Video interferance

[kenl]

Hi All,

I'm hoping that someone can help to point me in the right direction to track down the video interferance that I am getting.

In my early videos I was getting noise, I think from the ESCs, but this is much more.



I am using Nicks' (njs552) code and bottom side control board, (such good work) in his code when you press the start button on a PS2 controller it starts communication, Easytransfer I think.

Anyways that is when the pulsing begins, it was not present when I was using Nicks code and NOT using the Max488 chip, just using the Rx/Tx from the Arduino.

I have done the following so far:

Placed ferrites on the RS422 lines = no improvement

Placed a 0.1 capacitor on the +ve and -ve inputs (pins 1 & 4) to the Max488 = no improvement

Added a 10.0 uf capacitor to my board in general = no improvement

Bypassed the tether (cat 5) with separate video lines = small improvement

I am still to try a capacitor across the video pair, but I'm not sure what capacitance... would it help? Both ends?

I have also thought about powering the Max488 with 3.3v instead of 5, but that is just a wild guess?

It seems that the interference is not from the tether itself, but is amplified in the tether.

As a side note I do have Baluns each end, and have tried it without them and it seems to make no difference, does that mean the baluns are no good or they are not needed? Is there a test proceedure for them?

Lots and lots of questions sorry

Ken

[rossrov]

Have you tried soldering an electrolytic capacitor directly across the voltage supply pads on the camera PCB? If not, say a 100-220uF, maybe put a 0.1 uF in parallel with it. What supplies the camera power?

[kenl]

Hi Ross I haven't tried that, I will have to look at the PCB and see how the access is to the pads, when you say to put a 0.1 uF in parallel, you mean in parallel to the 100-220uF?

I have my camera power supply coming through a Power Filter I got from Hobby king. That is also new since the interference started, so I may isolate that too but I doubt it has anything to do with it. The picture is perfect up to the point I start communication.

[rossrov]

Yes, the 0.1 connects in parallel with the electro. The filter board will do the same thing as the two caps, in fact probably better due to the inductor on it. So if your camera power supply wires are not more than say 50mm long from camera to filter then probably don't worry about the additional caps.

Where does the camera video output wire route - does it go straight into the balun with shortish wires, or is snaking around a bit? Same with the camera ground to balun connection - noise can be picked up in ground wires too - referred to as an "earth loop".

Problem may not be in the ROV end. The monitor and topside comms probably share the same battery? Try a separate supply for the monitor and see what happens. Also look at the balun to monitor connection - wires ideally short in length for the unshielded portion

Only other thing I can think of without actually having the setup on the bench in front of me is if the comms wiring is incorrect and somehow loading up the power supply or causing excessive noise. Unlikely but just a thought

[kenl]

Lots of things to try there, thanks very much Ross, my cables are a bit snakey and in most cases more like 100mm than 50.
Also there are relays and what not to consider, but I have eliminated the relay with no change.

I still very much suspect the comms wiring, I will double check it today. I'm using the MAX488 chip, on the RS422 side I swap pins 5&8 around and pins 6&7 around .

[kenl]

Ok I think I may be going cross eyed by now, I bypassed the MAX488s and just used the Rx/Tx pins and a 20' cable.

The video interference disappeared and my code is now working, turns out there was no return communication from the bottom side arduino. I have double and triple checked my connections and still can't find the problem, I used THIS pinout and it seems to be correct when compared to the Data sheet even though that is not immediately clear to a beginner like me.

MAX488-circuits.jpg (19.28 KiB) Viewed 8525 times

I have a spare chip and have used that to bypass the fixed chips but it has not helped, so I don't quite know what to do there? Any ideas?

On a different note, just for a giggle I tried the Rx/Tx over my 110m tether, It works!! No problem!!

Edit, We can all stop looking now, my power supply to the MAX488 was not consistent, I've fixed it with a makeshift jumper for now and will try to track down the actual problem. Crystal clear video and two way communications Halleluja

[a_shorething]

Woohoo!

Glad you found it and thanks for posting the resolution. Too often people fail to do that and there are just a lot of problems in the knowledge base afterward.

Nice piece of detective work there.

[Billrose]

Well done fine bit of fault finding...

[kenl]

So I'm back with video interference, I think I will become the king of video interference .

A few weeks ago I went and tied up to a recently refurbished jetty to try and test the ROV where there may some fish and stuff, as soon as I put the rov in the water the screen went crazy with thick straight horizontal lines.



I at first thought it was an electrical fault on one of my motors, but then later on I thought, that doesn't make sense because guys are using these motors in open water so shorting out doesn't really come into it.

Then I thought the Jetty might have installed a fancy corrosion protection system, so I tried it on Saturday in a local canal and no problems!

Yay, or so I thought, took it out in my boat today and same thing exactly.... It's my echosounder, this never happened in my first few dives from the boat. My current thinking and hoping is that the OSD chip is somehow picking up the interference, because that was never in there before and everything else is much the same.

As soon as I dip any of the electrical bits (even the led's ) it just goes crazy and you can't see through it.

I was hoping to use just one way communication and send all my data, like heading and depth over the video signal with an OSD? Anyways I may be jumping the gun blaming the OSD, I will keep you posted.

Ken

[kenl]

Well had another dive today, minus the OSD breakout board.

Unfortunately it didn't change anything on the interference front.

I did however find out that the interference only comes on when the echo sounder is turned on (as I knew) AND the topside box is plugged into the echo sounder AV input AND the ROV is in the water.

So it's not just a matter of the sounder transmitting and creating the problem, the ROV has to be physically connected to it for it to be a problem.

The easiest solution is to buy a daylight viewable screen so I don't need to use the echo sounder one, or a wireless link.