Solving the connection problem between smart sensors and Bluetooth through near-field communication

　　Support for Low Energy (LE) data exchange is included in the Bluetooth specification version 4.0. Bluetooth Low Energy (BLE) is designed to support communication with data rates up to 1 Mbit/s, with distances up to about 50 meters, which is about 10 to 30 meters longer than typical Bluetooth. Bluetooth Low Energy (BLE) provides powerful credentials for connecting devices to the Internet of Things (IoT).

　　The device may only implement the BLE part of the Bluetooth specification, hence it is called Bluetooth Smart. For smart objects such as IoT endpoints, this is an ideal economical and energy-saving solution. On the other hand, devices like smartphones and tablets that support full Bluetooth specifications—not just LE, but also base rates and enhanced data rates (BR/EDR) up to 3 Mbit/s (now called Bluetooth Classic)—can interact with Bluetooth smart devices, known as Bluetooth smart devices.

　　All smartphones launched since the end of 2011 are smart. This allows developers to rely on the fact that a large number of potential users already have devices that interact with their products. These can be consumer products, such as smart lighting or environmental sensors in the home, or devices like smart sensors or machines in industrial settings. Industrial users can interact using their own devices, which are authorized by the company's BYOD (Bring Your Own) policy, or using designated mobile phones or tablets.

　　The ideal connection for smart objects at Shangtai

　　In addition to ease of interoperability, BLE offers several other important advantages as a connectivity technology for smart objects. Circuits and protocols can be implemented at low cost, and suitable software APIs are available for Windows, Apple, and Android devices. Small packets, short receive and transmission windows, and power schemes designed to maximize the time the radio spends in idle mode all contribute to extremely low energy demands and allow BLE devices to run from small coins for months or more. On the other hand, pairing Bluetooth devices is widely seen by consumers as a difficult process, potentially time-consuming and somewhat "hit or miss." Users trying to connect accessories to their phones usually need a reference manual to learn how to make the new device discoverable. Pairing usually requires multiple attempts, and security may be compromised, as few users change factory default keys to numbers that potential hackers cannot easily guess.

　　When a device has its own user input, this process is difficult to handle like with devices like buttons or switches, which are fundamental. In devices like IoT smart sensors, which may be completely headless, it can be even more difficult.

　　Paired with headless objects

　　To help overcome pairing difficulties, Bluetooth SIG has launched Secure Simple Pairing (SSP) starting from Bluetooth 2.0. SSP specifies four association models, including work, digital comparison, key input, and out-of-band (OOB). Key input and numeric comparison require users to enter a code or confirm that the two codes are the same. OOB is the best model for connecting headless devices without user interfaces. Just Works pairing uses the same protocol as digital comparison, but does not require user confirmation. While this can be used to pair devices without user interface keys or displays, it does not provide human protection in man-in-between security attacks. OOB pairing uses previously securely shared information instead of key input information.

　　Near Field Communication (NFC) can be used to share the data required for OOB pairing, thus providing a convenient and secure way to establish Bluetooth connections. NFC pairing is already supported in popular mobile operating systems, and by allowing the convenience of "tap pairing" when introducing new accessories like headphones or speakers to smartphones, consumer usage has been greatly simplified.

　　With built-in security devices, NFC can assist Bluetooth pairing with smart sensors without eliminating any of the widespread advantages of native BLE support on smartphones and tablets.

　　In addition to helping securely introduce new devices into the network, NFC can facilitate other interactions with headless IoT devices. Some examples include removing devices from the network, replacing old devices with new ones, and sending configuration data or retrieving information when Bluetooth connections are not activated. NFC also provides a way to wake up devices that have been completely powered off to maximize battery life and help connect them to Bluetooth networks.

　　Start the pairing process with NFC

　　Because when the host system loses power, passive NFC tags can communicate with the reader, and data such as network parameters and keys required for secure connection can be transmitted to the device before the first power-on. This can be done by tapping a new device on an NFC-enabled smartphone or gateway device (such as a home automation center). When the object is powered on, it can use a key to connect to the network and establish secure communication. Then, for security purposes, the key is removed from the label to prevent third-party interception. Similarly, NFC-enabled smartphones registered on devices can connect headless devices to the network with a tap. Other commands (such as resetting or disabling devices from the network) can be done in the same way, or by clicking to help replace or update the old device by copying configuration settings from one device to another.

