ZigBee and WLAN
In order to be able to control roller blinds, air conditioning or lamps not only via a smartphone but also via virtual private assistants (VPA), such as Alexa, Siri, Google Assistant, Bixby or Cortana, as well as other devices, like smoke detectors, alarm clocks or surveillance cameras, all the interconnected devices form a system that is usually connected via interfaces of the supplier clouds. Using these interfaces, a radio alarm clock can, via a WiFi network, receive the music from the Internet to wake you up in the morning and send a signal to Alexa to gradually increase the brightness of the bedroom light.
Communication between the VPA and the light source usually takes place via a ZigBee WLAN gateway or directly via WiFi. The advantage of this solution is that WiFi lamps do not require an extra device for communication but connect directly to the home WiFi router. Disadvantages are a relatively high level of standby power consumption and additional data traffic in the WLAN network. In very smart households, this can lead to a situation where the available data rate is no longer sufficient.
As a result, some suppliers use the ZigBee Light-Link protocol. It consumes less power than a WiFi connection and does not additionally load the WiFi network with data throughput. Compared to wireless technologies, such as ANT or Bluetooth 5, however, the level of power consumption is still relatively high. In addition, a ZigBee network occupies 5MHz in the 80MHz-wide 2.4GHz frequency band. This can cope with either three WiFi networks or 16 ZigBee networks in parallel, as well as combinations of both, e.g. two WiFi networks and five ZigBee networks. Too many networks result in frequency overlaps and thus to a drop in performance; for a short while, the network may even come to a complete standstill.
Thread
The thread protocol has recently made its way into more and more smart home applications. Since it supports the Internet protocol version 6 (IPv6), it offers many advantages over proprietary, locally restricted addressing. The brains behind the protocol is the Thread Group, a non-profit organization whose members include a number of large engineering companies.
Several alliances are available for the application profiles, including the ZigBee alliance with its dotdot solution. This is a kind of universal language for the Internet. If the radio alarm clock is to be able to control devices from different suppliers – e.g. also switch on the TV set to watch breakfast television – it is advisable to already integrate the thread protocol from the start to guarantee future interoperability, at least with regard to the hardware requirements.
Bluetooth
With Bluetooth 5, the Bluetooth Special Interest Group has also introduced operating modes that are of interest to smart home applications: For instance, the 2Mbps mode allows the transmission of video signals, e.g. from the camera of a robotic lawn mower or the door monitoring system. A 500kbps and a 125kbps mode enable increased transmission power and a longer coding of the individual bits, thereby ensuring wireless signals can be transmitted across several hundred meters and through several walls. In contrast to technologies based on IEEE802.15.4, such as ZigBee and Thread, Bluetooth 5 is already available in modern-day smartphones and is, therefore, also suitable for direct smartphone connection.
An addition to Bluetooth 5 is from Bluetooth 4.0 the Bluetooth Mesh 1.0 protocol as an intermediate level to support large networks with numerous devices. This Bluetooth protocol is also supported by smartphone compatibility, relatively low power consumption, and very low latency thanks to a flooded instead of a routing-based mesh structure.
ANT and EnOcean
If you want to go one step further, the radio alarm clock will not only turn on the music and the bedroom light, but it will do so at the ideal moment. It determines this with the aid of a smartwatch or fitness tracker, which is aware of the wearer’s sleep phase through pulse and movement detection. For the alarm clock to have access to these devices, it needs the ANT protocol. As this has become established with such devices; only a few exceptions work with Bluetooth. The reason for this is that ANT is the ultimate most economical wireless technology for sensors in the immediate vicinity – and thus perfect for all applications that can be operated with button cells or similar small energy storage devices for months and years without having to charge or change batteries.
Only the EnOcean sub-GHz standard is even more energy efficient. The protocol is not as efficient as ANT, but thanks to the patented energy harvesting extensions for the use of kinetic energy when operating switches, solar energy or thermal energy difference, EnOcean wireless technology makes it possible to do entirely without a separate energy storage system. EnOcean switches can already be found, for example, in Weber prefabricated houses. An existing light switch can also be used to tell the radio alarm clock that you are about to go to bed and to start a sleep timer.
NFC
However, if a device is equipped with all these wireless technologies, it is not exactly user friendly. As end users need to set up all the connections to their devices and systems. Near Field Communication (NFC) provides a helping hand in this situation. This means end customers only need a smartphone and must touch each device to be connected just once in order to set up the networks.
Everything in one module
Developers are therefore faced with the task of integrating all these wireless standards into the application. With the nRF52840 System-on-Chip (SoC) from Nordic Semiconductor, this is very simple indeed: The all-in-one solution offers not only a powerful microcontroller with wireless units for ZigBee, Thread, Bluetooth 5, Bluetooth Mesh, ANT, and NFC, but also a USB port. In addition, there are A/D converters for evaluating other sensors, encrypting data transmission, and protecting memory areas. The SoC is in fact only a little bit more expensive than a plain ZigBee solution.
At the heart of the nRF52840 is a 32Bit ARM® Cortex™ M4F processor running at 64MHz. Its on-Chip memory (1MB flash and 256kB RAM) provides enough space for simultaneous, multiple wireless protocols. The SoC also features high-resolution RSSI measurement and functions, such as EasyDMA, which reduce processor load and enable direct memory access. To lower the power requirements, all peripheral components feature clock and power management to ensure that they are turned off when not in use. The cryptographic coprocessor ARM® CryptoCell-310 provides a high degree of security. It supports a random number generator and many asymmetric, symmetric, and hash cryptographic services. Moreover, the coprocessor accelerates operations, saves CPU processing time, and reduces power consumption.
The nRF52840 is on-air compatible with Nordic Semiconductor’s nRF24, nRF51, and nRF52 series products.
Anyone who now misses the big EnOcean advantage can use an nRF52-based module that is compatible with EnOcean energy harvesting modules. This is available from Rutronik, as are solutions for all other wireless technologies. The wireless experts support customers when choosing the ideal solution for their individual application.
Autor: Bernd Hantsche, Director Embedded & Wireless
Rutronik | https://www.rutronik.com
