AC Voltage measurement using PIC16F877A microcontroller

AC voltage measurement using pic microcontroller and op-amp.You have came across many online tutorials  on various websites about voltage measurement using different microcontrollers. But all these tutorials are about measurement of low  DC voltage.In this project, you will learn how to measure high AC voltage using PIC16f877A micrcontroller.

In this tutorial, We will discuss ac voltage sensing with two method:

  1.  Using difference amplifier method
  2. Using potential transformer method

Alternating voltage measurement

To measure 220V AC, you need to step down this voltage. Because microcontrollers can’t measure voltage greater than 5V. If you give voltage more than 5V to the analog input of microcontroller, it will get damage permanently. To assure protection of microcontroller, you will need to step down 220 volt AC into AC  voltage whose peak value should be less than 5V. For example , 220V AV mean RMS voltage and its peak value is equal to 311 volt. similarly you have to step down high AC voltage of in such a way that its peak value should not be greater than 5 volt.

There are two methods to step down 220 alternating voltage into low alternating voltage which peak value should not be greater than 5 volt.

  • Potential Transformer ( All Electrical Engineering students must know about P.T and its use)
  • Difference amplifier  ( I will discuss difference amplifier method  in this project.)

Potential Transformer can also be used to step down 220 Alternation voltage.But why you want to spend more money? when you can do this with the help of cheap operational amplifiers and few resistors. Difference amplifier method is more economical than potential Transformer when you want to step down voltage less than 400 volt AC.

NOTE: Difference amplifier method is economical for voltage measurement less than 400 volt. Because above 400 volt, this method become expensive than potential Transformer. There are reasons behind it. I am not going to discuss reasons here.This method is suitable for final year students who want  to measure Alternating voltage and current.

Difference Amplifier circuit

Difference amplifier is used to amplify voltage from two voltage levels.In case of Alternating voltage we have two voltage level one is positive with respect to neutral and other is negative with respect to neutral. I will recommend you to Google about difference amplifier and its use.

you can adjust the gain of difference amplifier according to our requirement by selecting proper  values of resistors.In this project gain is equal to :

Gain=  R8/(R1+ R2+ R3)  ;

In Alternating voltage case second voltage level is zero. Because during positive cycle and negative cycle other side is considered zero or neutral. So output voltage will be

vout = gain * Vinput;

Difference amplifier to step down voltage

In Above picture, resistor R1, R2, R3 R4, and R5 have high values which do not allow high voltage to appear across op-amp. Because high input resistors are used that’s why micro ampere current will low and this way power loss will be in mili watts. According to difference amplifier gain formula our gain will be:

gain=   (22K)/( 1.2M + 1.2M + 2.2K) = 0.0091

NOTE:  you must make calculation according to peak value of sine wave. Because peak voltage is the maximum voltage input to micrcontroller analog pin.So with a .0091 gain, with respect to peak voltage of sine wave output voltage from op-amp is :

                                      Vout = .0091 * 311 = 2.8301 volt (peak output voltage)

As you see above figure we have connected other terminal of R7 to 5 volt instead of  ground as we do while using difference amplifier in many applications. R7 resistor is used to increase DC voltage level op-amp output. Sine wave have zero DC voltage level and  negative voltage cycle. Microcontroller can not read negative voltage.So we increase the DC level of sine wave by 5 volt.In this way negative voltage will not appear across  microntroller. Now output peak voltage from op-amp is 5 + 2.8301 = 7.8301 volt. But as I have mentioned , microcontrollers can not measure voltage greater than 5 volt.So as shown in above figure we have used voltage divider to divide voltage by 2.Hence output voltage is:

                                                            Vout = 7.8301/2 =  3.90155;

Capacitors C1, C2, and C3 are used to filter harmonics from input voltage and to provide protection to micrcontroller from harmonics.Now AN pin can be connected to microcontroller analog pin to measure voltage easily.

Video lecture on AC voltmeter design

To know about how to measure analog voltage using analog module of PIC16F877A microcontroller go through PIC microcontrollers tutorials..

