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Software Documentation - Onboard Computer

Overview

The main firmware of the onboard computer runs on an ESP32 platform, managing sensors, communication and parachute control during flight.

Architecture

Main File

Code Organization

setup()                 // Initialization of all components
├── setupLittleFS()     // File system
├── setupBMP()          // Pressure sensor
├── setupMPU()          // IMU
├── setupLoRa()         // Communication
└── setupServo()        // Servo motor

loop()                  // Continuous execution
├── readSensors()       // Data collection
├── handleParachute()   // Parachute control
├── logData()           // Storage
└── sendLoRa()          // Transmission

Modules and Sensors

1. BMP280 - Barometric Pressure Sensor

Function: Measure altitude and atmospheric pressure

Libraries:

  • Adafruit_BMP280
  • Wire (I2C)

Collected Data:

  • Relative altitude (m)
  • Pressure (hPa)
  • Base pressure (calibrated at setup)

Test Code: test/basico/basico.ino

Related Variables:

float base_altitude    // Initial altitude (reference)
float base_pressure    // Base pressure (hPa)
float previous_altitude // Previous height (for velocity calculation)
float max_altitude     // Maximum height reached

2. MPU6050 - IMU (Accelerometer + Gyroscope)

Function: Measure acceleration and rotation (flight dynamics data)

Libraries:

  • Adafruit_MPU6050
  • Adafruit_Sensor
  • Wire (I2C)

Collected Data:

  • Acceleration in X, Y, Z (m/s²)
  • Angular velocity in X, Y, Z (rad/s)
  • Sensor temperature (°C)

Related Variables:

sensors_event_t acc, gyr, temp  // Acceleration, gyroscope and temperature events

3. NEO-6M - GPS Module

Function: Get latitude, longitude, GPS altitude and time

Libraries:

  • TinyGPS++
  • Serial UART communication

Communication Pins:

  • RX_GPS: Pin 20 (receives data from GPS)
  • TX_GPS: Pin 21 (sends data to GPS)

Collected Data:

  • Latitude (°)
  • Longitude (°)
  • GPS Altitude (m)
  • Number of satellites
  • Date and time UTC

Features:

  • Waits 3 seconds in setup for synchronization
  • Uses GPS time to name log file

4. RFM95W - LoRa Module

Function: Long-range wireless communication with the base

Frequency: 868 MHz

Libraries:

  • LoRa
  • SPI

Communication Pins:

  • SS_LORA: Pin 7 (Chip Select)
  • RST_LORA: Pin 1 (Reset)
  • DIO0_LORA: Pin 2 (Interrupt)

Configuration:

#define LORA_FREQ 868E6      // Frequency
#define SYNC_WORD 0xF3       // Sync code

Transmitted Data: Concatenated string with data from all sensors in CSV format

5. Servo Motor - Parachute Control

Function: Open parachute at appropriate altitude

Pin: SERVO_PIN = 3

Positions:

  • MAXPOS = 0° (Parachute closed)
  • MINPOS = 90° (Parachute open)

Opening Criteria:

const float ALTITUDE_THRESHOLD = 750.0      // Minimum height (m)
const float ALTITUDE_DROP_THRESHOLD = 10.0  // Minimum drop from peak (m)
const float VELOCITY_THRESHOLD = 80.0        // Descent velocity minimum (m/s)

Control Function: handleParachute()

6. Buzzer - Signaling

Function: Indicate initialization status and operation

Pin: BUZZER_PIN = 0

Signals:

  • Alert: Multiple short beeps (initialization failure)
  • Success: Beep sequence (components started correctly)

Control Function: buzzSignal()

Storage System

LittleFS - File System

Function: Store telemetry data in real time

File Format: CSV

File Name:

  • If GPS is synchronized: HH_MM_SS-Dados.csv (GPS time)
  • If GPS not synchronized: {millis}-Dados.csv

CSV Header:

ID,Packet,Time,Latitude,Longitude,GPS_Altitude,Satellites,Date,Hours,Minutes,Seconds,
BMP_Altitude,Pressure,AccX,AccY,AccZ,GyroX,GyroY,GyroZ,Temp,ParachuteStatus

File Functions:

  • setupLittleFS() - Initializes the system
  • writeFile() - Creates new file with header
  • appendFile() - Adds line to file

Communication

Serial UART

  • Baud Rate: 115200
  • Use: Debug and real-time monitoring

LoRa

  • Range: Up to ~4 km (in open field)
  • Data Rate: ~1-5 kbps
  • Frequency: 868 MHz

Web Interface

Functionality: Asynchronous server on port 80

Endpoints:

  • GET / - Home page (HTML)
  • GET /api/files - List files in JSON
  • GET /api/file?name= - Download file
  • DELETE /api/file?name= - Delete file

Libraries:

  • ESPAsyncWebServer
  • WiFi
  • ArduinoJson

Adjustable Parameters

#define INTERVAL 200                              // Reading interval (ms)
const float ALTITUDE_THRESHOLD = 750.0            // Minimum height for parachute (m)
const float ALTITUDE_DROP_THRESHOLD = 10.0        // Drop from reference (m)
const float VELOCITY_THRESHOLD = 80.0              // Descent velocity minimum (m/s)
const String TEAM_ID = "#100"                     // Team ID

Execution Flow

  1. Initialization (setup)

    • Configure serial communication
    • Initialize I2C and SPI
    • Wait for GPS synchronization (3s)
    • Create log file
    • Initialize sensors and modules
    • Start web server

  2. Main Loop

    • Check 200ms interval
    • Read altitude and IMU
    • Calculate descent velocity
    • Check parachute opening criteria
    • Record data in file
    • Transmit via LoRa

  3. Parachute Control

    • Wait for minimum height
    • Monitor drop relative to peak
    • Check descent velocity
    • Open servo when all criteria are met

Support Code

The files in extras/ contain functional and tested code for reference:

Tests

Unit tests are located in test/:

Dependencies - Arduino Libraries

Library Version Use
Adafruit BMP280 Latest Pressure sensor
Adafruit MPU6050 Latest IMU
Adafruit Sensor Latest Sensor base
TinyGPS++ Latest GPS decoding
LoRa Latest LoRa module
ESP32Servo Latest Servo control
ArduinoJson ^6.0 JSON serialization
ESPAsyncWebServer Latest Web server

Development Notes

  • Synchronization: The system waits for GPS synchronization before flight starts
  • Redundancy: The parachute uses multiple criteria to prevent incorrect opening
  • Logging: All data is stored locally before transmission via LoRa
  • Power Efficiency: The ESP32 operates in continuous mode during flight