Interview: How to enable energy-friendly smart home technology

Ted Batey, Senior Marketing Manager of MCU products at Silicon Labs, talks about the role of MCUs in smart home technology and how to enable multi-functional low power wireless designs. 

Smart Home

Q1. What are smart homes and what roles do wireless MCUs or MPUs play in this application area?

Digital home automation products for “smart homes” encompass a wide spectrum of devices and applications including lighting control systems, smart thermostats and security systems. Despite this diversity of end applications, a task that many of these products have in common is routine data monitoring. This function can often be implemented with a relatively simple embedded MCU focused on basic data collection, processing and wireless connectivity. Whether such a connected device requires an 8-bit or 32-bit ARM MCU working in concert with a discrete transceiver or a wireless SoC (MCU + transceiver combination in a monolithic or SiP implementation) depends primarily on the overall system architecture, firmware complexity and form-factor constraints of the product. Looking beyond the CPU, the wider internal busses and advanced peripherals of 32-bit ARM-based MCUs enable substantially faster data movement and higher computational performance compared to 8-bit MCUs. For RFTS (“run fast, then sleep”) duty-cycled applications, this approach allows the processor to run for a shorter period of time, resulting in improved energy efficiency.

Q2. What are the wireless options (such as Wi-Fi, Bluetooth, ZigBee and sub-GHz) for smart home and Internet of Things application?


quote_2There is no one wireless or wireline technology that can efficiently serve all home automation application needs. To develop cost-effective smart home products, engineers need to be able to select the optimal physical network and protocol for their application. As a result, smart home products and networks will be based on a variety of wireless technologies.

For devices to be able to access the Internet, they will also need to support IP somewhere along the communications path. This implies either native IP support in the protocol (e.g. Wi-Fi) or routing of a non-IP-based protocol (e.g. Bluetooth low energy) through a gateway that supports IP (e.g. a smartphone).

Connected devices for home automation must able to use protocols that are lightweight and have data rates that reflect their requirements. IoT devices that connect through a centralized controller/gateway can employ proprietary standards given that their data is aggregated and converted to a standard format before being passed onto the Internet via the gateway device.

For low-bandwidth cost-constrained applications, 2.4 GHz ZigBee and sub-GHz low-power radio technologies offer a low-power wireless link that is easily integrated into embedded systems. For simple applications, such as garage door openers or systems requiring long-distance connectivity like irrigation systems, a sub-GHz radio is likely to provide the optimal approach. If two-way communication, security or a large number of devices need to be connected in a mesh network, ZigBee offers a robust implementation.

Employing a mesh topology is ideal for smart home applications such as security systems with wireless sensors. For these applications, the ZigBee protocol is ideal because it supports mesh topologies that allow nodes far from a network gateway to be reached indirectly through peer devices used as stepping stones. In addition, meshes can automatically configure new devices so that they leverage usage patterns that the system has already learned. Scalability is an important factor as well. Bluetooth, for example, is limited to just seven devices on a network while Wi-Fi is limited to 32. Networks based on Silicon Labs’ EmberZNet Pro ZigBee stack provide self-configuring and self-healing mesh connectivity that can be extended to interconnect hundreds or potentially thousands of devices on a single network.

The ZigBee protocol, pioneered by the ZigBee Alliance, exemplifies a framework that gives connected device manufacturers a straightforward way to develop standards-based products capable of interoperable M2M communications. ZigBee standard profiles, such as ZigBee Smart Energy, ZigBee Home Automation, ZigBee Building Automation, ZigBee Light Link and now ZigBee IP, provide interoperable platforms that simplify the development of IoT applications for smart homes and commercial buildings, intelligent lighting control systems, smart meters, and in-home energy monitoring systems.

Q3. What’s on the horizon with wireless protocol standards, multi-protocol integration for wireless ICs and low-power wireless chips?

As mentioned earlier, there is no “one-size-fits-all” wireless technology or standard for home and building automation applications. Each has its own set of strengths and limitations, and these wireless technologies will co-exist.

