I am using the APM 2 for both my quads and it is tricky to get the barometer covered to avoid errant airflow since it is below the daughterboard. To solve this, I ended up pretty much filling up my stack cover with breathable foam. But once that was done, I could barely see the on-board LED indicators.

Fortunately, the current code supports remote indicators without too much trouble.

If you look at the pin-out images on the Wiki, you will see that the AN pins are labeled Motor LEDs. They really don’t have a lot to do with the motors – but they do serve as pretty handy indicators.


If you look in the code, you will find defines for these pins as follows:

AN4 – Motor or Aux LED

AN5 – Motor or Beeper

AN6 – Motor or GPS

AN7 – Motor

AN8 – Motor

For my purposes, I focused on AN5 for the Beeper, AN6 for GPS indicator and AN7 as an Armed indicator.

The default seems to be to have the beeper enabled and the LEDs on. That is easy to change however. The different possibilities are set using bit masks to build the LED_mode parameter. A bit mask (if you already know, feel free to skip ahead) is simply a way of packing a bunch of on/off settings into one byte of data. A Byte is 8 bits, so you can have 8 different switches in one byte.  If you look at the following table, you will see a single bit is set to ‘1’ and the rest to ‘0’ in each row. To build the mask, you just add all the rows together and convert to a decimal number (or convert then add).

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


Note that the NAV settings cause the LEDs (either the motor LEDs, the GPS LED, or both) to blink 3 times when you hit a waypoint in AUTO flight.

The low battery flashing defaults to fast flash so setting that bit to 1 will enable slow flash. 


I really only want the beeper, the GPS and the Motor LEDs on, so I set the mode to decimal value 11 (which is binary 00001011). This should equate to: GPS Nav blink off, Motor LED Nav blink off, low battery flash fast, beeper on, AUX off, GPS on, Motor LEDs on..


The way you set this to be the value used is through the Mission Planner.


Establish a connection with the APM and the Mission Planner software. Go to the parameters list and find LED_Mode. It should be set to something like 9. Change that to 170 (or whatever you decide to use) and write the settings to the APM.

The outputs on the APM are 5V, so for most LEDs, you’ll need a resistor on the positive lead (the longer leg of the LED). In my case, the blue LED I was using required a 100 Ohm resistor and the red one required a 150 Ohm resistor (note – not going to explain it here, but there are a ton of online resources and calculators to figure out the resistor values needed for a given LED). I soldered up the resistors and LEDs to leads and cemented them at the edge of my stack cover’s base. For the beeper, I just used a 5V piezo beeper I happened to have lying around. Radio shack sells one that will work, but it isn’t very loud. If you want volume, you may need to shop around,


When you connect to the AN outputs, you need to run the negative lead to the ground pin (the one nearest the edge of the board) and the positive lead goes to the signal pin (the one farthest from the edge of the board). The middle pin is always 5 Volts so if you plugged in there, the LED or beeper would be always on.


Beeper goes to AN5, GPS to AN6 and the ARMED light goes to any other motor LED output, but I chose to just use AN7.


That’s all there is to it. When you turn on the APM, you the LEDs will stay off until it is booted, then will flash the same as the on-board ones. When a GPS lock is achieved, the GPS LED will stay lit. When the bird is armed, the red LED will blink out and once it is fully armed, it will light a solid red. The beeper will beep twice on arming, and once on disarm.


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  • I had all this working when I was using APMs, now that I am flying PixHawks and CUBEs exclusively, I wanted the same functionality.

  • Can someone help me, I accidently burnt a part in my rctimer annunciator circuit because of a wrong polarity (+/-) cable plug, I guess it's a regulator that blew off.
    Anybody know what kind of regulator type (or maybe any other electronic part) that I can use to replace the burnt part? Thank you for any help. 3702097404?profile=original

  • I read on http://copter.ardupilot.com/wiki/nav-leds/ that the LED_MODE parameter is no longer there, and sure enough I can't find it. Why was it removed? is there no longer a way to change led modes?

  • Thank you.  That is good news for sure.  

  • Stu: The PLA plastic I have used seems ok so far and I have been running them for about 3 hours.

  • The LEDs get very hot.  How does the plastic 3D printed holder handle the heat?  

  • If anyone wants a 3D printed holder for the LED indicator then have a look at this:https://tinkercad.com/things/3iaiOCs2iGW

  • i'm sorry but all these comments are confusing... can you update the post with correct binary/value sequence?

    sounds like the value should be 27 and not 11 in order to have the flashing led ...is that right?

  • I am having an issue after a fresh firmware install on my APM 2.x with my external LED's not flashing on low battery.

    "Disarm" flashes as it should and goes solid on "arming", however it will not flash on low battery. I have confirmed the connections to the APM as well as set the "LED_Mode" value to 9.

    I read somewhere that there is something in the code that can get corrupted, however I cant seem to find that post that references the issue/solution.

    Anyone have any ideas?

  • Alright, here it is!

    The RCTimer "annunicator" (from UAV Objects) has a BEC on it, and supplies power to the LEDs which are triggered by the four positive leads under the LEDs and the signal ground next to them.  The pins you want are (inboard) 6 for GPS and 7 for "armed status" with the ground connecting to any of the outboard pins in that UART block on the port side of the ArduFlyer board.

    3701777182?profile=originalThen in Mission Planner (I'm using 2.0.11), you turn on Advanced mode (in File menu), connect to your board via USB/COM, go into Configuration, then choose Full Parameter List.  LED_Mode should be easy to find at this list is in alphabetical order.  Change the value there to 11.  That translates to the binary value that turns on external LED as needed.

    3701777207?profile=originalNOTE:  This will have no effect until you connect the BEC/annunciator to buss power.  Powering the board from USB does not power the external LEDs.

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