AC Voltage measurement using PIC16F877A microcontroller

In this tutorial, we will learn to measure AC voltage using a pic microcontroller with two methods. One is using a potential transformer and the second one is using an op-amp as a difference amplifier. That means, in the first method, we will use a voltage transformer to step down 220V AC and in the second method, we will use an operational amplifier as a difference amplifier to step down high AC voltage. But for both methods, we will use pic microcontroller ADC to take AC voltage samples. For this tutorial, we will use the PIC16F877A microcontroller. However, the logic used in this tutorial can be used with other microcontrollers such as 8051, AVR, Arduino, Raspberry Pi, Beaglebone, etc.

You have come 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 methods:

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

Alternating Voltage Measurement using Difference Amplifier Method and Pic Microcontroller

To measure 220V AC, it is necessary to step down the voltage as microcontrollers are unable to measure voltages greater than 5V. Applying a voltage higher than 5V to the analog input of a microcontroller can result in permanent damage. Thus, in order to protect the microcontroller, it is crucial to step down the 220V AC voltage to an AC voltage with a peak value lower than 5V. For instance, 220V AC represents the RMS voltage, with a corresponding peak value of 311 volts. Therefore, it is essential to reduce the high AC voltage to a level where its peak value does not exceed 5 volts.

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

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

The Potential Transformer is capable of stepping down 220 Alternating current voltage. However, why would you want to spend more money when you can achieve this using inexpensive operational amplifiers and just a few resistors? The difference amplifier method proves to be more economical than using a Potential Transformer when stepping down voltages below 400 volts 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

The difference amplifier is a circuit used to amplify voltage between two different voltage levels. When dealing with alternating voltage, there are two distinct voltage levels: one is positive relative to neutral, and the other is negative relative to neutral. For more detailed information on the difference amplifier and its applications, I would suggest conducting a search on Google.

You can adjust the gain of the difference amplifier according to your requirements by selecting the proper values of resistors. In this project, the gain is equal to:

Gain=  R8/(R1+ R2+ R3)  ;

In the case of alternating voltage, the second voltage level is zero. This is because during the positive and negative cycles, the other side is considered to be zero or neutral. As a result, the output voltage will be zero during these cycles.

vout = gain * Vinput;

Difference amplifier to step down voltage

In the above picture, resistors R1, R2, R3, R4, and R5 have high values, which prevent high voltage from appearing across the op-amp. The use of high input resistors ensures that the current is in the microampere range, resulting in low power loss in the milliwatt range. According to the difference amplifier gain formula, the gain can be calculated as follows:

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

NOTE: Please make sure to calculate the peak value of the sine wave, as the peak voltage is the maximum voltage input to the microcontroller’s analog pin. Therefore, with a gain of 0.0091 in respect to the peak voltage of the sine wave, the output voltage from the op-amp is:

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

In the figure above, we can observe that the other terminal of R7 is connected to the 5-volt supply instead of the ground, which is typically done when using a differential amplifier in various applications. The purpose of the R7 resistor is to raise the DC voltage level at the output of the op-amp. Since a sine wave has a zero DC voltage level and negative voltage cycle, it becomes important to increase the DC level of the sine wave by 5 volts. By doing so, we prevent any negative voltage from appearing across the microcontroller. Consequently, the output peak voltage from the op-amp becomes 5 volts plus 2.8301 volts, resulting in a total of 7.8301 volts. However, it is important to note that microcontrollers are unable to measure voltages greater than 5 volts. To address this, as illustrated in the figure above, a voltage divider is employed to divide the output voltage by 2. This ensures that the output voltage level is within the microcontroller’s measurement range.

                                                            Vout = 7.8301/2 =  3.90155;

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

Video lecture on AC voltmeter design

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

Circuit Diagram

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

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

Complete circuit diagram:

Alternating voltage measurement circuit diagram
Alternating voltage measurement circuit diagram

AC Voltage Measurement Code Pic Microcontroller

Code for this project is written using MikroC. To download code for AC voltage measurement click on the link below:

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();
 }
}

AC Voltage Measurement using PT and Pic Microcontroller

In this section, we will see how to measure AC voltage using a potential transformer and Pic Microcontroller. In the last section, we have seen how to use an operational amplifier as a difference amplifier to step down AC voltage level from 220 volts AC to less than 5 volts AC. Here, we will delve further into the process of measuring AC voltage with the help of a potential transformer and a Pic Microcontroller. Understanding the intricacies and the practical applications of this setup is essential for accurate voltage measurements. By following the steps mentioned in the previous section, we can ensure that the AC voltage is accurately measured with the help of the potential transformer and Pic Microcontroller.