Furthermore, wireless standards like ZigBee and Bluetooth each continue to evolve to address industry and application needs. For example, this year the ZigBee Alliance has released ZigBee Home Automation 1.2, the Smart Energy Profile 2 standard and ZigBee IP, the first open standard for IPv6 wireless mesh networks.

Wireless MCU products must be able to support new standards as they become available. Wireless MCUs capable of multi-protocol integration will provide a flexible solution for today’s heterogeneous home automation network environments. Silicon Labs, a leading supplier of energy-friendly 8/32-bit MCUs, ZigBee SoCs and sub-GHz wireless ICs, is developing a new family of multi-protocol wireless MCUs that will also enable exceptionally low energy consumption required by battery-operated connected device applications.

Q4. What are Silicon Labs’ plans for next-generation 32-bit MCUs?

Silicon Labs’ objective in the MCU market is to provide the industry’s most energy-efficient ARM-based product portfolio. Our 32-bit EFM32 Gecko families include nearly 250 products with cores ranging from ARM Cortex-M0+ to Cortex-M4, and integrated flash memory from 4KB to 1MB, enabling a broad spectrum of energy-sensitive applications.

We recently introduced the EFM32 Zero Gecko MCU family based on the M0+ core. The Zero Gecko MCUs feature the industry’s most sophisticated energy management system with five energy modes that enable applications to remain in an energy-optimal state, spending as little time as possible in the energy-hungry active mode. In deep-sleep mode, Zero Gecko MCUs have an industry-leading 0.9 μA standby current consumption with a 32.768 kHz RTC, RAM/CPU state retention, brown-out detector and power-on-reset circuitry active. Active-mode power consumption scales down to 110 µA/MHz at 24 MHz with real-world code (prime number search algorithm) executed from flash. Current consumption is less than 20 nA in shut-off mode. The EFM32 MCUs further reduce power consumption and improve system responsiveness with a fast 2-microsecond wakeup time from standby mode.

Like all EFM32 Gecko products, the Zero Gecko MCUs include a best-in-class energy-saving feature called the Peripheral Reflex System (PRS) that significantly enhances system-level energy efficiency. The PRS monitors complex system-level events and allows different MCU peripherals to communicate directly with each other autonomously without involving the CPU. Leveraging the PRS, an EFM32 MCU can watch for a series of specific events to occur before waking the CPU, thereby keeping the Cortex-M0+ processor core in an energy-saving standby mode as long as possible and reducing overall system power consumption.
Next-generation ARM-based products from Silicon Labs will deliver further enhancements to energy efficiency as well as integrated wireless connectivity and multi-protocol support.

Q5. What about wireless MCUs for home automation designs? What are the optimal architectures for wireless MCU solutions? 

To address the requirements of home automation applications, wireless MCUs have emerged in recent years as an embedded processing solution offering a hybrid architecture that integrates an MCU core and wireless transceiver into a single device, either as a SiP or SoC solution. These highly integrated wireless MCU solutions offer several advantages over their discrete counterparts, including reduced BOM cost, component count, board space, power consumption and overall design complexity.

Building a monolithic CMOS SoC that integrates the MCU and radio subsystems in a single die poses several design challenges. For example, it’s necessary to use a process technology that is suitable for both the flash memory and processing functions of an MCU as well as RF operation. Because no single process is best for all functions, the IC designer must make tradeoffs that can impact performance, power, and/or cost. Another significant challenge is minimizing the impact of noise emission from the processor’s digital blocks on the transceiver’s RF performance.

With a SiP approach, process technology selection can be optimized for each die’s required functions. It may also be easier to manage the impact of noise from the MCU’s digital circuits on the RF circuitry. Physical distance between die helps ensure that the MCU’s clock frequencies do not cause spurs and/or blocked channels on the radio. Critical RF specifications such as sensitivity and range can also be optimized, ensuring interoperability without compromising radio performance.

Learn Silicon Labs’ smart home solutions here.

Watch how to design a high-end smartphone interface on io-homecontrol remote with with low power EFM32 Cortex-M3

Do you have any technical question for us? Visit our community page here. Our team will be happy to answer your question. 

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