　　The short communication range of NFC helps improve security and selectivity. Eavesdropping is very difficult when unauthorized parties need to be within a few centimeters of a device, and eavesdropping allows users to be confident that only the device they want to connect has received the network key.

　　The Bluetooth Technology Consortium and NFC Consortium have already provided interoperability for both technologies, such as device pairing and initiating communication to establish Bluetooth connections. The current Bluetooth standard not only supports OOB pairing to leverage advantages like NFC, but the NFC specification also includes the ability to connect devices to networks such as Bluetooth or Wi-Fi. There is also a protocol for connection switching, allowing immediate normal transmission to Bluetooth after pairing.

　　These features included in these two specifications allow NFC to be used for a variety of purposes, including selecting Bluetooth devices, enabling secure connections to Bluetooth devices, or launching applications on Bluetooth devices.

　　NFC simplifies device selection by eliminating Bluetooth discovery programs, which may require users to manually select desired devices from a list of any other devices within the included range. In this case, NFC allows Bluetooth addresses to be captured directly from tap devices.

　　When pairing Bluetooth devices with SSP OOB, NFC can be used to transmit the temporary keys required for BLE devices. This process. The key is contained in the payload of the standard NDEF (NFC Data Interchange Format) message. After exchanging OOB data, developers can use other features included in the Bluetooth specification to minimize the time needed to complete connection setup. One example is support for fast connection establishment, which is included in the General Access Profile (GAP). GAP defines Bluetooth device announcements, the processes for discovering each other, connecting, and handling security.

　　The application document jointly released by the NFC Forum and Bluetooth SIG provides in-depth information on Bluetooth Shangtai Secure Simple Pairing using NFC on device-to-device interaction and the switching mechanism between NFC and Bluetooth.

　　The integrated module simplifies the design

　　To achieve NFC pairing and NFC-triggered host wake-up, the device must have an NFC tag and BLE functionality. While these can be implemented as standalone ICs, integrated solutions that combine BLE and NFC for IoT devices offer smaller and potentially more energy-conscious solutions. Panasonic's PAN1761 BLE/NFC combo module is one example, combining single-mode BLE chips with NFC Forum 3 compatible tags in a compact surface-mount package. The module features an onboard ARM Cortex-M3 microcontroller and a 512 KBit EEPROM, capable of executing smart sensor applications and other code, as well as Bluetooth and NFC functions. The device features a zero-power standby mode, allowing applications to benefit from long battery life. If necessary, you can use the NFC scanner to reactivate it and automatically activate the Bluetooth connection.

　　This module is built using Toshiba's combined BLE/NFC ICs and includes a Toshiba Bluetooth stack that supports GAP and GASH. BLE Universal Attribute (GATT) profile on the chip. GAP supports central and peripheral roles, allowing PAN1761 to be used in gateway devices or smart objects to connect to gateways. The standard BLE profile can be integrated into application code.

　　Registering for the Toshiba Bluetooth Developer Zone grants access to supported software development kits (SDKs), which include Toshiba Pairing NFC packages. This simplifies OOB pairing using NFC by providing application source code and a "Pair Through NFC" library for the onboard Cortex-M3 processor. There is also an Android demo app with source code, along with app instructions on the concept of out-of-band pairing. An advanced BLE API that provides drivers for all module functions (Figure 1) helps with setup, connectivity, and data transfer.

　　Figure 1: Advanced APIs help developers use PAN1761.

　　PAN1761 module combines BLE/NFC IC and EEPROM with a 26 MHz crystal oscillator, Bluetooth antenna, and filter, as shown in Figure 2. An external NFC antenna is required. The online design tool "Panasonic NFC Design Navigator" can help engineers develop antenna designs and ensure correct routing and PCB layouts.

　　Figure 2: PAN1761 simplifies circuit design, saving PCB space and BOM costs. Layout and antenna design guides are provided.

　　Conclusion

　　NFC can help address the challenge of connecting miniature, low-power industrial smart sensors to Bluetooth with almost no or no user interface. Bluetooth SIG and NFC Forum have collaborated to provide NFC-assisted pairing, including support for connection switching in NFC specifications and OOB pairing in BLE specifications. The combined BLE/NFC tag module simplifies the solution by combining these two technologies within a single device. SDK support provides software developers with the features needed to quickly pair headless devices.