The main concept of our latest webcast, presented by Simon Slupik, was how Bluetooth Mesh networking has the potential to deliver relatively simple wireless lighting controls functions, ease of commissioning, with distributed communications across many nodes to avoid a single, centralized point of failure. However, by the time we arrived at the Q&A, I was most intrigued by the discussion of the relationship between the energy harvesting capabilities of self-powered switches in the device configuration and the robustness of communications across such a networking topology. Read on for specifics on that portion of the program, so to speak.
Maury Wright: Bluetooth does not need line of sight for communications [unlike visible light communications (VLC) networked architectures], but what about occupancy sensing or daylight harvesting functions?
Simon Slupik: Bluetooth radio, of course, does not have problems traversing wall; so this whole building, it functions as one big network with functional groups and zones that are configured as rooms or in other arrangements. In terms of occupancy and ambient light sensing, of course, to sense the light you typically need line of sight. The ambient light sensor needs to overlook the area that it is reporting about. As far as occupancy sensors go, there are multiple technologies and I mentioned this option with mesh fixture controllers… It has a separate, external sensor and that’s very often used when a vendor provides multiple options for occupancy sensing technologies because multiple or different [options] can be used. The most typical for indoor is passive infrared [PIR]; this is probably the majority of sensors, using PIR sensing elements, but you can use ultrasound, you can use radar technologies, you can use microwave. So some of those vendors offer multiple options for sensing heads. You may have a sensing head that is using a technology of your choice, that is connected to this Bluetooth fixture controller that’s one of the integration options.
MW: I know you talked a little bit about the switch technology from EnOcean; this user says, “Does this switch use a piezoelectric circuit to generate its own energy when pushing the toggle switch?”
SS: It uses magnetic generation circuits. There is a small coil and there is a magnet moving inside. So simply, when you press the switch, the magnet moves so it acts as a very small current generator. And it generates enough power to wake up the microprocessor that prepares the message, uses strong encryption for a high level of security, and then it wakes up the Bluetooth radio and the Bluetooth radio transmits multiple times to make sure the delivery rate is almost 100% — or effectively 100% — and then it goes to sleep until you press it next time. But in terms of energy harvesting, we are seeing an advent of multiple different energy harvesting technologies. You can use photovoltaic, there are Bluetooth sensors that use photocells as a source of energy and we’ve recently seen prototypes of Bluetooth sensors that use radio frequency harvesting. So these are maybe realized as a slightly bigger antenna; they are the size of a business card and they can be realized as simply stickers that you can attach to any piece of equipment. So we will be seeing a lot of innovation in this area of self-powered energy harvesting sensors, I believe, and they all use Bluetooth technology, that’s important.
MW: And the energy harvesting is certainly an interesting technology. But you could still use batteries.
SS: Oh, yes, of course. But there is just the maintenance, that’s probably why, especially for commercial/industrial use cases, people prefer using energy harvesting. And you also can use line power. I mean, there are Bluetooth switches available today that are simply line powered and you just, for retrofit projects, very often there were switches already so you just pull them out, the old switches; you install the Bluetooth switch, connect them to the line and they keep operating.
MW: The important synergy between energy harvesting and Bluetooth is the low-energy angle, that Bluetooth is able to support communications even with these energy harvesters not really producing that much power, right?
SS: Yeah, exactly, this is the nature of Bluetooth. So Bluetooth Mesh is a topology — which is a constellation of devices, how the network is built. It uses the underlying radio technology that we call Bluetooth Low Energy; this low energy is really low energy. [Laughs] It requires very little energy to transport the message, on the order of 20 μJ. Typically a harvester like this, in a switch, can produce about 10× more, that allows to transmit multiple times and that’s where the ultrahigh reliability comes from. If you transmit multiple times, the chances that none of the messages arrives are close to zero. That’s where the reliability of the system comes from.
Check out Simon Slupik’s full webcast presentation on demand, as well as these other information resources on lighting controls and Bluetooth Mesh.
EnOcean and Silvair partner on controls for Bluetooth-connected LED lighting
Choose open, interoperable lighting controls for commercial project success
Bluetooth Mesh paves the way to IoT smart lighting