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.

Components required

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

What is a potential transformer (PT)?

A potential transformer, also known as a voltage transformer, is a specific type of transformer that is used to decrease or “step down” the magnitude of AC voltage. Its primary purpose is to measure high voltage levels by transforming them into lower, more manageable values.

In this project, the potential transformer plays a crucial role in reducing the voltage from 220 volts AC to 12 volts AC. By utilizing a carefully calculated turns ratio, the secondary winding of the potential transformer consists of fewer turns than its primary winding, resulting in a significant decrease in voltage.

The turning ratio formula serves as a fundamental guideline for determining the appropriate number of winding turns, allowing the potential transformer to effectively step down the alternating current voltage and facilitate safe and accurate voltage measurement.

Ns/Np = Vs/Vp

What is bridge rectifier?

The bridge rectifier is an electronic circuit used to convert AC voltage into pulsating DC voltage. Essentially, it transforms the negative cycle of AC voltage into a positive cycle. So why do we need a bridge rectifier in this project? It’s because microcontrollers are unable to read negative voltage. Consequently, we must convert the negative half cycle of AC voltage into a positive cycle. The bridge rectifier is constructed by connecting rectifier diodes in a specific arrangement to form a bridge. For this purpose, we employ 1N4007 rectifier diodes to create an H Bridge.

Voltage Divider Circuit

The voltage divider circuit, as the name suggests, is used to divide voltage. It employs two resistors to achieve this. In this setup, a potential transformer steps down the 220V AC voltage to 12V AC. To convert the 12V AC into pulsating DC, a bridge rectifier is used. However, it is important to note that microcontrollers can only read voltages up to 5V. Therefore, the voltage divider circuit further divides the voltage into two parts, ensuring that less than 5V appears across the analog-to-digital converter pin of the PIC microcontroller. We will discuss the analog-to-digital converter in more detail later.

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:

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

The circuit diagram for measuring AC voltage is presented below. In this section, we have discussed all the components of this project.

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

The input to the circuit is a 220-volt AC voltage. A potential transformer is used to step down the voltage from 220 volts AC to 12 volts AC. After that, a bridge rectifier converts the stepped-down AC voltage into pulsating DC voltage. A voltage divider is then used to further divide the voltage into two parts.

The voltage of less than 5 volts appears across the analog-to-digital converter pin of the PIC16F877A microcontroller. Microcontrollers are essentially small microcomputers that only understand digital values. The built-in analog-to-digital converter module of the PIC16F877A microcontroller converts the analog values of the AC voltage into digital values. These digital values are then used in processing the data within the microcontroller.

Instructions written in the form of code instruct the microcontroller on what to do. The microcontroller itself does not perform any tasks on its own. You need to provide it with instructions by writing a program that outlines what you want it to do.

Proteus Simulation

The diagram below shows the simulation results of an AC voltage measurement project. The LCD displays a reading of 220 volts AC, which is measured using a microcontroller and the necessary components connected to it, including a potential transformer.

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

Code AC voltage Measurment using PT

The program given below is written using MikroC 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

These lines define the connections of the LCD module to the microcontroller’s pins. sbit stands for “single bit” and is used to specify the pin connections for the LCD control and data lines.

// 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;

These lines define the direction of the LCD pins. TRISBx_bit are used to configure the corresponding pins as input (1) or output (0). These lines specify that RB2 (LCD_RS), RB3 (LCD_EN), RB4 (LCD_D4), RB5 (LCD_D5), RB6 (LCD_D6), and RB7 (LCD_D7) are configured as outputs, so they will be used to control the LCD.

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;

These lines declare some variables used in the main function. maxpoint is a floating-point variable to store the maximum voltage value measured. i is an integer variable used as a loop counter. temp is an unsigned integer variable used to store the ADC reading. ch is an array of characters used to store the string representation of the voltage value.

float maxpoint = 0;
int i;
unsigned int temp = 0;
char ch[5];

In the main function, after initializing the LCD, it enters an infinite loop (while(1)). The loop does the following:

  • Displays “AC voltage” on the first line of the LCD using Lcd_Out.
  • It then starts a for loop that runs 500 times (from i = 0 to i < 500).
  • Inside the loop, it reads an analog voltage value from channel 0 of the ADC using ADC_Read(0) and stores it in the variable temp.
  • It then compares temp with the current maxpoint value, and if temp is greater, it updates maxpoint with the new value. This is done to find the maximum voltage value among the 500 readings.
  • After the loop, it processes the maxpoint value to convert it into an AC voltage value. The exact formula used for conversion is defined above.
  • The converted voltage value is then converted into a string using intToStr and stored in the ch array.
  • The voltage value is displayed on the second line of the LCD using lcd_out.

