Tips on designing smart home devices – Part 1

The smart home market is growing rapidly, with many developers striving to get a piece of the pie. As a result, competition is fierce. To create a highly competitive smart home device, designers want to make devices that are compatible with industry standards and easy to use. And they want to get these devices to market quickly.

While developers understand what they want in a smart home device, they also have specific questions about the design process, design criteria, the wireless protocol/standard, and cloud platforms.

In this series, we will answer some of the key questions developers have raised.

What are the design criteria to consider when creating a new smart home device?

Essentially, a smart home device is a remote control on/off switch with some built-in artificial intelligence (AI). Whether you are designing a smart thermostat or a remote sprinkler controller with weather sensing features, consider the following recommended design checklist. It can help remove some of the complexity from the technology platform decision.

• For a simple remote switch to be used for, say, turning a light on and off, you do not need a fancy design. Focus on low cost, simple switching. If you are designing a solution with an Apple or Android smartphone app offering comprehensive control of many household devices, you need to consider either the Zigbee or Z-Wave protocol and understand the smartphone platform. Both the Zigbee consortium and the Z-Wave consortium offer comprehensive design support.
• Typically the more compact the device, the higher the complexity and cost. For example, if you design a wearable home device to monitor residents’ vital signs and their safety, then compact size and reliability would be critical. Cost considerations become secondary. On the other hand, if you design a smart thermostat with no strict size constraints, then use commonly available components to reduce cost.
• Almost all smart home devices require a sensor of some sort, whether for temperature, motion, fluid detection, voice input, or light sensing. Many different types of solutions are available. Some are very basic, and others have built-in artificial intelligence (AI).
• Determine the required amount of storage and the need for dynamic and/or static memory within the unit. If the device communicates in real-time and does not need storage, the overall unit cost can be reduced.
• Wireless technology. There are many wireless technologies available for smart home devices. (See below answers for more details.)
• Energy management. Unless the device is connected to the AC supply, energy management will be a significant factor. The guidelines for a low power wide area network (LPWAN) device specify that battery life should be in the 5-to-10-year range. Consumers prefer the convenience of changing batteries infrequently. In your design, consider software development tools that provide energy profiling. Consider integrated solutions for ultimate energy savings, such as a microcontroller with built-in security and/or sensors. Finally, consider energy harvesting, which will potentially eliminate the use of batteries entirely.

Which smart home protocol /standard should I select?

For a long time, many different types of smart home protocols have been deployed. However, in recent years, Zigbee and Z-Wave have emerged as the two leading standards in the smart home marketplace. If you are designing a new smart home device, it is advisable to follow one of these standards. In late 2020 the Z-Wave Alliance announced an upgrade to its existing specification. The new Z-Wave LR (long-range) extends the wireless communication range from 300 feet to a range measured in miles. The Alliance plans to extend the range ever farther and stretch battery life up to 10 years. These actions will potentially expand applications beyond smart homes to smart buildings and smart cities.

Both Zigbee and Z-Wave have security provisions. Zigbee provides concentric layers of security measures, including Device-unique Joining Authentication, Device-unique Re-entry Authentication, Pairwise Privacy and Integrity, and Secure Over-the-Air (OTA) updates.

Z-Wave provides a software development kit (SDK) that includes the Z-Wave Security S2 Framework to eliminate the risk of man-in-the-middle attacks. The Framework also uses the Elliptic-curve Diffie-Hellman key agreement protocol, an industry-wide secure key exchange scheme, to increase security.

Part 2 will continue with additional design considerations including cloud platforms, developer tools, and a walk-thru of the design process.