LoRa is a Long Range, Low power radio access technology aimed at sensors and data collectors that need to send small packets of data infrequently. Coupled with the LoRaWAN protocol defined by the LoRa Alliance, It’s a good fit for many of our clients who want to send just a few bytes of data, and don’t want to carry a mobile phone sized product just to house a big enough battery.
We were lucky enough to be selected as one of only a handful of companies to work with Digital Catapult who had constructed an early LoRaWAN trial network in London, and we did some successful tests for some alternative tracking methodologies some of our clients were interested in as part of that.
This then led us to designing a very small tracking product, aimed at tagging small items such as pets, bags, wallets, etc. At 25mm diameter, it’s pretty small, and with a range of possible batteries that can be fitted, Bluetooth LE, GNSS positioning and LoRa, can offer an extensive mix of possibilities. For such a small device, we were very pleased to find the GNSS reception was as good as a bought-in module with 25mm patch antenna.
Then we went one step further and added wireless charging, NFC, alternative transmission bands and a big increase in the LoRa power, but still able to fit in a small discrete case. In fact, part of the brief was to make this inconspicuous, so we chose to put it in a key fob case and add some fully functional keys.
The unit regularly sends positional information, but the user is able to send an immediate position alonside a request for help, by pushing one of the buttons. The other button can be used to repurpose the internal software defined radio and, for example, send a request to open/close a garage door or access gate – again helping to disguise the primary function.
We tested the unit by putting it in a box on top of a car, and drove a route from our office and back. We managed to get regular reports to our LoRa gateway up to 10km away, and then occasional connections up to 15km. The route chosen passed through areas where the signal would be compromised (e.g. by high sided cuttings) specifically to see how it faired.
Considering our LoRa gateway setup isn’t particularly exotic (a 6dBi monopole antenna that barely reaches the roof of the 2 storey office building), we are certain this could be improved – but it is still pretty impressive for a keyfob that can last many months on a single charge of its coincell-sized battery.
Of course, in a real system, there would be a number of LoRaWAN basestations that would be receiving the signal, and the transmission wouldn’t be across open fields, but it’s still a good demonstration of what’s possible with modern RF signal encoding techniques.