Need some help! My first RGB projector project (expecting approx. 2W system)

[blowfly]

Adam - great explanation of your interlock circuit. Thanks!

Mike

[buffo]

Happy to help out.

Adam

[taggalucci]

I have been a bit quiet here with a few things going on in life. I have made a fair amount of progress with this projector; mostly with metal work, making all the fixings and working on the electrical and signal distribution. I am now turning my mind to the electronics and planing for the integration of the safety board and have come up with something I'm uncertain about... I have posted a query here.

I this is probably the last query I have before completing my wiring schematic (which I still plan to post here).

I will also upload some more photos.

[buffo]

If you are running differential signals (X+/X- and Y+/Y-), then you don't typically connect anything to the signal ground terminal.

If you were to connect it to anything, it would probably be to ILDA pin 25 (ground). However, this *can* cause artifacts in your scanned image, which is why it's not recommended.

I suggest you have a look at this article, written by Bill Benner of Pangolin. It explains the reasoning behind not connecting anything to the signal ground pin on the amps. (Note that the initial illustration in the article actually shows this ground connected to ILDA pin 25. This is so you understand the "wrong" way, before the article explains the "right" way.)

Adam

[taggalucci]

That's great. Thanks Adam

Yes, that article by Bill is great, and I've read that a few times over the past couple of weeks whilst working out the wiring design (for AC & DC). I have taken the previous advice and not wired the ground wires to the scanner amps. I've also gone to great pains to isolate all of the laser housings and scanning head block from the baseplate. I'm using a non-conductive (silicone-based) thermal transfer material for this. My design and preparation utilises a single point grounding scheme for both the AC (connected to the baseplate and housing) and DC (isolated from the baseplate etc), and these are kept separate from each other. Therefore DC ground in my design is connected to ILDA Pin 25.

I should have read the article more closely with respect to the scan fail. I've just noticed this...

If a scan-fail interlock were used, it would be connected to the X POSITION and Y POSITION signal from the scanner amplifier. But, there is something tricky to watch out for. You should consult the manufacturer of the scan-fail interlock to determine whether or not the scan-fail interlock itself has a differential position input. If the scan-fail monitor does not have a differential position input, you should NOT connect the “Signal ground” or “Position ground” from the scanner amplifier to the scan-fail monitor. Doing so would, again, destroy the single-point grounding scheme. The scan-fail monitor already has a ground connection to the “Central Grounding Point” established on the Power Connections diagram. You should only connect the scan-fail monitor to the scanner amplifier’s ground connection if the scan-fail monitor itself has differential inputs. Pangolin’s PASS safety system does have a differential position input, but most others do not.

My understanding is that this board does not have differential inputs, so (from the advice above) I should NOT connect the “Signal ground” or “Position ground” from the scanner amps to the SafeGuard Lite signal GND. Which is exactly what you've said

[taggalucci]

Well... I've finally got round to finishing the wiring schematics for the projector.

These represents my interpretation of the information kindly provided to me on this thread, in the context of my own set of chosen components.









Thanks particularly to Bill Benner (for his very informative wiring guide) and Adam Burns (for his excellent interlock controller circuit)

Now on with the construction... photos to follow

[taggalucci]

I've checked all of the wiring planned for the projector according to the schematics I posted and have found that the -5v terminals of the red and green CNI PSUs are internally connected to the -ve analogue modulation signal inputs. When all wired together, this causes all 3 modules -ve analogue modulation signals to form a common connection via DC ground. The Laser Century PSU does not exhibit this (when the others are disconnected).

I have confirmed that this is not caused by the possibility of the modules' casings grounding via the baseplate.

I'm not sure whether this is significant and should be accounted for in some way or ignored. Any thoughts you have would be appreciated

[buffo]

This is fairly common. Also, know that many laser controllers actually have the negative color signals connected internally to ILDA ground (pin 25). You can still have your single-point ground scheme though.

Adam

[taggalucci]

Thanks again Adam!

Here are some photos of the progress I've made (more to follow soon)...

External Remote...






Aluminium frame with top and bottom cover plates, sanded for painting...


This shows the two-shelf design which was inspired by some projectors I've seen here on PL. Top shelf providing mounting for the electronics (plate shown) and the second plate (not pictured) will be inverted and provide mounting for the lasers and optics.

Each of the 6 cover plates can be removed separately to allow easy access for inspection and maintenance. The inverted optics shelf prevents the rising heat from the electronics from affecting them but still facilitates easy access (from below) for adjusting the mirrors, dichro's etc.

Was a nice surprise to receive the frame yesterday and to feel how light-weight it is

Right, gotta get back to it

[taggalucci]

Further photos...

Scanner amps and blue laser PSU


All 3 laser PSUs in place


Relay


Electrical distribution


Electronics shelf pretty much complete


I'm expecting to be able to start on the optics shelf tomorrow and then work on the cooling, housing, and suspension.