# AC Voltage Measurement using Arduino – Difference Amplifier Technique

Ac voltage measurement using Arduino: In this article, we will see how to measure ac voltage using Arduino and the same project can also be used for AC voltage peak detection that is an AC voltage detector circuit using Arduino Uno. Firstly, we will see a difference amplifier method to design a voltage sensor using an operational amplifier. In the end, we will see how to write ac voltage / potential measurement code in Arduino programming.

## Arduino Based AC Voltmeter

This Arduino project will be a simple Arduino based ac voltmeter that can measure 220 volts very easily and without any need of an external sensor. I will start writing articles from this week on how to measure ac current, ac power, power factor using Arduino, and I have already written articles on all these topics using a pic microcontroller. But on the request of users, I will be also writing these articles using Arduino.

Check following articles which are based on pic microcontroller projects

So now lets see how to measure ac voltage using Arduino and how to design ac voltage sensor using Arduino and I recommend you to check arduino tutorials and Arduino projects first, if you are a beginner in Arduino programming.

### Components required for ac voltage measurement with Arduino

Followings are the main components required for the design of ac voltage detector with Arduino:

• Arduino Uno R3: It is the main component of this project. It measures analog voltage with the help of built-in analog channels and converter the analog measured voltage into a digital value and then we convert this measure digital value back into a voltage by multiplying it with the resolution factor of Arduino ADC.
• 16 x 2 LCD: Liquid crystal display is used to display measured voltage value. If you don’t know how to interface LCD with Arduino, I suggest you check this tutorial on lcd interfacing with Arduino.
• Difference amplifier: In this alternating voltage measurement method, difference amplifier is used to step down voltage from 220-volt ac to less than 3.3-volt ac. I will explain it in more detail in the next section of this article.

## AC Voltage Sensor with Op-Amp

To measure ac voltage with the help of Arduino, first of all, you need to design an alternating current voltage measurement sensor. For example, if you want to measure the voltage of magnitude 220 volt AC. you need to step down this voltage first. Because Arduino has built-in ADC channels and the maximum voltage that the Arduino analog channel can measure is 5 volts. Therefore, we can not measure voltage greater than 5 volts with the help of Arduino analog to digital converter directly. you should also know how to measure an analog voltage with the help of Arduino or how to use the analog channels of Arduino. if you don’t know, check this article on how to measure analog voltage with Arduino.

### Step Down AC Voltage

It will give you an idea on how to use analog channel of Arduino. Because it is a first step towards designing ac voltage sensor with Arduino and ac voltage detector meter with Arduino. As I have explained earlier, in this project I have used difference amplifier to step down voltage from 220 volt AC to less than 3.3 volt AC. Because built in ADC of Arduino can not measure voltage more than 5 volt. So we need to find a way to step down voltage. There are many other methods to step down voltage like potential transformer or step down transformer which is a expensive method for low cost applications. Voltage divider method, it is a least expensive method for this purpose. But it has disadvantage of less voltage range and more power consumption. So we can not use it critical power applications.

So I have come up with another method using operational amplifier. I have use operational amplifier for a step down purpose. Operational amplifier is used a difference amplifier. By adjusting the gain of operational amplifier, we step down the voltage to less than 3.3 volt. I have explained all the theory and working of difference amplifier for to step down ac voltage in separate article on ac voltage measurement using pic microcontroller. I recommend you to check it, if you want to get more understanding about this method.

### Step Down Voltage Circuit using Op-Amp

In this circuit, LM358 op-amp is used as a difference amplifier. Circuit diagram of difference amplifier is given below:

Input to difference amplifier is 220 volt ac and output of difference amplifier is less than 3.3 volt. I have also added 5 volt dc to ac to convert negative cycle into positive cycle. Because Arduino can not measure negative voltage directly. Again refer to the article on ac voltage measurement using pic microcontroller for more understanding and why I added 5 volt dc level to the circuit. Output of this circuit is fed to analog channel of Arduino which measures this voltage and after performing some calculations displays measured voltage value on LCD.

## Circuit diagram of AC voltage measurement using Arduino

Circuit diagram of ac voltage measurement using Arduino is given below. In this circuit, we used a 16×2 LCD to display voltage value. If you don’t know how to interface an LCD with Arduin, you should read this article:

## Arduino Code

``````
#include <LiquidCrystal.h>  // initialize the library with the numbers of the interface pins
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);
const int sensorIn = A3;
double Voltage = 0;
double VRMS = 0;
int i;

void setup(){
Serial.begin(9600);
lcd.begin(16,2); // set up the LCD’s number of columns and rows:
}

void loop(){

lcd.setCursor(0,0);
lcd.print("V=");
lcd.print(VRMS);
lcd.print("V");
Serial.print("V = ");
Serial.print(VRMS);
Serial.println("V");
delay(1000);
}

{
float max;
int i;
unsigned int temp=0;
float maxpoint = 0;
for(i=0;i<500;i++)
{
{
maxpoint = temp;
}
}

maxpoint = maxpoint *(10.0/1023.0);
maxpoint = (maxpoint -5.0);
maxpoint = maxpoint *110.1909091;
max=maxpoint *.707106781;
return max;
}``````

### How Code works?

First include the library of liquid crystal display and define the pin number of Arduino that we connect with 16×2 LCD.

``````#include <LiquidCrystal.h>
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);``````

We will use analog channel zero of Arduino (A0). This line defines the name of channel zero as a “sensorIn” pin. By doing this, we will use this symbolic name throughout the code instead of using ADC channel number.

