APM2.5 5V/Vcc Schematic

Frequently asked questions are about powering an APM2.5 or why the same does not work or why it has failed.

Here is a simplified schematic showing the major components of the 5V/Vcc circuit on the APM2.5

Target Audience: Readers who do not have Eagle or are confused about using it.

You Need: Basic electronic schematic reading ability


Note that I have separated the PWM Output section into the upper left corner with a heavy purple line that is bridged by the jumper JP1 on the APM2.5. This is to emphasize that diode D1 passes current through JP1 (and drops voltage). The remaining energy is then called 'Vcc'.  Everything outside the purple corner is Vcc.

This is why the USB will power the APM2.5 when connected to a computer/USB hub. Note the fuse on the APM2.5 side of the USB connector AND another fuse on the output of D1. Another change from APM2.0 is the D4 6.0V Zener diode. If an over voltage is applied to the board, D4 will crowbar what it can to protect devices.

As with APM2.0, any 5V source connected to any of the indicated Vcc/5V points outside the purple corner (with GND of course) will power the APM2.5.

Also of note is the 'Mystery Port'. This port takes 5VDC before D1 and the fuse and is called 'JP_VCC'. Other clues to the mystery are the lines to 'ADC 12' and 'ADC 13'. A mystery indeed!

Any errors in this drawing from editing are mine.

I hope this can be used as reference for solving problems.



27-FEB-2014 Eagle files are now located HERE


APM2_5 Simplified Power.PNG

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  • Developer
    Is your JP1 jumper installed?
  • Hello!

    I read your posts, looking arround for the answer of my problem. USB does supply power to the apm2.5, but comp does not recognize it (nothing happens). Earlier, by my mistake, I plugged wrong servo-cable to input port of apm2.5, the one from the gimbal controller motor driver, directly to apm2.5. As somebody said, "expensive smoke" was seen, motor driver of the gimbal controller was changed, receiver has been fried, and apm2.5 does not respond anymore. It says is "alive"  leds are blinking, cannot be armed and connected throug usb or data-link. 

    What should be checked, as possible reason, D4 or some of the fuses? Already changed D1 diode earlier, and was ok till now.

    Thanks all in advance!

  • Quick question: What is the limit to the amount of amps that I can pull from an Output of the APM2.5? I would like to power two servos from one APM Output. The servos together pull around 6.5 amps (Stall Current @ Locked). These are the servos: http://www.savoxusa.com/Savox_SH1290MG_Digital_Servo_p/savsh1290mg.htm & http://www.savoxusa.com/Savox_SC1258TG_Digital_Servo_p/savsc1258tg.htm

  • That's great, now I  can try RSSI, because ports A0,A1,A2 is already used for airspeed and attopilot and only port left for RSSI in mission planner is "mystery" A13. Now I know where they hide it :)

  • Doug,

    Yes - interesting idea about the interactive graphic. Let's first define some criteria so that a higher percentage of the Drone folks can make use of it shooting for 100%.  Your simplified schematic is a great start and most usefulf for the 10-15% of us that have some electrical schematic reading experience.  It's the best I've seen in explaining the many ways that the APM 2.5 can be powered and not powered!  This is becasue it takes the full schematic and weeds out the chaff that's of no importance to other than the electronic engineers.  I would like to see it modified into a type of functional schematic that all  the Drone folks can understand and use.  I don't think it would take too much in the way of modifications at least at the first step that I propose.  Although your schematic focuses on Vcc it should also include the 3.3V linear regulator that steps the voltage down for some components (Data Flash and others) but just a listing not electrical schematics. This is to stress the importance of providing clean power to the APM and what components will be adversely affected when not properly powered.  And it must include the Power Module that ships with every APM2.5. Yes it must include all the external communications connectors too but we do not need a schematic just the name of the connector and the group of parts that supports this connector in laymans terms ie GPS.  We must avoid terms like AT503B1610-MU simply replacing it with Data Flash which is shorter anyway.  Avoid terms like  UART, SPI_Mega and others that are meaningless to 90% of the droid group.  In summary drop all electronics acyronyms in favor of laymans terms for these functions.  Technical folks love acyronyms while laymen do not understand them!   

