LoRA + GPS trackers for Burning Man

A pair of homebrew trackers for off-the-grid location sharing, using Adafruit's Feather boards. Hardware mostly me, software mostly Drew. Built (in a rush) for Burning Man 2016, where the perfectly circular city layout makes it possible to accurately convert GPS co-ordinates to a street address (e.g. 4.15 & J-25m). For Afrikaburn, which does not use a perfectly circular layout due to terrain, we used a radial system, choosing a centre point and origin bearing and displaying a bearing as clock time and distance in metres (e.g. 9.45 + 600m).

Parts list

• Adafruit Feather 32u4 RFM95 LoRa Radio - 868 or 915 MHz
• Adafruit Ultimate GPS FeatherWing
• FeatherWing OLED
• LoRa Antenna Kit + uFL SMT connector (important! not included!)
• Lithium Ion Battery Pack - 3.7V 4400mAh
• Small hard plastic case (Muji)

Code

• https://github.com/mloudon/electrosew/blob/master/feather_send/feather_send.ino

Notes

• Batteries lasted a full week, with several hours of use each night, although we did tend to keep them switched off when both trackers were together.
• One of the things we plan to do at Burning Man this year is a proper range test. The first version used a wire antenna, and the range (in the city) seemed around 800m. The second version, with the external antenna, received a fix around 20km away! The reliability requirement for these is quite low - one fix every few minutes is probably fine - and at this level the range covered the entire Afrikaburn site.
• The 32u4 Feather boards have 32K of flash, which even with as much optimizing as we could do in limited time wasn't enough to use Adafruit's recommended GPS and packet radio libraries together. We got around this by using TinyGPS, the M0 Feathers have 256K, and currently the price is the same, so this is almost definitely the better choice.
• In testing, I found that switching from send to receive took the hardware a little time. If your radios aren't talking to eachother, try adding a short delay.
• For some reason, the OLED doesn't come on on startup - you need to press the reset button once first. Shrug.