By: Matt Rose, Western Region Wireless Specialist, Future Connectivity Solutions
Bluetooth Low Energy (BLE) is the hottest protocol on the market now. In little over five years it has established itself as the de facto point-to-point wireless standard for a number of low power and small-footprint applications. With billions of BLE-enabled smart devices on the market, the list of applications for this protocol is unlimited, with everything from the lowly kitchen toaster to high-end automobiles being considered for this new form of connectivity.
When deciding on which BLE (also marketed as Bluetooth Smart) solution is right for your application, you must consider a number of attributes: form factor, key electrical specifications, desired functionality, software development tools and technical support.
The most significant decision involves whether to pursue a module or a chip form factor. A module typically consists of the BLE-packaged device with protocol stack on board, a number of external components such as capacitors, resistors or memory and some type of antenna solution such as a chip, PCB trace or an RF output trace. While some applications such as hearing aids and other wearables require a package less than 3 x 3mm (Figure 1), most applications can take advantage of a module solution (Figure 2).
Typically it is recommended, unless there is a footprint requirement, that customers with estimated annual usages (EAUs) of less than 150k utilize a module solution. The benefits of a module include quicker time-to-market, less RF test equipment and engineering resources for prototype evaluation, inherent manufacturing quality and FCC certification for intentional emissions (Figure 3). FCC certification for unintentional emissions will still, most likely, be required but significant savings are found by using modules certified for intentional emissions and Bluetooth Special Interest Group (SIG) RF testing requirements. An additional benefit is that many module suppliers provide turnkey software implementations which again saves on total cost-of-solution and improves time-to-market.
Engineers are fascinated with comparing electrical specifications. Key specifications when evaluating BLE solutions are output power, effective range and antenna type, average and peak current draw, MCU processing power and the amount and type of memory available for applications, profiles and services.
The Bluetooth specification limits the maximum output power for BLE to +10dBm but many manufacturers limit their maximum output power to a lower value in order to save on average current draw. Maximum values of +7, +3 and 0dBm are typical. Some solutions offer variable output powers down to spec-required -20dBm. This is useful to limit the range when performing secured pairings to save on battery power in particular applications and to decrease the effective range in applications such as BLE-enabled door locks (see Figure 4). Typical ranges for these modules are 75 feet to 300 feet, noting that the effective throughput drops as the range increases. The maximum achievable range is dependent on the environment, the output power, the receiver budget (typically -90dB to -100dB), the antenna type and the nature of the other nodes in the network (i.e. iOS phone, Android phone, another module).
Current draw is an important factor when deciding on a solution, but it is important to factor in time and total average power when comparing solutions. Peak power in receive and transmit mode is important but so is sleep and dormant mode currents, especially for applications like beacons which can use the advertising packet to broadcast data. Peak power current draw typically varies from 5mA to 20mA and dormant/deep sleep currents range from 150nA to 600nA. The total average current will vary depending on specific applications due to the time component of the power profile. To facilitate the calculation of battery use in a product lifetime, some manufacturers provide tools to measure current and power usage as well as power profiles (Figure 5).
Another key factor when considering your BLE options is MCU speed. 16MHz clocks are common but some manufacturers have clock speeds of up to 48MHz. Higher clocks can be important in applications where throughput needs to be maximized, such as in emerging hearing aid audio applications or in driving a string of flashing LED lights.
Available memory type and amount can also be a driving factor. Some solutions utilize on-chip one time programmable (OTP) memory while others utilize flash or EEPROM memory. The amount of available on-chip memory for the application and profiles can vary from a few kB up to 256kB, and even more can be available if external memory is implemented. The amount of available memory affects the size of the application that can be implemented as well as the number and size of profiles and services.
A key area in evaluating a BLE solution is functionality. This includes plug-and-play capability, number and type of public profiles and services available, over-the-air (OTA) firmware upgrade capability, proprietary serial port profile (SPP) emulation and meshing capabilities. Companies with minimal software staff or projects with short timelines will benefit from a plug-and-play BLE solution (Figure 6). These modules typically come with an AT-command set or a scripting feature to make implementing BLE simple (Figure 7). Most solutions come with public profiles and services, while all are capable of creating private profiles and services. Public profiles are those as defined by the Bluetooth SIG and include health-related profiles for heart rate, glucose, and blood pressure monitoring as well as sports-related profiles for bicycling and running. The benefit of public profiles and services is that they are interoperable between vendor products and their unique addresses are only 16-bits long. However, most customers will create private (or custom) profiles and services and to make certain the addresses are unique they are 128-bits long.
An OTA firmware upgrade option may be important as well for non-disposable or non-consumer applications. In these situations, external memory is utilized to replace the entire application and profile layer, or a patching scheme can be implemented in order to minimize the amount of memory required for the upgraded firmware and where wireless standards such as Classic Bluetooth (version 3.0 and earlier) and Wi-Fi are data-pipe or cable-replacement protocols with effective baud rates of 1Mbps and up; BLE is more of a client-server model, where data is gathered by the peripheral and then transferred upon request to the client. The strength of BLE is in long battery life, low current applications instead of high-throughput applications such as high-quality audio or video. However, many customers have requested simple data-streaming functionality, so suppliers have implemented proprietary SPPs for streaming data at low baud rates. Depending on the application this may provide an effective throughput of 3kbps to 75kbps.
For some applications, such as lighting and inventory management, a mesh capability may be desired. Proprietary mesh solutions are currently available and it is anticipated that the next generation of Bluetooth specification will include a standardized mesh profile. The currently implemented mesh solution by CSR uses a flooding-mesh approach where a 20-byte data “envelope” is broadcast to each node in the network (Figure 8).
Other attributes to consider when implementing BLE are software tools and design support. Most BLE suppliers provide integrated development environments (IDEs) whose interfaces and capabilities offer differing appeal. Most IDEs are C-based compilers with significant learning curves but one unique solution offers a graphical user interface (GUI) approach which quickens time-to-market significantly (Figure 9). The source of design and production support is also an important factor when considering a supplier. Some solutions rely on internet forums for support, while the Future Connectivity Solutions group provides personal technical support for its franchised BLE solutions.
One last consideration for all manufacturers of BLE-enabled products is the Bluetooth SIG’s End Product Listing fee. This fee is required for all BLE-enabled devices and the cost is based on the manufacturer’s size, maturity and the number of products to be listed. For more information on how the fee will be calculated for your product, visit www.Bluetooth.org and look for the “Qualification & Listing” link.
In summary, many attributes must be considered when choosing which BLE solution is right for your application, regardless of whether the product is an inexpensive kitchen appliance or one whose purchase requires loan approval from a bank. Form factor, electrical specifications, functionality, software development tools and technical support are all significant parameters to be evaluated. With so many BLE devices on the market and even more on the horizon, finding the right solution can be as simple as consulting with your Future Connectivity Solutions team.