Forget the Gateway: How Bluetooth Mesh Networking Can Simplify Wireless Lighting Controls (MAGAZINE)

Programming is not new to wireless lighting control systems. Until recently, virtually all wireless solutions offering this functionality had one thing in common: they relied on a gateway to manage time management and trigger desired lighting schedules. A new standards-based service can meet lighting schedules without a gateway device by leveraging the capabilities of the open Bluetooth mesh protocol. This article will examine the benefits of this approach and the challenges that come with developing gatewayless scheduling functionality.

Standard Status

Bluetooth Mesh was adopted in 2017 as the first wireless standard designed specifically to address professional lighting applications. It aimed to address the three pain points – simplicity, scalability and reliability – while providing innovative lighting control and data management features. Global technology change always takes time, but Bluetooth mesh is making great strides, with more than 1,200 qualified products on the market and large-scale projects previously unachievable for standards-based wireless technologies. (See the Minneapolis 3,500+ node project that received the 2021 Sapphire Award for Design Excellence in Networked Lighting Controls for LLLC.)

Industry organizations have also shown their support for Bluetooth mesh technology. Collaboration between the Bluetooth Special Interest Group (SIG) and the DALI Alliance continues to grow, and the DesignLights Consortium has certified several Bluetooth mesh-based wireless control solutions. It’s still too early to consider Bluetooth mesh as a go-to wireless technology for lighting controls, but the standard seems well positioned. Given the fragmented landscape of wireless lighting control over the past decade, widespread adoption would be a real breakthrough for the lighting industry. In the meantime, new developments based on Bluetooth mesh continue to advance the standard. So-called node planning holds promise for advancing the technology.

Essence of decentralization

The Bluetooth mesh specification included timing procedures in nodes, so gatewayless scheduling was expected in the market at some point. As a contributor to the Mesh working group of the Bluetooth SIG, Silvair worked on this feature update. Node programming has proven to be a significant development effort and perhaps the most complex single feature developed as part of the company’s lighting control solutions.

Although the gateway-based scheduling service is already available, we needed to implement this feature to eliminate gateway hardware requirements. As control developers, we aim to extend the scope of functionality available for small to medium-sized projects where a gateway is not preferred due to, for example, internet connectivity limitations, the need to reduce hardware costs or a preference to keep the system offline. Sometimes a walkway device is not an option for projects that still benefit from the deployment of lighting programs. Being required to use a gateway in a lighting control system is a very different scenario than being able to use a gateway to access additional functionality, such as configuration or remote control.

The decentralized nature of the Bluetooth mesh makes it unique among other wireless communication standards. Bluetooth mesh lighting control systems do not need a gateway or other central controller to manage the entire network, as Bluetooth mesh places a software controller in each fixture. Implementing planning in nodes fulfills the promise of decentralization with the ability to provide cost-effective planning for projects of any size.

Time synchronization

Scheduling in nodes was difficult to develop due to the way a network without a central controller handles time synchronization. With gateway-based scheduling, the problem of time management is relatively simple. A gateway is always on and online. It can retrieve accurate current time information from an online server whenever needed and share this information with the entire network; therefore, running time tracking is not necessary. In the event of a power outage, the gateway simply checks the current time online when power is restored.

But things get complicated without this central controller and a constant connection to time servers. For example, how will individual nodes know the time without an internet connection? How do I prevent time from getting out of sync in the event of a partial or network-wide power outage?

A decentralized Bluetooth mesh network first solves these problems by defining the role of the “time authority”, or a node that keeps time for the entire network. Each individual fixture in the topology has its own internal clock based on the specified user-defined scenes, but all of these internal clocks synchronize with the time authority node. This ensures that schedules are triggered simultaneously for all affected nodes and zones.

The Time Authority role is assigned automatically during the provisioning process and can be performed by any node on the network. However, priority is given to a real-time clock (RTC) node – a dedicated piece of hardware with an RTC chip and, preferably, extended battery life to keep track of the time even without external power supply. As long as such a RTC node is available in the network, it will automatically become the network timekeeper.

All computer systems exhibit clock drift over time, which causes the system time to gradually deviate from the exact or “true” time. RTC hardware support helps minimize gradual time drift and ensure scheduling service accuracy; however, an RTC node is not required in a project that implements scheduling functionality in the node. In installations that include a PSTN node, time drift can reach 30 seconds per month. In installations without a PSTN node, the potential time drift increases to approximately 120 seconds per month.

Since most RTC nodes include battery backup, they can prevent time out of sync in the event of a network-wide power outage and automatically share the internal clock setting with the entire network. network as soon as power is restored.

A mobile app is the last key part of the time management process discussed here. During the commissioning process, the application injects the current time into the network, informing the network time authority of the current time (Fig. 1). In the future, whenever a need arises to recalibrate the time, perhaps to compensate for time drift or after a power outage when an RTC node is not present, a user can press the “time synchronization” button.

Translate complex technology into a simple user interface

Although the underlying timekeeping mechanisms are technical, the user interface part of the scheduling feature in Node can be simple and intuitive. As with multiple aspects of Bluetooth mesh lighting controls, complex network processes can be automated so that the end user is faced with only the basic decisions related to lighting control system operations.

The main steps of the planning configuration process are performed offsite in the web application, which is more detailed for planning and configuration. In the case of the Silvair application, the user specifies which lighting zones take advantage of the scheduling function by assigning a predefined scheduling scenario to the desired zones in the floor plans (Fig. 2). Then, the user defines the lighting scenes to be triggered at the desired times according to the lighting needs of the given space. These can be static scenes, where the user only sets the fixture output percentage, or dynamic scenes that involve automation based on occupancy or daylight. Next, the user creates and names the schedule events that will deploy these lighting scenes, entering parameters such as the day of the week and the time that a particular event will occur.

For each lighting zone, a user can specify up to 16 time events and four scenes triggered by their defined events. This provides flexibility in terms of fixture programming; for example, different schedules can be configured for different days of the week. Once the Scenes and Events are set up, the Offsite Programming setup is complete. The process is finalized during the on-site commissioning phase, which is carried out via the mobile application and a smartphone or tablet. The mobile app connects to luminaires and quickly deploys the pre-commissioning configuration. When the app adds installed luminaires to the network, it transfers all user-specified scheduling configuration settings to each commissioned luminaire. The app also injects the current time into the network so that its time authority node can track the time autonomously in the future. Luminaires can then begin to operate according to user-defined schedules.

Advanced control for all

By minimizing the hardware requirements for fixture programming, Bluetooth mesh allows this gateway-less strategy to be implemented in virtually any lighting project, regardless of scale or budget. The goal of developing Bluetooth mesh-based systems is to provide advanced controls that can be deployed and used in any type of commercial environment to generate cost savings and improve energy efficiency. Bluetooth mesh has more to offer in this respect and further developments are on the roadmap. The implementation of standards-based, node-integrated scheduling functionality is another important step in accelerating the global adoption of advanced lighting control strategies across many commercial enterprises.

Meet our expert

SIMON RZADKOSZ is a product marketing specialist for wireless connectivity and control company Silvair, with offices in San Francisco and Krakow, Poland. It covers smart lighting, IoT, wireless technologies and building automation.

A member of the Bluetooth Special Interest Group, Silvair offers Bluetooth mesh lighting control software that works with partner products in the Bluetooth ecosystem.

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