In summary, in this tutorial, we have learned how to measure AC voltage using two different methods and a PIC microcontroller.

You may also like to read:

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277 thoughts on “AC Voltage measurement using PIC16F877A microcontroller”

  4. 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

  6. 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

  11. 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

  17. 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

  18. 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

  20. 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

  30. 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

  31. 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

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

    Reply

  51. 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

  52. Thank u BILAL Malik friend ,

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

    Reply

  53. 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

  55. 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

  62. 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

  86. Hai,
    For the first method using difference amplifier, what is the wattage for resistor R1,R2,R3 and R4? Is it 10w,5w or 1/4w ?

    Reply

    • Thanks for the codes… I juts tried building the codes it’s having a lil problem .please kindly check the line code:

      ADC_Init();

      There is were I got stuck when trying to build my codes and running it..

      Please check and get back to me ..
      Thanks

      Reply

      • This code will work with Mikro C for PIC only and make sure to include adc library from the library manager

        Reply

  110. You could just use a voltage divider down to below 5V and use the PIC ADC at a 10Ksamples/s or some appropriate sample rate. This way you can do more than just get voltage……can calculate peak to peak, RMS, noise, etc…
    However, certain applications have regulatory requirements to isolate 220V, such as using a transformer (or optical)….for safety reasons….i.e. A voltage divider might not be enough.

    Reply

  113. I have a question.
    Why you not use bridge diode & divider voltage as beginning without potential transformer. We use another resistor values transforming 220V to less than 5V?

    Reply

  115. Hi
    while simulate , output always remain constant as 5 v
    even when i change ac source voltage o/p still 5 v
    or will it works by practical
    help

    Reply

  119. Thanks for an informative lesson. I have a few questions. First, many people talk about the dangers of this kind of circuit not being isolated. Is this safe as long as the circuit is correctly implemented? If people are worried about AC voltage being connected to the CPU by a stray wire, then clearly this could happen to any design, even an optoisolated one.

    Second, why the capacitor C3? What is that doing? It looks like just noise stabilization?

    Reply

  123. Hello,
    this is great contribution.
    I want to use ur idea in geophysics.
    After injecting a current from 220v ac modified sine wave with two electrode inserted in the earth, i will record the potential difference in another two electrodes that does not have any direct connection to the source electrodes.
    so my questions are
    1. can i use rectifier before/after the opamp to get positive voltage in micro-controller(i am using arduino uno).
    2. can i replace the opamp with 741 ic
    3. what do you suggest me to remove those noises(self potential of the earth) coming from the earth that does not have the same form from our modified sine wave. I saw some use synchronous rectifier tapping from the source as a reference signal.

    Reply

  125. anyone can explain the above mention code for voltage read?
    why we multiply the ADC_read(0) value with 10/1023 and after this take minus 5 from it?
    also tell me why we multiply it with 110.19 ?

    thank you

    Reply

  131. Hi, may I ask why is the input voltage for LM258 12v? Can I give it as 5V? Because If it is 12v, I have go put in an another DC source for this, which make it not really convinient compare to the project with transformers.

    Reply

  134. great job sir, i found your article here so intriguing and i am iterested. i will be very grateful if you send me the complete work with code for the AC voltmeter in my email @ kingsoftng@gmail.com. thank you sir! i am Kingsley, a computer engineering student from Nigeria.

    Reply

  139. 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.
    What are those reasons..?

    Reply

  142. hi bilal i have no experience in c language but there is something i’d like to explain me .
    i have a project of building an automatic voltage regulator in assembly language.

    your post on ac voltage measurment using difference amplifier surpases my mind .

    at the output of the op amp we should get an alternating voltage .so how can a pic read an altenative voltage ???
    what should be the value of the input voltage? that should be written in the assembly program for comparison ???
    what’s the value obtained after conversion in a 8bit pic ADC??? of 100v,140,180,200,220,240?

