3DR Radio + MinimOSD = no MAVlink :-(

Hi all, hope somebody can shed a light on my problem.

I have been flying 2 quads and a Skywalker for 1,5 years and many hundreds of flights with APMs and never had a problem. This time though, I can't get my head around what is going on.

I have replaced a normal APM 2.6 with HobbyKing's HKPilot Mega Mini which thanks to its small form factor fits my XuGong-10 frame nicely. I use the standard Y-cable to split telemetry across my MinimOSD and the 3DR Radio air module. But it doesn't work when I connect both!

Scenarios tested:

1) Only 3DR Radio connected

  • Solid telemetry connection to both Mission Planner and DroidPlanner2. Link stats show no dropped packets

2) Only MinimOSD connected

  • Solid OSD data streams, everything working normally

3) Both connected

  • MinimOSD displays 'No mav data!'
  • 3DR Radio has green solid light, no blinking red light (link ok, no data)

When I have both connected, the moment I unplug one, the other starts working right away. After migrating to the HKPilot Mega Mini I have never used the dual setup and therefore I am unsure if this is due to hardware or software differences.

I already thought it could be a brownout/power problem but adding a 5V UBEC for separate power doesn't fix it.

Setup:

HKPilot Mega Mini (APM 2.5.2) running APM:Copter 3.1.5

MinimOSD running minimosd-extra 2.4-r726

3DR Radio 915 MHz module running SiK firmware 1.9

xugong-10.jpg

hkpilot_mega_mini.jpg

mavlink_setup.jpg

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Replies

  • I had the exact same problem with the HKPilot Mega Mini.  I looked at the signal on my oscilloscope and found that the TX data line on the mavlink was pulled down too far with two loads on it.  I connected a non-inverting CMOS buffer (CD4050B) to just that pin and have both working now.

    If you look at my review of their combo version, I explained the problem and the work-around there also.

    • Hi Scott - I am in the same situation but can't find your review anywhere. Can you please reply with a link or a wiring layout. Thanks :)

    • Hey thanks, great that you found a solution and took the effort to comment here. Could you be so kind to give a little hint as to how things should be wired up? I will definitely try out what you you did and post back the results when it works :)

      BTW is this the correct part? http://uk.rs-online.com/web/p/buffers/0306673/

      • Did you solved your probleme with that chip, cause i do have the same problem wiyh the same apm.

        Thks in advance

      • That part looks fine.

        Connect the power and ground lines to +5V and ground.  Connect the TXD output from the APM to one of the inputs on the buffer.  Send the output of that buffer to the RXD signals on the OSD and the Telemetry radio.

        Connect all of the unused inputs on the 4050B to either power or ground.  You don't want floating inputs on CMOS devices.

         

        • Thanks, I found the schematic and your explanation matches exactly what I see there, thanks. I was wondering, could it be that the two loads are pulling a too high current from the TXD port (brown out) which could be solved by just placing a 100 Ohm resistor in the line, thus limiting the current that goes to the two loads? It could incur a small voltage drop but the receiving end could still detect it as HIGH.

          What do you think? I have resistors lying around but not this 4050B IC, I would need to order it.

          • Hello there I was having a mess of trouble trying to connect my apm2.6 with the minimosd both the traditional and the new micro and both are at the same point as you had with no mavlink infomation coming through from the APM but the mavlink indicator on the display is winking so anyhow could you please direct me to this link that you mention from Scott regarding the schematic so I can try this mod out as I'm at a dead end!.

            Thanks and how did the buffer chip you linked work out,was it good as I'll use that as a referance to order one here in Adelaide S.A.

            Cheers

            • Just did the MOD last nite and it work...

              Quote by Scott :

              "Connect the power and ground lines to +5V and ground.  Connect the TXD output from the APM to one of the inputs on the buffer.  Send the output of that buffer to the RXD signals on the OSD and the Telemetry radio.

              Connect all of the unused inputs on the 4050B to either power or ground.  You don't want floating inputs on CMOS devices."

              Thanks to Scott

          • Hi Jeroen and Scott. Could any of you please send me the link to the schematic? I can't find it. Thanks!

          • I doubt that would work. It all depends on how tolerant the inputs of the telemetry radio and OSD are.  You could try it if you have a scope or something to look a the signal.  Mine definitely went "glitchy" and didn't just droop with two loads.

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