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Project: Traveler ptFlex flight controller.

Introducing ptFlex Flight Controller

The ptFlex flight controller is the second generation of ATmega-based flight controller from Project: Traveler.  Like the first-generation ArduinoTrack, the ptFlex is a stand-alone APRS beaconing system developed for high altitude ballooning in near-space.  

Unlike the ArduinoTrack however, the bulky and sometimes fragile Arduino headers have been eliminated, and instead external interfacing can be accomplished with an I2C header, which adheres to SparkFun Electronic's Qwiic connector.  With a wide variety of off-the-shelf sensors from SparkFun and a separate area of the firmware dedicated to custom code, writing new features is simpler than ever.

To make the transmitter selection flexible, an 11 pin header is available on the ptFlex circuit board that is pin-compatible with the fixed-frequency Radiometrix HX-1 modules, or the Project: Traveler DRA818V transmitter modules which allow the frequency to be changed.

The ptFlex does utilize the same power connectors, programming cable, and basic functionality, making it an easy transition.  The ptConfigurator utility is still used to configure flight parameters, and is backwards compatible with the first generation ArduinoTrack.

ptConfigurator Software

The ptConfigurator (formerly ArduinoTrack Configurator) is the piece used to configure the flight settings of the ptFlex, which are stored in non-volatile EEPROM.  Downloading and installing ptConfigurator is easy on any modern Windows PC.  The configuration cable is used which provides a 5V TTL-level serial interface into the three-pin header on the ptFlex (or ArduinoTrack) flight controller to view and change the settings.

Design Files

Like the hardware and software before, the ptFlex system is all open-source hardware and software.  Full design files can be found at GitHub.


The hardware design is based on the Microchip ATmega328 microcontroller and a Ublox MAX-M8Q GPS module.  The transmitter can either be a DRA818V-based daughter board, a RadioMetrix HX-1 transmitter, or optionally interface off to another transmitter of your choosing.  

All of the hardware (except for the DRA818V transmitter module or Radiometrix HX-1 transmitter module) can be sourced from Digikey Electronics.  A Bill of Materials can be found inside of the ptFlex and Flex-Transceiver design repositories.

ptFlex Hardware GitHub Repository

Flex-Transceiver GitHub Repository


Firmware for the ptFlex is a fork from the tried-and-true ArduinoTrack flight controller.  

The main differences in the ptFlex firmware include:

  • Support for the new frequency-agile DRA818V transmitter module.
  • A new configuration string (PT0003) has been defined for the ptConfigurator.  (Older version of the ArduinoTrack Configurator will not work with the ptFlex, but ptConfigurator is backwards compatible with the ArduinoTrack).
  • A new custom.h/custom.c file has been stubbed in to facilitate easy insertion of custom sensor code, without modifying the core firmware files.

The most current firmware can always be found in GitHub.

ptFlex Firmware GitHub Repository

Further Reading

For further information about the ptFlex flight controller, check out the ptFlex Instruction Manual or contact us at Project: Traveler.  To buy a ptFlex kit, or a fully assembled ptFlex, visit the store located at Custom Digital Services, LLC.