Microcontrollers and Wireless Connectivity in Smart Appliances

Wireless connectivity is enabling smarter appliances that can communicate with other devices throughout the home and over the Internet. Choose the right wireless protocol and you’re off to a good start.

The days of the drab household appliance that sits mostly idle in the corner of a kitchen or bathroom have come to an end. Today’s appliances are sleek, functional designs that are innovative and form the centerpieces of most modern-day homes. One of the technological trends in appliance design that has gained a significant foothold in recent years is the smart appliance. These devices sport leading-edge technologies, including the ability to communicate wirelessly with other devices throughout the home and over the Web.

Smart appliance manufacturers see tremendous economic opportunities in directly communicating not only with appliances in the field, but also with the users of those appliances. Services such as remote diagnostics and firmware upgrades can be made more seamless to the user. Consumers also stand to gain economically, by removing the cost and obstacle of rewiring their homes through wireless connectivity.

In today’s marketplace, green applications for smart appliances have begun to emerge that are centered around energy usage and monitoring. Services such as Google PowerMeter have enabled consumers to gain instant access to their energy usage data. In turn, having this information has provided consumers with the impetus to undertake measures such as signing up for cost-saving energy usage plans that are offered by their utility companies. Utility companies are rapidly deploying wireless-enabled smart meters that connect to Home Area Networks (HANs), which allow them to provide load-control features to the smart appliances. The benefits are that the utility companies can better regulate their energy demands, collect valuable real-time usage data, and offer more suitable tiers of services to their customers. Using all this information, utility companies can more precisely predict and plan their future infrastructure expansion.

Manufacturers are able to bring wirelessly enabled smart appliances quickly to the marketplace by integrating two key building blocks into their products — wireless technology and advanced microcontrollers.


Additionally, large groups of technology companies have recently joined forces to form consortiums that have defined the framework of how these smart wireless appliances communicate with each other. The net effect of these developments has been the unleashing of design innovations within the application space of smart appliances. We are rapidly approaching the time when it will be commonplace to live in an affordable smart home with its many smart appliances, all wirelessly connected, as depicted in Figure 1.

However, these innovations are not without many design challenges. This article will discuss some of these challenges, and the trade-offs that are involved when choosing among the technologies that are used in a smart appliance. It begins with the choice of which wireless protocol to use.

Wireless technology choices

In terms of wireless networking protocols, the smart appliance manufacturer has a number of viable options to choose from. Some of the choices include Embedded Wi-Fi, ZigBee and proprietary protocols such as Microchip’s MiWi Development Environment.

Wi-Fi is the most widely used wireless protocol. It is the wireless equivalent of the wired Ethernet protocol that forms the backbone of today’s internet. Typically, Wi-Fi operates on high performance computers, which can handle data-intensive applications. Compared to traditional Wi-Fi, Embedded Wi-Fi performs a single or very limited number of functions, such as transmitting static images, but at relatively lower data rates.

Embedded Wi-Fi offers clear advantages in that any Wi-Fi enabled smart appliance is able to readily communicate over the Web. Typical data rates of 1-5 Mbps are supported, which make it suitable for control and monitoring applications. Embedded Wi-Fi operates in the universally available 2.4 GHz spectrum. This spectrum is an open and unlicensed frequency band and, as a consequence, is being used by other wireless technologies.

Another wireless option available to manufacturers is ZigBee. While Embedded Wi-Fi operates at data rates on the order of Mbps, ZigBee has a specified maximum data rate of 250 kbps, per the IEEE 802.15.4 radio standard. ZigBee positions itself as the lowpower and low-data-rate wireless protocol of choice for wireless sensor networks. ZigBee-enabled smart appliances can be made to operate with extremely low-power, while utilizing inexpensive microcontrollers such as Microchip’s PIC microcontrollers with eXtreme Low Power (XLP) technology. Other ZigBee strengths include its strong data security model, interoperability, and its expanding adoption across many application segments. Similar to Wi-Fi, ZigBee operates within the 2.4 GHz frequency band, utilizing sixteen defined channels, giving it flexibility in terms of channel hopping and frequency agility, in order to avoid noise and interference. As evidenced by its partnerships with both the Wi-Fi Alliance and HomePlug Consortium, the ZigBee Alliance is continuing to strengthen its interoperability credentials. ZigBee, along with Wi-Fi, have gained acceptance as viable networking technologies of choice for the U.S.-based SmartGrid Alliance.


Another option available to smart appliance manufacturers is the use of a proprietary wireless protocol, such as Microchip’s MiWi Development Environment. Proprietary protocols offer many advantages, including ease in customization for specific target applications; shortened development times when compared against open-standard protocols; less complexity; and ease of deployment. They also offer many opportunities for both innovation and IP creation. There is no need for the specialized certification that is often required by the open-standard protocols, which can bring a significant cost savings. Additionally, all of this adds up to a quicker time-to-market with a potentially lower cost device. However, the lack of interoperability with other manufacturers’ products could result in a narrower market segment for the device, or require the development of a gateway device to translate to other wireless networks.

