Please check out the main project page meanwhile.
The aim was to develop a low-cost platform for experiments in the stratosphere, based on a Raspberry Pi as flight computer with various sensors that can be attached modularly and cameras. For tracking the GPS coordinates are transmitted in real time over radio on the 2 meter band. The whole system is powered by 6 lithium AA batteries providing 3000 mAh each at 1.5 V (Energizer L91 or equivalent).
Physically, the modules stack onto the Raspberry Pi GPIO header and are packed into a styrofoam box with a quarter wavelength ground plane antenna for signal transmission attached, with the PCB with sensors needing to be exposed directly to the outside being electrically insulated and taped to the outside of the box.
The whole arrangement, including the parachute, weighs about 1 kg and can be carried by a 1200 g weather balloon.
Maximum altitude on test flights was ≈ 30 km.
The hardware used on the last flight was split up into several modules:
In future versions, power distribution, communication, GPS and internal sensors are planned to be combined into a single module for maximum space and weight efficiency.
The software is fairly simple as it only needs to log data and pictures and transmit critical tracking information to the ground station.
As the operating system for the Raspberry Pi a minimal Arch Linux ARM was chosen. The flight control software runs as a Linux daemon.
Pictures and sensor data of the 2014 flight are available here.