PIC MICROCONTROLLERS TUTORIALS

COMPLETE CIRCUIT DIAGRAM 

To know about LCD interfacing with PIC micronctrollers, go through pic microcontrollers        tutorials

 PIC MICROCONTROLLERS TUTORIALS

LCD displaying voltage value..
LCD displaying voltage value..

Complete circuit diagram:

Alternating voltage measurement circuit diagram
Alternating voltage measurement circuit diagram

If you want to get complete code and circuit diagram comment on this  with your email address.

AC voltage measurement code

Code for this project is written using Mikro C.To download code for AC voltage measurement click on link below :  [sociallocker]

sbit LCD_RS at RB2_bit;
sbit LCD_EN at RB3_bit;
sbit LCD_D4 at RB4_bit;
sbit LCD_D5 at RB5_bit;
sbit LCD_D6 at RB6_bit;
sbit LCD_D7 at RB7_bit;
sbit LCD_RS_Direction at TRISB2_bit;
sbit LCD_EN_Direction at TRISB3_bit;
sbit LCD_D4_Direction at TRISB4_bit;
sbit LCD_D5_Direction at TRISB5_bit;
sbit LCD_D6_Direction at TRISB6_bit;
sbit LCD_D7_Direction at TRISB7_bit;
float v;
char txt[5];
char txt1[5];
void voltage_READ(void)
 {
 float max;
 int i;
 int t[40];
 ADCON0.ADON=1;
 for(i=0; i<=39; i++)
 {
 v= ADC_Read(0); //Digital value convert
 v =v*(10.0/1023.0);
 v=(v-5.0);
 t[i]=v*110.1909091;
 }

 ADCON0.ADON=0;
 max=t[0];
 for(i=0; i<=39; i++)
 {
 if(max<t[i])
 max=t[i];
 }
 max=max*.707106781;
 intToStr(max, txt);
 Lcd_out(1,9,txt);
 delay_ms(1000);
 }
 
void main()
{
 Lcd_Init(); // Initialize LCD
 ADCON0.ADCS1=1;
 ADCON0.ADCS1=0;
 ADCON0.ADON=0;
 
 while(1)
 {

 Lcd_out(1,1, "Voltage:");
 voltage_READ();
 }
}

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Second method to measure AC voltage

In that article I have discussed each and everything you need to know to make ac voltage measurement project. In that article, I have used operational amplifier as a difference amplifier to step down ac voltage level from 220 volt ac to less than 5 volt ac. But I have seen many people struggling with that method. So I have decided to write a article on how to measure ac voltage using potential transformer and pic microcontroller with digital lcd display.

How to measure ac voltage: 

Ac voltage can be measure with following methods:

  • AC voltage measurement using digital millimeter
  • AC voltage measurement using analog voltmeter
  • AC voltage measurement using microcontroller
  • AC voltage measurement using potential transformer and digital display (I will discuss this method in this tutorial)
  • AC voltage measurement using difference amplifier and pic microcontroller 

As I have already discussed in this project, I will be using potential transformer to step down 220volt ac voltage to less than 5 volt ac. I will discuss it later why we need to step down ac voltage to measure it with the help of pic microcontroller.

Main components of ac voltage measure project:

Followings are the main components of ac voltage measurement project. Brief descriptions of all components are also given below:

What is potential transformer (PT)

Potential transformer is a type of transformer which is used to step down ac voltage. It is used to measure ac voltage by stepping down AC voltage. For example in this project, potential transformer is used to step down 220volt ac voltage to 12 volt ac. Potential transformer secondary winding have less turn than primary winding’s. So according to below mentioned turns ratio formula, it step down ac voltage.

Ns/Np = Vs/Vp

What is bridge rectifier?

Bridge rectifier is electronics circuit used to convert ac voltage into pulsating dc voltage. In other words it converts, negative cycle of AC voltage into positive cycle. Now the question is why we need bridge rectifier in this project? Because microcontrollers can’t reads negative voltage.  Therefore we need to convert negative half cycle of AC voltage into positive cycle. Bridge rectifier is made using rectifier diodes connected in a form to form a bridge. 1N4007 rectifier diodes are used to make H Bridge.

