Communications in a low energy Internet of Things

By Heiner Tendyck, Principal Engineer for Solution Marketing and Strategic Business Planning at Toshiba Electronics Europe

Cut the Wires; Now Lower the Power The Internet of Things (IoT) is developing quickly, creating an ‘always on’ interconnected world that requires low-cost, highly integrated smart devices capable of seamless intercommunication and low-power operation. Bluetooth® is proving a valuable solution in the IoT development scene thanks to advantages that range from certified interoperability to low design risk and rapid time-to-market. The emergence of Bluetooth Low Energy (BLE) has further strengthened the role that this technology can play in driving IoT designs forward.

Bluetooth Low Energy, now branded Bluetooth Smart by the Bluetooth SIG, satisfies important requirements for IoT connectivity. It combines advantages such as long communication range, ubiquity and low implementation costs, which are synonymous with Classic Bluetooth, yet has significantly lower power consumption thereby enabling applications to run for longer from a small and lightweight battery such as a coin cell. The Bluetooth SIG notes that analyst firms all over the world recognise Bluetooth Smart as a key enabler of the Internet of Things.

Bluetooth Smart can be used in a number of ways to connect the “fingers” of the IoT to the Internet. Bluetooth Smart IoT devices such as sensors, for example, can communicate with Bluetooth Smart Ready smartphones, or PC dongles. Native support for Bluetooth Smart is already provided in popular desktop and mobile operating systems, such as Windows® 8, iOS, OSX and Android. The Bluetooth-enabled smartphone, often labelled Bluetooth Smart Ready, is widely recognised as a key part of the IoT-human interface. BT SIG makes sure that such labelled phones comply to the standard and are interoperable to other BLE nodes.

The extremely low power consumption intrinsic to Bluetooth Smart now opens up many new opportunities to create different types of hubs for use in homes, in-car, in industrial scenarios, or in medical applications. Home automation is expected to be the fastest growing market for Bluetooth Smart technology over the coming years, and is likely to encourage integration of Bluetooth Smart technology into gateways such as routers or set-top boxes thereby enabling continuous remote monitoring and control of various nodes around the house. These may include door locks, ambient-light sensors, thermostats, switches and other devices to be controlled by a simple mobile or home gateway.

The maximum specified transmit power of +4dBm is enough to give Bluetooth Smart devices a communication range of up to 50 metres. This gives designers great flexibility to take advantage of Bluetooth for industrial sensing, such as collecting data from machines installed on a factory floor or from equipment such as autonomous vehicles used to monitor conditions in environments that are inaccessible or dangerous to human health. End users in industry may connect to Bluetooth-enabled equipment using a range of devices including Bluetooth-enabled PCs, smartphones, or dedicated sensor hubs.

Bluetooth Smart also has numerous potential automotive applications. These include low-power remote controls as well as improved keyless entry systems as well as many connected applications around the vehicle such as monitoring the driver’s health and ability to control the vehicle.

Bluetooth Smart is a good fit with the IoT applications that have been envisaged so far, as these often need to send short bursts of data at infrequent intervals. A Bluetooth Smart device can wake from deep sleep, send data, and return to deep sleep in three milliseconds. The same cycle can take up to 20 milliseconds in Bluetooth Classic. BLE also enables connection set up within 100msec, compared to several seconds in BT classic. Smaller packet size and fewer RF channels also contribute to savings in power consumption compared to Classic Bluetooth. The overthe-air data rate of 200-300kbps provides plenty of speed to transmit IoT messages quickly allowing the application to return rapidly to deep sleep.

Building Bluetooth Low-Energy Applications

A Bluetooth device may be expected to connect with Classic Bluetooth as well as Bluetooth Smart devices (“Dual Mode”). This type of device is known as Smart Ready, and has built-in support for both standards. A dual-mode IC such as Toshiba’s TC35661 Bluetooth Dual Mode single-chip LSI is suitable for this type of application.

The TC35661 has a low-power architecture and is fabricated using a power-efficient 65nm RFCMOS process. It can operate with a serial connection to a host MCU (in Dual Mode) or in stand-alone mode (single profile mode). In single profile mode, the upper stack including API, selected profiles and L2CAP as well as the HCI, Link Controller (LC), Link Manager Protocol (LMP) and RF drivers are embedded on the TC35661, as illustrated in figure 1. In this case the embedded stack and protocols are pre-certified, which enables developers to avoid the cost and time overheads associated with Bluetooth certification process.

Running in Dual Mode the device is managed by an external host processor across a serial UART interface and the embedded API. Toshiba offers driver software for these external hosts featuring high-level abstracted APIs e.g. for SPP or BLE GATT to enable dual mode functionality and take care of device initialisation, connection setup and communication with remote devices. Figure 2 illustrates how this high-level API helps to minimize development effort.

Bluetooth Smart-Compliant Integration

The Toshiba TC35667 is an ARM-based Bluetooth Smart Compliant IC created for use in Bluetooth Smart hubs or Bluetooth Smart devices such as sensors capable of connecting to a Smart or Smart ready hub. It integrates a complete Bluetooth 4.0 (BLE) modem and RF block, and has ultra low-power consumption with peak current 5.9mA (typical) in transmit mode, and deep-sleep power consumption of 0.1µA typical. The Generic Attributes (GATT) profile and Generic Access Profile (GAP) that allow Bluetooth devices to accomplish basic interactions smoothly are built-in. The user application can reside in the 32KByte programming area in the external EEPROM and are bootloaded from there.

The GATT profile supports Bluetooth Smart central and peripheral modes, allowing the TC35667 to interact with a host microcontroller when used in a hub application, or to perform in standalone mode when used as a device such as a sensor. Figures 3 and 4 show how the device can be used in standalone mode with minimal external components, or combined with a host microcontroller in a hub application.

Starter kits are available to help accelerate development of new Bluetooth Smart and Smart Ready applications, including IoT applications, using the TC35661 or TC35667.

Custom Profile Support

As the Internet of Things continues to evolve, new applications are expected to emerge that will require new profiles. A variety of BT SIG BLE profiles suitable for industrial, medical and automotive applications are already specified by the Bluetooth SIG and can be provided by Toshiba, including the Blood Pressure Profile, Heart-Rate Profile, Thermometer, Location and Navigation Profile and Proximity Profile. Toshiba has also created a proprietary SPP over BLE Profile which is not part of the BT SIG BLE profile set. Toshiba’s high-level API not only helps implementing existing profiles but also simplifies development of new proprietary profiles thereby maximizing flexibility to create more advanced IoT applications in the future and differentiate against other system solutions.

The Future:

Enhancing Usability The Bluetooth Smart Compliant IC functionality can be further extended to help simplify the set-up of IoT applications by integrating circuitry to operate a low-power NFC (Near-Field Communication) tag. Adding NFC functionality enables devices to be paired simply by touching. Devices can also take advantage of the NFC link to exchange small quantities of data, reducing system power consumption further below BLE level. Toshiba is currently finalising an NFC-Forum compliant Bluetooth/NFC Combo IC, which is pin-compatible with the TC35667 single-Bluetooth IC and includes features ensuring low power consumption, rapid wake-up from standby, and smooth handovers between NFC and Bluetooth communication.

Conclusion

By offering low power consumption, low cost and convenient ease of use, the Bluetooth Smart standard has quickly become recognized as a major enabling technology of the Internet of Things. IoT applications and markets are evolving quickly, and engineers need a combination of ultra low-power ICs and software and development support to ease integration, accelerate design and provide the flexibility to adapt and customise for the future.

www.toshiba.com


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