Hoping to build a Hot Air Balloon autopilot (no, I am not planning to defy science by flying against the wind!!). I need to build a controller that can automatically energise a relay that will cause a burner solenoid to operate in order to maintain level flight. I plan to use a BMP180/BME280 sensor to achieve the barometric pressure and use high/low thresholds from the required altitude i.e. + or - 1 Hectopascal, which is approximately +/- 9 metres. There are a few considerations - 1) a Hot Air Balloon does not react to burner input for 20-30 seconds, which complicates the firing algorithm 2) the length of burn will need to adjust to enable to minimal 'sine wave' possible (frequent short burns rather than less frequent longer burns). The above scenario would mean a pilot achieving level flight manually, then operating the autopilot. The system will need safety measures that would prevent the balloon bursting though the lower threshold without taking appropriate action. Later phases are likely to include the ability to climb or descend to specific altitudes, incorporate a GPS to show speed and track, enter current QNH pressure value (Mean Seal Level pressure) via a touchscreen or phone app and, later, adding LoRa functionality to pass data to the ground.
I would welcome any comments on this potential project.