Time to switch to free wireless protocol, says Arveni
“Although we build the micro energy harvesting modules from off-the-shelve components, the specific construction that we have adopted yields a very high mechanical-to-electrical energy conversion efficiency, up to 81% to be precise”, told us Jean-Frédéric Martin, Arveni’s founder and CEO.
“This not only compares very favourably with the typical 12 to 15% of energy conversion you get from competing energy-harvesting switches” Martin added, “but thanks to this high conversion efficiency, we are able to design our switches with a lower actuation force and less noisy, making them more comfortable to use”.
Strong from the experience gathered with building automation partners as a consultant and R&D engineering company, Arveni is now launching a line of battery-less wall switches, able to remotely control a relay & timer receiver unit through a very low power radio link whose protocol it is making open source.
Dubbed SARAH for "SmArt RAdio by Harvesters for building automation", the open-source and collaborative radio protocol operates in the 868.3 MHz ISM band, relying on frequency modulation to deliver a communication range of 20 to 100 meters indoor. Drawing less than 0.3W, SARAH is particularly light to operate but rugged enough to reliably send the short switch identifiers and on/off status messages to paired relays.
“When discussing with building automation system engineers, either coming from large groups such as Bouygues Construction, or from small and medium enterprises, all would beg for interoperability and access to the source code”, recalls Martin from the days Arveni operated as a design office for equipment manufacturers.
“While there are already many radio protocols available for building control and automation systems, such as KNX, Z-Wave, EnOcean or ZigBee, all implemented under various product brands, the lack of interoperability between the different brands often locks building automation system installers into one brand, for the sake of simplicity”, explains Martin.
“For system maintenance, in the case a part needs to be replaced or if a layout change is required, the new owners or installers have no other option but to come back to the original manufacturer, at a premium cost since no other third-party service provider can intervene on the parts”.
“So when we looked at implementing light radio links for our own battery-less switches, after trying out many of the existing protocols on the market and figuring out all the incompatibility and cost issues, we decided to develop our own. The big difference is that we make SARAH free to use and open-source”, says Martin. “We wanted to break free from monopolistic radio protocols that don’t let you mix and choose the best parts from different vendors”.
With this approach, manufacturers can have full access to the source code and even tweak the radio protocol and run a different version for a specific need, as long as they keep it open and release their patched version back to Arveni.
In return, Arveni will manage a repository of all existing versions and their typical use cases, checking the new patches for interoperability while updating public code libraries for engineers to implement SARAH on any low cost and low-power radio chip from the likes of Atmel, STmicro, or TI to name a few examples.
Supporting data rates of 125kbps, SARAH is a dynamic protocol with the data payload tuneable from 0 to 255 bytes. So the frame size can be increased in order to achieve sensor data communication, bidirectional communication and data encryption for example.
Fig. 1: Open and flexible, SARAH’s data frame format.
This length is indicated in the data frame before the actual payload so the relay listening to the message knows what to expect. A byte is also reserved for the manufacturer’s ID. 80μWs is needed for the first frame, then only 50 μWs for the following frames, and the messages are repeated 3 to 5 times for ruggedness.
Currently, Arveni offers a short- and a long-message version, together these implementations should cover about 70 to 80% of all applications according to the company.
The free radio protocol will save manufacturers and installers several euros per switch and sensor node, estimates Martin, but it will also enable the emergence of independent third-party maintenance services in this sector, and let innovative one-product companies compete with larger manufacturers on specific solutions.
This is also a clever way for Arveni to make some room for its core product, battery-less switches that the company claims are much better than competing offerings. The compact piezoelectric energy harvesting switches can snap into leading European brands of switch sockets including Legrand and Schneider, but Arveni will also consider licensing its piezoelectric technology to socket manufacturers.
Eco-designed to draw less than 0.3W, the whole system including the switch together with its paired relay & timer receiver unit will save homes and buildings tenants from 11 to 15 euros per year in electricity bill compared to competing solutions, claims Arveni (aside from the energy savings that can be realized using the timer function).
During installation, each relay & timer receiver is paired with one or several switches through a very simple manual procedure involving a program mode at the receiver during which the switches are activated across the wanted time interval. In effect, the timer can be programmed to switch off the lights from 30 seconds up to 7 days after they were initially switched on.
Fig. 2: The relay & timer unit is hollowed-out for a simple fit in a luminaire’s socket.
“This is a simple feature that most of the home & building automation professionals were looking for”, commented Martin. “You can switch off the lights at any time, but if you forget to do so, the timer will take care of it, for example at the end of the day in the office or in a hotel corridor, the time it takes you to walk through it”.
In new constructions, the switches can be mounted on bare walls at the owner’s request, without having to arrange specific wiring trenches. The switches together with the relay & timer receiver are also perfect retrofits for old building renovations.
Fig. 3: One could stick the wireless and battery-less switch onto any furniture.
They could even be stuck to a door or to a night table depending on the desired ergonomics (for example in hospitals where rooms can be re-organized). Martin is also keen to announce Arcom as one of its partners, the French company uses SARAH in its Aïther line of building automation products.
Visit Arveni at www.arveni.fr
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