    Reply

  145. hi how can a pic measure with accuracy the Ac voltage that comes from the op amp?
    can you also explain it with some formulas??
    in addition to that may you explain also
    v =v*(10.0/1023.0); why 10????
    v=(v-5.0); how v-5.0?????
    t[i]=v*110.1909091;

    Reply

    • v =v*(10.0/1023.0); why 10???? because of the voltage divider -> v =2*v*(5/1023.0)
      v=(v-5.0); how v-5.0????? Remove offset
      t[i]=v*110.1909091; Inverse Differential gain

      Regards

      Reply

      • @José Miguel

        v =v*(10.0/1023.0); why 10???? because of the voltage divider -> v =2*v*(5/1023.0)
        v=(v-5.0); how v-5.0????? Remove offset
        t[i]=v*110.1909091; Inverse Differential gain

        That does not add up,
        v =v*(10.0/1023.0); why 10???? because of the voltage divider -> v
        no way the maximum output from the ac setup can only amount to 3.915V given that the voltage divider halfs the output of the 7.831,
        it doesn’t make sense why you would equate it to 10!!!!

        t[i]=v*110.1909091; Inverse Differential gain ??? How is it calculated or the values just landed here from no where?

        Reply

    • Late reply but i hope this will help someone someday.

      1. Why He used 10. Originally, the resolution should be 5000mV/1023 (5V/1023) but because the negative half cycle was previously ignored since PIC cannot measure negative voltages, to compensate for that, you multiply by 2. i.e from +5v to 0V to -5V for normal sinusoidal signal. Note the 5000mV is actually the 5V supply to PIC. It has been used because the ADC module is using the supply voltage to the PIC as its reference voltage (Vref).

      2. About the V-5 ==>> Recall the DC level of the Stepped down signal was raised by 5V to eliminate negative voltages to the PIC Pin. Since the negative part of the cycle has now been adequately compensated in V = V * (5.0*2/1023.0), it is necessary to subtracted the added DC level raising voltage which is 5V. Thus, V-5.

      3. On t[i] = V * 110.1909091; I believe he used the already stated formula
      Vout = gain * Vin
      Since we now want to measure Vin,
      Vi = V/gain
      which is same as
      Vi = V * (1/gain)

      1/gain = 1/0.0091 = 109.190909143.
      Thus,
      Vi = V * 109.190909143.
      Can’t tell why he used 110.1909091 instead.
      Note, t is a variable (placeholder for Vi) and it is logging 40 different Vi levels (i.e. from 0 to 39) with respect to i that will make for better measurement accuracy and precision…
      Hence,
      t[i] = V * 109.1909091

      Thank you!

      Reply

  147. Hi Bilal,

    I read this article long time back, but didn’t got chance to used it.
    Now for one of my project I decided to use above explained circuit.
    I noticed one strange behaviour of above circuit which I am not able to understand fully.

    Circuit gives exact calculated gain, when R1 is connected to neutral of grid & live wire to R4.
    But moment we inter change the input connection gain of circuit comes totally different then previous case. Simulation does not show any behaviour like this.
    did you observe anything like this ???

    Reply

  150. Is a difference amplifier the same thing as a differential amplifier or are you referring to a method of measurement with an op amp? This was unclear to me.

    Thanks,

    Jay

    Reply

  152. Hello, I have a query. In the difference amplifier, I am giving the Amplitude of 311V (for 220v) but the LCD is showing 220v (No Fault) and for for the amplitude of 340V (240V), the LCD is showing 240v (No Fault).
    Then I realized that the circuit trips (Shows fault) when the voltage reaches to 260V in the LCD.
    I want to change this part. Can you please point out that which part of this code is needed to change?
    Your project is really awesome, but if you help me a little, it will be very much appreciable.
    Thanks in advance 🙂

    Reply

  154. Hi Mr. Bilal Malik. actually im interested to the “Alternating voltage measurement circuit diagram(with complete code)”.Which is it can measure 240Vac and current flow. So how can i get the code and circuit? if need pay or anything. Please reply me on nasaiieng@gmail.com. Thank You Mr Bilal Malik

    Reply

  155. Hello. Thank you very much for your helpfull ac measurement circuit.
    I built it in an pcb and make my own program. It work fine, but i am having a problem with the linearity.
    I adjust the voltage for 120V and it look fine, but when the voltage is low than 60V, the voltage measured is more or less 4 to 5V different. When the voltage is 180V, the measurement is more or less 10V Different.

    What could be the problem.?

    Reply

  156. And the divider voltage was not considered in the calculations….

    v= ADC_Read(0);
    v =v*(10.0/1023.0);
    …………
    v = v*2; -> divider voltage was not considered
    …………
    v=(v-5.0);
    t[i]=v*110.1909091;

    Reply

  159. Hi,
    why you are running for loop for only 39 times and where you are using t[40] value, it is confusing me,
    i am also not able to change the value of power supply to amplifier and to R11 resistor, it is by default Vcc, does that make any difference- dont know how to make 12v or 5v.

    How i can measure voltage being supplied by AC voltage source.

