AC Voltage Measurement without Transformer

Transformer-less AC Voltage Measurement

There is a method through which you can measure voltage easily without transformer (instrument transformer). I used a LCD 16×2 to display results and a microcontroller Atmega8 from the family of Atmel AVR Microcontrollers for Transformer less AC measurement. I will give you step by step details for measurement.

What is Importance?

Sometimes in circuits you have to measure AC voltages. But using a transformer makes things bulky. There should be some transformer less method to measure voltage. I will give a method through which measurement will become so easy, less bulky and without transformer. This method is really useful where you don’t need exact voltage value up to 3 decimal places. But still this method can give you exact values with 3-4 percent error.

Warning:Working on 220/110 AC Voltage is dangerous. If you know safety precautions for electricity then implement this project.

 Hardware Part:

Components Required for Project:

Click on the component name to buy the product from reliable sources:

Complete Circuit Diagram:

Circuit Diagram of Transformer less AC Voltmeter
Figure 1: Circuit Diagram of Transformer less AC Voltmeter

Complete Circuit Diagram with Proteus simulation is shown in the figure above. There is a voltage divider present just after the 220 Volt source. This voltage divider will cut off the voltage to microcontroller level.

Voltage output = 1k/(100k+1k) x Voltage input

Where voltage input = 311 volts (in case of 220 volt system)

Voltage output = 3.08 volts

I used 311 volts in 220 volt system because 220 is a RMS Value and in real system RMS values are nothing.  In real systems, we have to consider peak values during calculations.


Peak value = 220 x [square_root(2)]

Peak value = 311 volts

Now we have 3.08 peak-peak to voltage across 1K resistor. The problem here is that we cannot give negative cycles to the microcontroller. In some case negative cycles are very harmful for microcontroller. There are many methods to remove negative cycle issue. I used the easiest one. A diode is present after the divider which will work as rectifier here and cut off the negative cycles. A 10uf capacitor will remove the ripples. In the end a 4.7 volt zener is present which is only for the protection of Atmega8 microcontroller.  It will ensure that surges above 4.7 volt will not harm the Atmega8 microcontroller.

LCD Interfacing:

A 16×2 LCD is connected with Atmega8 microcontroller through 4 bit interfacing. This 4 bit interfacing saves us from extra wiring. As you can see I left four pins of LCD disconnected. I am not going to explain coding part of LCD interfacing here. If you need any help feel free to contact us.

Coding Part:

I will explain here some part of coding. You can get whole coding at the end of article.

// 10 Samples
 for (z=0; z <= 9; z++){
 v1[i] = adc_read(0);
 volts = volts + v1[z];
 volts = volts /10; // to take average

conv = volts * 0.377; // 386/1024
 lcd_print("Voltage = ");

I used 10 samples for every measurement. It is a good practice to use more than one sample for accuracy. adc_read() is a function to fetch the voltage present at the pin of Atmega8 microcontroller.

I multiplied measured value with (386/1024). This is basically the highest points of both analog and digital values. 386 is the highest RMS voltage which can apply and 1024 is the highest digital value which Atmega8 can attain due to 10 bit resolution of ADC.

Summary: If you have a microcontroller and little bit knowledge of ADC then measuring AC voltage without transformer is not a difficult task. Just take precautions while implementing on hardware.

If you need more help feel free to comment below and don’t forget to like our Facebookpage. 🙂 

To download Complete Code click the button below:

Complete CodeProteus File


23 thoughts on “AC Voltage Measurement without Transformer”

      1. Am not getting any output when I use the same circuit. Am getting 2.2v across the voltage divider. Is there anything wrong ?

  1. you put gnd and neutral common and experts says do not ever common ac and dc ground, is it right. Please correct me

    1. This is the common technique which used in all over the world during the measurement of AC voltage. Just be careful while implementing the technique.

      1. how can I in put code,you give this code to need convert aney formet or direct program tex file? what is vsine please iwant to know abaout two subject

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