Designing with Bluetooth Mesh: Chip or module?




To this point, this article series has covered an overview of Bluetooth mesh and how to select a device for an application. In this final installment, we will discuss whether discrete devices or a module should be used in a design.

The decision of whether to use discrete devices or a module has a very high impact on product’s success. Bluetooth Mesh is enabling IoT and connecting myriad things wirelessly that were either previously wired or not connected at all. A perfect example would be a light bulb. Most manufactured bulbs for consumer applications were controlled using a wall switch. Adding Bluetooth Mesh connectivity to these devices requires expertise that never existed inhouse.

In short, manufacturers new to wireless connectivity face the decision of whether to invest heavily in developing their own wireless expertise or implementing Bluetooth Mesh as a stand-alone module and concentrating resources on functional expertise. The following sections explore the complexities introduced by wireless connectivity and how to make the right decision while selecting between a module and discrete solution for your products.

While adding Bluetooth Mesh to a product, end-system cost and complexity are impacted by factors such as board design complexity, regulatory certifications, Bluetooth qualification, declaration, and listing. Let’s go through each of these one by one.

Designing Bluetooth Mesh-enabled products with discrete devices

Designing a board for Bluetooth Mesh requires expertise in RF board design. Specifically, Bluetooth Mesh requires an antenna and matching network. These add complexity to the board design. Appropriate antenna design and ground clearance are needed to achieve good antenna gain. Power supply-related components such as a decoupling capacitor are needed. Efficient routing is critical for stable system operation, and extra care is needed to ensure these circuits do not interfere with antenna performance. Clocks/crystals need special attention too. Any drift in frequency can result in packet loss, impacting throughput and power efficiency.

To handle all these complexities, experienced RF board designers are needed. To maintain in-house RF design expertise can be costly as the skills required are quite specialized. In addition, the board may require several spins it can provide the required performance.

The next challenge after board design is meeting regulatory certifications. Every Bluetooth Mesh product needs to receive one or more RF regulatory certifications based on the countries in which it will be sold.These certifications are ensure radiation levels are within acceptable limits and also that the operating frequency does not fall within any prohibited frequency band.

Almost every country has its own RF regulatory certification body. To sell a Bluetooth Mesh product in the United States, product need to obtain the Federal Communications Commission (FCC) certification. For Europe, product must obtain CE (Conformité Européene) certification. Japan requires MIC (Ministry of Internal Affairs and Communications) while Canada requires ISED (Innovation, Science and Economic Development), earlier known as IC (Industry Canada) certification.

If the product meets the RF requirements for these four regulatory certification it is likely that it will meet regulatory requirements for all other countries as well. However, each of these certifications requires a significant amount of testing. Tests are performed in labs approved by these regulatory bodies, meaning that not only certification, but failure as well, comes at a price. For example, if the board fails, it requires changes need to be made to the board design/components, then take it to the lab again. For each Bluetooth Mesh product, this certification can cost more than $20,000 if done right the first time. Beyond the certification cost, product rollout will be delayed based on the extra time spent for during each round of certification. In this competitive market time to market is essential for success.

Bluetooth Mesh products need to undergo testing at a Bluetooth SIG qualified test facility to be able to use the Bluetooth trademark. Product qualification ensures that products are interoperable with other Bluetooth Mesh devices. Also, declaration and listing are required to secure the legal rights to use Bluetooth brand name on the product and to market it as a Bluetooth Mesh product.

Designing Bluetooth Mesh-enabled products with a module

Before we get into the advantages and disadvantages of using a module in a design, let’s quickly review what a module is and what it offers. Modules are generally offered as a broad in terms of size, antenna type, and cost. Modules integrate most or all key components needed for Bluetooth Mesh device’s operation while achieving the performance required for the application. Using a module eliminates the complexity of RF layout design. There is an added cost for using a module, compared to build a discrete solution, but modules are the fastest and easiest way to add Bluetooth Mesh connectivity to a product if there is a lack of inhouse expertise.

The biggest advantage of using a module is that system designer can leverage the expertise that the module manufacturer has learned and gained over years. This expertise can be extensive, given that modules are used in multiple products across multiple industries. In short, system designers can access to all of the manufacturer’s expertise without having to make the upfront investment in developing inhouse RF expterise.

Note that some modules are fully-certified and eliminate the hassle and cost involved with securing the required regulatory certifications. For some designs, a small change in the board layout or component means a complete re-certification.

Selecting between module and discrete solution

Modules are appealing for all applications from R&D and certification point of view. The tradeoff is that they come at an additional cost compared to discrete devices. Traditionally, OEMs use the break-even point to determine whether to buy or build. This number balances the increased cost per board compared to the investment in time and money of developing inhouse expertise.

Because of the complexity and various costs involved, Bluetooth Mesh modules can be effective up to volumes in the range of 250K units. For higher volumes, a discrete devices-based approach is typically more economical. For many OEMs, however, price is not the only consideration. Overall, adding connectivity may not be that important in systems that are complex or require some application-specific certifications. The OEM would prefer to keep engineering resources focused on the company’s true value-add. There is also the added consideration of what it will take to maintain future upgradability of connectivity and the board re-spins and certifications that follow.

For any new product for which initial volumes are unpredictable, it is usually a good idea to start with a module. This keeps investments low. If product volume goes up, the product can migrate to a solution based on discrete devices. If this is the strategy, it is important thing to select a module that provides an easy transition path to discrete devices.

If the Bluetooth Mesh IC and module are provided by different vendors, migrating may require different development tools, increasing the complexity needed to make changes in the firmware. Selecting a vendor that manufacturers both IC, as well as the module, provides a significant advantage. In most cases, they also ensures that both discrete devices-based solution and module use the same development tools and software development kit. Thus, the firmware may not need any changes to complete this migration. This means you only require only a board re-spin and certification to bring down your products cost.

For example, Cypress provides IC as well as modules in various sizes and antenna options. discrete solution and modules based on that IC are supported in the same development tool providing a seamless path for migration. For example, the table below shows the example of CYW20819, a Bluetooth Mesh device, from Cypress and how it compares to its respective module. 

CYW20819 CYBT213043-02 (CYW20819-based module)
Software Development Kit (SDK) BT SDK BT SDK
Integrated Development Environment (IDE) ModusToolboxTM ModusToolbox
Transmit Power 4 dBm 4 dBm
Antenna No PCB
24-MHz crystal No Yes
Regulatory Certifications No FCC, ISED, MIC, CE

As shown in the table, both IC and module are supported by the same SDK and IDE that makes it easy to switch between module and discrete devices without additional investment in the firmware. At the same time, the module supports all device feature and provides all the advantages as integrated crystal and antenna and regulatory certifications.

Fully-certified modules can be a starting point for every Bluetooth Mesh product. For <250K units, the module-based solution is likely to be more economical compared to a discrete devices-based design. For higher volumes, discrete devices-based design can be more cost effective but require significant expertise to developed inhouse or outsourcing cost. If starting with a module, it is important to select a module that provides an easy migration path to discrete devices as volumes increase.

Read the previous articles in the “Designing with Bluetooth Mesh” series:
Part 1: Nodes and feature types
Part 2: Node communications
Part 3: Privacy and security
Part 4: Device requirements

Sachin Gupta is Product Marketing Manager at Cypress Semiconductor. He has more than 11-years of experience in product marketing and applications engineering roles. He has managed USB Type-C, Wi-Fi, Bluetooth, SoC and FPGA products in his product marketer roles. He can be reached at sachin.gupta@cypress.com.

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Original article: Designing with Bluetooth Mesh: Chip or module?
Author: Sachin Gupta