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What do You Know about Bluetooth Module and PCB

PCBONLINE Team Fri, Dec 22, 2023
Bluetooth technology

Bluetooth technology has revolutionized wireless communication among electronic devices within short proximity, finding widespread applications in products such as headphones, speakers, home appliances, industrial equipment, and medical devices.

A Bluetooth module is like a tiny set of special chips that helps devices talk to each other without any wires by using Bluetooth technology. Several considerations must be addressed when designing a Bluetooth module or PCB (printed circuit board).

Successful design of a Bluetooth module and its PCB requires a thorough understanding of its hardware and software components. In this article, we will delve into the Bluetooth technologies!

Introduction of Bluetooth Modules

A Bluetooth module is a PCBA (printed circuit board assembly) that integrates Bluetooth technology into electronic design and assembly. A Bluetooth module includes the printed circuit board along with other electronic components like antennas, power supplies, and connectors, to provide the essential infrastructure for devices to communicate wirelessly via Bluetooth technology.

Bluetooth module

Bluetooth module refers to the basic circuit set of chips integrated with Bluetooth function for wireless network communication. The Bluetooth module works in the global 2.4GHz ISM (industrial, scientific, medical) frequency band, and its data rate is 1Mbps.

Unlike many other wireless devices, Bluetooth can work in full duplex mode which means it can talk back and forth simultaneously making it advantageous.

The biggest feature of the Bluetooth module is that as long as two devices supporting Bluetooth transmission can achieve data transmission within the range of the transmission distance, this is something that other wireless modules cannot do because other wireless modules require a series of relevant configurations to achieve communication.

But, here's the catch, Bluetooth's transmission distance is very short. It only works well within about a dozen meters.

Other wireless gadgets, like those famous for short distances, can go much farther.

Also, its transmission rate is slow, which can be a bit of a drawback.

Bluetooth can be divided into three classes based on output power and distance of communication. The selection of a Bluetooth module is made based on the requirement of an application. Following are the power and distance ranges of each class:

Class 1

Output power: 100mW

Distance: 100m

Class 2

Output power: 2.5mW

Distance: 10m

Class 3

Output power: 1mW

Distance: 1m

Types of Bluetooth Modules

Bluetooth modules can be divided into many types, but according to their functions, Bluetooth modules can be roughly divided into three types:

1. Data transmission module for sending data

2. Audio module for handling audio

3. Audio + Data module that can do both

Data transmission module for sending data

Data transmission modules focus primarily on the wireless transmission of non-audio data between devices. They are designed for applications where the primary requirement is the transfer of information other than audio signals.

A typical Bluetooth data transmission module consists of a Bluetooth transceiver for connecting to other devices, an antenna for sending and receiving signals, a microcontroller for processing, and interface ports and power supply.

The "HC-05", a Class 2 Bluetooth module, is designed for seamless wireless serial communication. It operates as a slave Bluetooth device, establishing transparency in its operation once paired with a master Bluetooth device like a PC, smartphone, or tablet. Upon pairing, any data received through the serial input is promptly transmitted wirelessly. When the module receives wireless data, it is relayed through the serial interface without any alteration. Importantly, no user code specific to the Bluetooth module is required in the user microcontroller program. The following image shows an HC 05 module with different pins and their usage.

data transmission Bluetooth module

Data transmission Bluetooth modules find applications in scenarios where devices need to exchange information, such as file transfer between devices, communication between micro-controllers, and general-purpose wireless data connectivity.

Bluetooth Audio Module

Bluetooth audio modules are specialized for transmitting and receiving high-quality audio signals wirelessly. These modules may include features like audio codecs and signal processing to ensure a reliable and clear audio connection.

A Bluetooth audio module typically consists of an amplifier, codec, audio port for input and output, and microcontroller along with supporting assemblies like power supply, etc.

The "DFPlayer Mini MP3 Bluetooth Module" is an example of a Bluetooth audio module. It combines Bluetooth connectivity with an integrated MP3 player, allowing wireless audio streaming from Bluetooth-enabled devices. The module features an amplifier for driving speakers directly, multiple control interfaces, a built-in equalizer, and a compact size for easy integration. The following image shows the pin configuration of the module.

audio Bluetooth module

Bluetooth audio modules are commonly used in wireless audio systems, speakers, headphones, etc where the continuous transmission of high-fidelity audio is essential.

