Wireless Network Options for Smart LED Lighting Systems

High-power LED lighting is opening up many opportunities in the smart home. LED lights have a dramatically longer lifetime and lower power consumption than halogen or traditional incandescent bulbs, and are available in a wider range of colors.

LED lights also lend themselves much more effectively to digital control. A low-cost LED driver can dim the lights or even mix different colors. This opens up a wide range of applications in the smart home where the lights are all connected via a wireless network to a central controller. This means that the lighting in different rooms can be individually optimized, and even changed to suit the preference of the person in the room.

This capability opens up the question of which wireless technology to use. There are several different wireless networks running in the unlicensed 2.4 GHz band that can be used for such an application. These range from Bluetooth to ZigBee and its remote control variant, 6LoWPAN, to proprietary networks such as SmartMesh and Dust.

While adding wireless connectivity to LED lighting adds complexity and cost in comparison to the use of a simple dimmer switch, the additional control functions add more than enough value to offset these drawbacks.

Power consumption is an issue for wireless controllers, primarily for the need to minimize excessive heat. A higher temperature can reduce the lifetime of the LED lighting elements, and may require additional thermal management components and a higher temperature rating for the wireless controller. As space is always a concern, the focus is very much on integration to minimize the additional external components alongside the LED lighting elements in a given fixture, and being able to link directly to the LED driver is essential.

The desire for more sophisticated applications such as color mixing also drives the need for a microcontroller within the fixture. The ability to run the control software for the lighting system on the same microcontroller core that handles the wireless connectivity reduces the cost and complexity of the fixture design.

Bluetooth

An increasingly common approach to adding wireless connectivity to an LED lighting system is Bluetooth. This can handle the wireless connection to an LED fixture, controlling the LED driver from a single chip that integrates the 2.4 GHz wireless and the Bluetooth protocol stack. Such devices include the DA14580 from Dialog Semiconductor, which integrates an ARM Cortex-M0 controller core alongside the Bluetooth front-end transceiver and interfaces directly to the antenna to minimize the design complexity, and comes in a chip scale package. The transceiver is fully compliant with the Bluetooth 4.2 standard through dedicated hardware for the Link Layer implementation, and this supports the Bluetooth Smart firmware that includes the L2CAP service layer protocols, Security Manager (SM), Attribute Protocol (ATT), the Generic Attribute Profile (GATT) and the Generic Access Profile (GAP). Similarly the NRF51822 from Nordic Semiconductor can be used for a Bluetooth Smart link.

An advantage of Bluetooth is that the higher data rate of 1 Mbit/s allows other applications such as audio. Adding a speaker to the fixture provides additional value by streaming music from a smartphone in any room in the house.

The DA14580 supports flexible memory architecture for storing Bluetooth profiles and custom application code that runs on the Cortex-M0 processor via a simple scheduler.

One of the challenges for Bluetooth is that the connection is point-to-point, so a smartphone connects to an individual fixture. While this works well for centralized lighting, it can be a challenge for distributed lighting systems. One way around this in the future is being developed by the Bluetooth Special Interest Group to add mesh networking to the Bluetooth standard. This would allow Bluetooth transceivers to connect to each other to pass on commands and data to specific fixtures.

There are already proprietary mesh software protocols that sit on top of Bluetooth. The NRF51822 for example supports customized code running on the embedded Cortex-M0 processor that will provide mesh networking and a 2 Mbit/s data rate.

ZigBee

An alternative wireless system for LED lighting in the smart home that does provide mesh networking is ZigBee, which is based on the 802.15.4 standard. It has a lower bitrate of 250 Kbit/s for low power implementations and allows LED fixtures to connect to each other for distributed control. The mesh network is controlled from a ZigBee hub using a controller such as the CC2630 from Texas Instruments or the JN5169 from NXP that acts as the control center for the home, not only for lighting but also for sensors and actuators.

Figure 1: The ZigBee Alliance has defined a wireless protocol for LED Lighting that works alongside existing ZigBee smart devices.

The ZigBee Alliance has defined a wireless protocol specifically for LED smart lighting, backed by the major bulb makers. ZigBee Light Link provides a global standard for interoperable and very easy-to-use consumer lighting and control products. It allows wireless control over all their LED fixtures from bulbs and timers to remotes and switches. The standard lets users change the lighting remotely to reflect ambiance, task or season, all while managing energy use. The standard does not require any special devices to coordinate with the lighting network, and the automatic joining protocol for the mesh networking makes it easy to add and remove products.

As Light Link is a ZigBee standard, lighting products will interoperate with products using other ZigBee standards already in consumers’ homes, including ZigBee Home Automation, ZigBee Input Device, ZigBee Remote Control and ZigBee Health Care.

Figure 2: The protocol stack for ZigBee Light Link.

One potential drawback is that ZigBee is not implemented on smartphones or tablets and therefore requires a hub to provide the mesh networking. However, this hub can easily be controlled via Bluetooth from an app on a smartphone or tablet to provide the user interface.

SmartMesh and dust

Another protocol that is aimed at LED lighting is Dust. Like ZigBee it is based on the 802.15.4 physical layer, but uses the 6LoWPAN protocol instead. It too requires a hub to communicate to a smartphone or tablet.

The SmartMesh IP wireless networks are self-managing, low power internet protocol (IP) networks built from wireless nodes called motes. The LTC 5800-IPM, for example, uses highly integrated, low power radio design by Dust Networks alongside an ARM Cortex-M3 microcontroller running Dust’s embedded SmartMesh IP networking software.

The device features an on-chip power amplifier (PA) and transceiver so it only requires power supply decoupling, crystals, and an antenna with matching circuitry to create a complete wireless node. With Dust’s time-synchronized SmartMesh IP networks, all motes in the network may route, source or terminate data, and the software can be configured via a software Application Programming Interface (API).

Figure 3: The SmartMesh approach is based on the 802.15.4 6LoWPAN protocol and allows a low-cost microcontroller to be used.

The transceiver then interfaces to a low-cost microcontroller with a DC-DC output for controlling the LED bulb. This allows the bulb developer to choose a controller optimized for the particular LED lighting design, from a simple dimmer bulb to one capable of emitting various colors.

Conclusion

There are many different options for controlling LED lighting in the smart home. Bluetooth provides a direct interface to smartphones and tablets, but currently lacks a standard to implement a mesh network allowing many bulbs to be linked together. Proprietary mesh protocols can sit on top of standard transceivers, but limit the interoperability of LED bulbs. Similarly, the SmartMesh implementation of 6LoWPAN provides a low power implementation with the flexibility to use different microcontrollers, but still limits interoperability and requires a hub. 

ZigBee as a standard is the language for a wide variety of smart home applications, and it provides a dedicated profile for LED lighting that is interoperable with other ZigBee devices. Hubs that combine the ZigBee controller with a Bluetooth connection provide the best of both worlds with the widest coverage of wireless technologies.