Voltage divider circuit:

Voltage divider circuit as it name suggests is used to divide voltage. Two resistors are used to as voltage divider. Potential transformer step downs 220 volt AC in to 12 volt AC. After that bridge rectifier is used to convert 12 volt ac into pulsating dc.  But microcontroller cannot read voltage more than 5 volt. Therefore voltage divider circuit further divide the voltage in two parts and less than 5 volt appear across analog to digital converter pin of pic microcontroller. I will discuss later about analog to digital converter.

Liquid crystal display:

Liquid crystal display or LCD is used to used to display value of measured ac voltage. 16X2 LCD is used in this project.  LCD is interfaced with pic16f877a microcontroller. IF you don’t know how to interface LCD with PIC16F877A microcontroller, check following article:

LCD interfacing with pic16f877a microcontroller

PIC16F877A microcontroller:

PIC16F877A microcontroller is used in this project. PIC16F877A microcontroller is belongs to 16F family of pic microcontrollers. It have built in analog to digital converters module. Some of basic features of PIC16F877A microcontroller is given below:

For more information about pic16f877a microcontroller features and if you are new to microcontroller’s worlds, check following article.

Getting started with PIC16F877A microcontrollers

Circuit diagram of how to measure ac voltage using microcontroller

Circuit diagram of how to measure AC voltage project is given below. I have already explained all the components of this project above.

How to measure ac voltage using microcontroller
How to measure ac voltage using microcontroller

Input to circuit is 220 volt AC voltage. Potential transformer step downs 220 volt AC voltage in 12 volt AC. After that bridge rectifier converts step down AC into pulsating dc voltage. Voltage divider further divides the voltage into two parts. Voltage less than 5 volt appear across analog to digital converter pin of pic16f877a microcontroller. Microcontrollers are basically small micro computers which understand only digital values. Built in analog to digital converter module of pic16f877a microcontroller converts analog values of AC voltage into digital values. These digital values are used in processing of data with in microcontroller. Pieces of instructions written in the form of coding told microcontroller what to do. Microcontroller itself do not do anything. You tell him to do whatever you want him to perform by writing pieces of information called program.

Simulation result of how to measure ac voltage project:

Diagram below shows simlation results of ac voltage measurement project. LCD displays 220 volt AC which is measured with the help of microcontroller and necessary components connected with the microcontroller and potentioal transformer.

How to measure ac voltage using pic microcontroller
How to measure ac voltage using pic microcontroller

 List of components :

List of required componensts for how to measure ac voltage is given below:

Category,Reference,Value,Order Code
Capacitors,"C1",22pF,
Capacitors,"C2",22pF,
Resistor R1 = 30K , R2 = 10K, R3 = 10K;
Integrated Circuits,"U1",PIC16F877A,
Diodes,"D1",1N4007,
Diodes,"D2",1N4007,
Diodes,"D3",1N4007,
Diodes,"D4",1N4007,
Miscellaneous,"TR1",TRAN-2P2S PT,
Miscellaneous,"X1",CRYSTAL 8MHZ,

Program for how to measure AC voltage using PT

program given below is written using MIkro C compiler.

// LCD module connections
sbit LCD_RS at RB2_bit;
sbit LCD_EN at RB3_bit;
sbit LCD_D4 at RB4_bit;
sbit LCD_D5 at RB5_bit;
sbit LCD_D6 at RB6_bit;
sbit LCD_D7 at RB7_bit;

sbit LCD_RS_Direction at TRISB2_bit;
sbit LCD_EN_Direction at TRISB3_bit;
sbit LCD_D4_Direction at TRISB4_bit;
sbit LCD_D5_Direction at TRISB5_bit;
sbit LCD_D6_Direction at TRISB6_bit;
sbit LCD_D7_Direction at TRISB7_bit;
// End LCD module connections

float maxpoint = 0;
int i;
unsigned int temp=0;

char ch[5];

void main()
{

TRISA = 0XFF;// All input
TRISB0_bit = 1;//set as input
TRISB1_bit = 1;//set as input
ADC_Init();

// Initialize LCD configuration...
Lcd_Init();
Lcd_Cmd(_LCD_CLEAR); // Clear display
Lcd_Cmd(_LCD_CURSOR_OFF); // Cursor off

while(1)