    Gary McCray, in the Documentation Editors group, is dong a fantastic job of writing explanations with some illustrations and pictures and this will go a long ways.  You should take a peek if you have not already.  But there are I would guess half that don't read at least with enough detail to pick up  the power supply options and nuances to keep them out of trouble. Perhaps they read better after they get into trouble - our goal is to keep them out of trouble in the first place.

    In my experience as business owner of a DIY install avionics in full scale experimental aircraft, the verbal explanation is requied but the functional schematic is by far best and is supported by the explanations.  It is imperative to use the full schematic as the source document in making the functional schematics and you have done this nicely already.  It is also imperative to get the functional schematic down to something all can understand and apply to their varied projects.  Your simplified schematic is nearly there!

    If interested I can help advise how to acomplish this (no art work required) using your existing schematic format.  I feel it is first necessary to get the rules down.  Modification of your simplified schematic is the best place to start to set these rules.  Then if you have the time and want to continue the graphic (sounds fantastic to me) it would be quite a contribution to the Wiki and group in general.

    I spend summers in the N Pacific with poor communications.  Is there a way we can have a private conversation before I leave next week assuming you are still intersted? 480-588-6689 You have the technical expertise to do this - I do not.








  • Doug,

    Craig Elder put me onto your "simplified" schematic and is the best "picture" I've seen of how power is distributed about the APM2.5. 

    I have suggested it be included in the new Wiki but it may be slightly too technical for laymen as it is drawn.  Can it be simplified a bit without giving up much?  Specifically the top row plus the USB is great and dropping the notes about the values of resistors and part numbers with more simplistic part notes such as resistor, zener etc. could that work?  The fuse size 500ma is nice to know though and is understandable by all.  

    Could the lower part of the schematic showing the UARTs etc. be reduced to just one Vcc carrot and a listing in layman's terms the Vcc powered parts below the carrot ( no schematic for each)? 

    Just a thought at this point.

    The linked to schematic is a bit fuzzy.  Would a pdf output from Eagle be sharper? I sure would like a pdf for my files in any event.

    Thanks in advance for your thoughts.


  • hi

    i dont know if im at the right place but i have a problem with my apm 2.5.2

    after a calibration of my remote control nothing works.

    when i plug the apm to usb the power up i see led red and blue flashing and after only red flashing

    the tx and rx light always on, green led alive is on.

    and nothing is detected in windows.

    someone have an idea ?



  • When I connect power to my APM2.5, the leds ABC do not light up at all. I can contact the board through USB however. The ESCs are also not seeing the output pins except for pin 1. This has just occurred all of a sudden after several flights of having the board powered through the output side, with JP1 jumper connected.


  • USB problem


    When I connect the USB I get the flashing A and B led as they should. After a time they go out and the B led remains on solid and it won’t link to my computer. Any ideas on what to look for?


    The LED status information does not list this condition?





  • What are the pinouts of the I2C port?

    I'd like to setup a master/slave setup with an Uno = http://arduino.cc/en/Tutorial/MasterWriter- but need to know which pins are SDA, SCA, and GND.

    I don't see the I2C port on the APM2_5SimplifiedPower.PNG drawing - am I missing it?

    Nor on this doc: http://stuff.storediydrones.com/APM_v25.pdf

    I picked up a Hirose  four port connector - and it seems to fit:


    According to the manufacturer, pin 1 on this cable, corresponds to the single red wire:


    So I know which pins are 1-4 (counting one from red) - on the patch cable.

    I just need someone to decode the Eagle files and tell me which pins on the APM 2.5 I2C port are tied to SDA, SCA, and GND, so I can route the correct cabling to the Uno's A4, A5, and GND...


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