How to turn a home thermostat into a smart device: easing the connectivity challenge: Page 2 of 7

May 09, 2017 //By Vikram Ramanna
Consumers are developing a taste for smart home devices, thanks in part to the new sophistication of voice-controlled technologies such as Apple’s Siri Remote and the Alexa Voice Service on Amazon Echo, and of systems for the remote control of home devices such as Google’s Nest products.

This is why the use of a fully integrated hardware/software development platform helps engineers to greatly reduce the time and difficulties involved in implementing new smart home device designs. This article describes the elements and operation of one such platform.


Protocols supporting operation of connected devices

To support the types of remote- and voice-control functions and smart automation features available with platforms such as HomeKit or Works with Nest, a thermostat requires an internet connection, normally provided via a gateway such as a Wi-Fi router.

The device will also need to support application protocols such as HTTP, SMTP, NTP and MQTT to provide for communication with web and application servers over the internet. At the application layer, the thermostat may also run specific software elements such as Apple’s Homekit Accessory Protocol (HAP). Security is an essential requirement for connected devices, to maintain user privacy and to protect against intrusion into the home network. Secure transactions and message exchanges between the device and the cloud may be made over Secure Sockets Layer (SSL) with Transport Layer Security (TLS) 1.2 or other secure protocols.

Underlying the complex operations of the application layer, the security layer and the communications layer, the system architecture will require an operating system (OS) to handle prioritization and memory allocation. In a resource-constrained device such as a thermostat, this will be a real-time OS with a tiny memory footprint. Here, then, is the challenge for the thermostat designer: not only to provide for a robust Wi-Fi connection to a router, as well as in some cases a Bluetooth Low Energy connection to devices such as wireless sensors, but also to implement multiple protocols and the application software in an environment requiring rock-solid interoperability with third-party internet-connected devices and services.

It is a development task of considerable proportions and with many potentially unfamiliar technical difficulties to be mastered. It is for this reason that WICED, the Wireless Internet Connectivity for Embedded Devices technology from Cypress, was developed.

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