125kHz RFID Reader Circuit: Building an Access Control System

Welcome to our blog post where we will guide you through the process of building a 125kHz RFID reader circuit to create an access control system. RFID (Radio Frequency Identification) technology has various applications, and one of the most common uses is for security and access control. In this article, we will explain the fundamental concepts behind RFID technology, explore the components required, and provide step-by-step instructions to help you build your own RFID reader circuit.

Introduction to RFID Technology

Radio Frequency Identification (RFID) is a wireless technology that utilizes electromagnetic fields to automatically identify and track tags attached to objects. The tags contain electronically stored information, which can be wirelessly read by an RFID reader. A 125kHz RFID reader operates at the low-frequency range, making it suitable for short-range applications like access control systems.

Components Required

To build a 125kHz RFID reader circuit, you will need the following components:

  • Arduino Uno board
  • MFRC522 RFID module
  • Breadboard
  • Jumper wires
  • LEDs
  • Resistors

These components are readily available and affordable, making it accessible for hobbyists and beginners.

Building the Circuit

Follow these steps to build your 125kHz RFID reader circuit:

  1. Connect the MFRC522 RFID module to the Arduino Uno board using jumper wires.
  2. Set up the circuit on the breadboard, ensuring proper connections.
  3. Add LEDs and resistors to indicate the status of the RFID reader.
  4. Upload the necessary code to the Arduino board.
  5. Test the circuit by placing 125kHz RFID tags in proximity to the reader.

Make sure to double-check the connections and follow the circuit diagram provided to avoid any errors.

Programming the RFID Reader

Once the circuit is set up, you need to program the Arduino to read the RFID tags. We recommend using the Arduino IDE and the MFRC522 library, which simplifies the communication with the RFID module. The code will allow you to read the unique identifier (UID) of each tag and perform actions based on the information received.

Expanding the Project

Now that you have successfully built the basic RFID reader circuit, there are various ways to expand the project:

  • Integrate a buzzer or alarm system to create an audible alert when unauthorized access is detected.
  • Connect the Arduino board to a relay module to control electronic locks or other devices.
  • Build a web-based or mobile application to monitor and manage access control remotely.
  • Implement a database system to log and track access events.


Building a 125kHz RFID reader circuit to create an access control system is an exciting project that combines hardware and software elements. By following the steps outlined in this blog post, you can construct a functional RFID reader and experiment with additional features to enhance your access control system. RFID technology has a wide range of applications, and this project serves as an excellent introduction to its practical implementation. Have fun exploring the possibilities!

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