AC Protection Device Using Arduino and LM358 IC

In this article, we will build an AC protection device using Arduino, LM358 IC, relay, and other electronic components. The AC protection device is designed to safeguard electrical appliances from current surges, voltage fluctuations, and overloads. With an AC protection device, users can enhance the safety of household electronics. This project demonstrates step-by-step connections, circuit explanation, and working of the AC protection device in detail.

Introduction

Electrical appliances like refrigerators, fans, computers, and televisions are highly sensitive to over-voltage, under-voltage, and current overloads. Without proper safety mechanisms, these devices can get damaged permanently, leading to expensive repairs or replacements.

This is where an AC protection device comes into play. By automatically cutting off the supply when abnormal conditions occur, this system ensures the safe operation of household and industrial appliances.

In this project, we are going to design an AC protection device using:

• Arduino for control logic.

• LM358 IC for signal processing.

• Relay module for switching AC load.

• Current transformer for current sensing.

• Push buttons & LCD for user interaction and monitoring.

This article covers the working principle, detailed circuit explanation, components list, step-by-step build guide, and FAQs to help you fully understand the design and implementation.

 Materials for the Project

Circuit Diagram Explanation

The circuit of the AC protection device can be divided into the following functional blocks:

1. Power Supply Section

   • Arduino operates at 5V.

   • The LM358 IC also uses 5V from the Arduino.

2. Current Sensing Section

   • A current transformer (CT) senses the AC current drawn by the load.

   • The CT output is fed into the LM358 for signal conditioning.

   • Resistors create a proper biasing and voltage divider network for stable operation.

3. Voltage Protection Section

   • Multiple 470K resistors are used to scale down the AC input voltage for safe detection.

   • The scaled signal is fed into LM358 for monitoring.

4. Control Section (Arduino)

   • The Arduino reads processed signals from LM358.

   • Push buttons are connected for user settings (trip limits, reset, manual control).

   • LCD displays current, voltage, and device status.

5. Switching Section

   • A BC547 transistor acts as a driver to control the relay coil.

   • The relay switches the AC load ON/OFF depending on Arduino’s decision.

   • A diode (1N4148) is placed across the relay coil for back-EMF protection.

Download Circuit Diagram

Step-by-Step Guide to Build the AC Protection Device

Step 1: Connect the Arduino

• Place the Arduino Nano on the breadboard or PCB.

• Provide it with a regulated 5V supply.

Step 2: LM358 IC Wiring

• Pin 4 → Ground.

• Pin 8 → 5V supply from Arduino.

Step 3: Resistor Network

• Connect 10K resistor between pins 1 and 2 of LM358.

• Connect another 10K resistor between pin 2 and ground.

• Connect 47Ω resistor between pin 3 and ground.

• Connect 10K resistor between pin 7 and pin 6.

• Connect 4.7K resistor between pin 6 and ground.

• Connect 2.2K resistor between pin 5 and ground.

• Chain multiple 470K resistors in series between pin 5 and AC supply for voltage scaling.

Step 4: Current Transformer Connection

• Connect CT’s secondary output across pin 3 and ground of LM358.

Step 5: LCD Display

• VCC → 5V, GND → Ground.

• SDA → A4 (Arduino).

• SCL → A5 (Arduino).

Step 6: Push Buttons

• Button 1: One pin → D3, other → Ground.

• Button 2: One pin → D4, other → Ground.

• Button 3: One pin → D5, other → Ground.

Step 7: Relay Driver Circuit

• BC547 transistor → Pin 3 to ground.

• 1K resistor between transistor base and Arduino D2.

• Relay coil connected between 5V and collector of transistor.

• 1N4148 diode across relay coil.

Step 8: AC Load Connection

• Relay common → AC Line.

• Relay NO (Normally Open) → Load.

• Neutral directly → Load.

Step 9: Upload the code

So we have completed all the connections. Now let’s upload the code to Arduino and test the project.

Working Principle

• When the AC protection device is powered ON, the current transformer monitors the AC load current.

• The LM358 processes both current and voltage sensing signals and sends them to the Arduino.

• Arduino compares the values with safe limits set by the user.

• If the current exceeds the limit or voltage goes outside safe range, Arduino switches OFF the relay.

• The relay disconnects the load, protecting the device from damage.

• The LCD continuously displays current, voltage, and load status.

• Push buttons allow resetting the system, setting thresholds, and manual override.

Applications of AC Protection Device

• Home appliances protection (TV, refrigerator, washing machine).

• Industrial motors and pumps.

• Office equipment like computers and printers.

• General AC power safety systems.

FAQs

Q1. What is the main function of an AC protection device?
The AC protection device automatically disconnects the load when abnormal conditions like over-current, over-voltage, or under-voltage occur.

Q2. Can I use this project for three-phase systems?
This design is for single-phase AC loads. For three-phase, additional CTs and monitoring circuitry are required.

Q3. Which microcontroller can I use other than Arduino Nano?
You can use Arduino Nano, ESP32, or even PIC/AVR microcontrollers with minor code changes.

Q4. Is it safe to directly connect AC to Arduino?
No! That’s why resistors, CT, and LM358 are used to scale and isolate signals. Direct AC connection to Arduino will destroy it.

Q5. What rating of relay should I use?
Use a relay with a current rating higher than your load, typically 5A–10A for household appliances.