Z-Wave Proof of Concept for Eye on the Ice In-Ice Sensors

As outlined in my blog post about Modern RF Communications Modules, around 2008, my team at Norscan developed the Eye on the Ice system for Hans Wuthrich, Master Ice Maker.  It is a great system, and still works well.  Unfortunately, the Linx FHSS modules have gone obsolete.   For the moment, inventory is available to support the relatively small runs of production.  But, over the long haul, things will have to change.

In the meantime, Hans wants a small, low cost, perhaps disposable, in-ice sensor that could be used to accurately monitor ice temperature from several points of the rink.  He had an engineer doing some experimentation in this area, but since the frequency is 433 MHz, the FHSS module and it antenna are quite large, it was difficult to get it down much smaller than, say, 50 mm x 50 mm with a 150 mm antenna sticking out in one direction or another.

With a former colleague and friend, Filipe Fernandes – analog, RF and EMC developer extraordinaire –  we developed a proof of concept that met the requirements.  Battery operated from a single CR2032 cell, and only being about 32 mm diameter x 10 mm thick before enclosure, it used Z-Wave to send the temperature to a Raspberry Pi that had both a Z-Wave controller and an FHSS module attached.  The Raspberry Pi operated as a gateway, relaying incoming temperature reports into the Eye on the Ice network.

Although the system worked, we had issues with repeatability in manufacture, causing trouble with range.  One sensor was able to report from over 80 feet away, another from only 20 feet away.  We addressed this issue, but then had trouble with battery life.  It seems that the automatic operation of the Z-Wave protocol causes a sensor to continuously retry if it doesn’t get an acknowledgement from the controller.  We were sure that there was a way to deal with this, but the lower levels of the protocol and operation of a mostly-sleeping sensor were opaque and difficult to figure out.  It would have been time-consuming (and therefore expensive) to resolve these issues, so we abandoned the Z-Wave system and sought an alternative.

Per this blog entry, we found the solution in the form of a LoRa system.