For developers of IoT devices, Bluetooth Low Energy (BLE, aka, Bluetooth Smart) has many advantages. As the name implies, low energy consumption is among them, as is the availability of complete BLE modules that provide essentially drop-in wireless connectivity. The key to maximizing the benefits of BLE modules, though, is to play to BLE's strengths.
By now most developers have at least heard of Bluetooth. The wireless protocol, named for the Viking who converted the Danes to Christianity, originally appeared in wireless audio streaming applications. The BLE version, which became available with Bluetooth v4.0, targets low-power applications by reducing transmitter power and data rate compared to the core specification. (Bluetooth's current version is v4.2.) Unlike the full core specification, BLE is limited to a 50m range and 0.27 Mbps.
Developers new to using the BLE standard should treat these reductions are key points to consider in setting system expectations. Just because a design uses the BLE protocols does not mean that low energy consumption is guaranteed. The design's operating range and data rate have a role to play in establishing energy demands, as does the system's overall communications strategy. Developers will need to consider these factors carefully to achieve the promised low energy attribute.
There are other factors to consider when designing a BLE IoT device, as well. The user interface (UI) for the device, for instance, can involve built-in buttons and displays as with traditional embedded systems. Alternatively, designs can depend on an app running on a smartphone for its UI. Similarly, a device can use either a mobile phone or a fixed gateway device as its link to the Internet.
Developers can also choose to have their BLE devices always pair with a master to establish bidirectional communications, or operate in “advertising mode” for unverified one-way transmission of data in small amounts (around 30 bytes). Working in the advertising mode allows a BLE device such as a sensor to periodically send data to a listener without using the energy needed to establish and maintain a full, two-way link. The advertising interval and use of advertising modes such as scan request (which allows a listener to request additional data from the device) can significantly affect the energy use of a BLE design, however.
Design Savings
As with any type of wireless communications, BLE places significant demands on a design team's skills, particularly in the radio frequency (RF) arena. There is some help available. Integrated radio/microcontroller devices such as the Nordic Semiconductor nRF52832 and the Silicon Labs BGM12x can handle details like RF signal generation and detection, modulation, and BLE communications protocols all in an off-the-shelf package, but teams will still need RF expertise to handle factors such as board layout and antenna design. Once a design is complete, teams will then need to take their device through certification processes to prove compliance with various national regulatory standards as well as with the Bluetooth interoperability standards.
An SoC provides a processor and RF circuitry for BLE, but is not a complete communications system.
This is where BLE modules come into the picture. A BLE module is a fully-contained BLE transceiver with controller and built-in antenna that is preprogrammed to handle all a design's radio interactions. Some modules are available that serve purely as an IO device for a host controller, making the BLE connection the logical equivalent of a serial port for design purposes. Other modules are able to operate in a stand-alone (hostless) manner and make available their processor and other IO resources to developers to run application code, as well. Both module types come precertified with both the Bluetooth SIG (for interoperability) and various regulatory agencies.
An SoC-based module like this Laird BL652 SoC forms a drop-in BLE communications component, including antenna.
The full design and precertification of modules has a substantial effect on the cost and effort of creating a BLE-enabled IoT product. The need for RF expertise, for instance, drops dramatically as the module is essentially a drop-in component that already has the tricky details resolved. Similarly, precertification eliminates much of the effort and cost to get a product approved by regulatory agencies and listed with the Bluetooth SIG as a valid Bluetooth device.
Modules are available from a variety of vendors in many different configurations.
Module vendors warn, however, that the module's precertification does not entirely eliminate the regulatory barrier. The entire design, not just the radio subsection, must meet standards on unintended RF emissions. So developers must still ensure the rest of their design is certifiable and prove compliance through testing. Similarly, though the module is BLE certified, the end product using that module still needs registration with Bluetooth SIG.
Still, and perhaps most importantly, bypassing RF design and certification efforts by using a module can substantially reduce a project's timeline and get a product to market faster than a chip-based design. This time-to-market advantage along with the reduced design effort combine to provide a considerable cost advantage to using modules. In many cases that advantage can far outweigh the two weaknesses modules have compared to chip-based design: size and unit cost.
Chip versus Module
As can be seen in the above two photos, BLE modules are much larger than BLE SoCs. This makes sense, given that the module is most likely built around an SoC in the first place. But the module also contains additional components, interface and power conditioning circuitry, an antenna, and an RF shield, as well as being designed to be easy to drop into the IoT device design. While an SoC-based design would probably also have many of these elements, it might not need them all, lowering material costs. Further, the designer has control of parts selection, orientation, positioning, and the like. Thus an SoC-based design can be much more compact than one based on a module. This can also result in reduced PCB cost.
So far as unit cost is concerned, an analysis from Silicon Labs shows that their BLE module costs on the order of $3.07 in 100,000-piece quantities while their SoC costs as little as $0.99. For consumer products especially, that price difference can have a substantial effect on a product's profitability. When production volumes get into the millions per year, even a one-cent savings represents $10,000 or more on the bottom line.
If the module's size is problematic to the product design, as, say, might be the case with a wearable IoT device, then a BLE SoC might be the only practical choice despite the additional design time and effort involved. With cost, however, the choice is not as clear cut. The Silicon Labs analysis looked at total cost, including design and certification effort and lost market opportunity as well as materials cost, and calculated the break-even point for SoC versus module-based designs. While a specific result depends on several assumptions, it will take a total production of several 100,000 units to make an SoC-based BLE device design more cost effective than a module-based design
Given the design simplification and cost advantages that modules bring to BLE IoT designs, the next question to ask is which BLE module to use. Part two of this series will discuss the key selection criteria and design decisions that development teams should consider when choosing a BLE module, and provide access to a downloadable selection guide to help narrow the field.
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