    Awaiting response

    Reply

  161. Hello dear,
    thank you for this teach, I create this circuit but I have 2.5 volt in op-amp output(after R9), so I measurement input voltage, after R1,R4 I have 98.5V AC, after R2,R5 I have ~0.3 VAC and after R3,R6 I have ~0 VAC, so when I remove input 220 volt Output not change!!!
    Can you help me for knowing where is my mistake???
    thanks a lot.

    Reply

    • Hello,
      I use LM358, and couldn’t give a normal output, so when I remove the Op-Amp. I can see 3.01 VAC after 2.2K resistors. but when op-amp is in circuit output voltage is 0!!!!

      Reply

  169. pic 16f877a controllers adc can measures dc pulsating voltage or not…… if not how can i convert into steady dc… (i.e my input 2.5vdc pulsating voltage am required same voltage in steady dc voltage)….pls help me….

    Reply

  172. Nice tutorial. I want to ask concerning the linearity of the circuit. Has anyone built it in real life? Is the linearity recommendable? I just ask because I tried it on proteus, and I didn’t get very impressive results, so I am curious if anyone has actually built it.
    Thanks.

    Reply

  175. please i need the complete code for the AC voltmeter so i can design the setup as you have already done. Thank you sir

    Reply

  176. I see that you have used Separate 5v source for incresing dc level and powering pic. What can you suggest if you want to achieve same just by using AC input . Could you Explain that

    Reply

  180. Firstly thank you sir for ur support.
    I did as u instructed but at output of my LCD it was giving me 388v please what is d solution sir.

    Reply

  181. Hi, I am looking for low cost ac voltage sensing circuit. would you pls email me the method using difference amplifier??

    Reply

  183. Good day sir, I am Okoye Franklin from Enugu Nigeria, I what to no if I can get this project from you, How to Read AC voltage with comparator, Am using PIC16f886 MikroC.

    Reply

    • Just use the code, and change the registers to match with the ic u are using. I did the project using pic16f886, and it works quite well. Nice tutorial. I learnt a lot.

      Reply

  186. Differential amplifier still needs a ground reference through a resistor or a voltage divider in your case if want to DC bias the output. Without this the output will get saturated due to supply limitation and voltage difference b.w the inputs. This will probably never give you a true representation of 50hz sine wave on the output.

    Reply

  193. i need to measure 220v ac using pic16f676 without comparator please send me the whole code and the schematic circuit
    thank you

    Reply

  197. hey! this code helped me very well so far. it will help more if you can tell me how you calculated the multiplication and addition factors(values)……..thanks

    Reply

  199. Will you be able to do a tutorial to measure wide range of AC input not just 220VAC. I would say from 85VAC to 264VAC. That will be helpful.

    Thank You

    Reply

  207. Hi… Thanks for your circuited but … It can be so useful if you calculate the accuracy of this circuit by considering tolerance of resistors… I do that and Its too bad.
    Assume : v in peak = 300v , tolerance = +%5 , u Controller ADC = 10 bits , v ref = 3.3v
    gain = 0.00915827
    v out real = 2.74788 => v out adc = 2.748 => v in (calculated by u controller) = 301 v

    Assume : v in peak = 300v , tolerance R8 = +%5 , , tolerance R1 , R2 and R3 = +%5 ,u Controller ADC = 10 bits , v ref = 3.3v
    gain = 0.0101223
    v out real = 3.03669 => v out adc = 3.036 => v in (calculated by u controller)= 333.62

    ——————————————————————————————————————–

    Reply

    • Well, it depends on how many samples you take and then average them out. Also, using a correction factor always serves the purpose for low costs designs like this.

      Reply

  210. Explain this code more to me:
    maxpoint = ( maxpoint * 5 )/ (1023) ;
    maxpoint = maxpoint * 4;
    maxpoint = maxpoint + 1.4;
    maxpoint = maxpoint * 18;
    maxpoint = maxpoint * ( 1 / sqrt(2) );
    Thank so much

    Reply

  213. Hello thanks for your code on ac measurement. i understand the code and circuit but i dont understand why the array has to be 40 for sample measurement . How dose 40 sample reading only covers the 20ms of the full cycle of the ac voltage .
    How will using a different array number affect the reading.
    I will appreciate your kind response.
    Thanks

    Reply

  215. Wow, wonderful blog it is! Thanks for sharing the technical details about AC High Voltage Tester that includes ac voltage measurement using micro controller. Keep doing this great work!

    Reply

  216. sir we have made this project using Arduino microcontroller but we have made for measurement up to 480 volts. we have also made hardware circuit but we have an issue related to scaling. We have measured values practically those values are true but Arduino does not gives right value just due to scaling issue. Can you help us with this….?

    Reply

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