In this article, we are going to learn how to make a high voltage AC voltmeter using Arduino and we are going to measure 2500V. Utilizing the technique shown here, we can even measure more than this range. So let’s start our High Voltage AC voltmeter.

Disclaimer: Electricity is always dangerous. Proper skill is required to work with electricity. Do work at your own risk. The author will not be responsible for any misuse or harmful act or any mistake you make. The contents of this website are unique and copyright protected. Kindly don’t do any nonsensical act copying and claiming it as yours. Most of the articles published here are kept as open-source to help you. Take the knowledge for free and use it, but if you are interested you can buy the ready resources offered here. If you need any help or guide feel free to comment below, the author will try to help you. Thanks.

## High voltage measurement technique:

Measuring high voltage is not safe for anyone. But if it needs to be done, then we must find a safe way to do the job. We should not measure high voltages keeping one terminal connected with the measuring instrument. Connecting with a common terminal increases the risk of getting an electric shock, burn, or fire. That is why isolation is required. Sometimes this isolation is done through high-valued resistors, sometimes with optocouplers. But in the DC circuit, we can use high-valued resistors in series to form isolation. Adding an Op-Amp circuit, the process becomes more sensitive and accurate. To make our High Voltage AC voltmeter, we need to understand this measurement circuit first.

## Op-Amp based high voltage measurement circuit:

Most High Voltage AC voltmeter follows this circuit for measurement.

Here in this circuit, we use an Op-Amp (OPA350) and several resistors to make a floating or isolated voltage measuring circuit. The circuit simply measuring the voltage difference between two points. This differential amplifier circuit can be used in many types of measuring circuits where we can measure voltage differences of two points. Simple configuration and simple calculation.

Here, Gain = R9/(R2+R6+R7+R8)

## Circuit diagram:

Here is the circuit diagram of our High Voltage AC voltmeter:

## Arduino Coding:

Before reading the code, please check my other article about this, “How to make an AC voltmeter using Arduino UNO and 4×1 multiplexed Seven Segment display“. Then it will be easy to understand.

```#include <TimerOne.h>
const char segment_pins[] = {13, 12, 11, 10, 9, 8, 7, 6}; //segments a to g
const char digit_pins[] = {5, 4, 3, 2}; // 4digits
const int digit_number = 4;//for 4 digit segment
byte dot_position;//set dot position from right side.
bool dot_point = false; // having dot or not, true = have dot, false = no dot.

const int segment_array = // for common cathode segment only
{
{HIGH, HIGH, HIGH, HIGH, HIGH, HIGH, LOW, LOW}, //0
{LOW, HIGH, HIGH, LOW, LOW, LOW, LOW, LOW},     //1
{HIGH, HIGH, LOW, HIGH, HIGH, LOW, HIGH, LOW},  //2
{HIGH, HIGH, HIGH, HIGH, LOW, LOW, HIGH, LOW},  //3
{LOW, HIGH, HIGH, LOW, LOW, HIGH, HIGH, LOW},   //4
{HIGH, LOW, HIGH, HIGH, LOW, HIGH, HIGH, LOW},  //5
{HIGH, LOW, HIGH, HIGH, HIGH, HIGH, HIGH, LOW}, //6
{HIGH, HIGH, HIGH, LOW, LOW, LOW, LOW, LOW},    //7
{HIGH, HIGH, HIGH, HIGH, HIGH, HIGH, HIGH, LOW},//8
{HIGH, HIGH, HIGH, HIGH, LOW, HIGH, HIGH, LOW}, //9
};

void int_sev_segment()
{
for (int k = 0; k < 8; k++)
{
pinMode(segment_pins[k], OUTPUT);//I/O settings
}
for (int k = 0; k < digit_number; k++)
{
pinMode(digit_pins[k], OUTPUT);//I/O settings
}
for (int k = 0; k < 8; k++)
{
digitalWrite(segment_pins[k], LOW);//keep low
}
for (int k = 0; k < digit_number; k++)
{
digitalWrite(digit_pins[k], HIGH);//keep high = disable segments (CC)
}
Timer1.initialize(5000);//5000us = 5ms
Timer1.attachInterrupt(display_segment);
}

char digits;
void display_7segment(int number, byte dot)
{
digits = number / 1000u;//extract 1000th digit
digits = (number / 100u) % 10u;//extract 100th digit
digits = (number / 10u) % 10u;//extract 10th digit
digits = (number / 1u) % 10u;//extract 1st digit
dot_position = dot;
}

int digit_position = 0;
void display_segment(void) // called periodically using timer interrupt
{
for (int k = 0; k < digit_number; k++)
{
digitalWrite(digit_pins[k], HIGH);//reset digit pins
}
if (digit_position > 3)digit_position = 0;

for (int k = 0; k < 8; k++) //print the a to g segment pins
{
digitalWrite(segment_pins[k], segment_array[digits[digit_position]][k]);
if (digit_position == dot_position && dot_point == true)
{
digitalWrite(segment_pins, HIGH);//print dot point
}
}

if (digit_position == 3)
{
digitalWrite(digit_pins, LOW);
digitalWrite(digit_pins, HIGH);
digitalWrite(digit_pins, HIGH);
digitalWrite(digit_pins, HIGH);
}
else if (digit_position == 2)
{
digitalWrite(digit_pins, HIGH);
digitalWrite(digit_pins, LOW);
digitalWrite(digit_pins, HIGH);
digitalWrite(digit_pins, HIGH);
}
else if (digit_position == 1)
{
digitalWrite(digit_pins, HIGH);
digitalWrite(digit_pins, HIGH);
digitalWrite(digit_pins, LOW);
digitalWrite(digit_pins, HIGH);
}
else if (digit_position == 0)
{
digitalWrite(digit_pins, HIGH);
digitalWrite(digit_pins, HIGH);
digitalWrite(digit_pins, HIGH);
digitalWrite(digit_pins, LOW);
}
digit_position++;
}

long ac_voltage = 0;
unsigned int temp, maxpoint;
void setup()
{
int_sev_segment();//initialize seven segment program
}

void loop()
{
ac_voltage = 0; //clear previous result
temp = 0;
maxpoint = 0;
for (int i = 0; i < 10; i++)
{
for(int m=0;m<500;m++)
{
{
maxpoint = temp;
}
}
ac_voltage += maxpoint*2.455;
}
ac_voltage /= 10; //get average value

display_7segment(ac_voltage, 2); //display value of cnt, dot in position 1 from right side

}

// end```

## Test Result:

The test result of our High Voltage AC voltmeter:

## Conclusion:

In this project, you learned how to make an AC voltmeter that can measure 2500V (!!!) with Arduino and Op-Amp circuit. The result is displayed in multiplexed Seven segment display. We tested the voltmeter in the simulation. This project is now ready for practical use.

Kindly select voltage divider resistors carefully to measure higher voltage. Proper selection can increase the resolution of our voltmeter.

But keep in mind that electricity is always dangerous. Do work at your own risk.

I hope, you enjoyed this project and now you can make one for yourself. If you are stuck in the middle and need help, just ask. I’ll try my best to help you. Thank you, Enjoy! JLCPCB – Only \$2 for PCB Prototype (Any Color)

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#### MKDas

I'm Mithun from Bangladesh. Electronics is my passion, love to work with electronics. This is my personal blog. Besides my regular works, I write some articles here. Most of them are open-source and everything is presented in the easiest way so that anyone can understand and learn it. Thanks.  