It’s been a busy summer but I am finally back to working on LoRa again. My RAK3172 modules showed up after a month of waiting, but unfortunately they were all with IPEX and none without. RAK shipped me the correct modules, and was kind enough to let me keep the ones with IPEX connectors that were sent in error.
I decided to actually use the STM32cubemx generated code base. It’s not terrible to work through, but it is probably more difficult than implementing it yourself depending on what you’re doing.
I’ve been happy with the RAK3172, outside of RAK not posting internal schematics for the module and then finding out it doesn’t contain a txco despite previous documentation indicating it does. Apparently the chip shortage lead to them making the decision to swap out the txco for a regular crystal oscillator last minute without updating the documentation. The poor/incorrect documentation was disappointing, but I will say RAK wireless does seem to have good support on their community forum and they are quick to answer any questions. The RAK3172 might not be the best device for Meshtastic in it’s current form since it doesn’t have bluetooth, but I hope that in the future Meshtastic adds support for lower power IOT devices without bluetooth. Bluetooth is great for the final steps of interfacing with the user, but you really only need one BLE->LoRa bridge, putting BLE on each IOT device seems unnecessary.
I was able to get the power consumption of my demo board down to 3uA sleeping and around 75uA for RX duty cycled receiving. I believe the duty cycle specs were 1 RX period every second for SF10 BW125khz, but I would have to double check my notes. The minimum RX period is at least 8 symbol periods plus 1ms for oscillators to stabilize, so higher spread factors and lower bandwidth settings increase the power consumption by increasing the required length of the RX period.
I am going to finish implementing my custom Motion Sensor → Alarm project. At that point I’d like to look into adapting it to implement a system closer to SSB where each device has a append only feed and surrounding devices sync and propagate that feed. Although latency might be slightly higher, it should in effect essentially be mesh networking with flood routing and store then forward functionality.