On-Board Computer Proto

The flight computer prototype is built from an STM32F4Discovery Board associated with the STM32F4DIS-BB dev-card. The OBC is responsible for storing the telemetry data on SD-card, buld up the 64bytes long radio telemetry packets, gather GPS information and taking pictures with the integrated camera system.


The STM32F4Discovery Board is an ARM32 based development board produced by STMicroelectronics. The motherboard is integrated with the STM32F4DIS-BB shield and the STM32F4DIS-CAM camera module. The final modell is planned to build around an STM32F407xx microcontroller, will have an integraded camera and SD card slot.

STM32F4Discovery Board
  • STM32F407VGT6  32-bit ARM Cortex-M4F microcontroller, 1 MB Flash, 192 KB RAM
  • ST-LINK/V2 debugger on card
  • 3 V vagy 5 V voltage supply
  • LIS302DL/LIS3DSH ST MEMS 3-axis accelerometer
  • MP45DT02, ST MEMS audio sensor + mic
  • CS43L22, audio DAC eith integrated class D speaker driver
  • 8 LED
  • 2 pushbuttons (user and reset)
  • USB OTG with micro USB connector
  • Pin headers with all the I/O ports of the controller
  • Micro SD Card™ slot
  • 10/100 Ethernet  with RJ45 connector
  • RS232 with D-SUB-9 connector
  • 30pin DCIM Camrea connector
  • LCD connector
  • Communication pins (UART, I2C, SPI, CAN,
  • PWM and GPIOs)


The telemetry packets contained the radio amateur call-sign of the balloon, GPS coordinates, altitude, speed, internal temperature, stabilized voltage level and time stamp.


GPS coordinates, altitude and speed is provided by an NV08C-CSM module. This GPS reciever is designed for high-altitude operations and has an altitude limit of 50 kms (~32 miles), so we could track the entire flight of the balloon. The NV08C module communicates with the OBC through NMEA standard. Parsing the proper NMEA messages longitude, latitude, altitude and speed data could be processed. Each GPS NMEA word has time stamp which used for synchronize the system time. Time Sync is needed, because the Real Time Clock (RTC) unit of the OBC produce increasing slip due to the temperature decrease.

The internal temperature and the stabilized supply voltage is measured by the microcontroller of the communication unit. These data, the exchange between the COM and the OBC during the preparation of the radio communication action.