``const int sensorIn = A0;``

We define three global variables to store voltage value, adc digital value and to use with loops executions.

``````double Voltage = 0; // store ADC value
double VRMS = 0; //store RMS value of voltage
int i; // to keep count of loop value``````

Inside the setup function, we declare start the LCD library for 16×2 size using lcd.begin() function.

``lcd.begin(16,2); // set up the LCD’s number of columns and rows``

Before taking a look inside the loop() function, first lets see the working of voltage_READ() routine.

This is the main code of the Arduino AC voltmeter project. This function measures the peak voltage of the AC waveform and converts the peak voltage into a root mean square (RMS) voltage value.

Inside the AC voltage measurement function, first, we take 500 samples of AC voltage waveform using a for ‘loop’ and analog channel A0 of Arduino. Firstly, we initialize the “maxpoint” float type variable to zero and its value keeps updating with a new value of the ADC sample if the ADC sample value is greater than the currently hold value of “maxpoint”.

``````for(i=0;i<500;i++)
{
{
maxpoint = temp;
}
}``````

After that, this line converts the digital measured value of ADC into voltage.

``maxpoint = maxpoint *(10.0/1023.0);``

Finally, we get original measured value of voltage by multiplying voltage value with the gain of operational amplifier.

``````maxpoint = (maxpoint -5.0);
// subtract DC gain from the signal
maxpoint = maxpoint *110.1909091;
// multiply with inverse of gain
max=maxpoint *.707106781; // peak to rms conversion``````

## Related Arduino Projects

### 21 thoughts on “AC Voltage Measurement using Arduino – Difference Amplifier Technique”

1. Is there any disadvantage of such circuit because it is not isolated.

2. can you please send me the code of this ac voltage measurement circuit using arduino. I tried this circuit by in lcd i couldn’t get the voltage as you mentioned in the video. please help me.Giving my email below. Thanks

• let me know the issue you are facing by sharing your code in comments

This is a non-isolated method.
it is better to use an optocoupler or transformer before to opamp to avoid electric shock and ground level difference

• This method just works fine without any issue and I have implemented it many times. you will find this circuit in many modern inverters and power electronics circuits.
Although it is good to have optocoupler and transformer, But it will make system device costly.

4. You are right ????.
The reason behind that not just a 50 RS.
The circuit shown in above figure has better accuracy and precision.
Other circuits use a capacitor to filter ac components which is vulnerable to frequency.
Frequency is very according to load.
Please refer isolated opamps and ac voltage measuring ICs

5. Hello Sir
Yesterday i couldn’t reply you..i will tell what is the problem that i am facing when i am doing the project.. first of all i had referred your previous article ” Ac Voltage measurement using pic microcontroller “. I saw the code that you had given there for the ac voltage measurement using op-amp. i went through that code and i took the idea from there and i put it in my code.
i am using ATmega328P as my MCU for this project. i am not using Arduino for my project because in Arduino also they are using the same controller. But i am using avr studio as my IDE. i will give the code here.. I test this circuit in the proteus simulation. The problem that i am facing is when i run the code it doesn’t show the voltage that i can see in your simulation.i will share the pic also. Kindly check the code and tell me if there is any fault i made.
“””
#include
#include”LCD.h”
#include”DELAY.h”

unsigned int Buff;

volatile float Volt=0;

void main()
{

DDRD=0xff;
PORTD=0x00;

DDRC=0x00;
PORTC=0x00;

LCDInit();
Delay_ms(10);
LCDClear();
Delay_ms(5);
LCDDispStringXY(0,0,”Volt:-“);
Delay_ms(5);

while(1)
{
for(count=0;count<30;count++)
{
Delay_us(30);
}

Volt = Buff;

for(count=1;count<30;count++)
{
if(Volt<Buff[count])
{
Volt = Buff[count];
}
}

Volt *=0.707106781;

LCDDispIntXY(0,7,Volt,6);
Delay_ms(500);
}

}

{
}

{
ch &=0x0f;
} """

• Hi

Unfortunately I do not have tutorial related to atmega,
I will try to write about it in future

• Sir,Please send me the code ..

6. Hi Dear,
I am looking for a arduino module to check the the availability for Main AC Voltage i.e 220 V 50-60Hz. I have found one module for checking just the availability but i am stuck with the module which can give me the magnitude of the voltage means accurate reading either the voltage is very high or too low.
Regards.
Khurram

7. Hi

What is lowest and maximum range of AC voltage it can measure?

How to connect AC line and neutral here? I think we have to connect line voltage to + terminal side and neutral to – terminal side, is it? Please confirm

Thanks
Manjunath AN

8. Hi

What is lowest and maximum range of AC voltage it can measure?

How to connect AC line and neutral here? I think we have to connect line voltage to + terminal side and neutral to – terminal side, is it? Please confirm

Thanks
Manjunath AN

9. Hi,

1. Can I use LM358 instead of LM258? if Okay, Do I need to change any circuit?
2. Can I supply +5v instead of +12v to OPAMP?
3. What is the minimum and maximum AC voltage range it can measure?
4. How the ac line connection should be? My understanding is line voltage to + terminal neutral should give to – terminal? is it correct?

Thanks
Manju an

10. hi
can i have a code for voltage measurement with Arduino project please …
u can send to me by Email: [email protected]
Thanks

11. Hy
Please sir can you help me with the code for automatic transfer switch between solar inverter and grid
I am doing my project base on that and i saw your simulation video but i could’nt find the code
Am using arduino uno
Pls help me with the code

12. Does this circuit actually work? I made it in LTspice and the output looks like a turd.