Making Bluetooth Low Energy (LE) work for you
Well established as the preferred method of connecting accessories to mobile devices, Bluetooth Classic offers a very easy to use service where connected and paired devices are remembered and automatically reconnected when in range. At first sight, Bluetooth Classic would appear to be a useful technology for devices in the IoT space. However, Bluetooth Classic has a couple of major drawbacks that severely limit its usefulness for general IoT applications.
Written by Simon Bliss, Customer Applications Support Engineer, Alpha Micro Components.
The first is the connection limit of just seven devices per host. Whilst this is ok in the traditional mobile environment where the user will only be adding a few accessories, in the IoT space, even a simple connected home would probably exceed this connection limit.
The second problem is one of power consumption. Bluetooth Classic systems require connected devices to remain constantly powered so they can receive polls and commands from the host. This latter point makes it impractical to design small, battery powered sensors that have a button cell lifetime measured in years.
Bluetooth LE to the rescue
Bluetooth LE has been developed to overcome those drawbacks and provide additional features that transform Bluetooth into a very attractive solution for many small, low data-rate devices.
With Bluetooth LE there is no connection limit and the receiver is no longer required to remain powered up. This brings a huge power saving and simple Bluetooth LE devices can indeed run for years on a simple button cell.
Much of the Bluetooth LE protocol was originally developed by Nokia as their Wibree system but this was merged to the main Bluetooth standard in 2010 and is now fully integrated into the Bluetooth 4.0 specification as Bluetooth LE.
In addition to the freedom of limitless connections and extreme low power operation, Bluetooth LE includes three basic operating modes that open up tremendous opportunities.
The three modes are point-to-point, broadcast and mesh networking. Point-to-point is a connection between a master node and a slave node. Once connection has been established the master puts the slave into sleep mode but tells it when next to wake up.
The master also goes to sleep but wakes up in time to receive the requested data from the slave. The master is not limited to a single slave and can link with several slaves to form a star network. This wake/sleep process repeats to provide a robust data link with very low power consumption due to a transmit time that is typically just 3ms.
The BLE Broadcast mode, as its name suggests, is used to broadcast data to any device that’s within range and is at the heart of the popular iBeacon, AltBeacon and UriBeacon services.
These have many applications, such as triggering phone alerts to advise customers of a special offer or delivering information as a visitor approaches a museum exhibit.
The most recent addition to the Bluetooth LE family has been the arrival of mesh networking enabling M:M (Many-to-Many) communications (See Figure 1). The management of messages across the mesh network is handled using a publisher/subscriber style protocol that allows an individual node to receive/send from different groups.
This has sparked plenty of interest, with the commercial building sector being a prime example. The installation of Bluetooth LE enabled lighting in a mesh network has the potential to eliminate conventional light switches and the associated wiring and so facilitate centralised, intelligent lighting control. This would deliver significant installation and maintenance cost savings for commercial buildings. Mesh networking has many other applications in business and is a solution where large numbers of short-range connected devices are deployed.
Figure 1: M:M communications
Laird Technologies has been a key player in the Bluetooth field for many years and has a low cost, yet very advanced offering available with its BT900 modules. These are full, BT v4.0 Dual Mode, compliant modules supporting Bluetooth Classic and LE.
To speed development and help reduce design costs, the BT900 uses a SoC (System on Chip) approach that includes a Cortex-M3, 32-bit processor along with flash memory, supporting hardware and a choice of antenna. The BT900 also provides access to the M3’s GPIOs and can handle common communications protocols such as SPI, I2C, etc.
There is even provision for analogue signal measurement using the dual-channel ADC (Analogue to Digital Converter). As a result, using the Laird BT900 can significantly reduce the BOM cost and development effort for your product. This level of integration avoids the need for a dedicated microcontroller and many devices could comprise just the BT900, a power source and a sensor.
To make life even easier for developers, the BT900 also includes Laird's event-driven, smartBASIC programming language. Development with smartBASIC is straightforward and aided by the many downloadable examples that are available from the Laird support site. These serve as a useful starting point for many common applications. Once written, the smartBASIC code is compiled and downloaded to the BT900 via the UART or OTA (Over The Air). In addition to the excellent software support, Laird offers the attractively priced DVK-BT900-SA development kit. This comprises a BT900 with a selection of accessories and provides easy access to the BT900 and all its GPIOs to speed system development.
There is also the BT900-US, a USB Dongle that includes a BT900 module and can be used to add custom Bluetooth functionality to any device with a USB port.
Bluetooth LE provides a sophisticated and scalable solution for low-power, connected devices and has tremendous potential. That potential can be realised through the Laird BT900 modules with their integrated microcontroller and event driven smartBASIC programming language.