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PTERODACTYL: A Versatile Flight Computer for Stratospheric Ballooning

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Abstract

In the summer of 2020, the stratospheric ballooning team at xxx developed a versatile flight computer named PTERODACTYL (Payload To Enable Recording Of Data And Communication Telemetry Y (While) Lofted). PTERODACTYL is built on a custom, student-designed printed circuit board (pcb) and is based around a Teensy 3.5 microcontroller. It measures just under 10 cm by 10 cm, allowing it to fit inside a (mock) CubeSat. For a 2 to 3 hour stratospheric balloon flight, a PTERODACTYL can be powered by a single 9 volt lithium battery. It has on-board SD card logging, as well as a short-range XBee3 radio that allows it to communicate with nearby XBee3-enabled payloads on the same stack, such as other PTERODACTYLs units and/or an XBee3-commandable vent. The PTERODACTYL flight computer system has the following built-in sensors: gps (ublox M8N), pressure, 9-degree-of-freedom IMU, and two thermistors to measure on-board and external temperature. It also has headers to control two servos, as well as slide switches, momentary switches, and shorting plugs (for user input) plus 4 colored LEDs and a miniature OLED screen (to output information to the user). It is constructed using only through-hole soldering, for ease of assembly. The basic flight code, written to log readings from the basic sensor set, has been used by (and tweaked by) high school teachers, college/university students in freshman seminars and other students new to ballooning, as well as experienced ballooning students. The PTERODACTYL pcb breaks out some of the non-used Teensy pins, allowing easy access to UART, SPI, and I2C buses for more-advanced users. Our team has used the PTERODACTYL flight computer to run RM-60 Geiger counters, other gps modules (most notably the ublox M9N), QUIIC sensors (Sparkfun sells a variety of QUIIC sensors, but not all work in stratospheric conditions), real-time clock modules, other radio modules (a second XBee3, an RFD900, an RFM69), relays (to control sirens and heaters), and more. Due to the current difficulty in sourcing Teensy 3.5 microcontrollers, we recently designed a Teensy 4.1 version of the PTERODACTYL pcb and took the opportunity to rearrange the components to make the pcb more user-friendly and to add more functionality. In addition to the new microcontroller, the new PTERODACTYL board can be powered by a 3.7 volt battery or by 5 volt USB input, not just by 9 volt batteries. It is also directly compatible with both ublox M8N and M9N gps breakout boards, which can have different pinouts (depending on which company they are purchased from). The PTERODACTYL has been selected as a flight computer for the "engineering" side (AKA the "video streaming" side) of the National Eclipse Ballooning Project (NEBP). It will allow NEBP engineering teams easy access to "basic" sensor data and also provide a platform to which teams may add custom sensors and/or actuators. Once integrated with the NEBP Iridium modem system, the XBee3 will allow a PTERODACTYL to relay commands from the ground to other payloads on the stack (such as a vent) in near-real-time.

Keywords: stratospheric ballooning, flight computer

How to Cite:

Wallo, S., Posey, A., Wehling, P., Van Gerpen, A. & Flaten, J., (2023) “PTERODACTYL: A Versatile Flight Computer for Stratospheric Ballooning”, Academic High Altitude Conference 2022(1). doi: https://doi.org/10.31274/ahac.15639