Bluetooth Audio + Data Module

Combining the features of both data transmission and audio modules, Bluetooth audio + data modules provide a comprehensive solution for applications requiring both audio streaming and general-purpose data transfer.

Audio + Data Bluetooth modules often support multiple Bluetooth profiles to cater to diverse functionalities simultaneously. Examples include smart audio devices that can transmit audio and receive control commands or display data simultaneously.

The "RN52 Bluetooth Module by Microchip" is an example of a Bluetooth Audio plus Data Module, combining audio streaming capabilities with support for data communication. With features such as Bluetooth audio streaming, integrated with an audio processor, codecs, and a serial control interface, it offers a comprehensive solution for applications requiring both audio playback and data transfer wirelessly.

audio + data Bluetooth module

Bluetooth audio + data modules are suitable for scenarios like a smart home speaker system, where it can stream high-quality audio from Bluetooth-enabled devices while concurrently exchanging data with other smart devices in the network.

How Does a Bluetooth Module Work

Bluetooth networks, or piconets, employ a master/slave model to regulate data transmission. A piconet is an ad hoc network of wireless user devices using Bluetooth technology protocols. A single master device can connect with up to seven slave devices within a piconet. The following figure shows the connection between master and slaves in 2 piconets.

Bluetooth network

Each Bluetooth device possesses a unique 48-bit address, known as the BD_ADDR, displayed as a 12-digit hexadecimal value. The upper 24 bits represent an organization's unique identifier (OUI), identifying the manufacturer, while the lower 24 bits contribute to the device's uniqueness.

To establish a Bluetooth connection, there are three stages:

1. Devices discover each other by one sending an inquiry request, and others responding with their address and potentially their name.

2. After the inquiry, devices initiate the connection process, requiring knowledge of each other's addresses.

3. Devices enter the connection state, with options for active mode, sniff mode (power-saving), hold mode (temporary sleep), and park mode (deep sleep).

Factors in Developing a Bluetooth Module or PCB

Bluetooth module developing

To develop a Bluetooth-enabled device, the most important step is to fabricate a printed circuit board that can integrate the Bluetooth module with the main circuitry. The following factors are given to empower makers and engineers to develop Bluetooth PCB:

1. Bluetooth Module Selection

2. Circuit Design Considerations

3. PCB Layout Guidelines

4. Board Fabrication Process

5. Assembly and Testing

1. Bluetooth Module Selection

Deciding which Bluetooth module to develop is a pivotal step in the development process, and several criteria should be considered, such as Bluetooth version, data rate, range, sensitivity, power Modes, operating Voltage, FCC/CE certifications, and size. By carefully considering these factors, developers can make informed decisions at each stage of Bluetooth device creation.

2. Circuit Design Considerations

The circuit design of a Bluetooth PCB encompasses several key blocks, each playing a crucial role in ensuring seamless functionality. The major components include:


The antenna is designed on the edge of the PCB, facing forward as much as possible, and avoiding iron structural parts around it. It is grounded over a large area with multiple holes. Components, traces, and copper are not suggested to be placed around the antenna and its back.

Microcontroller (MCU)

The MCU interfaces using UART/SPI execute the primary application firmware.

Power supply

A dedicated power supply converts input and voltage to clean, regulated power for the Bluetooth module, MCU, and other ICs.

Indicators and controls

LEDs offer visual feedback on Bluetooth status, while buttons or switches empower users to control pairing, discovery, and other Bluetooth-related actions.

Support circuits

Additional components such as a crystal oscillator, capacitive touch sensors, audio codec, and battery charger may be necessary based on the specific application requirements.

External connectors:

Integration of connectors for USB, audio, sensors, etc., as needed for I/O expansion and connectivity.

3. PCB Layout Guidelines

For the effective functioning of a Bluetooth PCB, cautious attention must be given to the following considerations:


Optimal component placement is vital to minimize track lengths and reduce noise coupling.


