ANOTHER Ground/signal issue - comments anyone?

[Humphry]

Hey Vladimir,

Thanks for this. So [pin 25] should always be connected to projector case.. Which would obviously be connected to AC Ground. So that would be our central grounding point. Then we either attach [central grounding point] to [18][19][20] OR to [DC 0V] on the laser drivers? What determined which option I choose?

[Bbe]

Hi Fabian,

If input of the driver is not a differential, 18 19 20 pins must be attached to 0V (-) on the driver board(s).

Ideally connect it through a capacitor (0.1uf x 400v) to prevent DC currents, 25 pin is galvanically connected to your USB ground in FB3 and it is not a signal ground. By and large, you can forget about this pin

So [pin 25] should always be connected to projector case..

[catalanjo]

Nothing wrong with your diagram, except that it does not include the DMX board which you said was part of the setup which did not work properly.

I suspect that the ILDA OUT plug on projector was a balanced output coming from the DMX card so that it was trying to convert the DC zero volt line in the driver modules attached further down the line into a negative colour signal ... not good!

However if you do not include its wiring in your diagram it is difficult to be certain that this was indeed the cause of the problem.!

The absence of differential signal from FB3 is due to it using USB port as its PSU and at same time having no inverter in its design = cheap IMHO, since most noise immunity is eliminated as a result!

However if drivers have no differential input this immunity would be lost anyway unless you have an op-amp somewhere in your projector to receive the differential signals and change them to single ended, which might well be what someone had attempted to do with the DMX board since DMX lines are often horribly noisy!

I suspect that what Bbe is suggesting, is a method of shielding the ilda lines effectively to avoid induced noise, or reduce it to a minimum in the absence of differential immunity, whilst avoiding (with the capacitor) DC flow due to accumulated induced local AC ground differences (varying DC voltages), between your "control" location and your projector locations

I hope that makes some kind of sense to U.
Cheers

[Humphry]

Hi guys thanks for the comprehensive explanations. I have eliminated the "intelligent" laser board from the equation by.. well.. unscrewing and removing it from projector and so that beam problem has been rectified.

Not concerned about shielding, just my grounding scheme at a fundamental level. I would really like to take this opportunity considering I am talking to the *ahem* experts to confirm that I have wired my projectors correctly.

All my drivers are single ended. So in the diagram below I have tried to interpret BBE's advice as best I can, basically I create one [central grounding point] that connects 18, 19, 20, [AC Ground], [Power supply 0v (-)] all together?



And then I just leave pin 25 unconnected, as Pangolin says: "Note that the ILDA DB-25 pin 25 should NOT be connected to the �Central Grounding Point� if the AC ground connection is already connected there..."

Then regards scanner power supply ground. I connect [central grounding point] to [scanner power supply 0v] just like laser drivers.

[catalanjo]

That should work fine
Having re-read my earlier post ...I would just like to point out that your original problem, rather than being "Caused" by the DMX board on your old projector was really being "caused" by the lack of DMX boards (with their differential receivers) on the newer projectors along with the poor FB3 design! Differential signal lines are far better than single ended ones, as far as noise immunity is concerned, especially over long distances in electrically noisy environments!
However if you are using FB3 with no output buffering, this decision has already been taken by Pango, so removing (or modifying) the old DMX board remains as your only EASY option.

Just wanted to make clear where the "blame" (if you can call it that) actually resides, since I am getting a bit fed up of Chinese designers/manufacturers, getting a whole bunch of flack they often do not deserve. Sure they sell a lot of cheap crap, but this is primarily due to western customers, who demand cheap crap rather than pay for excellence, NOT due to some ingrained Chinese cultural thing!

Their culture (unlike ours), has revered and respected extreme excellence for thousands of years in a way which might benefit western cultures considerably, if we emulated it, rather than attempting to legislate for it.

OK end of rant!

Best of luck with your setup!

Cheers

[Humphry]

Hi!

Great, I will emulate that diagram.

One last question I have connected ILDA pin 25 to the shield surrounding all my ILDA cables, as well as the metal DB-25 hood which then connects to the projector case and therefore central grounding point. I have done this on both sides of all ILDA cables. Is this *bad*, *good* or will it not make any difference? I have definitely seen my projectors flicker when my laptop is running on a separate AC phase, and unplugging the laptop charger rectifies this. But then what should the shield be connected to if not pin 25? I am thinking that perhaps this is the culprit because it connects pin 25 to central grounding point when it should not be.

UPDATE: Last night when I connected central grounding point to 0v (-) DC on RGB lightspace laser driver, the power supply would not start (it would start up every 3 seconds then turn off like it was going into overload). I am 99% sure it is wired correctly. Does this seem possible or have I done something wrong?

OMG GROUND WIRING adofjnaperoigha[eoriuhg[aerigh


"Just wanted to make clear where the "blame" (if you can call it that) actually resides"

I see, thanks for explaining that the manufacturer is not at fault. FYI Lightspace was cleared from my mind since the get-go. In any goods-producing economy you get the horrible cheap knock-off stuff and China is no different, they just have a ridiculous scale of manufacture and tougher working conditions. I feel for some of the Chinese companies being boxed in as "Chinese - cheap" because in general, the Western world demands this from the country. This is definitely a stigma that I hope will change for the right reasons. Far too much cheap crap stuff wasted. It's even worse in 3rd world countries like South Africa where most people don't understand that quality saves you money.

[Bbe]

You are unlikely to get rid of the flicker, since the potential difference on the ground bus doing it. As for 25-pin, if you will not use it, there is a risk of damaging of your FB3.
You can apply a galvanic isolation in the AC circuit for your laptop, many sound engineers use this method to get rid of audio interference when impossible to provide a reliable AC ground.