Peer-to-Peer Direction-Finding Compass Device

A senior capstone project building a pair of handheld devices that point toward each other in crowded, off-grid environments like outdoor music festivals. Each unit has a GPS receiver, magnetometer/IMU, LoRa radio, and LED display. The two devices periodically broadcast their GPS coordinates over LoRa, compute the bearing and distance to each other, and display a directional arrow on screen that updates in real time as the user turns. No Wi-Fi or cell service required.

The project originally planned to use Meshtastic for LoRa communication, but we dropped it early on. Meshtastic is a monolithic firmware, and its module API didn't give us enough control over the system to drive our own display and navigation logic. We also realized that mesh networking is overkill for a two-device prototype: point-to-point LoRa communication is simpler, lower overhead, and sufficient to prove the concept. Going custom also gave us the opportunity to design the firmware from scratch on FreeRTOS, which is something we wanted to explore.

The firmware runs on FreeRTOS across both ESP32-S3 cores, with three tasks communicating through queues. Core 0 runs the radio task: it handles LoRa TX/RX via RadioLib using interrupt-driven async receive and broadcasts the device's GPS position every 3 seconds. Isolating radio on its own core ensures that multi-millisecond SPI transactions during packet TX never stall the display. Core 1 runs the navigation and display task at 20 Hz: it reads the IMU over I2C, gets a stable heading, computes bearing and distance from the latest positions, and renders the compass arrow and distance readout to the LED. GPS parsing also runs on Core 1, continuously feeding UART bytes from the UC6580 into TinyGPSPlus and pushing new fixes into a FreeRTOS queue. Inter-task communication uses xQueueOverwrite on single-item queues so the nav task always reads the most recent GPS and partner position without blocking.

The project is not yet complete! GPS is working on the Heltec board, and the FreeRTOS task architecture is being built. Next steps are LoRa communication between the two units, IMU integration and magnetometer calibration, and the compass display. This page will be updated as the system comes together.