http://www.edallhobby.com/en/-multirotors-/1539-rctimer-annunciator-for-arduflyerapm.html
■ ArduCopter 3.2 APM LED
A4 : Motor LED
A5 : Beeper - can drive a piezo buzzer directly (see below)
A6 : GPS - will flash with no GPS lock, solid with GPS lock
A7: Arming LED
■ Bit Number
7 6 5 4 3 2 1 0
0 0 0 0 0 0 0 1 = 1 Motor LEDs On/Off
0 0 0 0 0 0 1 0 = 2 GPS On/Off
0 0 0 0 0 1 0 0 = 4 AUX Function On/Off
0 0 0 0 1 0 0 0 = 8 Beeper On/Off
0 0 0 1 0 0 0 0 = 16 Low Battery Flash – fast/slow
0 0 1 0 0 0 0 0 = 32 Motor LEDs NAV blink On/Off
0 1 0 0 0 0 0 0 = 64 GPS LEDs Nav Blink On/Off
1 0 0 0 0 0 0 0 = 128 Not used