In addition, the backlight of the display (which consumes a lot of power) is adjusted according to the ambient light conditions. To regulate this efficiently with a small transistor (BC547 or equivalent NPN type), the PWM frequency has been lowered to allow clean on/off condition. The switching transistor is placed in the backlight line which runs to GND, the + of backlight is connected to +5v in series with a 22 ohm current limiting resistor. The modified PWM frequency implies that some time related ARDUINO instructions (like DELAY) have arguments adapted accordingly (approx x 3)
The display shows latitude, longitude, fix status ( 'FIX OK' or blinking 'NO FIX'), Speed over ground (SOG) en course over ground (COG), the Maidenhead locator and the UTC time. If no serial data from GPS is detected, an alarm message is shown. Battery condition is tested at startup and each minute about. A small buzzer alerts in case of low battery, no serial data received, or loss of fix. I didn't effectively check if the Maidenhead locator calculation is OK in the southern hemisphere and western longitudes. Remark : in V2.00 there was a mistake in locator conversion with S or W, which now was corrected in V2.10. Tested at QTH of Papeete - Tahiti and now OK !