OK- Another ground Question?? Sorry! :(

[smogthemog]

Fantastic explaination Adam, I totaly understand what you have said.

This is one darn good thing about this forum, you ask a question and you get MORE than just a half hearted answer, out of everyone

It gives me a warm feeling - lower than it should

Seriously, it's good to know that in this hobby I can dive head first into a laser project and more or less know that if I get stuck somewhere along the line, some bugger will pull you out of the poo!

So basically, depending on the outputs from your DAC, that need checking anyway before you go ahead and wire, all 'grounds' go back to the PSU grounding screw except the 'signal ground' which in most cases is to be not connected to anything. This includes the modulation 'minuses' (sp?), the LD grounds and pin 25 on the ILDA connector as well. All back to the PSU ground ??

[buffo]

So basically, depending on the outputs from your DAC, that need checking anyway before you go ahead and wire, all 'grounds' go back to the PSU grounding screw except the 'signal ground' which in most cases is to be not connected to anything.

Sort of. (See below) The ILDA ground (pin 25) connects to the PSU ground, yes. In addition, the grounds from the laser PSU's should also connect to this same ground.

This includes the modulation 'minuses' (sp?), the LD grounds and pin 25 on the ILDA connector as well. All back to the PSU ground ??

No. Here is where the trouble starts. Technically the modulation minus wires should be wired to the modulation minus pins on the ILDA connector (R- = 18, G- = 19, and B- = 20). However, *most* solid state lasers have the modulation minus wire connected to the input power ground internally. Plus the case of the laser is often at ground potential as well. Also, some controllers (notably, Pangolin) have the modulation minus outputs tied to ILDA ground. So there is a lot of confusion about what is really "ground" in this case.

Bottom line: Wire the modulation wires from your lasers to the plus and minus modulation pins on the ILDA connector (Red to 5&18, Green to 6&19, and Blue to 7&20). Then connect the power supply grounds (from the lasers *and* the scanner amp PSU) to the ILDA ground (pin 25). And of course, leave the signal input ground on the scanner amps unconnected.

Note that if your lasers are in direct contact with your metal baseplate (which is almost always the case), and the baseplate is in contact with the metal case (also normal), and the case is grounded via the incoming AC power (as you would expect), then you have created yet another ground loop between the projector and your controller! (D'oh!)

This should only be able to affect the modulation signal to the lasers, and in practice I have not heard of anyone having problems with this. Still, it's an imperfect solution. (In an ideal world I suppose you could isolate all the DC components inside the projector from the AC ground, thus you would only have a single ground point via the ILDA connector. But I don't know of anyone that has built a projector this way...)

Adam

[James Lehman]

No. Here is where the trouble starts. Technically the modulation minus wires should be wired to the modulation minus pins on the ILDA connector (R- = 18, G- = 19, and B- = 20). However, *most* solid state lasers have the modulation minus wire connected to the input power ground internally. Plus the case of the laser is often at ground potential as well. Also, some controllers (notably, Pangolin) have the modulation minus outputs tied to ILDA ground. So there is a lot of confusion about what is really "ground" in this case.

Adam

This is another case where someone had an idea for a standard and gave it to the world.

The idea wasn't always interpreted the right way and examples of hardware came out that violate the original concept.

Work-arounds were then added to the mix.

So now there is uncertainty, by design!

(I guess that's what happens when other people do stuff without asking me first! )

Let's fix the ILDA standards!

Please ?!

James.