Backup Emergency Recovery Transmitter (BERT)
BERT is the secondary transmitter we use for our high-altitude balloon flights. You can find our GitHub page here - https://github.com/M2I-HABET/BERT
Redundant Systems
BERT is completely independent of our main avionics system (HAR). It has its own power source, processor, GPS, and transmitter. Instead of using LoRa like HAR, BERT uses the Iridium network for data. As a backup system, it does not transmit as often as HAR. It also does not transmit as much data as HAR due to the limitations of the SatCOMM system. However, BERT’s primary purpose is to provide location information to ensure recovery, and it does that very well. BERT has been on several flights and provided reliable position data. The battery has also been proven to provide enough time (several days!) for transmissions if recovery cannot happen immediately.
Current Revision 4.0
BERT is currently in its fourth iteration. The early BERTs used amateur radio and APRS. We then moved BERT to use Iridium as the primary transmission method. Version 3 used a RockBlock module with an Adafruit Clue board. This system worked for a while and proved that the Iridium system and the newer Neo M9N GPS unit worked as expected (if put in the correct mode). However, we had a few problems with the Clue board, and while seeing additional data on the display was helpful, it was also prone to breaking. We also had some issues with the Clue board locking up. A watchdog timer helped to avoid a complete lockup, but the exact reason was never found. We then moved to Sparkfun’s Apollo boards that include the GPS and RockBlock unit all in one easy to use package. This made for a more compact design, and so far, this design has proven to be the most reliable. We do have a few bugs to work out, and we are working on switching to a binary system to reduce our current credit cost per transmission.