{
Lcd_Out(1,1,"AC voltage");

for(i=0;i<500;i++)
{
if(temp = ADC_Read(0),temp>maxpoint)
{
maxpoint = temp;
}
}
maxpoint = ( maxpoint * 5 )/ (1023) ;
maxpoint = maxpoint * 4;
maxpoint = maxpoint + 1.4;
maxpoint = maxpoint * 18;
maxpoint = maxpoint * ( 1 / sqrt(2) );
intToStr(maxpoint, ch);
lcd_out(2,1, Ltrim(ch));
maxpoint = 0;
}// while
}// void mai

I have made necessary comments in code for your understanding.If yo still have any issue in understanding of code, let me know.If you have no issue after reading this article your comments are welcome. you can also check these PIC16F877A projects:

257 thoughts on “AC Voltage measurement using PIC16F877A microcontroller”

  1. hello , iam idreesmuhamed , in the fact , your project is very important because iam electric engineer
    , please send to me the code and iam be thankfull for you .

    Reply
  2. The information provided on your page here turns very useful for me and i thanks you for this.
    I have made the simulation but having a little problem with the code so if you send me the code then i am very grateful to you.
    I am an electrical engineering student in Delhi Technological University and the topic here on this page is similar to my minor topic so please help me and send the code as soon as possible.

    Reply
  3. hi! can you explain me how to find the formular “for” look of source code:

    v=v*(10.0/1023.0);
    v=(v-5);
    t[i]=v*110.1909091;

    thanks you so much!

    Reply
  4. Nice work! you have shown a easy way to interface and measure high voltage using microcontroller. Thank you. but I am having some doubts, after calculating current through resistors, it is 9.57×10^-5 so by calculating voltage drop across R1, so (9.57×10^-5) x(2.2M) is 219.34V it should be low isn’t it? please guide me.

    Reply
  5. Thank you for sharing with us! I have assembled this ckt on bread board, without interfacing it with PIC. So the output voltage should be 7V DC(without voltage dividing) isn’t it? but mine is getting 5V DC so what might be the problem? or its normal ?

    Reply
  6. Hi Bilal Malik

    I would like to ask is this circuit is also applicable to 110Vac. I was able to try your circuit in 220Vac and I was successful on it but when I try to 100Vac it shows different voltage readings. I appreciate if you reply on my inquiry.

    thanks
    frendy

    Reply
  7. Hi there please send me your code for this AC voltmeter and ammeter project. I am very much interested in this project .
    Thanks a million

    Reply
  8. I am very much interesting to do PIC mcu projects with mikroC compiler. Especially AC voltage measurement by PIC mcu.Kindly send me the complete circuit diagram and Source code for 16F 877A AC voltage measurement projects.

    Reply
  9. Sir,
    will you pls mail me code of pic16f877a for closed loop voltage regulation of a converter in MPLAB if possible
    Regards,
    Chitra

    Reply
  10. Hi Friends,
    Can you explain this step on the source code:

    v=v*(10.0/1023.0);
    v=(v-5);
    t[i]=v*110.1909091;

    please explain how to find 110.1909091 value
    Thank U

    Reply
  11. Thank u BILAL Malik friend ,

    How to change the source code to the measure 3phase voltage (0-600v )
    please tell friend……

    Reply
  12. Hi friend
    I am try to adjust the gain of difference amplifier to change R8 value change to 15KOHm
    gain =15K(1.2m+1.2m+2.2K)
    gain = .0062443

    source code
    v=v*(10.0/1023.0);
    v=(v-5);
    t[i]=v*160.1467

    input voltage 14V but display voltage 21V
    how to sl the err plz tell frd ……..

    Reply
  13. Dear Bilal,

    I’m having proplems with the circuit. When I plug in the mains , the fuse turns off.
    Have you any idea what the problem could be?

    Iro

    Reply
  14. sir
    we are using pic18 . how to provide input to pic18 from potential divider circuit. ? code is not clear please explain in detail. please reply to my email id.thank you……….

    Reply
    • this code is not for potential divider. you have to make little bit changes in code to use directly with voltage divider second method can be used

      Reply

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