After the disappointment of the Z-Wave implementation of an in-ice sensor for the Eye on the Ice system, Filipe and I did a survey of other RF communications technologies, and settled on LoRa, per this blog entry. After evaluating several modules and then obtaining a few more, we settled on the AcSip S76S system-on-a-chip, which contains an STMicro STM32L073RZ Arm-Cortex M0+ MCU and a Semtech SX1276 LoRa Transceiver.
If used in the more-popular LoRaWAN mode, it is similar to Z-Wave, but has much longer range. However, there is also the less-sophisticated LoRa mode, where there is no inherent mesh networking and a much simpler simplex protocol, which is what we are using for our second proof-of-concept.
We’ve increased the battery size to a CR2450, giving us 600 mA-hr, much more than the approximately 230 mA-hr of the CR2032. However, in order to maintain decent RF antenna operation, we’ve had to split the device into two interconnected boards, complicating the design. We’re currently evaluating the performance and reviewing further options.
In any case, it sure seems like we can get much more consistent operation at up to 250 ft, with the correct dimensional parameters, even in 32 mm diameter size.