For those following the maker community, the concept of wearable technology is nothing new. Platforms like ARDUIO LILYPAD enable manufacturers to develop a wide variety of wearable systems, from artistic electronic fabrics to shirts and skirts, to T-shirts that tell us how many unread emails we have. Most of these projects have elements of fun or self-expression associated with them, but more and more engineers are being asked to develop electronics for wearable products. The first wave of consumer devices has been dominated by smartwatches, and even big industry names struggle to combine design, display and battery life. With updates to various crowd-funded websites, it's clear that there's a lot of innovation in the wearable sensor space.
For example, in the field of health, a project called Violet was launched on Kickstarter. Violet is a wearable sensor that measures how much UVA and UVB radiation we're exposed to, allowing us to enjoy the sun to get our vitamin D, but "cream it" before the exposure is harmful to our health. Another item, Leo, is a sensing system that wears the muscles around the calf in motion and promotes the indian gogo. Using 3D motion, heart rate and muscle activity sensors, the unit allows users to improve their workouts and avoid potential injuries.
Behind both products are similar core technologies that enable energy-efficient data collection and information sharing over wireless links. Power consumption displays are avoided by using the user's smartphone and an appropriate app to display the results. A closer look at the photos on the Violet Kickstarter campaign page suggests that it's the Bluetooth Low Energy (BLE) that enables these new products.
The Bluetooth SIG was originally introduced by Nokia, which incorporated this low-power wireless technology into the Bluetooth Core Specification version 4.0 in 2010. It's unfortunate that Bluetooth Smart brings consumers to the market, and unfortunately it is not backward compatible with pre-installed 4.0 Bluetooth devices. However, since many Bluetooth chipsets have programmable elements, some users may only need a firmware upgrade for support. This is possible because BLE uses the same radio and baseband technology as Bluetooth Basic Rate (BR) and Enhanced Data Rate (EDR), albeit with a different modulation scheme. After Bluetooth was established in the minds of consumers as a standard feature of mobile phones, adding BLE to the specification made it easier to launch power-sipping accessories and establish success in the smartphone market without having to develop solutions to hit the right beat. This product has a long life.
Channel width data rate
Air Data Throughput Connection Latency
(not connected)
BLE 2 MHz 40 Mbps 0.27 Mbps 6 ms
Bluetooth
BR/EDR 1 MHz 79 1-3 Mbps 0.7～2.1Mbps～100ms
Table 1: Brief comparison of Bluetooth BR/EDR and Bluetooth low energy parameters.
BLE provides a low-power wireless link suitable for exchanging small data packets with other devices, mainly smartphones. Short connection delays help save energy. A new profile, the GATT or Generic Attributes Profile, allows a smartphone, for example, to ask a BLE device and discover what services it has. A BLE-enabled product, as previously described, performs the role of a server in the wireless link. Therefore, they "serve" small packets, as described in their profile. These can be commonly agreed upon data types such as temperature, pressure or heart rate to simplify communication. The smartphone assumes the role of the client, just like a web browser, periodically interrogating the BLE server for new data. In the Bluetooth specification, the packets transmitted over the link are called "characteristics". As an example, the Health Thermometer Profile, or HTP, defines the characteristics of "temperature measurement" and "measurement interval" so that both parties can simply agree on the basic functionality expected of a wireless temperature measurement sensor.
TI Application Report SWRA420
Figure 1: In the application report SWRA420, TI provides a suitable radio design guide. For developers, there are many options in the design of solutions and the ability to partition.
