PL-26 Flight Computer Software

Embedded avionics firmware for PL-26, developed for the Unity Rise University of Liverpool Rocket Team for the 2025-26 launch.

This repository is the software component of a Year 3 MEng Individual Project (ELEC440) for the MEng Avionic Systems degree.

Project Context

• Author: Joseph Wood
• Module: ELEC440 MEng Individual Project
• Project Title: LASER - Rocket Flight Tracking and Control
• Rocket: PL-26 (Unity Rise, 2025-26)

What This Firmware Does

From src/main.cpp, the flight computer provides:

• Sensor acquisition from BMP390 (barometer), BNO085 (IMU/orientation), ICM20948 (IMU) and u-blox MAX-M10S GNSS
• INS/Dead reckoning algorithm integration via lib/INS_Model (INS_Model_C), generated using the Simulink C++ Coder
• SD card CSV logging using SD_MMC
• LoRa telemetry transmission at 868 MHz
• Wi-Fi SoftAP + HTTP server for configuration and file access
• FreeRTOS task-based software for task and core management with mutex-protected shared state

Runtime Architecture

Core tasks created in setup():

• highFrequencySensorTask - reads BMP3XX and BNO08x data and computes filtered vertical speed
• gpsTask - reads GNSS PVT data and updates GPS fields
• insTask - maps sensor inputs into INS_Model_C and updates INS outputs
• loggingTask - writes periodic CSV rows to SD card and flushes once per second
• loraTask - sends packed binary telemetry packets over LoRa
• webServerTask - services HTTP requests
• buttonTask - toggles logging pause/resume with debounce

Synchronization primitives:

• xSensorDataMutex protects shared sensor/INS data
• xSpiMutex arbitrates SPI access between sensors and LoRa

Data Outputs

SD Logging

At boot, firmware creates an incremented log file:

• /Flight_Data_<n>.csv

CSV columns include:

• Time (ms)
• BMP: temperature, pressure, altitude, vertical speed
• BNO: linear acceleration, gravity, quaternion
• GNSS: latitude, longitude, altitude, speed, heading
• INS: X_Estimate, Y_Estimate, Z_Estimate, Lat_Estimate, Long_Estimate

LoRa Telemetry

LoRa payload uses a packed TelemetryPacket (44 bytes) containing:

• altitude, vSpeed
• lat, lon
• qR, qI, qJ, qK
• insX, insY, insZ

Configured in code for:

• Band: 868E6
• CRC enabled
• Bandwidth 500E3, spreading factor 7, coding rate 4/5

Configuration

Configuration is saved on SD card at:

• /config.txt

Current contents:

pressure=1013.25

• pressure maps to seaLevelPressureHpa for barometric altitude reference.

Repository Structure

pl26-avionics-software/
|- include/
|- lib/
|  |- INS_Model/
|- src/
|  |- main.cpp
|- test/
|- platformio.ini
|- README.md
|- LICENSE.md

Build and Flash

This project uses PlatformIO, MCU is ESP32-S3-Mini-1-N8.

platformio run
platformio run --target upload
platformio device monitor -b 115200

Related Repositories

• Test code: https://github.com/UnityRiseUol/pl26-avionics-test-code
• Altium Designer hardware files: https://github.com/UnityRiseUol/pl26-avionics-hardware

Safety Notice

This software is developed for educational rocketry use. Please complete thorough testing and validation before flight.

License

Licensed under the MIT Licence. See LICENSE.md.