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I just changed my Diatone R349 flight controller because the old one broke. On my first test flight, I noticed the OSD is flickering very bad, sometimes losing it for more than 1 second, even when not armed.

The video feed is good, just the OSD flickering.

The VTX and camera are powered by an external 5v regulator. The rest is powered by the FC.

I've read that it could be a ground issue.

Could it be something else?

EDIT: This is my current hardware and wiring diagram. enter image description here

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  • $\begingroup$ Hey @JoRouss, welcome to the community! What kind of hardware are you running now? Have you tried retouching the solder joints for power and the analog camera signal? Sometimes just re-melting the joint can fix issues with intermittent connections. $\endgroup$ – ifconfig Apr 30 '20 at 21:44
  • $\begingroup$ @ifconfig Hey, I added my wiring diagram and hardware. What joint exactly could cause the OSD to flicker? $\endgroup$ – JoRouss Apr 30 '20 at 22:01
  • $\begingroup$ I just noticed the capacitor is on the FC, not affecting the 5v regulator. This might be the problem? $\endgroup$ – JoRouss Apr 30 '20 at 22:05
  • $\begingroup$ Nice diagram! Hrm, at this point it doesn't look like any solder joints you made assembling the quad could be at fault... If you look at your Mamba F405 FC board near the OSD chip, does anything look off? $\endgroup$ – ifconfig Apr 30 '20 at 22:06
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    $\begingroup$ The capacitor would be suspect if the VTX was cutting in and out because that could mean that it's receiving too noisy power. Although, it is worth noting that where you have the capacitor it is likely doing nothing because only the Crossfire RX is being powered off of the FC's 5v pads. $\endgroup$ – ifconfig Apr 30 '20 at 22:07
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I know I'm a bit late to the party, but I just had the same problem as you and your solution didn't work unfortunately. What I instead had to do was connect a +5V wire from the regulator to the FC, along with the ground wire that you connected.

I wasn't really satisfied with only solving the problem; I wanted to know how the OSD could flicker without affecting the rest of the video at all, and I think I have figured something out.

In both our cases the underlying problem was that the ESC (where the FC and thus OSD chip got it's power from) introduced noise in the output from the built in 5V regulator, which in turn causes a ground loop (At least in your case. In my case it might just have been a deficient regulator). When arming and applying throttle, the motors draws more current which in turns generates stronger magnetic fields that messes with the other electrical signals. This explains why some people (including me) can experience even more flickering when the motors spin faster.

But why is only the OSD affected by this problem, and not the rest of the video?


I haven't found any sources about this, so the following is just my hypothesis based on the information I could find, and what I already knew.

If we take a PAL signal for example, and black and white to make it easier (NTSC and PAL are the two types of systems used for analog FPV video, both quite similar), it uses the voltage level to determine the luminance level of each pixel in each scan line, where 1 V is completely white, and 0.3 V is black[1]. 0 Volts is used as a so called sync pulse, and between each new scan line there is a sync pulse.

Composite video signal [2]

My suspicion is that because the OSD chip in the FC effectively receives a different signal than the camera sent (because of a difference in potential between the two grounds*), it can miss sync pulses, and the OSD will appear as slight noise in the final image instead. Another theory is of mine is that the OSD chip will just give up when it doesn't receive what it expects.

When the signal finally comes to the VTX the ground potential is the same as the cameras, and the signal will be correct again (possibly with some unnoticeable noise).

*For example: imagine that the camera sends out a signal of 0.6 V. If the potential of the OSD chips ground is 0.1 V lower than that of the camera, it will interpret the signal as being 0.6 - (-0.1) = 0.7 volts.


I want to make it clear that this is just my (relatively) qualified guess, and you would probably have to measure the signals and know how the OSD chip works to know exactly what is going on. I would love to test this some more but unfortunately I don't own an oscilloscope, and a multimeter isn't really up to the task. Also, i would love to be proven wrong.


[1] http://martin.hinner.info/vga/pal.html
[2] https://en.wikipedia.org/wiki/PAL#/media/File:Composite_Video.svg

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I fixed it by adding a common ground between the 5v regulator and the flight controller. I can't explain the science behind this, but I took the answer from this video from Painless360

The flickering is completely gone, even when I punch the throttle.

New wiring diagram: enter image description here

EDIT: I will leave the post unanswered until someone intelligible explains this, and maybe other OSD flickering causes just to keep the post general to the question and not specific to my hardware and wiring.

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