A tremendous convergence of technology is taking place at homes across the globe. The number of wireless sensing Internet of Things (IoT) devices is expected to reach 5 billion by 2019, according to ON World. For one, the Internet has moved beyond letting consumers access oceans of information from their living room to enabling users to remotely control appliances and lighting. Sensors are increasingly monitoring conditions in the home like sunlight, motion, temperature, and moisture for optimum comfort and settings. Finally, advances in wireless technology are making these connections between home appliances and the Internet possible.
As these technologies combine, future homes will contain hundreds of connected nodes — appliances that are wirelessly connected — that will sense their environment, and which will be programmed to communicate information with other connected nodes and act according to the needs of the occupants, seamlessly bringing analog and digital together.
Though the consumer may find that the increased connectivity and prevalence of IoT make life simpler, the sensors and wireless technologies that make up IoT will become more complex. Designers are already challenged with getting all the systems to work alongside each other without complication. Consider the early IoT devices already in the home, like thermostats, lights and light switches, home security systems, and smart locks. “Smart” refrigerators can access the Internet. London-based technology company Berg announced a prototype washing machine that interacts with a smart phone app and has buttons on the console that order detergent. These devices and others are communicating data via a complicated network of wireless protocols, each with their own pros and cons for the particular device and application. This leaves embedded designers with plenty of decisions about which one works best for their needs.
So which protocol is right for your design?
While the considerations for choosing a protocol may seem endless, the decision begins by understanding what the system is trying to achieve. From there, important factors include: the operating environment of the network, how many devices need to talk to one another, power considerations, security, and device interoperability.
Ultimately, bandwidth is required for the node(s) in the system with a variety of protocols to choose from. “Most of these wireless technologies have a varying amount of available bandwidth, and it has to do with the radio frequency they’re using and the packet sizes they have — how many bytes I can fit into an individual message,” says Dave Egan, senior product manager, wireless mesh networks, at Silicon Labs, whose EM35x and EM358x Ember ZigBee SoC products support ZigBee PRO networking for a variety of connected home devices. There are a few main IoT protocol choices:
ZigBee. This protocol was established with low power in mind, and through several years of standardization work with application profiles, has added many operational capabilities to become highly interoperable, both at the radio level and the application level. For example, a home can contain several smart light bulbs from multiple vendors which can all coexist using a ZigBee approach. ZigBee’s strength is connecting a large number of nodes and creating a mesh network. The downside designers typically need to consider is if they want to manage all the complexity associated with connecting multiple devices and profiles.
Bluetooth. This is suitable when connecting a device to a mobile phone, which is a gateway to the Internet. Unlike ZigBee, where many devices are talking to one another, Bluetooth can be a natural choice when sending data from point A to point B such as pictures or streaming audio. Within Bluetooth, there is a Bluetooth Low Energy (BLE, now called Bluetooth Smart) specification, which does not necessarily use all the features that Bluetooth offers on a mobile phone, but was designed with embedded devices in mind. This can be an attractive option for battery operated, command and control low data-need applications.
WiFi. This is a natural first-choice for a lot of home IoT-based devices when a connection to the Internet is required, because it can provide access through the home’s router. A limitation of this protocol is the number of nodes directly supported. While low power versions are available, they are not as low power as some of the other protocols mentioned here. In some cases, WiFi may also be appropriate for connected devices, such as white goods where power requirements are not an issue.
Sub-GHz. This provides the designer with many options because it can support proprietary, customized protocols. In addition, their lower frequencies means longer range. If data rate requirements are low enough, there are countless possibilities at frequencies of 915 MHz in the U.S. down to 154 MHz. Engineers can find transceivers that can specify a frequency up and down this range. Besides propagation benefits, designers may choose a Sub-GHz strategy to avoid potential interference with 2.4-GHz frequency devices.
6LoWPAN. Within an IP stack, 6LoWPAN defines how an IPv6 packet can be reduced to fit into a smaller packet to accommodate a low data rate over a low power network and embedded devices. “You get all the beauty of ZigBee in terms of mesh networks,” says Richard Kerslake, director of marketing, wireless connectivity, at Texas Instruments, whose CC25x Series 6LoWPAN products support large-scale self-healing mesh networks. “6LoWPAN gives you IP to the node. From birth, it’s IoT aware.”
There may also be instances when a designer may want to turn to an IC vendor’s protocol to avoid interacting with competitive products. Microchip Technology, for example, offers an environment called MiWi, suited for low data-rate, low-power IEEE 802.15.4 ISM-band wireless networking applications. It offers application portability across the company’s transceivers and features a smaller footprint relative to the ZigBee compliant protocol stack. Proprietary protocols can help the designer get their wireless home networking solution to market quickly while offering easy scalability.
Don’t lose sleep over power
As with any other device that is battery powered, be sure to preserve as much battery life as possible at the node to give the unit a competitive advantage and provide savings to the consumer, or both. “We call them ‘sleepy end devices,’” says Egan. MCUs and wireless SoCs try to get sleep current as low as possible, with multiple sleep modes. “We’re down in the hundreds of nano Amps for a device that is asleep,” Egan says. “So the radio’s turned off, the MCU is idle, and there’s some amount of memory that is retained so that when the device wakes up, it can immediately start working again and won’t have to recover a lot of data from some nonvolatile memory.”
Although ZigBee networks and Bluetooth Smart-based designs are not as power-hungry, Kerslake says even small devices for the home can take advantage of WiFi technology for days and weeks when you effectively manage the time they need on the network. “Garmin has released watches using WiFi technology.” Using a self-contained network processor like the company’s CC3000 can let a device wake up, quickly send its data and return to sleep. “As long as you can do that quickly,” he says. “You can use WiFi even in the small, battery powered application.”
Play nicely with others
IC vendors can provide reference designs and products that can help a designer take a WiFi module and bridge the non-Internet wireless protocols in the home onto a single WiFi connection. That opens up the possibility of using hundreds of nodes on an IEEE 802.15.4 network, yet are still accessible via a smart phone. Mark Wright, WiFi product manager at Microchip Technology says because the company specializes in these embedded technologies, through its Gateway bridge product and a single PIC microcontroller (MCU), “You can put one MCU down, but actually run two or three of the protocols through a bridge.”
By offering more module-based solutions, vendors are giving designers more confidence their products work alongside others as desired. That could mean eliminating the worry of antenna design for their product. In addition, Microchip, Texas Instruments, Silicon Labs, and others help customers through the time consuming, and sometimes expensive process of getting their products certified. “Designers just install the module in their product,” says Wright. From there, they simply add the FCC number (or the marking of the local regulatory authority). “It’s about the whole cost of certification. Can I postpone that cost until we decide what we really want to build?,” says Kerslake. “Modules are becoming more important for our customers. It’s easy and fast to market.”
In the coming years, IoT will become an entire ecosystem in homes, industrial environments, and transportation. The success of your IoT solution will come down to how it performs in its operating environment, its coexistence with other devices in the ecosystem, efficiency, ease of scalability, and security. IC vendors are bringing SoCs, MCUs, processors and a wealth of tools and expertise to help your solution make itself at home using the right protocol for your needs.