Keep power and ground traces wider, utilize multiple vias when changing layers, and avoid placing noisy digital traces next to sensitive RF traces.

Impedance control

High-speed traces like USB must be impedance matched, typically to a 90Ω differential.

Antenna design

For compact Bluetooth devices, printed antennas etched onto the PCB offer sufficient performance without the need for external antennas.


Deploy multiple 0.1uF ceramic bypass capacitors near every IC to filter noise on the power distribution.


Establish a solid low-impedance ground plane to minimize ground noise and provide shielding.

4. Bluetooth PCB Fabrication

Bluetooth PCB

After designing the circuit, it is time to develop the PCB circuit board. Following are the suggestions to keep in mind while fabricating the PCB:

  • Choose an experienced PCB manufacturer capable of delivering quality at a reasonable cost.
  • Export fabrication files (Gerbers) from layout software, containing PCB etching, drilling, silkscreen, solder mask, and layer information.
  • Validate the footprint compatibility of chosen parts before fabrication.
  • For mass production, panelized multiple PCBs together on larger panels, later separated after completion.
  • Include lamination of copper layers, lithographic printing of etch patterns, etching, drilling, plating, solder mask application, silkscreen printing, and scoring/routing.
  • Finished PCBs should be shipped in protective packaging to prevent damage during transportation.

You can view the PCB fabrication process from the one-stop PCBA manufacturer PCBONLINE.

5. Bluetooth PCB Assembly and Testing

Finally, after PCB fabrication, the assembly and testing of Bluetooth modules include:

  • Procurement of different parts
  • Solder paste application using SMT stencil
  • Component placement
  • Reflow soldering and AOI (automatic optical inspection)
  • Coating for reliability in demanding environments
  • Comprehensive testing of Bluetooth functionality, IC programming (microcontroller), electrical performance, and device operation

The comprehensive PCBA manufacturing process ensures robust and reliable Bluetooth modules.

One-Stop PCBA Manufacturer for Bluetooth Modules

PCBONLINE is an EMS (electronic manufacturing service) supplier providing one-stop PCB fabrication and assembly for Bluetooth modules. It offers R&D, prototyping, PCB fabrication, component sourcing, PCB assembly, PCBA value-added, and box-build assembly to various PCBA modules and electronic products.

PCBA module manufacturer

Founded in 1999, PCBONLINE has two large advanced PCB manufacturing bases, one PCB assembly factory, and an experienced R&D team for PCBA modules including Bluetooth modules.

Advantages of PCBONLINE in Bluetooth modules:

PCBONLINE has strong PCB manufacturing capabilities for Bluetooth modules, proving FR4, high-frequency, flexible, rigid-flex, HDI PCBs, etc.

In PCB assembly for Bluetooth modules, advanced processes such as 3D solder paste inspection, 3D X-ray inspection, nitrogen reflow, and 3D AOI are available.

The professional R&D engineers at PCBONLINE with rich experience in Bluetooth module development and DFM.

No minimum quantity limit for Bluetooth PCBA orders. Proving one-on-one engineering support throughout the process.

For bulky production orders, PCBONLINE provides Bluetooth module R&D, sampling, and functional testing for free.

The electronic manufacturing at PCBONLINE is certified with ISO 9001:2015, ISO 9001:2016, IATF 16949, RoHS, REACH, UL, and IPC.

Besides Bluetooth modules, PCBONLINE has many successful R&D and manufacturing examples, such as battery cell contact systems, projectors, false eyelash UV disinfection boxes, etc. If you have issues with Bluetooth PCBA or want to get a quote, send emails to info@pcbonline.com.


This introductory article about Bluetooth modules and technology lists the types of Bluetooth modules and factors in their development. A Bluetooth module is a consumer electronic PCBA that features high density, small size, and strong functions in data and audio transfer. This article also introduces a one-stop PCBA manufacturer PCBONLINE. If you need Bluetooth module R&D, PCB, and PCBA, feel free to chat with PCBONLINE from the online chat window.

© This article is an original work of the PCBONLINE team. Please indicate the author PCBONLINE if you reprint. If the article is reproduced without permission or indicating the author's source, PCBONLINE reserves the right to investigate the infringement.
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