What are the Main Factors Influencing Wearable Design?

In today's competitive, highly competitive wearable market, the key to success is differentiated product features and services. Manufacturers and service providers compete for the same wearable "market pie." Successfully designing wearable products is a complex project. A successful product requires a perfect combination of cost, performance, functionality, and battery life, and must have a compelling look, feel, and performance to appeal to consumers. We need to focus on the end-user experience and explore usage scenarios to integrate different elements in wearable products and complete complex trade-offs. Typical embedded systems usually begin with functional and capability definitions, which are the key drivers of the project. Similarly, successful wearable product design needs to focus on the "user experience." These needs include the look, feel, and interaction with the end-user of the wearable product, as well as the impressions, feelings, and emotions it causes. Today there are many wearable products that monitor health and biometrics, track distances, record movement routes, estimate energy consumption, and make calls and email notifications, while seamlessly integrating and communicating with our smartphones. These wearable product designs are very user-focused; they are stylish, feature-rich, easy to use, affordable, and connectable to the Internet of Things (IoT).

The wearable market

The wearable market can be divided into three product categories, each of which requires a design trade-off, as shown in Figure 1:

Activity Tracker

These relatively simple products often do not include an LCD display. One of the benefits of this simplicity is that these products are economical, easy to use, and often have the longest battery life.

Fitness belts and “super watches” with small or medium monitors

These wearables may include a variety of biological and environmental sensors and choose the best balance between features/functions, battery life, and cost.

Smartwatches

The complex design of these watch sizes occupies the high-end market and usually runs on top of operating systems such as Android Wear. Smartwatches offer a feature-rich user experience, but more features and processing power consume more battery power and usually require charging every day.

Smartwatch is generally round in shape with a diameter between 42 to 45mm.  Although they are in round shape, most of them still use square-shape batteries which do not utilize the entire space of the watch they power. In contrast, customized shape batteries created by Grepow better fit into the empty spaces in watches and also increase the maximum capacity available. Furthermore, Grepow provides Smartwatch battery solutions for high discharge rates and high voltage cells.  Low-temperature cells can also be manufactured so that they can work even at -40℃. Grepow is ultimately a one-stop-shop for customization services.  Customers need only focus on the design of the product, and Grepow will provide the best solution for their specific battery systems.

Figure 1: Each type of wearable product requires a unique design trade-off

Micro Control Unit

A key device choice in wearable products is the microcontroller (MCU). Choosing an MCU with the excellent low-power operation is the key to most wearable applications. In today's 32-bit architecture, the ARM Cortex-M family has become the leading low-power processing platform. The Cortex-M0+ is a 2-stage pipeline architecture that provides the best trade-off between performance efficiency and low active mode current consumption. The Cortex-M3 and M4 processors offer a 3-stage pipeline with good power and performance balance. The M4 processor's single-precision floating-point unit and DSP extensions can greatly reduce execution time and energy consumption for software algorithms, such as the Kalman filtering algorithm commonly used to extract information from noisy sensor data. Smartwatches require more advanced processors (such as the Cortex-M7) and proprietary cores to trade off some of the power of higher processing power and high-bandwidth memory interfaces. Table 1 summarizes the key processing capabilities and feature requirements required for major wearable product types.

Table 1: ARM Cortex-M Series meets all types of wearable product needs

Choosing the right battery technology is also an important design consideration. Disposable batteries have the advantage of not requiring any special charging circuitry; they also have better energy density and provide more energy capacity. The downside is that they make the mechanical design more complicated and limit the ease of use of the overall product. Rechargeable batteries give a slimmer design. Regardless of the choice, wearable products require a small form factor, which limits the size and energy of the battery. Custom shaped batteries to fit into any and all available space in your product for maximum efficiency. By utilizing Grepow's proprietary formula in our custom shaped cells, it will empower you against your competition. In the pursuit of longer battery life, designers of wearable products cannot sacrifice good user experience for energy efficiency. Fortunately, MCUs now have a balance between optimal performance and low power optimization for longer battery life. In addition to low power current, fast wake-up time is also one of the key features. A fast transition from sleep to active state results in better system response and reduced power consumption. MCUs with flexible wake-up sources, ultra-low-power timers, and serial interfaces also offer designers a powerful choice. More advanced MCUs provide efficient peripherals even when the MCU is in a sleep state. A typical example of this autonomous peripheral technology is Silicon Labs' Peripheral Reflex System (PRS), shown in Figure 2, in the EFM32 Gecko MCU peripherals, such as analog-to-digital converters (ADCs) and direct memory. The access (DMA) engine is capable of autonomously responding to external input or interrupt triggering without any CPU involvement. This method sets the MCU to sleep and wakes up after the input from the sensor exceeds a pre-set threshold, rather than having the MCU constantly query the same sensor in an active, high-power state.

Figure 2: Peripheral reflection system saves system power by enabling the MCU peripheral to run autonomously and keeping the processor core in a sleep state

CMOS-based sensors on wearable products

CMOS-based sensors on wearable products provide the foundation for rich user experience, enabling new applications and use cases. There are three main categories of wearable product sensors: motion sensors, environmental sensors, and biosensors. Each sensor type provides a unique insight into end-user activity, environment, and health. When combined, they are more powerful. The combination and use of sensors in wearable products require many trade-offs. Optical sensors require materials that can penetrate light. The power of a particular sensor may need to be gated so that they do not become a permanent load on the battery, but this approach adds design complexity. The expected user experience, cost, and use cases ultimately drive the optimal level of sensor integration in wearable products.

Mobile apps

Mobile apps are an important part of any wearable solution, and Bluetooth Smart has quickly become the primary wireless solution for connecting wearables to mobile devices based on iOS and Android. Bluetooth Smart has an optimized low power mode of operation. However, adding and using a wireless connection increases design costs. Successful wearable designs require careful balancing. Wireless transmission is usually the highest energy consumer in a wearable system. Deciding how much and how often a message is transmitted or how often the wearable product synchronizes with the smartphone will have a huge impact on the battery life of the final product. The use of high data volumes can reduce battery life to hours or days. A more conservative approach may extend the life of the same product to weeks or months. The wearable market may no longer be in its infancy, and with the continuous breakthrough of low-power MCUs, CMOS-based sensors and wireless SoCs, we are now on the eve of a new era of wearable product innovation. As more accurate sensor-driven end-user data can be accessed more easily, the wearable device can reliably and uniquely identify the user. The transition from health and activity tracking to secure and reliable user identification opens up new opportunities in healthcare, security, mobile payments, and social networking. The first wearable product to get a compelling user experience at the right cost in these areas will be the next big winner in the market.

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