Texas Instruments' C256XQFNEM evaluation module is a reference design based on its family of cc256x Bluetooth and dual-mode controllers. These devices provide a Bluetooth 4 compliant solution to the Host Controller Interface (HCI) layer. This means that the radio, link controller and baseband and link manager are implemented on-chip and can be configured over a hardware UART interface via the standard Bluetooth HCI protocol. The rest of the Bluetooth stack (L2CAP, RFCOMM, SCO manager) and the required profiles need to be linked into the application code of the host controller. For ease of getting started, this evaluation board can be paired with one of TI's MSP 430 devices, such as the MCP430F538 experimenter board, and TI also offers a royalty-free Bluetooth stack. This also means that the cc256x device can be paired with any UART capable microcontroller capable of running a suitable Bluetooth stack. The reference design shows how many external components are required to obtain a qualified solution; thirteen capacitors, a 26 MHz crystal, a bandpass filter, and a copper tracking antenna. These devices consume less than 200 UA with a 3.6 V power supply when connected as a BLE host using a connection interval of 500 ms.
For those looking for a platform that covers a wide variety of Bluetooth applications, TI's Audio Application Assist mode may make sense. These allow the cc256x to handle the transmission of audio data to and from the hardware audio codec without intervention from the host MCU. Basically, the host establishes the audio connection and can then put the processing of the bluetooth stack on a lower priority. Simple microcontrollers can then be used, without an I interface.
Nordic NFR51822 Classic MCU Interface Image
Figure 2: The NFR51822 provides all the classic MCU interfaces as well as an integrated radio.
北欧半导体公司，其NFR51822，采用单芯片的方法，集成无线基带和微控制器成一个单一的6×6毫米QFN或3.5×3.8毫米WLCSP封装。BLE堆栈是一个预编译的二进制文件，允许使用它的应用程序代码被单独编译。根据配置，在40 KB和180 KB的闪存之间的某处仍然可从可用的256/128 KB内部存储器获得。此外，有16 kb的RAM连接到低功耗32位ARM CORTEX-M0 MCU。为了简化与传感器和其他系统的集成，串行接口(SPI/UART/2-WORE)和10位ADC的标准恭维可用，以及128位AES协处理器——实现安全数据连接所必需的。为了支持低功耗，NFR51822具有诸如用于RAM映射FIFOS的EasyDMA和允许片上模块自主触发彼此的可编程外围接口(PPI)等项。这两个特征都有助于确保设备能够在不需要CPU持续干预的情况下完成常规任务。
NFR51822 DK提供了一个很好的起点来评估这些产品。在该套件中有两个评估板，一个带有芯片天线，一个带有SMA连接器，简化了RF性能测量。还包括J-Link Lite调试器，该调试器可以与Keil MK-ARM Lite开发环境一起使用(可单独使用)。还有一个无线开发软件狗，它可以作为一个对等设备来测试开发过程中的无线链路。
CSR参考模块的图像
图3：CSR的参考模块是紧凑的，安装到这个能力启动工具箱目标板。
作为一种替代的、完全集成的方法，值得一看CSR公司的CSR1010μ能器件。容纳在一个5×5×0.6毫米，32引脚QFN封装，它运动64 KB的ROM和64 KB的RAM，为用户的应用程序，这是通过一个DMA能力的SPI接口从外部SPI或I C C串行EEPROM在启动时加载。CSR1010也不需要巴伦，因为它集成在芯片内部。DK-CSR1010开发套件包括一个带有参考设计模块的紧凑板。包括印刷电路板天线，完整的BLE模块可以小到25.5×18毫米，只需要十九个电容器，三个电感器，一个电阻器和16 MHz / 32千赫兹晶体，除了已经提到的串行EEPROM。如果需要的话，有十二个数字I/O以及选择10位ADC和DAC的选项。该工具包还包括CSR的μ能量SDK及其GCC工具链和XIDE开发环境。
那么，从哪里开始呢?如果你有一个你信任的低功耗MCU供应商和工具链，与蓝牙栈配对的TI cc256x是一个很好的起点。为了全面集成，北欧半导体NFR51822应该是高的名单上。CSRSμ能量缺乏从经典的微控制器供应商期望的广泛的接口阵列。然而，将这种蓝牙解决方案与一个小的、低功耗的MCU绑定在一起，以恭维μ能量器件的高无线集成是相当合理的。所以，如果你脑子里有一个BLE应用程序，那么是时候尝试其中的一个解决方案了。