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 comared 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.
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 ICs 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.
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.
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.
Continue to Part 2: BLE module selection guide