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Basics of Bluetooth Module

Updated: Mar 24


Bluetooth serves as a technological interface that facilitates the establishment of a protocol for data transmission between devices and helps any two devices connect wirelessly using Bluetooth Low Energy. The range of mediated data transfer for Bluetooth Low Energy modules is typically tens of meters, and data is conveyed within designated frequency bands.

A Bluetooth module is a small piece of hardware that combines Bluetooth technology and allows devices to communicate wirelessly. It consists of all the circuits and protocols required to create a Bluetooth connection, which enables short-range data transmission and communication between devices. Bluetooth modules are available in a variety of form factors and are suitable for both independent usage in research and prototyping as well as seamless integration into electrical products.

Circuit diagram

  • Bluetooth modules typically have a maximum communication range of around 100 meters, depending on the categorization. Thus, they have a limited scope.

  • The Bluetooth LE module's range is designed into the circuit.

  • Small data bundles may be sent between devices in different IoT connections or single-battery devices thanks to low-power Bluetooth modules, which use less energy and power.

  • The Bluetooth module circuit has several uses and is compatible with the 2.4GHz frequency band.

  • Bluetooth low energy may be integrated into any system with the right microcontroller.

Pin Definition

VCC - The VCC pin has a 5V connection.

GND - This pin is used to ground the module.

TXD - while having a connection to the Micro Controller Unit. Through the TXD pin, TXD sends out the data that the Bluetooth module has received in serial fashion.

RXD - The Bluetooth module subsequently transmits the serial data that RXD receives over a wireless protocol.

KEY - The Bluetooth module AT command and default modes can be switched between using this, through establishing a fixed value for the KEY pin.

STATE - The Bluetooth module's connectivity state, whether paired or unpaired, is indicated by the STATE.

Working Principle of the Bluetooth Module

There are no wires or connections needed to connect or communicate between any Bluetooth device and Bluetooth technology. The link is wireless and operates on radio waves, which have a limited range. When turned on, a chip within every Bluetooth device generates radio waves, which other Bluetooth devices may detect and connect to in order to initiate communication and the transfer of files, data, and other media.

When many Bluetooth-enabled devices are connected together, they create a piconet, and as long as they are all within range, they can all communicate with each other without any problems. In a connection such as this, one device—called the master—usually governs all other devices linked to it, which are called slaves.

Types of Bluetooth modules

Bluetooth modules fall into two major categories:

Bluetooth Classic Modules:

The conventional Bluetooth technology, commonly referred to as Bluetooth Classic, is supported by these modules. They are frequently used in applications that need functions like file sharing and audio streaming, as they are geared for faster data transmission rates. For applications where a greater power consumption is acceptable, including audio equipment and some industrial settings, Bluetooth Classic modules are appropriate.

Bluetooth Low Energy (BLE) Modules:

Bluetooth Smart modules, or BLE modules, are made especially for applications that need little power usage. They function with devices that have longer battery lives thanks to Bluetooth Low Energy technology. BLE modules are frequently found in wearable technology, IoT sensors, fitness and health trackers, and other battery-powered gadgets where energy economy is essential.

Examples using HC-05 Bluetooth module

Bluetooth Controlled LED Matrix

  • Description: Create a matrix of LEDs and control their patterns using a mobile app through Bluetooth. Use an Arduino board and the HC-05 module to receive commands from the app and update the LED matrix accordingly.

  • Components:

  • Arduino board (e.g., Arduino Uno)

  • HC-05 Bluetooth module

  • LED matrix

  • Jumper wires

  • Implementation: Connect the LED matrix to the Arduino, establish a Bluetooth connection with the HC-05 module, and write a program to interpret Bluetooth signals. Develop a mobile app that sends commands to change the LED patterns.

Bluetooth-Enabled Smart Home Automation

  • Description: Build a simple home automation system that can control lights, fans, or other devices using a smartphone or tablet. The HC-05 module facilitates communication between the home automation system and the mobile app.

  • Components:

  • Arduino or Raspberry Pi

  • HC-05 Bluetooth module

  • Relay modules for device control

  • Smartphone with a custom app

  • Implementation: Connect the relay modules to the Arduino or Raspberry Pi to control the devices. Establish Bluetooth communication using the HC-05 module and create a mobile app to send commands for device control.

Bluetooth-Enabled Temperature and Humidity Monitor

  • Description: Develop a wireless temperature and humidity monitoring system using a Bluetooth-enabled sensor and a mobile app. The HC-05 module enables communication between the sensor and the app.

  • Components:

  • Arduino board or a dedicated temperature and humidity sensor with Bluetooth capability

  • HC-05 Bluetooth module

  • Smartphone with a monitoring app

  • Implementation: Connect the sensor to the Arduino or use a pre-built sensor with Bluetooth capability. Utilize the HC-05 module for Bluetooth communication. Develop a mobile app to receive and display real-time temperature and humidity data.

Applications of the Bluetooth module

Wireless audio streaming:

Bluetooth modules facilitate wireless audio communication across various devices, including automotive audio systems, speakers, and headphones.

IoT and home automation:

Smart gadgets may link and interact with one another over Bluetooth modules, allowing for centralized automation and management within a home network.

Wearable devices:

Bluetooth modules are used by smartwatches, fitness trackers, and medical equipment to wirelessly send data and synchronize with computers or smartphones.

Industrial automation:

Bluetooth modules provide wireless communication between industrial equipment, including controllers, actuators, and sensors.

Automotive systems:

Car infotainment systems may benefit from wireless networking, hands-free calling, and music streaming thanks to Bluetooth modules.

Gaming controllers:

Gamers can have more mobility with the help of Bluetooth modules, which enable wireless communication between controllers and gaming systems.

Proximity sensing and tracking:

Bluetooth modules are useful for location-based services, beacon systems, and asset tracking.

Wireless data transfer:

Bluetooth modules eliminate the need for wires and connectors by enabling wireless file transmission between devices.


The foundation of contemporary wireless communication is without a doubt made up of Bluetooth modules. They have become vital in our technologically advanced world because to their capacity to support a wide range of applications, link devices with ease, and transport data effectively. Forward-thinking solutions and ever-higher wireless connectivity are made possible by Bluetooth technology, which is expected to continue growing.

Wireless connection between devices in a variety of sectors has been made possible by Bluetooth modules, which have completely changed wireless connectivity. Bluetooth modules continue to revolutionize the way we interact with technology because of their small size, low power consumption, and range of capabilities. Leveraging the potential of wireless communication in our daily lives requires an understanding of their capabilities and uses.


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