You can check the feature comparison for the three wireless technologies discussed in this article in Table 1.



Data security

Network data security is of primary importance, because of the sensitive nature of the information that may be transmitted between devices. Security for both Wi-Fi and ZigBee is based on a robust AES-128 algorithm, and operates within the framework that is described in the IEEE 802.11 and IEEE 802.15.4 specifications, respectively. The methodology for establishing and transporting security keys, and the authentication of devices are all defined by each of the specifications. Smart appliance manufacturers who choose a proprietary wireless protocol have the added challenge of selecting the appropriate security algorithm and services.

Independent of the encryption algorithm chosen, there are two important security-related factors that each manufacturer must be aware of. The first is whether the encryption algorithm is subject to export control laws. Products containing software or hardware algorithms must either restrict their key lengths or obtain specific export authorizations. Regardless of whether they are based in hardware or software, encryption algorithms have the same restrictions and must adhere to all export control laws. Secondly, regardless of the robustness of the encryption algorithm, data integrity will be severely compromised if the keys are compromised. Therefore, protection of the keys themselves is of vital importance. Device manufacturers should devise an appropriate method of key protection.

The smart appliance platform

Wireless smart appliances are generally built upon a platform that includes three major subsystems: the microcontroller, which acts as the brain of the appliance; the wireless protocol stack, which defines the logical connections amongst devices in a network; and the RF transceiver, which handles the transmission of packets over the air.

Today’s manufacturers have a wide selection of microcontrollers around which to design their smart appliance platforms. One of the major selection criteria is the cost of the microcontroller. Additional criteria are the size of its program and da ta memory, its power consumption, the availability of peripherals, and its processing speed.

Another important subsystem of the smart appliance platform is the wireless protocol stack. Its operation determines how the devices communicate, how many devices may be on a single Home Area Network (HAN), and the maximum data throughput. The protocol stack is often the most complex software module in the application firmware. The development time of the smart appliance can be greatly reduced, if software for the stack is already available. Moreover, the portability of a vendor’s stack across all of its microcontroller families is of primary importance. This gives the developer the flexibility to choose the 8-, 16- or 32-bit microcontroller that is most appropriate for a given platform, while maintaining the same protocol stack functionality and features.

The RF transceiver completes the major components of the smart appliance platform, handling the duties of transmitting the packets over the air. The choice of RF transceiver together with the wireless protocol determines the environment in which the smart appliance can operate. If a low-power application requires wireless communication through obstructions such as walls, then a Sub-GHz transceiver may be more suitable. By contrast, higher-frequency bands such as 2.4 GHz make for a better choice in applications requiring higher data throughput.

Traditionally, RF transceiver design is a very complex undertaking. To help alleviate this complexity, manufacturers have designed fully integrated and FCC/ETSI certified RF modules, such as Microchip’s MRF24WB0MA embedded Wi-Fi module. These modules include the RF transceiver, the functional antenna, and the supporting RF circuitry. Appliance manufacturers may simply include these modules in their designs, rather than acquiring the RF expertise to design the transceiver from the bottom up. Using modules reduces the time-to-market, risk, and development costs.

There is a strong interdependency between all three components of the platform. OEMs such as Microchip have recognized this interdependency and have developed complete platforms that are suitable for smart appliance development. For example, Microchip’s wireless development environment includes support for any combination of its 8-, 16- or 32-bit microcontrollers with sufficient MIPS and memory; RF transceivers both in the 2.4 GHz and Sub-GHz spectrums; and multiple wireless protocols, including Wi-Fi, ZigBee, RF4CE and MiWi proprietary.

Design considerations

A common pitfall that designers encounter as they develop a wirelessly enabled smart appliance is the failure to future-proof their devices. For example, choosing a wireless technology that cannot be scaled upward to accommodate the demand for the larger networks of the future is a problem. One design consideration is that even though these smart appliances are packed with the latest technology, their interfaces should be clean, intuitive, and simple for the user, or else these appliances may not gain wide acceptance in the marketplace.

Often, designers fail to take into account both the physical and RF environments in which their smart appliances will reside. Therefore, factors such as humidity, the thickness of walls, and the presence of microwaves must be considered when designing the device. The styling of an appliance and its functionality should be cohesive, such that the former does not degrade the latter.

Consideration should also be given to the appliances’ certification, particularly for those that employ open-standard protocols. The product’s certification is a key milestone that must be completed before the product can be sold.

Conclusion

In this article, the major components that make up a wirelessly enabled smart appliance platform were described. These components are the microcontroller, the protocol stack, and the RF transceiver. Innovations in each of these subsystems have enabled smart appliance manufacturers to integrate wireless communications capabilities into their products. Along with these innovations come design challenges, such as choosing the appropriate encryption algorithm and ensuring that the wireless networks in which these devices operate can be scaled upward as demand for the devices grow. Both consumers and manufacturers stand to benefit from these new wirelessly enabled smart appliances, as entities such as utility companies offer useful, cost-saving products and services based on these devices. The Google PowerMeter and load-control services are two such examples, with many more such services becoming available every day.