
delay_ms(1000); // add a delay of one second

This code is placed inside the while(1) loop function and it keeps executing. Inside this loop, ADC_Read(0) reads analog input signal value from AN0/RA0 pins and store this value into a variable “voltage”. Second line converts measured digital value back into analog voltage by multiplying voltage variable with resolution factor and voltage divider scale down factor. After that we display voltage value on LCD second line.

Before printing value on LCD, we first convert integer variable “voltage” into string by using inttostr() routine.

voltage = ADC_Read(0);
voltage = (voltage * 5 * 10)/ (1024);
inttostr(voltage,volt);
Lcd_Out(2,1,"Voltage = ");
Lcd_Out(2,11,Ltrim(volt));
Lcd_Out(2,13,"Volt");

This digital voltmeter using a pic can read voltage only between 0-40 volt. High voltage measurement voltmeter can also be designed using pic microcontroller and difference amplifier. The difference amplifier will be used to step down dc voltage instead of a voltage divider.

37 thoughts on “Digital voltmeter using pic microcontroller”

  1. thank you for your e mails .the problem I can not downloading the code of these projects .I like the project of greenhouse control .can you sending the code of greenhouse .best regards

    Reply
  2. hey man. great job here im probably gonna do this type of work next year and your stuff provides great insight for me, so thx. and i would like to know what is that little component on your circuit diagram that is next to the LCD and is kind of red, it’s written 40% on it.Can you please tell me what it is and what is its purpose there. Thank you already man

    Reply
  3. Thank you very much Mr.Bilal

    I understood everything, it was very clear except one thing

    voltage = (voltage * 5 * 10)/ (1024); resolution factor and voltage divider factor

    I tried to build this circuit and code to measure voltage between 0 – 12 V , you used it to measure between 0 – 40 V

    I applied this circuit

    http://i0.wp.com/microcontrollerslab.com/wp-content/uploads/2015/05/Digital-voltmeter-using-pic-microcontroller2.jpg

    I changed the battery (40 V) to 12 V and R1 = 10K , R2 = 5K

    I tried also with ( 9 V ), R1 = 5K , R2 = 4K

    to make sure the input voltage to MCU is 4 V as you did,

    I know to make this circuit measure form 0 – 12V or 0 – 9V I have to change this code depending on the resistors I used

    voltage = (voltage * 5 * 10)/ (1024); resolution factor and voltage divider factor

    Could you please help me and explain this part of code, and which part do i need to change and why ? please Mr.Bilal I need your help.

    Reply
  4. Assalam o alaikum
    Sir
    Plz tell me that i have always volt = 0 ….what’s the problem
    I design the same circuit and code …
    Thanks alot

    Reply
  5. Hello again,

    I have make a test board with pic 16f877a and i am trying first to show on my LCD the message you have write at your code without success. There is no problem with my programmer as i have tested with another hex file and works properly. Could you please advise whats wrong? I am using all the options you have at your video and i have generated the hex file over the Micro C program (Micro C Pro).

    Your assistance is much appreciate.
    Best Regards,

    Reply
  6. Hello Bilal,
    First of all, thank you for your detailed explanation, it is really useful.
    I’m trying to measure voltage across 2 DC sources in series using a PIC microcontroller. I need seperate measurements for each source. Would you please help me in that matter by showing me schematics on how it would be done.
    I’d appreciate it if you can contact me on [email protected]
    Thanks,
    BM

    Reply
  7. hi,
    i got the output in the software using the program and circuit mentioned in this page but i m unable to get the output in the hardware.i m using an 18 v battery and trying to display its voltage value.please help

    Reply
  8. why always voltmeter is used from any point on the circuit and the ground? why not used from one point to another point? for example: measure resistor’s voltage in middle of circuit? NOT USE the ground of reference

    Reply
  9. Can you please send me the c code source file for this project. I’ve interfaced as you’ve given & written the same code also but it’s not running of mikro c software

    Reply

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