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.

-=Doug

27-FEB-2014 Eagle files are now located HERE

APM2_5 Simplified Power.PNG

Yes, I think it is a quality issue with the APM *system* as supplied by the vendor. This could be components, soldering, pcb construction, connectors, etc.

Excellent news on your engineering background. You will be comfortable with the Eagle (software often used to represent the layers of the circuitry) screen caps that show component locations.

The most recent APM in my possession is a 3DR 2.6. There may have been a few tweaks and adjustments to the 'recipe' for the unit in the last two years. Craig Elder 3DR engineer put this discussion here almost 3 years ago because of the huge number of questions regarding wiring and connection issues relating to the APM.

I pulled the schematic from the Eagle files and simplified it for these kinds of discussions.

When I have time, I will try to create a table of voltage readings based on my newest APM2.6 with 3DR PM.

Note: I don't know what the other vendor's designator of '2.8' actually means. 2.6 mostly refers to moving the magnetometer off the main pcb.

-=Doug

Replies

- - - - Drone newbie > R. D. Starwalt October 14, 2015 at 10:18am
        
        Dear DOug,Bill
        
        I now connected the ground from radio telemetry to APM (see below image) as well but the situation remains.. My measured values are almost the same
        
        Is this a dangerous situation or as long as my hwvoltage value is steady 4.94V i could fly as is ???
        
        How should I identify the resistance on wires ???
        
        Developer
        
        Bill Bonney > Drone newbie October 13, 2015 at 12:19pm
        
        The ground needs to be connected from the radio to the APM board as well. GND must be there for the signal lines as a reference.
        
        I'm not sure why it's fluctuating but probably means 5V from another BEC is connected. Do you have ESCs with BECs connected. You may need to removed JP1
        
        Drone newbie > Bill Bonney October 13, 2015 at 12:59pm
        
        Dear Bill,
        
        ok i can try to connect the ground from radio to APM as well...
        
        I dont have any other BEC connected.. I am using the DHI E310 propulsion kit that uses the DJI 420S ESC. As far as I know those ESC's do not contain any BEC's...
        
        My JP1 jumper is already removed...
        
        Regards,
    - Developer
      
      Bill Bonney > Drone newbie October 12, 2015 at 1:17pm
      
      black wire from BEC goes to GND on the radio
Drone newbie October 9, 2015 at 5:49am

Dear Doug,

so as you mention probably the APMs that I am buying have some quality issues and thats why i am seeing the Vcc voltage fluctuations ???

My background says that i am an automotive/mechanical engineer working in the computational mechanics area. This means that I am a CAE (computer aided engineering) engineer that is involved with computer simulations for engineering problems like aerodynamics, crash tests, structural durability etc.

This means that I will not stop until I find the solution of a problem I come across (in our case with the APM). So you can drag me whenever you want as long as it leads to the solution of my problem. Unless I could consider my current situation acceptable and rely on it knowing that it will not lead to my quadcopter crashing because of voltage problems...

Please advise what should I do.

Thanks and Regards,
- R. D. Starwalt > Drone newbie October 9, 2015 at 6:23am
  
  Yes, I think it is a quality issue with the APM *system* as supplied by the vendor. This could be components, soldering, pcb construction, connectors, etc.
  
  Excellent news on your engineering background. You will be comfortable with the Eagle (software often used to represent the layers of the circuitry) screen caps that show component locations.
  
  The most recent APM in my possession is a 3DR 2.6. There may have been a few tweaks and adjustments to the 'recipe' for the unit in the last two years. Craig Elder 3DR engineer put this discussion here almost 3 years ago because of the huge number of questions regarding wiring and connection issues relating to the APM.
  
  I pulled the schematic from the Eagle files and simplified it for these kinds of discussions.
  
  When I have time, I will try to create a table of voltage readings based on my newest APM2.6 with 3DR PM.
  
  Note: I don't know what the other vendor's designator of '2.8' actually means. 2.6 mostly refers to moving the magnetometer off the main pcb.
  
  -=Doug
  - Drone newbie > R. D. Starwalt October 9, 2015 at 7:40am
    
    Dear Doug,
    
    I will wait for your response..
    
    changes in APM v2.8
    
    1) 100uf cap in Vcc and 10uf tantalum capacitor added to stop 3.3v bad gyro health issues
    2) Replacement of the (not used/redundant) 1.0mm 6p old GPS port with df13-4P I2C external compass port, putting the GPS and external compass ports next to each other, making for easier connections.
    3) Multifunction MUX port added in the old I2C port location, this lets users select an output from the bonding pad (Uart0, Uart2, I2C, OSD “default is OSD”. This new layout makes data transmission more stable with an isolation resistance.
    4) 3.3V and 5V Dataflash/Flashrom swapped trace problem corrected to the AT45DB161.
    5) External Compass enable/disable jumper added, verses having to cut a trace wire.
    
    Best Regards,
    - Drone newbie > Drone newbie October 9, 2015 at 1:32pm
      
      Dear Doug,
      
      I did tonight some measures again. Please have a look of my measures in the attached picture..
      
      The first fact is that I always get 0.3V lower measures if i measure between the GND of PM and the positive input PWM pin compared to the Servo and Output positive pins..
      
      THe second fact is that when I connect the HKpilot 500mW telemetry module I have some fluctuations of my voltage measure while if i connect a 100mW module the measure is almost solid.
      
      I dont know if this feedback helps
      
      Best Regards,
      - Developer
        
        Bill Bonney > Drone newbie October 9, 2015 at 6:52pm
        
        this link shows the main power bus and the reason for the 0.3V drop http://copter.ardupilot.com/wiki/common-powering-the-apm2/#apm_powe...
        
        The reason you are having an issue with the 500mW radio is it probably drawing two much power. The same happens with the RFD900 radio. You need to power it with a separate BEC from the APM, and not the power module.
        
        see http://copter.ardupilot.com/wiki/common-rfd900/
        
        if you connect a separate BEC, you will need to disconnect the 5V line on the molex connector to the board
        
        R. D. Starwalt > Bill Bonney October 10, 2015 at 6:47am
        
        Bingo Bill, I think you nailed it!
        
        If I had paid attention to the wattage rating on his first graphic, that should have triggered an alarm.
        
        DN - Your first APM is probably fine. I apologize for missing the clue. At least now you have two units to work with and we can add another bit of knowledge to the community.
        
        All my telem modules are 100mW units. With 5 times the power use, the issue becomes one of source (PM) current regulation. A similar situation can occur if users try to drive higher current servos in an ArduPlane setup.
        
        Thanks again Bill! I think DN can stop the hunt.
        
        -=Doug

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APM2.5 5V/Vcc Schematic

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