Team Tejas CanSat Firmware

Overview

Firmware for the Teensy 4.1 based CanSat platform handling sensors (BMP280, MPU6050, HMC5883, INA226, MICS-5524, L89 GNSS), telemetry via XBee, and SD logging.

Key Features

• Single persistent SD logging directory: Flight_<TEAM_ID>
• Telemetry CSV line ends with last command echo (cmd_echo)
• SD command gating while telemetry active
• Lightweight command dispatcher with conditional immediate response sending
• Altitude fusion (baro + GPS) with filtering
• Optimized GPS handling for 7semi L89 module

GPS (L89) Optimization

Implemented lean logic in gps.cpp:

• Configurable constants in constants.h:
  • GPS_BAUD_RATE (boot baud, default 9600)
  • GPS_HIGH_BAUD_RATE (optional 115200 if future reconfiguration added)
  • GPS_FIX_STALE_MS (default 1500 ms) marks data stale when no fresh sentences parsed
  • GPS_MIN_UPDATE_INTERVAL_MS throttles telemetry structure writes (default 200 ms)
• Tracks last_fix_ms and only marks a fix valid when a fresh valid sentence arrives.
• If stale, telemetry forced to sentinel values: lat=0, lon=0, altitude=-1000, satellites=0.
• Avoids unnecessary field updates more often than the configured interval.

Build

Use PlatformIO (Teensy 4.1). Example (PowerShell):

pio run

Or VS Code task: "Build CanSat Project".

Next Steps (Optional)

• Add dynamic GPS baud escalation (send module config to switch to 115200 then Serial2.updateBaudRate) if desired.
• Add checksum or CRC to telemetry lines.
• Implement binary telemetry mode.

Directory Structure (Partial)

• src/main.cpp – entrypoint
• lib/ – modular subsystem libraries
• lib/gps/ – GPS logic (gps.cpp, gps.h)
• lib/constants/constants.h – system-wide constants & command strings
• lib/storage/ – SD logging

License

See LICENSE file.