Digital voltmeter using pic microcontroller




In this project, digital voltmeter using pic microcontroller is designed. Digital voltmeter using pic can read voltage from  0-40 volt. This voltmeter can read only DC voltage. Digital AC voltmeter can also be designed using microcontrollers. Digital DC voltmeter is designed to measure DC voltage using PIC16F877A microcontroller. Voltage divider circuit is used to divide voltage into two parts. To prevent more than 5 volt appearing across pic microcontroller Because microcontroller can not read voltage more than 5 volt directly. 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 measured analog voltage.




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 following articles first:

Circuit diagram of digital voltmeter using pic microcontroller

circuit diagram of digital voltmeter using pic microcontroller is given below. 40 volt battery is used as q source whose voltage you want to measure. PIC16F877A microcontroller can not directly read 40 volt. Voltage divider circuit using 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 voltage with pic microcontroller

Resistor R1=18k and R2=2k is used as voltage divider. According to voltage division formula, voltage less than 5 volt appear across pic microcontroller in the case of maximum input voltage 40 volt.

 Vout = (R2 / R1+R2 ) * Vinput

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

Hence at maximum input voltage of 40 volt, only 4 volt appear across pic microcontroller which is less than 5 volt. PIC16F877A microcontroller has seven analog to digital converter channels. It’s means it can be interfaced with seven analog channels or it can measure seven analog quantities. In this project AN0 channel of pic16F877A microcontroller is used. ADC module of pic microcontroller converts analog signal into binary numbers. PIC16F877A microcontroller have 10 bit ADC. So it converts analog signal to 10 bit digital number which can be back converted into voltage using following calculation in programming of digital voltmeter. resolution is important to discuss here. resolution means value for which ADC increment by one. For example pic16f877A microcontroller have 10-bit ADC and it counts binary from 0-1023 for every minimum analog value of input signal. This minimum analog value is called resolution.ADC increment by one. For example pic16f877A microcontroller have 10-bit ADC and it counts binary from 0-1023 for every minimum analog value of input signal. This minimum analog value is called resolution.

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

In this project we are taking Verf+= 5 volt and Vref- = 0 volt . Hence by using these values in above formula:

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

It means for every analog signal of 4.87mV, ADC value increments by one. Liquid crystal display is used to display values of voltage. As shown in figure below. Below diagram shows the result of digital voltmeter using pic microcontroller and LCD display.

pic16f877a Digital voltmeter with LCD display

Video lecture

Digital voltmeter using pic program

Now lets discuss how to write program for digital dc voltmeter using pic microcontroller. Above I have discussed function of each components and its working in dc voltage measurement with pic microcontroller. Code for digital voltmeter is written using Mikro C  pro compiler. voltage measured by 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 read 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 input voltage value.

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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”);
}
}

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

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34 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

  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

  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.

  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

  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,

  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

  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

  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

  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

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