Fixes for issue#20 (low battery handling).
During GPS-fix, the battery voltage is now continuously monitored.
The GPS-fix is abandoned as soon as the battery voltage gets too low.
PM measurement is skipped then the battery voltage is too low.
Station is now reporting the lowest battery voltage that has occurred during the measurement cycle.
Power return should cause no power hickups/oscillations anymore.
Battery too low is indicated by sending GPS position (-1,-1).
Solar panel support for v1-v3 boards added, requiring addition of 2 extra resistors and a diode..
Fixes for issue#20 (low battery handling). During GPS-fix, the battery voltage is now continuously monitored. The GPS-fix is abandoned as soon as the battery voltage gets too low. PM measurement is skipped then the battery voltage is too low. Station is now reporting the lowest battery voltage that has occurred during the measurement cycle. Power return should cause no power hickups/oscillations anymore. Battery too low is indicated by sending GPS position (-1,-1). Solar panel support for v1-v3 boards added, requiring addition of 2 extra resistors and a diode..