GPS tracker unit philosophy
Adafruit Feather M0 LoRa 433MHz board
Adafruit GPS featherwing board
small <1000mAh lipo, or possible power feed from bike torch battery (4x18650)
Code is based around Radiohead RFM95 library for handling (currently) one-way telemetry.
Code to be uploaded when ready. Current status of code is that it will transmit position, speed, heading, altitude, battery level and 'panic button' status back to the server every 30 seconds, with a 500ms transmission slot per device, synchronised to the GPS clock and PPS output to prevent collisions with other devices.
LoRa transmission parameters need to balance reception distance, update frequency, battery life etc with the fact that the device is likely to be moving, and the pseudo time-division multiple access (TDMA) regime for avoiding collisions.