Logging
We used an Arduino microcontroller connected to a data logger shield to save data during the flight. On the shield a temperature and pressure
sensor are mounted. The data is then saved to an SD card every second. A real time clock was used to time stamp the data. Data could be saved for approxametly 5 hours before the 9 V battery ran out of power.
Cut down
Our first balloon landed halfway to the Faroe Islands and it was not possible to retrieve it. Since we did want to this to happen again we decided to implement a time controlled cut down mechanism as a saftey backup. Using the same Arduino as for the data logger, a simple code was written to switch on the cut down after a certain time. This time was set to 2 hours and 20 minutes. According to wind speeds this flight time would still let us land close enough to Reykjavik so that the helicopter would retrieve it. The cut down used a low resistance MOSFET transistor as a switch, a 9 V battery for power and a high resistance nichrome wire as a cutting device. The cut down mechanism worked well during the tests. The second flight worked as expected and the balloon popped before the cut down turned on.