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I'm a quadcopter FPV addict, and I'm building a new one.

As pointed out i will first explain some acronyms of the rc world

  • PDB (Power distribution board)
  • CCD (Type of camera sensor, cmos ccd... not really relevant to the question)
  • BEC (A filtered voltage regulator)
  • PDB (Power distribution board)
  • VTX (The video transmitter)

Usually, the video transmitters receives power from regulated 12 V or directly battery voltage (usually 7 V to 24 V)

Most of them also have a 5 V output that is really useful to power the camera.

In this case I'm using one really similar to this one: enter image description here

As you can see it does not have 5 V output so I'm using a good CCD camera that needs 12 V that will be provided by a separate BEC on the PDB.

My question is, the VTX (The video transmitter) has two different grounds, i suppose one is the 7-24 V power ground, and the other is the ground of the 12 V camera power.

As the VTX does not provide power to the camera, does it really need to have the camera ground? The camera will have the ground from the 12 V BEC and the VTX has the ground from its VCC power.

I could test this when some final parts arrive but if it does not work i will need to resolder a lot of things and i would like to avoid that.

Also the 12 V BEC already has a lot of things on its small pads so i would like to avoid soldering another ground to it.

EDIT

My PDB is something like this:

enter image description here

My camera is already on the 5V BEC and the VTX on the VCC pad so its not filtered and that will induce noise in my VTX right?

Can i say that i can solve it by using the other 12V BEC to power the VTX OR Conecting the second VTX ground to the same 5V BEC the camera is grounded to?

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    \$\begingroup\$ Replace the not-needed picture with a scheme of how you would estimate the grounding is best achieved - this is important and not the picture. \$\endgroup\$ – Andy aka Aug 1 '16 at 11:58
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    \$\begingroup\$ FPV CCD BEC PDB VTX \$\endgroup\$ – pipe Aug 1 '16 at 12:00
  • \$\begingroup\$ I think the best is to just connect the 2 grounds to the VTX but im asking if it is really necessary as i would like to avoid it. \$\endgroup\$ – Nanoc Aug 1 '16 at 12:05
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    \$\begingroup\$ Not many EE Stack contributors know that "FPV" stands for "First Person Video", let alone what it does. Ditto for all of the other 3-letter acronyms. Please edit your question to eliminate or annotate your acronyms with full-word descriptions. \$\endgroup\$ – FiddyOhm Aug 1 '16 at 15:00
  • \$\begingroup\$ Typically, EE.SE doesn't answer questions about devices, but does answer questions about design. Grounding is a design issue, if you could boil your question down to something relating to the grounding issue then that would be great. It would also be great if you could provide some kind of information like a block diagram of where the ground goes. \$\endgroup\$ – Voltage Spike Aug 2 '16 at 15:34
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FPV = First-person video? CCD = Charge Coupled Device. BEC = Battery Eliminator Controller? PDB = Power Distribution Block? VTX = Video Transmit? Not everyone knows what these acronyms stand for.

The top ground is probably "signal ground" for the video and audio, while the bottom ground is likely power ground. No datasheet was linked and googling "TS5840" finds only Chinese sellers.

Since a craft such as this contains several powerful electric motors, "power ground" is likely very noisy. Connecting all grounds together will probably work, but the result may be less appealing than expected. "Signal grounds" (if that's what it even is, cannot tell) are provided for a separate ground which carries less of this transient noise, which could affect signal quality.

If it were my aircraft, I'd wire signal ground right to the same ground the camera is using. Hopefully the camera is powered from something providing it's own ground, like a 5v regulator. Typically, low-ESR capacitance is provided on both the input and output of regulators, so I'd expect the ground there to be less noisy than say, connecting directly to the battery negative.

If you find the image quality to be lacking and suspect noise, try adding some capacitance across the +V and ground as close to the transmitter and camera as possible. A 10nF ceramic and 1uF tantalum cap (in parallel) on each should do a decent job of filtering power to them.

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    \$\begingroup\$ Kudos for trying, I gave up after the third acronym I had to google. \$\endgroup\$ – pipe Aug 1 '16 at 14:37
  • \$\begingroup\$ So i will get noise on the signal if i dont connect the video ground? but will i get noise if i power the VTX from the filtered 12V BEC? \$\endgroup\$ – Nanoc Aug 2 '16 at 10:58
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I think you are reading too much into it. Indeed, some devices have two grounds that are actually different, usually one for low-noise analog signals and one for everything else. In these cases they will be labeled with different names so you can differentiate them.

It is also not uncommon for devices to have multiple ground connections with no distinction between them whatsoever. Maybe the package had extra pins, or just one pin couldn't carry enough current, or maybe the device needs extra heat dissipation capacity.

For example, look at the top view of the ATMega 88:

enter image description here

It has not one, not two, but three grounds. They should all be connected to the ground plane.

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  • \$\begingroup\$ Boo, no. One of those grounds are supposed to be the Analog Ground, like the Analog VCC, and there should be specific isolation and filtering to prevent digital noise from the analog references. \$\endgroup\$ – Passerby Aug 2 '16 at 3:00

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