Build a Smart Energy Meter Using Arduino

Connect the LCD first and verify that it powers on correctly. 

Next, connect the ZMPT101B voltage sensor and ACS712 current sensor to the Arduino's analog inputs. 

Install the push button in an easily accessible location. 

Finally, connect the AC socket, ACS712 sensor, and ZMPT101B module according to the circuit. 

Double-check every connection before powering the system. Programming Logic 

Step 1: Initialize the Hardware 

Start by including the required libraries and defining the pins. 

#include <Wire.h> 
#include <LiquidCrystal_I2C.h> 
 
LiquidCrystal_I2C lcd(0x27, 16, 2); 
 
const int voltagePin = A0; 
const int currentPin = A1; 
const int buttonPin  = 2; 
 
float energy = 0.0; 
float cost = 0.0; 
 
const float tariff = 8.0;    // ₹ per kWh 
 
unsigned long previousMillis = 0; 

The LCD is initialized, the analog pins for the voltage and current sensors are assigned, and variables are created to store energy consumption and cost. 

 Step 2: Measure AC Voltage 

The Arduino reads multiple samples from the ZMPT101B sensor and converts them into an approximate RMS voltage. 

const float voltageCalibration = 0.80; 
 
int rawVoltage = analogRead(voltagePin); 
 
float voltage = (rawVoltage * (5.0 / 1023.0)) * 230.0 * voltageCalibration; 

In a practical project, multiple samples should be averaged before calculating the final voltage to improve stability. 

 Step 3: Measure Current 

The ACS712 outputs approximately 2.5V when no current is flowing. 

Subtracting this offset gives the actual current value. 

const float sensitivity = 0.185;   // ACS712 5A version 
 
int rawCurrent = analogRead(currentPin); 
 
float sensorVoltage = rawCurrent * (5.0 / 1023.0); 
 
float current = (sensorVoltage - 2.5) / sensitivity; 
 
if(current < 0) 
current = -current; 

If you're using the 20A or 30A ACS712 version, update the sensitivity value according to the module specifications. 

 Step 4: Calculate Power 

Once voltage and current have been measured, calculating power is straightforward. 

float power = voltage * current; 

This gives the instantaneous power consumption in watts. 

 Step 5: Calculate Energy Consumption 

Energy depends on both power and time. 

The Arduino continuously accumulates energy as the appliance operates. 

unsigned long currentMillis = millis(); 
 float hours = (currentMillis - previousMillis) / 3600000.0; 
 energy += (power * hours) / 1000.0; 
 previousMillis = currentMillis; 

Dividing by 1000 converts watt-hours into kilowatt-hours. 

 Step 6: Calculate Electricity Cost 

Once energy has been calculated, estimating the electricity bill becomes very simple. 

cost = energy * tariff; 

You can change the tariff value according to your local electricity board. 

For example: 

const float tariff = 7.5; 

or 

const float tariff = 9.0; 

 Step 7: Display Values on the LCD 

Display the live electrical parameters on the first screen. 

lcd.setCursor(0,0); 
lcd.print("V:"); 
lcd.print(voltage,1); 
 
lcd.print(" I:"); 
lcd.print(current,2); 
 
lcd.setCursor(0,1); 
lcd.print("P:"); 
lcd.print(power,1); 
lcd.print(" W"); 

When the push button is pressed, switch to the second page. 

lcd.clear(); 
 
lcd.setCursor(0,0); 
lcd.print("E:"); 
lcd.print(energy,3); 
lcd.print("kWh"); 
 
lcd.setCursor(0,1); 
lcd.print("Rs:"); 
lcd.print(cost,2); 

This provides a clean separation between real-time electrical measurements and accumulated usage statistics. 

 Step 8: Reset Energy Using the Push Button 

Holding the button for a few seconds resets the accumulated values. 

if(digitalRead(buttonPin) == LOW) 
{ 
    energy = 0; 
    cost = 0; 
} 

 Calibrating the Sensors 

Calibration is the most important part of this project. 

Voltage Calibration 

Measure the mains voltage using a digital multimeter. 

Compare it with the LCD reading. 

If the Arduino shows: 

Running an I2C scanner sketch can help identify the correct LCD address. 

 Readings Fluctuate Excessively 

Average more analog samples before performing calculations. 

Adding simple software filtering usually improves stability. 

Final Thoughts 

Building a smart energy meter is an excellent way to learn how Arduino can measure real-world electrical parameters and convert raw sensor data into useful information. Along the way, you'll gain experience with analog signal processing, sensor calibration, LCD interfacing, timing calculations, and embedded programming. 

For anyone interested in an energy meter project India, this build provides a practical introduction to energy monitoring using readily available Arduino components. Once you've mastered the basic version, you can gradually add wireless connectivity, cloud dashboards, and data logging to create a more advanced home energy monitoring system.